xk-469 and Neutropenia

To investigate the safety and pharmacokinetics of R(+)XK469, a quinoxaline analogue, in patients with advanced refractory solid tumours. Preclinical studies suggested that efficacy was independent of schedule but that toxicity was decreased by dividing the dose.. R(+)XK469 was initially administered as a 30 min intravenous infusion on days 1-5 of a 21-d cycle. Based on the demonstration of a long half-life, the dosing schedule was subsequently amended to infusion on days 1, 3 and 5 of a 21-d cycle. An alternate single-dose schedule of once every 21 d was also explored. Blood samples were collected for pharmacokinetic studies.. Dose-limiting toxicity (DLT) was neutropaenia. There was significant interindividual variability in clearance as evidenced by a coefficient of variation of 46%. A flat-dosing scheme (not based on body surface area) was justified by the absence of correlation between clearance and body surface area. A partial response was observed in a patient with nasopharyngeal carcinoma.. The recommended phase II doses are 850-1100 mg/d on days 1, 3 and 5 of a 21-d cycle and 2500 mg on day 1 of a 21-d cycle. The observed interpatient pharmacokinetic variability should prompt investigation into the presence of genetic polymorphism in relevant metabolizing enzymes.

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Drug Administration Schedule; Female; Humans; Infusions, Intravenous; Male; Maximum Tolerated Dose; Middle Aged; Neoplasms; Neutropenia; Quinoxalines; Treatment Outcome

XK469, a member of the quinoxaline family of antitumor agents, is believed to be unique in its ability to selectively target topoisomerase IIbeta. Based on encouraging pre-clinical data, a phase I trial was conducted to determine the dose limiting toxicity (DLT) and the maximum tolerated dose (MTD).. A 2B accelerated titration schema was employed. XK469 was administered as a 5 or 20 min IV infusion on days 1-5 every 21 days. The starting dose was 9 mg/m(2). Pharmacokinetics (PK) were conducted in cycles 1-3.. 22 patients (21 evaluable, mean age: 56 years, median performance status: 1) were enrolled. At dose level 11 (260 mg/m(2)/daily X 5), 1/6 patients experienced a DLT of grade 4 neutropenia. At 346 mg/m(2)/daily X 5, 2/2 patients experienced DLT's with one episode of febrile neutropenia and one grade 3 infection. The MTD was identified as 260 mg/m(2)/day. XK469 peak plasma levels and systemic exposure were proportional to dose indicating linear pharmacokinetics. However, secondary peaks in the PK profiles and a rapid decline in drug level from 23 to 24 h occurred in some patients. Drug infusion in the afternoon followed by dense sampling of levels during the elimination phase supported the hypothesis that the drug was being sequestered. No anti-tumor activity was identified.. Traditional PK sampling designs were inadequate to describe XK469 disposition. XK469 and related structures work through a unique mechanism of action. A further understanding of the specific mechanism of these compounds might uncover a unique avenue for future drug development.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Combined Modality Therapy; DNA Topoisomerases, Type II; DNA-Binding Proteins; Dose-Response Relationship, Drug; Enzyme Inhibitors; Female; Humans; Injections, Intravenous; Male; Middle Aged; Neutropenia; Protein Binding; Quinoxalines; Topoisomerase II Inhibitors; Treatment Outcome