Endocyte Adds Phase 3-Ready Prostate Cancer Drug with ABX Deal

Xconomy Indiana — 

Four months after two Endocyte drug candidates stumbled in early-stage studies, sparking a corporate shakeup, the company has signed a deal landing an experimental prostate cancer treatment that it says is ready for Phase 3 clinical trials.

West Lafayette, IN-based Endocyte (NASDAQ: ECYT) says it paid $12 million up front to German biochemicals company ABX in exchange for exclusive global rights to develop and commercialize the drug PSMA-617. ABX stands to gain milestone payments up to $160 million, plus royalties from sales if Endocyte can bring the drug to the market. The deal also gives ABX 2 million shares of Endocyte stock, as well as a warrant allowing ABX to purchase up to 4 million more Endocyte shares.

The newly licensed Endocyte drug is meant for prostate cancer patients whose disease has become resistant to other therapies, and has spread to their bones and organs, says CEO Mike Sherman. The drug delivers a radioactive payload directly to tumor cells by targeting protein specific membrane antigen (PSMA), a protein expressed by approximately 80 percent of patients who have this advanced cancer. Sherman says that changes in approaches to treating the disease have led oncologists to use late-stage treatments at earlier stages of the disease. PSMA-617 could provide an option to patients who have exhausted their treatment options, he says.

Delivering a drug payload in a targeted fashion is the hallmark of Endocyte’s own internally developed drugs. The company develops drugs called small molecule drug conjugates (SMDC). These treatments attach a drug payload to a targeting ligand, a molecule that binds to receptors on the cell of a target, such as cancer. This targeted approach is meant to spare healthy tissue. The company also develops imaging agents that allow clinicians to see what is happening with a patient’s cancer. Sherman says PSMA-617’s approach fits with the SMDC drug portfolio of Endocyte.

“I would suggest that it is an SMDC,” he says. “The difference is this drug is carrying a warhead that is a radioisotope, as opposed to the first few drugs we worked with that were carrying a chemotherapy.”

Phase 2 results for PSMA-617 were presented at a meeting of the European Society for Medical Oncology last month. The trial was an open label, single-arm study enrolling 30 castrate-resistant prostate cancer patients. In that trial, the drug showed a greater than 57 percent reduction in prostate-specific antigen in more than half of the patients. Furthermore, patients in the trial reported improved quality of life and reduction in pain. Side effects included dry mouth, nausea, and fatigue. Worldwide, PSMA-617 has been used in more than 300 patients so far, mostly under compassionate use, Sherman says. He adds that the recently reported Phase 2 results confirmed what has been observed in compassionate use of the drug.

Sherman says it’s too early to talk about the specifics of the Phase 3 clinical trial, including the projected cost, because Endocyte has yet to speak with the FDA. But Sherman says the company forecasts it will have more than $90 million in cash at the end of 2017. He adds that the trial is expected to start early next year, and would be completed as soon as 2020.

PSMA-617 gives Endocyte its first late-stage compound since vinafolide, an ovarian cancer drug that the company was developing in partnership with Merck (NYSE: MRK). Phase 3 studies halted in 2014 after an interim analysis could not show the drug worked. Endocyte ran into further problems last June after a review of two Phase 1 programs found that one was unlikely to work and a second, EC1169, would likely work only in a narrower group of prostate cancer patients. A corporate restructuring followed, which cut 40 percent of Endocyte’s staff.

As Endocyte now shifts its focus to PSMA-617, the company is paring back its efforts elsewhere. While the company is holding onto a cancer therapy it is researching with the Seattle Children’s Research Institute, Sherman says the company is looking to out-license its other drug programs, allowing Endocyte to focus on its newly acquired drug. Longer term, Sherman says Endocyte could develop PSMA-617 for other diseases.

Image of slide showing prostate cancer by the National Cancer Institute.