ACY-1215 for Relapsed/Refractory Lymphoid Malignancies

The emergence of epigenetic therapies has identified pan-class deacetylase (DAC) inhibitors as effective therapeutic agents for the treatment of lymphoma. While pan-class DAC inhibitors have led to FDA indications, clinical activity has been limited to the T-cell derived malignancies. The mechanism of action remains largely unknown and off-target effects lead to side effects including fatigue, gastrointestinal disturbances, and cytopenias. Recently, the development of isoform selective DAC inhibitors have opened the opportunity to investigate their mechanism. It is now recognized that DAC inhibitors not only have epigenetic properties, but have direct effects on transcription factors (p53), oncogenes (Bcl6), and protein degradation pathways (aggresome). Proteolysis occurs primarily through the ubiquitin-proteosome pathway. In states where this pathway is physiologically overwhelmed or therapeutically inhibited, the aggresome sequesters proteins for degradation. DAC6 is a class IIb deacetylase that facilitates misfolded protein transport to the aggresome for proteosome-independent proteolysis. Inhibition of the aggresome activates the unfolded protein response (UPR) pathway, a cellular quality control mechanism with two primary functions: (1) to promote survival during cellular endoplasmic reticulum (ER) stress by chaperoning proteins back for re-folding and halting further transcription until homeostasis is restored and (2) to signal CCAAT/enhancer binding protein (C/EBP)-homologous protein (CHOP) mediated apoptosis when homeostasis cannot be reestablished\[9\]. While most cells depend on both branches of the UPR to coordinate protein folding, lymphocytes physiologically down-regulate the UPR-apoptosis pathway, specifically CHOP, to allow for generation of high affinity antibodies. In addition to initiating genetic abnormalities (translocations and point mutations) lymphomas inherit this biology, and thus gain a survival advantage. It has been shown ACY-1215, an Histone Deacetylase 6 (HDAC6)-selective, orally active small-molecule enzyme inhibitor has had single agent activity in a panel of lymphoma cell lines and mouse models, and marked synergistic activity with several agents such as bortezomib, carfilzomib, and ibrutinib, unpublished data. ACY-1215 has been studied in vivo in models of multiple myeloma and lymphoma with marked activity both as a single agent and in combination with bortezomib. Therefore ACY-1215 will be investigated for treatment of lymphoma as a single agent leading to future studies evaluating its effects in combination with other targeted agents known to be active in lymphoma and synergistic with ACY-1215.