Abstract 1461: MK-4827, a PARP-1/-2 inhibitor, strongly enhances response of human lung and breast cancer xenografts to radiation
Authors: Wang Li , Mason Kathy A. , Ang K. Kian , Buchholz Thomas , Valdecanas David , Mathur Anjili , Buser-Doepner Carolyn , Toniatti Carlo , Milas Luka 
Published: August 2012

Abstract
The poly-(ADP-ribose) polymerase (PARP) inhibitor, MK-4827, is a novel potent, orally bioavailable PARP-1 and PARP-2 inhibitor currently in phase I clinical trials for cancer treatment. No preclinical data currently exist on the combination of MK-4827 with radiotherapy (XRT). We examined whether MK-4827 enhances radiosensitivity of a variety of human tumor xenografts of differing p53 status. Human lung cancer xenografts, Calu-6 (p53 null), A549 (p53 wild-type [wt]) and H-460 (p53 wt) and triple negative MDA-MB-231 human breast carcinoma xenografts were used. Tumor xenografts growing in the hind leg of nude mice were exposed to fractionated XRT at 8 mm (diameter). Fractionated XRT (2 Gy per fraction) was delivered for 7 (twice daily, 6 h in between) or 14 (once daily) consecutive days, total dose 28 Gy. MK-4827 was given by gavage once (50 mg/kg, 1 h before first XRT of the day) or twice daily (25 mg/kg, 1 h before each XRT of the day) starting when tumors were 6 mm diameter. Mice received (a) no treatment, (b) MK-4827, (c) XRT or (d) MK-4827 plus XRT. Tumor growth delay (TGD, days for tumors to grow from 8.0 mm to 12.0 mm) was the endpoint. Radiation enhancement factor (EF) was then calculated. MK-4827 alone had no effect on tumor growth for any of the tumors types. For p53 mutant Calu-6 xenografts TGD for untreated tumors was 13.2 ± 0.5 and for twice daily XRT was 30.9 ± 2.4 days. Combination of XRT for 7 days with MK-4827, 25mg/kg twice daily for 21 consecutive days, further extended TGD to 39.7 ± 2.0 days (EF 1.4) and 47.8 ± 4.0 days (EF 2.03) for MK-4827, 50mg/kg once daily. Maximum radiation enhancement was observed when MK-4827 was given at a dose of 50 mg/kg once daily. For XRT and MK-4827 given once daily, MK-4827 was continued until 2 days after completion of XRT, MK-4827 was found to be similarly effective and the EF was 1.7. For p53 wt H460and A459 xenografts, twice daily XRT and once daily MK-4827 was used. MK-4827 was continued until 2 days after completion of XRT. TGD for untreated H460 and A459 xenografts was 7.8 ± 0.5 and 33.2 ± 1.5 days respectively; whereas it was 15.6 ± 0.5 and 53.2 ± 3.1 days respectively for irradiated tumors. TGDs were further extended to 26.0 ± 3.5 days for H460 (EF 2.2) and 64.1 ± 4.2 days (EF 1.9) for A549 xenografts in MK-4827 plus XRT groups. Similarly, using MDA-MB-231 human breast carcinoma xenografts, the potency of combination treatment was greater than XRT alone showing essentially no local tumor regrowth until the occurrence of metastases. When MK-4827 was given as a single dose of 50 mg/kg and tumors were assayed for PAR, MK-4827 reduced PAR levels in tumors by 1 h after administration which persisted for up to 24 h. In conclusion, MK-4827 strongly enhanced the effect of radiation on a variety of human tumor xenografts irrespective of p53 status. The long lasting PARP inhibition (1-24h) potentially adds flexibility to future clinical trial design.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1461. doi:1538-7445.AM2012-1461