3 | MNPs: NOVEL BIOMEDICAL RESOURCES FOR ANTI-INFECTION OF SARS-COV-2
As an enveloped RNA virus, coronavirus is a major cause of human respiratory diseases. The spike glycoprotein (SGP) is known as the main target of antibodies having neutralizing potency and is also considered as an attractive target for therapeutic or vaccine development. MNPs as key and novel biomedical resources for the discovery of drugs to combat the COVID-19 pandemic (Table 1), will be more and more valuable.
Among MNPs library, 17 potential SARS-CoV-2 main protease (Mpr) inhibitors have been identified by structure-based techniques, and one of these compounds could be bioactive [28]. Marine bacteria and fungi-derived bioactive 15 compounds showed promising potential roles against SARS-CoV-2 RNA dependent RNA polymerase and methyltransferase [29]. Some new MNPs compounds (bioactive peptides) isolated from marine organisms (such as vertebrates, invertebrates, seaweeds, or other sea microorganisms) have a role of prevention on SARS-CoV-2 infection due to potential angiotensin converting enzyme (ACE) inhibition and anti-hypertensive activities [30]. The most potent marine-derived metabolite from Red-Sea invertebrates, erylosides B [31], showed a great inhibitor activity against the SARS-CoV-2 Mpro.
Some bioactive agents from marine polysaccharides and polysaccharide-based vaccine adjuvants were developed for the fight against SARS-CoV-2 and were used as therapeutic agents and vaccines of COVID-19 [32]. A naturally existing sulfated polysaccharide, lmbda-carrageenan, purified from marine red algae, could be a promising antiviral agent for preventing infection with several respiratory viruses since this polyanionic compound exerts antiviral activity by targeting viral attachment to cell surface receptors and preventing virus entry [33]. Novel marine sulfated polysaccharides can be developed further for prophylactic as well as therapeutic purposes due to potent anti-SARS-CoV-2 activity and affinity to the SGP [34]. As potential candidates of antiviral drug, marine sulfated polysaccharides can be used to prevent SARS-CoV-2 infection [35].
Carbohydrate-binding agents from MNPs like lectins from marine algae have shown antiviral activities against SARS-CoV-2 due to targeting of N-linked glycans of the SGP envelope of CoV, and could also serve as an attractive therapeutic approach for developing novel antivirals [36]. Marine-derived natural metabolites from the soft coral [Nephthea  sp.] can also be developed potential SARS-CoV-2 protease inhibitors [37]. As SARS-CoV-2 Mpro inhibitors, five MNPs (a benzo[f]pyrano[4,3-b]chromene, notoamide I, emindole SB beta-mannoside, and two bromoindole derivatives) were the most promising marine drug-like leads [38].
Up-to-date, FDA-approved marine drugs have the potential to inhibit the biological activity of SARS-CoV-2 main protease since they can bind at its active site and displace water molecules at this site [39]. The nontoxic and non-immunogenic polyphosphate, a physiological, metabolic energy (ATP)-providing polymer, could possibly also exert a protective effect against SARS-CoV-2-cell attachment [40]. These marine drugs which are already in clinical use for cancer treatment can also be used as a potential alternative to prevent and treat infected individuals with SARS-CoV-2 and its major variants (Delta and Omicron). Hence, the MNPs and their derivatives could be a promising source of structurally diverse new anti-RNA virus therapeutics [41].