Abstract 1586: Developing novel inhibitors of S100A4 for neuroendocrine (NE) and metastatic prostate cancer: systematic testing using relevant models and drug development techniques

S100A4, a calcium binding protein has been well studied as a marker of fibrosis and metastasis. We recently showed that in addition of being a metastatic marker, S100A4 is in fact an oncogene that plays an important role in the development of prostate cancer (CaP) and is amenable of targeting for the treatment of this lethal disease particularly neuroendocrine CaP (NE-CaP). Using a genetically engineered transgenic mouse model of NE-CaP, we show that knocking down of S100A4 significantly inhibited growth of prostate tumorigenesis and metastasis. Our noticeable finding is that S100A4 is secreted by prostatic tumors, and extracellular/soluble S100A4 acts as a growth factor that has the ability to confer aggressive potential to less aggressive or indolent tumor cells. We show that serum-S100A4 level is highly elevated in human CaP patients with aggressive disease regardless of their serum-PSA levels. We next asked if small molecule inhibitors could be developed to inhibit the activity if intracellular as well as extracellular S100A4. Using a highly robust Blue/Gene supercomputer-based in silico method, we screened a library of 5000 molecules and based on their binding efficacy to S100A4, identified potential inhibitors (SMI1 and SMI2). We next tested if SMI1 and SMI2 bind to the S100A4 protein in biological solution. We generated recombinant S100A4 protein and standardized an isothermal titration Calorimetry (ITC) assay for S100A4 binding. The ITC analysis (Kcal vs time) shows that both SMI1 and SMI2 inhibitors significantly bind to the S100A4 protein nevertheless SMI2 exhibited higher binding affinity to S100A4 than SMI1. Next, we used Surface Plasmon Resonance (SPR) method (accurate and sensitive technique) for detecting binding of inhibitors to S100A4. The SPR data (sensogram) shows that SMI1 and SMI2 bind to the S100A4 protein. The binding of S100A4 to Myosin IIA (MIIA) is known to disrupt the latter’s monomer-polymer equilibrium. This phenomenon is captured in solution (in terms of disassembly of MIIA filaments and change in turbidity). Using disassembly/ or turbidity assays as an index of S100A4 activity (where recombinant S100A4 and MIIA are incubated +/- inhibitors), we show that SMI1 and SMI2 inhibit the activity of S100A4 protein. Next, we tested efficacy of inhibitors in vitro and show that SMI1 and SMI2 therapies inhibit the growth, proliferation, migration and invasiveness of NE-CaP (TRAMPC2) and AI-CaP (DU145, PC3) cells. Notably, SMI1 and SMI2 therapies inhibited the growth-promoting effects of extracellular S100A4 and decreased activities of S100A4 downstream target proteins (MMP9 and NFκB). These data suggest that S100A4 inhibitors (SMI1 and SMI2) exhibit high anti-metastatic efficacy and are the potential candidates for treating NE-CaP and metastatic AI-CaP. The validation of SMI1 and SMI2 under in vivo models is underway in our laboratory. Citation Format: Mohammad Saleem, Arsheed A. Ganaie, Reihana Maqbool, Firdous A. Beigh, Syed Umbreen, Natalya G. Dulyaninova, Badrinath R. Konety. Developing novel inhibitors of S100A4 for neuroendocrine (NE) and metastatic prostate cancer: systematic testing using relevant models and drug development techniques [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1586. doi:10.1158/1538-7445.AM2017-1586