Background:
Despite the benefits of reperfusion therapy after myocardial infarction (MI), most patients still progress to heart failure. MI patients suffer irreversible loss of heart function due to cardiomyocyte (CM) death and tissue scarring. Growth factors (GFs) reduce scar size and limit CM apoptosis in preclinical studies, however native GFs have poor drug-like qualities and have not been successful in the clinic. Silver Creek Pharmaceuticals is developing a new class of targeted, growth factor-based therapeutics (Smart Growth Factors) that are engineered to have optimized pharmacokinetics, dynamics and safety profiles. Our first generation of SGFs use annexin-V (AnxV) to target IGF-1 to damaged CMs and selectively activate pro-survival signaling.
Methods and Results:
We used biophysical simulation to design an IGF-1-based SGF that selectively activated the PI3K pathway in damaged cells. SGFs were engineered to target IGF-1 to damaged cells through the binding of AnxV to phosphatidylserine exposed on the surface of apoptotic cells. These bispecific proteins were constructed with half-life modulators and linkers, then screened for their ability to selectively increase pAKT levels in apoptotic iPSC-derived human CMs. We identified a subset of SGFs that were able to selectively increase pAKT levels in apoptotic cells as compared to healthy cells (p<0.05). Based on these data, we tested the ability of SGFs to activate pro-survival signaling and reduce infarct size in a rat ischemia/reperfusion model of acute MI (AMI). SGFs were able to selectively prolong pAKT in the infarcted region of the left ventricle without activating signaling in remote healthy tissue out to 2 hours post-reperfusion (n=3-6/group, p<0.05). For efficacy studies, rats were subjected to 60 minutes of ischemia followed by 72 hours of reperfusion. A single IV dose of SGF (600 pmol/kg) administered at time of reperfusion was able to significantly reduce infarct size relative to the area-at-risk (infarct/AAR%) as compared to controls (p<0.05; SGF 12.7±5% n=10; wt IGF-1 20.3±3% n=8 and vehicle 27.6±7% n=12).
Conclusions:
This work demonstrates that SGFs selectively activate pro-survival signals in distressed CMs and lead to reduced infarct size in vivo without off-target effects.
Parasympathetic effects on in vivo rat heart can be regulated through an alpha 1-adrenergic receptor.
