A Phase 2 Trial of Verapamil for Reversal of Drug Resistance in Refractory Non - Hodgkin's Lymphoma

Park, Keun Chil; Ryoo, Baek Yeol; Im, Young Hyuk; Kang, Sung Wook; Lee, Jhin Oh; Yun, Taik Koo; Shin, Ho Sang

Abstract

PURPOSE: Drug resistance is one of the major obstacles to treatment of cancer. Multidrug resistance (MDR) caused by overexpression of p-glycoprotein (Pgp) in cancer cell membrane is a well-known mechanism of drug resistance in in vitro system and was reported to be a significant mechanism of resistance in non-Hodgkins lymphoma (NHL). Verapamil, a calcium channel blocker, is proven in vitro to overcome the MDR caused by Pgp. We performed a phase II trial of verapamil in patients with NHL refractory to EPOCH regimen (etoposide, prednisolone, vincristine, cyclophosphamide, and doxorubicin) to overcome the MDR caused by Pgp.
MATERIALS AND METHODS
Verapamil was administered via intravenous route from 1 hour before to 12 hour after the 96-hour infusion of etoposide, doxorubicin, and vincristine which were known to be substrates of Pgp in EPOCH regimen. The dose of verapamil was 0.15 mg/Kg in bolus and 0.2 mg/Kg/hr in infusion at the beginning and escalated by 0.05 mg/Kg/hr every 24 hours if there was no dose-limiting toxicities such as 2nd or 3rd degree AV block, hypotension, or congestive heart failure. Plasma verapamil concentrations were measured every 24 hour by gas chromatography. Mdrl expression level in tumor tissues was measured by RT-PCR.
RESULTS
From Feb. to Nov. 1994, 14 patients were treated with this protocoL However, poor tolerability and no response in these patients led to early closure of the study at this 1st stage of patient accrual according to Gehans method. Among 14 patients, 12 experienced 2nd or 3rd degree AV block and/or hypotension and required temporary cessation of infusion and reduction of verapamil dose. However, there was no congestive heart failure or treatment-related death. The peak concentrations of verapamil were 0.29-1.94 pM (mean 0.93 pM) and mean concentrations during the 4-day infusion were 0.22-1.21 pM (mean 0.6 pM). Mdrl expression levels measured in 6 patients were 0.99-14.43 U (median 4.39).
CONCLUSION
These results suggest that verapamil in this dose and schedule was neither tolerable nor effective for the reversal of drug resistance in NHL patients.