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Significant Agreements

Merck Agreement

As a result of a November 1990 agreement, the Company’s PEGylation technology was used to develop an improved version of the product INTRON A, PegIntron. Merck is responsible for marketing and manufacturing PegIntron on an exclusive worldwide basis and the Company receives royalties on worldwide sales of PegIntron for all indications. The Company has no involvement in the selling or marketing of PegIntron. Merck’s obligation to pay the Company royalties on sales of PegIntron terminates, on a country-by-country basis, upon the later of the date on which the last patent to contain a claim covering PegIntron expires in the country or 15 years after the first commercial sale of PegIntron in such country. Currently, expirations are expected to occur in 2016 in the U.S., 2018 in Europe and 2019 in Japan. The royalty percentage to which the Company is entitled will be lower in any country where a PEGylated alpha-interferon product is being marketed by a third party in competition with PegIntron where such third party is not Hoffmann-La Roche. Either party may terminate the agreement upon a material breach of the agreement by the other party that is not cured within 60 days of written notice from the non-breaching party or upon declaration of bankruptcy by the other party. During the quarter ended September 30, 2007, the Company sold a 25 -percent interest in future royalties payable to it by Merck on net sales of PegIntron occurring after June 30, 2007.

Sigma-Tau Group

The Company sold its former specialty pharmaceutical business to Klee Pharmaceuticals Inc. (now known as Sigma-Tau PharmaSource, Inc.), Defiante Farmacêutica, S.A and sigma-tau Finanziaria S.p.A. (collectively, the Sigma-Tau Group) in January 2010. In addition to the initial sale of assets which has been reflected in the Company’s financial statements for the year ended December 31, 2010, the sale agreement provides for certain potential future payments due to Enzon of up to $ 27.0 million contingent upon the achievement of the following regulatory approval-related milestones:

$ 5.0 million due for accelerated European Medicines Agency (EMA, formerly known as EMEA) approval, in addition to the amount due for non-accelerated EMA approval, for SC Oncaspar;

$ 5.0 million due for FDA approval for SS Oncaspar;

$ 7.0 million due for FDA approval for SC Oncaspar; and

$ 10.0 million due for non-accelerated EMA approval for SC Oncaspar.

In addition, the sale agreement provides for royalties potentially due to Enzon, beginning in 2010, of 5 to 10 percent on incremental net sales (net sales above a 2009 baseline amount) through 2014 of the Company’s former four marketed specialty pharmaceutical products sold to Sigma-Tau Group.

The Company has no direct involvement in, and no obligations to perform services or activities related to, obtaining the above regulatory approvals or achieving commercial sales for the four marketed products. The Company recognizes revenue only upon notification from Sigma-Tau Group that the conditions necessitating payment of the milestone or royalty were achieved. In the case of the royalty, revenue is recognized in the quarter following the quarter in which the sales occurred.

During the first quarter of 2011, the Company earned the $ 5.0 million due for FDA approval for SS Oncaspar. Approximately $ 0.5 million of royalty revenues were recognized in 2011 pursuant to this provision of the sale agreement. No additional revenue from this source was received, subsequently. There can be no assurance that the Company will receive any of the remaining $ 17.0 million of milestone payments or any future royalty revenues beyond those recognized to date. Our rights to receive royalties on sales of Oncaspar expired in 2014.

Santaris Pharma A/S License Agreement

In July 2006, the Company entered into a license agreement with Santaris Pharma A/S (Santaris) pursuant to which the Company obtained exclusive rights worldwide, other than in Europe, to develop and commercialize RNA antagonists directed against the HIF-1α and Survivin mRNA (which was returned to Santaris in late 2012), as well as RNA antagonists directed against six additional gene targets selected by the Company. Since inception of the agreement, initial acquisition of in-process research and development and milestone payments have been made totaling $ 34.0 million. This agreement provided that any one of the compounds licensed by us from Santaris could be returned to Santaris if the findings of our preclinical or clinical work do not support our continued investment. By September 2013, we returned all of the targets to Santaris.

Nektar Agreement

In January 2002, the Company entered into a PEGylation technology licensing agreement with Nektar under which the Company granted Nektar the right to grant sub-licenses for a portion of its patents related to its PEGylation technology to third-parties. Nektar had the right to sub-license Enzon’s patents that were defined in the January 2002 agreement and the Company will receive a royalty or a share of Nektar’s profits for any products that utilize the Company’s patented PEGylation technology. The Company’s receipt of royalties related to Nektar licenses ended in 2014. After the expiration of our sublicensed patents, we may be entitled to lesser immunity fees on a country-by-country and product-by- product basis for up to twelve years from the date of first sale of these drugs. Effective in January 2007, Nektar’s right to grant additional sublicenses was limited to a certain class of the Company’s PEGylation technology. Existing sublicenses granted by Nektar prior to January 2007 were unaffected.

In March 2014, the Company entered into a novation agreement with Zhejiang Hisun Pharmaceutical Co., Ltd. ("Hisun") and Belrose (the “Novation Agreement”), pursuant to which the parties confirmed the novation of our Collaboration Agreement with Hisun to Belrose. As a consequence of entering into the Novation Agreement, the Company received a gross amount of $550,000 from Hisun, the amount of a receivable previously written off, and paid $249,565 to Belrose. The recording of these transactions resulted in a net reduction of general and administrative expense of $300,435 during the first quarter of 2014.

On July 16, 2014, Belrose provided written notice to Hisun asserting multiple breaches by Hisun of the Collaboration Agreement including failure to pay $450,000 of milestone payments. Belrose provided Hisun up to 60 days to cure the breaches. On September 16, Belrose notified Hisun and the Company that it was terminating the Collaboration Agreement and demanded the return of material related to PEG-SN38 and a royalty-free right to any Hisun patents related to PEG-SN38. Hisun responded on September 16 that they rejected Belrose’s assertion that Hisun had committed multiple breaches and requested that Belrose continue its performance of technology transfer under the Collaboration Agreement.