A first-in-human phase Ib study to evaluate the MEK inhibitor GDC-0973, combined with the pan-PI3K inhibitor GDC-0941, in patients with advanced solid tumors.

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)...