KD5170, a novel mercaptoketone-based histone deacetylase inhibitor that exhibits broad spectrum antitumor activity in vitro and in vivo.

Histone deacetylase (HDAC) inhibitors have garnered significant attention as cancer drugs. These therapeutic agents have recently been clinically validated with the market approval of vorinostat (SAHA, Zolinza) for treatment of cutaneous T-cell lymphoma. Like vorinostat, most of the small-molecule HDAC inhibitors in clinical development are hydroxamic acids, whose inhibitory activity stems from their ability to coordinate the catalytic Zn2+ in the active site of HDACs. We sought to identify novel, nonhydroxamate-based HDAC inhibitors with potentially distinct pharmaceutical properties via an ultra-high throughput small molecule biochemical screen against the HDAC activity in a HeLa cell nuclear extract. An alpha-mercaptoketone series was identified and chemically optimized. The lead compound, KD5170, exhibits HDAC inhibitory activity with an IC50 of 0.045 micromol/L in the screening biochemical assay and an EC50 of 0.025 micromol/L in HeLa cell-based assays that monitor histone H3 acetylation. KD5170 also exhibits broad spectrum classes I and II HDAC inhibition in assays using purified recombinant human isoforms. KD5170 shows significant antiproliferative activity against a variety of human tumor cell lines, including the NCI-60 panel. Significant tumor growth inhibition was observed after p.o. dosing in human HCT-116 (colorectal cancer), NCI-H460 (non-small cell lung carcinoma), and PC-3 (prostate cancer) s.c. xenografts in nude mice. In addition, a significant increase in antitumor activity and time to end-point occurred when KD5170 was combined with docetaxel in xenografts of the PC-3 prostate cancer cell line. The biological and pharmaceutical profile of KD5170 supports its continued preclinical and clinical development as a broad spectrum anticancer agent.

Inhibition of inducible nitric oxide synthase expression by a novel small molecule activator of the unfolded protein response.

The transcription of inducible nitric oxide synthase (iNOS) is activated by a network of proinflammatory signaling pathways. Here we describe the identification of a small molecule that downregulates the expression of iNOS mRNA and protein in cytokine-activated cells and suppresses nitric oxide production in vivo. Mechanistic analysis suggests that this small molecule, erstressin, also activates the unfolded protein response (UPR), a signaling pathway triggered by endoplasmic reticulum stress. Erstressin induces rapid phosphorylation of eIF2alpha and the alternative splicing of XBP-1, hallmark initiating events of the UPR. Further, erstressin activates the transcription of multiple genes involved in the UPR. These data suggest an inverse relationship between UPR activation and iNOS mRNA and protein expression under proinflammatory conditions.

HIF-1 in cell cycle regulation, apoptosis, and tumor progression.

Cells in a low oxygen, or hypoxic, microenvironment must have the ability to sense oxygen levels in the nucleus in order to maintain oxygen homeostasis by gene regulation. Hypoxia inducible factor-1 (HIF-1) serves as a molecular bridge between the sensation and utilization of oxygen, and thus functions as a key player in oxygen homeostasis. HIF-1 is a heterodimeric transcription factor and is composed of two subunits, the oxygen-sensitive HIF-1alpha and constitutively expressed HIF-1beta. HIF-1 regulates the expression of a broad range of genes that facilitate acclimation to low oxygen conditions by changes in protein levels in circulation, metabolism, and proliferation. Appropriate temporal and spatial activation of HIF-1 is crucial not only in developmental and physiological processes, characterized by programmed cellular proliferation, but also in pathophysiological conditions such as tumorigenesis, which exhibit unregulated cellular proliferation. However, many contradictory reports as to the role of HIF-1 in the regulation of cellular proliferation have been put forward in recent years. In this review, our first aim is to summarize the current knowledge of oxygen-dependent HIF-1 activation mechanisms based on its structure. Then we will describe the proposed mechanisms through which HIF-1 regulates cellular proliferation of different cell types, including tumor cells as well as non-transformed, nonimmortalized cells under normoxic and hypoxic conditions.