Our laboratory uses genetic approaches in live zebrafish embryos and cultured human cancer cells to delineate novels targets for safer and more effective cancer treatments.
Current major focuses in the lab include:
1. Systematic dissection of the Chk1-suppressed apoptotic pathway.
Through a modifier genetic screen in zebrafish, we recently identified a novel pathway of programmed cell death that bypasses two of the most common genetic alterations in human cancers, p53 mutations and overexpression of BCL2. This apoptotic mechanism can be triggered by inhibitors of the Chk1 protein kinase on a DNA damage-sensitized background, and was therefore designated ‘Chk1-suppressed’ (CS) apoptotic pathway (Sidi et al., Cell 2008). The CS pathway appears to define a fundamentally new form of apoptosis, because its activity does not require core effectors of the classical mitochondrial or death-receptor apoptotic pathways. To identify genes required for CS apoptosis, we are performing forward and reverse genetic screens in our cell-culture and zebrafish models of CS apoptosis. Beyond illuminating a novel and evolutionarily conserved apoptotic mechanism, the identification of novel CS pathway components should delineate (i) novel and safer drug targets in the pathway; (ii) biologic indicators, or’biomarkers’, for predicting or evaluating drug efficacy in patients; and (iii) mechanisms of tumor cell resistance to Chk1 inhibitors, as well as strategies to restore treatment sensitivity. In a pilot siRNA screen, we have identified five novel CS pathway components, the characterization of which is underway.
2. The identification of synthetic lethal interactors of p53, PTEN, and other commonly altered genes in cancer.
We are interested in identifying genes whose loss is incompatible with the inactivation of a given tumor suppressor gene (e.g. p53, PTEN), but is otherwise viable in wild-type cells. The discovery of such ‘synthetic lethal’ interactors of widely mutated tumor suppressors is appealing from a therapeutic viewpoint, because systemic inhibition of these proteins in patients should be deadly to cancer cells but not normal cells. Zebrafish are ideally suited for synthetic lethal screens, because they offer the high-throughput capacity of cell culture systems within a live and intact vertebrate organism. In a candidate gene approach, we are using morpholino oligonucleotides or drugs that target potential synthetic lethal interactors of p53 or PTEN identified in cell-culture RNAi screens. For example, we are currently targeting kinases identified by the Ashworth group (ICR, UK) as mandatory for the survival of PTEN deficient cell lines. In addition, we plan to perform large-scale, unbiased genetic and chemical-genetic screens to identify novel synthetic lethal interactors of p53, the most commonly inactivated TSG in human cancers. Proof of principle for synthetic lethal screens in zebrafish comes from our in vivo validation of a synthetic lethal relationship between the FANCD2 tumor suppressor and the Chk1 kinase (Chen et al., Mol Cancer 2009).
Samuel Sidi, PhD
Room 24-16, -19, -28A
1468 Madison Avenue
New York NY 10029