Potential COVID-19 therapeutics from a rare disease: utilization of lipid dysregulation to combat viral infectivity

Strategic drug repurposing in combination with rapid testing of established molecular targets could provide a pause in disease progression and even may open a new therapeutic strategy to fight COVID-19. Recent studies demonstrated that SARS-CoV-2 shares extensive structural and functional conservation with SARS-CoV-1, that includes engagement of the same host cell receptor, called angiotensin-converting enzyme 2 (ACE-2) localized in cholesterol-rich microdomains of cell membrane.[1]  The lipid-enveloped viruses encounter the endosomal/lysosomal host compartment in a critical step of infection and maturation.

Niemann-Pick type C (NP-C) disease is a rare neurodegenerative, lipid storage disease, caused by the deficient efflux of lipids from the late endosome/lysosome. The gene causing NP-C disease (NPC1) has been strongly associated with viral infections, both as a filovirus receptor (e.g., Ebola) and through lysosome lipid trafficking. Consequently, NPC1 inhibitors or NP-C disease mimetics could serve as potential anti-SARS-CoV-2 agents. [2]

Fortunately, there are such clinically approved molecules that elicit antiviral activity in preclinical studies, without causing NP-C disease. Inhibition of NPC1 may impair viral SARS-CoV-2 infectivity via several lipid-dependent mechanisms, which disturb the microenvironment optimum for viral infectivity. Researchers suggest that known mechanistic information on NPC1 could be utilized to identify existing and future drugs to treat COVID-19. [3]   NP-C disease is surprisingly well studied despite its rarity (only about 500 cases worldwide). For decades, research scientists have used existing drugs as research tools to model the disease, to explore biochemical mechanisms standing behind the lipid storage disorder. Some of these molecules are clinically approved in the treatment of unrelated disorders. Impressively, a number of these NPC1 inhibitors reduce the infectivity of numerous viruses by hindering viral release into the cytosol and preventing viral replication. The host cell receptor (i.e., ACE2 in SARS-CoV-1 and SARS-CoV-2) and proteases (i.e., TMPRSS2 in SARS-CoV-1 and SARS-CoV-2) that facilitate SARS-CoV-2 entry into the host cell are localized in cholesterol- and sphingolipid-rich membrane domains.

Inhibiting NPC1 depletes these microdomains, so disturbing the dispersion of the host cell receptors and therefore reducing the possibility of virus „landing” and binding through viral Spike-protein at cell surface before internalization. The inhibition of NPC1 provides a dual blockade of viral entry into host cells and thus represents a means to inhibit SARS-CoV-2 infectivity. Numerous, readily available, NPC1 inhibitor drugs are effective in limiting viral infections, as detailed below:

The NPC1 inhibitor U18666A, a cationic amphiphile sterol dramatically reduced infectivity of SARS-CoV1, Ebola virus, Influenza A, Chikungunya, Hepatitis C, Zika, Dengue and HIV. [4-6]

Imipramine (an amphiphilic drug clinically approved to treat depression) or Itraconazole (a clinically approved antifungal drug) effectively blocked the activity of NPC1 and reduced infectivity of coronavirus and filoviruses. [5,7]

Similarly, Cepharanthine (an approved anti-inflammatory and anti-cancer drug) exhibited complete inhibition of the pangolin coronavirus model for COVID-19, perhaps by binding and inhibition of NPC1. [8]

An alternate approach is to use therapeutics that alter cholesterol homeostasis and mimic NP-C disease. Interestingly, Chloroquine, a top candidate of all approved drugs to treat COVID-19, mimics NP-C disease via inhibiting cholesterol esterification and autophagy – this clearly implicates NPC1 in a potential treatment for inhibiting SARS-CoV-2. [9]

Additionally, other cationic amphiphiles Chlorpromazine (approved to treat schizophrenia and depression) and Amiodarone (approved to treat cardiac arrhythmia) could be tested as candidate therapies for treating COVID-19; both compounds mimic NP-C disease, and inhibited SARS-CoV-1 and MERS-CoV. [10-11]

Amongst the approved drugs for the treatment of NP-C with direct effect on cholestrol/lipid trafficing, different types of 2-Hydroxypropyl-beta-cyclodextrins, (e.g.Trappsol Cyclo™ by CTD Inc. and VTS-270 by Vtesse) were designated as orphan drugs. (Clinical Trials.gov NCT02939547 and NCT02912793)

The above scientific results and publications seriously raise the hypothesis that the intracellular biochemical abnormalities inherent to lipid storage disorders in general, and particularly to Nieman Pick Type C may pose an “unfavorable” host cell environment for the landing, entry, trafficking, and fusion of SARS-CoV-2.

It is therefore postulated that the altered composition of the plasma membrane and lipid rafts in NP-C may affect the trafficking of ACE2, the primary host cell membrane receptor responsible for viral docking, thereby interfering with viral infection. [12]

1. Glende, J., et al. Importance of cholesterol-rich membrane microdomains in the interaction of the S protein of SARS-coronavirus with the cellular receptor angiotensin-converting enzyme 2. Virology, 2008. 381(2):215-21. doi: 10.1016/j.virol.2008.08.026

1. To, K.F. and Lo, A.W. Exploring the pathogenesis of severe acute respiratory syndrome (SARS): the tissue distribution of the coronavirus (SARS-CoV) and its putative receptor, angiotensin-converting enzyme 2 (ACE2). J Pathol, 2004. 203(3): 740-743.doi: 10.1002/path.1597
2. Sturly, S.L. et al. Potential COVID-19 therapeutics from a rare disease: weaponizing lipid dysregulation to combat viral infectivity J Lipid Res.2020; 61 (7):972-982. doi: 10.1194/jlr.R120000851. 
3.  Lu, F., et al. Identification of NPC1 as the target of U18666A, an inhibitor of lysosomal cholesterol export and Ebola infection. eLife, 2015; 4: e12177. https://doi.org/10.7554/eLife.12177.001
4. Wichit, S.,  et al. Imipramine inhibits Chikungunya virus replication in human skin fibroblasts  through interference  with intracellular cholesterol trafficking. Sci Rep, 2017; 7: 3145. https://doi.org/10.1038/s41598-017-03316-5
5. Tang, Y.,  et al. Deficiency of Niemann-Pick type C-1 protein impair  release of huma  immunodeficiency  virus type 1 and results in Gag accumulation in late endosomal/lysosomal compartments. J Virol, 2009; 83: 7982-95. doi: 10.1128/JVI.00259-09
6. Takano, T.,  et al. Antiviral activity of itraconazole against type I feline coronavirus infection. Vet Res, 2019; 50:5. https://doi.org/10.1186/s13567-019-0625-3
7. Lyu, J.,  et al. Pharmacological blockade of cholesterol trafficking by cepharanthine in endothelial cells suppresses angiogenesis and tumor growth. Cancer Lett, 2017; 409: 91-103. doi: 10.1016/j.canlet.2017.09.009
8. Liu, C., et al. Research and development on therapeutic agents and vaccines for COVID-19 and related human coronavirus diseases. ACS Cent Sci 2020; In Press.) doi: 10.1021/acscentsci.0c00272
9. Stadler, K.,  et al. Amiodarone alters late endosomes and inhibits SARSoronavirus infection at a post-endosomal level. Am J Respir Cell Mol Biol, 2008; 39: 142-9. https://doi.org/10.1165/rcmb.2007-0217OC
10. de Wilde, A.H.,  et al. Screening of an FDA-approved compound library identifies four small-molecule inhibitors of Middle East respiratory syndrome coronavirus replication in cell culture. Antimicrob Agents Chemother, 2014; 58: 4875-4884. doi: 10.1128/AAC.03011-14
11. R.A. Ballout, et al The lysosome: A potential juncture between SARS‐CoV‐2 infectivity and Niemann‐Pick disease type C, with therapeutic implications The FASEB Journal 05 May 2020, https://doi.org/10.1096/fj.202000654R