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A Novel Anti-Cancer Therapy: Inhibition of MUS81-EME1

Institution: University of California, Davis
Investigator(s): Sucheta Mukherjee, B.S.
Award Cycle: 2011 (Cycle 20) Grant #: 20DT-0036 Award: $60,000
Subject Area: Cancer
Award Type: Dissertation Awards

Initial Award Abstract
Tumor cells display genetic changes, such as mutations in tumor suppressor genes, which differentiate them from their surrounding normal tissue. Such changes can lead to uncontrolled tumor growth and more replicative stress in tumor cells than in normal cells. DNA damage-based anti-cancer therapies target this enhanced rate of replication in tumor cells, but are accompanied by adverse effects to non-cancerous tissues. An emerging strategy for anti-cancer therapy uses synthetic lethality, a genetic concept where the combination of two non-lethal mutations leads to lethality. This concept relies on the ablation of one pathway through loss-of-heterozygosity (LOH) of tumor suppressor genes and concomitant chemical inhibition of a suspected synthetic lethal pathway, in this case DNA damage repair by homologous recombination (HR). Therefore, we propose a novel approach to anti-cancer therapy that exploits the replicative stress that tumor cells experience during uncontrolled growth and disproportionately sensitizes them to DNA-damage based anti-cancer therapies. We speculate that tumor cells rely on HR for repair of DNA damage and recovery of stalled replication forks during constant cell division. HR is a DNA metabolic process involved in template-dependent repair or tolerance of DNA damage. Homo sapiens (Hs) MUS81-EME1 is a structure-specific DNA endonuclease implicated in HR that is involved in the recovery of stalled replication fork induced by interstrand cross-linking agents. Along with HsMUS81-EME1, the well-studied eukaryotic model, Saccharomyces cerevisiae Mus81-Mms4, has been shown to cleave various substrates involved in stalled replication fork recovery in vitro. In addition, a mouse knock-out model showed that lack of Mus81-Eme1 in normal cells does not have a severe phenotype but leads to sensitivity to interstrand crosslinks. Lastly, ScMus81-Mms4 has been shown to have synthetic lethal relationships with various genes involved in DNA damage repair, cell cycle checkpoints, and genome maintenance that may be mutated in cancer. These three reasons make HsMUS81-EME1 an attractive drug target in the HR pathway to enhance the efficacy of anti-cancer therapy that uses interstrand crosslinking agents. We hypothesize that inhibition of HsMUS81-EME1 will disproportionately sensitize tumor cells to interstrand crosslinking agents used in anti-cancer therapy that is standard treatment for lung cancer. This proposal has three specific aims for small molecule inhibitor discovery for HsMUS81-EME1: 1) Purification of HsMUS81-EME1, 2) Establishment of Forster Resonance Energy Transfer (FRET)-based high-throughput screen (HTS) for identification candidate small molecule inhibitors, and 3) Characterization of candidate inhibitors and identification of mechanism of inhibition. Identification of small molecule inhibitors for HsMUS81-EME1 will provide a novel strategy to disproportionately sensitize tumor cells to interstrand crosslinking agents. LOH of tumor suppressor genes has been reported in non-small cell lung cancer (NSCLC) patients with mutations in p53 tumor suppressor gene and has significantly higher occurrence in smokers versus non-smokers. A synthetic lethal approach with HsMUS81-EME1 inhibitors could disproportionately target tumor cells with LOH in NSCLC and spare surrounding non-tumor cells. If the genetic profile of cancer patients is not available for taking advantage of synthetic lethal relationships, at the very least, HsMUS81-EME1 inhibitors can be used in conjunction with DNA damage inducing anti-cancer therapy to enhance the therapeutic efficacy towards tumor cells while sparing non-replicating normal cells. This proposal represents a study towards drug development that may benefit a significant portion of lung cancer patients.