Anti-Myeloma Effects of Panobinostat in Combination with Duvelisib

Introduction: Panobinostat (Secura Bio) is a non-selective histone deacetylase inhibitor (HDACi) that has shown anti-tumor activity in preclinical studies in both solid and hematological malignancies. Duvelisib (Secura Bio) is an FDA-approved oral drug and a potent small molecule inhibitor of the delta (δ) and gamma (γ) isoforms of phosphoinositide-3 kinase (PI3K) with potential immunomodulating and antineoplastic activities. There is no data regarding in combination of an HDACi with duvelisib for multiple myeloma (MM) treatment. We evaluated the anti-myeloma effects of the panobinostat in combination with duvelisib. Methods: The human MM cell lines U266, RPMI 8226 and MM1s were obtained from ATCC. Primary MM tumor cells were isolated from MM patients' bone marrow (BM) aspirates and mononuclear cells (MCs) were isolated. The cells were seeded at 10 5 cells/well in 96-well plates and incubated for 24 h in the presence of vehicle, panobinostat or duvelisib alone, or the two drugs together for 48 h. Cell viability was quantified using the MTS cell proliferation assay. For the apoptosis assay, U266, RPMI 8226, MM1s, or primary MM tumor cells were cultured at 1 x 10 6 cells per well for 48 hours at 37°C in 5% CO2 with or without the addition of panobinostat or duvelisib. Next, the cells were washed twice with PBS, re-suspended in binding buffer, and stained with FITC-conjugated annexin V and fluorescent dye propidium iodide (PrI) following annexin V assay standard protocol (BioVision, USA). For each drug treatment, 1 x 10 5 gated events were recorded. Results and Discussion: The MTS cell proliferation assay showed that panobinostat alone inhibited cell proliferation of the MM cell lines U266 and MM1s but not RPMI8226. Panobinostat alone induced concentration-dependent inhibition of BMMCs. Panobinostat (20nM) in combination with duvelisib markedly increased inhibition of primary MM cell proliferation. Panobinostat alone induced MM cell apoptosis in all three MM cell lines. Panobinostat in combination with duvelisib enhanced MM cell apoptosis in MM1s but not U266 and RPMI 8226 cells. We further examined apoptosis of primary MM cell treated with panobinostat alone and in combination with duvelisib. The results showed panobinostat alone induced primary MM cell apoptosis and in combination with duvelisib markedly increased the induction of apoptosis. This study illustrates that the combination of panobinostat and duvelisib shows potent anti-MM effects in vitro and w