Therapeutic targeting of thec-fmsoncogene diminishes the growth of breast cancer cells and ductal hyperplasia in the mammary gland of the CSF-1 transgenic mouse model.

Abstract #3120 The macrophage colony-stimulating factor (CSF-1) is a cytokine produced by macrophages as well as epithelial cancer cells. By signaling via its receptor c-fms, CSF-1 induces growth/survival pathways in breast cancer cells. Defects in mammary gland development were observed in mice deficient in CSF-1/c-fms signaling, implicating this pathway in normal mammary development as well. In breast cancer, elevated levels of both CSF-1 and c- fms have been detected, with 80% of invasive breast carcinomas abnormally expressing c-fms. To study the role of CSF-1 signaling in breast cancer, we have previously generated mammary specific transgenic mouse models that over-express these factors (termed MMTV-CSF-1 and MMTV-c-fms). Both these transgenic mouse strains developed ductal hyperplasia and dysplasia as well as tumor formation. Our previous evidence also showed increase in cellular proliferation factors such as Cyclin D1 and PCNA in these mice. To examine which signaling pathways are altered in these mice, we have compared in this study the expression profile of target genes of signaling pathways in MMTV-CSF-1 mice and wild type mice using the Signal Transduction Pathway Finder RT-PCR array (Superarrray). Wnt signaling pathway was induced in the mammary gland of the MMTV-CSF-1 mouse strain compared to wild type, suggesting that this pathway may mediate CSF-1 signaling. In a proof-of-principle experiment, an MMTV-CSF-1 mouse was injected subcutanuously with neutralizing anti-c-fms antibody (Santacruz Biotech, 2-4A5) at a dose of 5 μg daily for 7 days. The treated mouse exhibited a decrease in the elevated ductal branching and hyperplasia that are characteristics of untreated MMTV-CSF-1 mice. This treatment also resulted in reversing many of expression alterations in MMTV-CSF-1 mice. For example, expression of the CSF-1 responsive gene Cyclin D1 was reduced by over 3-fold due to antibody treatment. Fas, the receptor for the pro-apoptotic factor Fas ligand, decreased by 5-folds in the MMTV-CSF-1 strain relative to wild type but increased 14-folds due to c-fms antibody treatment. The expression of the proapoptotic factor Bax increased about 4-fold, whereas the angiogenic factor Angiopoietin 1 was reduced by 60% due to anti-cfms antibody treatment. The treatment also reversed alterations in the expression of the wnt transcription factors Lef-1/TCF7. Because small molecule tyrosine kinase inhibitors that target c-fms, Gleevecâ (Imatinib, obtained from Novartis) and GW2580 (Calbiochem), are emerging, we examined their effects on the growth of SKBR3 breast cancer cells that express both CSF-1 and c-fms. Our data showed both these drugs inhibited the growth of SKBR3 cells, providing the rationale to test their effects on tumor formation and underlying biochemical effects in our transgenic preclinical models. The current studies warrant further investigation of treating breast cancer using antibody and small molecule drugs targeting CSF-1/c-fms signaling. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3120.