Yasuhiro Hashimoto, M.D. President and CEO MediBIC Co., Ltd. Daido Seimei Kasumigaseki Building 8F

Exhibit 10.18

Xxxxxxxx Xxxxxxxxx, M.D.

President and CEO

MediBIC Co., Ltd.

Daido Seimei Kasumigaseki Building 8F

0-0-0 Xxxxxxxxxxxx, Xxxxxxx-xx

Xxxxx 000-0000 Xxxxx

Re: Development Agreement between Threshold Pharmaceuticals, Inc., and MediBIC Co., Ltd.

Dear Yas,

I am writing you in regard to the Development Agreement between our companies having an Effective Date of 30 November 2004 and its accompanying side letter, both signed 2 December 2004. This letter confirms our understanding that, pursuant to the Development Agreement and side letter, Threshold has granted and hereby confirms its grant to MediBic of a non-exclusive license to use Threshold confidential information relating to glufosfamide for the limited purpose of preparing the Development Plan and any associated marketing plans as authorized under the Development Agreement, and if such Development Plan is agreed upon by the parties, this non-exclusive license to use Threshold confidential information shall continue for the time necessary for MediBIC to perform its obligations under the Development Plan.

In addition, this letter amends the Development Agreement to remove North Korea from the list of countries in the “Asian Territory” as defined in Section 1.3.

Please acknowledge your receipt of this letter and agreement by signing and returning one of the two duplicate originals provided to you.

Best regards,

/s/    XXXXXX X. XXXXXX        

Xxxxxx X. Xxxxxx

Chief Executive Officer

Threshold Pharmaceuticals, Inc.

ACCEPTED AND AGREED

/s/    XXXXXXXX XXXXXXXXX        

Xxxxxxxx Xxxxxxxxx, M.D.

President and CEO

MediBIC Co., Ltd