Gene Therapy Delivery of Bacterial Sodium Channels Improves Outcome Following Stroke
The research here is notable for having progressed as far as a non-human primate study, as the conventional wisdom is that delivery of bacterial genes into mammals via forms of gene therapy is a bad idea because of the potential for immunogenic reactions. It is hard to find funding for any such project, and almost impossible for it to progress far along the path of development in a biotech company. Investors are more skeptical than regulators and will be very wary even given good data. Nonetheless, this is an interesting project, even if it is a little far on the compensatory side of the house: it is better to aim at prevention of heart attacks than to aim at helping the survivors be less impacted.
Current clinical therapies for myocardial infarction (MI) and sudden cardiac death show limited efficacy. The ability to enhance amplitudes of peak sodium (Na+) current and calcium (Ca2+) transient in cardiomyocytes could uniquely prevent arrhythmias and improve the contractile function of infarcted hearts. Previously, we leveraged the small size of engineered prokaryotic voltage-gated Na+ channels (BacNav, <1 kb) to overcome the adeno-associated virus (AAV) size constraint on delivered sequences and demonstrated that BacNav expression can directly enhance cardiac excitability. Here, we investigated whether cardiomyocyte-specific BacNav expression can provide both antiarrhythmic and inotropic benefits to the injured heart.
Encouraged by the in vitro results, we tested therapeutic efficacy of BacNav delivery in a Cynomolgus macaque model of ischemia-reperfusion (I/R)-induced MI. On the I/R injury, 10^12 vector genome/kg self-complementary AAV9-MHCK7-BacNav-HA (human influenza hemagglutinin tag) or self-complementary AAV9-MHCK7-GFP (green fluorescent protein) virus was injected intramyocardially in and around the infarct. Sham-surgery animals served as control. Immunostaining for HA tag fused to BacNav 4 weeks post-AAV injection demonstrated robust transgene expression around the infarction site, with successful targeting of BacNav channels to the T-tubular sarcolemma.
Longitudinal monitoring of cardiac contractile function by transthoracic echocardiography (ECG) revealed that at 1 week post-MI, left ventricular ejection fraction was similarly decreased in BacNav- and GFP-treated animals compared with sham-injury controls. By 4 weeks post-MI, GFP-treated but not BacNav-treated animals showed further decrease in left ventricular ejection fraction and increase in left ventricular end-systolic volume, with BacNav 4-week values not being significantly different from sham animals. Simultaneously, left ventricular end-diastolic volume did not differ across groups or time points suggesting that AAV-mediated, cardiomyocyte-specific BacNav expression directly counteracted an MI-induced contractile deficit.
We also implanted loop recorders at the time of MI induction and analyzed occurrence of spontaneous arrhythmias from recorded ECG traces during the 4-week follow-up. All 6 animals in the GFP group developed arrhythmic events, whereas only 1 animal in the BacNav group and 2 animals in the sham group exhibited arrhythmias.