title: A phase I pharmacokinetic study of the P-glycoprotein inhibitor, ONT-093, in combination with paclitaxel in patients with advanced cancer.
abstract: BACKGROUND
  ONT-093 is an orally bioavailable inhibitor of P-glycoprotein (P-gp). In pre-clinical studies, ONT-093 could inhibit P-gp and reverse multidrug resistance at nM concentrations with no effect on paclitaxel pharmacokinetics. Phase I trials of ONT-093 in normal human volunteers showed no dose-limiting toxicities at serum concentrations associated with biologic activity achieved with doses ranging from 300 to 500 mg.
  
  
  METHODS
  Phase I pharmacokinetic trial of ONT-093 in doses from 300 to 500 mg administered before and after intravenous paclitaxel doses of 150 to 175 mg/m(2) repeated every 21 days. All patients received paclitaxel alone on cycle 1.
  
  
  RESULTS
  18 patients were enrolled onto 4 dose levels. Toxicity of the combination included neutropenia, arthralgia, myalgia, and peripheral neuropathy. Four of 6 patients receiving 500 mg doses of ONT-093 and paclitaxel at 175 mg/m(2) (dose level 4) had higher-grade neutropenia with cycle 2, with 1 patient experiencing febrile neutropenia. Plasma pharmacokinetic parameters of paclitaxel were unchanged between cycle 1 and 2 for dose levels 1 to 3, but at dose level 4, 45-65% increases in paclitaxel AUC were observed in 4 of the 6 patients. Mean C(max) of ONT-093 was 9 microM (range 5-15 microM) which were 3- to 5-fold higher than in single agent studies of ONT-093.
  
  
  CONCLUSIONS
  Doses of ONT-093 achieving serum concentrations associated with biological activity were well tolerated in combination with standard doses of paclitaxel. Toxicities of the combination in this schedule were mainly attributable to paclitaxel and dose-limiting toxicity was limited to febrile neutropenia. There was an apparent pharmacokinetic interaction between paclitaxel and ONT-093, possibly related in part to the excipient, Cremophor, present in the paclitaxel formulation.
authors: BC Cancer Agency, Vancouver, British Columbia, Canada. kchi@bccancer.bc.ca
authors: Kim N
authors: KN
authors: Chi
authors: Stephen K
authors: SK
authors: Chia
authors: Ross
authors: R
authors: Dixon
authors: Michael J
authors: MJ
authors: Newman
authors: Vince J
authors: VJ
authors: Wacher
authors: Branimir
authors: B
authors: Sikic
authors: Karen A
authors: KA
authors: Gelmon
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors; D000328:Adult; D000368:Aged; D000505:Alopecia / Q000139:chemically induced; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D018771:Arthralgia / Q000139:chemically induced; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D005260:Female; D006801:Humans; D007093:Imidazoles / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy*; D009503:Neutropenia / Q000139:chemically induced; D017239:Paclitaxel / Q000008:administration & dosage / Q000493:pharmacokinetics*; D011092:Polyethylene Glycols / Q000008:administration & dosage / Q000009:adverse effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D007093:Imidazoles; C410029:OC 144-093; C022131:cremophor; D011092:Polyethylene Glycols; D017239:Paclitaxel