Antiproliferative and proapoptotic activity of GUT-70 mediated through potent inhibition of Hsp90 in mantle cell lymphoma

Background: Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma with poor prognosis, requiring novel Anticancer strategies.

Methods: Mantle cell lymphoma cell lines with known p53 status were treated with GUT-70, a tricyclic coumarin derived from Calophyllum brasiliense, and the biological and biochemical consequences of GUT-70 were studied.

Results: GUT-70 markedly reduced cell proliferation/viability through G(1) cell cycle arrest and increased Apoptosis, with greater sensitivity in mutant (mt)-p53-expressing MCL cells than in wild-type (wt)-p53-bearing cells. Mechanistically, GUT-70 showed binding affinity to heat-shock protein 90 (HSP90) and ubiquitin-dependent proteasomal degradation of HSP90 client proteins, including cyclin D1, Raf-1, Akt, and mt-p53. Depletion of constitutively overexpressed cyclin D1 by GUT-70 was accompanied by p27 accumulation and decreased Rb phosphorylation. GUT-70 induced mitochondrial Apoptosis with Noxa upregulation and Mcl-1 downregulation in mt-p53 cells, but Mcl-1 accumulation in wt-p53 cells. Noxa and Mcl-1 were coimmunoprecipitated, and activated Bak. Treatment with a combination of GUT-70 and bortezomib or doxorubicin had synergistic antiproliferative effects in MCL cells that were independent of p53 status.

Conclusion: GUT-70 has pronounced antiproliferative effects in MCL with mt-p53, a known negative prognostic factor for MCL, through HSP90 inhibition. These findings suggest that GUT-70 has potential utility for the treatment of MCL.