The therapeutic response to high-dose
methotrexate (HD-MTX)
therapy for primary central nervous system
lymphoma (PCNSL) varies. Polyglutamylation is a reversible
protein modification with a high occurrence rate in
tumor cells. MTX incorporated into cells is polyglutamylated and strongly binds to
dihydrofolate reductase without competitive inhibition by
leucovorin (LV).
Tumor cells with high polyglutamylation levels are selectively killed, whereas normal cells with lower polyglutamylation are rescued by LV. We hypothesized that the extent of polyglutamylation in
tumor cells determines treatment resistance. Here, we investigated the therapeutic response of PCNSL to HD-MTX
therapy with LV rescue based on polyglutamylation status. Among 113 consecutive PCNSL patients who underwent HD-MTX
therapy in our department between 2001 and 2014, polyglutamylation was evaluated by immunostaining in 82 cases, with relationships between polyglutamylation and therapeutic response retrospectively examined. Human
malignant lymphoma lines were used for in vitro experiments, and folpolyglutamate
synthetase (FPGS), which induces polyglutamylation, was knocked down with
short-hairpin RNA, and a stable cell line with a low rate of polyglutamylation was established. Cell viability after MTX treatment with LV rescue was evaluated using
sodium butyrate (NaBu), a
histone-deacetylase inhibitor that induces polyglutamylation by elevating FPGS expression. The complete response rate was significantly higher in the group with polyglutamylation than in the non-polyglutamylation group [58.1% (25/43) and 33.3% (13/39), respectively] (p < 0.05), and progression-free survival was also significantly increased in the group with polyglutamylation (p < 0.01). In vitro, the relief effect of LV after MTX administration was significantly enhanced after FPGS knockdown in al cell lines, whereas enhancement of FPGS expression by NaBu treatment significantly reduced this relief effect. These findings suggested that polyglutamylation could be a predictor of therapeutic response to HD-MTX
therapy with LV rescue in PCNSL. Combination
therapy with HD-MTX and polyglutamylation-inducing agents might represent a promising strategy for PCNSL treatment.