Summary: Bosanquet and colleagues report that (1) fludarabine resistance in the DiSC assay correlates with patient survival in CLL; (2) apoptosis-related Bax and Bcl-2 expression do not correlate with patient survival; (3) reduced Bax expression correlates with resistance to alkylators, doxorubicin, and vincristine, but not with resistance to fludarabine or glucocorticoids; (4) Bcl-2 expression does not correlate with resistance to any drug. They conclude that apoptosis-activation pathways are different in the case of fludarabine and glucocorticoids than in the cases alkylators, doxorubicin, and vincristine.

Leukemia 2002 Jun;16(6):1035-44

Bax expression correlates with cellular drug sensitivity to doxorubicin, cyclophosphamide and chlorambucil but not fludarabine, cladribine or corticosteroids in B cell chronic lymphocytic leukemia.

Bosanquet AG, Sturm I, Wieder T, Essmann F, Bosanquet MI, Head DJ, Dorken B, Daniel PT.
Bath Cancer Research, Wolfson Centre, Royal United Hospital, Bath, UK.

In B-CLL, non-proliferating B cells accumulate due to defective apoptosis. Cytotoxic therapies trigger apoptosis and deregulation of apoptotic pathways contributes to chemoresistance. Loss of the apoptosis-promoting Bax has been implicated in resistance to cytotoxic therapy. We therefore evaluated ex vivo drug sensitivity of CLL, producing chemoresponse data which are prognostic indicators for B-CLL, in particular in the case of purine nucleoside analogs. To analyze the underlying mechanisms of drug resistance, we compared endogenous Bax and Bcl-2 expression to ex vivo response to eight drugs, and to survival in 39 B-CLL patients. We found that reduced Bax levels correlated well with ex vivo resistance to traditional B-CLL therapies - anthracyclines, alkylating agents and vincristine (all P < 0.04). Surprisingly, no such relationship was observed for the purine nucleoside analogs or corticosteroids (all P > 0.5). Mutational analysis of p53 could not explain the loss of Bax protein expression. Levels of Bcl-2 were not associated with sensitivity to any drug. In contrast to the ex vivo data, neither Bax or Bcl-2 expression nor doxorubicin sensitivity were associated with increased survival whereas sensitivity to fludarabine correlated with better overall survival (P = 0.031). These findings suggest that the resistance to purine nucleoside analogs and corticosteroids in B-CLL is due to inactivation of pathways different from those activated by anthracyclines, vinca alkaloids and alkylating agents and may be the molecular rationale for the efficacy of purine analogs in this disease.