Abstract 1291: APR-246 enhances tumor immunogenicity even in the absence of p53
Authors: Venkatesh Divya , Michels Judith , Liu Cailian , Budhu Sadna , George Mariam M. , Abrahmsen Lars , Zappasodi Roberta , Wolchok Jedd D. , Merghoub Taha 
Published: June 2022

Abstract
Despite the significant success of immunotherapy, more than 40% of cancer patients remain unresponsive or exhibit an insufficient response. Well-designed combinations of targeted therapy and immunotherapy have the potential to increase effectiveness of cancer treatment and overcome the absence of response to either therapy alone. Since targeted therapies that enhance tumor antigenicity can enhance the effectiveness of immune based therapies, we have built a compendium of in vitro and in vivo assays to evaluate the effect of multiple immunogenic drugs. In these assays, we use the preclinical melanoma cell line B16-F10 model as it is highly metastatic and responds poorly to immunotherapy alone. The tumor suppressor p53 is a key target both in terms of targeted therapy owing to its role in halting tumor progression as well as in combination with immunotherapy, since p53 has varied roles in immune modulation. APR-246 can activate p53 and elicit some p53-independent effects in various tumor models predominantly through the induction of endoplasmic reticulum stress and oxidative stress. Since these cellular stressors (including p53) have been shown to be capable of rendering tumor cells immunogenic, we hypothesized that APR-246 may also increase the antigenicity of tumor cells. Indeed, we observed that treatment of B16 cells with APR-246 increases their MHC expression. Additionally, in our in vitro co-culture assays, cells treated with APR-246 were able to activate antigen-specific cytotoxic T cells either directly or via CD11c+ cells. We also observed that mice immunized with APR-246-treated B16 cells and then implanted with healthy untreated melanoma cells, were able to confer prolonged tumor free survival. Taken together, we believe that APR-246 has the potential to make for a strong combination with immunomodulatory therapies owing to its immunogenic potential. Based on these observations, we rationally designed a combination treatment regimen that would further enhance the immunogenic effects elicited by APR-246 on tumor cells. The triple combination of APR-246 with the TLR4 agonist, Monophosphoryl lipid A (MPL) and the anti-CD40 antibody significantly reduced the growth of B16 tumor in C57BL/6J mice. Strikingly, using CRISPR generated B16 p53 KO cells, we have discovered that these effects of APR-246 exist even in the absence of p53, albeit slightly reduced. Therefore, our results indicate that combination of APR-246 with immunomodulatory agents may be effective in treating cancers irrespective of their genetic status of p53. Our finding suggests that drugs with immunogenic potential, in addition to their original therapeutic indication, such as APR-246 are good candidates for the improvement of various clinically relevant immune modulatory therapies. Note: D.V. and J.M. contributed equally to this work.
Citation Format: Divya Venkatesh, Judith Michels, Cailian Liu, Sadna Budhu, Mariam M. George, Lars Abrahmsen, Roberta Zappasodi, Jedd D. Wolchok, Taha Merghoub. APR-246 enhances tumor immunogenicity even in the absence of p53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1291.