Abstract 5054: Nanoformulation of talazoparib to increase efficacy when combined with temozolomide for the treatment of Ewing sarcoma xenografts
Authors: Baig Nabeela , Likhotvorik Rostislav , Baldwin Paige , Sridhar Srinivas , Kurmasheva Raushan 
Published: July 2017

Abstract
Ewing Family of tumors (EFT) comprises the fourth most common highly malignant childhood cancer. Although sustained event-free survival (EFS) can be achieved with intensive chemo-radiation therapy for patients with local-regional disease, this therapy is relatively ineffective in the treatment of metastatic disease with EFS of 12% at 5 years. Ewing sarcoma is characterized by a reciprocal translocation between chromosomes 11 and 22 that encodes a chimeric oncoprotein resulting from the fusion of EWSR1 to the FLI1 transcription factor in ~85% of tumors. Therapy for patients with EFT comprises surgery, intensive use of cytotoxic agents and radiation therapy. Dose intensification and dose compression has resulted in some improvement in outcome, but patents with advanced or metastatic disease at diagnosis still represent a challenge. Further, patients alive at 5 years from diagnosis still have a high probability of subsequent relapse. Further, long-term consequences of treatment included cardiac dysfunction, and secondary malignancies. Thus, more effective and less toxic therapies are required to treat patients with advanced disease.
Our studies, as part of the Pediatric Preclinical Testing Program (PPTP), identified the combination of the PARP inhibitor, talazoparib, with the DNA damaging agent temozolomide, as being highly synergistic in xenograft models of Ewing sarcoma, but not against other tumor types. In this study 5 of 10 Ewing tumor xenografts models showed dramatic regressions to the combination, while administered as single agents neither talazoparib or temozolomide were active. We have studied the talazoparib-temozolomide synergy in vitro, and results indicate that in models where there is no synergy as xenografts, the cell lines have either intrinsic resistance to talazoparib, temozolomide or both drugs. In mice, and in the clinical trial (NCT02116777), the talazoparib-temozolomide combination is toxic requiring a reduction in temozolomide dose to ~15% of its single maximum-tolerated dose.
We are exploring the use of nanoparticle-formulated talazoparib (npTLZ) developed by Nanomaterials Synthesis Laboratory at Northeastern University without tumor targeting or with antibody-mediated targeting to increase the tumor-drug delivery, reduce normal tissue toxicity (mainly thrombocytopenia), and potentially allow escalation of temozolomide dose. In the PPTP study, the MTD for temozolomide combined with free talazoparib (0.25 mg/kg PO BID daily x 5) was 12 mg/kg. Our recent data showed no toxicity of temozolomide at 66 mg/kg (PO daily x 5) in mice treated with npTLZ (0.5 mg/kg IV daily x 5), suggesting that npTLZ does not potentiate TMZ toxicity to normal mouse tissues. We anticipate that nanoparticle delivery of talazoparib combined with temozolomide will allow reduced toxicity while increasing the response rate for this combination in preclinical models of Ewing sarcoma.
Citation Format: Nabeela Baig, Rostislav Likhotvorik, Paige Baldwin, Srinivas Sridhar, Raushan Kurmasheva. Nanoformulation of talazoparib to increase efficacy when combined with temozolomide for the treatment of Ewing sarcoma xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5054. doi:10.1158/1538-7445.AM2017-5054