Bone Abstracts

Tumour stromal macrophages differentiate into tumour associated macrophages (TAMs), with characteristics resembling the immunosuppressive M2 polarization instead of the pro-inflammatory M1. TAMs have a central role in promoting tumour vascularization, cancer cell dissemination and suppression of anti-cancer immune response. Cancer cell dissemination leads to metastasis formation which, e.g. in breast cancer often happens in bone marrow. We have studied the in vitro modulation of that polarization by bisphosphonates (BPs) and breast cancer cell conditioned medium (CM). The effect of CM from the murine breast cancer cell line 4T1, on the J774 murine macrophage cell line response to LPS stimulus was tested. 4T1 CM, but not control 3T3 CM decreased NO₂^- production and increased IL6 and MMP-9 mRNA expression by J774 cells upon LPS stimulus. BPs uptake by macrophages is improved by liposome encapsulation of the drugs. The analysis of the effects of free and liposome encapsulated BPs on J774 cells, revealed the expected increase in potency of the liposome encapsulated drugs to induce apoptosis. At sublethal doses, clodronate (CLO) led to the intracellular accumulation of AppCCl₂p and zoledronate (ZOL) to isopentenyl pyrophosphate (IPP), triphosphoric acid 1-adenosin-5′-yl ester 3-(3-methylbut-3-enyl)ester (ApppI) and unprenylated proteins. To establish if these drugs also affect the cell polarization status, free and liposome drugs were tested prior to LPS stimulus. According to our preliminary analysis, in the presence of 4T1 CM liposome encapsulated ZOL enhanced the expression of M1-type mediators, but did not downregulate the expression of M2-type mediators. In conclusion, in our model breast cancer cells were able to alter macrophage polarization and liposome encapsulated ZOL was able to modulate that effect. The relevance of this in tumour propagation needs further studies.