^99mTc-MAG3-PEG8-c(RGDYK) uptake in melanoma tumor

Objectives Integrin αvβ3 plays a significant role in tumor angiogenesis and is a receptor for the extracellular matrix proteins with the exposed arginine-glycine-aspartic (RGD) tripeptide sequence. This study endeavored the development and biological evaluation of a new integrin receptor radiotracer for tumor detection, nominally cyclo 1-5 (RGDdYK) conjugated with MAG3 and spacer PEG8, radiolabeled with ^99mTc.

Methods 10μl of a 751.6 μM solution of MAG3-PEG8-c(RGDYK) was labeled with ^99mTc using sodium tartrate dissolved in labeling buffer (ammonium bicarbonate, ammonium acetate, ammonium hydroxide) along with stannous chloride solution. Reaction was induced by heating at 100°C for 20 min. Radiochemical evaluation was performed by ITLC and was confirmed by HPLC analysis. Internalization assays of the ^99mTc-peptide were performed in melanoma cells (B16F10 and SKMEL28). Biodistribution and images were carried out in Nude mice bearing the same cells 2h post-injection. Blocking studies were also conducted by co-injection of 75.2 nmol of cold RGD.

Results Radiochemical purity of the radiotracer was 97.2 ± 0.53 %, with a retention time of 10.92 min in HPLC analysis. Internalization of the radiotracer in SK-MEL-28 and in B16F10 cells was respectively 96.13% and 53.55% after 30 min of incubation and these values remained stable until 120 min. Tumor uptake was remarkably greater for animals bearing SK-MEL-28 cells (7.85 ± 2.34 %ID/g) than for B16F10 cells (1.06 ± 0.19 %ID/g). The tumor was 85% blocked in animals with SK-MEL-28 melanoma.

Conclusions ^99mTc- MAG3-PEG8-c(RGDYK) is a promising radiotracer for melanoma diagnosis due to its specificity , particularly to human SK-MEL-28 cells.

Research Support We want to thank the National Nuclear Energy Commission (CNEN/Brazil) for a postgraduate scholarship support