Abstract 4711: 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
Authors: Locatelli Silvia L. , Tartari Silvia , Castagna Luca , Rubino Luca , Viswanadha Srikant , Sportelli Peter , Santoro Armando , Carlo-Stella Carmelo 
Published: May 2015

Introduction: The phosphatidylinositol 3-kinase (PI3K) pathway is consistently activated in relapsed/refractory Hodgkin lymphoma (HL), suggesting that TGR-1202, a novel/selective inhibitor of the delta isoform of PI3K (PI3K-δ), might represent an attractive therapeutic option. The anti-CD30 monoclonal antibody, Brentuximab Vedotin (BV), 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 may have significant clinical impact in the treatment of relapsed/refractory HL. Our study was aimed at investigating the activity and mechanism(s) of action of TGR-1202 in combination with BV in HL cell lines.

Methods and Results: The combination of TGR-1202 (10 μM) and BV (10 ng/ml) synergistically inhibited the mean (±SEM) growth of HL cells (TGR-1202: -40 ± 4%; BV: -30 ± 2%; TGR-1202/BV: -85 ± 1%). This finding was associated with a 4-fold increase of G2/M phase (TGR-1202: 18 ± 1%; BV: 18 ± 1%; TGR-1202/BV: 72 ± 3%), a 3-fold reduction of cells in S phase (TGR-1202: 25 ± 1%; BV: 23 ± 1%; TGR-1202/BV: 9 ± 1%), and a marked Cyclin B1 and p21 overexpression. Upon TGR-1202/BV treatment, cell death values were increased 3-fold over single agents (TGR-1202: 27 ± 2%; BV: 27 ± 2%; TGR-1202/BV: 75 ± 2%). Analysis of caspase-3 and PARP cleavage and blocking experiments with the pan-caspase inhibitor Z-VAD-FMK revealed a caspase-dependent cell death mechanism. In addition, the anti-lymphoma effects of TGR-1202 were associated with a marked time-dependent inhibition of PI3K/Akt pathway and dephosphorylation of GSK-3β, Aurora kinases, and stathmin, suggesting that modulation of molecules associated with microtubule polymerization are critically involved in TGR-1202/BV-triggered cell death. To assess potential effects on microtubule dynamics, α-tubulin was detected by indirect immunofluorescence microscopy in HL cells treated with TGR-1202 and/or BV. Compared with controls, TGR-1202 and BV treatment alone led to an average 10% loss of microtubules while the combined TGR-1202/BV treatment resulted in a potent synergistic microtubule disruption, as shown by values of α-tubulin inhibition of 40% (P ≤.0001) and the presence of irregular microtubule fragments throughout the cytosol. Additionally, TGR-1202/BV was found to interfere with the mitotic spindle integrity which may suggest that the G2/M arrest and cytotoxicity of the combined TGR-1202/BV treatment primarily arises from the inhibition of tubulin polymerization.

Conclusions: TGR-1202 enhances the anti-tumor activity of BV by increasing drug-induced apoptosis and tubulin disruption in HL cell lines. Our data provide a strong rationale for evaluating TGR-1202 in combination with BV in patients with relapsed/refractory HL.

Citation Format: Silvia L. Locatelli, Silvia Tartari, Luca Castagna, Luca Rubino, Srikant Viswanadha, Peter Sportelli, Armando Santoro, Carmelo Carlo-Stella. 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. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4711. doi:10.1158/1538-7445.AM2014-4711