NKTR-102 Shows Encouraging Anti-Tumor Activity in Ovarian Cancer in Phase 1 and Preclinical Data Presented at the ECCO 15 and 34

NKTR-102 Shows Encouraging Anti-Tumor Activity in Ovarian Cancer in Phase 1 and Preclinical Data Presented at the ECCO 15 and 34th ESMO Multidisciplinary Congress

Nektar commences second stage of Phase 2 clinical trial of NKTR-102 in platinum-resistant ovarian cancer ahead of schedule

BERLIN and SAN CARLOS, Calif., Sept 22, 2009 /PRNewswire-FirstCall via COMTEX News Network/ -- Nektar Therapeutics (Nasdaq: NKTR) presented favorable data today on lead oncology program, NKTR-102, demonstrating encouraging Phase 1 and preclinical anti-tumor activity of the investigational compound in ovarian cancer. These data were presented at the European CanCer Organisation (ECCO) and the European Society for Medical Oncology (ESMO) 2009 Joint Multidisciplinary Congress in Berlin, Germany.

"As highlighted in our data presented today at ECCO/ESMO, we continue to see encouraging signs suggesting that NKTR-102's improved pharmacokinetics could result in an enhanced therapeutic profile," said Lorianne Masuoka, M.D., Chief Medical Officer. "We are also pleased with the rapid enrollment of the first stage of our Phase 2 clinical study in platinum-resistant ovarian cancer. Although many patients are not yet evaluable for response, we have already achieved a sufficient number of confirmed responses to open the second stage for both regimens in the study earlier than anticipated. This important new compound may offer a valuable new treatment option to overcome chemo-resistance in patients with recurrent ovarian cancer."

NKTR-102 is a novel prodrug of irinotecan that was designed using Nektar's proprietary small molecule advanced polymer conjugate technology platform. Nektar's proprietary technology is being used to significantly improve the half-life and potentially enhance the therapeutic profile of important chemotherapeutic agents and also to create novel, oral small molecule drug candidates across multiple therapeutic areas.

In the preclinical studies presented today, NKTR-102 was evaluated at three dose levels and compared to three equivalent dose levels of irinotecan in a platinum-resistant 2780 ovarian cancer mouse model. NKTR-102 showed clear superiority over irinotecan at all dose levels, with 100% of animals demonstrating partial or complete tumor regression with NKTR-102 compared to only 1 of 10 animals with a partial response at the highest irinotecan dose. NKTR-102 was also better tolerated than irinotecan at all doses tested.

Data were also presented on patients with recurrent ovarian cancer from the Phase 1 dose-escalation study of single agent NKTR-102. Of five patients with ovarian cancer in the study, two were evaluable for efficacy. Both patients showed significant anti-tumor activity, including tumor reductions of up to 37% and a decrease in CA-125 marker levels of up to 80%. These patients had failed multiple prior therapies and had progressed following prior platinum-based therapy. Pharmacokinetic data from this same Phase 1 study showed increased and sustained SN38 exposure with administration of NKTR-102 compared to expected SN38 levels following irinotecan administration.

Phase 2 Study of NKTR-102 in Platinum-Resistant Ovarian Cancer Commences Second Stage

The company also announced today that a phase 2 study evaluating two dose regimens (q14 and q21 days) of single-agent NKTR-102 in patients with platinum-resistant ovarian cancer is ongoing. Enrollment of the first stage of this two-stage study is complete for both regimens (20 patients per regimen).

Data Presentation for NKTR-102

The poster presentation from today's "Gynecologic Cancer Session" at the ECCO15/ESMO 34 2009 Multidisciplinary Conference can be found on Nektar's website. www.nektar.com/product_pipeline/oncology_nktr-102.html

Poster 161 - Abstract 8015: Hoch et al.,"NKTR-102 Demonstrates Nonclinical and Phase 1 Clinical Anti-tumor Activity in Ovarian Cancer"

About NKTR-102

Nektar is developing NKTR-102, a novel prodrug which is a PEGylated form of irinotecan. NKTR-102 was invented by Nektar using its advanced polymer conjugate technology platform and is the first oncolytic that leverages Nektar's platform. Using a proprietary approach that directly conjugates the drug to a unique polymer architecture, Nektar is the first company to have created a PEGylated small molecule with a unique pharmacokinetic profile that has demonstrated therapeutic activity in patients.

In addition to the ongoing Phase 2 study in platinum-resistant ovarian cancer, NKTR-102 is also currently being tested in two separate Phase 2 clinical trials in metastatic breast cancer and second-line colorectal cancer.

About Nektar

Nektar Therapeutics is a biopharmaceutical company developing novel therapeutics based on its PEGylation and advanced polymer conjugation technology platforms. Nektar's technology and drug development expertise have enabled nine approved products in the U.S. or Europe for leading biopharmaceutical company partners, including UCB's Cimzia(R), Roche's PEGASYS(R) for hepatitis C and Amgen's Neulasta(R) for neutropenia. Nektar has created a robust pipeline of potentially high-value therapeutics to address unmet medical needs by leveraging and expanding its technology platforms to improve and enable molecules. Nektar is currently conducting clinical and preclinical programs in oncology, pain and other therapeutic areas. NKTR-102, PEGylated irinotecan, is currently in Phase 2 clinical studies in ovarian, breast and colorectal cancer. NKTR-105, PEGylated docetaxel, is currently in a Phase 1 clinical study in patients with refractory solid tumors.

Nektar is headquartered in San Carlos, California, with additional R&D operations in Huntsville, Alabama and Hyderabad, India. Further information about the company and its drug development programs and capabilities may be found online at http://www.nektar.com.

    Nektar Investor Inquiries:
    Jennifer Ruddock/Nektar Therapeutics       1 650-631-4954
    Susan Noonan/SAN Group                     (212) 966-3650

    Nektar Media Inquiries:
    Karen Bergman/BCC Partners                 (650) 575-1509
    Michelle Corral/BCC Partners               (415) 794-8662

This press release contains forward-looking statements that reflect Nektar's current views regarding the potential, progress, and clinical plans for NKTR-102 and the value and potential of Nektar's advanced polymer conjugate technology platform. These forward-looking statements involve risks and uncertainties, including but not limited to: (i) NKTR-102 are in the early stages of clinical development and the risk of failure is high and can unexpectedly occur in one or more cancer indications being studied; (ii) the timing of the commencement or end of clinical trials may be delayed or unsuccessful due to slower than anticipated patient enrollment, drug manufacturing challenges, changing standards of care, clinical trial design, or unanticipated clinical outcomes; (iii) clinical trials are long, expensive and uncertain processes and the risk of failure of any product candidate that is in clinical development remains high and can unexpectedly occur at any stage due to efficacy, safety or other factors; (iv) Nektar's patent applications for its proprietary or partner product candidates may not issue, patents that have issued may not be enforceable, or intellectual property licenses from third parties may be required in the future; and (v) the outcome of any existing or future intellectual property or other litigation related to Nektar's proprietary product candidates. Other important risks and uncertainties are detailed in Nektar's reports and other filings with the Securities and Exchange Commission, including its most recent Quarterly Report on Form 10-Q. Actual results could differ materially from the forward-looking statements contained in this press release. Nektar undertakes no obligation to update forward-looking statements, whether as a result of new information, future events or otherwise.