BCL-2 PROTEIN EXPRESSION AND P53 GENE MUTATION IN CHRONIC LYMPHOCYTIC-LEUKEMIA - CORRELATION WITH IN-VITRO SENSITIVITY TO CHLORAMBUCIL AND PURINE ANALOGS

Background and Objective. Bcl-2 oncogenic protein expression plays a m ajor role in blocking the apoptotic mechanism. p53 gene mutations have also been suggested to account for the chlorambucil resistance in CLL . Thus we studied the relationship between bcl-2 protein expression, p 53 gene mutations and in vitro drug sensitivity in CLL. Methods. Fifty -three samples from untreated CLL patients in early disease stages wer e tested in vitro for chemosensitivity to chlorambucil (CLB), fludarab ine (FAMP) and 2-chlorodeoxyadenosine (2-CDA) using the MTT assay. Int racellular bcl-2 protein expression was evaluated by flow cytometry an alysis. p53 gene mutations were detected by using polymerase chain rea ction (PCR)-single strand conformation polymorphism (SSCP) analysis. R esults. The median LD50 values were 1.55 mu M, 4.41 mu M and 58.2 mu M for 2-CDA, FAMP and CLB, respectively. About 23%, 41% and 11% of samp les were defined as being sensitive to FAMP, 2-CDA and CLB, respective ly, when samples were clustered for LD50 threshold values correspondin g to the plasmatic levels of the drug. No statistically significant di fference in bcl-2 protein expression was noted between sensitive and r esistant samples for each drug. A p53 gene mutation was detected in 4 of the 30 cases studied and all of them were among samples resistant t o CLB. Interpretation and Conclusions. Bcl-2 expression is not an indi cator of in vitro response to drugs in CLL; similarly, although the fo ur cases showing a p53 gene mutation were associated with CLB resistan ce, drug resistant samples were also observed in the group of patients showing wild type p53, suggesting multiple mechanisms of drug resista nce in CLL. (C) 1997, Ferrata Storti Foundation.