CAL-101, an Oral p110 Isoform-Selective PI3 Kinase Inhibitor, Demonstrates Preclinical Activity in Hematologic Cancer Cells.

Preclinical Results Presented at the American Society of Hematology Annual Meeting

SEATTLE -- Calistoga Pharmaceuticals, Inc., the leader in the development of isoform-selective PI3 kinase inhibitors for the treatment of cancer and inflammatory diseases, today announced the presentation of data demonstrating that the Company's oral, p110(delta) selective PI3 kinase inhibitor CAL-101 has broad preclinical anti-tumor activity against a range of hematologic malignancies. Data were presented in an oral presentation and two poster presentations at the American Society of Hematology's 50th Annual Meeting and Exposition in San Francisco, CA.

Results presented by Dr. Brian Lannutti, Senior Scientist, Calistoga Pharmaceuticals, demonstrated that p110, whose expression under normal conditions is largely restricted to leukocytes, was highly expressed in >90% of hematologic cancer cell lines, including diffuse large B cell lymphoma, mantle cell lymphoma and acute lymphocytic leukemia (ALL) and in primary ALL patient samples. When these cell lines and primary patient cells were treated with CAL-101, evidence of pathway inhibition and cytotoxicity was observed, supporting the role of p110 in these malignancies.

"These findings demonstrate the potential of CAL-101 to selectively target the PI3K pathway in hematologic malignancies to induce cancer cell death," said Dr. Neill Giese, PhD, Chief Scientific Officer of Calistoga Pharmaceuticals. "We have demonstrated preclinical proof of concept with this selective approach and we believe it may circumvent the potential toxicities that would likely result from pan PI3K inhibition."

Separate poster presentations of studies conducted in Dr. John Byrd's laboratory at the Comprehensive Cancer Center at The Ohio State University and Dr. Kenneth Anderson's laboratory at the Dana-Farber Cancer Institute at Harvard Medical School demonstrated preclinical efficacy for CAL-101 in models of chronic lymphocytic leukemia and multiple myeloma, respectively.

"Our ongoing Phase 1 clinical trial provides our first opportunity to validate this novel approach in patients with hematological malignancies," noted Dr. Carol Gallagher, Pharm.D., Chief Executive Officer of Calistoga Pharmaceuticals. "CAL-101 is the first in a portfolio of selective PI3 kinase agents that we plan to evaluate clinically for the treatment of cancer and inflammatory diseases."

Calistoga Pharmaceuticals

Calistoga Pharmaceuticals is developing multiple compounds that selectively target the PI3 kinase pathway. The PI3 kinase family regulates immune cell activation and stimulates cell proliferation, growth, motility, metabolism and survival and is often upregulated in cancer and inflammatory diseases. Calistoga is a private company headquartered in Seattle, Washington. For more information, visit the Company's website at: www.calistogapharma.com.