title: Clinical and pharmacologic study of multidrug resistance reversal with vinblastine and bepridil.
abstract: OBJECTIVE
  To achieve an adequate plasma concentration of bepridil, a calcium channel blocker, which reverts multidrug resistance (MDR) in vitro, when administered in combination with vinblastine in patients with advanced colorectal cancer, a tumor characterized by high MDR1 gene expression. To study the pharmacokinetics of both drugs, tolerability and antitumor activity in relation to the MDR1 expression in tumor tissue.
  
  
  METHODS
  Sixteen colorectal cancer patients entered the study. Bepridil was administered by central venous catheter as 5-mg/kg bolus over 30 minutes, followed by 12 mg/kg for 12 hours and 5 mg/kg for 24 hours. Vinblastine 5 mg/m2 was administered as an intravenous (i.v.) bolus 24.5 hours after the start of bepridil. MDR1/P-glycoprotein (Pgp) expression was assessed in 14 tumor samples by immunohistochemistry and RNase protection assay.
  
  
  RESULTS
  The bepridil plasma level was greater than 2 mumol/L at the time of vinblastine administration in all patients investigated. At the dose used in the study, bepridil produced a QTc-prolongation more than 50 ms, which prevented further dose escalation. However, cardiac toxicity was asymptomatic in all treated patients, and other side effects were mild. MDR1/Pgp expression was positive in nine of 14 cases. Of fifteen patients assessable for response, one complete remission of 8 months' duration and 14 progressions were observed. The responding patient attained complete remission again when re-treated on progression with vinblastine alone.
  
  
  CONCLUSIONS
  Bepridil plasma concentrations needed in vitro to modulate MDR could be achieved in this study with tolerable toxicity; however, despite most tumors being MDR1/Pgp-positive, no response was obtained that could be attributed to the drug combination. Mechanisms of drug resistance other than MDR are probably implicated in drug resistance of colorectal cancer.
authors.affiliation: Department of Medical Oncology, Free University Hospital, Amsterdam, The Netherlands.
authors.forename: S C
authors.initials: SC
authors.lastname: Linn
authors.forename: C K
authors.initials: CK
authors.lastname: van Kalken
authors.forename: O
authors.initials: O
authors.lastname: van Tellingen
authors.forename: P
authors.initials: P
authors.lastname: van der Valk
authors.forename: C J
authors.initials: CJ
authors.lastname: van Groeningen
authors.forename: C M
authors.initials: CM
authors.lastname: Kuiper
authors.forename: H M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: G
authors.initials: G
authors.lastname: Giaccone
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000328:Adult; D000368:Aged; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use*; D015764:Bepridil / Q000008:administration & dosage / Q000009:adverse effects; D002352:Carrier Proteins / Q000187:drug effects*; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D004351:Drug Resistance; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000187:drug effects*; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000187:drug effects*; D016896:Treatment Outcome; D014747:Vinblastine / Q000008:administration & dosage / Q000009:adverse effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D014747:Vinblastine; D015764:Bepridil