BACKGROUND AND PURPOSE Neuropilin‐1 (NRP1) is a VEGF receptor that is widely expressed in normal tissues and is involved in tumour angiogenesis. MNRP1685A is a rodent and primate cross‐binding human monoclonal antibody against NRP1 that exhibits inhibition of tumour growth in NPR1‐expressing preclinical models. However, widespread NRP1 expression in normal tissues may affect MNRP1685A tumour uptake. The objective of this study was to assess MNRP1685A biodistribution in tumour‐bearing mice to understand the relationships between dose, non‐tumour tissue uptake and tumour uptake.

EXPERIMENTAL APPROACH Non‐tumour‐bearing mice were given unlabelled MNRP1685A at 10 mg·kg⁻¹. Tumour‐bearing mice were given ¹¹¹In‐labelled MNRP1685A along with increasing amounts of unlabelled antibody. Blood and tissues were collected from all animals to determine drug concentration (unlabelled) or radioactivity level (radiolabelled). Some animals were imaged using single photon emission computed tomography – X‐ray computed tomography.

KEY RESULTS MNRP1685A displayed faster serum clearance than pertuzumab, indicating that target binding affected MNRP1685A clearance. I.v. administration of ¹¹¹In‐labelled MNRP1685A to tumour‐bearing mice yielded minimal radioactivity in the plasma and tumour, but high levels in the lungs and liver. Co‐administration of unlabelled MNRP1685A with the radiolabelled antibody was able to competitively block lungs and liver radioactivity uptake in a dose‐dependent manner while augmenting plasma and tumour radioactivity levels.

CONCLUSIONS AND IMPLICATIONS These results indicate that saturation of non‐tumour tissue uptake is required in order to achieve tumour uptake and acceptable exposure to antibody. Utilization of a rodent and primate cross‐binding antibody allows for translation of these results to clinical settings.