Tumor-Associated Macrophages Suppress the Cytotoxic Activity of Antimitotic Agents

Antimitotic agents, including Taxol, disrupt microtubule dynamics and cause a protracted mitotic arrest and subsequent cell death. Despite the broad utility of these drugs in breast cancer and other tumor types, clinical response remains variable. Tumor-associated macrophages (TAMs) suppress the duration of Taxolinduced mitotic arrest in breast cancer cells and promote earlier mitotic slippage. This correlates with a decrease in the phosphorylated form of histone H2AX (gamma H2AX), decreased p53 activation, and reduced cancer cell death in interphase. TAMs promote cancer cell viability following mitotic slippage in a manner sensitive to MAPK/ERK kinase (MEK) inhibition. Acute depletion of major histocompatibility complex class II low (MHCIIlo) TAMs increased Taxol-induced DNA damage and apoptosis in cancer cells, leading to greater efficacy in intervention trials. MEK inhibition blocked the protective capacity of TAMs and phenocopied the effects of TAM depletion on Taxol treatment. TAMs suppress the cytotoxic effects of Taxol, in part through cell non-autonomous modulation of mitotic arrest in cancer cells, and targeting TAM-cancer cell interactions potentiates Taxol efficacy.