The trial is approved for patients who have seen their cancer progress after first-line therapy. This is an extension of an ongoing human phase I clinical trial of PAC-1 alone in patients with various late-stage cancers. Phase I trials are designed to test the safety of new drugs in human patients.
PAC-1 is unusual in that it is able to cross the blood-brain barrier, a formidable obstacle to most anti-cancer drugs. The drug targets procaspase-3, an enzyme that is overexpressed in many cancer cells, said University of Illinois chemistry professor Paul Hergenrother, who discovered PAC-1’s anti-cancer effects more than a decade ago. After tests in human cell lines and rodents proved promising, Hergenrother and veterinary oncologist Dr. Timothy Fan, a professor of veterinary clinical medicine at Illinois, tested PAC-1 in pet dogs with a variety of naturally occurring cancers.
“Most cancers have elevated levels of procaspase-3,” Hergenrother said. “When it is turned on, procaspase-3 kills cells.”
Cancer cells override this normal cell-recycling pathway, however, he said.
“PAC-1 restores the activation of procaspase-3 and, because this enzyme is elevated in cancer cells, targets cancer cells over noncancerous cells,” he said.
PAC-1 has been evaluated in pet dogs with naturally occurring osteosarcoma, lymphoma and, most recently, glioma — a brain cancer similar to glioblastoma in humans. One 2016 study found that the combination of PAC-1 with doxorubicin, a chemotherapeutic agent that also is used in humans, saw tumor reductions in four of four dogs with lymphoma and in three of six dogs with osteosarcoma. The trials in dogs continue and, so far, have found PAC-1 to be safe, with few observable side effects apart from occasional gastrointestinal distress. The researchers report their latest findings in rodents and in dogs with brain cancer in the journal Oncotarget.