ATNT-01ABT-414 MONO- OR COMBINATION THERAPY WITH TEMOZOLOMIDE (TMZ) RECHALLENGE IN PATIENTS WITH RECURRENT GLIOBLASTOMA (GBM) AND AMPLIFIED EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR): A PHASE I STUDY

Abstract

BACKGROUND: Aberrant EGFR signaling plays a vital role in GBM oncogenesis. ABT-414 is an antibody-drug conjugate with a toxic payload (monomethylauristatin F) linked to ABT-806, an antibody targeted to activated EGFR. This phase I, open-label, 3-arm study (NCT01800695) evaluates ABT-414 mono- or combination therapy with TMZ rechallenge in patients with GBM. Herein, we report outcomes in recurrent GBM. METHODS: Eligible patients (≥18 years) had recurrent supratentorial GBM and Karnofsky performance status ≥70. ABT-414 was given intravenously every 2 weeks with TMZ rechallenge (150-200 mg/m2 days 1-5 q28; Arm B) or as monotherapy (Arm C). ABT-414 dose escalation used a modified continual reassessment method. Primary objectives were to assess ABT-414 safety, maximum tolerated dose (MTD), and recommended phase II dose (RPTD); secondary objectives included antitumor activity evaluation. RESULTS: As of April 2015, 19 Arm B patients were treated in 4 dose groups (0.5-1.5 mg/kg), and 27 Arm C patients were treated at 1.25 mg/kg. In Arms B/C, 10/17 patients had amplified EGFR. Most common grade 3/4 treatment-emergent adverse events in either arm were keratitis (11%/19%), γ-glutamyltransferase increase (16%/0%), convulsions (11%/0%), fatigue (11%/0%), and thrombocytopenia (11%/4%). ABT-414 MTD was 1.5 mg/kg in Arm B and was not reached in Arm C; RPTD is 1.25 mg/kg for both arms. Best objective responses were complete response (CR) in 3 patients and a partial response (PR) in 1 patient in Arm B, and 1 CR and 1 PR in Arm C patients (all confirmed responses were observed in patients with EGFR amplification).Objective response rate among EGFR-amplified subjects was 22.2% (6/27). CONCLUSIONS: RPTD for ABT-414 is 1.25 mg/kg for both combination therapy with TMZ rechallenge and monotherapy. ABT-414 demonstrated a unique safety profile including ocular AEs, and appears to have antitumor activity in recurrent GBM with EGFR amplification.