P53, MDM-2, BAX and BCL-2 and Drug Resistance in Chronic Lymphocytic Leukemia

Abstract

Most antitumor agents exert their cytotoxic effect through the induction of apoptosis, and this process may be mediated through an elevation in p53 protein, with a subsequent increase in bax and decrease in bcl-2. p53 also increases mdm-2 expression and mdm-2 may then bind and inactivate p53. Cells from 31 patients with chronic lymphocytic leukemia (CLL) were treated in vitro with 2-chlorodeoxyadenosine (CdA), arabinosyl-2-fluoroadenine (F-ara-A), or chlorambucil (CLB) and drug sensitivity measured using the MTT assay. The protein levels of bax and bcl-2 were measured in CLL cells from 25 patients, and were found to be higher in leukemic cells than in normal B cells. The bcl-2 levels varied three-fold, the bax levels fifteen-fold, and the bax:bcl-2 ratios ranged from 0.44 to 2.91. The expression of mdm-2 mRNA was measured in CLL cells from 28 patients and was found to vary twenty-fold. However, no correlation was observed between drug sensitivity to CdA, F-ara-A, or CLB and the cellular levels of mdm-2 mRNA, or the protein levels of bax or bcl-2, or the bax:bcl-2 ratio. Treatment of CLL cells having wild type p53 with CdA, F-ara-A or CLB produced an increase in p53 protein and mdm-2 mRNA. This was not observed in cells having a p53 mutation, and these cells were highly resistant to both CLB and the nucleoside analogs. In contrast to the nucleoside analogs and CLB, dexamethasone and vincristine had no effect on mdm-2 mRNA levels. Treatment of CLL cells containing a wild type p53 gene with CdA, F-ara-A, or CLB, did not produce any consistent changes in bax or bcl-2. Thus, CdA, F-ara-A and CLB appear to act in CLL cells through a p53-dependent pathway, whereas this does not occur with dexamethasone or vincristine. The cellular levels of mdm-2, bcl-2, bax or the bax:bcl-2 ratios are not predictive indicators of clinical sensitivity in CLL, but an increase in mdm-2 levels after drug treatment is indicative of p53 function in these cells.

Chemosensitivity of B cell chronic lymphocytic leukemia and correlated expression of proteins regulating apoptosis, cell cycle and DNA repair

“…42 Furthermore, sensitivity to FLUD is p53-dependent whereas sensitivity to DEX is not. 43 This contrasts to observations of Silber et al 40 who reported a correlated in vitro sensitivity to FLUD and to CBU.…”

“…As of yet, determining the in vitro chemosensitivity of B-CLL cells has not been useful to predict the clinical course of the disease or the response to cytostatic treatment. 7,8,43,47 Varying expression of cofactors modulating cell death of B-CLL cells in vitro may produce functionally heterogeneous cell preparations. For example, interferon-␥ and -␣, interleukin-2 and basic fibroblast growth factor have been described to modulate in vitro apoptosis of B-CLL cells.…”

High expression of Bfl‐1 contributes to the apoptosis resistant phenotype in B‐cell chronic lymphocytic leukemia

“…12,32,33 However, not all studies have identified an association between Bcl-2 or Bax expression and chemoresistance and/or outcome in B-CLL, implying that also other factors play a role. 34,35 Here we have found higher expression of mcl-1 and bcl-2 in rB-CLL as compared with sB-CLL. However our present results emphasize the role of another anti-apoptotic bcl-2 family member, bfl-1, for the development of the apoptosis resistant phenotype as the expression of this regulatory protein strongly discriminated between the 2 groups in our study.…”

Nucleoside analogues: mechanisms of drug resistance and reversal strategies

“…[169][170][171] These events lead to induction of apoptosis. 172,173 Various investigators have shown that B-CLL and AML patients with mutations in the p53 gene displayed resistance to fludarabine, 2-CdA or ara-C and/or poorer response and shorter remission and/or overall survival [174][175][176][177] (Table 5). Conversely, other authors failed to find any relationship between p53 abnormalities and resistance to NA in these diseases.…”