Phase Ib/II Study Evaluating Orteronel (Without Prednisone) Combined With Itraconazole In Men With Castration-Resistant Prostate Cancer (CRPC)

Hedgehog (Hh) pathway signaling may be important in prostate cancer progression and this pathway is upregulated in the castration-resistant state. More potent (maximal) castration achievable by CYP17 inhibition, using orteronel, may further upregulate Hh pathway activation. Itraconazole administered at high doses (600 mg/day) may function as a modest Hh inhibitor. In a pilot phase II trial, investigators have shown that single-agent high-dose itraconazole produced PSA reductions in 29% of men with metastatic castration-resistant prostate cancer (CRPC), reduced circulating tumor cell counts in 62% of patients with unfavorable baseline counts, and prolonged progression-free survival compared to historical data. Moreover, clinical responses to itraconazole appeared to correlate with Hh pathway suppression, as measured by GLI1 mRNA analysis from serial skin biopsies. Investigators propose to evaluate the potent CYP17/lyase inhibitor, orteronel, in combination with itraconazole at escalating dose levels (100 mg BID, 200 mg BID, 300 mg BID) in men with non-metastatic or metastatic CRPC by conducting an open-label phase Ib/II trial. Importantly, unlike the related compound, ketoconazole, itraconazole very rarely results in adrenal suppression. Side effects previously seen at the highest dose of itraconazole (600 mg/day) were mild and included nausea, rash, diarrhea, vomiting, hypokalemia, edema, headache, hypertension, fever, pruritis, and abnormal liver function tests. Of note, orteronel will be given without concurrent prednisone in this trial. This is because the combination of itraconazole and corticosteroids can lead to Cushing's syndrome (hypercortisolism) by impairing corticosteroid metabolism through CYP3A4. Therefore, this study provides an opportunity to evaluate a steroid-free orteronel combination regimen. If this combination is safe and tolerable, subsequent studies would aim to compare the clinical efficacy of orteronel-itraconazole versus orteronel alone using a randomized phase II trial design.