Preclinical Assessment of a Novel CDC7 Inhibitor: Genomewide RNAi Screening Identifies Unique Synergetic and Resistance Genes,

Abstract 3570

Despite extensive drug discovery efforts, drug-candidate failure and patients relapsing in the clinic remain as persistent problems. While insufficient drug-gene engagement leads to drug failure, de novo escape mutations give rise to patients relapsing, calling the need for systemic studies on how genes influence drug responsiveness. Towards this end, we have explored a functional short hairpin RNA (shRNA) based genomic screening platform aimed at interrogating drug-gene engagement and assessing its consequences on signaling pathways. We propose this concept as a novel way to evaluate drug candidates prior to clinical trials enabling liability assessment and predicting clinical outcome. We took advantage of the arrayed shRNA library produced in lentiviral particles and characterized by several obvious advantageous features including shRNA targeting one hairpin at a time and on the fly high content whole well microscopy imaging analysis. We carried out three parallel genomewide shRNA screens in the absence or presence of the novel CDC7 kinase inhibitor (MSK-777) at its IC20 and IC50 and have identified several gene candidates that influence MSK-777 sensitivity and resistance. These include synergizers that enhance MSK-777 sensitivity and rescuers that confer MSK-777 resistance. IPA analysis mapped clusters of these hits to multiple major pathways among them were the NF-kB pathway, the ubiquitin-proteasome pathway, DNA replication, and several epigenetic regulatory genes. We will present and discuss this concept together with the emerging pathways as a means to identify both key therapeutic targets and biomarkers of sensitivity and resistance. Thus, allowing for not only a broader applicability of assessing candidate genes that modulate specific drug agents, but also for the identification of a tailored and more efficacious therapeutic regimen to treat cancer.