Abstract 3948: Development of bone-targeted Ron inhibitors to treat osseous metastases from breast cancers (2022)

Abstract Purpose: About 500,000 people each year worldwide die from metastatic breast cancer. More than 70% of these metastatic breast cancer patients have bone metastases and median survival time from diagnosis of bone metastasis is only 2-3 years. As breast cancer bone metastases are primarily osteolytic, patients suffer from significant morbidities, including severe pain, pathological fractures, nerve compression, and hypercalcemia. Previously, it was shown that RON receptor tyrosine kinase mediates breast cancer outgrowth at metastatic sites, promotes osteolytic bone destruction, and induces systemic immune suppression. We hypothesized that inhibition of RON in specialized resident macrophages and/or osteoclasts will eliminate metastasis through dual effects of blocking osteolysis and enhancing anti-tumor immunity. In this study, we have developed several bis(phosphonate) or phosphate conjugates of BMS-777607 and LY2801653, and report their accumulation in the bone microenvironment along with effects on osteolysis and tumor burden. Methods: We have utilized novel synthetic schemes for synthesis of the drug conjugates. In vitro kinase assays were performed using ADP-Glo RON kinase assay kit (Promega). Hydroxyapatite binding assay was used to determine binding of drug conjugates to the bone mineral. Changes in phosphorylation of RON was demonstrated by Western blotting. Plasma pharmacokinetics and bone accumulation of lead drug conjugates in mice was assessed by mass-spectrometry. An intratibial bone metastasis model in which MSP-expressing MMTV-PyMT tumor cells are injected into the tibia of mice was used to assess the effect of treatment with lead drug conjugates. Results: Seven novel drug conjugates were synthesized and inhibited RON kinase activity with an IC50 of 0.060-2.4 µM. Three drug conjugates demonstrated better hydroxyapatite binding when compared with BMS-777607. In agreement with the in vitro kinase activity, a variable decrease in the phosphorylation of RON was observed in cells treated with the drug conjugates. ZB-28, a monophosphonate derivative of BMS-777607, showed higher accumulation in the bone when compared with BMS-777607 but failed to block tumor-mediated bone osteolysis in an intratibial bone metastasis mouse model. Currently, a cleavable phosphate conjugate of BMS-777607 (ZB-32) is undergoing testing in the same mouse model. We have confirmed that ZB-32 and its hydrolyzed product ZB-33 accumulate in the bone to a significantly higher level than BMS-777607. These results along with preliminary ADME will be presented. Conclusion: Targeting RON kinase in the bone microenvironment is a promising approach to alleviate morbidities observed in breast cancer patients with bone metastases. We present novel bone-targeting conjugates of BMS-777607 and highlight the potential for clinical development. Citation Format: Trason Thode, Jaime Fornetti, Ryan Rodriguez del Villar, Alexis Weston, Serina Ng, Srikanta Dana, Raffaella Soldi, Mohan Kaadige, Hariprasad Vankayalapati, Srinivas Kasibhatla, Alana Welm, Sunil Sharma. Development of bone-targeted Ron inhibitors to treat osseous metastases from breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3948.