The rapid geographic expansion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the infectious agent of Coronavirus Disease 2019 (COVID-19) pandemic, poses an immediate need for potent drugs that can help contain the outbreak. Enveloped viruses infect the host cell by cellular membrane fusion, a crucial mechanism required for virus replication. The SARS-CoV-2 spike glycoprotein, due to its primary interaction with the human angiotensin-converting enzyme 2 (ACE2) cell-surface receptor, is considered as a potential target for drug development. Based on in silico screening followed by in vitro studies, here we report that the existing FDA-approved Bcr-Abl tyrosine kinase inhibitor, imatinib, inhibits SARS-CoV-2 with an IC50 of 130 nM. We provide initial evidence that inhibition of virus fusion may explain the antiviral action of imatinib. This finding is significant since pinpointing the mode of action allows evaluating the drug's affinity to the SARS-CoV-2-specific target protein, and in turn, helps make inferences on the potency of the drug and evidence-based recommendations on its dosage. To this end, we provide evidence that imatinib binds to the receptor-binding domain (RBD) of SARS-CoV-2 spike protein with an affinity at micromolar, i.e., 2.32 ± 0.9 µM, levels. We also show that imatinib inhibits other coronaviruses, SARS-CoV and MERS-CoV, possibly via fusion inhibition. Based on promising in vitro results, we propose the Abl kinase inhibitor (ATKI), imatinib, to be a viable repurposable drug candidate for further clinical validation against COVID-19.
In this paper, the potential use of electroresponsive poly(acrylic acid) (PAA) gels as reversible enzyme activity regulators is analyzed. This was evaluated by measuring the glucose conversion by hexokinase embedded PAA hydrogels under external electrical stimuli. Hexokinase physically entrapped within PAA gels showed a significant increase in activity under an electrical stimulus as compared to in the absence of a stimulus. Kinetic studies revealed that the change in reaction rate could be attributed to the change of V max under a stimulus, while K m was unaffected by the stimulus, which suggested that the increase in reaction rate under an electrical stimulus was due to increased accessibility of the active site. Optimum stimuli-responsive behavior that resulted in maximum conversion under a stimulus and minimum conversion in the absence of a stimulus was obtained at 5.5 pH and 30 °C. The significant difference between the pH optima for the entrapped enzyme and the pure enzyme can be attributed to the acidic nature of the polymeric matrix. Higher cross-linker concentrations resulted in a reduction of both enzyme release and glucose conversion, and a reasonable trade-off between conversion and release could be obtained at 5% cross-linker concentration. Application of a stepwise electrical stimulus revealed that the entrapped enzymes could sustain responsive properties over multiple cycles of electrical switching. Entrapped hexokinase also showed much better reusability compared to pure hexokinase, a combined result of higher enzyme retention and increased stability. No significant impact of the polymer on the interaction between enzyme and glucose was observed. Thus, this system enables electro-responsive modulation of enzyme activity without any reduction in enzyme activity. The studies revealed that conjugation of electro-responsive polymers to enzymes has the potential to reversibly modulate enzymatic reactions via the application of external electrical stimuli, which is promising for bioprocessing and enzymatic separation applications.
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