A phase I study of MDM2 antagonist RG7112 in patients (pts) with relapsed/refractory solid tumors.
e13600^ Background: RG7112 is a small molecule MDM2 antagonist, designed to non-genotoxically activate p53. A phase I dose escalation (DE) was performed, followed by a sarcoma biomarker extension (EXT) in pts with wild type TP53. Methods: 106 pts (58M, 48 F), median age 57.9 yrs (range 22-84) participated; 76 in 9 cohorts (DE) from 20 to 1800 mg/m2, orally QD x 10 q28 days. 30 pts with sarcoma were treated at MTD (2500 mg) (EXT) with pre-and on dose (d5+/-2) biopsies. Analyses included TP53 mutation (AmpliChip), MDM2 amplification (ISH), p53 and p21 IHC, MDM2 RT-PCR, Ki-67, TUNEL and [18F]-FLT-PET. Blood was obtained for PK and MIC-1, a PD marker of p53 activation. Results: DE: MTD was1440 mg/m2/d (2500 mg flat dose). PK was ~dose linear (t½ 1-1.5 d) with high variability (CV~70%) in AUC and Cmax . Adverse events included nausea/GI and exposure-related neutropenia/thrombocytopenia. 3 DLTs: diarrhea, pancytopenia, hyponatremia occurred (at ≥ 640 mg/m2). Evidence of activity included: 1) concentration dependent increase in plasma MIC-1 (% baseline), 2) decrease in [18F]-FLT PET and PR each in liposarcoma pts at 1800 mg/m2 and 1440 mg/m2, respectively. EXT: Grade3/ 4 cytopenias at MTD precluded subsequent cycles in 6/8 pts (10 day schedule). Dosing was changed to 5 days, and only 3 patients had Gr3/4 cytopenias. 8/22 pts remained on study for >4 cycles, including 2 pts with SD for 7 and 9 cycles respectively. 3 of 4 EXT pts had decreased [18F]-FLT-PET activity. Biopsies (pre- and on treatment) demonstrated: 1) increase in p53 (median 1.5 fold change (X) by IHC, n=15); 2) increase in p21 (median 2.7X by IHC, n=14); 3) increase in MDM2 (median 2.5X by RT-PCR, n = 27); 4) decrease in % Ki-67(+) cells (median % change from baseline -65.4%, range -91% to +275%, n=17 ); 5) increase in TUNEL(+) cells of 9.0 (density of + cells/mm2, range -26.2 to +45.5, n=22). These results were seen both in tumors with and without MDM2 gene amplification, and in multiple sarcoma subtypes. Conclusions: RG7112 has manageable AEs (GI ) and cytopenias correlating with AUC. Single agent disease control, and biomarker activity was seen in both MDM2 amplified and non-amplified, heavily pretreated soft tissue sarcoma pts, with changes reflecting activation of p53-related pathways.