Jinxia Deng

Small molecule inhibitors of Stat3 signaling pathway

Constitutive activation of the Signal Transducers and Activators of Transcription 3 (Stat3) meditated signaling pathway is very important for cell growth and survival. Compelling evidence from mechanistic studies with antisense, RNA interference (RNAi), peptides, and small molecular inhibitors indicate that blocking Stat3 signaling can lead to successful suppression of tumor cell growth and apoptosis. Thus, Stat3 is an attractive molecular target for the development of novel cancer therapeutics. In this article, we present the first comprehensive review focusing on small molecule inhibitors that effectively block the Stat3 signaling pathway. These inhibitors, from a structural point of view, are divided into five classes of compounds. They include (1) natural products and derivatives, such as curcumin, resveratrol and others, (2) tyrphostins, (3) platinum-containing complexes, (4) peptidomimetics, and (5) azaspiranes. Some compounds may have multiple targets including Stat3 protein, therefore these compounds need further optimization and validation. The purpose of this review is to provide a resource for researchers interested in Stat3 targeted small molecules which will be beneficial for database development and template design for future drug development.

Preclinical Evaluation of Novel Triphenylphosphonium Salts with Broad-Spectrum Activity

Background Recently, there has been a surge of interest in developing compounds selectively targeting mitochondria for the treatment of neoplasms. The critical role of mitochondria in cellular metabolism and respiration supports this therapeutic rationale. Dysfunction in the processes of energy production and metabolism contributes to attenuation of response to pro-apoptotic stimuli and increased ROS production both of which are implicated in the initiation and progression of most human cancers. Methodology/Principal Findings A high-throughput MTT-based screen of over 10,000 drug-like small molecules for anti-proliferative activity identified the phosphonium salts TP187, 197 and 421 as having IC50 concentrations in the submicromolar range. TP treatment induced cell cycle arrest independent of p53 status, as determined by analysis of DNA content in propidium iodide stained cells. In a mouse model of human breast cancer, TP-treated mice showed significantly decreased tumor growth compared to vehicle or paclitaxel treated mice. No toxicities or organ damage were observed following TP treatment. Immunohistochemical staining of tissue sections from TP187-treated tumors demonstrated a decrease in cellular proliferation and increased caspase-3 cleavage. The fluorescent properties of analog TP421 were exploited to assess subcellular uptake of TP compounds, demonstrating mitochondrial localization. Following mitochondrial uptake cells exhibited decreased oxygen consumption and concomittant increase in mitochondrial superoxide production. Proteomics analysis of results from a 600 target antibody microarray demonstrated that TP compounds significantly affected signaling pathways relevant to growth and proliferation. Conclusions/Significance Through our continued interest in designing compounds targeting cancer-cell metabolism, the Warburg effect, and mitochondria we recently discovered a series of novel, small-molecule compounds containing a triphenylphosphine moiety that show remarkable activity in a panel of cancer cell lines as well as in a mouse model of human breast cancer. The mechanism of action includes mitochondrial localization causing decreased oxygen consumption, increased superoxide production and attenuated growth factor signaling.

Pharmacophore Guided Discovery of Small-Molecule Human Apurinic/Apyrimidinic Endonuclease 1 Inhibitors

Human apurinic/apyrimidinic endonuclease 1 (APE1) is an important enzyme in the base excision repair (BER) pathway that is essential for the repair of abasic sites in the genome. Evidence for APE1 as an attractive therapeutic target in anticancer drug development has been demonstrated by studies that link overexpression of APE1 in many cancers to resistance of tumor cells to radio- and chemotherapy. APE1 also shows a protective effect in several cancer cell models to a variety of DNA damaging agents. This study represents the first rational design of selective small-molecule APE1 inhibitors utilizing a three-dimensional interaction-based pharmacophore perception. All of our most potent molecules show inhibitory activity below 10 muM and are selective for APE1 inhibition.

Novel opportunities for thymidylate metabolism as a therapeutic target

For over 40 years, the fluoropyrimidine 5-fluorouracil (5-FU) has remained the central agent in therapeutic regimens employed in the treatment of colorectal cancer and is frequently combined with the DNA-damaging agents oxaliplatin and irinotecan, increasing response rates and improving overall survival. However, many patients will derive little or no benefit from treatment, highlighting the need to identify novel therapeutic targets to improve the efficacy of current 5-FU-based chemotherapeutic strategies. dUTP nucleotidohydrolase (dUTPase) catalyzes the hydrolysis of dUTP to dUMP and PPi, providing substrate for thymidylate synthase (TS) and DNA synthesis and repair. Although dUTP is a normal intermediate in DNA synthesis, its accumulation and misincorporation into DNA as uracil is lethal. Importantly, uracil misincorporation represents an important mechanism of cytotoxicity induced by the TS-targeted class of chemotherapeutic agents including 5-FU. A growing body of evidence suggests that dUTPase is an important mediator of response to TS-targeted agents. In this article, we present further evidence showing that elevated expression of dUTPase can protect breast cancer cells from the expansion of the intracellular uracil pool, translating to reduced growth inhibition following treatment with 5-FU. We therefore report the implementation of in silico drug development techniques to identify and develop small-molecule inhibitors of dUTPase. As 5-FU and the oral 5-FU prodrug capecitabine remain central agents in the treatment of a variety of malignancies, the clinical utility of a small-molecule inhibitor to dUTPase represents a viable strategy to improve the clinical efficacy of these mainstay chemotherapeutic agents. [Mol Cancer Ther 2008;7(9):3029–37]

Design of second generation HIV-1 integrase inhibitors

The prospect of HIV-1 integrase (IN) as a therapeutically viable retroviral drug target is on the verge of realization. The observed preclinical and clinical performance of beta-diketo containing and naphthyridine carboxamide compounds provides direct proof for the clinical application of IN inhibition. These validated lead compounds are useful in the design and development of second generation IN inhibitors. The results from preclinical and clinical studies on the first generation IN inhibitors reiterate a demand for novel second generation inhibitors with improved pharmacokinetic and metabolic properties. Pharmacophore-based drug design techniques facilitate the discovery of novel compounds on the basis of validated lead compounds specific for a drug target. In this article we have comprehensively reviewed the application of pharmacophore-based drug design methods in the field of IN inhibitor discovery.

Patented small molecule inhibitors of p53–MDM2 interaction

The interaction between p53 and murine double minute 2 (MDM2) provides an attractive drug target in oncology. Small molecule inhibitors of this interaction have not only provided strong evidence for blocking the protein–protein interaction, but are also extremely useful as biological probes and ultimately as novel therapeutics. Here, a comprehensive review of the patented small molecule inhibitors of the p53–MDM2 interaction are provided. These inhibitors are divided into eight classes of compounds that include cis-imidazolines, benzodiazepines, fused indoles, substituted piperazines, substituted piperidines, aryl boronic acids, spiro-indoles, and α-helix mimetic compounds. The best documented class of compounds, cis-imidazolines (e.g., Nutlins) are selective and potent inhibitors of the p53–MDM2 interaction, and selected examples exhibit potency in the nanomolar range. Nutlins induce apoptosis in p53 wild-type cells and show in vivo efficacy in mice xenograft models. Additional strategies briefly discussed in this review, and which are under current exploration in targeting the p53 pathway, include the inhibition of MDM2-mediated p53 ubiquitylation and restoration of DNA-binding activity of mutant p53 protein using small molecules.

Discovery of Novel Anticancer Compounds Based on a Quinoxalinehydrazine Pharmacophore

Quinoxalinehydrazines represent a novel class of compounds with excellent potency in a panel of cancer cell lines. A prototype compound, SC144, showed significant in vivo efficacy in mice xenograft models of human breast cancer cells. The subsequent structure–activity relationship study resulted in the discovery of SC161 with better potency in cancer cell lines. Further exploring the possible conformational space by a 10 ns molecular dynamics simulation as presented herein, resulted in various pharmacophore orientations. The trajectory analysis indicated that in most of the simulation time, the molecule stays favorably in a compact planarlike orientation. We therefore built a pharmacophore model based on the cluster containing the highest number of frames to represent the most probable orientation. The model was used to screen a subset of our small molecule database containing 350,000 compounds. We selected 35 compounds for the initial cytotoxicity screen. Seventeen compounds belonging to oxadiazolopyrazine and quinoline class displayed cytotoxicity in various cancer cell lines. Five of them, compounds 2, 6, 15, 16, and 19, all bearing an oxadiazolopyrazine scaffold, showed IC50 values <3 μM in certain tumor cell lines. The most potent compound, 2, showed IC50 values <2 μM in HCT116 p53+/+, HCT116 p53−/−, and HEY cells, and 8 μM in NIH3T3 cells. This study shows that conformational sampling of a lead small molecule followed by representative pharmacophore model development is an efficient approach for the rational design of novel anticancer agents with similar or better potency than the original lead but with different physicochemical properties.

Abstract 2542: Preclinical studies of novel phosphonium salts with broad-spectrum activity

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Proliferation under selective pressures exerted by an unstable microenvironment, requires tumor cells employ adaptive mechanisms that confer growth advantage. Adaptation to adverse conditions results in cellular phenotypes that typify neoplastic transformation and offer unique opportunities for selective targeting of cancer cells. Agents that target tumor cell mitochondria with high selectivity hold clinical significance due to the adaptive, modulatory and essential role of this organelle in cancer cell energy production, metabolism and apoptosis. To this end, we have identified a series of novel, mitochondriotropic phosphonium salts, (TP compounds), that have shown broad-spectrum anti-cancer and anti-angiogenic activity in preclinical evaluation. A high-throughput MTT-based screen of over 10,000 drug-like small molecules for anti-proliferative activity identified the phosphonium salts TP187, 197 and 421 and numerous close analogues as having IC50 concentrations in the sub-micromolar range. TP treatment induced cell cycle arrest, lowered oxygen consumption, and increased mitochondrial superoxide production. Administered as single agents in a mouse model of human breast cancer, TP compounds significantly decreased tumor growth with no observed toxicities. Protein microarray data demonstrated significant down-regulation of integrin and growth factor mediated signaling pathways governing key processes including cancer cell survival, proliferation and tumor angiogenesis. At low micromolar concentrations, TP compounds prevented integrin-mediated cell adhesion to fibronectin and vitronectin coated substrates and tumor cell haptotaxsis on vitronectin coated boyden chambers. Similar concentrations of TP compound also prevented growth factor induced endothelial cell tube formation in 3-D culture using basement membrane extracts. Taken together, these results suggest that as mitochondria-targeted agents, TP compounds act to inhibit tumor cell proliferation and angiogenic capacity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2542. doi:10.1158/1538-7445.AM2011-2542