Inhibition Of DNA Methyltransferase 1 Potentiates Antitumor Immunity In Oral Squamous Cell Carcinoma & Case Report

Part one Research of DNMT1 expression in oral squamous cell carcinomaObjective: DNA methylation has been recognized as a key mechanism of tumorigenesis,progression,and resistance.DNA methyltransferase 1(DNMT1),which is the most abundant DNA methyltransferase,has been considered to be involved in the tumorigenesis of multiple solid tumors,such as breast cancer,lung cancer,colorectal cancer,and oral squamous cell carcinoma(OSCC).However,the role of DNMT1 in OSCC is less clearly described.What is more,the effects on the immune microenvironment of DNMT1 have not become appreciated.In this study,we determine the role of DNMT1 in OSCC progression and immunity.Methods: We determine the expression levels of DNMT1 and the association of clinical parameters by analyzing human OSCC tissue microarrays.The survival curve was plotted by Kaplan-Meier survival analysis with the log-rank test.In the 4MOSC1 OSCC mouse model,immunohistochemistry was used to analyze the expression of DNMT1 in tumor tissue.Results: Compared within the oral mucosa,we found DNMT1 was significantly increased in OSCC.In cancer progression,DNMT1 expression was significantly increased in advanced lesions.After comparing the expression of DNMT1 in OSCC tissue and LNs by paired t-test,DNMT1 expression was found to be significantly higher in corresponding LNs.Kaplan–Meier survival analysis showed that a high level of DNMT1 conferred a worse prognosis in OSCC patients.By screening our human tissue microarray database,we found that VISTA,PD-L1,B7-H4,and PAK2 were associated with the expression of DNMT1 in human OSCC samples.Then we examined the expression of DNMT1 in the 4MOSC1 OSCC mouse model.DNMT1 was more highly expressed in OSCC than in healthy mice.Conclusions: In this study,we found that DNMT1 was overexpressed in human OSCC tissue.High DNMT1 levels in OSCC are associated with a worse prognosis.The expression of DNMT1 is related to tumor immunosuppression.In our 4MOSC1 mouse model,we found DNMT1 over expressed in tumor tissue,which provides a prerequisite for the further study of the role of DNMT1 in the tumor immunity of OSCC.Part two Research of improving antitumor immunity by inhibition of DNMT1Objective: The immunosuppressive tumor microenvironment in OSCC plays a crucial role in the resistance of immune checkpoint blockade(ICB).Many immune cells and molecules are involved in the formation of the immunosuppressive microenvironment or play tumorigenic roles in OSCC.Treatment against DNMT1 is likely to affect the aforementioned cells and molecules in the tumor microenvironment(TME),which in turn affects tumor therapy.For the further study of the role of DNMT1 in the tumor immunity of OSCC,we use immunocompetent mouse models to explore the effect of the inhibition of DNMT1 in mice.Methods: Two different types of OSCC mouse models were established to explore the effects of DNMT1 inhibitor on the TME.Flow cytometry was used to explore the changes of immune cells of inhibition of DNMT1.And immunohistochemistry was used to analyze the effect of DNMT1 inhibitor on the immunosuppressive microenvironment.Results: After treatment with DNMT inhibitor,tumor growth and tumor burden were sufficiently reduced in 4MOSC1 and 4MOSC2 OSCC mouse models.We found that inhibition of DNMT1 markedly decreased the percentage of myeloid-derived suppressor cells(MDSCs)in the spleen.Additionally,T cells were increased in DNMT1 inhibitor-treated mice.Immunohistochemistry experiments also showed that the DNMT1 inhibitor increased the tumor infiltration of T cells.Remarkably,the expression levels of VISTA,B7-H4 and PAK2 decreased significantly after DNMTi treatment when compared with the control group in two different OSCC mouse models.And in the 4MOSC1 OSCC mouse model,we found that DNMT1 inhibitor treatment can improve PD-L1 expression.Conclusions: DNMT1 inhibitor treatment exhibited powerful anticancer abilities in our animal models.Inhibition of DNMT1 effectively reinvigorates effector T cells on the one hand and improves the immunosuppressive environment on the other hand by decreasing MDSCs in two types of immunocompetent OSCC mouse models.This study reveals that DNMT1 may also exert therapeutic effects by affecting the tumor immune microenvironment and that combined treatment with DNMT1 inhibitors and ICB may lead to better treatment outcomes for oral cancer patients.