Heat Shock Protein 90 (HSP90) Inhibition by the Small Molecule 17-AAG Induces Cell Cycle Arrest and Apoptosis in Anaplastic Large Cell Lymphoma (ALCL) Irrespective of ALK Expression: Role of Akt, ERK and ALK Kinases in the Molecular Mechanisms of 17-AAG Anti-Tumor Activity.

Anaplastic Large Cell Lymphoma (ALCL) is a CD30 positive T-cell/null non-Hodgkin lymphoma which in many cases features a chromosomal translocation between tyrosine kinase nucleophosmin and anaplastic lymphoma kinase (NPM-ALK). Several groups demonstrated that patients with ALCL that do not express ALK have poor prognosis when treated with conventional chemotherapy, suggesting that these patients may require novel therapeutic approaches. Although the heat shock protein 90 (HSP90) has been shown to chaperone NPM-ALK, the effect of HSP90 inhibition on ALCL survival is not known. Furthermore, the effect of HSP90 inhibition on ALCL that do not express ALK is unknown. In the present study, the expression of HSP90 was evaluated in both ALK+ and ALK- primary and cultured ALCL cells. All of the ALK+ ALCL cases (21/21) and 58% (7/12) of the ALK- ALCL cases overexpressed HSP90, as determined by immunohistochemistry. In addition, 3 cell lines, two ALK+ (Karpas299 and SUDHL1) and one ALK- (Mac2A) were evaluated and were found to overexpress HSP90, as determined by western blot. The small molecule inhibitor 17-AAG induced antiproliferative effect in both ALK+ and ALK- ALCL derived cell lines. Inhibition of HSP90 in ALCL induces apoptosis, which was in part mediated by activation of the caspase pathway. Furthermore, 17-AAG depleted ALK kinase in ALK+ ALCL cells, in addition to depletion of the pro-survival Finally, AKT kinase. 17-AAG also decreased ERK phosphorylation, without altering total ERK levels in both ALK+ and ALK− ALCL cells. Moreover, 17-AAG reduced cyclin D1 and MDM2 levels which was associated with cell cycle arrest at G0/G1 phase. Finally, 17-AAG demonstared synergy with doxorubicin chemotherapy in the ALCL cell lines. Taken together, our data provide an excellent proof-of-principle for the potential therapeutic value of HSP90 inhibitors in ALCL, especially for ALK-negative subtype. Furthermore, our data suggest that 17-AAG may enahnce the effect of conventional chemotherapy in ALCL.