Evaluation of entinostat alone and in combination with standard‐of‐care cytotoxic agents against rhabdomyosarcoma xenograft models

Abstract

Background: Entinostat, a selective class I histone deacetylase inhibitor, has been reported to enhance the activity of cytotoxic agents and suppress expression of PAX3-FOXO1 in alveolar rhabdomyosarcoma (ARMS). Procedures: Entinostat was tested against three rhabdomyosarcoma cell lines using 96-hour drug exposure. Entinostat alone or in binary combination with vincristine, actinomycin D or cyclophosphamide was tested in ARMS and two embryonal rhabdomyosarcoma (ERMS) xenograft models. Tumor growth was measured at weekly intervals. Drug-induced changes in acetylated histone H3(K9) and entinostat pharmacokinetics were determined. Results: In vitro, the IC50 concentration of entinostat ranged from 280 to 1300 nM. In vivo, entinostat significantly inhibited the growth of only Rh10 xenografts. For most studies, entinostat did not potentiate the activity of the cytotoxic agent. Exceptions included the vincristine and entinostat combination for Rh10 and the entinostat and actinomycin D combination for Rh10 and Rh18, although the effects were modest. For Rh18, the combination of entinostat with vincristine showed evidence of an antagonistic interaction compared with single-agent vincristine. Pharmacokinetic studies showed the average Cmax was 569.4 ng/mL (1.51 μM) with Tmax at 15 minutes, and total exposure (AUC0–12 h) was 435.6 h × ng/mL. Entinostat treatment increased acetylated histone H3. Conclusions: Entinostat demonstrated modest antitumor activity in only one of four models at dose and shedule that gave drug exposures relevant to human treatment. The addition of entinostat to standard-of-care cytotoxic agents was in most instances no more effective than the cytotoxic agents used alone. Entinostat demonstrated target inhibition with increased histone 2A acetylation.

Histone deacetylase inhibitors dysregulate DNA repair proteins and antagonize metastasis-associated processes

“…This also applies to the doses that can be achieved without significant toxicity in RCC patients. A recent report found that up to 1.51 µM MS-275 was achieved without gross toxicity in mice, but large variation of maximal plasma concentrations from 4 to 53.1 ± 92.4 and a half-life from 33.4 to 150 h occurred in humans (Connolly et al 2017;Kurmasheva et al 2019), indicating unexplained large patient-to-patient variability. The maximum-tolerated dose of VPA was reported to range, for example, from 50 mg/kg daily to 140 mg/kg/day, which is within the therapeutic serum concentrations of VPA from 0.35 to 0.7 mM (Bug et al 2005;Münster et al 2007;Phiel et al 2001).…”

A phase 1 study of entinostat in children and adolescents with recurrent or refractory solid tumors, including CNS tumors: Trial ADVL1513, Pediatric Early Phase‐Clinical Trial Network (PEP‐CTN)

“…Recently, entinostat was also evaluated in combination with chemotherapy in mouse models for rhabdomyosarcoma and was not found to enhance the standard therapy 17 . Preclinical studies with entinostat have found a synergistic effect with check point inhibitors and in combination with hormonal therapy for patients with homone receptor‐positive, HER2‐negative breast cancers, but clinical trials have yet to demonstrate a clinical benefit 18–21 . As more preclinical data in immunomodulation in pediatric solid tumors becomes available the role of entinostat in immunomodulation and if a synergistic effect will need to be explored.…”

Induction of a SALL4-dependency for targeted cancer therapy

“…We next evaluated whether this sequential drug treatment strategy would work in vivo. H1299 cells were implanted into non-obese diabetic scid gamma (NSG) mice and treated with sequential injections of DAC and ENT both at a dose of 2.5 mg/kg according to published protocols ( Figure 5D) (35)(36)(37). As shown in Figure 5D-E, tumors were monitored and measured on day 17, 24, and day 31, and were harvested on day 32 after various treatments.…”