ACY-241

ACY-241 is a new, selective and orally available inhibitor of HDAC6 [1][2].

Histone deacetylase 6 (HDAC6) is an enzyme that removes acetyl groups from an ε-N-acetyl lysine on a histone, allowing the histones to wrap the DNA more tightly. HDAC6 plays an important role in transcriptional regulation and cell cycle progression.

ACY-241 is a new, selective and orally available HDAC6 inhibitor. In MM and MCL cells, the addition of ACY-241 to either lenalidomide (len) or pomalidomide (pom) resulted in synergistic increases in apoptosis and further reduced the expression of transcription factors MYC and IRF4 [1]. In multiple solid tumor cell lines, combination treatment with ACY-241 and paclitaxel resulted in enhanced inhibition of cell proliferation and increased cell death, compared with either single agent alone [2].

In MM xenograft model, combination treatment with ACY-241 and pomalidomide was well tolerated with no overt toxicity and significantly extended survival [1]. In xenograft models of pancreatic and ovarian cancer, combination treatment with ACY-241 and paclitaxel significantly increased mitotic cells with multipolar spindles. ACY-241 dose-dependently increased α-tubulin hyperacetylation [2].

References:
[1].  Quayle SN, Almeciga-Pinto I, Tamang D, et al. Selective HDAC inhibition by ricolinostat (ACY-1215) or ACY-241 synergizes with IMiD® immunomodulatory drugs in Multiple Myeloma (MM) and Mantle Cell Lymphoma (MCL) cells. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research, 2015, Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5380.
[2].  Huang P, Almeciga-Pinto I, Jordan M, et al. Selective HDAC inhibition by ACY-241 enhances the activity of paclitaxel in solid tumor models. In: Proceedings of the 2015 AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, Massachusetts. Philadelphia (PA): AACR

Selective HDAC inhibition by ACY-241 enhances the activity of paclitaxel in solid tumor models.[Pubmed:27926524]

Oncotarget. 2017 Jan 10;8(2):2694-2707.

ACY-241 is a novel, orally available and selective histone deacetylase (HDAC) 6 inhibitor in Phase 1b clinical development in multiple myeloma (NCT 02400242). Like the structurally related drug ACY-1215 (ricolinostat), ACY-241 has the potential for a substantially reduced side effect profile versus current nonselective HDAC inhibitor drug candidates due to reduced potency against Class I HDACs while retaining the potential for anticancer effectiveness. We now show that combination treatment of xenograft models with paclitaxel and either ricolinostat or ACY-241 significantly suppresses solid tumor growth. In cell lines from multiple solid tumor lineages, combination treatment with ACY-241 and paclitaxel enhanced inhibition of proliferation and increased cell death relative to either single agent alone. Combination treatment with ACY-241 and paclitaxel also resulted in more frequent occurrence of mitotic cells with abnormal multipolar spindles and aberrant mitoses, consistent with the observed increase of aneuploid cells. At the molecular level, multipolar mitotic spindle formation was observed to be NuMA-dependent and gamma-tubulin independent, suggesting that treatment-induced multipolar spindle formation does not depend on centrosomal amplification. The significantly enhanced efficacy of ACY-241 plus paclitaxel observed here, in addition to the anticipated superior safety profile of a selective HDAC6 inhibitor versus pan-HDAC inhibitors, provides a strong rationale for clinical development of this combination in patients with advanced solid tumors.

Enhancement of pomalidomide anti-tumor response with ACY-241, a selective HDAC6 inhibitor.[Pubmed:28264055]

PLoS One. 2017 Mar 6;12(3):e0173507.

Thalidomide-based Immunomodulatory Drugs (IMiDs(R)), including lenalidomide and pomalidomide, are effective therapeutics for multiple myeloma. These agents have been approved with, or are under clinical development with, other targeted therapies including proteasome inhibitors, alphaCD38 monoclonal antibodies, as well as histone deacetylase (HDAC) inhibitors for combination therapy. HDAC inhibitors broadly targeting Class I and IIb HDACs have shown potent preclinical efficacy but have frequently demonstrated an undesirable safety profile in combination therapy approaches in clinical studies. Therefore, development of more selective HDAC inhibitors could provide enhanced efficacy with reduced side effects in combination with IMiDs(R) for the treatment of B-cell malignancies, including multiple myeloma. Here, the second generation selective HDAC6 inhibitor citarinostat (ACY-241), with a more favorable safety profile than non-selective pan-HDAC inhibitors, is shown to synergize with pomalidomide in in vitro assays through promoting greater apoptosis and cell cycle arrest. Furthermore, utilizing a multiple myeloma in vivo murine xenograft model, combination treatment with pomalidomide and ACY-241 leads to increased tumor growth inhibition. At the molecular level, combination treatment with ACY-241 and pomalidomide leads to greater suppression of the pro-survival factors survivin, Myc, and IRF4. The results presented here demonstrate synergy between pomalidomide and ACY-241 in both in vitro and in vivo preclinical models, providing further impetus for clinical development of ACY-241 for use in combination with IMiDs for patients with multiple myeloma and potentially other B-cell malignancies.

Citarinostat (ACY241) is a second generation potent, orally active and high-selective HDAC6 inhibitor with an IC50 of 2.6 nM (IC50s of 35 nM, 45 nM, 46 nM and 137 nM for HDAC1, HDAC2, HDAC3 and HDAC8, respectively). Citarinostat has anticancer effects.

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