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Background Glioblastoma (GBM) has a devastating median survival of only one year. Treatment includes resection, radiation therapy, and temozolomide (TMZ); however, the latter increased median survival by only 2.5 months in the pivotal study. A desperate need remains to find an effective treatment. Methods We used the Connectivity Map (CMap) bioinformatic tool to identify candidates for repurposing based on GBM’s specific genetic profile. CMap identified histone deacetylase (HDAC) inhibitors as top candidates. In addition, Gene Expression Profiling Interactive Analysis (GEPIA) identified HDAC1 and HDAC2 as the most upregulated and HDAC11 as the most downregulated HDACs. We selected PCI-24781/abexinostat due to its specificity against HDAC1 and HDAC2, but not HDAC11, and blood-brain barrier permeability. Results We tested PCI-24781 using in vitro human and mouse GBM syngeneic cell lines, an in vivo murine orthograft, and a genetically engineered mouse model for GBM (PEPG - PTENflox/+; EGFRvIII+; p16Flox/− & GFAP Cre +). PCI-24781 significantly inhibited tumor growth and downregulated DNA repair machinery (BRCA1, CHK1, RAD51, and O6-methylguanine-DNA- methyltransferase (MGMT)), increasing DNA double-strand breaks and causing apoptosis in the GBM cell lines, including an MGMT expressing cell line in vitro. Further, PCI-24781 decreased tumor burden in a PEPG GBM mouse model. Notably, TMZ + PCI increased survival in orthotopic murine models compared to TMZ + vorinostat, a pan-HDAC inhibitor that proved unsuccessful in clinical trials. Conclusion PCI-24781 is a novel GBM-signature specific HDAC inhibitor that works synergistically with TMZ to enhance TMZ efficacy and improve GBM survival. These promising MGMT-agnostic results warrant clinical evaluation.

PURPOSE: Belinostat is a second-generation histone deacetylase inhibitor (HDI) predominantly metabolized by UGT1A1-mediated glucuronidation. Two common polymorphisms (UGT1A1*28 and UGT1A1*60) were previously associated with impaired drug clearance and thrombocytopenia risk, likely form increased drug exposure. This latter phenomenon has been observed with other HDIs such as abexinostat, panobinostat, romidepsin, and vorinostat. It was the intention of this brief report to expand a population pharmacokinetic (PPK) model to include a pharmacodynamic (PD) model describing the change in platelet levels in patients with cancer administered belinostat as a 48-h continuous intravenous infusion, along with cisplatin and etoposide. METHODS: The PPK/PD model developed here introduced an additional rate constant to a commonly used mechanistic myelo-suppression model to better describe the maturation of megakaryocytes into platelets before degradation and a feedback mechanism. The model employed a proportional error model to describe the observed circulating platelet data. RESULTS: Several covariates were explored, including sex, body weight, UGT1A1 genotype status, liver, and kidney function, but none significantly improved the model. Platelet levels rebounded to baseline within 21 days, before the next cycle of therapy. Simulations predicted that higher belinostat drug exposure does cause lower thrombocyte nadirs compared to lower belinostat levels. However, platelet levels rebound by the start of the next belinostat cycle. CONCLUSIONS: This model suggests a q3week schedule allows for sufficient platelet recovery before the next belinostat infusion is optimal.

// Eric Deutsch 1, 2, 3 , Elizabeth Cohen-Jonathan Moyal 4 , Vanesa Gregorc 5 , Paolo Andrea Zucali 6 , Jean Menard 7 , Jean-Charles Soria 8 , Ioana Kloos 9 , Jeff Hsu 10 , Ying Luan 10 , Emily Liu 10 , Remus Vezan 10 , Thorsten Graef 10 , Sofia Rivera 1, 2, 3 1 Department of Radiation Oncology, Gustave-Roussy Cancer Campus, Villejuif, France 2 INSERM 1030 Molecular Radiotherapy, Villejuif, France 3 Faculte de Medecine, Universite Paris-Sud, Universite Paris-Saclay, Le Kremlin-Bicetre, France 4 Department of Radiation Oncology, Institut Claudius Regaud, Toulouse, France 5 Department of Medical Oncology, Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale San Raffaele, Milan, Italy 6 Department of Medical Oncology and Haematology, Humanitas Cancer Center, IRCCS, Rozzano, Italy 7 Department of Radiation Oncology, Hopital Saint-Louis, Paris, France 8 DITEP (Departement d’Innovations Therapeutiques et Essais Precoces), Gustave Roussy Cancer Campus, Villejuif, France 9 Institut de Recherches Internationales Servier, Clinical Pharmacokinetics, Suresnes, France 10 Pharmacyclics LLC, an AbbVie Company, Sunnyvale, CA, USA Correspondence to: Eric Deutsch, email: eric.deutsch@gustaveroussy.fr Keywords: abexinostat, histone deacetylase inhibitor, radiotherapy, solid tumors, brain lesions Received: July 28, 2016 Accepted: November 14, 2016 Published: December 24, 2016 ABSTRACT Current treatments for advanced solid tumors tend to be only palliative. Although radiotherapy is administered with a curative intent, radioresistance and dose-limiting toxicities pose limitations to treatment. Abexinostat, an oral pan-histone deacetylase inhibitor, demonstrated enhanced sensitivity to radiation in various solid tumor cell lines. We conducted an exploratory, phase 1, dose-escalation study of abexinostat in combination with standard hypofractionated radiotherapy in patients with advanced solid tumors treated in a palliative setting. Among 58 treated patients, the median age was 61.5 years (range, 20-82); 47% of the patients had M1 stage disease, and 95% had received previous chemotherapy alone or chemotherapy in combination with surgery and/or radiotherapy. The recommended phase 2 dose was determined to be 90 mg/m 2 (140 mg). Of the 51 patients evaluable for response, best overall response was 8% (1 complete response [CR], 3 partial responses [PRs]), and best loco-regional response was 12% (1 CR and 5 PRs) at a median follow-up of 16 weeks. Of note, patients with target or non-target brain lesions showed encouraging responses, with 1 patient achieving a best loco-regional response of CR. Treatment-emergent grade ≥3 adverse events (AEs) were few, with most common being thrombocytopenia (17%), lymphopenia (12%), and hypokalemia (7%). Six patients (10%) discontinued treatment due to AEs. No grade ≥3 prolongation of the QTc interval was observed, with no treatment discontinuations due to this AE. Oral abexinostat combined with radiotherapy was well tolerated in patients with advanced solid tumors. The combination may have potential for treatment of patients with brain lesions.

Histone deacetylase (HDAC) inhibitor abexinostat is under investigation for the treatment of various cancers. Epigenetic changes including aberrant HDAC activity are associated with cancers, including myelodysplastic syndromes (MDS), acute myeloid leukemia (AML), and acute lymphoblastic leukemia (ALL). In this phase 1 dose-escalation study, 17 patients with relapsed/refractory higher-risk MDS, AML, or ALL received oral abexinostat (60, 80 [starting dose], 100, or 120 mg) twice daily (bid) on Days 1-14 of 21-day cycles. The most common treatment-related grade ≥3 adverse events were thrombocytopenia (29%) and neutropenia (24%), none of which led to discontinuation. Maximum-tolerated dose was not reached. Of 12 evaluable patients, best response was stable disease in 1 patient. This study was closed due to limited clinical benefit. Future development of oral abexinostat 100 mg bid in patients with MDS, AML, or ALL should focus on combination regimens. ISRCTN registry: 99680465.

Cancer cells contain significant alterations in their epigenomic landscape, which several enzyme families reversibly contribute to. One class of epigenetic modifying enzymes is that of histone deacetylases (HDAC), which are receiving considerable scrutiny clinically as a therapeutic target in many cancers. The underlying rationale is that inhibiting HDACs will reverse dysregulated target gene expression by modulating functional histone (or other) acetylation marks. This perspective will discuss a recent paper by Markozashvili and co-workers which appeared in Gene, which indicates that the mechanisms by which HDAC inhibitors (HDACis) alter the epigenetic landscape include widespread alternative effects beyond simply controlling regional epigenetic marks. HDACs are involved in many processes/diseases, and it is not surprising that HDACis have considerable off-target effects, and thus a major effort is being directed toward identification of inhibitors which are selective for HDAC isoforms often uniquely implicated in various cancers. This Perspective will also discuss some representative work with inhibitors targeting individual HDAC classes or isoforms. At present, it is not really clear that isoform-specific HDACis will avoid non-selective effects on other unrecognized activities of HDACs.

Purpose: Additional targeted therapeutics are needed for the treatment of lymphoma. Abexinostat is an oral pan-histone deacetylase inhibitor (HDACi) displaying potent activity in preclinical models. We conducted a multicenter phase I/II study (N = 55) with single-agent abexinostat in relapsed/refractory lymphoma. Experimental Design: In phase I, 25 heavily pretreated patients with any lymphoma subtype received oral abexinostat ranging from 30 to 60 mg/m2 twice daily 5 days/week for 3 weeks or 7 days/week given every other week. Phase II evaluated abexinostat at the maximum tolerated dose in 30 patients with relapsed/refractory follicular lymphoma or mantle cell lymphoma. Results: The recommended phase II dose was 45 mg/m2 twice daily (90 mg/m2 total), 7 days/week given every other week. Of the 30 follicular lymphoma and mantle cell lymphoma patients enrolled in phase II, 25 (14 follicular lymphoma, 11 mantle cell lymphoma) were response-evaluable. Tumor size was reduced in 86% of follicular lymphoma patients with an investigator-assessed ORR of 64.3% for evaluable patients [intent-to-treat (ITT) ORR 56.3%]. Median duration of response was not reached, and median progression-free survival (PFS) was 20.5 months (1.2–22.3+). Of responding follicular lymphoma patients, 89% were on study/drug >8 months. In mantle cell lymphoma, the ORR was 27.3% for evaluable patients (ITT ORR 21.4%), and median PFS was 3.9 months (range, 0.1–11.5). Grade 3–4 treatment-related adverse events (phase II) with ≥10% incidence were thrombocytopenia (20%), fatigue (16.7%), and neutropenia (13.3%) with rare QTc prolongation and no deaths. Conclusions: The pan-HDACi, abexinostat, was overall well tolerated and had significant clinical activity in follicular lymphoma, including highly durable responses in this multiply relapsed patient population. Clin Cancer Res; 22(5); 1059–66. ©2015 AACR.

Introduction Several inhibitors of histone deacetylase have been shown to enhance chemotherapy induced apoptosis and reduce sarcoma tumor volume in preclinical models. We sought to determine the MTD, PK/PD, safety and toxicity of the histone deacetylase inhibitor (HDACi) abexinostat (PCI-24781) when administered with doxorubicin in patients with metastatic sarcomas.

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Despite prominent role of radiotherapy in lung cancer management, there is an urgent need for strategies increasing therapeutic efficacy. Reversible epigenetic changes are promising targets for combination strategies using HDAC inhibitors (HDACi). Here we evaluated on two NSCLC cell lines, the antitumor effect of abexinostat, a novel pan HDACi combined with irradiation in vitro in normoxia and hypoxia, by clonogenic assays, demonstrating that abexinostat enhances radiosensitivity in a time dependent way with mean SER10 between 1.6 and 2.5 for A549 and H460. We found, by immunofluorescence staining, flow cytometry assays and western blotting, in abexinostat treated cells, increasing radio-induced caspase dependent apoptosis and persistent DNA double-strand breaks associated with decreased DNA damage signalling and repair. Interestingly, we demonstrated on nude mice xenografts that abexinostat potentiates tumor growth delay in combined modality treatments associating not only abexinostat and irradiation but also when adding cisplatin. Altogether, our data demonstrate in vitro and in vivo anti-tumor effect potentiation by abexinostat combined with irradiation in NSCLC. Moreover, our work suggests for the first time to our knowledge promising triple combination opportunities with HDACi, irradiation and cisplatin which deserves further investigations and could be of major interest in the treatment of NSCLC.

Purpose This phase I trial evaluated epigenetic modulation of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor by using a histone deacetylase abexinostat in combination with pazopanib to enhance response and reverse resistance. Patients and Methods Pazopanib was administered once a day on days 1 to 28 and abexinostat was administered orally twice a day on days 1 to 5, 8 to 12, and 15 to 19 (schedule A) or on days 1 to 4, 8 to 11, and 15 to 18 (schedule B). Dose escalation (3 + 3 design) in all solid tumors was followed by dose expansion in renal cell carcinoma (RCC). Results Fifty-one patients with RCC (N = 22) were enrolled, including 30 (59%) with one or more lines of prior VEGF-targeting therapy. Five dose-limiting toxicities, including fatigue (n = 2), thrombocytopenia (n = 2), and elevated AST/ALT (n = 1), were observed with schedule A; one dose-limiting toxicity was observed (elevated AST/ALT) was observed with schedule B. Grade ≥ 3 related adverse events included fatigue (16%), thrombocytopenia (16%), and neutropenia (10%). The recommended phase II dose was established as abexinostat 45 mg/m2 twice a day administered per schedule B plus pazopanib 800 mg/d. Objective response rate was 21% overall and 27% in the RCC subset. Median duration of response was 9.1 months (1.2 to > 49 months). Eight patients (16%) had durable control of disease for > 12 months. Durable tumor regressions were observed in seven (70%) of 10 patients with pazopanib-refractory disease, including one patients with RCC with ongoing response > 3.5 years. Peripheral blood histone acetylation and HDAC2 gene expression were associated with durable response to treatment. Conclusion Abexinostat is well tolerated in combination with pazopanib, allowing prolonged exposure and promising durable responses in pazopanib- and other VEGF inhibitor-refractory tumors, which supports epigenetically mediated reversal of treatment resistance.

International audience; Histone deacetylase inhibitors are members of a class of epigenetic drugs that have proven activity in T-cell malignancies, but little is known about their efficacy in B-cell lymphomas. Abexinostat is an orally available hydroxamate-containing histone deacetylase inhibitor that differs from approved inhibitors; its unique pharmacokinetic profile and oral dosing schedule, twice daily four hours apart, allows for continuous exposure at concentrations required to efficiently kill tumor cells. In this phase II study, patients with relapsed/refractory non-Hodgkin lymphoma or chronic lymphocytic leukemia received oral abexinostat at 80 mg BID for 14 days of a 21-day cycle and continued until progressive disease or unacceptable toxicity. A total of 100 patients with B-cell malignancies and T-cell lymphomas were enrolled between October 2011 and July 2014. All patients received at least one dose of study drug. Primary reasons for discontinuation included progressive disease (56%) and adverse events (25%). Grade 3 or over adverse events and any serious adverse events were reported in 88% and 73% of patients, respectively. The most frequently reported grade 3 or over treatment-emergent related adverse events were thrombocytopenia (80%), neutropenia (27%), and anemia (12%). Among the 87 patients evaluable for efficacy, overall response rate was 28% (complete response 5%), with highest responses observed in patients with follicular lymphoma (overall response rate 56%), T-cell lymphoma (overall response rate 40%), and diffuse large B-cell lymphoma (overall response rate 31%). Further investigation of the safety and efficacy of abexinostat in follicular lymphoma, T-cell lymphoma, and diffuse large B-cell lymphoma implementing a less dose-intense week-on-week-off schedule is warranted. (Trial registered at: EudraCT-2009-013691-47).

3022 Background: We previously reported the initial phase 1b study results of PAZ + ABX, a potent pan-HDAC inhibitor, demonstrating acceptable toxicity profile and encouraging anti-tumor activity (Aggarwal et al. JCO 2017). We report the long-term follow up of exceptional responders and additional correlative analyses associated with clinical outcomes. Methods: Key efficacy endpoints included objective response rate and duration of response. Peripheral blood histone acetylation, HDAC expression, and plasma VEGF levels were analyzed and associated with clinical outcomes. Results: 51 pts (RCC subset; N = 22) were enrolled between June 2012 and October 2015. 10 pts (20%) had experienced disease progression on prior PAZ; 59% had received any prior VEGF-targeting therapy. 9 evaluable pts (18%) (N = 6 RCC; 2 thyroid; 1 mesothelioma) achieved partial tumor response (PR), of which 6 had prior progression on VEGF-targeting therapy. 7/10 (70%) of pts with prior disease progression on PAZ monotherapy had reduction in tumor burden on study. The median duration of response was 9.1 months (range 1.2 to 70+), and clinical benefit rate (PR or stable disease > 6 months) was 33%. Five treatment-refractory pts achieved durable PRs lasting for > 2 years duration, and one previously PAZ-refractory patient with RCC remains on treatment with ongoing PR for > 6 years. Higher HDAC2 expression was associated with prolonged progression-free survival (median PFS 5.9 vs. 3.5 months, log-rank p = 0.02). Induction of histone acetylation on ABX lead-in treatment was associated with subsequent time to progression (p = 0.002). On-treatment plasma VEGF levels were inversely correlated with PBMC histone acetylation (p = 0.02). Conclusions: Markedly durable responses with PAZ + ABX are achievable, including in pts with PAZ- and VEGF-refractory RCC and other solid tumor malignancies. Host factors including HDAC expression and acetylation status may identify those most likely to benefit. A randomized phase 3 study is underway of PAZ + ABX as a first- or second-line therapy in pts with locally advanced or metastatic RCC (RENAVIV; NCT03592472). Clinical trial information: NCT01543763.

TPS681 Background: Abexinostat is a pan-histone deacetylase (HDAC) inhibitor that has shown promising activity in prior pre-clinical studies and early phase clinical trials. A phase 1b study of pazopanib plus abexinostat (Aggarwal et al. J Clin Oncol 2017) demonstrated strikingly durable responses in patients (pts) with clear cell renal cell carcinoma (RCC), including one patient with previously refractory disease with ongoing response for > 5 years’ duration. Induction of histone acetylation in peripheral blood mononuclear cells (PBMCs) was associated with durable treatment response. We hypothesize that the addition of abexinostat to pazopanib will significantly improve outcomes in patients with clear cell RCC. Methods: RENAVIV is a global, randomized, double-blind, placebo-controlled, two arm phase 3 study of pazopanib plus abexinostat versus pazopanib plus placebo, in pts with locally advanced or metastatic RCC with clear cell component. Up to one prior line of immunotherapy is allowed. Prior VEGF-targeting tyrosine kinase inhibitor treatment is prohibited. Stratification factors include: 1) Prior immunotherapy (yes/no) and 2) prognostic group (good, intermediate, poor). Pts randomized to pazopanib + placebo have the option of crossing over to receive pazopanib plus abexinostat at the time of disease progression. The primary endpoint is PFS by independent review committee. Secondary endpoints include PFS by investigator assessment, overall survival, safety, objective response rate (ORR), duration of response, patient-reported quality of life, and outcomes in cross-over population. Planned correlative studies include association between histone acetylation and HDAC expression in PBMCs with clinical outcomes. The total planned accrual is 413 pts, estimated to provide 90% power to detect a hazard ratio of 0.67 in the comparison of PFS between experimental versus control arms, with an overall two-sided type I error rate of 0.025. A pre-specified minimum of 50% of patients are required to have received prior immunotherapy. The first patient was enrolled in October 2018. Clinical trial information: NCT03592472.

Background: Around 20% of patients initially diagnosed with local stage breast cancer will develop metastatic breast cancer, with an about 23% median 5-year survival rate from diagnosis. Patients whose tumors express ER and PR (ER+, PR+) are frequently treated with antiestrogens and aromatase inhibitors (AI). Primary and secondary resistances to hormone therapy lead to tumor progression and shorten survival expectancy. In preclinical models, treatment of ER+ breast cancer cells with HDAC inhibitors leads to transcriptional down regulation and post-translation modification of the ER. This treatment reverses tamoxifen-induced ER stabilization, followed by induction of pro-apoptotic genes and apoptotic cell death. Epigenetic modulation of ER signaling by HDAC inhibitor represents a novel strategy to reverse hormonal resistance. Abexinostat is a hydroxamate-based pan-HDAC inhibitor of class I/II, in phase I/II clinical trials. Abexinostat inhibits tumor growth in a panel of commonly used ER+ breast cancer cell lines including ATCC and NCI. Abexinostat potentiates the anti-tumor activity of tamoxifen in vitro in ER+ breast cancer cells, by down-regulation of ER protein expression and its pro-growth response genes (PgR, Cyclin D). It abrogates AKT cell signaling by directly down-regulating AKT1 at the transcriptional and post-translational level. Furthermore, cell death is induced by activating the apoptotic program. Study design: phase I dose-finding of abexinostat for 4 consecutive days each week of a 3-week cycle given in combination with daily tamoxifen at 20 mg. Dose levels of abexinostat, 120, 140 and 160 mg bid, of 3 to 6 patients will be explored. Two dose de-escalation levels (100/80 mg) are allowed depending on toxicity. Dose-Limiting Toxicities assessment will be done at the end of cycle 2. Once the Maximum Tolerated Dose is determined up to 20 additional patients will be treated at the recommended dose in a confirmatory cohort. Main eligibility criteria: Female≥ 18 years with histologically confirmed primary adenocarcinoma of the breast; ER+ (IHC≥ 10%), HER2- tumors. Patients must have had tumor progression on an AI administered for advanced/metastatic disease OR recurrence while on or within 12 months of completion of adjuvant AI, OR recurrence within 12 months of adjuvant tamoxifen completion and must have had up to 3 prior chemotherapy regimens in metastatic/advanced setting. Patients must have progressive tumor measurable or evaluable (RECIST criteria version 1.1). Main objectives: Primary: to assess the safety and the tolerability of the combination treatment and to determine a recommended Phase II dose. Secondary: to determine the pharmacokinetic profile of both the drugs in combination and metabolites; to measure tumor response to the combination; to measure drug target inhibition by assessing acetylation state of histones proteins, HbF level and HDAC2 expression in peripheral blood mononuclear cells and in peripheral blood samples; to assess circulating tumor cells; to analyze biomarkers on tissue sample and pharmacogenomic of genes implicated in the metabolism of combination (optional). Status: Study opened in September 2012, currently recruiting. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT1-4-05.

Abexinostat, an oral pan-histone deacetylase inhibitor (HDACi), was evaluated in patients with advanced solid tumours in two single agent phase I studies (PCYC-402 and CL1-78454-002). In PCYC-402 study testing four different administration schedules, the maximum tolerated dose (MTD) was established at 75 mg/m(2) BID (twice daily) and the recommended dose at 60 mg/m(2) BID regardless of the schedule tested. The dose limiting toxicity (DLT), consistently observed across all these schedules, was reversible thrombocytopenia. The CL1-78454-002 study was initially investigating an additional schedule of 14 days on/7 days off. While testing two first cohorts, thrombocytopenia was observed without reaching DLT. To address this issue, a pharmacokinetic/pharmacodynamic (PK/PD) model was used to predict the optimal schedule allowing higher doses with minimal thrombocytopenia. Several administration schedules were simulated using this model. A 4 days on/3 days off schedule was associated with the smallest platelet decrease. Accordingly, the CL1-78454-002 study was amended. After reaching MTD1 (75 mg/m(2) BID) with the initial schedule, subsequent cohorts received abexinostat on a revised schedule of 4 days on/3 days off, starting at one dose level below MTD1 (60 mg/m(2) BID). As expected, the dose-escalation continued for two more dose levels beyond MTD1. The MTD2 reached for this optimised schedule was 105 mg/m(2) BID and the recommended dose 90 mg/m(2) BID. In conclusion, early understanding of toxicities and PK determination allowed us to build a PK/PD model of thrombocytopenia, which predicted the optimal administration schedule. This optimised schedule is currently used in the trials in solid tumours with abexinostat.

Histone deacetylase inhibitors (HDACi) have been actively explored as anti-cancer agents due to their ability to prevent deacetylation of histones, resulting in uncoiling of chromatin and stimulation of a range of genes associated in the regulation of cell survival, proliferation, differentiation and apoptosis. During the past several years, many HDACi have entered pre-clinical or clinical research as anti-cancer agents with satisfying results. Out of these, more than 8 novel hydroxamic acid based HDACi i.e., belinostat, abexinostat, SB939, resminostat, givinostat, quisinostat, pentobinostat, CUDC-101 are in clinical trials and one of the drug vorinostat (SAHA) has been approved by US FDA for cutaneous T-cell lymphoma (CTCL). It is clear from the plethora of new molecules and the encouraging results from clinical trials that this class of HDAC inhibitors hold a great deal of promise for the treatment of a variety of cancers. In this review, we classified the hydroxamic acid based HDACi on the basis of their structural features into saturated, unsaturated, branched, un-branched and 5, 6-membered cyclic ring linker present between zinc binding group and connecting unit. The present article enlists reports on hydroxamic acid based HDACi designed and developed using concepts of medicinal chemistry, demonstrating that hydroxamate derivatives represent a versatile class of compounds leading to novel imaging and therapeutic agents. This article will also provide a complete insight into various structural modifications required for optimum anticancer activity.

A population pharmacokinetic/pharmacodynamic (PK/PD) model was developed to describe the thrombocytopenia (dose-limiting toxicity) of abexinostat, a new histone deacetylase inhibitor. An optimal administration schedule of the drug was determined using a simulation-based approach. Early PK and PK/PD data were analysed using a sequential population modeling approach (NONMEM 7), allowing for the description of a PK profile and platelet-count decrease after abexinostat administration with various administration schedules. Simulations of platelet count with several administration schedules over 3-week treatment cycles (ASC) and over a day (ASD) were computed to define the optimal schedule that limits the depth of thrombocytopenia. An intermediate PK/PD model accurately described the data. The administration of abexinostat during the first 4 days of each week in a 3-week cycle resulted in fewer adverse events (with no influence of ASD on platelet count profiles), and corresponded to the optimal treatment schedule. This administration schedule was clinically evaluated in a phase I clinical trial and allowed for the definition of a new maximum tolerated dose (MTD), leading to a nearly 30% higher dose-intensity than that of another previously tested schedule. Lastly, a final model was built using all of the available data. The final model, characterizing the dose-effect and the dose-toxicity relationships, provides a useful modeling tool for clinical drug development.

Characterization of long-term responders in a phase I trial evaluating the role of epigenetic modulation of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor by using a histone deacetylase abexinostat in combination with pazopanib to enhance response and reverse resistance. Patients and Methods: Pazopanib was administered once a day on days 1 to 28 and abexinostat was administered orally twice a day on days 1 to 5, 8 to 12, and 15 to 19 (schedule A) or on days 1 to 4, 8 to 11, and 15 to 18 (schedule B). Dose escalation (3 + 3 design) in all solid tumors was followed by dose expansion in renal cell carcinoma (RCC). Histone acetylation and HDAC2 expression were correlated long-term responders, >1y). Results: Fifty-one patients including RCC (N = 22) were enrolled, including 30 (59%) with one or more lines of prior VEGF-targeting therapy. Toxicities and PK studies were reported previously. 7 pts had response > 23 months (23-60+), including 5/22 patients with RCC, and one patient with medullary thyroid and thymic neurondocrine cancer. Long-term response was associated with high HDAC2 expression in PBMCs, increased histone acetylation, and modulation of VEGF level. Conclusion: Epigenetic modulation with HDAC inhibitors is strongly dependent on host factors to promote long-term benefit to abexinostat and pazopanib in pretreated patients. Citation Format: Rahul Aggarwal, Nela Pawlowsk, Jennifer Grabowsky, Armand Harb, Kamran Abri-Lavasani, Scott Thomas, Pamela N. Munster. Long-term responders to epigenetic modulators: abexinostat and pazopanib [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A173.

International audience; Background We determined the safety, pharmacokinetics, pharmacodynamics, and antitumour activity of abexinostat in B-cell lymphoma or chronic lymphocytic leukaemia. Patients and methods Thirty-five patients received oral abexinostat 30, 45, or 60 mg/m(2) bid in a 3 + 3 design in three 21-day schedules: 14 days on treatment in schedule 1 (D1-14); 10 days in schedule 2 (D1-5 and D8-12); and 12 days in schedule 3 (D1-4, D8-11, and D15-18). Safety, tumour response, plasma concentration, and histone H3 acetylation were measured. Results Two dose-limiting toxicities occurred in each schedule (one grade 3 febrile neutropenia; five grade 4 thrombocytopenia) at 60 mg/m(2) bid (maximal tolerated dose). The recommended dose was 45 mg/m(2) bid; schedule 1 was considered optimal. Non-haematological drug-related toxicities included grade 1 or 2 diarrhoea (43%), nausea (23%), and vomiting (11%); haematological toxicities included thrombocytopenia (31% grade 3, and 26% grade 4), which remained manageable and reversible on withdrawal. Of 29 evaluable patients, there were 2 complete and 6 partial responses; median duration of response was 14.6 months (range 3-16.5 months) (1 cycle is equivalent to 0.75 months). There was no evidence for nonlinear pharmacokinetics. There was a correlation between dose and histone acetylation. Conclusion Abexinostat has manageable toxicity and induced some durable complete and partial responses in B-cell lymphoma or chronic lymphocytic leukaemia. Our results suggest most favourable responses in patients with follicular lymphoma, though further research would be needed to confirm this finding.

In this study, we investigated the cytotoxic effects of a broad-spectrum histone deacetylase (HDAC) inhibitor, PCI-24781, alone and in combination with the proteasome inhibitor bortezomib in neuroblastoma cell lines. The combination was shown to induce synergistic cytotoxity involving the formation of reactive oxygen species. The cleavage of caspase-3 and PARP, as determined by western blotting, indicated that cell death was primarily due to apoptosis. Xenograft mouse models indicated increased survival among animals treated with this combination. The Notch signaling pathway and MYCN gene expression were quantified by reverse transcription-polymerase chain reaction (PCR) in cells treated with PCI-24781 and bortezomib, alone and in combination. Notch pathway expression increased in response to an HDAC inhibitor. NFKB1 and MYCN were both significantly down regulated. Our results suggest that PCI-24781 and bortezomib are synergistic in neuroblastoma cell lines and may be a new therapeutic strategy for this disease.

Several publications have suggested that histone deacetylase inhibitors (HDACis) could reverse the repression of estrogen receptor alpha (ERα) in triple-negative breast cancer (TNBC) cell lines, leading to the induction of a functional protein. Using different HDACis, vorinostat, panobinostat, and abexinostat, we therefore investigated this hypothesis in various human TNBC cell lines and patient-derived xenografts (PDXs). We used three human TNBC cell lines and three PDXs. We analyzed the in vitro toxicity of the compounds, their effects on the hormone receptors and hormone-related genes and protein expression both in vitro and in vivo models. We then explored intra-tumor histone H3 acetylation under abexinostat in xenograft models. Despite major cytotoxicity of all tested HDAC inhibitors and repression of deactylation-dependent CCND1 gene, neither ERα nor ERβ, ESR1 or ESR2 genes respectively, were re-expressed in vitro. In vivo, after administration of abexinostat for three consecutive days, we did not observe any induction of ESR1 or ESR1-related genes and ERα protein expression by RT-qPCR and immunohistochemical methods in PDXs. This observation was concomitant to the fact that in vivo administration of abexinostat increased intra-tumor histone H3 acetylation. These observations do not allow us to confirm previous studies which suggested that HDACis are able to convert ER-negative (ER−) tumors to ER-positive (ER+) tumors, and that a combination of HDAC inhibitors and hormone therapy could be proposed in the management of TNBC patients.

Background In the clinical development of oncology drugs, the recommended dose is usually determined using a 3 + 3 dose-escalation study design. However, this phase I design does not always adequately describe dose-toxicity relationships. Methods 125 patients, with either solid tumours or lymphoma, were included in the study and 1217 platelet counts were available over three treatment cycles. The data was used to build a population pharmacokinetic/pharmacodynamic (PKPD) model using a sequential modeling approach. Model-derived Recommended Doses (MDRD) of abexinostat (a Histone Deacetylase Inhibitor) were determined from simulations of different administration schedules, and the higher bound for the probability of reaching these MDRD with a 3 + 3 design were obtained. Results The PKPD model developed adequately described platelet kinetics in both patient populations with the inclusion of two platelet baseline counts and a disease progression component for patients with lymphoma. Simulation results demonstrated that abexinostat administration during the first 4 days of each week in a 3-week cycle led to a higher MDRD compared to the other administration schedules tested, with a maximum probability of 40 % of reaching these MDRDs using a 3 + 3 design. Conclusions The PKPD model was able to predict thrombocytopenia following abexinostat administration in both patient populations. A model-based approach to determine the recommended dose in phase I trials is preferable due to the imprecision of the 3 + 3 design.

EBV-related nasopharyngeal carcinomas (NPCs) still raise serious therapeutic problems. The therapeutic potential of the histone-deacetylase (HDAC) inhibitor Abexinostat was investigated using 5 preclinical NPC models including 2 patient-derived xenografts (C15 and C17). The cytotoxicity of Abexinostat used either alone or in combination with cis-platin or irradiation was assessed in vitro by MTT and clonogenic assays using 2 EBV-negative (CNE1 and HONE1) and 3 EBV-positive NPC models (C15, C17 and C666-1). Subsequently, the 3 EBV-positive models were used under the form of xenografts to assess the impact of systemic treatments by Abexinostat or combinations of Abexinostat with cis-platin or irradiation. Several cell proteins known to be affected by HDAC inhibitors and the small viral non-coding RNA EBER1 were investigated in the treated tumors. Synergistic cytotoxic effects of Abexinostat combined with cis-platin or irradiation were demonstrated in vitro for each NPC model. When using xenografts, Abexinostat by itself (12.5 mg/kg, BID, 4 days a week for 3 weeks) had significant anti-tumor effects against C17. Cooperative effects with cis-platin (2 mg/kg, IP, at days 3, 10 and 17) and irradiation (1 Gy) were observed for the C15 and C17 xenografts. Simultaneously two types of biological alterations were induced in the tumor tissue, especially in the C17 model: a depletion of the DNA-repair protein RAD51 and a stronger in situ detection of the small viral RNA EBER1. Overall, these results support implementation of phase I/II clinical trials of Abexinostat for the treatment of NPC. A depletion of RAD51 is likely to contribute to the cooperation of Abexinostat with DNA damaging agents. Reduction of RAD51 combined to enhanced detection of EBER 1 might be helpful for early assessment of tumor response.

Purpose: Cancer stem cells (CSC) are the tumorigenic cell population that has been shown to sustain tumor growth and to resist conventional therapies. The purpose of this study was to evaluate the potential of histone deacetylase inhibitors (HDACi) as anti-CSC therapies. Experimental Design: We evaluated the effect of the HDACi compound abexinostat on CSCs from 16 breast cancer cell lines (BCL) using ALDEFLUOR assay and tumorsphere formation. We performed gene expression profiling to identify biomarkers predicting drug response to abexinostat. Then, we used patient-derived xenograft (PDX) to confirm, in vivo, abexinostat treatment effect on breast CSCs according to the identified biomarkers. Results: We identified two drug-response profiles to abexinostat in BCLs. Abexinostat induced CSC differentiation in low-dose sensitive BCLs, whereas it did not have any effect on the CSC population from high-dose sensitive BCLs. Using gene expression profiling, we identified the long noncoding RNA Xist (X-inactive specific transcript) as a biomarker predicting BCL response to HDACi. We validated that low Xist expression predicts drug response in PDXs associated with a significant reduction of the breast CSC population. Conclusions: Our study opens promising perspectives for the use of HDACi as a differentiation therapy targeting the breast CSCs and identified a biomarker to select patients with breast cancer susceptible to responding to this treatment. Clin Cancer Res; 19(23); 6520–31. ©2013 AACR.

Hydroxamate-based histone deacetylase inhibitors (Hb-HDACIs), such as vorinostat, belinostat and panobinostat, have been previously shown to have a wide range of activity in hematologic malignancies such as cutaneous T-cell lymphoma and multiple myeloma. Recent data show that they synergize with a variety of cytotoxic and molecular targeted agents in many different solid tumors, including breast, prostate, pancreatic, lung and ovarian cancer. Hb-HDACIs have a quite good toxicity profile and are now being tested in phase I and II clinical trials in solid tumors with promising results in selected neoplasms, such as hepatocarcinoma. This review will focus on their clinical activity and safety in patients with advanced solid neoplasms.