Development of Anticancer Agents

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Development of immunomodulatory drugs: The antiangiogenic properties of thalidomide reported by D'Amato and colleagues prompted its clinical evaluation in various solid tumors, including prostate cancer. Thalidomide has demonstrated clinical activity in various malignancies affecting immunomodulatory and angiogenesis pathways. The development of novel thalidomide analogs with improved efficacy and decreased toxicity is an ongoing research effort in our laboratory. Previously, we showed that one of the products of cytochrome P450 2C19 isozyme biotransformation of thalidomide, 5'-OH-thalidomide, is responsible for the drug's antiangiogenic activity. Based on the chemical structure of this metabolite, we collaborate with Drs. Nigel Greig (NIA, NIH) and Michael Gutschow to synthesize novel thalidomide analogs, evaluate them using in vitro and in vivo models to assess activity, and characterize their structure-activity-relationships for further rational drug design. We have synthesized over 315 novel analogs of thalidomide and screened them for inhibition of inflammation and angiogenesis using various in vitro, ex vivo, and in vivo drug development models (e.g., rat aorta ring model, human saphenous vein model, cultured endothelial cells, migration and tube formation assays). In collaboration with Dr. Neil Vargesson, we conduct an in vivo screen of a library of new analogs to determine which agents demonstrate activity using the in vivo zebrafish and chicken embryo model systems. We identified the most potent of these agents and have patented them. We continue to develop these compounds, which appear to have minimal side effects in initial preclinical toxicology studies and may have improved pharmacology over the FDA approved thalidomide and immunomodulatory drugs (IMiDs) lenalidomide and pomalidomide. We have recently completed characterization of the cytotoxicity, antiangiogenic and anti-inflammatory properties of polyfluorinated benzamides as well as tested them in IMiD-resistant multiple myeloma models. Studies are ongoing to identify potential leads in three dimensional (3D) myeloma spheroid models which will subsequently be evaluated for in vivo toxicology and pharmacology studies in xenograft models as well as to understand the mechanisms of action since the compounds are structurally similar to thalidomide but lacks the glutarimide moiety that binds to the drug's target,cereblon (CRBN). The binding of these IMiDs to CRBN alters the substrate specificity of the ligase, thereby mediating multiple effects that are exploited in cancer therapy. Due to its antiangiogenic and anti-immunomodulatory activity, thalidomide continues to be of clinical interest despite its teratogenic actions, and efforts to synthesize safer, clinically active thalidomide analogs are continually underway. We conducted a structure-activity relationship study to evaluate the antiangiogenic activity and in silico CRBN binding analysis of novel thalidomide analogs. In silico pharmacophore analysis and molecular docking with a crystal structure of human cereblon were used to investigate the cereblon binding abilities of the novel thalidomide analogs. Studies are ongoing for SAR analysis of rationally designed and synthesized IMiD analogs. Development of HIF-1alpha inhibitors: The hypoxia-inducible factor (HIF) is fundamentally involved in tumor angiogenesis, invasion, and energy metabolism. Inhibition of HIF-1 represents an attractive therapeutic strategy for targeting hypoxia, a hallmark of many solid tumors, and tumor angiogenesis. One promising approach for directly inhibiting HIF-1 activity is by disrupting the tight binding between HIF-1alpha and p300. Previously, our laboratory developed an in vitro fluorescence binding assay that can be used in a high-throughput screen to identify small-molecule inhibitors of HIF-1a through inhibiting the binding interaction between the C-terminal transactivation domain (CTAD) of HIF-1a and the cysteine/histidine-rich 1 (CH1) domain of p300. Using our HIF-1alpha/p300 assay, we performed high-throughput screen of NCI's Natural Products Repository in collaboration with the Molecular Targets Laboratory (NCI). This effort led to the discovery of a series of pyrroloiminoquinone alkaloids including discorhabdin and makaluvamine alkaloids, originating from a Latrunculia sp. of marine sponge, as potential HIF-1a/p300 inhibitors. Efforts are ongoing to extract more discorhabdins from New Zealand sponges in order to continue preclinical studies to further understand the mechanisms of these novel compounds. Epidithiodiketopiperazines (ETPs) possess diverse biological activities including anticancer, antifungal, antibacterial and antiviral properties. ETPs are known as a class of compounds that have been shown to inhibit HIF-1alpha with the ETP core itself being sufficient to block the HIF-1alpha and p300 interaction in vitro. There is considerable interest in synthetic chemistry of these natural products and preparation of analogs is actively pursued; however, they are structurally challenging to synthesize. This study is undertaken to screen synthetic ETP analogs rationally designed and synthesized by our collaborator Dr. Tom Snaddon and to determine the activity of these novel compounds in biological assays. We have recently patented several lead compounds with promising activity and will further evaluate them in preclinical models.