Abstract A049: The sfRon kinase as a potential novel target for breast cancer therapy

Background: Our recent data revealed striking predominance of an alternatively transcribed form of the Ron receptor tyrosine kinase, known as short-form Ron (sfRon), in breast cancer. sfRon is the major active Ron isoform in breast tumors from patients, and has remarkable effects on metastasis. sfRon lacks the extracellular ligand-binding domain, but organizes into a constitutively-active receptor. Our in vitro studies revealed that overexpression of sfRon in breast cancer cell lines promotes aggressive phenotypes including an epithelial-mesenchymal transition and invasion through basement membranes. We observed that sfRon strongly signals through the PI3K pathway and that interaction between sfRon and PI3K was required for sfRon function. In vivo studies revealed striking results that expression of sfRon was sufficient to convert slow growing non-metastatic tumors into fast growing tumors that spontaneously metastasized from the mammary gland to liver, spleen and bones. An increased understanding of how sfRon contributes to tumor progression and metastasis is critical. Such data carries additional importance because sfRon does not require ligand binding for activity, appears to function in a manner distinct from full length Ron, and may not be targetable using standard approaches such as antibody inhibitors (e.g. RON8, which is now being tested in clinical trials). Instead, our data suggest that inhibition of Ron kinase activity, which would block both Ron and sfRon, would be preferable and that inhibition of downstream PI3K might also be effective in breast tumors expressing sfRon. Results: Through collaborations with various pharmaceutical companies we have obtained several compounds that specifically target Ron/sfRon kinase (e.g. ASLAN002) or PI3 kinase (e.g. BKM120). Our in vitro data demonstrate that ASLAN002 inhibits the activity of sfRon kinase in MCF7 breast cancer cells. The drug also completely blocked PI3K signaling downstream of sfRon. Our studies also showed BKM120 to be a potent inhibitor of PI3K pathway in sfRon-expressing breast cancer cells, effective in doses as low as 250 nM. We have also shown that, while the RON8 antibody inhibits activity of full length Ron kinase, it is not effective against sfRon activity. Based on these promising in vitro results, we extended our work to in vivo assays. We used NOD/SCID mice to orthotopically transplant sfRon-expressing MCF7 cells. After tumors reached 200mm3 we initiated treatment every other day with vehicle control, RON8 antibody, ASLAN002, BKM120, or ASLAN002+BKM120 combination therapy. Our data showed that although the RON8 antibody designed to target Ron is not effective against tumors expressing sfRon, monotherapy with ASLAN002 or BKM120 significantly inhibited tumor growth. However, the most effective treatment regimen was ASLAN002+BKM120 combination therapy. Most importantly, we also observed reduced formation of metastasis in mice treated with ASLAN002, BKM120, or the combination therapy compared to vehicle controls (% of spontaneous metastasis: 44%, 44%, and 33% vs 75%, respectively). Conclusion: Our experimental approach supports the novel concept to use Ron and PI3K pathway inhibitors as potential new therapeutic strategies in breast cancer. These data could have significant impact on future clinical trials for both Ron and PI3K inhibitors, which has high potential to impact patients in the short-term. Citation Format: Magdalena Bieniasz, Najme Faham, Alana L. Welm. The sfRon kinase as a potential novel target for breast cancer therapy. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A049.