Suberoylanilide hydroxamic acid reduces acute graft-versus-host disease and preserves graft-versus-leukemia effect by inhibiting histone deacetylation

Abstract

Pro-inflammatory cytokines and the loss of gastrointestinal tract integrity contribute to acute graft-versus-host disease (GVHD) whereas the donor cytotoxic responses are critical for graft-versus-leukemia (GVL) preservation. Suberoylanilide hydroxamic acid (SAHA) is an anti-tumor agent that inhibits the activity of histone deacetylases (HDAC) and reduces the production of proinflammatory cytokines. Using a well characterized allogeneic murine BMT model B6 (H-2b) → B6D2F1 (H-2b/d) we studied the effects of HDAC inhibition by SAHA on acute GVHD. Recipients were transplanted with 2x10 6 donor T and 5x106 BM cells after13 GY TBI. Intra-peritoneal injections of 35 mg/kg/day of SAHA from days +3 to day +7 increased histone H3 acetylation in splenocytes harvested 7 days after BMT, confirming the inhibition of HDAC enzymes. SAHA treatment significantly reduced the serum levels of pro-inflammatory cytokines such as TNF-a, IL-1β and IFN-γ (P < 0.04) in the allogeneic recipients on day +7 after BMT. Intracytoplasmic staining by flow cytometry and RPA analysis of the host splenocytes on day +7 confirmed the decrease in the cytokine protein and mRNA. SAHA significantly improved the survival (P < 0.002) and reduced intestinal damage from GVHD of the allogeneic recipients . However SAHA did not suppress the donor T cell expansion in vivo and the proliferative and cytotoxic responses to host antigens in vitro measured 7 and 14 days after BMT. To test the effect of SAHA on GVL effects, recipients were injected with lethal doses of P815 (H-2d) tumor cells at the time of BMT. SAHA treatment resulted in significantly improved leukemia-free survival after allogeneic BMT (P < 0.05) whereas all the syngeneic BMT recipients of SAHA died of tumor ruling out direct anti-tumor effects of SAHA. Furthermore SAHA increased H3 acetylation in the splenocytes from both the syngeneic and allogeneic leukemic recipients on day +7, confirming that inhibition of HDAC enzymes alone is not sufficient for leukemia free survival in this system. We also tested the effect of SAHA in a second allogeneic BMT model (BALB/c → B6), where it also significantly improved survival (P < 0.001) and preserved GVL effects when recipient mice were injected with lethal doses of EL-4 (H-2b) tumor (P < 0.04). We conclude that HDAC inhibition regulates acute GVHD in these models and suggest that this class of pharmacologic agents may provide a novel strategy to reduce GVHD while maintaining the beneficial GVL effects.