Seattle-based Calistoga Pharmaceuticals has taken another peek at preliminary results from an ongoing clinical trial of its drug that’s made to block one of the hottest targets in cancer biology, and it continues to like what it’s seeing.
Researchers saw that five of 17 evaluable patients (29 percent) with chronic lymphocytic leukemia had at least partial tumor shrinkage after a single one-month cycle of therapy on Calistoga’s CAL-101 drug candidate by itself, without help from combination therapy, according to data presented over the weekend at a leukemia research meeting in Barcelona. All of the patients had gotten standard treatments before enrolling, and half of them had relapsed before entering the Calistoga trial, researchers said.
The new findings strengthen Calistoga’s body of evidence in a year in which it has started to create some buzz on the national stage. The company raised $30 million in venture capital in May from Frazier Healthcare Ventures, Alta Partners, Three Arch Partners, and Amgen Ventures. A few weeks later, it became clear why Calistoga attracted that much cash. It reported at a pair of cancer meetings that its drug was causing tumor shrinkage in about half of the first 24 evaluated patients in its first clinical trial, even at less than ideal doses, for patients with non-Hodgkin’s lymphoma, acute myeloid leukemia, and chronic lymphocytic leukemia.
The latest data also confirms that Calistoga, along with a number of tough competitors, is pursuing what biologists consider one of the hottest targets in cancer biology. It’s called the PI3 kinase pathway, which controls critical cell processes like proliferation, migration, and cell survival. When these normal functions get flipped into an overactive mode, it’s a hallmark of cancer cells growing out of control as well as an immune system going haywire and attacking healthy tissue.
“We’re seeing robust responses,” in relapsed patients, says Carol Gallagher, Calistoga’s CEO, who I reached by phone while she was attending the meeting in Barcelona. “This is very encouraging data.”
Encouraging as it may be, Calistoga has also learned some important things about side effects. Patients got either a 200 milligram or 350 milligram dose of CAL-101, and saw some signs of elevated liver enzymes in the bloodstream at those doses, which can be a sign of liver damage. The side effects were reversible when patients quit taking the drug, but that effect has gotten Calistoga thinking about whether patients would be better off taking a lower dose in subsequent trials, to strike the best balance between safety and effectiveness, Gallagher says. The company has seen tumor shrinkage with doses as low as 50 and 100 milligrams, she says.
That said, there were other interesting findings from this trial. To put it in context, Gallagher first explained the “partial responses” that are reached when scientists saw at least a 50 percent shrinkage in lymph node tumors, in addition to a 50 percent decline in lymphatic cancer cells circulating through the bloodstream.
That’s important to physicians, but what’s particularly intriguing is the next finding. Calistoga
