The acquisition of genomic alterations is a defining feature of human cancers. Cancer chemotherapy relies upon the cell death or apoptotic pathway to eradicate cells containing these alterations. The maintenance of appropriate methylation levels in DNA is necessary during normal DNA replication and mitosis. Disruption of correct and appropriate methylation leads to non-mutagenic changes associated with transcriptional silencing in tumor cells. Transcriptional silencing of genes along the apoptotic pathway abrogates the efficacy of chemotherapy and such tumors are refractory to classical therapy and associated with a poor prognosis. Epigenetic methylation of cytosine in DNA occurs at CpG sites in dense clusters of CpG dinucleotide repeats within gene promoters and is catalyzed by DNA methyl transferase enzymes (Dnmt's). Therapeutics that can inhibit Dnmt can reactivate genes silenced by hypermethylation, therefore, the design and development of novel Dnmt inhibitors is a worthy goal especially as the silenced genes remain intact and functional. We have constructed unique libraries of natural product derivatives based upon natural product isolation, combinatorial biosynthesis and parallel combinatorial synthesis. Our libraries are composed of structures that retain the topological and stereochemical complexity of natural products yet are straightforward to prepare. In screening our libraries against the human Dnmt-1 enzyme we discovered that compounds with an isoindolinone core scaffold were excellent inhibitors with Ki values as low as 20 micromolar. In this application we seek to demonstrate that we can develop potent and selective inhibitors of Dnmt-1. We further seek to demonstrate that our inhibitors cause reactivation of a model epigenetically silenced gene, human MLH1.
The chemical modification of DNA by cytosine methylation plays a crucial role in the control of which genes are actively expressed. The balance between modified and unmodified states is important and is often perturbed in cancer cells, silencing their ability to undergo programmed cell death in response to appropriate stimuli including cancer chemotherapy. As a consequence such cancers are often refractory to treatment and associated with a poor prognosis. The ability to block DNA methylation has the potential to re-activate the programmed death of cancer cells. We seek to develop new drugs that can precisely block these processes and that have the potential to either be therapeutic agents or new tools for basic investigation of the processes leading to cancer. Drug candidates identified from a unique hybrid natural products - synthetic chemistry hybrid library will be further structurally developed and their potential as anti-cancer drugs explored by mechanistic analysis.
