The main protease, M^pro(or 3CL^pro) in SARS-CoV-2 is a viable drug target because of its essential role in the cleavage of the virus polypeptide. Feline infectious peritonitis, a fatal coronavirus infection in cats, was successfully treated previously with a prodrug GC376, a dipeptide-based protease inhibitor. Here, we show the prodrug and its parent GC373, are effective inhibitors of the M^profrom both SARS-CoV and SARS-CoV-2 with IC₅₀values in the nanomolar range. Crystal structures of SARS-CoV-2 M^prowith these inhibitors have a covalent modification of the nucleophilic Cys145. NMR analysis reveals that inhibition proceeds via reversible formation of a hemithioacetal. GC373 and GC376 are potent inhibitors of SARS-CoV-2 replication in cell culture. They are strong drug candidates for the treatment of human coronavirus infections because they have already been successful in animals. The work here lays the framework for their use in human trials for the treatment of COVID-19.

Sustained, indolent immune injury of the vasculature of a heart transplant limits long-term graft and recipient survival. This injury is mitigated by a poorly characterized, maladaptive repair response. Vascular endothelial cells respond to proangiogenic cues in the embryo by differentiation to specialized phenotypes, associated with expression of apelin. In the adult, the role of developmental proangiogenic cues in repair of the established vasculature is largely unknown. We found that human and minor histocompatibility–mismatched donor mouse heart allografts with alloimmune-mediated vasculopathy upregulated expression of apelin in arteries and myocardial microvessels. In vivo, loss of donor heart expression of apelin facilitated graft immune cell infiltration, blunted vascular repair, and worsened occlusive vasculopathy in mice. In vitro, an apelin receptor agonist analog elicited endothelial nitric oxide synthase activation to promote endothelial monolayer wound repair and reduce immune cell adhesion. Thus, apelin acted as an autocrine growth cue to sustain vascular repair and mitigate the effects of immune injury. Treatment with an apelin receptor agonist after vasculopathy was established markedly reduced progression of arterial occlusion in mice. Together, these initial data identify proangiogenic apelin as a key mediator of coronary vascular repair and a pharmacotherapeutic target for immune-mediated injury of the coronary vasculature.

Abdominal aortic aneurysm (AAA) remains the second most frequent vascular disease with high mortality but has no approved medical therapy. We investigated the direct role of apelin (APLN) in AAA and identified a unique approach to enhance APLN action as a therapeutic intervention for this disease. Loss of APLN potentiated angiotensin II (Ang II)-induced AAA formation, aortic rupture, and reduced survival. Formation of AAA was driven by increased smooth muscle cell (SMC) apoptosis and oxidative stress in Apln^−/y aorta and in APLN-deficient cultured murine and human aortic SMCs. Ang II-induced myogenic response and hypertension were greater in Apln^−/y mice, however, an equivalent hypertension induced by phenylephrine, an α-adrenergic agonist, did not cause AAA or rupture in Apln^−/y mice. We further identified Ang converting enzyme 2 (ACE2), the major negative regulator of the renin-Ang system (RAS), as an important target of APLN action in the vasculature. Using a combination of genetic, pharmacological, and modeling approaches, we identified neutral endopeptidase (NEP) that is up-regulated in human AAA tissue as a major enzyme that metabolizes and inactivates APLN-17 peptide. We designed and synthesized a potent APLN-17 analog, APLN-NMeLeu9-A2, that is resistant to NEP cleavage. This stable APLN analog ameliorated Ang II-mediated adverse aortic remodeling and AAA formation in an established model of AAA, high-fat diet (HFD) in Ldlr^−/− mice. Our findings define a critical role of APLN in AAA formation through induction of ACE2 and protection of vascular SMCs, whereas stable APLN analogs provide an effective therapy for vascular diseases. Significance Vascular diseases remain a major health burden, and AAAs lack effective medical therapy. We demonstrate a seminal role for APLN in AAA pathogenesis based on loss-of-function and gain-of-function approaches and included human vascular SMCs and AA tissue obtained from patients. We identified NEP as a dominant inactivating enzyme for native APLN-17. This allowed us to design and synthesize a stable and bioactive APLN analog resistant to NEP degradation that showed profound therapeutic effects against AAA. Our study clearly defines the APLN pathway as a central node in the pathogenesis of AAA and elucidate a therapeutic strategy of enhancing the APLN pathway by using a stable APLN analog to treat AAA.

The term “synthon engineering” is introduced for the directed manipulation of the molecular packing architecture including the system of secondary interactions caused by the respectively fine tuned synthons.