Calistoga Pharmaceuticals Presents Interim Clinical Efficacy Results from Ongoing Clinical Trial of CAL-101 at the International

Calistoga Pharmaceuticals Presents Interim Clinical Efficacy Results from Ongoing Clinical Trial of CAL-101 at the International Workshop on Chronic Lymphocytic Leukemia

Treatment with CAL-101 Resulted in Partial Responses in 29 Percent and Biologic Responses in 94 percent of Patients with Relapsed or Refractory Chronic Lymphocytic Leukemia

 SEATTLE--(BUSINESS WIRE)--Calistoga Pharmaceuticals, Inc., the leader in the development of isoform-selective phosphatidylinositol 3 kinase (PI3K) inhibitors for the treatment of cancer and inflammatory diseases, today announced the presentation of interim results from the ongoing Phase 1 trial evaluating CAL-101, an oral delta-selective PI3K inhibitor, demonstrating promising clinical responses in patients with relapsed or refractory chronic lymphocytic leukemia (CLL). Data were presented at the Thirteenth International Workshop on Chronic Lymphocytic Leukemia in Barcelona, Spain.

At this interim assessment, 29 percent of CLL patients treated in the cohort expansion dose levels had partial responses observed after 28 days of therapy (1 cycle) and 94 percent have achieved evidence of biologic activity with a greater than 50 percent decrease in lymphadenopathy (shrinkage of lymph node tumors). Five out of six partial responders continue treatment with CAL-101, with the longest response greater than 224 days. All patients had prior rituximab and fludarabine therapy and nearly half of the patients had prior alemtuzamab therapy. Half of the patients were refractory to their last therapy prior to entering the study.

A low incidence of hematologic toxicity was observed. The dose limiting toxicity in the study was an elevation of transaminases (ALT and AST), which has been both monitorable and reversible and patients are usually able to resume therapy at a lower dose.

"Both the extent and durability of responses in these relapsed and refractory CLL patients treated with CAL-101 are very promising," said Dr. Albert Yu, M.D., Chief Medical Officer, Calistoga Pharmaceuticals. "We continue to enroll patients and the results of this study will help us select an optimal biologic dose for future studies."

These interim results are part of a cohort expansion of the ongoing Phase 1 trial of CAL-101, which is enrolling patients with relapsed or refractory CLL, indolent non-Hodgkin's lymphoma (NHL), aggressive NHL, acute myeloid leukemia (AML), and multiple myeloma (MM). Clinical response data evaluating at least 90 patients is expected to be available by the end of 2009.

"These encouraging results support future evaluation of CAL-101 in CLL patients both as a single agent and in combination with standard regimens," noted Carol G. Gallagher, Pharm. D., Chief Executive Officer of Calistoga Pharmaceuticals. "We anticipate starting Phase 2/3 clinical studies in 2010."

CAL-101 is a potent and selective inhibitor of the delta isoform of PI3K with 40- to 300-fold selectivity over other PI3K isoforms. In preclinical efficacy studies, CAL-101 demonstrated inhibition of the PI3K pathway, decreases in cellular proliferation, and/or cell death in primary CLL and AML cells and in a range of NHL cell lines.

About Calistoga Pharmaceuticals

Calistoga Pharmaceuticals is the leader in developing innovative medicines targeting selected isoforms of the PI3 kinase pathway to improve the health of patients with cancer and inflammatory diseases. Calistoga Pharmaceuticals has a portfolio of proprietary compounds. The Company's most advanced compound, CAL-101, a delta-selective PI3K inhibitor, is under clinical evaluation in patients with hematologic malignancies. CAL-263, also a delta-selective PI3K inhibitor, is under Phase 1 evaluation and is being developed for patients with inflammatory diseases. Calistoga is a private company headquartered in Seattle, Washington. For more information, visit the Company's website at: www.calistogapharma.com.

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