The PI3K-δ Inhibitor TGR-1202 In Combination With Brentuximab Vedotin (SGN-35) Synergistically Induces G2/M Phase Arrest and Cell Death Via Inhibition Of Tubulin Polymerization In Hodgkin Lymphoma Cell Lines

• Published in: Blood 2013-11, Vol.122 (21), p.1835-1835
• Main Authors: Locatelli, Silvia L, Tartari, Silvia, Rubino, Luca, Brusamolino, Ercole, Castagna, Luca, Sportelli, Peter, Santoro, Armando, Carlo-Stella, Carmelo
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V122.21.1835.1835

The phosphatidylinositol 3-kinase (PI3K) pathway is consistently activated in relapsed/refractory Hodgkin lymphoma (HL), suggesting that TGR-1202, a novel inhibitor of the delta isoform of PI3K (PI3K-δ), in clinical development for patients with hematologic malignancies, might represent an attractive therapeutic option. The anti-CD30 monoclonal antibody Brentuximab Vedotin (BV) conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE) has recently been reported to induce an overall response rate of 75% in relapsed/refractory HL, but is associated with limited response duration. Combination therapies aimed at enhancing the anti-tumor activity of BV and reducing its side effects may have significant clinical impact in the treatment of relapsed/refractory HL. The present study was aimed at investigating the activity and mechanism(s) of action of the PI3K-δ inhibitor TGR-1202, in combination with BV in non-clinical models of HL. Three HL cell lines, including L-540, KM-H2 and L-428, were used to test the effects of TGR-1202 alone, BV alone, or the combination of TGR-1202 with BV. Cell cycle effects and cell survival were determined by flow cytometry and Western blotting (WB). Additionally, WB was used to assess modulating effects of TGR-1202 on the PI3K/AKT pathway as well as microtubule interacting proteins. Cyclin B1, p21, and α-tubulin were detected by indirect immunofluorescence microscopy. The activity of TGR-1202 and/or BV on microtubule distribution and polymerization were quantified using a three-dimensional volume rendering technique. TGR-1202 and BV used as single agents were able to induce a time- and dose-dependent inhibition of cell proliferation and induction of cell death in all cell lines. Compared to the single agent effects, the combination of TGR-1202 (10 µM) and BV (10 ng/ml) synergistically inhibited the mean (±SEM) growth of L-540, KM-H2, and L-428 cell lines (TGR-1202: 40 ± 4%; BV: 30 ± 2%; TGR-1202/BV: 85 ± 1%). Inhibition of cell proliferation induced by the 2-drug combination was associated with a dramatic G2/M cell cycle arrest. Upon TGR-1202/BV treatment, the mean (±SEM) percentages of cells in G2/M phases were increased by 4-fold (72 ± 3%) as compared to TGR-1202 (18 ± 1%) or BV (18 ± 1%) alone. This finding was paralleled by a 3-fold reduction of cells in S phase (TGR-1202: 25 ± 1%; BV: 23 ± 1%; TGR-1202/BV: 9 ± 1%, mean ± SEM) and a marked Cyclin B1 and p21 overexpression. In comparison to each drug as a singl