Combining PCI-24781, a Novel Histone Deacetylase Inhibitor, with Chemotherapy for the Treatment of Soft Tissue Sarcoma

Abstract

Purpose: Histone deactylase inhibitors (HDACi) are a promising new class of anticancer therapeutics; however, little is known about HDACi activity in soft tissue sarcoma (STS), a heterogeneous cohort of mesenchymal origin malignancies. Consequently, we investigated the novel HDACi PCI-24781, alone/in combination with conventional chemotherapy, to determine its potential anti-STS-related effects and the underlying mechanisms involved. Experimental Design: Immunoblotting was used to evaluate the effects of PCI-24781 on histone and nonhistone protein acetylation and expression of potential downstream targets. Cell culture-based assays were utilized to assess the effects of PCI-24781 on STS cell growth, cell cycle progression, apoptosis, and chemosensitivity. Quantitative reverse transcription-PCR, chromatin immunoprecipitation, and reporter assays helped elucidate molecular mechanisms resulting in PCI-24781-induced Rad51 repression. The effect of PCI-24781, alone or with chemotherapy, on tumor and metastatic growth was tested in vivo using human STS xenograft models. Results: PCI-24781 exhibited significant anti-STS proliferative activity in vitro, inducing S phase depletion, G 2 /M cell cycle arrest, and increasing apoptosis. Superior effects were seen when combined with chemotherapy. A PCI-24781-induced reduction in Rad51, a major mediator of DNA double-strand break homologous recombination repair, was shown and may be a mechanism underlying PCI-24781 chemosensitization. We showed that PCI-24781 transcriptionally represses Rad51 through an E2F bindingsite on the Rad51 proximal promoter. Although single-agent PCI-24781 had modest effects on STS growth and metastasis, marked inhibition was observed when combined with chemotherapy. Conclusions: In light of these findings, this novel molecular-based combination may be applicable to multiple STS histologic subtypes, and potentially merits rigorous evaluation in human STS clinical trials.Antimetastatic soft tissue sarcoma (STS) systemic therapies remain elusive, resulting in 50% 5-year overall survival rates remaining stagnant for at least 30 years (1). New approaches are urgently needed yet difficult to develop because STS are rare and typified by marked intratumor and intertumor heterogeneity (2), rendering identification of specific STS subtype molecular "addictions" and their inhibition problematic (3). Alternatively, identifying target pathways that serve as convergence points for multiple STS subtypes is appealing; histone deacytelase inhibition is one such potential therapeutic strategy not yet explored in STS (4).Chromatin structure is affected by posttranslational core-histone modifications, including acetylation and deacetylation (5). Core-histone acetylation states, important for chromatin structure, function, and gene expression, are controlled by opposing actions of histone acetyl transferase enzymes and histone deacetylases (HDAC; ref. 6). The histone acetyl transferase enzymes:HDAC balance is crucial for normal cell growth maintenance; deregulat...

Phase 1 study of the oral histone deacetylase inhibitor abexinostat in patients with Hodgkin lymphoma, non-Hodgkin lymphoma, or chronic lymphocytic leukaemia

“…It inhibits growth and induces apoptosis in various tumour cell lines [10][11][12][13][14]. Abexinostat is being tested in patients with refractory solid tumours or haematological malignancies.…”

PCI-24781 (abexinostat), a novel histone deacetylase inhibitor, induces reactive oxygen species-dependent apoptosis and is synergistic with bortezomib in neuroblastoma

“…PCI-24781 (abexinostat; Pharmacyclics, Inc.) is a novel, second-generation phenyl hydroxamic acid–based, orally bioavailable HDAC inhibitor that has previously been shown to have activity in vitro and in vivo against a broad array of cancers, including hematopoietic malignancies and bone and soft-tissue sarcomas (13, 22–24). It has also shown good tolerability and activity in Phase I and II clinical trials against lymphoma, as well as against solid tumors in Phase-I trials (25).…”

Chromatin Modifications Associated with DNA Double-strand Breaks Repair as Potential Targets for Neurological Diseases

“…Interestingly, the effects of HDAC inhibition on E2F1 activity and on the expression of its target genes, appears to be cell type-specific. In cancer cells, HDAC inhibition decreases the recruitment of E2F1 to DNA repair genes such as Rad51, Brca1 or Chk1, and represses their expression [39,41,44,45]. On the contrary, in noncancerous cells, E2F1 transcriptional targets are activated in response to HDAC inhibition [42]; for example, HDAC inhibition by trichostatin A or sodium butyrate increases E2F1 expression in neurons [40].…”