pH-responsive theranostic nanocomposites as synergistically enhancing positive and negative magnetic resonance imaging contrast agents.

Background: The rational design of theranostic nanoprobe to present responsive effect of therapeutic potency and enhanced diagnostic imaging in tumor milieu plays a vital role for efficient personalized cancer therapy and other biomedical applications. We aimed to afford a potential strategy to pose both T ₁ - and T ₂ -weighted MRI functions, and thereby realizing imaging guided drug delivery and targeted therapy.
Results: Theranostic nanocomposites Mn-porphyrin&Fe ₃ O ₄ @SiO ₂ @PAA-cRGD were fabricated and characterized, and the nanocomposites were effectively used in T ₁ - and T ₂ -weighted MRI and pH-responsive drug release. Fluorescent imaging also showed that the nanocomposites specifically accumulated in lung cancer cells by a receptor-mediated process, and were nontoxic to normal cells. The r ₂ /r ₁ ratio was 20.6 in neutral pH 7.4, which decreased to 7.7 in acidic pH 5.0, suggesting the NCs could act as an ideal T ₁ /T ₂ dual-mode contrast agent at acidic environments of tumor. For in vivo MRI, T ₁ and T ₂ relaxation was significantly accelerated to 55 and 37%, respectively, in the tumor after i.v. injection of nanocomposites.
Conclusion: The synthesized nanocomposites exhibited highly sensitive MRI contrast function no matter in solution, cells or in vivo by synergistically enhancing positive and negative magnetic resonance imaging signals. The nanocomposites showed great potential for integrating imaging diagnosis and drug controlled release into one composition and providing real-time imaging with greatly enhanced diagnostic accuracy during targeted therapy.