# EDGAR Filing Document

**Accession Number:** 0000882361
**File Stem:** 0001171843-25-005463
**Filing Date:** 2025-8
**Character Count:** 17120
**Document Hash:** 5807e0b50a4dcec4d26fb0440fc9d457
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001171843-25-005463.hdr.sgml**: 20250818

**ACCESSION NUMBER**: 0001171843-25-005463

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 14

**CONFORMED PERIOD OF REPORT**: 20250818

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20250818

**DATE AS OF CHANGE**: 20250818

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Aptose Biosciences Inc.
- **CENTRAL INDEX KEY:** 0000882361
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** A6
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-32001
- **FILM NUMBER:** 251226310

**BUSINESS ADDRESS:**
- **STREET 1:** 66 WELLINGTON STREET WEST, SUITE 5300
- **STREET 2:** TD BANK TOWER BOX 48
- **CITY:** TORONTO
- **STATE:** A6
- **ZIP:** M5K 1E6
- **BUSINESS PHONE:** 310-849-8060

**MAIL ADDRESS:**
- **STREET 1:** 66 WELLINGTON STREET WEST, SUITE 5300
- **STREET 2:** TD BANK TOWER BOX 48
- **CITY:** TORONTO
- **STATE:** A6
- **ZIP:** M5K 1E6

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Aptose Biosciences Inc., (formerly LORUS THERAPEUTICS INC.)
- **DATE OF NAME CHANGE:** 20140905

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** LORUS THERAPEUTICS INC
- **DATE OF NAME CHANGE:** 19990308

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** IMUTEC PHARMA INC
- **DATE OF NAME CHANGE:** 19970113

?xml version='1.0' encoding='ASCII'? Form 8-K

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

### Washington, D.C. 20549
_________________

### FORM 8-K
_________________

#### CURRENT REPORT

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

#### Date of Report (Date of earliest event reported): August 18, 2025
_______________________________

#### Aptose Biosciences Inc.
(Exact name of registrant as specified in its charter)

_______________________________

---

| | | |
|:---|:---|:---|
| **Canada** | **001-32001** | **98-1136802** |
| (State or Other Jurisdiction of Incorporation) | (Commission File Number) | (I.R.S. Employer Identification No.) |

---

#### 66 Wellington Street West, Suite 5300

#### TD Bank Tower, Box 48

#### Toronto, Ontario M5K 1E6 Canada
(Address of Principal Executive Offices) (Zip Code)

(647) 479-9828

(Registrant's telephone number, including area code)

(Former name or former address, if changed since last report)

_______________________________

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:

---

| | | |
|:---|:---|:---|
| Title of each class | Trading Symbol(s) | Name of each exchange on which registered |
| None | N/A | N/A |

---

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. ☐

**Item 7.01. Regulation FD Disclosure.**

On August 18, 2025, the Registrant issued a press release, a copy of which is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

In accordance with General Instruction B.2 of Form 8-K, the information in the press release attached as Exhibit 99.1 hereto shall not be deemed to be "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), nor shall such information be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

**Item 9.01. Financial Statements and Exhibits.**

(d) Exhibits

---

| | |
|:---|:---|
| **<u>Exhibit Number</u>** | **<u>Description</u>** |
| [99.1](exh_991.htm) | [Press Release dated August 18, 2025](exh_991.htm) |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document) |

---

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

---

| | | |
|:---|:---|:---|
|  | **Aptose Biosciences Inc.** | **Aptose Biosciences Inc.** |
| Date: August 18, 2025 | By: | <u>/s/ William G. Rice, Ph.D.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</u> |
|  |  | William G. Rice, Ph.D. |
|  |  | Chairman, President, and Chief Executive Officer |

---

## Exhibit 99.1

**EXHIBIT 99.1**

**Aptose Reports Early Data Demonstrating Tuspetinib Improves Standard of Care Treatment Across Diverse Populations of Newly Diagnosed AML in Phase 1/2 TUSCANY Trial**

* *Addition of Tuspetinib (TUS) to Venetoclax (VEN) and Azacitidine (AZA) is being developed as safe and mutation agnostic frontline therapy for AML*

* *Addition of TUS to VEN+AZA improves response rates; 100% CR/CRh at 80 mg and 120 mg*

* *Addition of TUS to VEN+AZA improves MRD-negativity rates; 78% among responders*

* *100% CR/CRh in FLT3 wildtype AML, representing 70% of AML population*

* *100% CR/CRh and MRD-negativity rates in TP53, RAS and FLT3*-ITD *mutated AML*

* *Broad spectrum activity and excellent safety profile continue at 120 mg dose to date*

SAN DIEGO and TORONTO, Aug. 18, 2025 (GLOBE NEWSWIRE) -- Aptose Biosciences Inc. ("Aptose" or the "Company") (OTC: APTOF, TSX: APS), a clinical-stage precision oncology company developing the tuspetinib (TUS)-based triple drug frontline therapy to treat patients with newly diagnosed AML, today provided a data update from the Phase 1/2 TUSCANY trial in newly diagnosed AML. The trial was initiated in December 2024, and the growing body of positive data includes the recently completed third cohort of 120 mg TUS in the TUS+VEN+AZA triplet therapy. Data to date from ten (10) patients across all three cohorts, 40 mg, 80 mg or 120 mg TUS dose in TUS+VEN+AZA, support the use of TUS with standard of care treatment across all AML populations, including those carrying mutations that are the most difficult to treat and those with mutated and unmutated (wildtype) FLT3 genes.

The TUS+VEN+AZA triplet is being developed as a safe and well-tolerated mutation agnostic frontline therapy to treat large, mutationally diverse populations of newly diagnosed AML patients who are ineligible to receive induction chemotherapy. At the 120 mg TUS dose level in combination with VEN+AZA, as with the prior reported 40 mg and 80 mg TUS dose cohorts, no significant safety concerns or dose limiting toxicities (DLTs) have been observed in the TUSCANY trial, including no prolonged myelosuppression in Cycle 1 of subjects in remission, no reports of drug-related QTc prolongation or differentiation syndrome (DS), and no treatment-related deaths. Nine out of ten dosed patients remain on study across all dose cohorts and enrollment is being advanced to the 160 mg TUS dose level following the Cohort Safety Review Committee (CSRC) meeting.

"We already have data from three different TUS dose levels in the TUSCANY trial, and the data continue to strengthen at higher doses of TUS and over time. We are building a strong case for TUS+VEN+AZA as a triplet frontline therapy of choice to address a broad AML population, including subgroups with the most adverse of mutations," said William G. Rice, Ph.D., Chairman, President and Chief Executive Officer of Aptose.

**Data highlights**:

**Comparison of CR/CRh<sup>1</sup> Response rates<sup>2-5</sup>**:

---

| | | |
|:---|:---|:---|
|  | VEN+AZA<sup>2</sup> | TUS+VEN+AZA |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;All subjects | 65% | 90% (9/10) |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;NPM1-mutant | 67% | 100% (2/2) |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FLT3-ITD | 61% | 100% (2/2) |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TP53-mutant | 52% | 100% (2/2) |

---

**Comparison of MRD-negativity<sup>6</sup> rates** among All Subjects and among CR/CRh Responders<sup>3</sup>:

---

| | | |
|:---|:---|:---|
|  | VEN+AZA<sup>2,3</sup> | TUS+VEN+AZA |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Among All Subjects | 23.4% | 70% (7/10) |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Among CR/CRh Responders | 40.9% | 78% (7/9) |

---

**Comparison of MRD-negativity rates** among more difficult-to-treat Patient Subpopulations defined as Lower Benefit (*TP53*-mutated) and Intermediate Benefit (*FLT3*-ITD or *RAS*-mutated) relative to VEN+AZA<sup>5</sup>:

---

| | | |
|:---|:---|:---|
|  | VEN+AZA<sup>3,5</sup> | TUS+VEN+AZA |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Intermediate Benefit | 27.9% | 100% (3/3) |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Lower Benefit | 14.5% | 100% (2/2) |

---

**TUS+VEN+AZA - CR/CRh** and **MRD-negativity rates** among Subjects with Adverse Mutations:

---

| | |
|:---|:---|
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TP53, FLT3-ITD, RAS mutations: | Achieved CR/CRh and MRD-negativity |
|  | 100% (5/5) |

---

"As illustrated in the data highlights, the addition of TUS to VEN+AZA appears to boost response rates and MRD-negativity while maintaining favorable safety and tolerability," said Rafael Bejar, M.D., Ph.D., Chief Medical Officer of Aptose, "and the 100% CR/CRh and 100% MRD-negativity rates among the five biallelic *TP53*-mutant, *FLT3*-ITD, and *RAS*-mutant AML cases are exciting to see, as this can correlate with longer overall survival. We have observed a trend towards achieving CRs more quickly at the higher dose levels, so we are keen to see the activity as we advance into the 160 mg TUS dose cohort."

**Key messages:**

* Addition of TUS to VEN+AZA demonstrates excellent CR/CRh rates

100% CR/CRh among all subjects treated at 80 mg and 120 mg TUS dose levels
Appear to be achieving CR earlier with 120 mg TUS than with 40 mg or 80 mg 

* Addition of TUS to VEN+AZA demonstrates excellent MRD-negativity rates

MRD-negativity in 7 of 9 (78%) already achieved in patients who responded to therapy
Expect patient survival to be extended with continued long-term treatment 

* Excellent safety and well tolerated with no dose-limiting toxicities (No DLT) at completed dose levels

* Broad-spectrum activity including patients with adverse *TP53*, *RAS* and *FLT3*-ITD
mutations

* No loss of MRD-negativity observed to date, including in one patient with over 7 months of follow up

* MRD-negativity and remissions continue to mature over time on therapy

* No relapses reported to date and no treatment related deaths

* The only non-responder was a patient at the initial TUS dose level (40 mg) that did not achieve TUS exposures
previously associated with response

Additional data are included in the new Aptose corporate presentation <u>here</u>.

**TUSCANY: TUS+VEN+AZA Triplet Phase 1/2 Study**

The tuspetinib-based TUS+VEN+AZA triplet therapy is being advanced in the TUSCANY Phase 1/2 trial with the goal of creating an improved frontline therapy for newly diagnosed AML patients that is active across diverse AML populations, durable, and well tolerated.

The TUSCANY triplet Phase 1/2 study, being conducted at 10 leading U.S. clinical sites by elite clinical investigators, is designed to test various doses and schedules of TUS in combination with standard dosing of AZA and VEN for patients with AML who are ineligible to receive induction chemotherapy. A convenient, once daily oral agent, TUS is being administered in 28-day cycles. Multiple U.S. sites are enrolling in the TUSCANY trial with anticipated enrollment of 18-24 patients by late 2025. Data will be released as it becomes available.

More information on the TUSCANY Phase 1/2 study can be found on www.clinicaltrials.gov (<u>here</u>: https://www.clinicaltrials.gov/study/NCT03850574).

**About Aptose**

Aptose Biosciences is a clinical-stage biotechnology company committed to developing precision medicines addressing unmet medical needs in oncology, with an initial focus on hematology. The Company's lead clinical-stage, oral kinase inhibitor tuspetinib (TUS) has demonstrated activity as a monotherapy and in combination therapy in patients with relapsed or refractory acute myeloid leukemia (AML) and is being developed as a frontline triplet therapy in newly diagnosed AML. For more information, please visit www.aptose.com.

**Forward Looking Statements** 

This press release may contain forward-looking statements within the meaning of Canadian and U.S. securities laws, including, but not limited to, statements relating to the therapeutic potential and safety profile of tuspetinib (including the triplet therapy) and its clinical development, the anticipated enrollment rate in the TUSCANY trial and the timing thereof, as well as statements relating to the Company's plans, objectives, expectations and intentions and other statements including words such as "continue", "expect", "intend", "will", "should", "would", "may", and other similar expressions. Such statements reflect our current views with respect to future events and are subject to risks and uncertainties and are necessarily based upon a number of estimates and assumptions that, while considered reasonable by us are inherently subject to significant business, economic, competitive, political and social uncertainties and contingencies. Many factors could cause our actual results, performance or achievements to be materially different from any future results, performance or achievements described in this press release. Such factors could include, among others: our ability to obtain the capital required for research and operations and to continue as a going concern; the inherent risks in early stage drug development including demonstrating efficacy; development time/cost and the regulatory approval process; the progress of our clinical trials; our ability to find and enter into agreements with potential partners; our ability to attract and retain key personnel; changing market conditions; inability of new manufacturers to produce acceptable batches of GMP in sufficient quantities; unexpected manufacturing defects; and other risks detailed from time-to-time in our ongoing quarterly filings, annual information forms, annual reports and annual filings with Canadian securities regulators and the United States Securities and Exchange Commission.

Should one or more of these risks or uncertainties materialize, or should the assumptions set out in the section entitled "Risk Factors" in our filings with Canadian securities regulators and the United States Securities and Exchange Commission underlying those forward-looking statements prove incorrect, actual results may vary materially from those described herein. These forward-looking statements are made as of the date of this press release and we do not intend, and do not assume any obligation, to update these forward-looking statements, except as required by law. We cannot assure you that such statements will prove to be accurate as actual results and future events could differ materially from those anticipated in such statements. Investors are cautioned that forward-looking statements are not guarantees of future performance and accordingly investors are cautioned not to put undue reliance on forward-looking statements due to the inherent uncertainty therein.

For further information, please contact:

**Aptose Biosciences Inc.**

Susan Pietropaolo

Corporate Communications & Investor Relations

201-923-2049

spietropaolo@aptose.com

<sup>1</sup> Complete Response / Complete Response with Partial Hematological Recovery

<sup>2</sup> DiNardo et al. New England Journal of Medicine, August 2020; Volume 383(7):617-629.

<sup>3</sup> Pratz et al. Journal of Clinical Oncology, December 2021; Volume 40 (8):855-865.

<sup>4</sup> Othman et. al. Blood Neoplasia; September 2024; Volume 1 (3):1-11.

<sup>5</sup> Döhner et. al. Blood. 2024 November 21;144(21):2211-2222.

<sup>6</sup> MRD-negative indicates that the amount of Measurable Residual Disease, as assessed by central flow cytometry, is such that the proportion of leukemic cells in a bone marrow sample falls below <0.1%