New study by Japanese researchers from Tohoku University, Kyushu University, Okayama University and the National Institutes of Natural Sciences, Okazaki-Japan has alarmingly found that the U.S. FDA approved and heavily promoted drug for COVID-19 ie Remdesivir activates the urotensin II receptor and induces cardiomyocyte dysfunction that can lead to heart issues that can also end up with fatal outcomes.
The study findings were published on a preprint server and are currently being peer reviewed. https://www.biorxiv.org/content/10.1101/2022.08.08.503256v1
Following the completion of the Adaptive COVID-19 Treatment Trial 1 (ACTT-1) (7), which demonstrated remdesivir’s superiority over placebo for improving time to recovery in hospitalized COVID-19 patients, remdesivir has been one of the most commonly prescribed medications for patients hospitalized for COVID-19 infection.
Importantly, the ACTT-1 investigators reported that 0.2% of patients receiving remdesivir, but not patients receiving placebo, showed arrythmias (other than atrial fibrillation, supraventricular tachycardia, ventricular tachycardia, and ventricular fibrillation), although these cardiovascular effects was not considered as significant adverse effects.
However, the percentage of patients experiencing arrythmias could be underestimated, since early clinical trials are insufficiently powered to detect uncommon adverse events (39). Indeed, a large retrospective pharmacovigilance cohort study, which used the medical records from more than 130 countries and 20 million patients, reported that cardiac arrest, bradycardia, and hypotension is associated with remdesivir use (10).
The elevation of plasma remdesivir concentration is associated with an increase in field potential duration with decreased Na+ peak amplitudes and spontaneous beating rates, which might potentially induce prolonged QT interval and torsade de point (40, 41).
Importantly, the cardiac adverse effects appear to be directedly caused by remdesivir, since they were reported to resolve within 24-48 hours of discontinuing remdesivir (42, 43). To date, the precise mechanism underlying the remdesivir’s cardiac side effects has remained unclear with no means of predicting the populations susceptible to its cardiac side effects and no specific treatment for the cardiotoxicity. Therefore, there is a pressing need to understand how remdesivir induces the cardiac dysfunction.
Using an unbiased and large-scale GPCR screening strategy, we identified that remdesivir, but not molnupiravir and favipiravir, selectively activates UTS2R. Interestingly, UTS2R is highly expressed in heart tissue, including cardiomyocytes. Activation of UTS2R by Urotensin-II (UT2), the endogenous ligand of UTS2R, has been implicated in cardiac dysfunction.
For example, the plasma level of UT2 and expression level of UTS2R in cardiomyocytes are elevated in patients with end-stage congestive heart failure (44). In line with these previous studies, we found that activation of UTS2R by remdesivir at a concentration of 1 μM induced electrical abnormalities and contraction force impairment in cultured cardiomyocytes, both of which resemble the reported cardiac side effects in humans.
Furthermore, these adverse effects were effectively blocked by antagonizing UTS2R or inhibiting its downstream signaling. Clinically, remdesivir is administrated intravenously at a dose of 200 mg once followed by 100 mg daily for a total of 5-10 days in adults and children ≥40 kg.
The estimated peak plasma concentration of remdesivir is 9.03 μM in healthy adults and can be higher in patients with renal or hepatic impairment because of its renal and biliary excretion (45). Our results suggest that the clinical dosage of remdesivir is sufficient to activate UTS2R, and patients with renal or hepatic impairment may be at high risk for adverse events mediated through the remdesivir-UTS2R axis.
Notably, our GPCR assay clearly showed that remdesivir has no effect on adenosine receptors, of which the activation can also impact cardiac functions. Thus, the activation of UTS2R is likely responsible for the cardiac side effects.
An important finding of this study is that single-nucleotide variants (SNVs) in the coding region of UTS2R have large impacts on its response to remdesivir. This result is in line with previous studies that show SNVs in GPCR genes are associated with the pathophysiology of various diseases, including CV diseases, and affect therapeutic outcomes (46).
While 40% of SNVs in UTS2R (44/110) showed at least a twofold reduction in potency toward remdesivir compared to WT receptor, and 56% (62/110) showed no remarkable change (within the range of an 0.5-fold to 2-fold change), we identified four gain-of-function SNVs that showed more than two-fold increase in the response to remdesivir. Notably, D1303.32G was a variant at the same amino acid for which we identified a gain-of-function mutation (D1303.32N) using in silico modeling, indicating the importance of D1303.32 residue in remdesivir recognition.
Activation of GPCR often induces recruitment of β-arrestin to the receptor, followed by receptor internalization to the intracellular compartment. This internalization terminates GPCR activation and promotes secondary signaling pathways (47). Interestingly, unlike the endogenous ligand UT2, which effectively induces β-arrestin recruitment (Fig 1C) (48), remdesivir-mediated UTS2R activation did not induce β-arrestin recruitment.
Thus, our results suggest that remdesivir is a G-protein-biased ligand (Fig. 1C, S1A). Such biased activation of UTS2R by remdesivir may have an important impact on cardiac function in a way that allows prolonged activation of UTS2R without β-arrestin-mediated shutdown and thereby an exaggeration of downstream signaling and enhanced cardiotoxic effects.
Upon ligand binding, GPCRs, including UTS2R, initiate conformational change that induces the activation of heterotrimeric G proteins and dissociation of Gα and Gβγ subunit complexes. Gα proteins include Gαs, Gαi/o, Gαq/11, and Gα12/13 proteins, which are responsible for downstream signaling transduction.
Members of the Gαi/o family are widely distributed, including in the cardiac system, where they are highly expressed and act to regulate myocardial contractility and heart rate via modulation of ion channels (36). For example, resting heart rate is controlled by cholinergic signals mediated through muscarinic M2 Gαi-coupled receptors.
These effects occur by inhibition of adenylyl cyclase (AC) and by Gβγ-inhibition of a potassium channel in the sinoatrial node. The transduction mechanism of UTS2R is the coupling and activation of Gαi/o as well as Gαq (28), consistent with the UT2-UTS2R axis being implicated in CV regulation through complex signaling pathways, both physiologically and pathologically. Our results using NRCMs clearly showed that the remdesivir-mediated decrease in myocardial contraction is dependent on Gαi/o, but not Gαq/11 (Fig. 3F).
Since NRCMs resemble the phenotype of atrial myocytes (49), the decrease in myocardial contractility under constant pacing by remdesivir indicates impairment of calcium handling (50), which is consistent with the slowing of the heart rate, a distinctive cardiovascular side effect of remdesivir (10).
Despite the discovery that remdesivir can activate UTS2R and cause cardiotoxicity, the lack of clinical evidence is a major limitation of this study. Yet, as the allele frequencies of the gain-of-function variants are low (Fig. S4B) and usage of remdesivir is expected to decline due to the recent prevalence of the Omicron COVID-19 variant with its milder symptoms, a large-scale clinical study on the association between remdesivir sensitivity and genomic variance is challenging to execute.
Additionally, we have not determined the precise molecular mechanisms that induce the UTS2R-dependent proarrhythmic risk of remdesivir. Possible explanations are the impaired regulation of gene expression or trafficking of ERG potassium channels, which are essential for electrical activity in the heart (51).
Alternatively, the chronic and cumulative cardiotoxic effects of remdesivir-UTS2R axis are consistent with a downstream impact on translation and transcription. In addition, a previous study suggested that remdesivir-related cardiotoxicity can be caused by mitochondrial dysfunction (52) since the active form of remdesivir shows an inhibitory effect toward mitochondrial RNA polymerase (mtRNAP) at a high dose (53).
However, treatment with remdesivir at 10 μM, which is equivalent to the maximum plasma concentration following remdesivir administration in humans (27), did not affect the steady-state levels of mitochondrial respiratory complex proteins (Fig. S3G). Although we do not exclude the possibility that remdesivir might affect mitochondrial metabolism through UTS2R signal transduction, the current data suggests that the remdesivir-UTS2R axis is the major off-target of remdesivir.
In conclusion, to our knowledge, this is the first report showing that remdesivir is a selective agonist of UTS2R and that remdesivir-mediated UTS2R activation underlies drug- mediated cardiotoxicity. Furthermore, we discovered that specific SNVs in UTS2R can increase the sensitivity to remdesivir. Thus, this study provides mechanistic insights into remdesivir- mediated cardiac side effects and the therapeutic opportunity to prevent the aversive events in the future.