Bosutinib (SKI-606), a dual Src/Abl tyrosine kinase inhibitor: Preliminary results from a phase 1 study in patients with advanced malignant solid tumors

Abstract

3552 Background: Bosutinib (SKI-606) is a potent, low molecular weight, orally active, competitive inhibitor of both Src and Abl tyrosine kinases. Elevations of Src kinase activity occur in a variety of human tumor types and are correlated with aggressiveness. We conducted a phase 1 study in patients (pts) with advanced solid tumors to assess tolerability, safety, pharmacokinetics (PK), and preliminary antitumor activity of bosutinib. Methods: Patients in cohorts of 3–6 received 50, 100, 200, 300, 400, 500 or 600 mg bosutinib orally on study day 1 and then once daily beginning on day 3. Timed blood samples were collected on days 1–3, 15 and 16 for PK analysis. Tumor assessments (modified RECIST criteria) were made at baseline and the end of every third cycle (21 days/cycle). Collection of tissue samples for analysis of Src biomarkers was optional. Results: Preliminary data are presented for 51 pts (median 57 years, 57% women). Three pts who received 600 mg bosutinib/day had drug-related dose-limiting toxicity of grade 3 diarrhea (2 pts) and grade 3 rash (1 pt). Gastrointestinal (GI) toxicity was reported among 6 pts in the 500-mg maximum tolerated dose (MTD) lead-in cohort so that 400 mg was selected as the MTD. Drug-related adverse events (AEs), any grade, occurring in =25% of pts were nausea (67%), diarrhea (55%), anorexia (45%), vomiting (43%), asthenia (41%). The only grade 3 drug-related AE occurring in =5% of pts was diarrhea (14%). After oral administration, bosutinib exposure increased in a dose-dependent manner. Multiple-dose exposure was nearly 2- to 3-fold higher than single-dose exposure. Mean elimination half-life was approximately 17 to 21 hours, supporting a once-daily dosing regimen. Six pts had stable disease >15 weeks (2 pts each with breast, colorectal cancer, non-small cell lung cancer [NSCLC]) and 1 pt had stable disease >52 weeks (pancreatic cancer). Conclusions: Bosutinib was generally well tolerated with predominantly gastrointestinal AEs. Accrual and evaluation of an expanded cohort restricted to patients with colorectal, pancreatic, and NSCLC tumors is ongoing. The patient with pancreatic cancer has had stable disease >52 weeks. No significant financial relationships to disclose.