Inhibition of TAMs improves the response to docetaxel in castration-resistant prostate cancer

For men with castration-resistant prostate cancer (CRPC), androgen-deprivation therapy (ADT) often becomes ineffective requiring the addition of docetaxel, a proven effective chemotherapy option. Tumor-associated macrophages (TAMs) are known to provide protumorigenic influences that contribute to treatment failure. In this study, we examined the contribution of TAMs to docetaxel treatment. An increased infiltration of macrophages in CRPC tumors was observed after treatment with docetaxel. Prostate cancer cells treated with docetaxel released more macrophage colony-stimulating factor (M-CSF-1 or CSF-1), IL-10 and other factors, which can recruit and modulate circulating monocytes to promote their protumorigenic functions. Inhibition of CSF-1 receptor kinase signaling with a small molecule antagonist (PLX3397) in CRPC models significantly reduces the infiltration of TAMs and their influences. As such, the addition of PLX3397 to docetaxel treatment resulted in a more durable tumor growth suppression than docetaxel alone. This study reveals a rational strategy to abrogate the influences of TAMs and extend the treatment response to docetaxel in CRPC.