NeoBOMB1, a GRPR-Antagonist for Breast Cancer Theragnostics: First Results of a Preclinical Study with [ 67 Ga]NeoBOMB1 in T-47D Cells and Tumor-Bearing Mice.

Background: The GRPR-antagonist-based radioligands [Ga-67/68/In-111/Lu-177]NeoBOMB1 have shown excellent theragnostic profiles in preclinical prostate cancer models, while [Ga-68]NeoBOMB1 effectively visualized prostate cancer lesions in patients. We were further interested to explore the theragnostic potential of NeoBOMB1 in GRPR-positive mammary carcinoma, by first studying [Ga-67]NeoBOMB1 in breast cancer models; Methods: We investigated the profile of [Ga-67]NeoBOMB1, a [Ga-68]NeoBOMB1 surrogate, in GRPR-expressing T-47D cells and animal models; Results: NeoBOMB1 (IC(50)s of 2.2 +/- 0.2 nM) and [Ga-nat]NeoBOMB1 (IC(50)s of 2.5 +/- 0.2 nM) exhibited high affinity for the GRPR. At 37 degrees C [Ga-67]NeoBOMB1 strongly bound to the T-47D cell-membrane (45.8 +/- 0.4% at 2 h), internalizing poorly, as was expected for a radioantagonist. [Ga-67]NeoBOMB1 was detected >90% intact in peripheral mouse blood at 30 min pi. In mice bearing T-47D xenografts, [Ga-67]NeoBOMB1 specifically localized in the tumor (8.68 +/- 2.9% ID/g vs. 0.6 +/- 0.1% ID/g during GRPR-blockade at 4 h pi). The unfavorably high pancreatic uptake could be considerably reduced (206.29 +/- 17.35% ID/g to 42.46 +/- 1.31% ID/g at 4 h pi) by increasing the NeoBOMB1 dose from 10 pmol to 200 pmol, whereas tumor uptake remained unaffected. Notably, tumor values did not decline from 1 to 24 h pi; Conclusions: [Ga-67]NeoBOMB1 can successfully target GRPR-positive breast cancer in animals with excellent prospects for clinical translation.