PSA-Targeted Alpha-, Beta-, and Positron-Emitting Immunotheranostics in Murine Prostate Cancer Models and Nonhuman Primates.

PURPOSE

Most patients with prostate cancer treated with androgen receptor (AR) signaling inhibitors develop therapeutic resistance due to restoration of AR functionality. Thus, there is a critical need for novel treatment approaches. Here we investigate the theranostic potential of hu5A10, a humanized mAb specifically targeting free PSA ().

EXPERIMENTAL DESIGN

LNCaP-AR (LNCaP with overexpression of wildtype AR) xenografts (NSG mice) and _Hi- transgenic mice were imaged with Zr- or treated with Y- or Ac-labeled hu5A10; biodistribution and subcellular localization were analyzed by gamma counting, PET, autoradiography, and microscopy. Therapeutic efficacy of [Ac]hu5A10 and [Y]hu5A10 in LNCaP-AR tumors was assessed by tumor volume measurements, time to nadir (TTN), time to progression (TTP), and survival. Pharmacokinetics of [Zr]hu5A10 in nonhuman primates (NHP) were determined using PET.

RESULTS

Biodistribution of radiolabeled hu5A10 constructs was comparable in different mouse models. Specific tumor uptake increased over time and correlated with PSA expression. Treatment with [Y]/[Ac]hu5A10 effectively reduced tumor burden and prolonged survival ( ≤ 0.0054). Effects of [Y]hu5A10 were more immediate than [Ac]hu5A10 (TTN, < 0.0001) but less sustained (TTP, < 0.0001). Complete responses were observed in 7 of 18 [Ac]hu5A10 and 1 of 9 mice [Y]hu5A10. Pharmacokinetics of [Zr]hu5A10 were consistent between NHPs and comparable with those in mice. [Zr]hu5A10-PET visualized the NHP-prostate over the 2-week observation period.

CONCLUSIONS

We present a complete preclinical evaluation of radiolabeled hu5A10 in mouse prostate cancer models and NHPs, and establish hu5A10 as a new theranostic agent that allows highly specific and effective downstream targeting of AR in PSA-expressing tissue. Our data support the clinical translation of radiolabeled hu5A10 for treating prostate cancer.