Adaptation and innovation of anti-cancer epigenetic targeting therapeutic strategies for the treatment of murine chronic graft vs host disease

Abstract

Each year in the United States nearly 200,000 patients receive a diagnosis of a hematological cancer. While the treatment of these conditions has improved remarkably over the last few decades, nearly a quarter of these patients are expected to die from their disease. Much of the improvement in treatment comes from advancements in the field of allogenic hematopoietic stem cell transplant (aHSCT), the only curative therapy for the treatment of hematological malignancies. While aHSCT is an incredibly powerful technique, it comes with the major drawback of inducing graft vs host disease (GVHD), the second leading cause of mortality following aHSCT after reoccurrence of the original disease. Chronic GVHD in particular has proven difficult to manage. cGVHD is an auto-immune-like condition that arises as a result of donor-derived immune cells attacking the recipient tissues post-transplant. The current standard of treatment for cGVHD involves broad steroid immunosuppression, however in cases where steroid refractory forms of the disease arise treatment options are extremely limited. Murine modeling of cGVHD has proven to be a highly effective method for the development and preclinical testing of novel therapies. Based on these studies, it has been determined that the germinal center reaction (GCR) forms a critical step in the pathogenesis of cGVHD, as it is necessary for the development of allo-antibodies that drive fibrotic tissue damage which characterizes the condition. As such, the development of novel therapeutics that disrupt this reaction is of particular interest for the treatment of cGVHD. Epigenetic targeting drugs inhibit enzymes involved in chromatin remodeling and changing the epigenetic landscape of cells. Their use in cancer treatment is primarily driven by the drug’s impact on the aberrant epigenome that arises in cancer cells. In the studies presented here, we sought to leverage this strategy for the treatment of cGVHD, not by targeting aberrant epigenomic changes, but instead using these compounds to disrupt cellular processes necessary for the pathogenesis of cGVHD in particular the GCR. To that end, we tested the preclinical efficacy of three different classes of epigenetic targets in the treatment of cGVHD. We first investigated the potential of BET-bromodomain inhibitor JQ1, which inhibits a number of epigenetic reader enzymes, in particular BRD4. We show that while JQ1 has great impact in a fibrotic model of cGVHD that recapitulates pulmonary dysfunction from bronchiolitis obliterans (BOS), its impact in inflammatory models of GVHD is limited. Next, we tested the role of the epigenetic writer EZH2 in the pathogenesis and treatment of cGVHD. We show that not only is EZH2 necessary for the establishment of cGVHD, but that a novel small molecule inhibitor of EZH2, JQ5, is highly effective in treating multiple murine models of the disease. We further demonstrate that while both of these strategies disrupt the GCR, they do so through the regulation of unique sets of genetic targets, which may have important implications for their clinical translation. Finally, we tested the role of the dynamic DNA demethylases TET2 and TET3 in cGVHD. We show that TET3 is critical for the initiation of disease not through inhibition of the GCR, but by changing the reaction to alter the IgG class switching of antibody secreting B cells. In doing so Tet3 loss of function prevents the development of fibrotic pathology while preserving adaptive immune activity. These trials demonstrate not only the preclinical efficacy of these therapeutic targets but show that the targeting of epigenetic regulators of the GCR is a viable avenue for the development of further therapies for the treatment of cGVHD.