A phase Ib study of sorafenib (BAY 43-9006) in patients with Kaposi sarcoma

Background. We conducted a phase Ib study of sorafenib, a vascular epithelial growth factor receptor (VEGFR), c-kit, and platelet derived growth factor receptor (PDGFR)-targeted treatment in Kaposi sarcoma (KS). We evaluated drug-drug interactions between sorafenib and ritonavir, an HIV medication with strong CYP3A4 inhibitory activity. Methods. Two cohorts were enrolled: HIV-related KS on ritonavir (Cohort R) and HIV-related or classical KS not receiving ritonavir (Cohort NR). Sorafenib dose level 1 in cohort R (R1) was 200 mg daily and 200 mg every 12 hours in cohort NR (NR1). Steady-state pharmacokinetics were evaluated at cycle 1, day 8. KS responses and correlative factors were assessed. Results. Ten patients (nine HIV⁺) were enrolled: R1 (eight), NR1 (two). Median CD4⁺ count (HIV⁺) was 500 cells/µL. Dose-limiting toxicities (DLTs) were grade 3 elevated lipase (R1), grade 4 thrombocytopenia (R1), and grade 3 hand-foot syndrome (NR1). Two of seven evaluable patients had a partial response (PR; 29%; 95% CI 4%-71%). Steady-state area under the curve of the dosing interval (AUC_TAU) of sorafenib was not significantly affected by ritonavir; however, a trend for decreased AUC_TAU of the CYP3A4 metabolite sorafenib-Noxide (3.8-fold decrease; p=.08) suggests other metabolites may be increased. Conclusion. Sorafenib was poorly tolerated, and anti-KS activity was modest. Strong CYP3A4 inhibitors may contribute to sorafenib toxicity, and ritonavir has previously been shown to be a CYP3A4 inhibitor. Alternate antiretroviral agents without predicted interactions should be used when possible for concurrent administration with sorafenib.