Resistance to HER2-targeted anti-cancer drugs is associated with immune evasion in cancer cells and their derived extracellular vesicles.

Neuromedin U (NmU) -a neuropeptide belonging to the neuromedin family- plays a substantial role in HER2-positive breast cancer, correlating with increased aggressiveness, resistance to HER2-targeted therapies and overall significantly poorer outcome for patients. However, the mechanism through which it exerts these effects remains unclear. To elucidate this, initially we used HER2-positive breast cancer cells stably over-expressing NmU. These cells and their released extracellular vesicles (EVs) had increased amounts of the immunosuppressive cytokine TGFβ and the lymphocyte activation inhibitor PD-L1. Furthermore, these cells also showed enhanced resistance to antibody-dependent cell cytotoxicity (ADCC) mediated by trastuzumab, indicating a role of NmU in enhancing immune evasion. All these features were also found in HER2-targeted drug-resistant cells which we previously found to express higher levels of NmU than their drug-sensitive counterparts. Interestingly, EVs from drug-resistant cells were able to increase levels of TGFβ in drug-sensitive cells. In our neo-adjuvant clinical trial, TGFβ levels were significantly higher in EVs isolated from the serum of patients with HER2-overexpressing breast cancers who went on to not respond to HER2-targeted drug treatment, compared with those who experienced complete or partial response. Taken together, our results report a new mechanism-of-action for NmU in HER2-overexpressing breast cancer that enhances resistance to the anti-tumor immune response. Furthermore, EV levels of TGFβ correlating with patients' response versus resistance to HER2-targeted drugs suggests a potential use of EV-TGFβ as a minimally-invasive companion diagnostic for such treatment in breast cancer.