Speaker
Description
Introduction. The development of new integrin-selective molecules suitable for therapeutic or imaging purposes are currently of interest in development of effective personalized medical platforms.
Recently, a bifunctional chimeric echistatin-RGD-peptide, RGDechi, has been reported as a potent and selective antagonist of αvβ3, in which the echistatin portion is essential for such selectivity [1]. Herein, RGDechi and three truncated derivatives functionalized with a cysteine (1-4) (fig 1), were synthetized and labeled with the [99mTc][Tc(N)PNP43]-synthon ([PNP43=(CH3)2P(CH2)2N(C2H4OCH3)(CH2)2P(CH3)2]) (99mTc1-4) as basis for selective integrin recognition.
Methods. RGDechi and derivatives were synthetized and conjugated to cysteine to allow the labelling with the [99mTc][Tc(N)PNP]-synthon [2], and characterised by HPLC. The chemical identity of 99mTc-RGDechi complexes was determined by carrier-added experiments supported by radio/UV-HPLC and LC-MS analyses. Dilution and transchelation stability studies of 99mTc-RGDechi complexes were carried out. Biological properties and binding specificity studies to the receptors were assessed on a panel of cancer cells expressing different levels of αvβ3 and αvβ5. Finally, the pharmacokinetic profiles of the more promising candidates 99mTc1 and 99mTc2 were evaluated both on healthy and melanoma-bearing mice. Their metabolism and metabolite identification are also performed.
Results. Peptides were efficiently labelled with the [99mTc][Tc(N)(PNP)]-synthon. The compounds were stable at least for 18 hours in the reaction mixture. Dilution and transchelation studies demonstrated a high stability. In vitro binding data evidenced that the [99mTc][Tc(N)(PNP)]-synthon does not affect the biological properties of the peptides. The truncate 99mTc4, which lack of the last five C-terminal amino acid, lost the selectivity to αvβ3. Biodistribution studies conducted on 99mTc1 and 99mTc2 showed that the compounds selectively localize in tumour models expressing αvβ3 and fails to accumulate in those expressing αvβ5 receptors [3].
Conclusion. 99mTc1-2 are able to discriminate between endogenously expressed integrins αvβ3 and αvβ5 and possess favorable pharmacokinetics characterized by low liver uptake and rapid elimination from non-target tissues resulting in positive target-to-non-target ratios. Results are promising; the presented construct can be considered the starting point for the development of agents for the selective detection of αvβ3 expression by SPECT.
References
[1] Del Gatto A, Zaccaro L et al, [2006], J Med Chem; 49(11):3416-20
[2] Bolzati C, Boschi A, et al, [2002], J Am Chem Soc; 124(38):11468-79
[3] Bolzati C, Salvarese N, et al [2018], J Med Chem; 21(8):9596-9610
