Inhibition of SARS-CoV-2 entry through the ACE2/TMPRSS2 pathway is a promising approach for preventing/limiting virus entry into host cell and/or reducing viral load.
ACE2 is expressed in the respiratory epithelium and in the nasal epithelial cells. TMPRSS2 is expressed in lung and bronchial epithelial cells as well as in the nasal epithelial cells[i],[ii]. The virus SARS-CoV-2 (similarly to other viruses of the SARS family) invades human cells by binding to ACE2 through interaction with ACE2 is mediated via the spike (S) glycoprotein on SARS-CoV-2 surface. Initial spike protein priming relies upon human transmembrane protease, serine 2 (TMPRSS2) and is essential for entry of SARS-CoV-2 (Figure 1)[iii]. Literature data provide a firm evidence that inhibition of the above-mentioned host genes, either by siRNA or by other means, abolishes infection with related viruses including SARS-CoV-2[iv], thus justifying this strategy for prophylaxis/treatment of COVID-19.
- Lepton has the technology for local administration of modified siRNAs
to achieve efficient delivery throughout the lung, both to bronchial
and alveolar epithelium in both rodents and non-human primates
- Durable target gene knockdown (~ 1 month)
- High knockdown efficiency
- Favorable safety profile
The envisioned use of LN-011, siRNAs targeting ACE2, and LN-012 targeting TMPRSS2 is via local delivery to the airways in a form of a nebulized solution via mask inhalation to the nasal, oral and pharyngeal mucosa, bronchial epithelium and the lungs. The inhalation of siRNA will only cause minimal penetration into the systemic circulation, hence avoiding potentially broader side effects that could arise from the systemic treatment with therapeutic antibodies.
The initial planed indication will be prevention of development of severe disease and death in high risk subjects bearing relatively low viral load. At later stages, the treatment may be considered as a prophylaxis for public.
Targeting host genes for prevention of viral infection has certain advantages:
- RNA viruses are prone to rapid evolution through mutagenesis, and therefore, can change the RNA structure abolishing the effect of specific anti-viral siRNA compounds.
- Inhibition of host genes is likely to be effective also against newly emerging strains and all viruses in the Coronaviridae family that utilize these genes for viral entry and spreading. Moreover, there is some evidence that TMPRSS2 is also utilized by influenza virus[v]
- The siRNA against the viral RNA could affect the virus only after it enters the target epithelial cells. The exponential multiplication of the virus once it enters the cell is extremely rapid and may surpass potential siRNA activity against the virus genes, even when given as a prophylactic. Inhibition of host genes prevents not only viral spreading but also the very entry of the virus into the cells.
- The approach has advantages over vaccines, among other, since the appearance of novel viruses that utilize the same host cell interaction strategy will require development of new vaccines, whereas siRNA drugs will be still effective against the same host proteins and ready for use.
- In addition, the most vulnerable population (elderly and immune-compromised) may have problems with mounting strong immune response to vaccination.
Remarkable Additional Indications for LN-011
Inhibition of TMPRSS2 by the small molecule camostat mesilate is a proven therapy for the treatment of chronic pancreatitis and postoperative reflux esophagitis[vi]. Importantly, differently from siRNAs, small molecules are generally promiscuous, do not exclusively bind to the desired target, and hence may cause side-effects. siRNAs exclusively bind to the target without undesired side-effects. In addition, the duration of effect of siRNA drug is several months, much longer than of most small molecules and most suitable for chronic diseases.
Chronic pancreatitis is inflammation of the pancreas that progresses in time and leads to permanent damage with severe impact on quality of life and life-threatening long-term sequelae including diabetes mellitus and pancreatic cancer[vii]. Industrialized countries have estimated an annual incidence rate of 5-12/100,000 people who will develop chronic pancreatitis. The prevalence of chronic pancreatitis is 50/100,000 people[viii]. Pancreatic cancer is the 4th leading cause of cancer death, accounting for 7% of all cancer deaths in the USA. The disease causes approximately 3% of all cancers. The general 5-year survival rate for people with pancreatic cancer is 9%. [ix]
TMPRSS2 is expressed in prostate epithelial cells and is needed for normal prostate function. However, it is upregulated in prostate cancer patients[x],[xi]. It has been shown that inhibition of TMPRSS2 reduces prostate cancer cell invasion and metastasis[xii]. Prostate cancer is one of the most frequently diagnosed malignancies worldwide, and the second leading cause of cancer death in males in USA. PCa progression is a slow process, which undergoes several stages including prostatic intraepithelial neoplasia, adenocarcinoma, and metastasis. Metastasis is the major cause for the morbidity and mortality of PCa patients. Currently, there is no effective therapy available for metastatic PCa patients.[xiii]
[i] Sungnak et al. SARS-CoV-2 Entry Genes Are Most Highly Expressed in Nasal Goblet and Ciliated Cells within Human Airways. Nat Med. 26(5):681-687, 2020.
[ii] Iwata-Yoshikawa N., Okamura T., Shimizu Y., Hasegawa H., Takeda M., Nagata N. TMPRSS2 contributes to virus spread and immunopathology in the airways of murine models after coronavirus infection. J. Virol. 2019 Mar 15;93(6) doi: 10.1128/JVI.01815-18. Available from:
[iii] Ragia, G., Manolopoulos, V.G. Inhibition of SARS-CoV-2 entry through the ACE2/TMPRSS2 pathway: a promising approach for uncovering early COVID-19 drug therapies. Eur J Clin Pharmacol 76, 1623–1630 (2020). https://doi.org/10.1007/s00228-020-02963-4
[iv] Hoffmann M et al, SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor. Cell. 181(2):271-280, 2020.
[v] Limburg H, Harbig A, Bestle D, Stein DA, Moulton HM, Jaeger J, Janga H, Hardes K, Koepke J, Schulte L, Koczulla AR, Schmeck B, Klenk HD, Böttcher-Friebertshäuser E. TMPRSS2 Is the Major Activating Protease of Influenza A Virus in Primary Human Airway Cells and Influenza B Virus in Human Type II Pneumocytes. J Virol. 2019 Oct 15;93(21):e00649-19. doi: 10.1128/JVI.00649-19. PMID: 31391268; PMCID: PMC6803253.
[vi] Uno, Y. Camostat mesilate therapy for COVID-19. Intern Emerg Med 15, 1577–1578 (2020). https://doi.org/10.1007/s11739-020-02345-9
[vii]Pancreatitis and the risk of pancreatic cancer. International Pancreatitis Study Group.
Lowenfels AB, Maisonneuve P, Cavallini G, Ammann RW, Lankisch PG, Andersen JR, Dimagno EP, Andrén-Sandberg A, Domellöf LN Engl J Med. 1993 May 20; 328(20):1433-7.
[x] Lucas, Jared M et al. “The androgen-regulated protease TMPRSS2 activates a proteolytic cascade involving components of the tumor microenvironment and promotes prostate cancer metastasis.” Cancer discovery vol. 4,11 (2014): 1310-25. doi:10.1158/2159-8290.CD-13-1010
[xi] Yu J, Yu J, Mani RS, Cao Q, Brenner CJ, Cao X, et al. (May 2010). “An integrated network of androgen receptor, polycomb, and TMPRSS2-ERG gene fusions in prostate cancer progression”. Cancer Cell. 17 (5): 443–54. doi:10.1016/j.ccr.2010.03.018. PMC 2874722. PMID 20478527.
[xii] Ko CJ, Hsu TW, Wu SR, Lan SW, Hsiao TF, Lin HY, Lin HH, Tu HF, Lee CF, Huang CC, Chen MM, Hsiao PW, Huang HP, Lee MS. Inhibition of TMPRSS2 by HAI-2 reduces prostate cancer cell invasion and metastasis. Oncogene. 2020 Sep;39(37):5950-5963. doi: 10.1038/s41388-020-01413-w. Epub 2020 Aug 10. PMID: 32778768; PMCID: PMC7416816.
[xiii] Ko, C., Hsu, T., Wu, S. et al. Inhibition of TMPRSS2 by HAI-2 reduces prostate cancer cell invasion and metastasis. Oncogene 39, 5950–5963 (2020). https://doi.org/10.1038/s41388-020-01413-w