Abstract
<div>Abstract<p><b>Purpose:</b> PARP is essential for recognition and repair of DNA damage. In preclinical models, PARP inhibitors modulate topoisomerase I inhibitor–mediated DNA damage. This phase I study determined the MTD, dose-limiting toxicities (DLT), pharmacokinetics (PK), and pharmacodynamics (PD) of veliparib, an orally bioavailable PARP1/2 inhibitor, in combination with irinotecan.</p><p><b>Experimental Design:</b> Patients with advanced solid tumors were treated with 100 mg/m<sup>2</sup> irinotecan on days 1 and 8 of a 21-day cycle. Twice-daily oral dosing of veliparib (10–50 mg) occurred on days 3 to 14 (cycle 1) and days −1 to 14 (subsequent cycles) followed by a 6-day rest. PK studies were conducted with both agents alone and in combination. Paired tumor biopsies were obtained after irinotecan alone and veliparib/irinotecan to evaluate PARP1/2 inhibition and explore DNA damage signals (nuclear γ-H2AX and pNBS1).</p><p><b>Results:</b> Thirty-five patients were treated. DLTs included fatigue, diarrhea, febrile neutropenia, and neutropenia. The MTD was 100 mg/m<sup>2</sup> irinotecan (days 1 and 8) combined with veliparib 40 mg twice daily (days −1–14) on a 21-day cycle. Of 31 response-evaluable patients, there were six (19%) partial responses. Veliparib exhibited linear PK, and there were no apparent PK interactions between veliparib and irinotecan. At all dose levels, veliparib reduced tumor poly(ADP-ribose) (PAR) content in the presence of irinotecan. Several samples showed increases in γ-H2AX and pNBS1 after veliparib/irinotecan compared with irinotecan alone.</p><p><b>Conclusions:</b> Veliparib can be safely combined with irinotecan at doses that inhibit PARP catalytic activity. Preliminary antitumor activity justifies further evaluation of the combination. <i>Clin Cancer Res; 22(13); 3227–37. ©2016 AACR</i>.</p></div>
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