Background: Bortezomib is the first proteasome inhibitor to show preliminary evidence of activity against solid tumors. Findings from preclinical studies prompted a Phase I trial to determine the maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs) of bortezomib in combination with gemcitabine in patients with recurring/refractory advanced solid tumors. The effect of gemcitabine on proteasome inhibition by bortezomib in whole blood was also investigated.
Methods: Bortezomib was administered as an intravenous bolus injection on Days 1, 4, 8, and 11, with gemcitabine (30-minute infusion) on Days 1 and 8 of a 21-day cycle. Groups of > or =3 patients were evaluated at each dose level. Escalating doses of gemcitabine 500 mg/m(2) to 1000 mg/m(2) with bortezomib 1.0 mg/m(2) to 1.5 mg/m(2) were planned.
Results: There were no DLTs in patients receiving bortezomib 1.0 mg/m(2) and gemcitabine 500 mg/m(2) to 1000 mg/m(2) in the first 3 dose levels. Dose-limiting nausea, vomiting, gastrointestinal obstruction, and thrombocytopenia occurred in 4 of 5 evaluable patients in dose level 4 (bortezomib 1.3 mg/m(2), gemcitabine 800 mg/m(2)), establishing bortezomib 1.0 mg/m(2) and gemcitabine 1000 mg/m(2) as the MTD. Most common Grade > or =3 toxicities were neutropenia (6 patients), thrombocytopenia (5 patients), gastrointestinal disorders (6 patients), and general disorders (4 patients) such as fatigue. One patient with nonsmall cell lung carcinoma achieved a partial response and 7 achieved stable disease. Inhibition of 20S proteasome activity by bortezomib was unaffected by gemcitabine coadministration.
Conclusion: Dosages of bortezomib and gemcitabine suitable for further evaluation of antitumor activity have been established.