# EDGAR Filing Document

**Accession Number:** 0001636282
**File Stem:** 0000950170-23-005699
**Filing Date:** 2023-3
**Character Count:** 61908
**Document Hash:** f4ab913a9e44919f45bc1bb8e4903d37
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000950170-23-005699.hdr.sgml**: 20230302

**ACCESSION NUMBER**: 0000950170-23-005699

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 54

**CONFORMED PERIOD OF REPORT**: 20230302

**ITEM INFORMATION**: Results of Operations and Financial Condition

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20230302

**DATE AS OF CHANGE**: 20230302

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Aeglea BioTherapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001636282
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **IRS NUMBER:** 464312787
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-37722
- **FILM NUMBER:** 23696384

**BUSINESS ADDRESS:**
- **STREET 1:** 805 LAS CIMAS PARKWAY
- **STREET 2:** SUITE 100
- **CITY:** AUSTIN
- **STATE:** TX
- **ZIP:** 78746
- **BUSINESS PHONE:** (512) 942-2935

**MAIL ADDRESS:**
- **STREET 1:** 805 LAS CIMAS PARKWAY
- **STREET 2:** SUITE 100
- **CITY:** AUSTIN
- **STATE:** TX
- **ZIP:** 78746

?xml version="1.0" encoding="ASCII"? 8-K

**UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549**

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**FORM** 8-K

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**CURRENT REPORT**

**Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934**

**Date of Report (Date of earliest event reported):** March 02, 2023<br>

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AEGLEA BIOTHERAPEUTICS, INC.

**(Exact name of Registrant as Specified in Its Charter)**

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| | | |
|:---|:---|:---|
| Delaware | 001-37722 | 46-4312787 |
| **(State or Other Jurisdiction<br>of Incorporation)** | **(Commission File Number)** | **(IRS Employer<br>Identification No.)** |
| 805 Las Cimas Parkway<br>Suite 100 |  |  |
| Austin**,** Texas |  | 78746 |
| **(Address of Principal Executive Offices)** |  | **(Zip Code)** |

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**Registrant's Telephone Number, Including Area Code:** (512) 942-2935<br>

**(Former Name or Former Address, if Changed Since Last Report)**

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Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

**Securities registered pursuant to Section 12(b) of the Act:**

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| | |
|:---|:---|
| **<br>Title of each class** | **<br>Name of each exchange on which registered** |
| Common Stock, $0.0001 Par Value Per Share<br> AGLE | The Nasdaq Global Market |

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Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

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**Item 2.02 Results of Operations and Financial Condition.**

On March 2, 2023, Aeglea BioTherapeutics, Inc. (the "Company") issued a press release announcing its financial results for the quarter ended December 31, 2022. A copy of the press release is attached as Exhibit 99.1 to this report.

The information in this Item 2.02, including Exhibit 99.1 to this report, shall not be deemed to be "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended (the "Securities Act"). The information contained in this Item 2.02 and in the accompanying Exhibit 99.1 shall not be incorporated by reference into any other filing under the Exchange Act or under the Securities Act, except as shall be expressly set forth by specific reference in such filing.

**Item 7.01 Regulation FD Disclosure.**

On March 2, 2023, the Company also updated its corporate presentation. A copy of the corporate presentation is attached as Exhibit 99.2 to this report.

The information in this Item 7.01, including Exhibit 99.2 to this report, shall not be deemed to be "filed" for purposes of Section 18 of the Securities Exchange Act, or otherwise subject to the liabilities of that section or Sections 11 and 12(a)(2) of the Securities Act. The information contained in this Item 7.01 and in the accompanying Exhibit 99.2 shall not be incorporated by reference into any other filing under the Exchange Act or under the Securities Act, except as shall be expressly set forth by specific reference in such filing.

**Item 9.01 Financial Statements and Exhibits.**

(d) Exhibits

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| | |
|:---|:---|
| &nbsp;&nbsp;Exhibit <u>Number</u> | &nbsp;&nbsp; <br><u>Description</u> |
| &nbsp;&nbsp;99.1 | &nbsp;&nbsp;[<u>Press release issued by Aeglea BioTherapeutics, Inc. regarding its financial results for the quarter ended December 31, 2022, dated March 2, 2023.</u>](agle-ex99_1.htm)<br>|
| &nbsp;&nbsp;99.2 | &nbsp;&nbsp;[<u>Corporate Presentation.</u>](agle-ex99_2.htm)<br>|
| &nbsp;&nbsp;104 | &nbsp;&nbsp;Cover Page Interactive Data File (embedded within the Inline XBRL document) |

---

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**SIGNATURES**

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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| | | | |
|:---|:---|:---|:---|
|  |  |  | **AEGLEA BIOTHERAPEUTICS, INC**. |
| Date: | March 2, 2023 | By:  | /s/ Jonathan Alspaugh |
|  |  |  | Jonathan Alspaugh<br>Chief Financial Officer |

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## Ex-99

![img256443366_0.jpg](img256443366_0.jpg) Exhibit 99.1

**Aeglea BioTherapeutics Reports Fourth Quarter and Full Year 2022 Financial Results and Provides Program Updates**

Jeffrey Goldberg, experienced biotech executive, appointed president and CEO; further strengthened senior management team with appointments of chief medical officer and chief product officer

$57.3 million of cash, cash equivalents, marketable securities, and restricted cash as of December 31, 2022, which is expected to fund operations into the fourth quarter of 2023

**Austin, Texas, March 2, 2023 -** Aeglea BioTherapeutics, Inc. (NASDAQ:AGLE), a clinical-stage biotechnology company developing a new generation of human enzyme therapeutics as innovative solutions for rare metabolic diseases, today announced financial results for the fourth quarter and full year 2022, and provided program updates.

"Since joining the company, I have been impressed by the programs and the potential impact that they may have on patient lives. In 2023, we are highly focused on execution, specifically the generation of data from our pegtarviliase Phase 1/2 clinical trial in Classical Homocystinuria and, assuming success with those data, preparations to advance into a potential pivotal trial," said Jeffrey Goldberg, president and chief executive officer of Aeglea. "We are also continuing to work with our partner Immedica Pharma AB to support the EMA [European Medicines Agency] review process for the Marketing Authorization Application for pegzilarginase for the treatment of Arginase 1 Deficiency. A decision by the EMA regarding the approval of the pegzilarginase Marketing Authorization Application is expected in late 2023. By delivering on these objectives, I believe we will be in a strong position to bring forward solutions that can positively impact the lives of our patient communities."

**Program and Corporate Updates**

Pegtarviliase in Homocystinuria

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Received Fast Track Designation from the U.S. Food and Drug Administration (FDA). Fast Track Designation is designed to expedite the FDA's review of innovative, new drugs that demonstrate the potential to address unmet medical need.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Announced in late November 2022 the completion of dosing of two patients in the third cohort of the Phase 1/2 clinical trial. Patients in the third cohort receive 1.35 mg/kg of pegtarviliase administered subcutaneously once weekly.

Pegzilarginase in Arginase 1 Deficiency

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Transitioning patients who participated in the PEACE Phase 3 long-term extension (LTE) and Phase 1/2 open-label extension (OLE) studies into one simplified open-label trial. The PEACE LTE and Phase 1/2 OLE studies were closed in the first quarter of 2023.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Continuing to progress the review of the Marketing Authorization Application submission with the EMA for the potential approval of pegzilarginase. EMA approval can facilitate possible patient access and regulatory approval in many other geographies, including Latin America and the Middle East.

Corporate

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Appointed Jeffrey Goldberg, a highly experienced executive with strong operational and rare disease background, as president and chief executive officer.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Strengthened senior management team with the promotions of Linda Neuman, MD, MBA, to chief medical officer and Cortney Caudill, MBA, to the newly created role of chief product officer. Ms. Caudill will serve as a strategic leader and team supervisor of Aeglea's clinical programs.

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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•Implemented changes to corporate structure to increase operational efficiency. Additionally, the company halted preclinical work on Cystinuria and other unnamed pipeline programs. The company will evaluate potential strategic options for these programs in order to maximize their value.

**Upcoming Events**

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;•ACMG Annual Clinical Genetics Meeting, Salt Lake City, Utah

oLong-Term Efficacy and Safety of Pegzilarginase for Arginase 1 Deficiency: 2 Years of Experience in the Phase 2 Extension Study

oFeatured platform presentation on March 16, 2023 at 8:45-9:00 am MST

**Fourth Quarter 2022 Financial Results** 

Aeglea recognized development fee revenues of $0.2 million in the fourth quarter of 2022, as a result of its license and supply agreement with Immedica Pharma AB for the commercial rights to pegzilarginase in Europe and several countries in the Middle East (License and Supply Agreement). The revenues recorded in the fourth quarter of 2022 are related to manufacturing services. Aeglea recognized $3.6 million for the fourth quarter of 2021 in development fee revenues.

Research and development expenses totaled $14.3 million for the fourth quarter of 2022 and $16.8 million for the fourth quarter of 2021. The decrease was primarily related to a decrease in Biologics License Application (BLA) activities for pegzilarginase and reductions in headcount and recruiting activities.

General and administrative expenses totaled $5.0 million for the fourth quarter of 2022 and $7.3 million for the fourth quarter of 2021. This decrease was primarily due to a reduction in commercialization activities for pegzilarginase and a reduction in headcount and related expenses.

Net loss totaled $18.8 million and $20.4 million for the fourth quarter of 2022 and 2021, respectively, which includes non-cash stock compensation expense of $1.4 million and $2.1 million for the fourth quarter of 2022 and 2021, respectively.

**Full Year 2022 Financial Results**

As of December 31, 2022, Aeglea had available cash, cash equivalents, marketable securities and restricted cash of $57.3 million. The company expects its cash, cash equivalents and marketable securities will enable it to fund its operating expenses and capital expenditure requirements into the fourth quarter of 2023.

Aeglea recognized development fee revenues of $2.3 million in the year ended December 31, 2022, as a result of its License and Supply Agreement. The revenues recorded in the year ended December 31, 2022 are primarily related to the PEACE Phase 3 clinical trial and the submission of the BLA. Aeglea recognized $18.7 million in license and development fee revenues for the year ended December 31, 2021.

Research and development expenses totaled $58.6 million for the year ended December 31, 2022 and $57.1 million for the year ended December 31, 2021. The increase was primarily associated with activities involved in closing the PEACE Phase 3 trial and initiation activities for the new open-label study for the treatment of patients with Arginase 1 Deficiency and Investigational New Drug-enabling activities conducted for AGLE-325 in the first half of the year. These increases were partially offset by decreases due to the completion of non-clinical toxicology studies for pegtarviliase and a reduction in preclinical lab activities.

General and administrative expenses totaled $28.5 million for the year ended December 31, 2022 and $27.3 million for the year ended December 31, 2021. This increase was primarily due to an increase in commercial capabilities and infrastructure expenses in the first half of the year.

Net loss totaled $83.8 million and $65.8 million for the years ended December 31, 2022 and 2021, respectively, which includes non-cash stock compensation expense of $7.1 million and $8.0 million for the years ended December 31, 2022 and 2021, respectively.

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**About Pegtarviliase in Homocystinuria**

Pegtarviliase is a novel recombinant human enzyme, which is engineered to reduce elevated levels of total homocysteine circulating in the plasma by degrading the amino acid homocysteine and its dimer. Pegtarviliase is currently being studied in a Phase 1/2 clinical trial for the treatment of patients with Classical Homocystinuria, a rare inherited disorder of methionine metabolism that results in elevated levels of total homocysteine. Homocysteine accumulation plays a key role in multiple progressive and serious disease-related complications, including lens dislocation, skeletal abnormalities, vascular complications and neurologic effects, as well as the potential for sudden and early death. In preclinical studies, pegtarviliase improved important disease-related abnormalities and survival in a mouse model of Homocystinuria. Pegtarviliase has received both U.S. and EU Orphan Drug Designation as well as U.S. Rare Pediatric Disease and Fast Track Designations.

**About Pegzilarginase in Arginase 1 Deficiency**

Pegzilarginase is a novel recombinant human enzyme engineered to degrade the amino acid arginine and has been shown to rapidly and sustainably lower levels of the amino acid arginine in plasma. Aeglea is developing pegzilarginase for the treatment of people with Arginase 1 Deficiency (ARG1-D), a rare debilitating and progressive disease characterized by the accumulation of arginine. ARG1-D presents in early childhood and patients experience spasticity, seizures, developmental delay, intellectual disability and early mortality. The PEACE Phase 3 clinical trial met its primary endpoint with a 76.7% reduction in mean plasma arginine compared to placebo. Additionally, 90.5% of pegzilarginase treated patients achieved normal plasma arginine levels.

**About Aeglea BioTherapeutics**

Aeglea BioTherapeutics is a clinical-stage biotechnology company redefining the potential of human enzyme therapeutics to benefit people with rare metabolic diseases with limited treatment options. Aeglea is investigating pegtarviliase in an ongoing Phase 1/2 clinical trial for the treatment of Classical Homocystinuria. Pegtarviliase has been granted Rare Pediatric Disease Designation. Aeglea's other clinical program, pegzilarginase, achieved the primary endpoint of arginine reduction in the PEACE Phase 3 clinical trial and has received both Rare Pediatric Disease and Breakthrough Therapy Designations. The Marketing Authorization Application for pegzilarginase is currently under review with the European Medicines Agency. For more information, please visit http://aeglea.com.

**Safe Harbor / Forward Looking Statements** 

<br> This press release contains "forward-looking" statements within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. Forward-looking statements can be identified by words such as: "anticipate," "intend," "plan," "goal," "seek," "believe," "project," "estimate," "expect," "strategy," "future," "likely," "may," "should," "will" and similar references to future periods. These statements are subject to numerous risks and uncertainties that could cause actual results to differ materially from what we expect. Examples of forward-looking statements include, among others, statements we make regarding our ability to achieve further cost-savings and organizational efficiencies, the timing of announcements and updates relating to our clinical trials and related data, including the clinical data for our Phase 1/2 trial of pegtarviliase in Classical Homocystinuria, the timing and success of our clinical trials and related data, including the potential initiation of a Phase 3 trial of pegtarviliase in Classical Homocystinuria, the timing and expectations for regulatory submissions and approvals, including the Marketing Authorization Application for pegzilarginase in Europe the expected impact of macroeconomic conditions, including inflation and rising interest rates, our ability to obtain regulatory approval for, and commercialize, pegzilarginase, recognize milestone and royalty payments under our agreement with Immedica, our ability to enroll patients into our clinical trials, the expected impact of macroeconomic conditions, including inflation and rising interest rates, on our operations and clinical trials, success in our collaborations, the length of time that we believe our existing cash resources will fund operations, the number of possible treatment candidates in potential addressable markets of our product candidates and the potential therapeutic benefits and economic value of our product candidates. Further information on potential risk factors that could affect our business and its financial results are detailed in our most recent Annual Report on Form 10-K for the year ended December 31, 2022 filed with the Securities and Exchange Commission (SEC), and our other reports as filed with the SEC. We undertake no obligation to publicly update any forward-looking statement, whether written or oral, that may be made from time to time, whether as a result of new information, future developments or otherwise.

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**Contact Information:**

**Investors & Media**

Kelly Boothe, Ph.D.<br>Vice President, Investor Relations & Corporate Communications<br>512.399.5458<br>investors@aeglea.com

media@aeglea.com

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**Financials**

**Aeglea BioTherapeutics, Inc.**

**Consolidated Balance Sheets**

**(Unaudited, in thousands, except share and per share amounts)**

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| | | |
|:---|:---|:---|
|  | **December 31,** | **December 31,** |
|  | **2022** | **2021** |
| **ASSETS** | **ASSETS** | **ASSETS** |
| CURRENT ASSETS |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;Cash and cash equivalents | $34863 | $15142 |
| &nbsp;&nbsp;&nbsp;&nbsp;Marketable securities | 20848 | 77986 |
| &nbsp;&nbsp;&nbsp;&nbsp;Development receivable | 375 | 815 |
| &nbsp;&nbsp;&nbsp;&nbsp;Prepaid expenses and other current assets | 6172 | 4948 |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Total current assets | 62258 | 98891 |
| Restricted cash | 1553 | 1838 |
| Property and equipment, net | 3220 | 4549 |
| Operating lease right-of-use assets | 3430 | 3806 |
| Other non-current assets | 683 | 842 |
| TOTAL ASSETS | $71144 | $109926 |
| **LIABILITIES AND STOCKHOLDERS' EQUITY** | **LIABILITIES AND STOCKHOLDERS' EQUITY** | **LIABILITIES AND STOCKHOLDERS' EQUITY** |
| CURRENT LIABILITIES |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;Accounts payable | $677 | $3319 |
| &nbsp;&nbsp;&nbsp;&nbsp;Operating lease liabilities | 625 | 436 |
| &nbsp;&nbsp;&nbsp;&nbsp;Deferred revenue | 517 | 2359 |
| &nbsp;&nbsp;&nbsp;&nbsp;Accrued and other current liabilities | 12837 | 14030 |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Total current liabilities | 14656 | 20144 |
| Non-current operating lease liabilities | 4004 | 4608 |
| Deferred revenue, net of current portion | 2179 | 1217 |
| Other non-current liabilities |  | 16 |
| TOTAL LIABILITIES | 20839 | 25985 |
| Commitments and Contingencies (Note 9) |  |  |
| STOCKHOLDERS' EQUITY |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;Preferred stock, $0.0001 par value; 10,000,000 shares authorized as of <br> December 31, 2022 and 2021; no shares issued and outstanding as of <br> December 31, 2022 and 2021 |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;Common stock, $0.0001 par value; 500,000,000 shares authorized as of <br> December 31, 2022 and 2021, 65,350,343 shares and 49,355,130<br> shares issued and outstanding as of December 31, 2022 and 2021, <br> respectively | 6 | 5 |
| &nbsp;&nbsp;&nbsp;&nbsp;Additional paid-in capital | 475971 | 425765 |
| &nbsp;&nbsp;&nbsp;&nbsp;Accumulated other comprehensive (loss) income | (48) | (20) |
| &nbsp;&nbsp;&nbsp;&nbsp;Accumulated deficit | (425624) | (341809) |
| TOTAL STOCKHOLDERS' EQUITY | 50305 | 83941 |
| TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY | $71144 | $109926 |

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**Aeglea BioTherapeutics, Inc.**

**Consolidated Statements of Operations**

**(Unaudited, in thousands, except share and per share amounts)**

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| | | | |
|:---|:---|:---|:---|
|  | **Year Ended December 31,** | **Year Ended December 31,** | **Year Ended December 31,** |
|  | **2022** | **2021** | **2020** |
| Revenue: |  |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;License | $— | $12000 | $— |
| &nbsp;&nbsp;&nbsp;&nbsp;Development fee | 2329 | 6739 |  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Total revenue | 2329 | 18739 |  |
| Operating expenses: |  |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;Research and development | 58579 | 57069 | 59638 |
| &nbsp;&nbsp;&nbsp;&nbsp;General and administrative | 28531 | 27319 | 21843 |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Total operating expenses | 87110 | 84388 | 81481 |
| Loss from operations | (84781) | (65649) | (81481) |
| Other income (expense): |  |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;Interest income | 837 | 111 | 593 |
| &nbsp;&nbsp;&nbsp;&nbsp;Other expense, net | (7) | (122) | (5) |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Total other income (expense) | 830 | (11) | 588 |
| Loss before income tax expense | (83951) | (65660) | (80893) |
| &nbsp;&nbsp;&nbsp;&nbsp;Income tax benefit (expense) | 136 | (141) |  |
| Net loss | $(83815) | $(65801) | $(80893) |
| Net loss per share, basic and diluted | $(0.99) | $(1.00) | $(1.52) |
| Weighted-average common shares outstanding, basic and diluted | 84280785 | 65744611 | 53371730 |

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## Ex-99

![Slide 1](agle-ex99_2s1.jpg)

Redefining the Possible.Human Enzyme Therapies for People with Rare Diseases Corporate Overview – March 2023 Nasdaq: AGLE Exhibit 99.2

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![Slide 2](agle-ex99_2s2.jpg)

Forward Looking Statements©2023 Aeglea BioTherapeutics This presentation and the accompanying oral presentation contain "forward-looking" statements that are based on our management's beliefs and assumptions and on information currently available to management. Forward-looking statements include all statements other than statements of historical fact contained in this presentation, including information concerning our current and future financial performance, business plans and objectives, current and future clinical and preclinical development activities, timing and success of our ongoing and planned clinical trials and related data, the timing of announcements, updates, results of our clinical trials and related data, our ability to obtain and maintain regulatory approval, the potential therapeutic benefits, safety profile and economic value of our product candidates, potential growth opportunities, financing plans, use and adequacy of financing plans, the length of time that we believe our existing cash resources will fund operations, competitive position, industry environment and potential market opportunities. Forward-looking statements are subject to known and unknown risks, uncertainties, assumptions and other factors including, but not limited to, those related to the success, cost and timing of our product candidate development activities and ongoing and planned clinical trials; our plans to develop and commercialize targeted therapeutics, including our lead product candidates pegzilarginase and pegtarviliase and our other product candidates; the design, progress of patient enrollment and dosing in our clinical trials; the ability of our product candidates to achieve applicable endpoints in clinical trials; the safety profile of our product candidates in clinical trials; the potential for data from our current and future clinical trials to support a marketing application, as well as the timing of these events, including data for our Phase 1/2 trial of pegtarviliase in Classical Homocystinuria, the MAA for pegzilarginase in Europe, and potential resubmission of a BLA for pegzilarginase in the U.S.; the potential for preclinical studies to be predictive of current or future clinical trials; our ability to obtain funding for our operations, development and commercialization of our product candidates; the expected impact of macroeconomic conditions, including inflation and rising interest rates, on our operations and clinical development activities; the timing of and our ability to obtain and maintain regulatory approvals; our ability to obtain regulatory approval for, and commercialize, pegzilarginase, and recognize milestone and royalty payments under our licensing and supply agreement with Immedica; the potential for expedited development and review of pegtarviliase and pegzilarginase as a result of their regulatory designations; the number of possible treatment candidates in potential addressable markets of our product candidates; the rate and degree of market acceptance and clinical utility of our product candidates; the size and growth potential of the markets for our product candidates, and our ability to serve those markets; our commercialization, marketing and manufacturing capabilities and strategy; future agreements with third parties in connection with the potential commercialization of our product candidates; our expectations regarding our ability to obtain and maintain intellectual property protection; our dependence on third party manufacturers; our ability to develop our own commercial manufacturing facility; the success of competing therapies that are or may become available; our ability to attract and retain key scientific or management personnel; and our estimates regarding expenses, future revenue, capital requirements, the length of time that we believe our existing cash resources will fund operations, and needs for additional financing. Moreover, we operate in a very competitive and rapidly changing environment, and new risks may emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. In light of these risks, uncertainties and assumptions, the forward-looking events and circumstances discussed herein may not occur and actual results could differ materially and adversely from those anticipated or implied in the forward-looking statements. Further information on these and other factors that could affect these forward-looking statements is contained in our most recent Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission (SEC) and other reports filed by the SEC. You should not rely upon forward-looking statements as predictions of future events. Although our management believes that the expectations reflected in our forward-looking statements are reasonable, we cannot guarantee that the future results, levels of activity, performance or events and circumstances described in the forward-looking statements will be achieved or occur. We undertake no obligation to publicly update any forward-looking statements, whether written or oral, that may be made from time to time, whether as a result of new information, future developments or otherwise.

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![Slide 3](agle-ex99_2s3.jpg)©2020 Aeglea BioTherapeutics. External Our vision is to redefine the possible, pioneer bold science with human enzymes and deliver groundbreaking medicines that transform lives. We are on a mission to change lives by bringing innovative therapies to underserved rare disease communities.

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![Slide 4](agle-ex99_2s4.jpg)©2023 Aeglea BioTherapeutics. External Redefining the Possible with Human Enzyme Therapies Strong Scientific Foundation Patient-Focused Approach With engineered human enzymes, we believe we can: Impact underlying key metabolites that drive clinical manifestations Address unmet medical needs with rationally-designed characteristics (e.g., half-life, specificity) Develop therapies for a range of rare metabolic diseases By working closely with the patient community, we believe we can: Understand the patient and HCP perspective and experience Design clinical trials with the patient perspective in mind Help make patients' and families' voices heard Discover gaps in education and resources and help to fill them

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![Slide 5](agle-ex99_2s5.jpg)

Program Research Phase 1/2 Phase 3 Regulatory Review Addressable Market Geographic Rights Pegtarviliase Homocystinuria ~25,000 Patients1 Worldwide rights Pegzilarginase Arginase 1 Deficiency >2,500 Patients2 Retain rights outside of Europe and Middle East3 Preclinical Programs Including Cystinuria Cystinuria Worldwide rights Aeglea's Human Enzyme Therapies for Rare Metabolic Diseases 1 ~25,000 represents estimated treatment candidates in 38 addressable markets of Classical Homocystinuria based on results of U.S. ICD-10 claims analysis extrapolated to global markets; all figures rounded. Estimates also based on internal assumptions and data from Sellos-Moura et al 2020 2 Catsburg C et al 2022 ; Diez-Fernandez et al. Mutations and common variants in the human arginase 1 (ARG1) gene: impact on patients, diagnostics and protein structure considerations. Hum Mutat. 2018 Aug;39(8):1029-10502 3 Ex-U.S. license and supply agreement with Immedica to commercialize pegzilarginase in Europe and several countries in the Middle East (European Economic Area, United Kingdom, Switzerland, Andorra, Monaco, San Marino, Vatican City, Turkey, Saudi Arabia, United Arab Emirates, Qatar, Kuwait, Bahrain and Oman) 4 Market Authorisation Application (MAA) validated by the European Medicines Agency (EMA) and currently under review; Company in dialogue with the U.S. Food and Drug Administration following Refusal to File Letter MAA Validated by EMA4©2023 Aeglea BioTherapeutics

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![Slide 6](agle-ex99_2s6.jpg)

Highlights and Upcoming Milestones Pegtarviliase in Homocystinuria: Fast Track Designation received from FDA Currently dosing in cohort 3 at 1.35 mg/kg once weekly in Phase 1/2 clinical trial Pegzilarginase in Arginase 1 Deficiency: MAA under review with EMA, potential decision on approval in late 2023 Continuing to engage with FDA to identify potential path to BLA resubmission Corporate: Jeff Goldberg appointed CEO in November 2022 – highly experienced executive with strong operational and rare disease background $57.3 million in cash and available funds1 as of December 31, 2022; projected runway into fourth quarter of 2023©2023 Aeglea BioTherapeutics 1 Includes cash, cash equivalents, marketable securities, and restricted cash

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Pegtarviliase – Potential Best-in-Class Treatment for Homocystinuria

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Classical Homocystinuria (HCU) Classical Homocystinuria: A Rare Metabolic Disorder With Serious and Potentially Deadly Complications Also known as cystathionine beta synthase (CBS) deficiency, Classical Homocystinuria is a serious and progressive metabolic disorder characterized by elevated levels of the amino acid homocysteine. There are no approved disease-modifying treatments for HCU, i.e., addressing high levels of homocysteine1 Toxic levels of homocysteine can lead to sudden catastrophic events, including death Manifestations, which are often irreversible, can occur in early childhood and worsen over time Serious Disease Complications Eyes Lens dislocation, glaucoma, severe near-sightedness Nervous System Intellectual and developmental delays, behavioral abnormalities, seizures Vascular Life-threatening thrombotic events, heart attack, stroke Skeletal Long bone (Marfanoid) features, skeletal deformities, osteoporosis©2023 Aeglea BioTherapeutics 1Betaine, approved by the FDA in 1996, can lower homocysteine levels in the blood through remethylation to methionine but does not metabolize homocysteine and clear it from the body

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With Persistently High Total Homocysteine Levels, Patients Remain at Risk for Serious and Life-Threatening Complications Compliance with severe dietary restrictions and amino acid supplementation is extremely challenging and represents a lifelong burden Vitamin B6 is largely ineffective at lowering tHcy to guidance levels for the majority of patients Betaine can be associated with both safety and tolerability issues such as hypermethioninemia, nausea, gastrointestinal distress, and body odor Patients with Classical HCU Live With Both Disease and Treatment Burden "To get the family to cope with a very difficult life, and to have them compliant for life … is a very big challenge." - EU Key Opinion Leader "For patients with Classical Homocystinuria, [the biggest challenge] would be compliance with diet." - U.S. Key Opinion Leader One patient's daily protein supplement, which is only one portion of his treatment regimen©2023 Aeglea BioTherapeutics tHcy = total homocysteine

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Classical HCU: A Sizeable Patient Population at Serious Risk of Severe Complications Over 80% of patients are unable to achieve total homocysteine levels <50 µM with B6 alone, the definition of B6 responsiveness This translates into an estimated ~25,000 treatment candidates in global addressable markets,1 approximately 8,500 of whom are in the U.S., EU4, and UK Average Age of Diagnosis…2 1 Data on file. Adapted from Sellos-Moura et al 2020. 2 Kozich, Sokolova, Morris, et al. 2021. 3 Mudd, Skovby et al. 1985. …And Often Occurs After Severe Complications2,3 Although Non-Responders and Partial Responders are generally diagnosed earlier in life, that diagnosis typically occurs several years following presentation of initial symptoms At time of diagnosis: 79% Non-Responders and Partial Responders have experienced a lens dislocation 29% Non-Responders and Partial Responders have experienced a thromboembolic event 7.0 14.0 21.5 36.0 ER FR PR NR Age of Dx B6 Status Classical HCU by B6 Responsiveness2©2023 Aeglea BioTherapeutics

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Pegtarviliase: An Innovative Enzyme Approach to Lowering Homocysteine Pegtarviliase Mechanism Engineered Cystathionine -Lyase (CGL) enzyme mutated to change its native substrate specificity from cystathionine to both homocysteine and its dimer Concentration gradient drives homocysteine out of tissues and into plasma Equilibrium in plasma favors dimer over monomer Flux enables further metabolism of both monomer and dimer 1Mudd, Skovby et al. 1985, Al-Dewik, Ali et al. 2019; 2Mudd, Skovby et al. 1985, Wilcken and Wilcken 1997, Yap and Naughten 1998 Therapeutic Rationale Elevated levels of plasma total homocysteine increase risk for disease manifestations1 Reduction of plasma total homocysteine has been correlated with reduced risk of developing disease manifestations2 Generally accepted aim of treatment is to lower the plasma total homocysteine concentration below certain thresholds to reduce risk of disease-related events Depiction of Normal and Therapeutic Metabolism©2023 Aeglea BioTherapeutics

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Experimental Design: 10-day old CBS knockout mice were dosed with pegtarviliase twice per week for 5 weeks to ensure they were able to grow to sufficient size for future blood sampling Prior to a single subcutaneous dose of pegtarviliase, there was a two-week wash out To ensure accurate tHcy assessment, an inhibitor of pegtarviliase was used in sample collection to block further in vitro metabolism of tHcy2 Pegtarviliase Treatment Resulted in Dose-Dependent Response and Statistically Significant Lowering of Homocysteine in Mouse Model Single Subcutaneous Dose in CBS Knockout Mouse Model1 \* p < 0.05 by Manley Cox test Pegtarviliase (1.0 mg/kg, SC) Pegtarviliase (10.0 mg/kg, SC) Plasma tHcy (µM) Hours 1 Daige C. et al. Poster presented at ASHG 2020 Virtual Meeting. 2 Thornloe K. et al. Poster presented at ACMG 2022 Meeting; tHcy = total homocysteine; SC = subcutaneous \* \* \* \*©2023 Aeglea BioTherapeutics

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![Slide 13](agle-ex99_2s13.jpg)©2023 Aeglea BioTherapeutics Preclinical Data Support Once-Weekly Dosing of Pegtarviliase Significant Survival Benefit in Knockout Mouse1,2 1 Daige C. et al. Poster presented at ASHG 2020 Virtual Meeting. 2 Mice were maintained on betaine until weaning; tHcy = total homocysteine Pegtarviliase (10 mg/kg, BIW) Pegtarviliase (3 mg/kg, BIW) Pegtarviliase (1.0 mg/kg, BIW) Vehicle (BIW) Significant survival benefit with pegtarviliase at 1 mg/kg twice per week (BIW) Twice-weekly dosing in mice typically translates to once-weekly dosing in humans Pharmacological Effect on Homocysteine Levels in Normal Animals Substantial decreases in homocysteine after single subcutaneous dose in toxicology studies with cynos (above) and rats (data not shown) Vehicle Pegtarviliase 2 mg/kg Pegtarviliase 6 mg/kg Pegtarviliase 20 mg/kg

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Phase 1/2 Clinical Trial to Generate Proof-of-Concept and Path to Pivotal Trial Cohort 2 Cohort 3 PART 1 (Intravenous) PART 2 (Subcutaneous) Dose 0.45 mg/kg n = 4 Dose 1.35 mg/kg Ongoing Dose 0.15 mg/kg n = 3 Cohort 1 Cohort 5 (optional) Continuing to Dose Patients in Cohort 3  Cohort 4 (optional)  Endpoints & Design Key Inclusion Criteria Safety and tolerability Pharmacokinetics Reduction in plasma homocysteine levels 4 once weekly doses Classical HCU diagnosis Plasma homocysteine ≥50 µM with documented history of plasma homocysteine ≥80 µM ≥12 years of age (≥18 years of age in U.S. and certain Australian sites)©2023 Aeglea BioTherapeutics

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Data from cohorts 1 through 3 may be sufficient for discussions with FDA on pivotal trial design Manufacturing at commercial scale Stable, high-concentration liquid formulation Engagement with the patient and HCP communities to educate and increase awareness Orphan Disease, Fast Track and Rare Pediatric Disease designations for Homocystinuria Advancing a Potential Best-in-Class Therapy for Classical HCU Patients Addressing an Unmet Need While Focusing on Patient Convenience Preparing for Rapid Transition to Phase 3 Pivotal Trial Efficacy: cohort 1 showed reduction in total homocysteine levels in all patients Safety: Adverse events have been mild to moderate in data gathered to date Toxicology data indicates a large dosing window Potential for convenience of a single once-weekly injection at home©2023 Aeglea BioTherapeutics

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Pegzilarginase for Arginase 1 Deficiency

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The Progressive Impact of Persistently High Plasma Arginine1-4 Arginase 1 Deficiency (ARG1-D) Disease Overview Infancy2-4,7,8 Initial 6-12 months may be uneventful May present with seizures, episodes of hyperammonemia: irritability, feeding difficulties, poor appetite, nausea/vomiting, decreased alertness Toddlerhood (2-4 years) 2,3,7-9 Spasticity in lower limbs (toe walking) Seizures, avoidance of protein is common and intellectual disability Childhood (5-10 years) 2,3,5,6,9 Progressive spasticity and growth impairment Declining neuromotor and intellectual capabilities Increasing dependence on walking aids Loss of mobility Decrease/loss of vocabulary/language Adolescence (11-17 years)2,3,5,10 Potential loss of ambulation and bowel/bladder control Severe intellectual disability Adulthood (18+ years) 2,3,11,12 Continued decline with increasing disability that may result in early mortality 1 Diez-Fernandez C, et al. Hum Mutat. 2018;39:1029-1050. 2 Carvalho DR, et al. Pediatr Neurol. 2012;46:369-374. 3 Crombez EA, Cederbaum SD. Mol Genet Metab. 2005;84:243-251. 4 De Deyn PP, et al. Hyperargininemia: a treatable inborn error of metabolism. In: Guanidino Compounds in Biology and Medicine. London, UK: John Libbey Company Ltd.; 1997:53-69. 5 Prasad A, et al. J Child Neurol. 1997;12:301-309. 6 Amayreh W, et al. Dev Med Child Neurol. 2014;56:1021-1024. 7 Scaglia F, Lee B. Am J Med Genet C Semin Med Genet. 2006;142C:113-120. 8 Sin YY, et al. J Mol Med (Berl). 2015;93:1287-1296. 9 Cai X, et al. Medicine (Baltimore). 2018;97:e9880. 10 Schlune A, et al. J. Amino Acids. 2015;47:1751-1762. 11 Sun A, et al. Arginase deficiency. In: Adam MP, et al, eds. GeneReviews®. Seattle, WA: University of Washington, Seattle; 2020. 12 Diaz GA, et al. Poster presented at: 13th European Paediatric Neurology Society (EPNS) Congress; September 17-21, 2019; Athens, Greece. Poster P06-34. Current Standard of Care Focused on lowering plasma arginine levels and controlling hyperammonemia with: Severe dietary protein restriction Amino acid supplementation Ammonia scavengers Ineffective at controlling plasma arginine levels Significant Unmet Need High arginine levels Severe and progressive disease with early mortality Easily diagnosed but often missed due to lack of awareness No approved therapies to address high arginine levels ARG1-D is a serious, progressive disease with early mortality and high unmet medical need. It is caused by a mutation in the arginase 1 enzyme, resulting in persistently high levels of arginine.©2023 Aeglea BioTherapeutics

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Pegzilarginase Program Overview Commercial Opportunity >2,500 patients in global addressable markets1 High unmet medical need No approved therapies to address high arginine levels Regulatory Designations U.S. Rare Pediatric Disease (PRV eligible) Breakthrough Therapy U.S. Orphan Drug EU Orphan Drug Pegzilarginase is a novel recombinant human enzyme engineered to lower arginine levels MAA Under Review with EMA, Potential Decision on Approval in Late 2023 PEACE Phase 3 Clinical Trial First placebo-controlled trial ever conducted in ARG1-D Pegzilarginase reduced arginine levels by 76.7%, normalized arginine levels in 90.5% of patients Positive trend in mobility measure Well-tolerated 31 patients enrolled in long-term extension study Phase 1/2 and Open-Label Extension Trials 13 patients remain on therapy, duration from 2-4 years Arginine lowering was rapid and durable Improvements in functional measures sustained over time First Clinical Program Ever Conducted in ARG1-D 1 Catsburg C et al 2022©2023 Aeglea BioTherapeutics

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PEACE Phase 3 Trial: Marked and Sustained Reduction in Plasma Arginine Primary Endpoint: Reduction in Plasma Arginine\* Enns G, et al. Poster presented at SIMD 2022 Annual Meeting; \*Based on arithmetic mean of values from visit and preceding 3 visits, boxes represent middle 50% with error bars depicting 95% confidence interval; ǂ Statistical analysis based on geometric mean; †Nominal p value, based on arithmetic mean of values from visit and preceding 3 visits 200 µM 115 µM 40 µM Normal Range Clinical Guideline Primary Endpoint Met – 24 Week Analysis 76.7% reduction from baseline in mean plasma arginine with pegzilarginase treatment compared to placebo (p<0.0001)ǂ Proportion of Patients Reaching Normal Arginine Levels (p<0.0001†)©2023 Aeglea BioTherapeutics

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PEACE Phase 3 Trial: Mobility Assessed by GMFM-E and 2MWT Pegzilarginase Placebo 12 Weeks 24 Weeks 12 Weeks 24 Weeks MCID1, 2 GMFCS I (4.0 units) GMFCS II (2.8 units) Positive Trend in GMFM-E in Placebo-Controlled Study Suggests Potential Improvement in Mobility Time LS Mean Difference P Value 12 Weeks 6.4 units p=0.0568 24 Weeks 4.6 units p=0.1087 Pegzilarginase Placebo 12 Weeks 24 Weeks 12 Weeks 24 Weeks Mean Change from Baseline in 2MWT Time LS Mean Difference P Value 12 Weeks 14.1 m p=0.2085 24 Weeks 5.5 m p=0.5961 Mean Change from Baseline in GMFM-E Enns G, et al. Poster presented at SIMD 2022 Annual Meeting; 1 MCID is minimal clinically important difference defined in Cerebral Palsy population. 2Oeffinger D et al 2008; GMFM-E = Gross Motor Function Measure Part E; 2MWT = 2-minute walk test; GMFCS = Gross Motor Function Classification System ; LS = least squares©2023 Aeglea BioTherapeutics

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In a patient-level analysis clinically important differences between treatment arms were evident for both arginine normalization and clinical responses 16 of 17 pegzilarginase treated patients normalized arginine levels compared to no patients receiving placebo Clinical response criteria for ≥1 assessment were met by 11 of 17 patients receiving pegzilarginase compared with 4 of 9 patients receiving placebo 8 of 17 pegzilarginase treated patients met clinical response criteria on ≥2 outcomes With placebo, no patient met clinical response criteria on ≥2 clinical assessments PEACE Phase 3 Patient-Level Outcomes: Impact of Pegzilarginase Across Efficacy Endpoints Enns G, et al. Poster presented at SIMD 2022 Annual Meeting; Patient-level outcomes analysis conducted on GMFCS Level I-III patients (pegzilarginase, n=17, placebo, n=9) Individual Outcomes for Evaluable Patients Show Impact Across Arginine Levels and Mobility, Providing Further Evidence of Efficacy GMFCS Level I-III Patients Patient pArg GMFM-E 2MWT GMFM-D Pegzilarginase 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Placebo 1 2 3 4 5 6 7 8 9 Met criteria for clinical improvement or normalized pArg Met criteria for clinical worsening or pArg >200 µmol/L Did not meet criteria for improvement or worsening Data not available©2023 Aeglea BioTherapeutics

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PEACE Phase 3: Pegzilarginase Safety Profile Enns G, et al. Poster presented at SIMD 2022 Annual Meeting; AE = Adverse Event; \*Serious AEs were hyperammonemia/hyperammonemia-related events and vomiting Pegzilarginase was Well-Tolerated with No Discontinuations in Pivotal Study Due to Adverse Events No discontinuations due to treatment-emergent adverse events Most treatment-emergent adverse events were mild or moderate in severity Hypersensitivity reactions were mild/moderate, infrequent and managed with routine medical care Serious adverse events included hyperammonemia and vomiting (1 patient)©2023 Aeglea BioTherapeutics

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Regulatory and Program Status MAA Under Review by EMA MAA filing accepted in August 2022 Potential decision on approval in late 2023 Manufacturing in place to support commercialization in Europe and Middle East Continuing to engage with FDA to identify potential path towards BLA resubmission Refusal to File (RTF) Received for BLA Regulatory Status Next Steps Ongoing Discussions with Potential ROW Partners Latin America remains a significant commercial opportunity EU authorization, if granted, can be used to enable access in many other countries Clinical Trial Transition Underway New open-label trial to provide continued access for study patients in one streamlined, cost-effective study©2023 Aeglea BioTherapeutics

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Summary

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Highlights and Upcoming Milestones Pegtarviliase in Homocystinuria: Fast Track Designation received from FDA Currently dosing in cohort 3 at 1.35 mg/kg once weekly in Phase 1/2 clinical trial Pegzilarginase in Arginase 1 Deficiency: MAA under review with EMA, potential decision on approval in late 2023 Continuing to engage with FDA to identify potential path to BLA resubmission Corporate: Jeff Goldberg appointed CEO in November 2022 – highly experienced executive with strong operational and rare disease background $57.3 million in cash and available funds1 as of December 31, 2022; projected runway into fourth quarter of 2023©2023 Aeglea BioTherapeutics 1 Includes cash, cash equivalents, marketable securities, and restricted cash

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Financial Summary $ Millions Year Ended 12/31/22 Year Ended 12/31/21 Revenue $2.3 $18.7 R&D Expense $58.6 $57.1 G&A Expense $28.5 $27.3 Net Loss $83.8 $65.8 Cash and available funds as of December 31, 2022: $57.31 million (no debt) As of February 21, 2023, 94.3 million2 common shares and pre-funded warrants outstanding Expected funding runway: into fourth quarter of 2023 1 Includes cash, cash equivalents, marketable securities and restricted cash. 2Includes 65.4 million common shares outstanding and 28.9 million pre-funded warrants.©2023 Aeglea BioTherapeutics

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805 Las Cimas Parkway Suite 100 Austin, TX 78746 aeglea.com

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Homocysteine Metabolism & Pegtarviliase Mechanism of Action Methionine Homocysteine Cystathionine Cysteine Cystathionine ß-Synthase (CBS) Homocysteine monomer Homocystine dimer/disulfide ~30% ~1% ~70% Protein-Bound Homocysteine Betaine Pyridoxine (B6) Intracellular Serine Dietary Protein Pegtarviliase Naturally Occuring Metabolites Engineered CGL enzyme metabolizes non-protein-bound forms Pyridoxal Phosphate X Cofactor Remethylation Cystathionine γ-Lyase (CGL) Homocysteine Accumulation Total Homocysteine Species in Plasma1 Extracellular Transport 1. Morris et al J Inherit Metab Dis 2017 Pegtarviliase: Engineered human enzyme metabolizes multiple forms of free homocysteine to naturally occurring metabolites Plasma Equilibrium©2023 Aeglea BioTherapeutics

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Natural History Study of 629 Untreated Classical Homocystinuria Patients Elevated levels of homocysteine Mortality by age 30 23% 4% Most common cause of death Thromboembolism Lens dislocation in 50% Age 6 Age 10 Median IQ 56 78 Chance of thrombosis by age 15 27% 12% Increased Mortality and High Risk of Severe Complications B6-responsive = 231 All patients = 629 B6-non-responsive = 231 MORTALITY NATURAL HISTORY Mudd et al, 1985. Kluijtmans et al, Am. J. Hum. Genet. 65,59-67, 1999 B6-non-responsive B6-responsive©2023 Aeglea BioTherapeutics

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Pegtarviliase Treatment Improved Pathologies and Corrected Disease Manifestations in a Mouse Model of Homocystinuria Disease Resolution Disease Reversal Dosing Begins Day 10 CBS-/- Macro-steatosis Disease Progression AGLE-177-HIS 25 mg/kg + Betaine Day 23 CBS-/- AGLE-177-HIS 25 mg/kg Day 60 CBS-/- PBS + Betaine Day 23 CBS-/- Macro-steatosis and necrosis Premature Death Healthy liver from wild-type animal Reversal of Severe Liver Abnormalities in CBS Knockout Mouse Model1 Reductions in total plasma homocysteine led to improvements in disease-related abnormalities P = 0.0407 AGLE-177 10 mg/kg Vehicle Beneficial Impact on Osteoporosis2 Increased bone mineral density (BMD) in preclinical model of Homocystinuria with multiple doses 1 Daige C. et al. Poster presented at ASHG 2018; 2 Daige C. et al. Poster presented at ASHG 2020 Virtual Meeting, CBS -/- mice were dosed SC BIW with AGLE-177 starting at D10 through Day 169 were evaluated for bone mineral density (BMD) by dual-energy X-ray absorptiometry; AGLE-177-HIS = AGLE-177/pegtarviliase modified to include a polyhistidine tag; CBS -/- = CBS knockout mouse model©2023 Aeglea BioTherapeutics

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PEACE Baseline Demographics Demographic Characteristic Pegzilarginase n=21 Placebo n=11 Overall N=32 Age at Enrollment, y Mean (SD) 9.6 (6.16) 12.9 (6.77) 10.7 (6.47) Range 2-28 5-29 2-29 Age Category, n (%) 2y to less than 6y 5 (23.8) 1 (9.1) 6 (18.8) 6y to less than 12y 8 (38.1) 4 (36.4) 12 (37.5) 12y to less than 18y 7 (33.3) 4 (36.3) 11 (34.4) 18y or older 1 (4.8) 2 (18.2) 3 (9.4) Sex, n (%) Male 12 (57.1) 7 (63.6) 19 (59.4) Female 9 (42.9) 4 (36.4) 13 (40.6) Region, n (%) U.S. 8 (38.1) 6 (54.5) 14 (43.8) Ex-U.S. 13 (61.9) 5 (45.5) 18 (56.3)©2023 Aeglea BioTherapeutics

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PEACE Baseline Clinical Characteristics Clinical Characteristic Pegzilarginase n=21 Placebo n=11 Overall N=32 Plasma Arginine, µM/L Mean\* (SD) 365.4 (93.7) 471.7 (79.9) 402.0 (101.8) Median (range) 368.2 (202-572) 483.7 (294-573) 398.2 (202-573) GMFCS level, n (%) 1 9 (42.9) 5 (45.5) 14 (43.8) ≥2 12 (57.1) 6 (54.5) 18 (56.2) GMFM-E Mean (SD) 48.3 (19.9) 46.5 (24.6) 47.7 (21.5) Median (range) 53 (5-71) 56 (0-72) 54 (0-72) 2MWT Mean (SD) 109 (55.7) 99.9 (49.0) 105.8 (52.8) Median (range) 122 (2-202) 102 (0-171) 118 (0-202) \*Based on arithmetic mean©2023 Aeglea BioTherapeutics

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Pegzilarginase Significantly and Sustainably Reduces Plasma Arginine Levels in Phase 1/2 & OLE Plasma Arginine in Response to Pegzilarginase in Phase 1/2 & OLE Studies Baseline: Baseline plasma arginine on standard disease management was markedly elevated 20 Week Analysis1: Median plasma arginine was 112µM Median plasma arginine reduction was 277µM 56 Week Analysis2: Median plasma arginine was 99µM 10/13 patients achieved plasma arginine within the normal range (40-115µM) 13/13 patients achieved plasma arginine within the target range (<200µM) 389 171 127 112 99 OLE – Open-label extension 1 Diaz, GA, et al, J Inherit Metab Dis. 2021;44:847-856; 2 Diaz, GA et al, Presented at 2020 European Academy of Neurology Annual Meeting©2023 Aeglea BioTherapeutics

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Mobility Assessments Capture Potential Clinical Benefit of Pegzilarginase in Phase 1/2 Trial & OLE Continuous Analysis Mean Change from Baseline GMFCS – Level II/III GMFCS – Level I CE = Ceiling Effect 20 Week Analysis:11/14 (79%) 56 Week Analysis:11/13 (85%) Categorical Responder Analysis2 1Adapted from Diaz, GA et al, Presented at 2020 European Academy of Neurology Annual Meeting; 2Clinical Responder defined by achievement of a clinically meaningful response in one or more of three mobility assessments; GMFCS = Gross Motor Function Classification System; OLE = open-label extension; GMFM-E = Gross Motor Function Part E; 6MWT = 6-minute walk test Change from Baseline at 56 Week Analysis1 Not Assessed Not Assessed CE CE 7 8 9 5 1 6 2 10 12 11 16 14 15 Green = Overall Clinical Responder2 Patient # GMFM-E (Units) 6MWT (Meters) Baseline Deficit 151 Endpoint Analysis 20 weeks 56 weeks GMFM-E Overall 5 units 6 units Baseline Deficit 8 units 9 units 6MWT Overall 32 m 45 m©2023 Aeglea BioTherapeutics

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Improvements in Mobility Measures Sustained Over Time in Phase 1/2 and OLE Endpoint Change from Baseline for Phase 1/2 & OLE Studies3 20-week analysis (N=13) 32-week analysis (N=13) 56-week analysis (N=13) 104-week analysis (N=9)4 GMFM-E 4.2 units 4.1 units 5.8 units 7.1 units 6MWT 32.2 m 21.3 m 44.9 m 38.3 m Part 1: SAD N=16 0 ~10 Weeks Phase 1/2 Part 2: Weekly Doses 0 8 Weeks N=14 N=15 24 96 0 Open-Label Extension 12 N=13 ongoing Open-Label Extension 48 1 MCID is minimal clinically important difference defined in Cerebral Palsy population. 2Oeffinger D et al 2008; 3 Analysis weeks are calculated by adding the 8 weeks from Part 2 of the Phase 1/2 study to the weeks of treatment in the open-label extension (OLE) study (e.g., 8 weeks of Part 2 + 12 weeks of OLE is the 20-week analysis), baseline values were taken at Part 1 of the study; 4 13 patients remain in the OLE study, 9 of 13 patients had 96-week mobility assessments conducted; GMFM-E = Gross Motor Function Measure Part E; 6MWT = 6-minute walk test; GMFCS = Gross Motor Function Classification System; SAD = single ascending dose Mean Change from Baseline in GMFM-E Mean Change from Baseline in 6MWT Mean Change (Units) Mean Change (Meters) MCID1, 2 GMFCS I (4.0 units) GMFCS II (2.8 units)©2023 Aeglea BioTherapeutics

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Measuring the Functional Impact of Spasticity in ARG1-D Gross Motor Function Classification System (GMFCS) Overall description of current motor function based on: Movements such as sitting, walking Use of mobility devices Gross Motor Function Measure (GMFM) Part E Assesses unaided mobility without bracing or assistive devices 24 tasks involving walking forward/backward, running, jumping and ascending/descending stairs with a score range of 0-72 Timed Walk Tests Evaluates aided mobility with any needed bracing or assistive devices over a defined period of time 2 mins (2MWT) 6 mins (6MWT) Classification of Mobility: Measures of Change in Mobility: Level V not pictured: adapted seating and assistance with transfers, and utilize wheeled power mobility independently or manual mobility with assistance in most settings GMFCS graphic adapted with permission from The Royal Children's Hospital Melbourne, Australia©2023 Aeglea BioTherapeutics

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Double-blind portion of trial complete – topline data announced December 2021 Key Endpoints Analysis Primary: Plasma arginine reduction Reduction of plasma arginine compared to placebo Secondary: GMFM-E (walking, running & jumping) 2-Minute Walk Test (distance walked in 2 min) Continuous analysis Improvement compared to placebo PEACE Phase 3 Study Design \*Dosing is weekly and, if needed, dose is modified based on plasma arginine levels with maintenance of blinding. ǂThe first 8 weeks of the open-label extension will be blinded. All study participants remain on current disease management for the duration of the trial. Dose adjustments in the double-blind treatment period can be made to optimize plasma arginine control for levels outside the range of 50-150µM. If needed, weekly doses can be increased to 0.15 and 0.2 mg/kg or reduced to 0.05mg/kg; ARG1-D = Arginase 1 Deficiency; IV = intravenous; R = randomized. Patients with ARG1-D ≥2 years old Plasma arginine >250 µM (mean) Baseline deficit in clinical response assessments Placebo IV R2:1 Long Term Extensionǂ Pegzilarginase 0.1 mg/kg\* IV 24 weeks Up to 150 weeks n=11 N=32 n=21 N=31©2023 Aeglea BioTherapeutics

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Patient-Level Outcomes: Mobility in Select Patients Pegzilarginase-Treated Patients Achieving Clinical Response on ≥2 Mobility Outcomes and No Worsening at Week 24 Normalization of Mobility in Progressive Disease Supports the Potential Impact of Pegzilarginase Treatment Patient (Age) GMFM-E (Score Range, 0-72 units) 2MWT\* GMFM-D (Score Range, 0-39 units) 1 (6 years old) Improved by 7 Total score: 69 Improved by 34m to 152m Achieved normal age/sex-matched mean Improved by 2 Total score: 35 2 (6 years old) Improved by 18 Total score: 45 Improved by 46m to 96m Achieved 56% of normal age/sex-matched mean Improved by 4 Total score: 32 3 (12 years old) Improved by 6 Achieved maximum score Improved by 43m to 167m Achieved 82% of normal age/sex-matched mean Improved by 5 points Achieved maximum score 6 (14 years old) Improved by 9 Total score: 62 No worsening Improved by 8 Total score: 37 16 (2 years old) Improved by 11 Total score: 52 Improved distance by 44m\* to 150m Exceeded normal age/sex-matched mean Improved by 8 Total score: 32 17 (3 years old) Improved by 21 Total score: 62 Improved distance by 95m to 164m Exceeded normal age/sex-matched mean No worsening Ages are at the time of enrollment; Normalization defined at ±15% of age/sex-matched mean distance per the NIH toolbox; \* Reflects change from Week 12, distance at baseline not assessed owing to age©2023 Aeglea BioTherapeutics

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Attractive Commercial Opportunity and a Targeted Launch Plan 1 Catsburg C et al 2022 2 Licensing and supply agreement signed with Immedica Pharma AB in March 2021; countries in agreement include European Economic Area, United Kingdom, Switzerland, Andorra, Monaco, San Marino, Vatican City, Turkey, Saudi Arabia, United Arab Emirates, Qatar, Kuwait, Bahrain and Oman. Prevalence of >2,500 Patients1with Significant Unmet Need United States >250 patients Western Europe and Middle East2 >900 patients Rest of World >1,350 patients (including 700 in LatAm, 400 in Asia Pacific) PatientIdentification Accelerating the diagnosis and identification of patients through ongoing HCP engagement Disease Educationand Awareness Driving HCP dialogue about the devastating and progressivenature of ARG1-D Access and Reimbursement Ensuring payer understanding ofthe significant clinical and economic burden of ARG1-D Organizational Readiness Establishing an internal mindset and infrastructure to meet the needs of the global ARG1-D patient community A Focused Effort to Ensure a Successful Launch©2023 Aeglea BioTherapeutics