Document:

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                                                                   Exhibit 10.48

                                KENNEDY PARTNERS
                              65 Wilsondale Street
                                 Dover, MA 02030
                               phone 508-785-2453
                               mobile 508-259-8135
                                fax 815-331-0243
                             jwk@kennedypartners.com

September 13, 2001

Mr. Mark L. Nelson
Chairman, President & CEO
Polar Molecular Corporation
Denver, CO 80237

eMail: ggorman@polarmolecular.com
cc:    ampolich@aol.com

Dear Mark,

Kennedy Partners will act as the exclusive investment banking representative of
Polar Molecular Corporation (hereinafter referred to as "PMC" or "the Company"),
generally, in the consideration and implementation of strategic corporate
finance initiatives and development, in advice and support of the private
placement of up to $1.5 million already underway by the Company to be closed as
soon as possible (the "Bridge Refinancing"), and, most particularly, in the
private placement of up to $10 million of equity or equity related securities to
one or more institutional or strategic, corporate investors (the "Institutional
Placement").

A space is provided below for your signed acceptance of the terms of this
engagement.

The roll of Kennedy Partners--

Kennedy Partners effectively will work as an extension of PMC's Management and
Board in the preparation and implementation of the Institutional Placement and
other related opportunities that may arise in the course of the engagement.
Specifically, work will include:

          .    Review of PMC's current financial condition, business plan,
               long-term strategic objectives, and near-term financing
               requirements, including most particularly the bridge loan
               arranged earlier this year by APS Financial Services;

          .    Study of PMC's joint marketing alliance with Total Fina Elf and
               proposed mutual opportunity and review of PMC's additional
               strategic relations and tactics, including with Ford, BP Amoco,
               and Octel;

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Mr. Mark L. Nelson
Polar Molecular Corporation
September 13, 2001
Page 2

          .    Assistance in structuring of proposals to and negotiations with
               shareholders of PMC and other prospects that PMC identifies or
               other prospects that Kennedy Partners identify to invest in the
               Bridge Refinancing;

          .    Assistance in structuring of proposals to and negotiations with
               APS Financial Services in regards to the conversion and/or
               extension of the outstanding $800,000 secured bridge loan held by
               their clients;

          .    Assistance in preparation of private placement memorandums and
               materials that will be appropriate for the Bridge Refinancing and
               Institutional Placement, including cooperation with your
               attorneys, accountants, and other representatives in the course
               of preparing these documents, contracts, due diligence
               investigation and closing of any transaction(s).

          .    Assistance with communication, qualification, and negotiation of
               other means of raising financing that may arise during the term
               of this engagement.

The terms of engagement--

Kennedy Partners is prepared to commence this engagement immediately on the
following terms:

     .    $7,500 monthly retainer payable in cash commencing with the first
          payment due upon signing of this engagement letter and payable each
          month thereafter beginning with October on the 1st of the month
          continuing until terminated by PMC in writing.

          PMC shall have the option each month to pay Kennedy Partners, in lieu
          of $7,500 in cash, $3,000 in cash plus options to purchase 6,000
          shares of Common Stock*, or in a cash amount between $3,000 and
          $7,5000 plus a number of options adjusted proportionately.

     .    Reimbursement of all reasonable out-of-pocket expenses.

     .    Success fee payable with respect to (any financing by Hunt Investment
          Company excluded) the Bridge Refinancing in regards to any portion of
          such financing purchased by investors introduced to PMC directly by
          Kennedy Partners or indirectly by referrals from persons or firms
          introduced by Kennedy Partners upon the closing(s) of such a
          transaction determined in an amount as follows:

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*   Having an option exercise price equal to the lower of price per share of the
    Placement or $1.00 per share (giving pro forma effect to the approved 1 for
    10 reverse stock split.

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Mr. Mark L. Nelson
Polar Molecular Corporation
September 13, 2001
Page 3

          .    3% of funds raised payable in cash.

          .    5% of securities sold payable in options to acquire like kind. *

     .    Success fee payable with respect to the Institutional Placement upon
          the closing(s) of any such a transaction(s) with any and all investors
          determined in an amount as follows:

          .    3% of funds raised payable in cash with a minimum cash fee of
               $150,000.

          .    5% of securities sold payable in options to acquire like kind.*

     .    Success fee payable with respect to any syndicated, retail or other
          successful financing placed by other agents of PMC upon the closing(s)
          of any such a transaction(s) determined in an amount as follows:

          .    5% of securities sold payable in options to acquire like kind.*

The following provisions shall also apply:

     .    Kennedy Partners will be provided with copies of closing documents
          prior to each closing and notified at least one week in advance as to
          the time and place of closing.

     .    Kennedy Partner's right to receive a success fee for any completed
          transaction involving PMC or other parties that may contact PMC or
          Kennedy Partners in this context during the course of this engagement
          shall remain in effect in regards to a transaction with PMC or any
          such prospect that is either consummated or in regards to which
          discussions are commenced within 12 months from the termination in
          writing of monthly retainer payments pursuant to this letter of
          engagement; except in regards to this extension provision, that in the
          case of (i) a Bridge Refinancing transaction, this provision would
          apply only to investors introduced directly or indirectly by Kennedy
          Partners, (ii) an Institutional Placement, all shareholders of and
          lenders to PMC as of the date of this engagement letter shall be
          excluded, and (iii) any syndicated, retail or other successful
          financing placed by other agents of PMC, this provision would apply
          only to transactions closed within 4 months from the termination in
          writing of monthly retainer payments.

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*    Having an option exercise price equal to the lower of price per share of
     the Placement or $1.00 per share (giving pro forma effect to the approved 1
     for 10 reverse stock split.

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Mr. Mark L. Nelson
Polar Molecular Corporation
September 13, 2001
Page 4

Accuracy of information and indemnification--

As is customary in assignments such as this, PMC agrees to indemnify Kennedy
Partners, including its affiliates, and hold it harmless in connection with the
performance of its responsibilities under this engagement against any losses,
claims, damages, expenses, or liabilities (including legal fees and other
expenses reasonably incurred in defending same) to which Kennedy Partners, its
affiliates, agents, or any person acting on its behalf may become subject
arising out of or based on: (i) any act taken or omitted by PMC or any person or
entity at the request of or with the consent of PMC pursuant to our engagement
hereunder, or (ii) any allegations of any of the foregoing. It is understood,
however, that neither Kennedy Partners, its affiliates, agents, nor any person
acting on its behalf shall be indemnified if it is determined that such person
acted in bad faith or was guilty of gross negligence or willful misconduct.

Assignment--

If in the event Kennedy Partners is acquired by another firm or Wade Kennedy
becomes a member of another firm, this engagement may by be assigned to such
firm on the same terms upon the approval of PMC, which approval shall not be
unreasonably withheld.

Any disputes--

Both PMC and Kennedy Partners agree that if any dispute should arise between
them under this engagement letter which can not be resolved by mutual agreement,
such dispute will be submitted to binding arbitration for resolution in the
Commonwealth of Massachusetts.

If the terms and provisions set forth above are acceptable, please execute two
copies of this agreement and return one together with the initial retainer
payment of $7,500.

Very truly yours,

/s/  J. Wade Kennedy
----------------------------------------
     J. Wade Kennedy

Accepted:

POLAR MOLECULAR CORPORATION

By:  /s/ Mark Nelson                                     9-14-2001
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                                                                   Exhibit 10.49

                           LOAN EXTENSION AND RELEASE
                              AND WAIVER AGREEMENT

     This Loan Extension and Release and Waiver Agreement (this "Agreement") 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 the time stated herein.

                                    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 Holder and the Company desire to extend the due date of the Note and
     amend the terms for repayment of the Note;

C.   The Company and the Holder are party to a Preemptive Rights Agreement dated
     January 31, 2000 (the "Preemptive Rights Agreement"), pursuant to which the
     Holder was granted the right to maintain its ownership interest in the
     Company by purchasing securities of the Company at the same price and upon
     the same terms of any subsequent offering made by the Company prior to
     January 31, 2002;

D.   The Holder has communicated to the Company that the Holder is not
     interested in purchasing any more of the Company's securities;

E.   The Company has made additional securities offerings since the date of the
     Preemptive Rights Agreements and anticipates making further securities
     offerings for which the Holder has not exercised or does not desire to
     exercise its preemptive rights pursuant to the Preemptive Rights Agreement;
     and

F.   The Company has requested that the Holder waive, and the Holder has agreed
     to waive any preemptive rights that it may have under, and release any
     claims that the Holder may have against the Company pursuant to the
     Preemptive Rights Agreement.

                                    AGREEMENT

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

1.   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 1,
     2002, subject to the other repayment terms set forth herein.

2.   Terms of Repayment. The Company shall repay principal and interest amounts
     outstanding under the Note in accordance with the payment schedule attached
     hereto as Exhibit A. Notwithstanding the terms of the payment schedule set
     forth in Exhibit A hereto, the Company may prepay principal and interest
     without premium or penalty. All

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     payments to be made pursuant to this Agreement are in addition to the
     principal amount of $7,500, which the Company owes to the Holder for
     reimbursement of attorney fees pursuant to the terms of the Purchase
     Agreement between the Company and Holder, dated as of October 25, 2001.

3.   Consideration. As consideration for entering into this Agreement, the
     Company shall issue the Holder 50,000 shares of the Company's common stock
     for each month that the obligations under this Agreement remain
     outstanding, up to an aggregate of 250,000 shares. A certificate
     representing the first 50,000 shares of the Company's common stock will be
     delivered to the Holder upon due execution of this Agreement, and an
     additional certificate representing 50,000 shares of the Company's common
     stock will be issued to the Holder upon each monthly anniversary of the
     Original Due Date, until the earlier of (i) repayment in full of the
     obligations hereunder, or (ii) such time as the Company has issued the
     Holder an aggregate of 250,000 shares of the Company's common stock
     pursuant to this Agreement.

4.   Effect of this Agreement.

     (a)  The Holder hereby agrees that as of the Effective Date of this
          Agreement the Company shall not be in default under the Note or under
          any other related agreement including, without limitation, the
          Security Agreement (the "Security Agreement") between the Company and
          the Holder dated as of October 25, 2001. The Holder hereby waives any
          remedies it may have had under the Note or the Security Agreement
          prior to the Effective Date of this Agreement as a result of the
          Company's failure to pay the Note in full on or before the Original
          Due Date (although the Holder retains any remedies relating to any
          future defaults).

     (b)  The Company hereby agrees that failure to repay the Note in accordance
          with this Agreement and the repayment terms set forth on Exhibit A
          hereto or failure to perform or comply in any material respect with
          any of the obligations set forth in this Agreement shall constitute an
          Event of Default (as that term is defined in the Note) under the Note
          and the Security Agreement. Notwithstanding anything herein, upon the
          occurrence of such an Event of Default hereunder, the Holder shall be
          entitled to all rights and remedies provided for by the terms of the
          Note and the Security Agreement.

     (c)  Other than those terms specifically addressed by this Agreement, the
          terms of the Note shall not be altered or amended by this Agreement.
          In the event of a conflict between the terms of the Note and this
          Agreement, the terms of this Agreement shall control and be binding on
          the Holder and the Company.

5.   Effective Date. This Agreement shall become effective upon the receipt by
     the Holder of a payment of $50,000, which amount shall be paid no later
     than February 28, 2002. The Holder hereby agrees to not exercise any remedy
     that may be available to it for non-payment of the Note including without
     limitation exercising its remedies under the Note or the Security Agreement
     until the earlier of March 1, 2002 or such time as the

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     Company gives notice in writing to the Holder of its intention not to make
     the payment set forth above on or before February 28, 2002.

6.   Release and Waiver. The Holder hereby absolutely and unconditionally
     releases and forever discharges the Company, together with its directors,
     officers, agents and employees from any claims, demands or causes of action
     of any kind, nature or description arising under or in connection with the
     Preemptive Rights Agreement, and hereby further waives any default or event
     of default existing thereunder, whether known or unknown.

7.   Notices. Any notice or other communication hereunder shall be in writing
     and shall be mailed by certified mail, return receipt requested,
     transmitted by facsimile, or delivered against receipt to the party to whom
     it is to be given (a) if to the Company, at 4600 S. Ulster St. Suite 700
     Denver, Colorado 80237, facsimile: (303) 804-3825, or (b) if to the Holder,
     at the address or facsimile number set forth on the signature page hereof
     (or, in either case, to such other address or facsimile number as the party
     shall have furnished in writing in accordance with the provisions of this
     Section 6). Each such notice or other communication shall for all purposes
     of this Agreement be treated as effective or as having been given when (x)
     delivered if delivered personally, (y) if transmitted by facsimile, upon
     conclusion of the transmission, or (z) if sent by certified mail, at the
     time of certification thereof.

8.   Miscellaneous

     (a)  This Agreement shall be binding on the Company and its successors, and
          shall inure to the benefit of the Holder, its successors and assigns.
          Any reference to the Holder shall include any holder in due course of
          the Note.

     (b)  This Agreement, the Note and the Security Agreement together
          constitute the entire agreement between the Holder and the Company
          with respect to the subject matter hereof and supersedes all prior
          oral or written agreements and understandings, if any, relating to the
          subject matter hereof.

     (c)  Each provision of this Agreement shall be considered separate. If for
          any reason any provision or provisions hereof are determined to be
          invalid or contrary to applicable law, such invalidity shall not
          impair the operation of or affect the remaining portions of this
          Agreement.

     (d)  This Agreement may be executed in one or more counterparts, each of
          which shall be deemed an original, but all of which shall together
          constitute one and the same instrument.

                            [SIGNATURE PAGE FOLLOWS]

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     The undersigned have executed this Agreement 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.
Address:  2750 Auburn Court
          Auburn Hills, MI 48326
Fax:      248-852-5174

By: /s/    Bruce Becker
    ------------------------------------------
    Name:  Bruce Becker
    Title: President

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