Abstract CT204: Preliminary results from PiSARRO, a phase Ib/II study of APR-246, a mutant p53 reactivating small molecule, in combination with standard chemotherapy in platinum-sensitive ovarian cancer
Authors: von Euler Mikael , Wiman Klas G. , Gabra Hani , Brenton James D. , Basu Bristi , Vergote Ignace , Gourley Charlie , Smith Austin , Alfredsson Jessica , Mohell Nina , Green John A. 
Published: August 2015

APR-246 (PRIMA-1MET) is the first clinical-stage compound that reactivates mutant p53. This phase Ib part of a proof of concept study aims to determine the recommended phase II dose (RP2D) of APR-246 in combination with carboplatin and pegylated liposomal doxorubicin (PLD) in platinum sensitive High Grade Serous Ovarian Cancer (HGSOC). Despite high response rates from carboplatin in combination with paclitaxel in first-line treatment of ovarian cancer, most patients relapse and develop resistance. Partially platinum sensitive patients relapse between 6 and 24 months and are commonly treated with second -line carboplatin and PLD (Pujade-Lauraine et al. JCO, 2010). The mechanisms of platinum resistance are multifactorial; two of the main causes are mutations in p53 and increased levels of intracellular glutathione. Like the analog PRIMA-1, APR-246 is a pro-drug that is converted to the active form MQ, which restores wild type conformation to mutant p53 (Lambert et al. Cancer Cell, 2009). In addition, APR-246 has been shown in vitro to reduce glutathione levels, resensitize cancer cells to platinum drugs, and induce ROS levels and ER stress (Mohell et al. Abstract #1801, AACR 2014; Lambert et al. Oncogene, 2010). In the first-in-human phase Ia study, APR-246 monotherapy was found to have a satisfactory safety and pharmacokinetic profile allowing it to be combined with full dose chemotherapy (Lehmann et al., JCO, 2012).

The ongoing phase Ib/II study is enrolling patients with recurrent platinum sensitive HGSOC with positive p53 staining on immunohistochemistry. The phase Ib study has a 3+3 dose escalation design with 3 planned dose levels. APR-246 is administered as a 6h i.v. infusion on 4 consecutive days every 4 weeks. On day 4, APR-246 is given concomitantly with carboplatin AUC 5 and PLD 30 mg/m2. In the phase II part, 164 patients will be randomized to standard chemotherapy with or without APR-246. To date patients have been enrolled to all 3 dose cohorts. One DLT of ruptured diverticulum occurred at the 2nd dose level. No new safety concerns have emerged. The pharmacokinetic profile has not indicated any interaction between APR-246 and the chemotherapy. The first 3 patients have completed their therapy and are now in follow up. All 3 had partial response (PR) by RECIST 1.1 and 2/2 evaluable also had PR by GCIC.

In conclusion, early results from the ongoing clinical study are encouraging and support the continued development of APR-246 in the phase II part of the study comparing platinum based standard chemotherapy with or without APR-246 in patients with HGSOC with mutant p53. Preliminary results from all three dose levels and the RP2D will be presented at the meeting.

Citation Format: Mikael von Euler, Klas G. Wiman, Hani Gabra, James D. Brenton, Bristi Basu, Ignace Vergote, Charlie Gourley, Austin Smith, Jessica Alfredsson, Nina Mohell, John A. Green. Preliminary results from PiSARRO, a phase Ib/II study of APR-246, a mutant p53 reactivating small molecule, in combination with standard chemotherapy in platinum-sensitive ovarian cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT204. doi:10.1158/1538-7445.AM2015-CT204