Document:

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                                                                   Exhibit 10.52

                             THIRD AMENDMENT TO THE
                           LOAN EXTENSION AND RELEASE
                              AND WAIVER AGREEMENT

     This Third Amendment to the Loan Extension and Release and Waiver Agreement
(this "Amendment") is entered into by and between Polar Molecular Corporation, a
Delaware corporation (the "Company"), and Affiliated Investments L.L.C., a
Michigan limited liability company (the "Holder"), to be effective as of January
31, 2003.

                                    RECITALS

A.   The Company issued to the Holder a promissory note (the "Note") in the
     principal amount of $600,000 dated as of October 25, 2001.

B.   The Company and the Holder have entered into a Loan Extension and Release
     and Waiver Agreement, as amended by the First Amendment to the Loan
     Extension and Release and Waiver Agreement effective as of May 31, 2002,
     and by the Second Amendment to the Loan Extension and Release and Waiver
     Agreement effective as of October 1, 2002, (the "Original Loan Extension"),
     pursuant to which certain terms of the Note have been amended.

C.   The Company and the Holder now wish to amend the Original Loan Extension to
     provide for the extension of additional credit under the Note in the
     aggregate principal amount of $75,000 (the "Additional Credit Amount").

D.   The parties hereto acknowledge that the Company made a payment of principal
     and interest in the amount of $50,000 at the end of February of 2002 on the
     Note (as defined in the Original Loan Extension), and that the principal
     balance owed on the Note as of January 31, 2003 after giving effect to this
     Amendment is $649,000.

                                    AGREEMENT

     In consideration of the foregoing and the mutual promises contained herein,
the Holder and the Company hereby agree as follows:

1.   Paragraph 1 of the Original Loan Extension is hereby amended in its
     entirety to read as follows:

     "1.  (a) Principal Amount. As of January 31, 2003, the principal amount
          outstanding under the Note shall be increased by $75,000 and all
          references to outstanding principal contained in the Note shall hereby
          be changed to "$649,000" (which represents the aggregate principal
          amount outstanding under the Note as of January 31, 2003).
          Notwithstanding the extension of the Additional Credit Amount,
          interest shall not accrue against the Additional Credit Amount prior
          to February 1, 2003; following which date interest shall accrue as
          provided in the Note on the aggregate principal amount of $649,000.

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          (b) Extension of Due Date. The final maturity date of December 26,
          2001 (the "Original Due Date") set forth in the Note is hereby
          extended to June 30, 2003, subject to the other repayment terms set
          forth herein."

2.   Exhibit B to the Original Loan Extension is hereby replaced in its entirety
     with the contents of Attachment I to this Amendment, which reflects the
     grant of an additional 100,000 shares of the common stock of the Company as
     consideration to the Holder for entering into this Amendment.

3.   Wire Transfer of Funds. Holder hereby agrees to wire transfer the
     Additional Credit Amount as follows:

     Holme Roberts & Owen LLP - Trust Account
     Held for: Polar Molecular Corporation 46887-00050
     Account No. 1010920111
     Routing No. 102000076
     Wells Fargo Bank West, N.A.
     1740 Broadway
     Denver, CO 80274

4.   No Other Changes. Except as explicitly amended by this Amendment, all of
     the terms and conditions of the Original Loan Extension shall remain in
     full force and effect.

                            [SIGNATURE PAGE FOLLOWS]

                                       2

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     The undersigned have executed this Amendment to be effective as of the date
set forth herein.

COMPANY:

POLAR MOLECULAR CORPORATION

By: /s/ Mark L. Nelson
    ------------------------------------
        Mark L. Nelson, President and
        Chief Executive Officer

HOLDER:

AFFILIATED INVESTMENTS, L.L.C.

By: /s/ Bruce E. Becker
    ------------------------------------
        Bruce E. Becker, President

                                       3<PAGE>

                                                                   Exhibit 10.53

                               FIRST AMENDMENT TO
                            LOAN EXTENSION AGREEMENT

     This First Amendment to Loan Extension Agreement (this "Amendment") is
entered into by and between Polar Molecular Corporation, a Delaware corporation
(the "Company"), and Lockhart Holdings, Inc. (the "Holder") to be effective as
of January 31, 2003.

                                    RECITALS

A.   The Company issued to the Holder a Promissory Note (the "Note") in the
     principal amount of $200,000 dated as of October 19, 2001;

B.   The Holder and the Company have entered into a Loan Extension Agreement
     (the "Loan Extension Agreement"), pursuant to which certain terms of the
     Note have been amended; and

C.   The Holder and the Company now desire to amend the Loan Extension to
     provide for the extension of additional credit under the Note in the
     aggregate principal amount of $25,000 (the "Additional Credit Amount"); and

D.   The Holder and the Company acknowledge that the outstanding principal
     amount under the Note as of January 31, 2003 after giving effect to this
     Amendment is $225,000.

                                    AGREEMENT

     In consideration of the foregoing and the mutual promises contained herein,
the Holder and the Company hereby agree as follows:

1.   Section 1 of the Loan Extension Agreement is hereby amended to read in its
     entirety as follows:

     "1. Section 1 of the Note is hereby amended to read in its entirety as
     follows:

     "1. Conversion. The holder of this Note (the "Holder") is entitled, at its
     option, on the Maturity Date to notify the Company to convert up to fifty
     percent (50%) of the outstanding principal amount of this Note into options
     to purchase fully paid and nonassessable shares of common stock, $0.0001
     par value, of the Company ("Common Stock"), at the initial price of $.20
     per share of Common Stock (the "Conversion Price"). The Conversion Price
     shall be subject to adjustment as specified in Section 5 hereof. Conversion
     of this Note shall be effected by surrender of this Note to the Company at
     its address specified below (or such other address as the Company shall
     have given written notice to the Holder hereof), together with a request
     that this Note be converted to options to purchase Common Stock as
     specified herein.""

2.   A new paragraph shall be added to the Loan Extension Agreement to read in
     its entirety as follows:

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     "7.  Principal Amount. As of January 31, 2003, the principal amount
          outstanding under the Note shall be increased by $25,000 and all
          references to outstanding principal contained in the Note shall hereby
          be changed to "$225,000" (which represents the aggregate principal
          amount outstanding under the Note as of January 31, 2003).
          Notwithstanding the extension of the Additional Credit Amount,
          interest shall not accrue against the Additional Credit Amount prior
          to February 1, 2003; following which date interest shall accrue as
          provided in the Note on the aggregate principal amount of $225,000."

3.   Wire Transfer of Funds. Holder hereby agrees to wire transfer the
     Additional Credit Amount as follows:

     Holme Roberts & Owen LLP - Trust Account
     Held for: Polar Molecular Corporation 46887-00050
     Account No. 1010920111
     Routing No. 102000076
     Wells Fargo Bank West, N.A.
     1740 Broadway, Denver, CO 80274

4.   Consideration. As consideration for entering into this Amendment, the
     Company (i) has agreed to reduce the conversion price of the convertible
     portion of the Note as reflected in paragraph 1 of this Amendment and (ii)
     shall issue the Holder 25,000 shares of the Company's common stock.

5.   No Other Changes. Except as explicitly amended by this Amendment, all of
     the terms and conditions of the Loan Extension Agreement shall remain in
     full force and effect.

                            [Signature Page Follows]

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     The undersigned have executed this Amendment to be effective as of the date
first set forth herein.

COMPANY:

POLAR MOLECULAR CORPORATION

By:  /s/ Mark L. Nelson
     ---------------------------------
         Mark L. Nelson, President and
         Chief Executive Officer

HOLDER:

LOCKHART HOLDINGS, INC.

By:  /s/ Thomas J. Gillespie
     ---------------------------------------
         Thomas J. Gillespie, Jr., President

                                       3<PAGE>

                                                                   Exhibit 10.54

                                 PROMISSORY NOTE

U.S. $100,000.00                                                Denver, Colorado
                                                                February 7, 2003

     FOR VALUE RECEIVED, Mark L. Nelson ("Borrower") promises to pay to the
order of Polar Molecular Corporation, a Delaware corporation ("Holder") the
principal sum of One Hundred Thousand Dollars ($100,000.00), with interest on
the unpaid principal balance from February 7, 2003, until paid, at an interest
rate equal to the Prime Rate (as determined from time to time by any major
commercial bank and published as its "prime rate"), plus one percent (1%) (the
"Interest Rate"), all in accordance with the terms and provisions hereof.

1.   Maturity Date. The entire principal and unpaid interest hereunder, and all
     Overdue Amounts (if any), shall be due and payable in full on February 7,
     2007 (the "Maturity Date").

2.   Interest. All outstanding principal shall bear interest at the Interest
     Rate per annum and all interest accrued to date shall be due and payable
     annually on February 7 of each year beginning February 7, 2004 and ending
     on the Maturity Date.

3.   Optional Prepayment. The Borrower may prepay the principal amount and any
     accrued interest outstanding under this Promissory Note (this "Note"), in
     whole or in part, at any time without premium or penalty.

4.   Overdue Amounts. If the Borrower fails to pay in full any amount payable by
     the Borrower hereunder on the due date thereof (an "Overdue Amount"), the
     Borrower will pay on the date he pays such Overdue Amount interest on the
     Overdue Amount, at the rate of the lesser of (i) the maximum lawful rate or
     (ii) 15% per annum, in each case for the actual number of days during the
     period from and including such due date to but excluding the date of actual
     payment of the Overdue Amount and all accrued interest herein.

5.   Payments Generally. Payments received for application to this Note shall be
     applied: first, to the payment of any costs of enforcing this Note; second,
     to the payment of any Overdue Amounts and accrued interest thereon at the
     increased rate specified in Clause 5 above; third, to accrued interest as
     specified in Clause 2 above; and the balance applied in reduction of the
     principal amount hereof. Any partial prepayment shall be applied against
     the principal amount outstanding and shall not postpone the due date of any
     subsequent payments or change the amount of such payments.

6.   Acceleration. If any payment required by this Note is not paid when due,
     the entire principal amount outstanding and interest accrued thereon shall
     become due and payable at the option of the Holder if Borrower fails to
     cure such non-payment within 30 days of receipt of written notice of such
     non-payment ("Acceleration"). To exercise this option, the Holder shall
     give the Borrower written notice specifying the amount of the non-

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     payment and the date upon which the Borrower must cure such non-payment
     before the Holder can exercise its option to accelerate the Note and the
     obligations hereunder (the "Acceleration Notice"). In the event that the
     Borrower cures such non-payment by paying all unpaid amounts, including any
     Overdue Amounts pursuant to Clause 4 hereof, prior to the acceleration date
     set forth in the Acceleration Notice, the terms of this Note shall be fully
     reinstated as they were immediately before such notice and no default shall
     have been deemed to have occurred hereunder. The Holder shall be entitled
     to collect all reasonable costs and expenses of enforcing this Note and the
     Holder's rights hereunder, including, but not limited to, reasonable
     attorneys' fees.

7.   Payments Generally; Tax Gross Up. All payments to be paid hereunder shall
     be made to the Holder in U.S. Dollars, free and clear of any taxes,
     deductions, withholdings and charges and without any set off or
     counterclaim, by delivery of certified clerk or other freely transferable
     and immediately available funds to the Holder at the address set forth in
     Clause 9 hereof.

8.   Waiver of Presentment, Notice of Dishonor, etc. The Borrower and all other
     makers, sureties, guarantors and endorsers hereof waive presentment,
     demand, notice of dishonor, notice of acceleration and protest, and assent
     to any extension of time with respect to any payment due under this Note,
     to any substitution or release of collateral and to the addition or release
     of any party. No waiver of any payment or other right under this Note shall
     operate as a waiver of any other payment or right.

9.   Notice. Any notice to the Borrower provided for in this Note shall be in
     writing and shall be given and be effective upon (1) delivery to the
     Borrower, or (2) mailing such notice by certified mail, return receipt
     requested, addressed to the Borrower at 4875 DTC Blvd., Building 2 No. 103,
     Denver, Colorado 80237, or to such other address as the Borrower may
     designate by notice to the Holder. Any notice to the Holder shall be in
     writing and shall be given and be effective upon (1) delivery to the
     Holder, or (2) by mailing such notice by certified mail, return receipt
     requested, to the Holder at 4600 South Ulster Street, Suite 940, Denver,
     Colorado 80237, or to such other address as the Holder may designate by
     notice to the Borrower.

10.  Governing Law. This Promissory Note shall be governed by, and construed in
     accordance with the laws of, the State of Colorado without reference to any
     conflict of law principles thereof.

     This Note is executed and delivered as of the day and year first above
written.

                                              BORROWER:

                                              /s/ Mark L. Nelson
                                              ----------------------------------
                                              Mark L. Nelson

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