Cancer-testis antigens (CTA), such as NY-ESO-1, MAGE-A1, and MAGE-A3, are immunogenic
proteins encoded by genes, which are normally expressed only in male germ cells but are activated by ill-defined epigenetic mechanisms in human
tumors, including
lung cancers. Previously, we reported induction of these CTAs in
cancer cells, but not normal cells, by
DNA-demethylating agents and
histone deacetylase inhibitors using clinically achievable exposure conditions. In the present study, we evaluated
chromatin alterations associated with repression/activation of
cancer-testis genes in
lung cancer cells to further develop gene-induction regimens for
cancer immunotherapy. Repression of NY-ESO-1, MAGE-A1, and MAGE-A3 coincided with
DNA hypermethylation, recruitment, and binding of
polycomb-group proteins, and
histone heterochromatin modifications within the promoters of these genes. Derepression coincided with DNA demethylation, dissociation of polycomb
proteins, and presence of
euchromatin marks within the respective promoters. Short hairpin RNAs were used to inhibit several
histone methyltransferases (KMT) and
histone demethylases (KDM) that mediate
histone methylation and repress gene expression. Knockdown of KMT6, KDM1, or KDM5B markedly enhanced deoxyazacytidine (DAC)-mediated activation of these
cancer-testis genes in
lung cancer cells.
DZNep, a pharmacologic inhibitor of KMT6 expression, recapitulated the effects of KMT6 knockdown. Following DAC-
DZNep exposure,
lung cancer cells were specifically recognized and lysed by allogeneic lymphocytes expressing recombinant
T-cell receptors recognizing NY-ESO-1 and MAGE-A3. Combining
DNA-demethylating agents with compounds, such as
DZNep, that modulate
histone lysine methylation may provide a novel epigenetic strategy to augment
cancer-testis gene expression as an adjunct to adoptive
cancer immunotherapy.