Calistoga Pharmaceuticals Reports Additional Clinical Responses in Ongoing Clinical Trial of CAL-101, an Isoform-Selective PI3 Kinase Inhibitor, Under Evaluation in Patients with Hematologic Malignancies

Partial Responses Demonstrated in 50 Percent of Evaluable Patients Treated in Phase 1 Trial

Results Presented at the European Hematology Association Congress

SEATTLE--(BUSINESS WIRE)--Jun 6, 2009 - 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 presented additional results from the ongoing Phase 1 trial of CAL-101, an oral, p110δ(delta) selective PI3 kinase inhibitor, demonstrating partial clinical responses in 12 of 24 evaluable patients with hematologic malignancies. Data were presented at the European Hematology Association 14th Congress in Berlin, Germany.

New data highlighted interim results from the cohort expansion of the ongoing Phase 1 trial, which has enrolled an additional 20 patients with relapsed or refractory chronic lymphocytic leukemia (CLL), B-cell non-Hodgkin's lymphoma (NHL), or Acute Myeloid Leukemia (AML). Results demonstrated that 6 of 12 evaluable patients from this cohort had a partial response at their first, one-month evaluation. Partial response is defined as a decrease of at least 50 percent in tumor burden. Results from the initial dose escalation part of this trial, in which 12 patients were treated, were recently reported at the American Society of Clinical Oncology. Overall, partial responses have been observed in 12 of the 24 currently evaluable patients. To date, one dose limiting toxicity has been observed, and the majority of adverse events were mild or moderate in severity.

Calistoga Pharmaceuticals continues to evaluate the efficacy and safety of CAL-101 in patients in this trial and complete data evaluating at least 72 patients is expected to be available later this year.

“As we enroll additional patients, we are pleased that we continue to see about half the patients responding to CAL-101 single agent treatment, an encouraging response rate in patients who have advanced cancer,” said Albert Yu, M.D., Chief Medical Officer of Calistoga Pharmaceuticals. “However, these data are preliminary. We are carefully monitoring the safety profile of CAL-101, and additional patient experience will be necessary to fully characterize the potential benefit and risk of treatment with CAL-101.”

“The early clinical activity demonstrated with CAL-101 validates our isoform-selective PI3K approach. We have not seen data reporting these types of clinical responses with any of the other competitor PI3K programs,” said Carol Gallagher, Pharm.D., Chief Executive Officer of Calistoga Pharmaceuticals. “Further, the responses have been observed in patients with different disease etiologies including CLL, mantle cell lymphoma, marginal zone lymphoma, and follicular lymphoma, suggesting that CAL-101 has the potential to benefit broad numbers of patients with hematologic malignancies.”

CAL-101 is a potent inhibitor of PI3K p110δ with 40- to 300-fold selectivity for the delta isoform as compared to 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 a range of NHL cell lines.

In addition to CAL-101, Calistoga Pharmaceuticals has a pipeline of isoform-selective PI3K inhibitors. This includes CAL-263, a delta isoform-selective PI3K inhibitor for treatment of patients with inflammatory diseases such as asthma, chronic obstructive pulmonary disease and rheumatoid arthritis; and CAL-120, a PI3K inhibitor inhibiting the beta and delta isoforms of PI3K for treatment of patients with solid tumors. The Company plans to advance CAL-101 and CAL-263 into Phase 2 clinical studies and CAL-120 into Phase 1 evaluation in 2010.

About Calistoga Pharmaceuticals

Calistoga Pharmaceuticals is dedicated to developing innovative medicines targeting selective 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 selectively targeting isoforms of the PI3K pathway. The Company's most advanced compound, CAL-101, a p110δ selective PI3K inhibitor, is under clinical evaluation in patients with hematologic malignancies. Calistoga is a private company headquartered in Seattle, Washington. For more information, visit the Company's website at: www.calistogapharma.com.

Contact: Rathbun Communications, Inc.
Julie Rathbun, 206-769-9219
Julie@rathbuncomm.com

Posted: June 2009

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