2566 Background: Both RAS/RAF/MEK and PI3K/Akt signaling pathways are deregulated in many tumor types. Targeting both pathways may be more efficacious than targeting either pathway alone. In preclinical models, concurrent administration of GDC‑0973, a potent, selective, MEK1/2 inhibitor and GDC-0941, a potent class I PI3K inhibitor, shows improved efficacy compared to either agent alone dosed continuously or intermittently. Methods: A phase Ib dose-escalation study with 3+3 design was initiated in patients (pts) with advanced solid tumors to evaluate the safety and pharmacokinetics (PK) of oral dosing of GDC-0973 and GDC-0941. Pts received: concurrent GDC-0973 + GDC-0941 once daily (qd) on a 21 day on/7 day off (21/7) schedule; intermittent GDC-0973 on Days 1, 4, 8, 11, 15, 18 of a 28 day cycle + GDC-0941 qd on a 21/7 schedule (MEK int); or GDC-0973 + GDC-0941 qd on a 7 day on /7 day off schedule (7/7). Starting doses were 20 mg GDC-0973 + 80 mg GDC-0941 (21/7), 100 mg GDC-0973 + 130 mg GDC-0941 (MEK int); 40 mg GDC-0973 + 130 mg GDC-0941 (7/7). Serial plasma PK samples, FDG-PET, and CT scans were obtained. Results: 78 pts have enrolled. DLTs were G3 lipase (n=1), G4 CPK elevation (n=1). Compared to the 21/7 MTD of 40 mg GDC-0973 + 100 mg GDC-0941, higher doses of GDC-0973 + GDC-0941 were tolerated on the MEK int schedule. Overall, adverse events related to the study drug combination in ≥ 20% pts were diarrhea, rash, nausea, fatigue, vomiting, decreased appetite, dysgeusia, and elevated CPK. Preliminary analysis indicated PK of GDC-0973 and GDC-0941 are not altered when dosed in combination. Of 46 evaluable pts, 26 had an FDG-PET partial metabolic response (≥ 20% decrease in mean SUVmax from baseline) at ≥1 time points. Partial responses were observed in 3 pts (mBRAF melanoma, mBRAF pancreatic ca, mKRAS endometrioid ca); 5 pts had stable disease ≥ 5 months. Conclusions: Combination dosing of GDC‑0973 and GDC-0941 is generally well tolerated, with toxicities similar to those observed in single agent GDC-0973 and GDC-0941 phase 1 trials. There are early signs of anti-tumor activity. Dose escalation on MEK int and 7/7 schedules continues and updated data will be presented.
Phase Ib Study of Combination Therapy with MEK Inhibitor Binimetinib and Phosphatidylinositol 3‐Kinase Inhibitor Buparlisib in Patients with Advanced Solid Tumors with
RAS/RAF
Alterations