Histone deacetylase (HDAC) enzymatic activity has been linked to the transcription of DNA in cancers including multiple myeloma (MM). Therefore, HDAC inhibitors used alone and in combination are being actively studied as novel therapies in MM. In the present study, we investigated the preclinical activity of ACY-1215, an HDAC6-selective inhibitor, alone and in combination with bortezomib in MM. Low doses of ACY-1215 combined with bortezomib triggered synergistic anti-MM activity, resulting in protracted endoplasmic reticulum stress and apoptosis via activation of caspase-3, caspase-8, and caspase-9 and poly (ADP) ribosome polymerase. In vivo, the anti-MM activity of ACY-1215 in combination with bortezomib was confirmed using 2 different xenograft SCID mouse models: human MM injected subcutaneously (the plasmacytoma model) and luciferase-expressing human MM injected intravenously (the disseminated MM model). Tumor growth was significantly delayed and overall survival was significantly prolonged in animals treated with the combination therapy. Pharmacokinetic data showed peak plasma levels of ACY-1215 at 4 hours after treatment coincident with an increase in acetylated ␣-tubulin, a marker of HDAC6 inhibition, by immunohistochemistry and Western blot analysis. These studies provide preclinical rationale for acetylated ␣-tubulin use as a pharmacodynamic biomarker in future clinical trials.

Purpose Histone deacetylase (HDAC) inhibition improves the efficacy of proteasome inhibition for multiple myeloma but adds substantial toxicity. Preclinical models suggest that the observed synergy is due to the role of HDAC6 in mediating resistance to proteasome inhibition via the aggresome/autophagy pathway of protein degradation. Experimental Design We conducted a phase 1/2 trial of the HDAC6-selective inhibitor ricolinostat to define the safety, preliminary efficacy, and recommended phase 2 dose in combination with standard proteasome inhibitor therapy. Patients with relapsed or refractory multiple myeloma received oral ricolinostat on days 1–5 and 8–12 of each 21-day cycle. Results Single agent ricolinostat therapy resulted in neither significant toxicity nor clinical responses. Combination therapy with bortezomib and dexamethasone was well tolerated during dose escalation but led to dose-limiting diarrhea in an expansion cohort at a ricolinostat dose of 160 mg twice daily. Combination therapy at a ricolinostat dose of 160 mg daily in a second expansion cohort was well tolerated, with less severe hematologic, gastrointestinal, and constitutional toxicities compared with published data on non-selective HDAC inhibitors. The overall response rate in combination with daily ricolinostat at ≥160 mg was 37%. The response rate to combination therapy among bortezomib-refractory patients was 14%. Samples taken during therapy showed dose-dependent increases of acetylated tubulin in peripheral blood lymphocytes. Conclusions At the recommended phase 2 dose of ricolinostat of 160 mg daily, the combination with bortezomib and dexamethasone is safe, well tolerated, and active, suggesting that selective inhibition of HDAC6 is a promising approach to multiple myeloma therapy.

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Bortezomib is a proteasome inhibitor that has direct antitumor effects. We and others have previously demonstrated that bortezomib could also sensitize tumor cells to killing via the death ligand, TRAIL. NK cells represent a potent antitumor effector cell. Therefore, we investigated whether bortezomib could sensitize tumor cells to NK cell-mediated killing. Preincubation of tumor cells with bortezomib had no effect on short-term NK cell killing or purified granule killing assays. Using a 24-h lysis assay, increases in tumor killing was only observed using perforin-deficient NK cells, and this increased killing was found to be dependent on both TRAIL and FasL, correlating with an increase in tumor Fas and DR5 expression. Long-term tumor outgrowth assays allowed for the detection of this increased tumor killing by activated NK cells following bortezomib treatment of the tumor. In a tumor purging assay, in which tumor:bone marrow cell mixtures were placed into lethally irradiated mice, only treatment of these mixtures with a combination of NK cells with bortezomib resulted in significant tumor-free survival of the recipients. These results demonstrate that bortezomib treatment can sensitize tumor cells to cellular effector pathways. These results suggest that the combination of proteasome inhibition with immune therapy may result in increased antitumor efficacy.

A feature shared by many inflammatory lung diseases is excessive neutrophilic infiltration. Neutrophil homing to airspaces involve multiple factors produced by several distinct cell types. Hepoxilin A3 is a neutrophil chemo-attractant produced by pathogen infected epithelial cells hypothesized to facilitate neutrophil breach of mucosal barriers. Using a Transwell model of lung epithelial barriers infected with P. aeruginosa, we explored the role of hepoxilin A3 in neutrophil trans-epithelial migration. Pharmacological inhibitors of enzymatic pathways necessary to generate hepoxilin A3, including phospholipase A2 and 12-lipoxygenase, potently interfere with P. aeruginosa-induced neutrophil trans-epithelial migration. Both transformed and primary human lung epithelial cells infected with P. aeruginosa generate hepoxilin A3 precursor arachidonic acid. All four known lipoxygenase enzymes capable of synthesizing hepoxilin A3 are expressed in lung epithelial cell lines, primary small airway epithelial cells, and human bronchial epithelial cells. Lung epithelial cells produce increased hepoxilin A3 and lipid derived neutrophil chemotactic activity in response to P. aeruginosa infection. Lipid derived chemotactic activity is soluble epoxide hydrolase sensitive, consistent with hepoxilin A3 serving a chemotactic role. Stable inhibitory structural analogues of hepoxilin A3 are capable of impeding P. aeruginosa-induced neutrophil trans-epithelial migration. Finally, intranasal infection of mice with P. aeruginosa promotes enhanced cellular infiltrate into the airspace as well as increased concentration of the 12-lipoxygenase metabolites hepoxilin A3 and 12-HETE. Data generated from multiple models herein provide further evidence that hepoxilin A3 is produced in response to lung pathogenic bacteria and functions to drive neutrophils across epithelial barriers.

The purpose of these studies was to determine the minimal requirements to induce granzyme B, cytotoxic granules and perforin-dependent lytic capacity. To our surprise, both IL-2 and IL-15 induced not only proliferation, but also profound granzyme B and lytic capacity from CD8 + T cells in the absence of antigen or TCR-stimulation. Mouse splenocytes were incubated with mouse r-IL-2 or r-IL-15 for three days, tested by anti-CD3 redirected lysis and examined for intracellular granzyme B and for T cell activation markers. With 10 −8 M IL-2 or IL-15, there was excellent lytic activity at 1:1 effector to target ratios mediated by T cells from wild type but not from perforin-gene-ablated mice, consistent with multiclonal activation. Lower interleukin concentrations induced less lytic activity. Granzyme B was undetectable on day 0, and greatly elevated on day 3 in CD44 hi CD8 + T cells as detected by flow cytometry. Cytokines alone elevated the granzyme B as much as concanavalin A combined with the cytokines. Some ex vivo CD8 + T cells were CD122 + , as were the cultured granzyme B + cells, thus both populations had low affinity receptors for the interleukins. Only some of the activated cells were proliferating as detected by CFSE labeling. When the cytokines were withdrawn, the cells lost lytic activity within 24 hours and then within the next 24 hours, died. Our results suggest that high concentrations of either IL-2 or IL-15 will activate the lytic capacity and granzyme B expression of many T cells and that antigen recognition is not required.

Thalidomide-based Immunomodulatory Drugs (IMiDs®), 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, αCD38 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® 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.

Purpose: New therapies are needed to treat immune checkpoint inhibitor–resistant non–small cell lung cancer (NSCLC) and identify biomarkers to personalize treatment. Epigenetic therapies, including histone deacetylase inhibitors, may synergize with programmed cell death-1 (PD-1) blockade to overcome resistance. We report outcomes in patients with anti-programmed cell death ligand-1 [PD-(L)1]–resistant/refractory NSCLC treated with pembrolizumab plus entinostat in ENCORE 601. Patients and Methods: The expansion cohort of ENCORE 601 included patients with NSCLC who previously experienced disease progression with immune checkpoint inhibitors. The primary endpoint for the phase II expansion cohort is overall response rate (ORR); safety, tolerability, and exploratory endpoints are described. Results: Of 76 treated patients, 71 were evaluable for efficacy. immune-regulated RECIST–assessed ORR was 9.2% [95% confidence interval (CI): 3.8–18.1], which did not meet the prespecified threshold for positivity. Median duration of response was 10.1 months (95% CI: 3.9–not estimable), progression-free survival (PFS) at 6 months was 22%, median PFS was 2.8 months (95% CI: 1.5–4.1), and median overall survival was 11.7 months (95% CI: 7.6–13.4). Benefit was enriched among patients with high levels of circulating classical monocytes at baseline. Baseline tumor PD-L1 expression and IFNγ gene expression were not associated with benefit. Treatment-related grade ≥3 adverse events occurred in 41% of patients. Conclusions: In anti–PD-(L)1–experienced patients with NSCLC, entinostat plus pembrolizumab did not achieve the primary response rate endpoint but provided a clinically meaningful benefit, with objective response in 9% of patients. No new toxicities, including immune-related adverse events, were seen for either drug. Future studies will continue to evaluate the association of monocyte levels and response.