Epigenetic modifiers enhance the synergistic cytotoxicity of combined nucleoside analog-DNA alkylating agents in lymphoma cell lines.

Hematopoietic stem cell transplantation is used for treatment of lymphoma. In an attempt to design an efficacious and safe prehematopoietic stem cell transplantation conditioning regimen, we investigated the cytotoxicity of the combination of busulfan (B), melphalan (M), and gemcitabine (G) in lymphoma cell lines in the absence or presence of drugs that induce epigenetic changes. Cells were exposed to drugs individually or in combination and analyzed by the MTT proliferation assay, flow cytometry, and Western blotting. We used ~IC(10) drug concentrations (57 µM B, 1 µM M and 0.02 µM G), which individually did not have major effects on cell proliferation. Their combination resulted in 50% inhibition of proliferation. Reduction to almost half concentration (20 µM B, 0.7 µM M and 0.01 µM G) did not have significant effects, but addition of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (0.6 µM) to this combination resulted in a marked (~65%) growth inhibition. The cytotoxicity of these combinations correlates with the activation of the ataxia telangiectasia mutated-CHK2 pathway, phosphorylation of KRAB-associated protein-1, epigenetic changes such as methylation and acetylation of histone 3, and activation of apoptosis. The relevance of epigenetic changes is further shown by the induction of DNA methyltransferases in tumor cells with low constitutive levels of DNMT3A and DNMT3B. The addition of 5-aza-2'-deoxycytidine to (BMG+suberoylanilide hydroxamic acid) further enhances cell killing. Overall, BMG combinations are synergistically cytotoxic to lymphoma cells. Epigenetic changes induced by suberoylanilide hydroxamic acid and 5-aza-2'-deoxycytidine further enhance the cytotoxicity. This study provides a rationale for an ongoing clinical trial in our institution using (BMG+suberoylanilide hydroxamic acid) as pre-hematopoietic stem cell transplantation conditioning for lymphoma.

Synergistic action of the novel HSP90 inhibitor NVP-AUY922 with histone deacetylase inhibitors, melphalan, or doxorubicin in multiple myeloma.

Heat shock protein 90 (HSP90) is a promising target for tumor therapy. The novel HSP90 inhibitor NVP-AUY922 has preclinical activity in multiple myeloma, however, little is known about effective combination partners to design clinical studies. Multiple myeloma cell lines, OPM-2, RPMI-8226, U-266, LP-1, MM1.S, and primary myeloma cells were exposed to NVP-AUY922 and one of the combination partners histone deacetylase inhibitor NVP-LBH589, suberoylanilide hydroxamic acid (SAHA), melphalan, or doxorubicin, either simultaneously or in sequential patterns. Effects on cell proliferation and apoptosis were determined. Synergistic effects were evaluated using the method of Chou and Talalay. Combined sequential incubation with NVP-AUY922 and SAHA showed that best synergistic effects were achieved with 24 h preincubation with SAHA followed by another 48 h of combination treatment. Combination of NVP-AUY922 with SAHA, NVP-LBH589, melphalan, or doxorubicin resulted in synergistic inhibition of viability, with strong synergy (combination index < 0.3) in the case of melphalan. Importantly, resistance of the RPMI-8226 cell line and relative resistance of some primary myeloma cells against NVP-AUY922 could be overcome by combination treatment. These data show impressive synergistic action of the novel HSP90 inhibitor NVP-AUY922 with melphalan, doxorubicin, NVP-LBH589, and SAHA in multiple myeloma and build the frame work for clinical trials.

Induction therapy in a multiple myeloma mouse model using a combination of AS101 and melphalan, and the activity of AS101 in a tumor microenvironment model.

OBJECTIVE: We previously showed that the organotellurium compound, ammonium trichloro (dioxyethylene-0-0') tellurate (AS101), has antitumoral activity in multiple myeloma (MM) cell lines. Here, we evaluated the antimyeloma activity of AS101 combined with low-dose melphalan, and also examined the activity of AS101 in the myeloma tumor microenvironment. MATERIALS AND METHODS: Isobologram analysis was performed to determine the interactions of AS101 and melphalan as a combination therapy. Growth arrest, apoptosis, and CD81 antigen were detected by flow cytometry. Using the 5T33MM mouse model, we evaluated mouse survival and serum levels of vascular endothelial growth factor (VEGF) and IgG(2b) paraprotein. We established cocultures of MS-5 bone marrow stromal cells and 5T33 MM cells in order to examine AS101 activity in a myeloma microenvironment model. RESULTS: Combined treatment of AS101 with melphalan in vitro resulted in a synergistic inhibitory effect on growth, G(2)/M phase growth arrest, reduced IgG(2b) secretion, apoptotic cell death, and reduced fibronectin-mediated adhesion of MM cells. AS101 reduced VEGF secretion and protein expression in myeloma and cocultured cells, downregulated production of the matrix metalloproteinases (MMPs), MMP-9 and MMP-2, and also inhibited growth of the treated myeloma coculture. Combined treatment using AS101 and low dose of melphalan in vivo resulted in modest survival improvement of myeloma-bearing mice and in reduced IgG(2b) and VEGF serum levels. CONCLUSIONS: AS101 in combination with a subtherapeutic dose of melphalan had increased beneficial effect relative to each agent alone in a mouse MM model. In addition, AS101 might be useful for targeting interactions between myeloma cells and the bone marrow microenvironment.