The purpose of this study is to evaluate the optimal dose of 2X-121 as single agent therapy at 600 mg daily (split BID 200 mg morning + 400 mg evening) compared to 800 mg daily (split BID 400 mg morning + 400 mg evening) in recurrent, advanced ovarian cancer patients that have platinum-resistant disease, defined as progression within 6 months after the last dose of platinum-based chemotherapy, or are platinum ineligible. The optimal dose will be selected based on an integrated analysis of PK/PD, safety, and efficacy data.