3.3. Prediction of the absorption, distribution, metabolism, excretion, and toxicity (ADMET) profile In addition to testing the physiochemical efficiency of a given molecule to inhibit the target protein, other parameters such as absorption, distribution, metabolism, excretion, and toxicity (ADMET) of the inhibitor play a critical role on demonstrating the likelihood of success of a drug. Utilization of in-silico ADMET profiling, in combination with in vivo and in vitro predictions in the initial stage of the screening process, can significantly fasten the drug discovery process by minimizing the number of potential safety problems. Hence, we performed a detailed ADMET profiling to evaluate the drug likeliness of the four polyphenols: EGCG, TF2a, TF2b, TF3 that exhibited the highest score from the MD simulation and MM-PBSA study along with the positive control remdesivir. Human colon adenocarcinoma-2 cell line (Caco2) permeability and human intestinal absorption (HIA) are key parameters to decide the total bioavailability of a drug. All the five compounds (EGCG, TF2a, TF2b, TF3, and remdesivir) showed comparatively low Caco2 permeability potential (<8 × 10−6 cm/s) and could be absorbed via the human intestine (Larregieu & Benet, 2013). EGCG, TF2a, TF2b, TF3, and remdesivir were predicted to be substrates of permeability glycoprotein (P-glycoprotein), which is an efflux membrane protein. However, remdesivir was predicted as a P-glycoprotein I inhibitor, and EGCG and TF3 as a P-glycoprotein II inhibitor, whereas TF2a and TF2b as both P-glycoprotein I and II inhibitor. Hence, above mentioned five compounds could regulate the physiological functions of P-glycoprotein (see Table S3 in the Supplementary Information). The distribution of a drug is regulated by many parameters such as lipid-solubility, concentration in plasma and binding ability to plasma proteins, transport proteins, etc. The volume of distribution at steady-state (VDss) suggests that EGCG, TF2a, TF2b, TF3, and remdesivir had a lower theoretical dose required for uniform distribution in the plasma. Further, the degree of diffusion across the plasma membrane increases in the following order remdesivir < EGCG < TF2a < TF2b < TF3 (Table S4 in the Supplementary Information) as measured by the fraction that is in the unbound state. The predictions through the distribution of the drugs via the central nervous system and blood-brain barrier suggest that these five compounds are poorly distributed to the brain and unable to penetrate the central nervous system. However, the medium level of the lipophilicity of the drugs suggests that they would have no negative impact on nervous system exposure. Cytochromes P450 (CYP) isozymes play crucial roles in drug metabolism. It has been observed that TF2a, TF3, and remdesivir are a substrate of CYP3A4 and hence, can be efficiently metabolized by CYP3A4. On the other hand, EGCG is a CYP3A4 inhibitor (Table S5 in the Supplementary Information). On a separate note, EGCG is predominantly metabolized in the small intestine and liver by the conjugate formation of glucuronide, methyl sulfates in the urine and plasma (Chow et al. 2005). Among the five compounds, TF2b and TF3 were predicted as the substrate of renal organic cation transporter-2 (Renal OCT2), as shown in Table S6 in the Supplementary Information. While EGCG, TF2a, and remdesivir are possibly cleared through other available routes such as bile, breath, faces, and sweat. EGCG remains intact in the plasma and later excreted via bile and metabolized by colon microflora. It is also expected that all the compounds are absorbable via oral prescription. We have also analyzed the toxicity profiles for EGCG, TF2a, TF2b, TF3 as well as remdesivir (see Table 7). The toxicity prediction from the AMES test (Salmonella typhimurium reverse mutation assay) exhibited that all the compounds could be considered as non-mutagenic agents. High toxicity was observed for all the compounds in Tetrahymena pyriformis. EGCG, TF2a, TF2b, TF3, and remdesivir were shown to inhibit the human ether-a-go-go-related gene II (hERG II). However, Remdesivir has been shown to induce hepatotoxicity, whilst EGCG, TF2a, TF2b, TF3 are not likely to be associated with hepatotoxicity. The maximum recommended tolerated dose (MRTD) in human prediction shows that remdesivir violate MRTD whereas natural polyphenol EGCG, TF2a, TF2b, TF3 do not fall into this category. Remdesivir does not possess high acute toxicity whereas EGCG, TF2a, TF2b, and TF3 regarded as high acute toxic compound as it falls under minnow toxicity. Additionally, none of the compounds predicted to be associated with skin sensitization. Table 7. Predicted toxicity profile of EGCG, TF3, TF2b, TF2a, and remdesivir. S. No. Compounds name Toxicity prediction       Properties Predicted values 1 EGCG AMES toxicity No     Maximum tolerated dose (Human) 0.441 (log mg/kg/day)     hERG I inhibitor No     hERG II inhibitor Yes     Oral rat acute toxicity (LD50) 2.522 (mol/kg)     Oral rat chronic toxicity (LOAEL) 3.065 (log mg/kg_bw/day)     Hepatotoxicity No     Skin sensitivity No     T. pyriformis toxicity 0.285 (µg/L)     Minnow toxicity 7.713 log mM 2 TF3 AMES toxicity No     Maximum tolerated dose (Human) 0.438 (log mg/kg/day)     hERG I inhibitor No     hERG II inhibitor Yes     Oral rat acute toxicity (LD50) 2.482 (mol/kg)     Oral rat chronic toxicity (LOAEL) 7.443 (log mg/kg_bw/day)     Hepatotoxicity No     Skin sensitivity No     T. pyriformis toxicity 0.285 (µg/L)     Minnow toxicity 9.738 log mM 3 TF2b AMES toxicity No     Maximum tolerated dose (Human) 0.438 (log mg/kg/day)     hERG I inhibitor No     hERG II inhibitor Yes     Oral rat acute toxicity (LD50) 2.482 (mol/kg)     Oral rat chronic toxicity (LOAEL) 5.322 (log mg/kg_bw/day)     Hepatotoxicity No     Skin sensitivity No     T. pyriformis toxicity 0.285 (µg/L)     Minnow toxicity 8.685 log mM 4 TF2a AMES toxicity No     Maximum tolerated dose (Human) 0.439 (log mg/kg/day)     hERG I inhibitor No     hERG II inhibitor Yes     Oral rat acute toxicity (LD50) 2.484 (mol/kg)     Oral rat chronic toxicity (LOAEL) 5.035 (log mg/kg_bw/day)     Hepatotoxicity No     Skin sensitivity No     T. pyriformis toxicity 0.285 (µg/L)     Minnow toxicity 4.898 log mM 5 Remdesivir AMES toxicity No     Maximum tolerated dose (Human) 0.15 (log mg/kg/day)     hERG I inhibitor No     hERG II inhibitor Yes     Oral rat acute toxicity (LD50) 2.043 (mol/kg)     Oral rat chronic toxicity (LOAEL) 1.639 (log mg/kg_bw/day)     Hepatotoxicity Yes     Skin sensitivity No     T. pyriformis toxicity 0.285 (µg/L)     Minnow toxicity 0.291 log mM