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

Based on recent favorable in vitro and in vivo activity of several HDACi (histone deacetylase inhibitors) in HL (Hodgkin lymphoma), we investigated the in vitro activity of SNDX-275, an oral, class 1 isoform of selective HDACi in HL-derived cell lines.

Proliferation and cell death were examined by MTS assay, Annexin-V/PI and FACS analysis. For combination studies, cells were incubated with SNDX-275 (0.1-2 μM) and either ABT-737 (0.01-0.2 μM), Obatoclax (0.1-2 μM), Gemcitabine (1-20 nM) or Bortezomib (1-20 nM) for 72 hours. Gene and protein expression were measured by RT-PCR, Western blot, and immunohistochemistry. A multiplex assay was used to determine 30 cytokines and chemokines.

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 histone-3 acetylation, up-regulated p21 expression, and activated the intrinsic apoptosis pathway by down-regulating the XIAP (X-linked inhibitor of apoptosis protein), which was associated with activation of Caspase 9 and 3. Similarly to other HDACis, SNDX-275 decreased the expression of anti-apoptotic Bcl-2 and Bcl-xL, while level of Mcl-1 and pro-apoptotic Bax remained the same level. Combination studies demonstrated that SNDX-275 had more synergistic effect when combined with Bcl-2 inhibitors ABT-737 or Obatoclax and less when combined with Gemcitabine or Bortezomib. Dysregulated cytokine/chemokine production has been shown previously to contribute to HL pathology, including immune tolerance of the cancer cells. Hence, we measured the effect of SNDX-275 on pathways that may contribute to an anti-tumor immune response. Increased IL12 p40-70, IP10, and RANTES, and decreased IL13, IL4 and TARC levels were found, thus favoring Th1-type cytokines/chemokines. Recent data has demonstrated that a variety of epigenetic-modulating drugs may up-regulate the expression of CTAs (cancer testis antigens), leading to a favorable immune response. SNDX-275 was able to induce CTA expression of SSX2 and NY-ESO only in one cell line whereas MAGE-A4 was induced in both HL cell lines.

Our studies demonstrate that SNDX-275 has a dual effect on apoptotic and immunomodulatory pathways in HL, which can be enhanced by the addition of agents targeting cell survival pathways. Phase II studies with SNDX-275 in HL are ongoing, future clinical studies should investigate combinations with SNDX-275.

No relevant conflicts of interest to declare.