On June 6, at the meeting of the American Society of Clinical Oncology (ASCO), a University of Pittsburgh scientist working with New York-based Stemline Therapeutics revealed that two patients in an early trial of the company’s drug had recovered from advanced malignant glioma—a deadly form of brain cancer. Another patient, a 10-year-old girl in a pediatric trial of the drug, saw her tumors shrink more than 50 percent.
Stemline’s presentation was overshadowed by more advanced cancer research presented by the likes of Pfizer and Bristol-Myers Squibb. But for the tiny team at Stemline, the conference—its first ASCO appearance—was still a major milestone for the drug, called SL-701. “We were pretty excited,” says Ivan Bergstein, CEO of Stemline. “They put us in a large amphitheater, and we got a good turnout.”
The crowds likely showed up in force because of a growing interest in the company’s approach, which is to attack cancer stem cells (CSCs)—master cells that are “tumorigenic,” or tumor-forming. Those cells are among the most important targets in the war against the disease. That’s because CSCs tend to resist standard cancer treatments, such as chemotherapy. So even if a patient’s tumor is greatly diminished with chemo, the CSCs within the tumor often survive, causing relapse and ultimately death.
Bergstein, a hematologist and oncologist by training, founded Stemline in 2003. The company developed a technology platform that can isolate CSCs with fluorescent markers, which in turn speeds up the process of screening for compounds that help combat the virulent cells. The technology, called StemScreen, has produced several of Stemline’s clinical candidates. The company’s two most advance projects are SL-701 and a treatment for blood cancers called SL-401, both of which are progressing in the clinic towards the pivotal late-stage trials that will be required for FDA approval.
Stemline’s scientists selected the drugs over other molecules that showed up in the screening process largely because of their “dual effect,” Bergstein says. “They hit the non-stem-cells, as well as the stem cells,” he explains. SL-701, for example, which Stemline licensed from the University of Pittsburgh, is a therapeutic vaccine that mobilizes the immune system by attacking multiple targets on both tumor cells and cancer stem cells. “Our prediction is that the dual effect will make the tumor shrinkage more durable” than it is with standard chemo and radiation, Bergstein says. And though the clinical program is not advanced enough to produce solid survival data, in the early trials, “the population as a whole is living longer,” Bergstein says.
SL-401 is also a dual-acting drug. It targets the interleukin-3 receptor (IL-3R), which is overly abundant in the cancer cells and stem cells of many blood cancers, including acute myeloid leukemia (AML). In two trials of the drug that Stemline presented
