Preclinical investigations using [ 177 Lu]Lu-Ibu-DAB-PSMA toward its clinical translation for radioligand therapy of prostate cancer

[ 177 Lu]Lu-Ibu-DAB-PSMA was previously characterized with moderate albumin-binding properties enabling high tumor accumulation but reasonably low retention in the blood. The aim of this study was to investigate [ 177 Lu]Lu-Ibu-DAB-PSMA in preclinical in vivo experiments and compare its therapeutic efficacy and potential undesired side effects with those of [ 177 Lu]Lu-PSMA-617 and the previously developed [ 177 Lu]Lu-PSMA-ALB-56. BALB/c nude mice without tumors were investigated on Day 10 and 28 after injection of 10 MBq radioligand. It was revealed that most plasma parameters were in the same range for all groups of mice and histopathological examinations of healthy tissue did not show any alternations in treated mice as compared to untreated controls. Based on these results, a therapy study over twelve weeks was conducted with PC-3 PIP tumor-bearing mice for comparison of the radioligands’s therapeutic efficacy up to an activity of 10 MBq (1 nmol) per mouse. In agreement with the increased mean absorbed tumor dose, [ 177 Lu]Lu-Ibu-DAB-PSMA (~ 6.6 Gy/MBq) was more effective to inhibit tumor growth than [ 177 Lu]Lu-PSMA-617 (~ 4.5 Gy/MBq) and only moderately less potent than [ 177 Lu]Lu-PSMA-ALB-56 (~ 8.1 Gy/MBq). As a result, the survival of mice treated with 2 MBq of an albumin-binding radioligand was significantly increased ( p < 0.05) compared to that of mice injected with [ 177 Lu]Lu-PSMA-617 or untreated controls. The majority of mice treated with 5 MBq or 10 MBq [ 177 Lu]Lu-Ibu-DAB-PSMA or [ 177 Lu]Lu-PSMA-ALB-56 were still alive at study end. Hemograms of immunocompetent mice injected with 30 MBq [ 177 Lu]Lu-Ibu-DAB-PSMA or 30 MBq [ 177 Lu]Lu-PSMA-617 showed values in the same range as untreated controls. This was, however, not the case for mice treated with [ 177 Lu]Lu-PSMA-ALB-56 which revealed a drop in lymphocytes and hemoglobin at Day 10 and Day 28 after injection. The data of this study demonstrated a significant therapeutic advantage of [ 177 Lu]Lu-Ibu-DAB-PSMA over [ 177 Lu]Lu-PSMA-617 and a more favorable safety profile as compared to that of [ 177 Lu]Lu-PSMA-ALB-56. Based on these results, [ 177 Lu]Lu-Ibu-DAB-PSMA may has the potential for a clinical translation.