PHASE-I AND PHARMACODYNAMIC STUDY OF THE TOPOISOMERASE I-INHIBITOR TOPOTECAN IN PATIENTS WITH REFRACTORY ACUTE-LEUKEMIA

Purpose: To determine the feasibility of escalating the hydrophilic to poisomerase I (topo I)-inhibitor topotecan (TPT) above myelosuppressiv e doses in adults with refractory or relapsed acute leukemias and to a ssess pharmacodynamic determinants of TPT action. Patients and Methods : Seventeen patients received 33 courses of TPT as a 5-day infusion at doses ranging from 0.70 to 2.7 mg/m(2)/d. Pharmacologic studies were performed to determine the TPT concentrations at steady-state (C-ss) a nd to examine parameters in the patients' leukemic blasts ex vivo that may be related to TPT sensitivity, eg, tope I content, p-glycoprotein (Pgp) expression, and the inhibitory effects of relevant TPT concentr ations on the growth of blast colonies in clonogenic assays relative t o the range of TPT C-ss values achieved. Results: Severe mucositis of the oropharynx and perianal tissues was intolerable at TPT doses great er than 2.1 mg/m(2)/d, the recommended dose for phase If studies in le ukemia. One complete response (CR) in a patient with chronic myelogeno us leukemia in blast crisis (CMLB) and one partial response (PR) in a patient with acute myelogenous leukemia (AML) were noted. Significant reductions in circulating blast-cell numbers occurred in all courses, and complete leukemia clearance from the peripheral blood, albeit tran sient, wets noted in 11 courses. TPT C-ss values ranged from 4.8 to 72 .5 nmol/L. Colony-forming assays showed that the TPT LD(90) (dose that inhibits the growth of leukemia blast colonies by 90%) values for bla sts varied from 6 to 22 nmol/L, a range that overlapped with TPT C-ss values. In view of these variations in TPT sensitivity, several aspect s of topo I-mediated drug action were also studied. In 10 of 11 sample s, the multidrug resistance (Mdr) modulator quinidine altered nuclear daunorubicin (DNR) accumulation and whole-cell TPT accumulation by les s than 15%, which suggests that Pgp-mediated effects on drug efflux ar e insufficient to explain the fourfold range of TPT sensitivities in t he colony -forming assays. Immunohistochemistry showed that topo I woo expressed in all of the blasts from individual patients without detec table cell-to-cell heterogeneity in each marrow. Western blots indicat ed that topo I content varied over a 10-fold range. Although the sampl e size was small, topo I content appeared to be higher in acute lympho blastic leukemia (ALL), intermediate in AML, and lower in CML-B. Topo I content did not appear to be related to the proliferative status of the blasts. Conclusion: These results indicate that substantial dose e scalation of TPT above myelosuppressive doses reached in solid-tumor p atients is feasible in patients with refractory leukemia, that biologi cally relevant TPT C-ss values are achievable, and that further develo pmental trials are warranted. (C) 1994 by American Society of Clinical Oncology.