Biology subjects

Morehead, L. C.

Publications and source records attributed to Morehead, L. C..

3 recordsLinked to original sources

bioRxiv2023

Increased response to immune checkpoint inhibitors with dietary methionine restriction

Dietary methionine restriction, defined as reduction of methionine intake by around 80%, reproducibly decreases tumor growth and synergizes with cancer therapies. Here, we combined dietary methionine restriction with immune checkpoint inhibitors in a model of colon adenocarcinoma. In vitro, we observed that methionine restriction increased the expression of MHC-I and PD-L1 in both mouse and human colorectal cancer cells. We also saw an increase in the gene expression of STING, a known inducer of type I interferon signaling. Inhibition of the cGAS-STING pathway, pharmacologically or with siRNA, blunted the increase in MHC-I and PD-L1 surface and gene expression following methionine restriction. PD-L1 expression was also This indicated that the cGAS-STING pathway in particular, and interferon in general, is playing a role in the immune response to methionine restriction. We then combined dietary methionine restriction with immune checkpoint inhibitors targeted against CTLA-4 and PD-1 in a MC38 colorectal cancer tumor model in C57BL/6 mice. The combination treatment was five times more effective at reducing tumor size than immune checkpoint inhibition alone in males. We noted sex differences in the response to dietary methionine restriction for the MC38 tumor model in C57BL/6 mice. Finally, we observed an increase in PD-L1 protein expression in MC38 tumors from animals who were fed a methionine-restricted diet. Furthermore, the distribution of CD8 staining changed from mostly peripheric in the controls, to intratumoral in the methionine-restricted tumors. MHC-I, which has a high basal expression in MC38 cells, was highly expressed in all tumors. These results indicate that methionine restriction improves the response to immune checkpoint inhibitors in mice, and that this improvement is associated with the cGAS-STING pathway and interferon signaling.

cancer biology↗

bioRxiv2023

Characterization of methionine dependence in melanoma cells

Dietary methionine restriction is associated with a reduction in tumor growth in preclinical studies and an increase in lifespan in animal models. The mechanism by which methionine restriction inhibits tumor growth while sparing normal cells is incompletely understood. We do know that normal cells can utilize methionine or homocysteine interchangeably (methionine independence) while most cancer cells are strictly dependent on methionine availability. Here, we compared a typical methionine dependent and a rare methionine independent melanoma cell line. We show that replacing methionine, a methyl donor, with its precursor homocysteine generally induced hypomethylation in gene promoters. This decrease was similar in methionine dependent and methionine independent cells. There was only a low level of pathway enrichment, suggesting that the hypomethylation is generalized rather than gene specific. Whole proteome and transcriptome were also analyzed. This analysis revealed that contrarily to the effect on methylation, the replacement of methionine with homocysteine had a much greater effect on the transcriptome and proteome of methionine dependent cells than methionine independent cells. Interestingly, methionine adenosyltransferase 2A (MAT2A), responsible for the synthesis of s-adenosylmethionine from methionine, was equally strongly upregulated in both cell lines. This suggests that the absence of methionine is equally detected but triggers different outcomes in methionine dependent versus independent cells. Our analysis reveals the importance of cell cycle control, DNA damage repair, translation, nutrient sensing, oxidative stress and immune functions in the cellular response to methionine stress in melanoma.

molecular biology↗

bioRxiv2022

Inhibition of DNA-PKcs impairs the activation and cytotoxicity of CD4+ helper and CD8+ effector T cells

Modulation of T cell activity is an effective strategy for the treatment of autoimmune diseases, immune-related disorders and cancer. This highlights a critical need for continued investigation of proteins that regulate T cell function. The kinase DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is emerging as a potent regulator of the immune system spurring interest in its use as a therapeutic target for immune-related diseases. In murine models of autoimmune disease including asthma and rheumatoid arthritis, treatment with small molecule DNA-PKcs inhibitors, which are in clinical trials for cancer therapy, decreased disease severity. Additionally, DNA-PKcs inhibitors reduced T cell-mediated graft rejection and extended graft survival in a murine allogenic skin graft rejection model. These in vivo studies suggest the therapeutic use of DNA-PKcs inhibitors for autoimmune and T cell-mediated disorders. In this study, we sought to further characterize the effects of DNA-PKcs inhibitors on T cells to better understand their clinical potential. We determined that pharmacological inhibition of DNA-PKcs abrogated activation of murine and human CD4+ and CD8+ T cells as evident by reduced expression of the activation markers CD69 and CD25. Furthermore, inhibition of DNA-PKcs impeded metabolic pathways and proliferation of anti-CD3/CD28 activated CD4+ and CD8+ T cells as well as peptide-stimulated OTI-CD8+ T cells. This reduced the ability of OTI-CD8+ T cells to kill cancer cells and the expression of IFN{gamma} and the cytotoxic genes eomes, perforin and granzyme B. These results suggest a novel role for DNA-PKcs in early T cell activation. Furthermore, our data support the therapeutic potential of DNA-PKcs inhibitors on diseases of immune dysregulation.

immunology↗