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                             CO-PROMOTION AGREEMENT

                                     BETWEEN

                           INEX PHARMACEUTICALS, INC.

                                       AND

                           ENZON PHARMACEUTICALS, INC.

                                January 19, 2004

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>

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                                TABLE OF CONTENTS

Article 1 Interpretation.......................................................1
    1.1   Definitions..........................................................1

Article 2 Co-Promotion.........................................................3
    2.1   Co-Promotion Rights..................................................3
    2.2   Use by Inex of Representatives.......................................4
    2.3   Enzon's Back Office Responsibilities.................................4

Article 3 Coordination.........................................................4
    3.1   Coordination of Activities...........................................4
    3.2   Reporting Relationships..............................................4
    3.3   Supervision and Management of Personnel..............................4
    3.4   Training.............................................................5
    3.5   Communication........................................................5
    3.6   Marketing  Subcommittee..............................................5

Article 4 Promotional Material.................................................5
    4.1   Approved Promotional Materials.......................................5
    4.2   Provision of Enzon's Promotional Materials...........................5
    4.3   Approval of Inex's Promotional Material..............................5
    4.4   Use of Promotional Materials.........................................6
    4.5   Corporate Logos......................................................6
    4.6   Website..............................................................6

Article 5 Compliance...........................................................7
    5.1   Consistent Statements................................................7
    5.2   Medical Science Liaisons.............................................7
    5.3   Communications to Sales Representatives and
          Medical Science Liaisons.............................................7
    5.4   Standards............................................................7

Article 6 Payments by Enzon....................................................8
    6.1   Reporting and Payment of Co-Promotion Commercialization Costs........8
    6.2   Additional Sales Representatives and Medical Science Liaisons........8
    6.3   Payment of Co-Promotion Costs........................................8
    6.4   Notice of Other Promotional Activities...............................9
    6.5   Taxes; Indemnification...............................................9

Article 7 Termination..........................................................9
    7.1   Term of Agreement....................................................9
    7.2   Termination for Breach...............................................9
    7.3   Termination upon Bankruptcy.........................................10
    7.4   Effect of Termination...............................................10
    7.5   Survival of Obligations; Return of Confidential Information.........11

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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Article 8 Miscellaneous.......................................................11
    8.1   Assignment..........................................................11
    8.2   Counterparts........................................................12
    8.3   Exhibits and Appendices.............................................12
    8.4   Force Majeure.......................................................12
    8.5   Further Assurances..................................................12
    8.6   Modification........................................................12
    8.7   No Agency...........................................................12
    8.8   No Solicitation or Hiring of Employees..............................13
    8.9   Non-Use of Names....................................................13
    8.10  Notices.............................................................13
    8.11  Publicity...........................................................14
    8.12  No Third Party Beneficiaries........................................15
    8.13  Waiver..............................................................15

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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                             CO-PROMOTION AGREEMENT

This CO-PROMOTION AGREEMENT dated as of the 19th day of January, 2004 between
Inex Pharmaceuticals, Inc., a corporation duly incorporated pursuant to the laws
of Delaware, USA, having a registered office at Corporation Trust Center, 1209
Orange Street, Wilmington, DE 19801 (hereinafter referred to as "Inex"), and
Enzon Pharmaceuticals, Inc., a corporation duly incorporated pursuant to the
laws of Delaware, having a principal place of business at 685 Route 202/206,
Bridgewater, New Jersey 08807 (hereinafter referred to as "Enzon").

INTRODUCTION

A. Enzon is a pharmaceutical company with operations in research and
development, import, manufacture and sale of pharmaceutical products;

B. Inex is in the business of developing, manufacturing and selling certain
pharmaceutical products, including Vincristine Sulfate Liposomes Injection (as
further defined in this Agreement);

C. Of even date hereof, the Parties have entered into a Product Supply Agreement
pursuant to which Inex will supply to Enzon Vincristine Sulfate Liposomes
Injection (the "Product Supply Agreement");

D. Of even date hereof, the Parties also have entered into a Development
Agreement for the development of Vincristine Sulfate Liposomes Injection and for
the purpose of providing for the Regulatory Approval of, and conveying certain
rights to Enzon with respect to, Inex's Vincristine Sulfate Liposomes Injection
product in the Territory (the "Development Agreement"); and

E. Subject to the terms and conditions set forth in this Agreement, the Parties
wish to set out certain co-promotion rights for Inex and Enzon in the Territory.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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NOW, THEREFORE, the Parties, intending to be legally bound, hereby agree as
follows:

                            Article 1 Interpretation

1.1   Definitions

Unless otherwise defined in this Agreement, capitalized terms used in this
Agreement shall have the meaning set out therefor in the Product Supply
Agreement or the Development Agreement (in the event of a conflict, the Product
Supply Agreement shall prevail). For purposes of this Agreement, the following
terms will have the meanings set forth below:

      1.1.1   "Code" or "Codes" means the Code on Interactions with Healthcare
              Professionals promulgated by the Pharmaceutical Research and
              Manufacturers of America (PhRMA) and the American Medical
              Association (AMA) Guidelines on Gifts to Physicians from Industry,
              as either of the foregoing may be amended from time to time.

      1.1.2   "Commercialization" means the activities customarily associated
              with sales of pharmaceutical products including without
              limitation, Manufacturing, DDMAC Activities, price and
              reimbursement negotiations, pre-launch and launch activities,
              marketing, sales, distribution, Co-Promotion, Post-Approval
              Clinical Activities, the development, prosecution, registration
              and maintenance of trademarks, trade names and domain names, and
              pharmaco-vigilance in each country in the Territory.

      1.1.3   "Co-Promotion" or "Promotion" means:

              (a)       Detailing and/or other related activities, including the
                        provision of medical information services or medical
                        liaison support, and

              (b)       market research, journal advertising, direct mail
                        programs, participation in trade shows, symposia,
                        congresses and other medical meetings; and

              (c)       MSL Activities;

              undertaken by Enzon, or by Inex in concert with Enzon's marketing
              personnel and sales force to augment Enzon's marketing and sale of
              VSLI. When used as a verb, "Co-Promote" or "Promote" means to
              engage in such activities.

      1.1.4   "Co-Promotion Costs" means, with respect to Co-Promotion of the
              Product by Inex or its Representatives, Inex's personnel cost of
              Sales Representatives and Medical Science Liaisons including ***.
              For greater certainty, "Co-Promotion Costs" are not included in
              Commercialization Costs as defined in the Product Supply
              Agreement.

      1.1.5   "Detail" means a face-to-face meeting (including live video
              presentation) with a physician; other medical professional with
              prescribing authority; or office nurse or medical paraprofessional
              with influence over pharmaceutical

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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              prescribing or treatment regimes for patients in the Territory
              during which scientific and/or medical information about the
              Product is discussed. When used as a verb, the term "Detailing"
              means to engage in the activity of a Detail.

      1.1.6   "Medical Science Liaison" means an individual employed by either
              Party to perform MSL Activities.

      1.1.7   "MSL Activities" means through the use of Medical Science Liaisons
              the maintenance of effective relationships with clinical
              investigators with respect to the Product in the Territory. MSL
              Activities would also include responding to physicians' requests
              for medical information with respect to the Field.

      1.1.8   "Pharmacovigilance" means all the activities associated with
              maintaining an effective drug safety monitoring system and adverse
              events reporting system in compliance with the requirements of
              Regulatory Authorities.

      1.1.9   "Product Labeling" means:

              (a)       the full prescribing information for the Product,
                        including any required patient information, as approved
                        by Regulatory Authorities; and

              (b)       all labels and other written, printed, or graphic matter
                        upon any container, wrapper, or any package insert,
                        utilized with or for the Product.

      1.1.10  "Promotional Materials" means all written, printed, graphic,
              electronic, audio or video matter, including journal
              advertisements, sales visual aids, direct mail, direct-to-consumer
              advertising, web pages, web links, Internet postings, broadcast
              advertisements, sales reminder aids (e.g., scratch pads, pens and
              other such items) and reprints intended for use or used by the
              Parties in connection with any Promotion, except the Product
              Labeling.

      1.1.11  "Sales Representative" means an individual employed by either
              Party or whose services are contracted for by either Party and who
              engages in Co-Promotion.

      1.1.12  "Standards" means the Accreditation Council for Continuing Medical
              Education (ACCME) Standards for Commercial Support of Continuing
              Medical Education, as they may be amended from time to time.

      1.1.13  "Term" shall have the meaning set out in Section 7.1.

                             Article 2 Co-Promotion

2.1   Co-Promotion Rights

Inex shall have the right to engage in Co-Promotion activities with respect to
VSLI in the Territory pursuant to and in accordance with the provisions of this
Agreement.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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2.2   Use by Inex of Representatives

To the extent Inex does engage in Co-Promotion activities, it will do so through
its own employees or, subject to the approval of Enzon, not to be unreasonably
withheld, through its Representatives, such Representatives to include a
contract sales force.

2.3   Enzon's Back Office Responsibilities

Notwithstanding any Co-Promotion activities engaged in by the Parties, Enzon
shall remain responsible to book all sales of VSLI, conduct reimbursement
negotiations, conduct Pharmacovigilance, handle returns/recalls and order
processing, invoicing and collection, distribution, warehousing, inventory and
receivables, collection of sales data from hospitals and other end users and all
other customer service related functions and the like.

                             Article 3 Coordination

3.1   Coordination of Activities

Enzon and Inex shall cooperate on the determination of activities to be
undertaken by Inex employees and its Representatives engaged in Co-Promotion on
both a geographic and physician base basis. Due consideration will be given to
ensure that Inex employees and its Representatives have no lesser economic
opportunity than Enzon employees for their respective geographic and physician
assignments.

3.2   Reporting Relationships

To the extent they are engaged in Co-Promotion, Inex employees and its
Representatives shall be subject to the control and direction of Enzon. For the
purposes of conducting Co-Promotion, such Inex employees and Representatives
shall have reporting responsibilities and be subordinate to the Enzon managers
to whom their peer level Enzon employees report and are subordinate. Enzon
managers will work cooperatively with their peer level Inex employees and Inex's
Vice President, Sales & Marketing or such other executive officer as Inex
designates in the management of such Inex employees and Representatives. To the
extent the same Inex employees and its Representatives are engaged in
promotional activities related to products other than VSLI, they shall not be
subject to the control and direction of Enzon.

3.3   Supervision and Management of Personnel

Inex shall cooperate with Enzon promptly and reasonably with respect to the
supervision and management of its employees and its Representatives engaged in
Co-Promotion. Subject to Section 3.1, Inex shall consider in good faith and give
due weight to and, to the extent practicable, accommodate the recommendations of
Enzon with respect to the management of Inex's employees and its Representatives
engaged in Co-Promotion, including such matters as territorial assignments,
performance improvement and disciplinary actions, promotions, demotions,
terminations, etc. In addition, to the extent practical, the Parties will employ
similar compensation systems to foster strategic alignment and to foster
positive relations between each Party's personnel engaged in Co-Promotion.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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3.4   Training

Inex shall have the opportunity to review all training materials prior to their
use. Inex employees and its Representatives engaged in Co-Promotion shall be
subject to the same training, knowledge and performance requirements to which
their peer level Enzon employees are subject. They shall attend the same
training sessions and the same sales and other meetings that Enzon employees are
required to attend. Enzon shall bear all costs of organizing and conducting any
training sessions, except for travel and out-of-pocket costs incurred by Inex
personnel which shall be shared by Inex and Enzon pursuant to Section 6.1.

3.5   Communication

Each Party shall have the right to arrange for its employees and Representatives
directly involved in Co-Promotion of the Product to visit the other Party at the
other Party's offices, and to discuss related activities with the technical and
business personnel and consultants of such Party, provided that such visits
shall be upon reasonable prior notice and during normal business hours and shall
not unreasonably interrupt the operations of such Party.

3.6   Marketing Subcommittee

The Joint Steering Committee shall create a subcommittee, to be called the
Marketing Subcommittee, which will be constituted of such persons and engage in
such activities regarding Co-Promotion as shall be determined by the Joint
Steering Committee.

                         Article 4 Promotional Material

4.1   Approved Promotional Materials

In its Co-Promotion, Inex shall use only the Promotional Materials approved by
Enzon in writing and the trademarks, tradenames and domain names maintained by
Enzon and Inex for VSLI. Enzon shall bear all costs related to the preparation
and production of promotional materials for use by Inex employees and its
Representatives.

4.2   Provision of Enzon's Promotional Materials

Enzon shall provide Inex with sufficient final copies of all Promotional
Materials concurrently with Enzon's finalization of the form of same, and in any
event, prior to any public dissemination of same.

4.3   Approval of Inex's Promotional Material

Enzon shall have absolute discretion to approve all Promotional Materials
prepared by Inex prior to their use by Inex in Co-Promoting the Product. Enzon
shall designate an employee contact to whom Inex shall send for approval all
Promotional Materials.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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4.4   Use of Promotional Materials

      4.4.1   Each Party shall own all Intellectual Property Rights in any
              Promotional Materials created or developed by such Party.

      4.4.2   Inex will provide to Enzon prior to their use Promotional
              Materials that Inex creates for use outside the Territory. Inex
              will consider in good faith any comments or suggestions made by
              Enzon concerning such Promotional Materials.

      4.4.3   Inex reserves the right to use outside the Territory all
              Promotional Material created by Inex and approved by Enzon for use
              inside the Territory.

      4.4.4   Inex shall have the opportunity to review Promotional Materials
              created by Enzon.

      4.4.5   Enzon and Inex will cooperate in good faith with Inex's
              Representatives, and Inex will use Commercially Reasonable Efforts
              to cause its Representatives to cooperate in good faith with Enzon
              and Inex, with respect to the preparation of Promotional Materials
              for, and the use of such materials in, different geographic
              markets on a global basis.

4.5   Corporate Logos

All training materials and Promotional Materials shall bear both Parties'
corporate logos in equal prominence. During the Term, each Party grants to the
other, the non-exclusive right to use its corporate logo in the Territory solely
for the purpose of the Promotion of the Product in accordance with the terms of
this Agreement. Each Party will use commercially reasonable efforts to protect
the other Party's corporate name, logo and symbol. Each Party acknowledges that
the other Party owns all right, title and interest in such other Party's
corporate name, logo and symbols and all good will associated therewith and that
any and all use of corporate name, logo or symbols under the Related Agreements,
and any good will associated with such use, shall inure exclusively to the
benefit of the owner of such name, logo or symbol.

4.6   Website

On any website relating solely to the Product that is owned or controlled by, or
operated on behalf of, Enzon to promote the Product (the "Websites"), Enzon
shall place (or cause to have placed) the Inex logo and accompanying text
provided by Inex, or such other Inex logo and accompanying text as Inex may
designate from time to time in writing to Enzon, subject to review and approval
of any such text by Enzon. Any such logo and accompanying text shall be given
appropriate placement on such websites and shall link to a uniform resource
locator ("URL") address designated by Inex, which URL address may be changed by
Inex from time to time upon reasonable notice to Enzon; provided, however, that
before providing any such link to a URL address, Enzon shall have the right to
review and approve the contents thereof. Inex grants Enzon the right to
establish a link to the Websites or other websites designated by Enzon and
approved by Inex from specific websites relating solely to the Product owed or
controlled by, or operated on behalf of, Inex. Enzon also grants Inex the right
to place (or cause to have

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                     - 7 -


placed) the Enzon logo and accompanying text provided by Enzon, or such other
Enzon logo and accompanying text as Enzon may designate from time to time in
writing to Inex, on such Inex websites, subject to review and approval of any
such text by Inex. The content of the websites owned or controlled by Inex
relating solely to the Product and accessible in the Territory, and the portions
of other websites owned or controlled by Inex that relate to the Product and are
directed at Commercializing the Product shall be subject to the review and
approval of Enzon, which approval shall not be unreasonably withheld.

                              Article 5 Compliance

5.1   Consistent Statements

In connection with each Party's Promotion and Detailing of the Product, neither
Party shall make, nor permit its Sales Representatives to make, any statement,
representation or warranty, oral or written, to any person that is inconsistent
with the Product Labeling or the Promotional Materials. Each Party shall
promptly notify the other Party of and provide the other Party with a copy of
any correspondence or other reports or complaints received by a Party from any
Regulatory Authority, or any third party claiming that any Promotional Materials
are inconsistent with the Product Labeling or are otherwise in violation of
Regulatory Requirements.

5.2   Medical Science Liaisons

Each Party shall conduct MSL Activities using only Medical Science Liaisons who
have sufficient technical training and experience to perform such activities in
a manner consistent with the practice by leading pharmaceutical and
biotechnology companies of such activities within the Field. Each Party shall
require each Medical Science Liaison to attend training before such Medical
Science Liaison is permitted to conduct MSL Activities.

5.3   Communications to Sales Representatives and Medical Science Liaisons

Enzon shall provide Inex with copies of general communications (including
communications sent electronically or by voice mail) disseminated by Enzon to
the Sales Representatives and Medical Science Liaisons and relating to
strategies for the Promotion or Detailing of the Product or the conduct of MSL
Activities, as applicable.

5.4   Standards

In addition to its obligations to comply with Regulatory Requirements, each
Party shall:

      5.4.1   Promote the Product in conformity with the practices and
              procedures relating to the education of the medical community set
              forth in the Standards; and

      5.4.2   promptly notify the other Party of and provide the other Party
              with a copy of any correspondence or other reports with respect to
              the Promotion of the Product or the conduct of the MSL Activities
              that a Party receives from:

              (a)       the Accreditation Council for Continuing Medical
                        Education (ACCME) relating to either Party's compliance
                        with the Standards;

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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              (b)       the PhRMA and the AMA relating to either Party's
                        compliance with the Codes; and

              (c)       the Division of Drug Marketing, Advertising and
                        Communications (DDMAC), of the FDA in relation to either
                        Party's compliance with Applicable Laws.

                          Article 6 Payments by Enzon

6.1   Reporting and Payment of Co-Promotion Costs

Enzon shall reimburse Inex for 50% of the Co-Promotion Costs of Inex's
Co-Promotion to augment Enzon's efforts up to a maximum of 30 sales persons and
medical science liaisons in accordance with the following:

      6.1.1   after launch of the Product and until Enzon has achieved Net Sales
              of the Product of at least $*** in any rolling four Commercial
              Quarter period, the number of Sales Representatives and Medical
              Science Liaisons shall not exceed ***;

      6.1.2   after Enzon has achieved Net Sales of the Product of at least $***
              in any rolling four Commercial Quarter period, but before it has
              achieved annual Net Sales of the Product of at least $*** in any
              rolling four Commercial Quarter period, the number of Sales
              Representatives and Medical Science Liaisons shall not exceed ***;
              and

      6.1.3   after Enzon has achieved Net Sales of the Product of at least $***
              in any rolling four Commercial Quarter period:, the number of
              Sales Representatives and Medical Science Liaisons may increase to
              *** or such number of Sales Representatives and Medical Science
              Liaisons above *** as mutually agreed to by the Parties in writing
              (and in accordance with such agreement).

6.2   Additional Sales Representatives and Medical Science Liaisons

Notwithstanding the foregoing, Inex may at any time utilize Sales
Representatives and Medical Science Liaisons in excess of the numbers set out in
Sections 6.1.1, 6.1.2 and 6.1.3 at Inex's expense, provided that such Sales
Representatives and Medical Science Liaisons comply with the terms of this
Agreement and Inex bears any incremental costs of Enzon associated with such
Sales Representatives and Medical Science Liaisons.

6.3   Payment of Co-Promotion Costs

On a quarterly basis, within 12 Business Days after the end of each Calendar
Quarter, Inex shall send Enzon invoices for 50% of its Co-Promotion Costs
accompanied by the appropriate documentation, including a listing of
expenditures in reasonably specific detail. Enzon shall pay such invoices within
thirty (30) days after receipt of same. Any Co-Promotion Costs incurred by Inex
or its Representatives in a particular quarter and not reflected in the invoice
delivered pursuant to the foregoing sentence shall be captured in subsequent
invoice(s).

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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6.4   Notice of Other Promotional Activities

If any Inex employee or Representative engaged in Co-Promotion is to commence
promotional activities with respect to any other product, Inex will provide
written notice thereof to Enzon at least 60 days prior to the commencement of
such other promotional activities. Enzon shall not be obligated to reimburse
Inex with respect to any promotional activities related to other products. For
purposes of determining Enzon's reimbursement obligations, the Commercialization
Costs for any employee engaged in such other promotional efforts shall be
allocated between VSLI and the other products on an equitable basis.

6.5   Taxes; Indemnification

The Inex employees and Representatives engaged in the Co-Promotion shall not be
deemed to be employees of Enzon. Inex shall be responsible for all income tax
withholding and similar obligations to all relevant taxing and other authorities
associated with all personnel engaged in Co-Promotion. Enzon's sole financial
obligations shall be to make the reimbursement payments directly to Inex as set
forth in this Agreement. Inex hereby does indemnify and shall defend Enzon
against and hold it harmless from any and all claims and/or liabilities that may
arise out of any characterization of, or attempt to characterize, any person
engaged in the Co-Promotion as an employee of Enzon.

                             Article 7 Termination

7.1   Term of Agreement

This Agreement shall become effective on the Effective Date and, unless earlier
terminated as provided for herein, shall expire, on a country-by-country basis,
upon the expiration of any of the Related Agreements and such period shall be
the "Term" under this Agreement.

7.2   Termination for Breach

Each Party shall be entitled to terminate this Agreement by written notice to
the other Party in the event that the other Party shall be in material default
of any of its obligations hereunder, and shall fail to remedy any such default
within sixty (60) days after notice thereof by the non-breaching Party. Any such
notice shall specifically state that the non-breaching Party intends to
terminate this Agreement in the event that the breaching Party shall fail to
remedy the default. Any such notice shall set out expressly the actions required
of the breaching Party to remedy the default. If such default is not corrected,
the non-breaching Party shall have the right to terminate this Agreement by
giving written notice to the Party in default provided the notice of termination
is given within six (6) months of the default and prior to correction of the
default.

7.3   Termination upon Bankruptcy

      7.3.1   This Agreement may be terminated by a Party by providing written
              notice to the other Party upon:

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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              (a)       the bankruptcy, liquidation or dissolution of the other
                        Party;

              (b)       the filing of any voluntary petition for bankruptcy,
                        dissolution, liquidation or winding-up of the affairs of
                        the other Party; or

              (c)       the filing of any involuntary petition for bankruptcy,
                        dissolution, liquidation or winding-up of the affairs of
                        the other Party which is not dismissed within one
                        hundred twenty (120) days after the date on which it is
                        filed or commenced.

      7.3.2   Notwithstanding the foregoing, either Party may seek the waiver of
              the operation of Section 7.3.1 in advance of any event giving rise
              to a right of termination under Section 7.3.1(b), and, provided
              that:

              (a)       the requesting Party is in good standing and not in
                        breach of any of the terms of the Related Agreements;

              (b)       the requesting Party is in reasonable financial
                        condition; and

              (c)       the Party whose consent is sought will not be prejudiced
                        by granting such waiver,

              the Party whose consent is sought will not unreasonably withhold
              its consent to such waiver. Such waiver may be revocable in the
              event of a material adverse change in circumstances related to the
              requesting Party not contemplated at the time of granting the
              waiver.

7.4   Effect of Termination

The termination of this Agreement for any reason will be without prejudice to:

      7.4.1   Inex's right to receive all payments accrued from Enzon as of the
              effective date of such termination;

      7.4.2   Inex's right to receive reimbursement for all costs and
              liabilities incurred by Inex as of the date of Inex's receipt of
              Enzon's notice of termination, which cost and liabilities Inex has
              properly and reasonably incurred in its obligations hereunder. For
              greater certainty, such costs and liabilities shall include all
              reasonable and necessary non-cancellable obligations entered into
              prior to Inex's receipt of Enzon's notice of termination, but
              arising after Inex's receipt of Enzon's notice of termination; and

      7.4.3   any other legal, equitable or administrative remedies as to which
              either Party may then or thereafter become entitled.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
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7.5   Survival of Obligations; Return of Confidential Information

      7.5.1   The provisions of Article 1, Sections 4.4.1, 4.4.3, 4.4.5, Article
              5, Section 6.5, Article 7 and Article 8 will survive any
              expiration or termination of this Agreement in accordance with
              their terms.

      7.5.2   Upon any termination of this Agreement pursuant to Article 7,
              except as contemplated hereby, each Party shall promptly return to
              the other Party all written Confidential Information, and all
              copies thereof (except for one archival copy to be retained by a
              person designated by such Party (who shall not make such
              Confidential Information generally available to employees or other
              representatives of such Party) for the purpose of confirming which
              information to hold in confidence hereunder), of the other Party
              which is not covered by a license surviving such termination.

                            Article 8 Miscellaneous

8.1   Assignment

      8.1.1   The rights and obligations set out in this Agreement are personal
              to each Party and for this reason, except as expressly set out in
              this Agreement, this Agreement will not be assignable by either
              Party in whole or in part, nor will either Party subcontract any
              of its obligations hereunder without the prior written consent of
              the other Party, which consent shall not be withheld or delayed
              unreasonably; provided, however, that the restriction contained
              herein will in no way limit the rights of either Party to:

              (a)       assign or subcontract any right or obligation hereunder
                        to any of its Affiliates; or

              (b)       appoint as its agent for any purpose of this Agreement
                        any such Affiliate; or

              (c)       assign any right or obligation hereunder to any person
                        or entity that:

                        (i)   purchases all or substantially all of its assets
                              to which this Agreement relates or

                        (ii)  purchases all or substantially all of the stock of
                              either Party; or

                        (iii) acquires or is combined with either Party in a
                              merger or some other form of business combination.

      8.1.2   This Agreement will be binding upon and will enure to the benefit
              of the parties hereto and to any permitted assignee or successor
              of either party.

      8.1.3   Subject to other provisions of this Section 8.1, if one Party
              validly assigns or subcontracts any or all of its obligations
              hereunder, such assigning or

<PAGE>
                                     - 12 -


              subcontracting Party agrees to remain bound by all of its
              responsibilities and obligations hereunder.

      8.1.4   Any and all assignments of this Agreement or any interest herein
              not made in accordance with this Section 8.1 will be void ab
              initio.

8.2   Counterparts

This Agreement may be executed in any number of counterparts, each of which
shall be deemed an original but all of which together shall constitute one and
the same instrument.

8.3   Exhibits and Appendices

Each exhibit hereto is incorporated by reference and made a part of this
Agreement.

8.4   Force Majeure

In the event that either Party is prevented from performing or is unable to
perform any of its obligations under this Agreement due to any act of God; fire;
casualty; flood; war; strike; lockout; failure of public utilities; injunction
or any act, exercise, assertion or requirement of governmental authority;
epidemic; destruction of production facilities; riots; insurrection; failure of
transportation; inability to procure or use materials, or any other cause beyond
the reasonable control of the Party invoking this Section 8.4 if such Party
shall have used its reasonable efforts to avoid such occurrence, such Party
shall give notice to the other Party in writing promptly, and thereupon the
affected Party's performance shall be excused and the time for performance shall
be extended for the period of delay or inability to perform due to such
occurrence.

8.5   Further Assurances

Each Party hereto agrees to execute, acknowledge and deliver such further
instruments and do all such further acts as may be necessary or appropriate to
carry out the purposes and intent of this Agreement.

8.6   Modification

No waiver, alteration or modification of any of the provisions hereof shall be
binding unless made in writing and signed by the Parties by their respective
officers thereunto duly authorized.

8.7   No Agency

Except as explicitly set forth herein, nothing herein shall be deemed to
constitute either Party as the agent or representative of the other Party, or
both Parties as joint venturers or partners for any purpose. Inex shall be an
independent contractor, not an employee of Enzon, and the manner in which Inex
renders its services under this Agreement shall be within Inex's sole
discretion. Neither Party shall be responsible for the acts or omissions of the
other Party, and neither Party will have authority to speak for, represent or
obligate the other Party in any way without prior written authority from the
other Party.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                     - 13 -


8.8   No Solicitation or Hiring of Employees

During the Term and for one year thereafter, neither Inex nor Enzon shall,
without the prior consent of the other Party, solicit the employment of or hire
any person who during the course of employment with the other Party was involved
with activities under the Commercialization Plan and who when solicited or to be
hired is a current employee of the other Party.

8.9   Non-Use of Names

Except as otherwise expressly set out in this Agreement, neither Party shall use
the name of the other Party, nor any adaptation thereof, in any advertising,
promotional or sales literature without prior written consent obtained from such
other Party in each case (which consent shall not be unreasonably withheld or
delayed).

8.10  Notices

Any notice or other communication in connection with this Agreement must be in
writing and if by mail, by registered mail, return receipt requested, and shall
be effective when delivered to the addressee at the address listed below or such
other address as the addressee shall have specified in a notice actually
received by the addressor.

If to Inex:

       Inex Pharmaceuticals, Inc.
       c/o Corporation Trust Center
       1209 Orange Street
       Wilmington, DE 19801

       Attention: President and CEO

       With copies to:

       Inex Pharmaceuticals Corporation
       100-8900 Glenlyon Parkway
       Burnaby, British Columbia
       Canada V5J 5J8
       Fax: 604-419-3202
       Attention: Sr. V.P. Commercial Operations;

       With a copy to:

       Inex Pharmaceuticals Corporation
       100-8900 Glenlyon Parkway
       Burnaby, British Columbia
       Canada V5J 5J8
       Fax: 604-419-3202
       Attention:  Business Development

       and:

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                     - 14 -


      Lang Michener
      1500-1055 West Georgia Street
      Vancouver, British Columbia
      Canada V6E 4N7
      Fax: 604-685-7084
      Attention: Leo Raffin

      and:

      Farris, Vaughan, Wills & Murphy
      2600 - 700 West Georgia Street
      Vancouver, British Columbia
      Canada V7Y 1B3
      Fax: 604-661-9349
      Attention: James Hatton

      If to Enzon:

      ENZON PHARMACEUTICALS, INC.
      685 Route 202/206
      Bridgewater, New Jersey
      08807
      Fax: 908.541.8680
      Attention: Vice President, Business Development

      with a copy to:

      Enzon Pharmaceuticals, Inc.
      685 Route 202/206
      Bridgewater, NJ 08807
      Fax: 908.541.8838
      Attention: General Counsel

8.11  Publicity

Except as required by law, stock exchange or Regulatory Authority:

      8.11.1  neither Party, nor any of its Affiliates, shall originate any
              publicity, news release or other public announcement, written or
              oral, relating to this Agreement or the existence of an
              arrangement between the Parties, without the prior written
              approval of the other Party and agreement upon the nature and text
              of such announcement or disclosure, which approval shall not be
              unreasonably withheld;

      8.11.2  the Party desiring to make any such public announcement or other
              disclosure shall inform the other Party of the proposed
              announcement or disclosure in reasonably sufficient time prior to
              public release, and shall provide the other Party with a written
              copy thereof, in order to allow such other Party to comment upon
              such announcement or disclosure; and

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                     - 15 -


      8.11.3  notwithstanding the foregoing, the Parties agree that the press
              release set out as an Exhibit to the Product Supply Agreement
              shall be released by the Parties upon execution and delivery of
              this Agreement by both Parties.

8.12  No Third Party Beneficiaries

Except as expressly set out in this Agreement, nothing in this Agreement is
intended to or shall confer upon any Third Part any legal or equitable right,
benefit or remedy of any nature whatsoever.

8.13  Waiver

The waiver by either Party of a breach or a default of any provision of this
Agreement by the other Party shall not be construed as a waiver of any
succeeding breach of the same or any other provision, nor shall any delay or
omission on the part of either Party to exercise or avail itself of any right,
power or privilege that it has or may have hereunder operate as a waiver of any
right, power or privilege by such Party.

IN WITNESS WHEREOF, the Parties have executed this Co-Promotion Agreement as of
the date first above written.

Inex Pharmaceuticals, Inc.

By: /s/ David J. Main
    ---------------------------
Name:  David J. Main
Title: President & CEO


Enzon Pharmaceuticals, Inc.

By: /s/ Arthur J. Higgins
    ---------------------------
Name:  Arthur J. Higgins
Title: Chairman & CEO


*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.