Abstract
The integrin α(v)β(6), an epithelium-specific cell surface receptor, is overexpressed on numerous malignancies, including the highly lethal pancreatic ductal adenocarcinomas. Here, we developed and tested a novel α(v)β(6)-targeting peptide, DOTA-5G (1) radiolabeled with (68)Ga, for PET/CT imaging and (177)Lu for treatment. With the goal to develop a radiotheranostic, further modifications were made for increased circulation time, renal recycling, and tumor uptake, yielding DOTA-albumin-binding moiety-5G (2). Methods: Peptides 1 and 2 were synthesized on solid phase, and their affinity for α(v)β(6) was assessed by enzyme-linked immunosorbent assay. The peptides were radiolabeled with (68)Ga and (177)Lu. In vitro cell binding, internalization, and efflux of (68)Ga-1 and (177)Lu-2 were evaluated in α(v)β(6)-positive BxPC-3 human pancreatic cancer cells. PET/CT imaging of (68)Ga-1 and (68)Ga-2 was performed on female nu/nu mice bearing subcutaneous BxPC-3 tumors. Biodistribution was performed for (68)Ga-1 (1 and 2 h after injection), (68)Ga-2 (2 and 4 h after injection), and (177)Lu-1 and (177)Lu-2 (1, 24, 48, and 72 h after injection). The (177)Lu-2 biodistribution data were extrapolated for human dosimetry data estimates using OLINDA/EXM 1.1. Therapeutic efficacy of (177)Lu-2 was evaluated in mice bearing BxPC-3 tumors. Results: Peptides 1 and 2 demonstrated high affinity (<55 nM) for α(v)β(6) by enzyme-linked immunosorbent assay. (68)Ga-1, (68)Ga-2, (177)Lu-1, and (177)Lu-2 were synthesized in high radiochemical purity. Rapid in vitro binding and internalization of (68)Ga-1 and (177)Lu-2 were observed in BxPC-3 cells. PET/CT imaging and biodistribution studies demonstrated uptake in BxPC-3 tumors. Introduction of the albumin-binding moiety in (177)Lu-2 resulted in a 5-fold increase in tumor uptake and retention over time. Based on the extended dosimetry data, the dose-limiting organ for (177)Lu-2 is the kidney. Treatment with (177)Lu-2 prolonged median survival by 1.5- to 2-fold versus controls. Conclusion: (68)Ga-1 and (177)Lu-2 demonstrated high affinity for the integrin α(v)β(6) both in vitro and in vivo, were rapidly internalized into BxPC-3 cells, and were stable in mouse and human serum. Both radiotracers showed favorable pharmacokinetics in preclinical studies, with predominantly renal excretion and good tumor-to-normal-tissue ratios. Favorable human dosimetry data suggest the potential of (177)Lu-2 as a treatment for pancreatic ductal adenocarcinoma.