<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-

<PAGE>

     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

                                       2