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.
Asterisk with author names denotes non-ASH members.