Efficient in vivo targeting of the myocardial scar using Moloney murine leukaemia virus complexed with nanoparticles.

During myocardial infarction, native myocardium is replaced by a fibrous scar, impairing cardiac pump function and leading to potentially life-threatening ventricular tachycardias. Gene therapy-based targeting of the cardiac scar is essential for short- and long-term treatment of post-infarct sequelae. However, there are currently no effective methods to target and transduce cardiac (myo)fibroblasts (FB) in vivo. Therefore, Moloney murine leukaemia virus (MMLV) encoding for the fluorescent reporter mCherry complexed with magnetic nanoparticles (MNP) in combination with magnetic steering was tested. This approach strongly increased the transduction rate of FB by four-fold in vitro. Additionally, injection of MMLV/MNP complexes into the forming scar during exposure of the heart to a magnetic field to increase virus dwell-time 3 days after left ventricular cryo-injury, a time when FB proliferation in the infarct peaks, yielded efficient transduction of resident FB. We further assessed the functional impact of overexpressing the gap junction protein connexin 43 (Cx43). MMLV-mediated Cx43 overexpression (MMLV-Cx43) in FB increased the formation of functional gap junctions in vitro and substantially lowered post-cryo-injury ventricular tachycardia incidence (by 50%), as demonstrated by in vivo electrophysiological testing 2 and 8 weeks after MMLV/MNP injection into the lesion. This anti-arrhythmic effect was probably the result of a decrease in the heterogeneity of conduction around and across the scar, as observed by optical mapping in isolated hearts overexpressing Cx43. Thus, MMLV/MNP complexes combined with magnetic steering offer an efficient strategy for targeting and transducing FB in vitro and in vivo, allowing modulation of the functional properties of cardiac scars. KEY POINTS: Genetic targeting and efficient transduction of (myo)fibroblasts (FB) in vivo are necessary to modify the properties of cardiac scars for therapeutic benefit. However, this has proven highly inadequate because of a lack of suitable viral vectors. We complexed Moloney murine leukaemia virus (MMLV) with magnetic nanoparticles (MNP) and applied a magnetic field to achieve prominent in vitro transduction of FB. Magnet-assisted in vivo injections of MMLV/MNP complexes into the developing scar enabled efficient transduction of cardiac tissue-resident FB. MMLV-Cx43-based overexpression of connexin 43 increased the density of functional gap junctions in FB in vitro. Following direct injection of the virus into the developing cardiac scar in a murine cryo-lesion model, electrophysiological in vivo testing showed that the incidence of ventricular tachycardia was reduced by 50% at 2 and 8 weeks post-treatment with MMLV. Our approach enables efficient targeting and transduction of FB in the cardiac scar, providing a blueprint for translation.