anti-herpesvirus properties (homoharringtonine and emetine; Figure 1 ) were detected for their ability to effectively inhibit the replication of SARS-CoV-2 in vitro with EC 50 (50% effective concentration) values of 2.55 and 0.46 µM, respectively [10] . However, the study did not disclose the mechanisms by which both compounds induced anti-SARS-CoV-2 activity. On the other hand, such outcomes might open the door to further investigations to optimize and design these compounds as effective drugs to combat COVID-19. Since we are all interested in gathering the latest scientific findings and knowledge regarding COVID-19 and its possible treatment, I would like to share with the readers of the journal Viruses some in-depth details about the above-mentioned compounds.
Homoharringtonine (recently known as omacetaxine mepesuccinate) is a natural alkaloid derived from some species of the Cephalotaxus genus and belongs to the class of cephalotaxus alkaloids [11] . This drug is a protein synthesis inhibitor and was approved by the U.S. Food and Drug Administration (FDA) for curing chronic or accelerated phase chronic myeloid leukemia [12] . In previous preclinical investigations, this compound was reported with powerful antiviral activity against herpesviruses such as herpes simplex virus 1, pseudorabies virus, and varicella-zoster virus [13, 14] .
Emetine is a natural alkaloid isolated from Psychotria ipecacuanha and belongs to the class of emetine alkaloids [15] . Emetine is a protein synthesis inhibitor used to treat amoebiasis. However, some unfavorable outcomes were reported to be associated with its use, including cardiotoxicity [16] . Its noticeable anti-herpes properties were described against herpes simplex virus 2, cytomegalovirus, and bovine herpesvirus 1 [17] [18] [19] .
Notably, the comprehensive review article that has been published in the journal Viruses (Special Issue "Recent Advances in Herpesviruses Research: What's in the Pipeline?") by Treml et al. [20] documented a large number of natural bioactive molecules and macromolecules with anti-herpes simplex virus properties along with their mechanisms of action. Although this paper has focused on the bioactivity against herpes simplex viruses, we cannot rule out that the reviewed natural products might have additional antiviral effects on various types of coronavirus, including SARS-CoV-2. On the other hand, this valuable review article might serve as a template to hunt down potential compounds that may be considered in further preclinical studies for evaluation against SARS-CoV-2. To date, there are several promising treatments for COVID-19 under investigation, but none with proven clinical efficacy. Therefore, all efforts should be gathered to overcome this serious problem and save the lives of many people all over the world.
Finally, special thanks should be given to all of the authors, reviewers, and editorial staff, who contributed to the Special Issue "Recent Advances in Herpesviruses Research: What's in the Pipeline?" and made this issue conceivable, both at Viruses and in the broader academic community.