Rationally designed treatment for solid tumors with MAPK pathway activation: a phase I study of paclitaxel and...

In the preclinical setting, phosphorylation and subsequent proteosomal degradation of the proapoptotic protein BIM confers resistance to paclitaxel in solid tumors with RAS/RAF/MAPK pathway activation. Concurrent administration of the proteasome inhibitor bortezomib enables paclitaxel-induced BIM accumulation, restoring cancer cell apoptosis in vitro and producing tumor regression in mice in vivo. A phase I study was conducted to determine the maximum tolerated dose (MTD) of paclitaxel and bortezomib combinatorial treatment. Sixteen patients with refractory solid tumors commonly exhibiting mitogen-activated protein kinase (MAPK) pathway activation were treated weekly with paclitaxel and bortezomib. Starting doses were 40 mg/m(2) for paclitaxel and 0.7 mg/m(2) for bortezomib. A modified continual reassessment method adapted for 2-drug escalation was used for MTD determination with 3-patient cohorts treated at each dose level. MTD was reached at 60 mg/m(2) paclitaxel and 1.0 mg/m(2) bortezomib, the recommended phase II dose. Therapy was overall well tolerated. Most frequently observed toxicities included anemia (in 43.75% of patients, one grade 3 event), fatigue (in 43.75% of patients, one grade 3 event beyond cycle 1), and neuropathy (in 31.25% of patients, one grade 3 event after cycle 1). Of 15 evaluable patients, one non-small-cell lung carcinoma (NSCLC) patient with paclitaxel exposure at the adjuvant setting had a partial response and five patients had stable disease (SD); median disease stabilization was 143.5 days; three NSCLC patients had SD lasting 165 days or longer. Thus, rationally designed weekly treatment with paclitaxel and bortezomib in solid tumors with MAPK pathway activation, including previously taxane-treated malignancies, is a tolerable regimen with preliminary signals of antitumor activity worthy of further investigation.