Inhibiting DNA methylation activates cancer testis antigens and expression of the antigen processing and presentation machinery in colon and ovarian cancer cells.

Cornelia Siebenkäs,Stephen B Baylin,Katherine B Chiappinelli,Jana Jeschke,Nita Ahuja,Angela A Guzzetta,Anup Sharma,Rajita Vatapalli,David Wai Chan

doi:10.1371/journal.pone.0179501

Abstract

Innovative therapies for solid tumors are urgently needed. Recently, therapies that harness the host immune system to fight cancer cells have successfully treated a subset of patients with solid tumors. These responses have been strong and durable but observed in subsets of patients. Work from our group and others has shown that epigenetic therapy, specifically inhibiting the silencing DNA methylation mark, activates immune signaling in tumor cells and can sensitize to immune therapy in murine models. Here we show that colon and ovarian cancer cell lines exhibit lower expression of transcripts involved in antigen processing and presentation to immune cells compared to normal tissues. In addition, treatment with clinically relevant low doses of DNMT inhibitors (that remove DNA methylation) increases expression of both antigen processing and presentation and Cancer Testis Antigens in these cell lines. We confirm that treatment with DNMT inhibitors upregulates expression of the antigen processing and presentation molecules B2M, CALR, CD58, PSMB8, PSMB9 at the RNA and protein level in a wider range of colon and ovarian cancer cell lines and treatment time points than had been described previously. In addition, we show that DNMTi treatment upregulates many Cancer Testis Antigens common to both colon and ovarian cancer. This increase of both antigens and antigen presentation by epigenetic therapy may be one mechanism to sensitize patients to immune therapies.

Highlights

Cancer causes nearly one out of four deaths in the United States; progress against this disease has been limited by the difficulty of therapeutically targeting cancer cells without affecting the surrounding normal cells
To test whether multiple antigen processing and presentation genes were increased by DNA methyltransferase inhibitors (DNMTis) treatment, we performed qRT-PCR on 8 colon cancer cell lines with and without 5-AC treatment
B2M, which encodes the small chain of the major histocompatibility complex I (MHC I) molecule crucial for MHC I assembly, was expressed at lower levels in colon cancer cell lines relative to normal colon (Fig 1A, Fig 2A, S1A Fig) 3/8 colon cancer cell lines significantly upregulated B2M after treatment with low doses of 5-AC (Fig 1A)

Summary

Introduction

Cancer causes nearly one out of four deaths in the United States; progress against this disease has been limited by the difficulty of therapeutically targeting cancer cells without affecting the surrounding normal cells. Cancer cells often have markedly different “epigenomes” than normal cells and exhibit profound changes in DNA methylation of cytosines at CpG dinucleotides These changes include global loss of methylation at regions such as repetitive elements that must be silenced for genome stability and gain of methylation at the promoter regions of tumor suppressor and other genes. Treatment with the DNMTi 5-AC sensitizes mouse melanoma cells to subsequent anti-CTLA4 therapy [4], likely through activation of the interferon response and subsequent signaling to host immune cells. This epigenetic treatment upregulates interferon signaling in tumor cells and causes host immune cells to selectively target tumor cells for destruction

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Results

Conclusion