ASSET PURCHASE AGREEMENT

Exhibit 10.173

CONFIDENTIAL TREATMENT REQUESTED. CONFIDENTIAL PORTIONS OF THIS DOCUMENT HAVE BEEN REDACTED AND HAVE BEEN FILED SEPARATELY WITH THE U.S. SECURITIES AND EXCHANGE COMMISSION

****** DENOTES CONFIDENTIAL TREATMENT REQUESTED

ASSET PURCHASE AGREEMENT

THIS ASSET PURCHASE AGREEMENT (this “AGREEMENT”) dated as of September 29, 2005 by and between Anthra Pharmaceuticals, Inc., a Delaware corporation (“SELLER”), and Valera Pharmaceuticals, Inc., a Delaware corporation (“BUYER”).

BACKGROUND

Seller was engaged in the business of developing, manufacturing and selling pharmaceutical products that utilized Valrubicin (as defined in Section 1) as the active ingredient including a product marketed in the United States under the trademark Valstar(R) (the “BUSINESS”). The production, marketing and sale of Valstar was halted due to a manufacturing issue. Buyer desires to purchase from Seller, and Seller desires to sell, transfer and assign to Buyer, certain assets and rights associated with the Business in the United States and Canada including, without limitation, any and all of Seller’s rights to manufacture, market, distribute and sell in the United States and Canada pharmaceutical products that have Valrubicin as the active ingredient, and in connection therewith Buyer has agreed to assume certain liabilities associated with the future operation of the Business in the United States and Canada, all on the terms and conditions of this Agreement.

TERMS

NOW THEREFORE, in consideration of the representations and warranties, covenants and conditions set forth herein, and intending to be legally bound hereby, Buyer and Seller agree as follows:

1. Definitions. The following terms, as used herein, have the following meanings:

“ACQUIRED ASSETS” has the meaning set forth in Section 2.1.

“ACQUIRED CONTRACTS” means the agreements described in paragraph (k) of Exhibit A.

“ACTUAL KNOWLEDGE OF SELLER” means the actual (and not constructive or imputed) knowledge of the directors of Seller (without independent investigation or inquiry).

“ACTUAL KNOWLEDGE OF BUYER” means the actual (and not constructive or imputed) knowledge of the directors and officers of Buyer (without independent investigation or inquiry).

“AFFILIATE” means, with respect to a Party, any entity controlling, controlled by or under common control with such Party. For purposes of this definition, “control” means ownership of more than 50% of the outstanding voting securities of the entity or the power to direct the management and policies of the entity, whether by ownership of securities, contract or otherwise.

“ASSUMED LIABILITIES” has the meaning set forth in Section 2.2.

“BILL OF SALE AND ASSIGNMENT” has the meaning set forth in Section 2.1.

“BUSINESS DAY” means any Monday, Tuesday, Wednesday, Thursday or Friday, other than any such day on which the Federal Reserve Bank of New York is closed.

“CELLTECH” means a UK company registered number 2159282 whose main address is 208 Bath Road, Slough, Berkshire, SL1 3WI, UK and its subsidiaries and affiliates.

“CELLTECH DEVELOPMENT AGREEMENT” means the development agreement, dated as of July 15, 1997, between Seller and Celltech, as the assignee of Medeva California Inc. (as such agreement may have been amended).

“CLOSING” has the meaning set forth in Section 3.1.

“CLOSING DATE” has the meaning set forth in Section 3.1.

“COMMERCIAL SALE” means, with respect to a particular Product, the sale by or on behalf of the Marketers for use or consumption by the general public of such Product, provided, however, that sales of such Product for research, development, clinical trials, investigation and/or evaluation shall not be deemed sales for use or consumption by the general public.

“CURRENT FORMULATION” means Valrubicin at a concentration of 40 mg/ml in 50% Cremophor(R) EL (polyoxyethyleneglycol triricinoleate)/ 50% dehydrated alcohol or other formulations that are accepted by the FDA without the regulatory requirement for a formal clinical study to be submitted in support of such change in formulation.

“EXCLUDED LIABILITIES” has the meaning set forth in Section 2.3.

“FDA” means the United States Food and Drug Administration and any successor entity thereto.

“FINANCIAL STATEMENTS” shall mean (a) the audited balance sheet and income statement of Buyer at December 31, 2003 and December 31, 2004 and the related statements of operation and cash flows and the statements of changes in stockholders’ equity of the Buyer for the years ended December 31, 2003 and December 31, 2004 and the accompanying footnotes thereto, and (b) the balance sheet and income statement of Buyer as of August 31, 2005 for the eight (8) month period then ended. Copies of the Financial Statements are attached hereto as Exhibit D.

“GOVERNMENTAL BODY” means any federal, state, municipal or other governmental department, commission, board, bureau, court, agency, authority or instrumentality, domestic or foreign.

2

“INCLUDED INDICATIONS” means BCG-refractory carcinoma-in-situ (CIS) of the bladder.

“INTELLECTUAL PROPERTY” has the meaning set forth in Section 4.5.

“IRS” means the Internal Revenue Service.

“LICENSE AGREEMENT” means an agreement (or, if more than one agreement, the combination of agreements) between Buyer and a Third Party in which Buyer grants such Third Party the right to make, use or sell a Product or Valrubicin. A License Agreement may also involve the supply of a Product or Valrubicin by Buyer to the Third Party.

“LICENSE FEES” means, with respect to the License Agreement with Paladin Labs and any arrangement pursuant to which Buyer provides Valrubicin or the Product to any Third Party other than a Marketer or Paladin Labs, or in respect of which License Fee Buyer has a payment obligation owing to Seller that is not considered to be payable pursuant to Section 2.5(a)(i) or (a)(ii) hereof, the excess of (i) the proceeds received by Buyer under the License Agreement (including, without limitation, marketing fees, license fees, commission fees, and option fees but specifically excluding research and development fees and proceeds from sales of Product by Buyer to any Third Party, but in no case reduced by taxes on net or gross income), over (ii) the direct “cost of goods sold” allocable to supplies of Valrubicin or the Product so provided by Buyer (exclusive of overhead), calculated in accordance with GAAP and in the manner reflected in Buyer’s Financial Statements.

“MARKETERS” means Buyer, its Affiliates, licensees pursuant to a License Agreement (other than Paladin Labs), or permitted transferees or assignees.

“NDA” means the New Drug Application relating to Valrubicin approved by the FDA on September 25, 1998.

“NET SALES” means the total gross sales invoiced and collected by the Marketers with respect to the Commercial Sale of the Product on a worldwide basis for use in any indication by the Marketers less the aggregate of: (i) normal and customary returns, rebates, recalls, chargebacks and discounts (such as those granted or required pursuant to arrangements with Medicare, Medicaid and other third party payors), in each case actually allowed and taken; (ii) freight, transport and delivery, including insurance (if separately identified on the invoice); and (iii) any sales tax, value added tax, goods and services tax or any other tax, customs or duties that may be imposed on the sale of the Product, which taxes, customs or duties are included in gross sales invoiced, but not including any taxes assessed against income derived from such sales.

“NEW FORMULATIONS” means any formulation of Valrubicin other than the Current Formulation.

“OTHER INDICATIONS” means all indications other than Included Indications approved by the FDA.

“PALADIN LABS” means Paladin Labs Inc.

“PARTY” means Seller or Buyer, as the context requires.

3

“PERSON” means any natural person, corporation, general partnership, limited partnership, limited liability company, proprietorship, joint venture, trust, association, union, entity, or other form of business organization or any governmental body whatsoever.

“PRF” means Paul Royalty Fund, L.P., a Delaware limited partnership.

“PURCHASE PRICE” has the meaning set forth in Section 2.4.

“PRODUCT” means any and all dosage forms of any finished product that has Valrubicin as its active ingredient.

“REGULATORY APPROVALS” means the technical, medical and scientific licenses, registrations, authorizations, permits, certificates, consents, confirmations, clearances and approvals (including the prerequisite manufacturing approvals or authorizations, marketing authorizations based upon such approvals and labeling approvals related thereto) that are required by any Regulatory Authority for the manufacture, distribution, marketing, storage, transportation, use and sale of Valrubicin in the territory over which the Regulatory Authority has jurisdiction.

“REGULATORY AUTHORITY” means the FDA or the comparable Governmental Body of another country or jurisdiction having regulatory oversight over matters similar to that of the FDA.

“SALE OF THE PRODUCT” means a transaction in which Buyer receives up-front or any other consideration for the sale, license or grant of co-promotion rights of the Product, other than royalties or transfer fees in respect of the sale or distribution of the Product.

“TRANSACTION DOCUMENTS” has the meaning set forth in Section 4.1.

“TAX RETURNS” means any return, declaration, report, claim for refund, or information return or statement relating to Taxes, including any schedule or attachment thereto, and including any amendment thereof.

“TAX” means any federal, state, local or foreign income, gross receipts, license, payroll, employment, excise, severance, stamp, occupation, premium, windfall profits, environmental, customs duties, capital stock, franchise, profits, withholding, social security (or similar), unemployment, disability, real property, personal property, sales, use, transfer, registration, value added, alternative or add-on minimum, estimated, or other tax of any kind whatsoever, including any interest, penalty, or addition thereto, whether disputed or not.

“THIRD PARTY” means any person or entity other than Buyer, Seller or their respective Affiliates.

“VALRUBICIN” means the compound commonly known as N-Trifluoroacetyl adriamycin-14-valerate whose Chemical Abstracts registry number is 56124-62-0.

4

2. Sale and Purchase of Assets.

2.1 Acquired Assets. Subject to the terms and conditions of this Agreement, at the Closing and in consideration of the payments made or to be made by Buyer to Seller as described herein, Buyer agrees to purchase and accept from Seller and Seller agrees to convey, sell, transfer, assign and deliver to Buyer, all of Seller’s right, title and interest in and to the assets, properties and privileges set forth on Exhibit A hereto and in the Bill of Sale and Assignment (the “BILL OF SALE AND ASSIGNMENT”) attached as Exhibit B hereto (such assets, properties and privileges are hereinafter referred to as the “ACQUIRED ASSETS”).

2.2 Assumed Liabilities. Subject to the terms and conditions of this Agreement, at the Closing, Buyer shall assume and agree to pay, perform, fulfill and discharge the liabilities and obligations described in the Agreement of Assumption of Liabilities (the “AGREEMENT OF ASSUMPTION OF LIABILITIES”) attached as Exhibit C (such liabilities and obligations being the “ASSUMED LIABILITIES”). Buyer may, upon providing to Seller documentation that reasonably substantiates payment of such Assumed Liabilities, offset against amounts payable to Seller pursuant to Section 2.4(b) and Section 2.5 an amount equal to Assumed Liabilities actually paid by Buyer up to $250,000.

2.3 Excluded Liabilities. Notwithstanding any provision in this Agreement or any other writing to the contrary, Buyer is assuming only the Assumed Liabilities and is not assuming any other liability or obligation of Seller or any of its respective Affiliates (or any predecessor owner of all or part of its business and assets) of whatever nature whether presently in existence or arising or asserted hereafter. Without limiting the generality of the foregoing, Buyer is not assuming any liability in respect of: (a) products or services provided by Seller prior to the Closing Date including, without limitation, all product liability arising out of the development, testing, manufacture, marketing or sale of the Product or any other product prior to the Closing Date; (b) any agreements or contracts of Seller that are not Acquired Contracts including any and all contracts that relate to the licensing, manufacturing, marketing, distribution or sale of Products outside the United States and Canada; or (c) any regulatory or other obligation in relation to the licensing, manufacturing, marketing, distribution or sale of Products outside the United States and Canada. All such other liabilities and obligations shall be retained by and remain obligations and liabilities of Seller (all such liabilities and obligations not being assumed being herein referred to as the “EXCLUDED LIABILITIES”).

2.4 Purchase Price.

(a) In consideration of the sale, transfer and delivery by Seller to Buyer of the Acquired Assets and of the other agreements of the parties set forth herein (including, without limitation, the assumption by Buyer of the Assumed Liabilities), Buyer agrees to pay to Seller the following amounts (collectively, the “PURCHASE PRICE”):

(i) US$75,000 upon the execution and delivery of this Agreement by both Buyer and Seller;

(ii) the amounts payable under Section 2.4(b); plus

(iii) the amounts payable under Section 2.5; plus

(iv) the amounts payable under Section 2.6.

5

(b) Buyer shall pay the following amounts to Seller:

(i) US$75,000 at the Closing;

(ii) US$150,000 no later than 135 days after the Closing;

(iii) US$150,000 no later than 270 days after the Closing;

(iv) US$150,000 no later than 405 days after the Closing; and

(v) [******] in cash or by wire transfer of immediately available funds within 10 business days after the calendar quarter in which there have been [******] in cumulative Net Sales since the Closing.

2.5 Revenue Share on Net Sales.

(a) Buyer shall also pay to Seller or to Seller’s designee an amount equal to:

(i) [******] of Net Sales derived from sales of Product utilizing for the Current Formulation;

(ii) with respect to Net Sales derived from sales of Product utilizing New Formulations which sales are made prior to the end of the calendar quarter during which the eighth anniversary of the Closing occurs: (A) [******] of Net Sales of such Product for Included Indications, and (B) [******] of Net Sales of such Product for Other Indications; provided that if a third party (other than an Affiliate, successor, licensee or assignee of Buyer) begins marketing or selling a product using Valrubicin as its active ingredient in the United States with an approved indication similar to the Included Indication and it is demonstrated to the reasonable satisfaction of Seller that such third party achieved during the previous calendar year a market share of [******], the rates described in clauses (i) and (ii)(A) above shall be reduced to [******] of Net Sales for the subsequent calendar year (the percentages of Net Sales so payable by Buyer to Seller under this Section 2.5(a), the “REVENUE SHARING PERCENTAGE”); and

(iii) [******] of License Fees.

Buyer shall make all payments under this Section 2.5(a) no later than 45 days following the completion of each calendar quarter following the Closing by wire transfer of immediately available funds to an account designated by Seller in writing prior to the date on which payment is due. The amount so remitted on each such date shall equal the Revenue Sharing Percentage of Net Sales for the immediately preceding calendar quarter. The total cumulative amount of payments payable under this Section 2.5(a) shall not exceed US$9,625,000.

(b) Together with each payment required under Section 2.5(a), Buyer shall furnish to Seller a written report showing: (i) the gross amount invoiced for Commercial Sales during the most recently completed calendar quarter; (ii) the gross amount actually collected from Commercial Sales during the most recently completed calendar quarter; (iii) the deductions permitted in calculating Net Sales; (iv) the calculation of Net Sales from Commercial Sales during the most recently completed calendar quarter; (v) the amount payable to Seller under this Section 2.5 in respect of Net Sales; (vi) the withholding taxes, if any, required to be deducted in respect of the amount payable to Seller under this Section 2.5; and (vii) the amount, if any, of Assumed Liabilities actually paid by Buyer and offset pursuant to Section 2.2 hereof.

****** CONFIDENTIAL TREATMENT REQUESTED

6

(c) Buyer shall keep complete and accurate records in sufficient detail to support the calculation of Net Sales and the determination of the amounts payable under this Section 2.5. Upon the written request of Seller or PRF and not more than once in each calendar year or more than once as to any calendar quarter, Buyer shall permit an independent certified public accounting firm of nationally recognized standing, selected by Seller or PRF and reasonably acceptable to Buyer, to have access during normal business hours to such of the records of Buyer as may be reasonably necessary to verify the accuracy of the reports delivered under Section 2.5 for any calendar quarter ending less than 3 years prior to the date of such request. The accounting firm shall be required to execute and deliver to Buyer a non-disclosure agreement in a form reasonably acceptable to Buyer before Buyer shall be required to give the accounting firm access to its records. If such accounting firm concludes that additional amounts are owed to Seller under this Section 2.5, then Buyer shall pay the additional amounts within 30 days after the date Seller delivers to Buyer such accounting firm’s written report that describes in reasonable detail the methods and calculations it used to determine the amounts payable to Seller under this Section 2.5. Seller shall bear the costs and expenses of any inspection under this Section 2.5; provided, however, that if the inspection discloses that Buyer underpaid Seller by more than 5%, then Buyer shall pay the reasonable fees and expenses charged by the accounting firm, not to exceed US$25,000.

(d) If the FDA approves an Other Indication, Buyer and Seller will agree upon a mechanism to track and measure sales from Included Indications and Other Indications.

2.6 Additional Purchase Price. In addition to the Purchase Price payable to Seller pursuant to Sections 2.4 and 2.5, if during any calendar year following the Closing, aggregate Net Sales for such calendar year is equal to [******], then Buyer shall also pay Seller an amount equal to [******] no later than 45 days after the completion of such calendar year, provided that the aggregate amount payable under this Section 2.6 shall not exceed [******] (i.e., a maximum of 4 payments of [******] per year for up to four years in which Net Sales meet or exceed [******]. To the extent that Buyer has incurred and paid costs directly associated with clinical studies related to the approval of New Formulations and/or Other Indications, Buyer shall provide to Seller documentation detailing such costs. Buyer may offset against amounts payable to Seller pursuant to this Section 2.6 up to $500,000 of monies payable for such costs to the extent such costs have not been offset pursuant to Section 2.2 hereof.

2.7 Withholding. If Buyer is required under any applicable law to withhold any amount due under this Agreement in respect of any taxes payable by Seller, Buyer may withhold such amounts and pay Seller the balance of the amount due after such withholding; provided that Buyer promptly pays the amount withheld to the proper government authority and provides Seller with receipts of such payment.

2.8 Transfer of Acquired Assets. In the event of a sale by Buyer of the Acquired Assets (including, without limitation, a Sale of the Product by Buyer), or the transfer of the Acquired Assets as part of a sale, merger or

****** CONFIDENTIAL TREATMENT REQUESTED

7

consolidation of Buyer, or as part of a transfer of all or substantially all of the assets of Buyer, all payments payable by Buyer under Sections 2.4(b)(i)-(iv) shall become immediately due and payable, and except as set forth below, no consent of Seller to such sale or transfer shall be required. A sale or transfer of the Acquired Assets by Buyer, other than (a) as part of a sale, merger or consolidation of Buyer or (b) as part of a transfer of all or substantially all of the assets of Buyer, shall require the prior written consent of Seller to such sale or transfer, which consent may not be unreasonably withheld or delayed. With respect to any transfer of the Acquired Assets (including, without limitation, as part of a sale, merger or consolidation of Buyer, or as part of a transfer of all or substantially all of the assets of Buyer), the acquiror or successor entity, as applicable, shall be required to expressly acknowledge and assume all obligations of Buyer hereunder unless such assumption occurs by operation of law.

2.9 No Marketing Obligations. Seller acknowledges and agrees that: (a) Buyer has no implied or express obligations to Seller to obtain or maintain any Regulatory Approval in respect of the Product in any jurisdiction; (b) Buyer has no implied or express obligations to Seller in respect of the marketing and sale of the Product including, without limitation, any obligation to use commercially reasonable, best efforts or other efforts to market and sell the Product; (c) although Buyer and Seller have discussed in general terms the potential market for the Product in the United States in treating the Included Indication, Buyer has made no representations, warranties or guarantees to Seller regarding the amount of Net Sales that Buyer may achieve in any time period; (d) Buyer is not in any way obligated to achieve any amount of Net Sales; and (e) Buyer has complete discretion in determining whether, when and how to market the Product.

2.10 Tax Allocation. By the Closing, Buyer and Seller shall agree to a written allocation of the Purchase Price (including the amount of any Assumed Liabilities properly treated for tax purposes as consideration for the Acquired Assets) among the Acquired Assets, as required under Section 1060 of the Internal Revenue Code of 1986, as amended (the “ALLOCATION SCHEDULE”). Seller and Buyer shall follow and use the Allocation Schedule in all Tax Returns, filings or other related reports made by them to any Governmental Body. To the extent that disclosures of this allocation are required to be made by the parties to the IRS under the provisions of Section 1060 of the Internal Revenue Code of 1986, as amended or any regulations thereunder, Buyer and Seller will disclose such reports to the other prior to filing with the IRS.

2.11 Transfer Taxes. Buyer shall be responsible for the payment of all transfer, documentary, sales, use, stamp, registration and other such Taxes and fees (including any penalties and interest), if any, which may be payable with respect to the transactions contemplated by this Agreement. Buyer will file all necessary Tax Returns and other documentation with respect to all such transfer, documentary, sales, use, stamp, registration and other such Taxes and fees and, if required by applicable law, Seller will join in the execution of any such Tax Returns and other documentation. Buyer may offset against amounts payable to Seller pursuant to Section 2.5(a) hereof any such tax and fees so paid upon presenting to Seller documentation that reasonably substantiates such payment.

8

3. Closing.

3.1 Closing. Subject to the terms and conditions of this Agreement, the consummation of the transactions contemplated by this Agreement (“CLOSING”) shall be held at the offices of Pepper Hamilton LLP, counsel to Buyer, 400 Berwyn Park, 899 Cassatt Road, Berwyn, Pennsylvania 19312 on DECEMBER 15, 2005 at 10:00 a.m., or such earlier date that shall be mutually agreed upon by the parties in writing (the “CLOSING DATE”).

3.2 Conditions to Closing.

(a) The obligations of Buyer and Seller to consummate the Closing are subject to the satisfaction of the following conditions:

(i) No provision of any applicable law or regulation and no judgment, injunction, order or decree shall prohibit the consummation of the Closing.

(ii) Each other party to this Agreement shall have executed and delivered each of the Transaction Documents to be entered into by it, in each case substantially in the form attached as an exhibit to this Agreement, and any other documents or items required to be delivered by it pursuant to Section 3.3.

(b) The obligation of Buyer to consummate the Closing is subject to the satisfaction of the following further conditions:

(i) (A) The representations and warranties of Seller contained in this Agreement at the time of its execution and delivery and in any certificate or other writing delivered by Seller pursuant hereto, shall be true and correct in all material respects at and as of the Closing Date, as if made at and as of such date and (B) Buyer shall have received a certificate signed by the an authorized signatory of Seller to the foregoing effect.

(ii) No Governmental Body shall have issued any order and no proceeding challenging this Agreement or the transactions contemplated hereby or seeking to prohibit, alter, prevent or materially delay the Closing shall have been instituted by any Person before any Governmental Body and be pending.

(iii) Seller shall have received any required consents (i) to the assignment of each of the agreements listed in Schedule 4.4(c), and (ii) from each third party having a contractual right to consent to the transactions contemplated by this Agreement, in each case in form and substance reasonably satisfactory to Buyer and its counsel, and no such consent shall have been revoked.

(iv) The existing security agreements between PRF and Seller shall have been amended to terminate PRF’s security interest in the Acquired Assets, and Seller shall have obtained the Collateral Agent’s signature on any documents necessary to effect such termination.

(v) Buyer shall have performed or complied with in all material respects all agreements and covenants required by this Agreement to be performed or complied with by it on or prior to the Closing, and Seller shall have received at the Closing a certificate from an appropriate officer of Buyer to that effect.

9

(vi) Seller shall have obtained any required approval of shareholders of Seller to the consummation of the transactions contemplated by this Agreement.

(vii) The Celltech Development Agreement and any rights or interests of Celltech pursuant thereto or granted thereunder shall have been terminated, with a letter agreement from Celltech (or its successor) indicating that there are no remaining rights or interest in favor of Celltech or remaining obligations to Celltech (other than certain payment obligations which may be owed by Seller from payments received by Buyer under Section 2 of this Agreement) thereunder.

Seller shall have provided Buyer a fully executed copy of such agreement or instrument terminating the Celltech Development Agreement.

(viii) Seller shall have delivered to Buyer fully executed documents, in form and substance reasonably satisfactory to the Buyer and Buyer’s lenders, providing for releases and discharges of all liens attaching to any of the Acquired Assets.

(ix) The FDA shall not have indicated in writing that it will require a Phase III clinical trial as a condition to reintroduction of the Product into the United States for use in the Included Indication; provided, however, that if the FDA indicates orally on or after November 10, 2005 that it will require a Phase III clinical trial but such indication has not been confirmed in writing by the FDA, the obligation of Buyer to consummate the Closing shall be delayed until the date that is the earlier of (a) 35 days following the date of such oral requirement from the FDA, and (b) the business day next succeeding any retraction or rescission by the FDA, either orally or in writing, of such oral requirement. If written confirmation from the FDA regarding imposition of such clinical trial requirement is received within such 35 day period then Buyer shall not be obligated under this subsection to consummate the Closing.

(c) The obligation of Seller to consummate the Closing is subject to the satisfaction of the following further conditions:

(i) [Reserved]

(ii) (A) The representations and warranties of Buyer contained in this Agreement at the time of its execution and delivery and in any certificate or other writing delivered b