The Histone Deacetylase (HDAC) Inhibitor Entinostat (SNDX-275) Targets Hodgkin Lymphoma through a Dual Mechanism of Immune Modulation and Apoptosis Induction.

SNDX-275 is an oral, class 1 isoform selective HDACi. Phase 1 studies in leukemia demonstrated the agent has a long half-life and that weekly or every other week dosing is sufficient for antitumor activity. Based on recent favorable in vitro and in vivo activity of several HDAC inhibitors in HL, we investigated the in vitro activity of SNDX275 in HL-derived cell lines.

For apoptosis and gene expression analysis 05 × 10⁶ cells were incubated with 0.1-2 μM of SNDX-275 for 24-72 hours before they were examined for proliferation and cell death by the MTS assay and the annexin-PI and FACS analysis. For combination studies, cells were incubated with 0.1-2 uM of SNDX-275 and 1-20 nM of either gemcitabine or bortezomib for 48-72 hours. Gene and protein expression were measured by RT-PCR, western blot, and immunohistochemistry. SNDX-275 effects on a panel of 30 cytokines and chemokines was assayed on 05 × 10⁶ cells after incubation of 48 hrs using a multiplex assay.

SNDX-275 induced cell death in a dose and time dependent manner with an IC50 of 0.4 μM. At the molecular level, SNDX-275 increased H3 acetylation, up-regulated p21 protein expression, and activated the intrinsic apoptosis pathway by down-regulating the anti-apoptotic X-linked inhibitor or apoptosis (XIAP) protein, which was associated with activation of caspase 9 and 3. Combination studies demonstrated that SNDX-275 had synergistic effects when combined with gemcitabine and bortezomib. To further investigate the potential for SNDX-275 activity in HL we measured the effect of SNDX-275 on pathways that may contribute to an anti-tumor immune response. Dysregulated cytokine/chemokine production has been shown to contribute to HL pathology, including immune tolerance of the cancer cells. SNDX-275 increased IL12 p40-70, IP10, and RANTES, and decreased the level of IL13 and IL4, thus favoring Th1-type cytokines/chemokines. In addition, recent data has demonstrated that a variety of epigenetic-modulating drugs may up-regulate the expression of cancer testis tumor associated antigens, leading to a favorable immune response. None of the lines expressed the CTAs without induction. SNDX275 was able to induce CTA expression of SSX2 in L428 but not HDLM2 whereas MAGE-A was induced in both HL cell lines. NY-ESO expression was not induced.

Our studies demonstrate that SNDS-275 has dual effect on apoptotic and immunomodulatory pathways in HL. Furthermore, this data demonstrates that SNDX-275 may upregulate CTAs suggesting that this treatment may render the tumor more immunogeneic and susceptible to immune mediated killing with tumor-specific cytotoxic T lymphocytes. The selectivity profile of SNDX-275 also suggests that HDAC1 and 2 are the primary targets for HDAC inhibition in these cells. Phase 2 studies with SNDX-275 in HL are ongoing.

Younes:MethylGene: Honoraria, Research Funding.