Abstract 2404: MDM2 inhibitor Idasanutlin potentiate therapeutic agents in Diffuse Large B-Cell Lymphoma by targeting MDM2 and XIAP
Authors: Gu Juan J. , Thompson Samuel , Mavis Cory , Torka Pallawi , Hernandez-Ilizaliturri Francisco 
Published: September 2020

Abstract
Purpose: In patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL), resistance to rituximab confers chemotherapy-resistance and poor response to salvage regimens. MDM2 is an E3 ligase which regulates the degradation of multiple cellular protein targets, but is known best as the major negative regulator of the tumor suppressor, p53. Recently, we demonstrated that MX69, a MDM2 inhibitor, re-sensitized resistant DLBCL cell lines to chemotherapy agents or small inhibitors (i.e. Venetoclax) in vitro by blocking the MDM2 protein-XIAP RNA interaction, led to both MDM2 and XIAP degradation, thus establishing the feasibility of this approach for overcoming rituximab and chemotherapy resistance in DLBCL. We now report the activity of Idasanutlin, an investigational Nutlin-family MDM2 antagonist, in pre-clinical models of R-chemo resistant B-cell lymphoma.
Methods: We used a panel of rituximab sensitive and R-chemo resistant B-cell lymphoma cell lines representing activated B-cell-like (ABC) DLBCL (TMD8, U2932); germinal center B-cell like (GCB) DLBCL (RL, RL 4RH, OCILy2); double hit DLBCL (DHL4, DHL6, DOHH2, VAL, ROS50), and Burkitt's lymphoma (Raji and Raji 4RH). Cells were exposed to escalating doses of Idasanutlin as single agent and in combination with various chemotherapeutic agents and small molecule inhibitors for 24, 48 and 72 hrs. Differences in cell viability were evaluated by PrestoBlue. IC50 was calculated by GraphPad and Coefficient of synergy was calculated using CalcuSyn. Low mitochondrial potential was detected by staining cell with DiOC6 followed by flow cytometric analysis. Western blot was used to detect changes in MDM2, XIAP and PUMA expression.
Results: In vitro exposure to Idasanutlin demonstrated dose- and time-dependent cell death in DLBCL cell lines, IC50 ranged from 0.7uM to 63.07uM at 48h. Idasanutlin at the dose of 1uM was able to disrupt mitochondria and lowered the mitochondrial membrane potential in both ABC and GCB cell lines at 48 h. Idasanutlin reduced the expression of MDM2 in TMD8, U2932, VAL, OCILy2 DHL4 and ROS50 cell lines. XIAP expression was reduced in VAL and DHL4. PUMA, the downstream product of p53 activation, was increased after idasanutlin exposure in all cell lines. Idasanutlin demonstrated significant synergy with chemotherapeutic reagents (etoposide and vincristine), proteasome inhibitors (carfilzomib and ixazomib), Bcl-2 inhibitor venetoclax and Bruton tyrosine kinase inhibitor ibrutinib.
Conclusion: Idasanutlin showed promising cell-of-origin agnostic anti-tumor activity as a single agent and in combination with several small molecule inhibitors in pre-clinical models of DLBCL. It decreased MDM2 and XIAP protein level and induced PUMA expression. Its unique mechanism of action through p53 modulation makes it an attractive partner for use in a variety of clinical settings in B-cell lymphomas.
Citation Format: Juan J. Gu, Samuel Thompson, Cory Mavis, Pallawi Torka, Francisco Hernandez-Ilizaliturri. MDM2 inhibitor Idasanutlin potentiate therapeutic agents in Diffuse Large B-Cell Lymphoma by targeting MDM2 and XIAP [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2404.