177Lu-CTT1403 is the therapeutic analogue of 18F-CTT1057, a phosphoramide based PET agent developed for the therapy of prostate cancer which entered Phase I clinical trial in January 2019.

PSMA is over-expressed on prostate cancer and this expression increases as the cancer metastasizes and becomes castrate-resistant. These phosphoramidate-based agents bind irreversibly to PSMA, and unlike other agents targeting PSMA, this distinctive mode of binding enhances uptake and internalization by tumor cells leading to enhanced accumulation of the drugs within the tumor.

The first phase I study was initiated in January 2019, for the evaluation of both the imaging agent 18F-CTT1057 and the therapeutic agent 177Lu-CTT1403. In this study some patients will also be imaged with 68Ga-PSMA-11. The study is expected to be completed by end of 2021.