Implementation of P22 Viral Capsids As Intravascular Magnetic Resonance <i>T</i>₁ Contrast Conjugates via Site-Selective Attachment of Gd(III)-Chelating Agents

Abstract

P22 viral capsids and ferritin protein cages are utilized as templating macromolecules to conjugate Gd­(III)-chelating agent complexes, and we systematically investigates the effects of the macromolecules’ size and the conjugation positions of Gd­(III)-chelating agents on the magnetic resonance (MR) relaxivities and the resulting image contrasts. The relaxivity values of the Gd­(III)-chelating agent-conjugated P22 viral capsids (outer diameter: 64 nm) are dramatically increased as compared to both free Gd­(III)-chelating agents and Gd­(III)-chelating agent-conjugated ferritins (outer diameter: 12 nm), suggesting that the large sized P22 viral capsids exhibit a much slower tumbling rate, which results in a faster <i>T</i>₁ relaxation rate. Gd­(III)-chelating agents are attached to either the interior or exterior surface of P22 viral capsids and the conjugation positions of Gd­(III)-chelating agents, however, do not have a significant effect on the relaxivity values of the macromolecular conjugates. The contrast enhancement of Gd­(III)-chelating agent-conjugated P22 viral capsids is confirmed by in vitro phantom imaging at a short repetition times (TR) and the potential usage of Gd­(III)-chelating agent-conjugated P22 viral capsids for in vivo MR imaging is validated by visualizing a mouse’s intravascular system, including the carotid, mammary arteries, the jugular vein, and the superficial vessels of the head at an isotropic resolution of 250 μm