In vitro study on efficacy of PHELA, an African traditional drug against SARS-CoV-2

Abstract

In 2019, coronavirus has made the third apparition in the form of SARS-CoV-2, a novel strain of coronavirus that is extremely pathogenic and it uses the same receptor as SARS-CoV, the angiotensin-converting enzyme 2 (ACE2). However, more than 182 vaccine candidates have been announced; and 12 vaccines have been approved for use, although, even vaccinated individuals are still vulnerable to infection. In this study, we investigated PHELA, recognized as an herbal combination of four exotic African medicinal plants namely; Clerodendrum glabrum E. Mey. Lamiaceae, Gladiolus dalenii van Geel, Rotheca myricoides (Hochst.) Steane & Mabb, and Senna occidentalis (L.) Link; as a candidate therapy for COVID-19. In vitro testing found that PHELA inhibited > 90% of SARS-CoV-2 and SARS-CoV infection at concentration levels of 0.005 mg/ml to 0.03 mg/ml and close to 100% of MERS-CoV infection at 0.1 mg/ml to 0.6 mg/ml. The in vitro average IC₅₀ of PHELA on SARS-COV-2, SARS-CoV and MERS-COV were ~ 0.01 mg/ml. Secondly in silico docking studies of compounds identified in PHELA showed very strong binding energy interactions with the SARS-COV-2 proteins. Compound 5 showed the highest affinity for SARS-COV-2 protein compared to other compounds with the binding energy of - 6.8 kcal mol^-1. Our data showed that PHELA has potential and could be developed as a COVID-19 therapeutic.

Figure 1

PHELA extract inhibition of SARS-CoV-2. (A) Wuhan strain, (B) a South African strain isolated during the first wave of the pandemic, and (C) the N501Y.V2 variant were incubated with the extract before infection of 293-T cells ACE.MF. After 72 h incubation the inhibition of infection was determined by measuring luminescence. Data shown represent the results of three independent experiments, and bars represent the means ± standard deviation.

Figure 2

Evaluation of the PHELA extract cytotoxicity in 293-T ACE.MF cells. The extract was incubated with 293T-ACE.MF cells for 72 h followed by the determination of cytotoxicity using the MTT assay. Data shown are means ± standard deviation of three independent experiments.

Figure 3

PHELA extract inhibition of SARS-CoV related coronaviruses. (A) SARS-CoV, and (B) MERS-CoV were incubated with the extract before infection of 293-T cells ACE.MF or Vero cells, respectively. After 72 h incubation the inhibition of infection was determined by measuring luminescence. Data shown represent the results of three independent experiments, and bars represent the means ± standard deviation.

Figure 4

Three dimension (3D) structure of (A) Compound 5 in complex with SARS-CoV-2 protein (highest binding energy) (B) 2-D representations of docked complex of Compound 5 in complex SARS-CoV-2 protein displaying the interactions with amino acid residues.

Figure 5

Three dimension (3D) structure of (A) Compound 1 in complex with SARS-CoV-2 protein (highest binding energy) (B) 2-D representations of a docked complex of Compound 1 in complex SARS-CoV-2 protein displaying the interactions with amino acid residues.

Figure 6

3D structure of (A) Baricitinib in complex SARS-CoV-2 protein (B) 2-D representations of a docked complex of Baricitinib in complex SARS-CoV-2 protein displaying the interactions with amino acid residues.