Calistoga Pharmaceuticals, Inc, the leader in the development of isoform-selective phosphatidylinositol 3 kinase (PI3K) inhibitors for the treatment of cancer and inflammatory diseases, announced the initiation of a phase-1 trial of CAL-101, the company’s oral, PI3K delta inhibitor, in combination with standard of care agents Rituxan (rituximab) and/or Treanda (bendamustine) in patients with relapsed or refractory indolent non-Hodgkin’s lymphoma or chronic lymphocytic leukaemia.

The open-label, multicenter trial will evaluate the safety and efficacy of CAL-101 in three different regimens: CAL-101 plus rituximab, CA-101 plus bendamustine, and CAL-101 plus rituximab and bendamustine. The study is expected to enrol approximately 36 patients at multiple centres in the United States. “Given the encouraging efficacy and safety we have observed with CAL-101 in our ongoing single-agent trial, it is a logical next step to evaluate the safety and efficacy of the addition of CAL-101 to current standard of care regimens,” said Carol Gallagher, chief executive officer of Calistoga Pharmaceuticals.

CAL-101 is an oral, small molecule delta selective PI3 kinase inhibitor, a first in class compound, with greater than 200-fold selectivity in cell-based assays for the delta isoform as compared to other class 1 PI3K isoforms. CAL-101 is designed to induce cancer cell death and inhibit signalling pathways associated with cancer cell dependence on the tumour microenvironment.

Interim results from the ongoing phase-1 single agent study of CAL-101 in patients with relapsed or refractory haematologic malignancies have demonstrated overall response rates of 71 per cent, 75 per cent, and 29 per cent for patients with indolent NHL, mantle cell lymphoma, and CLL, respectively. The median duration of response is not yet determined as the majority of patients who responded continue on therapy. CAL-101 was generally well tolerated with a low incidence of haematologic adverse events. The dose-limiting toxicity is an elevation of liver transaminases. These elevations occur at a low frequency, are monitorable and reversible, and most patients continue therapy on a reduced dose. To date, over 120 patients have been enrolled in the CAL-101 single agent trial.

“Although rituximab and bendamustine have demonstrated clinical benefit in relapsed and refractory patients with indolent NHL and CLL, patients could benefit from a regimen that could provide impoved depth & durability of response in a greater number of patients without adding additional toxicity,” said Albert Yu, chief medical officer of Calistoga Pharmaceuticals. “This trial will provide the first understanding of the efficacy and safety of CAL-101 combination therapy.”

Calistoga has also initiated a long-term safety extension study to allow patients who derive clinical benefit at the end of the 12-month treatment period in standard CAL-101 protocols to continue on CAL-101 treatment until disease progression.

Calistoga Pharmaceuticals is dedicated to developing targeted therapy to improve the health of patients with cancer and inflammatory diseases.