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Calistoga Pharmaceuticals' CAL-101, an Oral Delta Isoform-Selective PI3 Kinase Inhibitor, Demonstrates Clinical Activity in Patients with Hematologic Cancers

Partial Responses in Six of Twelve Patients Treated During Dose Escalation in Phase 1 Study

Results Presented at the American Society of Clinical Oncology (ASCO) Annual Meeting

SEATTLE--(BUSINESS WIRE)--May 30, 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 clinical data on the Company's oral, p110δ(delta) selective PI3 kinase inhibitor CAL-101 demonstrating anti-tumor activity in six of twelve patients with hematologic malignancies treated during a Phase 1 clinical trial. Data were presented at the American Society of Clinical Oncology (ASCO) Annual Meeting in Orlando, Florida.

The dose escalation part of the ongoing Phase 1 study enrolled 12 patients with relapsed or refractory chronic lymphocytic leukemia (CLL) or B-cell non-Hodgkin's lymphoma (NHL) in which CAL-101 was administered orally across four dose levels. Initial results from the study demonstrated a partial clinical response in 6 out of 12 patients treated with CAL-101. Partial response is defined as a decrease of at least 50 percent in tumor burden. CAL-101 was well tolerated with no dose-limiting toxicity in any of these patients. The study continues to enroll patients with CLL, NHL, and acute myeloid leukemia (AML) in a cohort expansion phase.

“Our center enrolled the first patient in the study, and we were surprised and pleased to observe a response in this patient even at the lowest dose level.” noted Ian Flinn, M.D., Sarah Cannon Cancer Center. “Based on these early results, CAL-101 appears to be clinically active.”

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.

“It is unusual to see this proportion of patients having a response to a novel agent in the initial dose escalation part of a Phase 1 cancer study,” said Albert Yu, M.D., Chief Medical Officer of Calistoga Pharmaceuticals. “We saw responses in patients with CLL as well as different sub-types of NHL, suggesting CAL-101 may have broad applicability in hematologic malignancies.”

“We are pleased to be the first company to demonstrate clinical activity with p110 delta selective PI3K inhibition in the treatment of patients with hematologic malignancies,” noted Carol Gallagher, Pharm.D., Chief Executive Officer of Calistoga Pharmaceuticals. “We look forward to advancing our other isoform-selective PI3K inhibitor compounds to evaluate their clinical benefit in patients with other forms of cancer as well as inflammatory diseases.”

In addition to CAL-101, Calistoga Pharmaceuticals has a pipeline of isoform-selective PI3K inhibitors including 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. In 2010, the Company plans to advance CAL-101 and CAL-263 into Phase 2 clinical studies and CAL-120 into Phase 1 evaluation.

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:

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

Posted: June 2009