RESULTS OF A CLINICAL-TRIAL IN HUMANS WITH REFRACTORY CANCER OF THE INTRACELLULAR HISTAMINE ANTAGONIST, N,N-DIETHYL-2-[4-(PHENYLMETHYL)PHENOXY]ETHANAMINE-HCL, IN COMBINATION WITH VARIOUS SINGLE ANTINEOPLASTIC AGENTS

Purpose: We assessed N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine- HCl (DPPE) potentiation of chemotherapy in vitro and performed a pharmacokinetic study and phase I/II trial of DPPE, combined with various single agents, in patients with advanced refractory cancer. Patients and Methods: In vitro chemopotentiation by DPPE was assessed in drug-sensitive and -resistant (multidrug resistant-positive [MDR+]) human tumor cells using a colony survival assay. The effect of DPPE and verapamil on the intracellular concentration of daunorubicin in MDR+ cells was compared. For the clinical study, subjects with progressive malignancy received a weekly infusion of a maximally tolerated dose of DPPE (240 mg/m2) over 80 or 440 minutes, in conjunction with a single chemotherapy drug to which, in most cases, the patient's tumor was previously resistant. Concentrations of DPPE in blood and urine were determined by high-performance liquid chromatography (HPLC). Results: In vitro, micromolar concentrations of DPPE potentiated (fivefold to 10-fold) chemotherapy cytotoxicity to both drug-sensitive and - resistant cells, but did not inhibit the p-glycoprotein pump; in vivo, serum levels of DPPE were 3 to 5 μmol/L at the end of 80 minutes and 1 to 2 μmol/L after 440 minutes of infusion. Of 48 patients monitored for a minimum of four DPPE/chemotherapy treatment cycles, 16 (33%) progressed, 12 (25%) stabilized, 12 (25%) improved, and eight (17%) responded (one complete and seven partial remissions). Four of 11 subjects who did not respond to the 80- minute infusion regimen improved with the 440-minute infusion; one had a partial remission of melanoma. In more than 600 patient-treatments, bone marrow toxicity was negligible (mean absolute neutrophil count [ANC] > 2.0 x 109/L). Acute CNS symptoms associated with DPPE infusions were of relatively short duration (1 to 4 hours); delayed toxicity attributable to DPPE consisted of mild nausea and/or fatigue (1 to 2 days). Conclusion: Although preliminary, the results suggest that more structured trials should be performed to determine whether DPPE may increase the therapeutic index of certain chemotherapy drugs.