Cancer Testis Antigens Residing on the X-Chromosome Are Preferentially Derepressed in Myeloid Leukemic Cells by the DNA Demethylating Agent 5-Aza-2’-Deoxycytidine (DAC).

Introduction: Azanucleoside DNA demethylating agents upregulate large sets of genes in vitro. Cancer testis antigens (CTAs) are a growing group of immunogenic proteins that provide attractive targets for cancer-specific immunotherapy in solid tumors. In contrast, only a very limited number of studies has been performed on epigenetic regulation of CTAs in myeloid leukemia. A single report suggested specific in vivo induction of CTA mRNAs in blasts from AML and MDS pts treated with intermediate-dose Decitabine (DAC;

Materials and Methods: Myeloid cell lines were treated over 72 hrs with 50–200 nM DAC. RNA was isolated from peripheral blood blasts of AML pts treated with DAC (135mg/m² over 72 hours within the 00331 phase II trial) before and during early phase of the treatment (= days 2, 5 from start of DAC) when circulating blasts were still >40% (mean 75%). Expression analyses were performed by Western Blot (NY-ESO-1), qPCR (NY-ESO-1, MAGEA1, MAGEA3, Myeloblastin), and by HG-U133plus 2.0 mRNA microarray.

Results: The five myeloid cell lines Kasumi-1, U937, HL60, K562 and NB4 did not express NY-ESO-1 protein. Upon treatment with DAC, NY-ESO-1 was markedly de-repressed in 3/5 cell lines (Kasumi-1, U937, HL60). Induction of expression was dose- and time-dependent, with maximum induction at day 6, and reversible with prolonged culturing up to day 21. No derepression was seen when U-937 and HL-60 were treated with equitoxic low concentrations of cytarabine (not a Dnmt inhibitor). MAGEA1, MAGEA3 and the LAA Myeloblastin (MBN) were also induced by DAC in Kasumi-1, with the strongest effect observed for NY-ESO-1 and the least for MBN (high baseline expression). Expression analyses were extended to all 67 CTAs present on the U133plus array (45 located on the X-chromosome, 22 autosomally), of which 11/67 (17%) were induced >2 fold in Kasumi-1. Notably, all 11 CTA genes were X-chromosomal, whereas 0/22 autosomal CTAs showed reinduction (p= 0.008 by Fisher-Exact test). 2/9 LAA genes (22%) were also reinduced. In primary AML blasts from 9 pts, DAC treatment resulted in >2fold induction of 3 CTAs and 5 LAAs. qPCR demonstrated NY-ESO-1 upregulation in 2/5 patients, with a maximum at day 5 from start of treatment.

Conclusions: Marked derepression of NY-ESO-1 and other CTAs by treatment of myeloid cell lines with an azanucleoside DNA demethylating agent occurred preferentially with genes residing on the X chromosome, in line with a major role of DNA methylation for their regulation. Derepression by DAC was also observed in vivo, albeit less marked and occurring early during treatment. One of the therapeutic effects of low-dose DNA demethylating agents on leukemic myeloid blasts may be mediated via upregulation of antigens rendering the malignant cells more immunogenic.