Background: Glycoprotein NMB (GPNMB), also known as osteoactivin, is expressed in 25-40% of breast cancers and is associated with an increased risk of recurrence. This is the first study of CR011-vcMMAE, a fully-human monoclonal anti-GPNMB antibody conjugated to the tubulin inhibitor monomethylauristatin E (MMAE), in pts with breast cancer.Methods: Eligible pts with MBC had ³ 2 prior chemotherapy regimens, including a taxane, an anthracycline, and capecitabine; and ECOG PS ≤ 2. Doses were escalated to 1.88 mg/kg IV q3w (the maximum tolerated dose [MTD] in a previous study of patients with melanoma) using a standard 3+3 design followed by a Ph II expansion at the MTD. Pts received CR011-vcMMAE until disease progression (PD) or intolerable toxicity. The primary endpoint of the Ph II study was 12-week progression free rate, defined as the proportion of patients who were alive and free of progressive disease 12 weeks from the first dose of CR011-vcMMAE. A Simon two-stage minimax design was used (p0=0.1; p1=0.3, α=β=0.1) with 16 patients in the first stage and a total of 25 pts. Secondary endpoints included objective response rate and duration of response. IHC with a goat polyclonal antibody to GPNMB was performed on pt biopsy specimens.Results: In Ph I, 14 pts were treated with CR011-vcMMAE at 1.0 mg/kg (n=3), 1.34 mg/kg (n=5), and 1.88 mg/kg (n=6). In the first 2 pts at 1.34 mg/kg, dose limiting toxicity of worsening peripheral sensory neuropathy was observed. Pts with baseline neuropathy worse than grade 1 were subsequently excluded. There were 3 partial responses, one confirmed, and 1.88 mg/kg q3w was selected for Ph II. In Ph II, 14 pts with MBC (median age 57 years, range 34 - 76) had a median of 5 prior regimens; median follow up was 6 weeks; 12 pts are ongoing (median duration 6 weeks, range 1 - 14 weeks). Two pts were progression-free at 12 weeks, therefore the study has met the criteria for advancement to the second stage. The most common AEs were rash (61%), fatigue (50%) and alopecia (50%). The most common grade 3/4 AEs were neutropenia (17%) and neuropathy (11%). IHC staining of 5 patient biopsies revealed 2 with positive GPNMB expression, including one of the patients with PR.Conclusions: CR011-vcMMAE is active and well-tolerated in heavily pretreated pts with advanced breast cancer. The Phase II study has met the criteria for advancement into the second stage, and enrollment is ongoing.
Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6096.