A tripodal ruthenium-gadolinium metallostar as a potential α(v)β(3) integrin specific bimodal imaging contrast agent.

Gd(III)-containing metallostar contrast agents are gaining increased attention, because their architecture allows for a slower tumbling rate, which, in turn, results in larger relaxivities. So far, these metallostars find possible applications as blood pool contrast agents. In this work, the first example of a tissue-selective metallostar contrast agent is described. This RGD-peptide decorated Ru(II)(Gd(III))(3)metallostar is synthesized as an α(v)β(3)-integrin specific contrast agent, with possible applications in the detection of atherosclerotic plaques and tumor angiogenesis. The contrast agent showed a relaxivity of 9.65 s(-1) mM(-1), which represents an increase of 170%, compared to a low-molecular-weight analogue, because of a decreased tumbling rate (τ(R) = 470 ps). The presence of the MLCT band (absorption 375-500 nm, emission 525-850 nm) of the central Ru(II)(Ph-Phen)(3)-based complex grants the metallostar attractive luminescent properties. The (3)MLCT emission is characterized by a quantum yield of 4.69% and a lifetime of 804 ns, which makes it an interesting candidate for time-gated luminescence imaging. The potential application as a selective MRI contrast agent for α(v)β(3)-integrin expressing tissues is shown by an in vitro relaxometric analysis, as well as an in vitroT(1)-weighted MR image.