Institute of Biomedical Sciences

Title

The effect of the mutational signature in response to immuno-epigenetic therapies in melanoma

Document Type

Poster

Abstract Category

Cancer/Oncology

Keywords

melanoma, HDAC6, PD-L1, mutation

Publication Date

Spring 5-1-2019

Abstract

Melanoma is the deadliest type of skin cancer, and it is estimated to affect 96,500 people in the United States in 2019. Current treatments include targeted therapy (i.e., the BRAF inhibitor Vemurafenib), epigenetic modifiers, and immunotherapy, such as immune checkpoint inhibitors (ICI). Most of the preclinical evaluations for the above therapies have been done using mouse melanoma models, including B16 and SM1. Although the molecular mechanisms involved in the pathogenesis of melanoma have been elucidated using the B16 cells, this model is not suitable for the preclinical in vivo testing of combination therapies because its genetic alterations are not well defined and it does not resemble human melanoma histologically. Our group has previously studied the combination of histone deacetylase 6 inhibitors (HDAC6i) and ICI using the SM1, which is an immunogenic, BRAFV600E/V600E mouse model, which resulted in a significant reduction of tumor growth. However, this model ignores the potential contribution of other relevant oncogenic mutations occurring in human melanoma (i.e., PTEN, P53). In this regard, HDAC6 has been reported to deacetylate PTEN and p53. Therefore, in this study, we aim to investigate the role of HDAC6 in these relevant oncogenic pathways. For this purpose, multiple isogenic mouse models were used: SM1, YUMM1.7 (BRAFV600E/wt, Pten-/-, Cdkn2a-/-), YUMM3.3 (BRAFV600E/wt, Cdkn2a-/-), YUMM4.1 (Pten-/-, Cdkn2a-/-), and YUMM5.2 (BRAFV600E/wt, Tp53-/-). In this study, we assessed the cytotoxic properties of the HDAC inhibitors Panobinostat, Mocetinostat, and Nexturastat A, and Vemurafenib 48 hours post-treatment. We observed that YUMM5.2 cells are as sensitive to pan-HDAC inhibition as SM1, while more selective HDACi induce cytotoxicity in a dose-dependent manner. Furthermore, YUMM1.7 is more sensitive to BRAF inhibition than any other model. We also observed different basal expression of oncogenic proteins like c-jun and STAT3, and the immunosuppressive protein PD-L1 across all these isogenic cell lines. The expression of PD-L1 was further characterized using luciferase reporter assays, where we observed significant difference between the SM1 and YUMM models. Specifically, we found that YUMM cells have higher PD-L1 expression than SM1 models, suggesting that these isogenic cell lines are more immunosuppressive, and they may represent a more realistic model. Overall, these results indicate the role that the mutational signature may have on the response to epigenetic and targeted therapy, and suggests that the genetic alterations in a tumor should be considered prior to treatment administration in order to obtain a more personalized anti-tumor response.

Open Access

1

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Presented at Research Days 2019.

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The effect of the mutational signature in response to immuno-epigenetic therapies in melanoma

Melanoma is the deadliest type of skin cancer, and it is estimated to affect 96,500 people in the United States in 2019. Current treatments include targeted therapy (i.e., the BRAF inhibitor Vemurafenib), epigenetic modifiers, and immunotherapy, such as immune checkpoint inhibitors (ICI). Most of the preclinical evaluations for the above therapies have been done using mouse melanoma models, including B16 and SM1. Although the molecular mechanisms involved in the pathogenesis of melanoma have been elucidated using the B16 cells, this model is not suitable for the preclinical in vivo testing of combination therapies because its genetic alterations are not well defined and it does not resemble human melanoma histologically. Our group has previously studied the combination of histone deacetylase 6 inhibitors (HDAC6i) and ICI using the SM1, which is an immunogenic, BRAFV600E/V600E mouse model, which resulted in a significant reduction of tumor growth. However, this model ignores the potential contribution of other relevant oncogenic mutations occurring in human melanoma (i.e., PTEN, P53). In this regard, HDAC6 has been reported to deacetylate PTEN and p53. Therefore, in this study, we aim to investigate the role of HDAC6 in these relevant oncogenic pathways. For this purpose, multiple isogenic mouse models were used: SM1, YUMM1.7 (BRAFV600E/wt, Pten-/-, Cdkn2a-/-), YUMM3.3 (BRAFV600E/wt, Cdkn2a-/-), YUMM4.1 (Pten-/-, Cdkn2a-/-), and YUMM5.2 (BRAFV600E/wt, Tp53-/-). In this study, we assessed the cytotoxic properties of the HDAC inhibitors Panobinostat, Mocetinostat, and Nexturastat A, and Vemurafenib 48 hours post-treatment. We observed that YUMM5.2 cells are as sensitive to pan-HDAC inhibition as SM1, while more selective HDACi induce cytotoxicity in a dose-dependent manner. Furthermore, YUMM1.7 is more sensitive to BRAF inhibition than any other model. We also observed different basal expression of oncogenic proteins like c-jun and STAT3, and the immunosuppressive protein PD-L1 across all these isogenic cell lines. The expression of PD-L1 was further characterized using luciferase reporter assays, where we observed significant difference between the SM1 and YUMM models. Specifically, we found that YUMM cells have higher PD-L1 expression than SM1 models, suggesting that these isogenic cell lines are more immunosuppressive, and they may represent a more realistic model. Overall, these results indicate the role that the mutational signature may have on the response to epigenetic and targeted therapy, and suggests that the genetic alterations in a tumor should be considered prior to treatment administration in order to obtain a more personalized anti-tumor response.