IN-VITRO SENSITIVITY OF CHRONIC LYMPHOCYTIC-LEUKEMIA B-CELLS TO FLUDARABINE, 2-CHLORODEOXYADENOSINE AND CHLORAMBUCIL - CORRELATION WITH CLINICOHEMATOLOGICAL AND IMMUNOPHENOTYPIC FEATURES

Background. Chlorambucil (CLB), 2-chlorodeoxyadenosine (2-CDA) and flu darabine (FAMP) are among the most widely used drugs in chronic lympho cytic leukemia (CLL). Therefore we evaluated in vitro sensitivity to t hese drugs and cross-resistance of purine analogs. In addition, we cor related the in vitro data with the main clinico-hematological variable s and surface markers. Patients and Methods. Eighty CLL samples obtain ed from 63 untreated and 17 treated CLL patients were tested in vitro with the MTT assay. Lethal dose (LD)50 values were calculated to deter mine sensitivity to CLB, 2-CDA and FAMP. Results. Samples were cluster ed either for a one-log increase of LD50 values or for LD50 threshold values of 3 mu M for FAMP, 0.3 mu M for 2-CDA and 7 mu M for CLB, whic h correspond to the therapeutically achievable plasmatic levels of the se drugs. A higher number of samples sensitive to 2-CDA were identifie d by the first approach; with the second method the relative order of sensitivity was FAMP>2-CDA>CLB. Concerning 2-CDA and FAMP cross-resist ance, out of 61 samples resistant to 2-CDA, 29.5% were sensitive to FA MP. Conversely, 13.9% out of 43 samples resistant to FAMP were: sensit ive to 2-CDA. No correlation was found between the main clinico-hemato logical features and the LD50 values of each drug either considering t he whole series or only the untreated cases. In vitro drug sensitivity was also evaluated during: the steady-state of the disease and at dis ease progression in six untreated cases. We observed a mean increase i n the LD50 values of about 13, 38 and 22 times for CLB, FAMP and 2-CDA , respectively. Among the treated cases, the LD50 values of both purin e analogs and CLB correlated with bone marrow histology. CLL cells exp ressing CD14, CD11c, CD11b, and FMC7 were more resistant in vitro to p urine analogs but not to CLB.Conclusions. This study suggests that i) the purine analogs exert a greater cytotoxic effect on CLL cells; ii) 2-CDA and FAMP are not cross-resistant in vitro in a percentage of CLL samples, iii) a possible change in LD50 values may be related to modi fication of the disease status, and iv) the expression of certain surf ace markers, which are CLL-unrestricted, identifies samples with highe r in vitro resistance to purine analogs.