Development of a Radiogallium-Labeled Heterodivalent Imaging Probe Targeting Negative Charges and Integrin on the Surface of Cancer Cell Membranes.

Radiopharmaceuticals targeting tumor-specific environments are powerful tools for cancer diagnosis and treatment. We previously demonstrated the considerable high tumor uptake of the cationic amphiphilic peptide, Ga-NOTA-KV6, in vivo. However, because this radioligand shows a relatively rapid clearance from the tumor over time, further structural optimization is necessary. In this study, to enhance tumor accumulation and retention, we synthesized and evaluated a heterobivalent radiogallium-labeled radiotracer, [Ga]Ga-DOTA-KV6-Mal-c(RGDyK) ([Ga]), fusing the KV6 peptide targeting negatively charged sites on the cancer cell membrane and cyclic RGD peptide targeting integrin αβ on the cancer cell membrane. Cellular uptake study revealed high accumulation of [Ga] in integrin αβ-expressing U-87MG cancer cells, but uptake was significantly inhibited in the presence of an excess of the cyclic RGD peptide, c(RGDyK) (). Peptide exhibited integrin αβ-binding affinity comparable to those of RGD peptides and DOTA-Mal-c(RGDyK) (). In vivo biodistribution studies of U-87MG tumor-bearing mice revealed that [Ga] exhibited better accumulation and retention in tumor tissues than [Ga]Ga-DOTA-KV6-Mal-Et ([Ga]; without the RGD peptide motif) and [Ga]Ga-DOTA-Mal-c(RGDyK) ([Ga]; without the KV6 peptide motif). Single-photon emission computed tomography analysis also revealed high signals of [Ga] in tumor tissues, which were significantly blocked in the presence of excess peptide . Although reducing radiotracer accumulation in nontumor tissues, such as the kidneys, remains a challenge, our developed approach exhibits potential to enhance the selectivity and retention of radiopharmaceuticals in tumor tissues.