Abstract 5454: Novel STAT3:STAT3 small-molecule inhibitors as potential anticancer agents

Transcription factors are important targets for cancer therapy. The inhibition of protein-protein interactions (PPIs) within signalling pathways known to be key regulators of transcriptional activity is a viable approach to novel chemotherapeutic strategies. Proof-of-concept studies in cell-culture and animal models have validated the potential of small-molecule inhibitors of STAT3 signalling in cancer therapy. In particular, the protein-protein interaction between two STAT3 monomers (i.e., the dimerisation event in the signalling cascade) has been identified as a valid target to inhibit DNA-binding and the resultant transcriptional activation. Of the approximately 20 small-molecule STAT3 inhibitors reported in the literature to date, only three are described as potential STAT3:STAT3 dimerisation inhibitors, and these have IC50 values in STAT3-expressing cell lines of between 10-90 μM. Using in silico and medicinal chemistry-based approaches based on a published X-Ray structure of STAT3 (PDB: ID-1BG1) to identify “hit” inhibitors, a focussed library (approx. 50 members) was designed around one such “hit” and synthesized employing an efficient 4-step linear approach. Library members were then entered into a screening cascade involving initial evaluation of their ability to inhibit STAT3:STAT3 interaction in a Fluorescent Polarisation (FP)-based primary PPI binding assay. “Hit” molecules from this primary assay were then studied in two cell-based assays designed to test for STAT3 selectivity. The first was a comparative MTS assay between STAT3-expressing MDA MB231 breast cancer cells and STAT3-null colon A4 cells. The second was a luciferase reporter assay designed to measure transcription inhibition in STAT3-Luc-transformed Hela cells compared to SV40-Luc-transformed Hela control cells. A potential “lead” molecule, RH06, emerged from this screening cascade with potentially selective STAT3 inhibitory activity in the low micromolar (i.e., ∼1 µM) region. RH06 is currently being studied for its effect on STAT3 and pSTAT3 signal activation, and its potentially differential effect on upstream and downstream mediators (i.e., JAK2, Bcl-xl, Cyclin D1 and pSTAT1). Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philad