Birinapant sensitizes platinum-resistant carcinomas with high levels of cIAP to carboplatin therapy

Abstract

Platinum drugs are the frontline therapy in many carcinomas, including high-grade serous ovarian cancers. Clinically, high-grade serous carcinomas have an apparent complete response to carboplatin, but tumors invariably recur and response to platinum drugs diminishes over time. Standard of care prohibits re-administration of platinum drugs to these patients who are labeled as having platinum-resistant disease. In this stage patients are treated with non-platinum agents and outcomes are often poor. In vivo and in vitro data presented here demonstrate that this clinical dogma should be challenged. Platinum drugs can be an effective therapy even for platinum-resistant carcinomas as long as they are combined with an agent that specifically targets mechanisms of platinum resistance exploited by the therapy-resistant tumor subpopulations. High levels of cellular inhibitor of apoptosis proteins cIAP1 and 2 (cIAP) were detected in up to 50% of high-grade serous and non-high-grade serous platinum-resistant carcinomas. cIAP proteins can induce platinum resistance and they are effectively degraded with the drug birinapant. In platinum-resistant tumors with ≥22.4 ng of cIAP per 20 µg of tumor lysate, the combination of birinapant with carboplatin was effective in eliminating the cancer. Our findings provide a new personalized therapeutic option for patients with platinum-resistant carcinomas. The efficacy of birinapant in combination with carboplatin should be tested in high-grade serous carcinoma patients in a clinical trial.

Combination therapy: sensitizing platinum-resistant tumors

Carboplatin efficacy can be restored by administering it with birinapant, a drug combination that targets platinum-resistant cancer cells. Platinum-based chemotherapeutics are used to treat almost 50% of cancer patients. Despite excellent initial response rates, tumor growth recurs in most patients as they develop resistance to therapy. Sanaz Memarzadeh and colleagues at the University of California, Los Angeles, show that the addition of birinapant to carboplatin eliminates platinum-resistant ovarian cancer cells by degrading the cell death-inhibiting proteins cIAP1 and cIAP2. Carboplatin and birinapant co-therapy restored the efficacy of the chemotherapeutic in human tumor samples and in mice with platinum-resistant tumors. Furthermore, the levels of cIAP protein in the resistant cells were predictive of the therapeutic response. These findings will help to select clinical trial patients that are most likely to benefit from this combination therapy.