Targeting myeloid chemotaxis to reverse prostate cancer therapy resistance

Inflammation is a hallmark of cancer 1 . In patients with cancer, peripheral blood myeloid expansion, indicated by a high neutrophil-to-lymphocyte ratio, associates with shorter survival and treatment resistance across malignancies and therapeutic modalities 2 – 5 . Whether myeloid inflammation drives progression of prostate cancer in humans remain unclear. Here we show that inhibition of myeloid chemotaxis can reduce tumour-elicited myeloid inflammation and reverse therapy resistance in a subset of patients with metastatic castration-resistant prostate cancer (CRPC). We show that a higher blood neutrophil-to-lymphocyte ratio reflects tumour myeloid infiltration and tumour expression of senescence-associated mRNA species, including those that encode myeloid-chemoattracting CXCR2 ligands. To determine whether myeloid cells fuel resistance to androgen receptor signalling inhibitors, and whether inhibiting CXCR2 to block myeloid chemotaxis reverses this, we conducted an investigator-initiated, proof-of-concept clinical trial of a CXCR2 inhibitor (AZD5069) plus enzalutamide in patients with metastatic CRPC that is resistant to androgen receptor signalling inhibitors. This combination was well tolerated without dose-limiting toxicity and it decreased circulating neutrophil levels, reduced intratumour CD11b + HLA-DR lo CD15 + CD14 − myeloid cell infiltration and imparted durable clinical benefit with biochemical and radiological responses in a subset of patients with metastatic CRPC. This study provides clinical evidence that senescence-associated myeloid inflammation can fuel metastatic CRPC progression and resistance to androgen receptor blockade. Targeting myeloid chemotaxis merits broader evaluation in other cancers. A translational study demonstrates the role of myeloid inflammatory cells in driving disease progression and treatment resistance in prostate cancer and shows that these cells can be targeted therapeutically.