Abstract 1669: Identification of mutant KRas-Raf-1 binding disruptors

Mutant KRas is a major driver of human cancer, yet currently no clinically approved therapies that directly target mutant KRas are available. In order to identify novel drugs that bind either mutant KRas or its effector Raf-1, we used alpha-screen and GST-pull down assays to identify disruptors of KRas G12D binding to the Ras-binding domain of Raf-1. From a novel, natural product-inspired chemical library called Complexity To Diversity (CTD), we have identified a series of 5 hits that belong to a family of gibberellic acid-derived compounds and 2 hits from a family of pleuromutilin-derived compounds. At present we are using Differential Scanning Fluorimeter (DSF) and Isothermal calorimetry (ITC) assays to determine whether these hits bind to KRas G12D or Raf-1 RBD. These studies may lead to identifying chemical probes that can be developed to target mutant KRas-driven cancers.

Citation Format: Rajanikanth Vangipurapu, Liwei Chen, Perry Kennedy, Karen C. Morrison, Paul J. Hergenrother, Said M. Sebti. Identification of mutant KRas-Raf-1 binding disruptors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1669.

Natural products as starting points for the synthesis of complex and diverse compounds

Covering: up to 2013. Natural products and their derivatives are used as treatments for numerous diseases. Many of these compounds are structurally complex, possessing a high percentage of sp(3) hybridized carbons and multiple stereogenic centers. Due to the difficulties associated with the isolation of large numbers of novel natural products, lead discovery efforts over the last two decades have shifted toward the screening of less structurally complex synthetic compounds. While there have been many success stories from these campaigns, the modulation of certain biological targets (e.g. protein-protein interactions) and disease areas (e.g. antibacterials) often require complex molecules. Thus, there is considerable interest in the development of strategies to construct large collections of compounds that mimic the complexity of natural products. Several of these strategies focus on the conversion of simple starting materials to value-added products and have been reviewed elsewhere. Herein we review the use of natural products as starting points for the generation of complex compounds, discussing both early ad hoc efforts and a more recent systematization of this approach.

Total synthesis, stereochemical assignment, and biological activity of all known (-)-trigonoliimines

A full account of our concise and enantioselective total syntheses of all known (-)-trigonoliimine alkaloids is described. Our retrobiosynthetic analysis of these natural products enabled identification of a single bistryptamine precursor as a precursor to all known trigonoliimines through a sequence of transformations involving asymmetric oxidation and reorganization. Our enantioselective syntheses of these alkaloids enabled the revision of the absolute stereochemistry of (-)-trigonoliimines A, B, and C. We report that trigonoliimines A, B, C and structurally related compounds showed weak anticancer activities against HeLa and U-937 cells.

Synthesis and anticancer activity of all known (-)-agelastatin alkaloids

The full details of our enantioselective total syntheses of (-)-agelastatins A-F (1-6), the evolution of a new methodology for synthesis of substituted azaheterocycles, and the first side-by-side evaluation of all known (-)-agelastatin alkaloids against nine human cancer cell lines are described. Our concise synthesis of these alkaloids exploits the intrinsic chemistry of plausible biosynthetic precursors and capitalizes on a late-stage synthesis of the C-ring. The critical copper-mediated cross-coupling reaction was expanded to include guanidine-based systems, offering a versatile preparation of substituted imidazoles. The direct comparison of the anticancer activity of all naturally occurring (-)-agelastatins in addition to eight advanced synthetic intermediates enabled a systematic analysis of the structure-activity relationship within the natural series. Significantly, (-)-agelastatin A (1) is highly potent against six blood cancer cell lines (20-190 nM) without affecting normal red blood cells (>333 μM). (-)-Agelastatin A (1) and (-)-agelastatin D (4), the two most potent members of this family, induce dose-dependent apoptosis and arrest cells in the G2/M-phase of the cell cycle; however, using confocal microscopy, we have determined that neither alkaloid affects tubulin dynamics within cells.

Synthesis and Anticancer Activity of Epipolythiodiketopiperazine Alkaloids

The epipolythiodiketopiperazine (ETP) alkaloids are a highly complex class of natural products with potent anticancer activity. Herein, we report the application of a flexible and scalable synthesis, allowing the construction of dozens of ETP derivatives. The evaluation of these compounds against cancer cell lines in culture allows for the first expansive structure-activity relationship (SAR) to be defined for monomeric and dimeric ETP-containing natural products and their synthetic cognates. Many ETP derivatives demonstrate potent anticancer activity across a broad range of cancer cell lines, and kill cancer cellsviainduction of apoptosis. Several traits thatbode well for the translational potential of the ETP class of natural products includeconcise and efficient synthetic access, potent induction of apoptotic cell death, activity against a wide range of cancer types, and a broad tolerance for modifications at multiple sitesthat should facilitate small-molecule drug development, mechanistic studies, and evaluation in vivo.

Differential effects of procaspase-3 activating compounds in the induction of cancer cell death

The evasion of apoptosis is a key characteristic of cancer, and thus strategies to selectively induce apoptosis in cancer cells hold considerable promise in personalized anticancer therapy. Structurally similar procaspase activating compounds PAC-1 and S-PAC-1 restore procaspase-3 activity through the chelation of inhibitory zinc ions in vitro, induce apoptotic death of cancer cells in culture, and reduce tumor burden in vivo. Ip or iv administrations of high doses of PAC-1 are transiently neurotoxic in vivo, while S-PAC-1 is safe even at very high doses and has been evaluated in a phase I clinical trial of pet dogs with spontaneously occurring lymphoma. Here we show that PAC-1 and S-PAC-1 have similar mechanisms of cell death induction at low concentrations (less than 50 μM), but at high concentrations PAC-1 displays unique cell death induction features. Cells treated with a high concentration of PAC-1 have a distinctive gene expression profile, unusual cellular and mitochondrial morphology, and an altered intracellular Ca(2+) concentration, indicative of endoplasmic reticulum (ER) stress-induced apoptosis. These studies suggest strategies for anticancer clinical development, specifically bolus dosing for PAC-1 and continuous rate infusion for S-PAC-1.

Goodpasture syndrome. Localization of the epitope for the autoantibodies to the carboxyl-terminal region of the alpha 3(IV) chain of basement membrane collagen

The autoantibodies of patients with Goodpasture syndrome are primarily targeted to the noncollagenous (NC1) domain of the alpha 3(IV) chain of basement membrane collagen (Saus, J., Wieslander, J., Langeveld, J. P. M., Quinones, S., and Hudson, B. G. (1988) J. Biol. Chem. 263, 13374-13380). In the present study, the location of the Goodpasture epitope in human alpha 3NC1 was determined, and its structure was partially characterized. This was achieved by identification of regions of alpha 3NC1 which are candidates for the epitope and which are structurally unique among the five known homologous NC1 domains (alpha 1-alpha 5); amino acids that are critical for Goodpasture antibody binding, by selective chemical modifications; and regions that are critical for Goodpasture antibody binding, by synthesis of 12 alpha 3NC1 peptides and measurement of their antibody binding capacity. The carboxyl-terminal region, residues 198-233, was identified as the most likely region for the epitope. By experiment, lysine and cysteine were identified as critical amino acids for antibody binding. Three synthetic peptides were found to inhibit Goodpasture antibody binding to alpha 3NC1 markedly: a 36-mer (residues 198-233), a 12-mer (residues 222-233), and a 5-mer (residues 229-233). Together, these results strongly indicate that the Goodpasture epitope is localized to the carboxyl-terminal region of alpha 3NC1, encompassing residues 198-233 as the primary antibody interaction site and that its structure is discontinuous. These findings provide a conceptual framework for future studies to elucidate a more complete epitope structure by sequential replacement of residues encompassing the epitope using cDNA expression products and peptides synthesized chemically.