In a recent study published in Scientific Reports, researchers evaluated the efficacy of PHELA, a traditional African drug, against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in vitro.
SARS-CoV-2 proteins such as spike (S), membrane (M), nucleocapsid (N), and envelope (E) have been recognized as therapeutic targets. Therefore, scientists have focussed on developing SARS-CoV-2 protein-targeted treatments to widen the therapeutic landscape of coronavirus disease 2019 (COVID-19).
PHELA is an herbal combinational drug consisting of four exotic African plant extracts, which are as follows: Gladiolus dalenii van Geel, Clerodendrum glabrum E. Mey. Lamiaceae, Senna occidentalis (L.) Link and Rotheca myricoides (Hochst.) Steane & Mabb, and PHELA treatment improved white blood cell (WBC) counts (lymphocytes and neutrophils) among immunosuppressed (by drugs) rats, and no adverse effects were reported among monkeys in a previous toxicology analysis.
Furthermore, the drug was reported safe in a phase I clinical trial conducted on healthy humans. The authors of the present study previously reported that PHELA reversed the immunosuppression induced by cyclosporine and dexamethasone among rats with no effects on the immunological system.
About the study
In the present study, researchers analyzed the anti-SARS-CoV-2 efficacy of PHELA in vitro.
The abovementioned plants were obtained and their parts were dried and grounded to form a homogenous powder, which was subsequently sterilized by gamma radiations. Subsequently, the plant compounds were extracted in specific amounts and analyzed using ultra-performance liquid chromatography (UPLC).
Human angiotensin-converting enzyme 2 (ACE2)-expressing 293T cells (or 293-T ACE.MF cells) and Vero cells were obtained for cell culture experiments. SARS-CoV-2 pseudovirus was prepared by co-transfection of two plasmids, one encoded SARS-CoV-2 E, and the other encoded the pNL4-3.luc.RE gene or luciferase reporter gene. SARS-CoV-2 E genes of the Wuhan-Hu-1 strain (GeneBank: MT039874.1) and the first wave South Africa virus (GeneBank: MT324062.1) were used for the analysis.
The N501Y.V2 mutation-containing SARS-CoV-2 variant was prepared by introducing the corresponding mutation in the Wuhan-Hu-1 strain. Subsequently, SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) pseudoviruses were also prepared. The effective concentrations of PHELA and the average half-maximal inhibitory concentration (IC50) values against SARS-CoV, SARS-CoV-2, and MERS-CoV were determined.
In addition, PHELA cytotoxicity was assessed using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT assays), and the tissue culture infectious dose (TCID50) values were determined. Further, in silico molecular docking analyses were performed to assess the binding interactions of liquid chromatography-mass spectrometry (LC-MS)-identified molecular compounds with SARS-CoV-2 proteins.
Results and discussion
PHELA inhibited the entry of SARS-CoV-2 into human ACE2-expressing 293 T cells. At the highest concentration of PHELA tested, complete (100%) inhibition of all SARS-CoV-2 strains tested was observed. The South Africa strain demonstrated the highest sensitivity to PHELA (IC50 of 0.0013 mg/ml), whereas the IC50 value for the Wuhan-Hu-1 strain was 0.010 mg/ml and for the 501Y.V2-containing mutant SARS-CoV-2 strains was 0.024 mg/ml.
In the cytotoxicity analysis, PHELA was found to be non-toxic at concentrations used in the study. However, otherwise low toxicity was observed for other experimental concentrations (TC50 value of 0.48 mg/ml). Additionally, SARS-CoV and MERS-CoV inhibition were attained with IC50 values of 0.0035 mg/ml and 0.0590 mg/ ml, respectively.
The findings indicated that the sensitivity of SARS-CoV to PHELA was 16-fold higher than MERS-CoV and highlighted the promising potential of PHELA to be used as a repurposed agent for other coronaviruses such as SARS-CoV and MERS-CoV. PHELA treatment inhibited SARS-CoV and SARS-CoV-2 by >90% at concentrations ranging between 0.005 and 0.03 mg/ml and almost completely inhibited MERS-CoV at concentrations ranging between 0.1 and 0.6 mg/ml.
The average IC50 values of in vitro PHELA treatment for MERS-CoV, SARS-COV, and SARS-CoV-2 were approximately 0.01 mg/ml. Further, in silico molecular docking analysis showed that PHELA was very strongly bound to proteins of SARS-CoV-2, and compound 5 demonstrated the greatest affinity for proteins of SARS-COV-2 and the binding energy for the corresponding interaction was -6.8 kcal mol−1.
The substantially lower sensitivity of MERS-CoV to PHELA in comparison to SARS-CoV, SARS-CoV-2 Wuhan-Hu-1 strain, and the N501Y.V2-containing SARS-CoV-2 variant could be due to differences in the envelope S proteins of the viruses. SARS-CoV and SARS-CoV-2 are also more genetically similar to each other than to MERS-CoV, and the SARS-CoV and SARS-CoV-2 viruses both use ACE2 receptors for entry into the host. The substantially lower sensitivity of the N501Y.V2-containing SARS-CoV-2 variant to PHELA compared to the Wuhan-Hu-1 strain underpins the genetic similarity between SARS-CoV and SARS-CoV-2.
Overall, the study findings highlighted the broad spectrum of activity of PHELA with promising potential as a therapeutic agent against SARS-CoV, SARS-CoV-2, and MERS-CoV.