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a clear molecular biomarker—an activated progesterone receptor, or APR, that Arno, citing preclinical data it’s obtained, thinks is abnormally turned on in certain tumors. It’ll then find patients with those biomarkers, and initially drive onapristone towards a cancer type where there isn’t a lot of competition—endometrial cancer, when cancerous cells grow in the lining of the uterus.
Patients with endometrial cancer can either get surgery, hormone or radiation therapy, or chemotherapy. But Mattes notes that the effectiveness of these options can be limited, invasive (in the case of surgery), or altogether difficult to tolerate. So by tailoring onapristone to a specific, targeted subset of endometrial cancer patients , Arno believes onapristone has a shot to be awarded status as an orphan drug, giving it longer market exclusivity. Arno’s also thinking about using the drug to treat prostate cancer patients possessing the APR biomarker that are no longer responding to hormone suppressing drugs like abiraterone (Zytiga, sold by Johnson & Johnson) or enzalutamide (Xtandi, sold by Medivation).
“We think that this space is less crowded and we can achieve a higher level of specificity going after those two tumor types as the initial development strategy,” Mattes says.
This is all a ways away, of course. With the new cash infusion, Arno will begin only its first human clinical trials of onapristone, and has to produce good results before it can think about the idea of holding the rights to an orphan drug, or wooing Opko or another suitor to form a partnership or buy it outright. Right now, it’s organizing two separate Phase I studies designed to find the best dose to give to patients in its next trials, and see what safety and efficacy signals it gets.
In one study, which is expected to start in the coming days, Arno will enroll women who have tumors—not just endometrial, but otherwise—that are progesterone receptor-positive, or PR+. In the other, which should start early next year, it’s enrolling men whose prostate cancer no longer responds to hormone therapy.
This will lead to a Phase 2 trial Arno aims to start in the fourth quarter of 2014 for patients with metastatic endometrial cancer. Since Arno will specifically target PR+ patients in that trial, it’s banking on getting the type of evidence that will wow the FDA, and give it enough juice to file a new drug application. Mattes is eyeing the idea of selling onapristone as an endometrial cancer treatment somewhere in late 2016 or early 2017.