Introduction
In December 2019, an outbreak of severe acute respiratory infections was
reported in the Chinese city of Wuhan. In the meantime, the disease
named COVID-19 (Corona Virus Disease-19) has flooded the globe and
became the deadliest respiratory disease pandemic since 1918 when the
Spanish influenza pandemic killed more than 50 million
people(1,
2). The culprit of the current COVID-19
pandemic outbreak is the novel coronavirus (CoV) which was named as
severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by the
International Committee on Taxonomy of Viruses (ICTV). SARS-CoV-2 such
as SARS-CoV and MERS-CoV which all can cause severe respiratory illness
belong to the closely related ß-corona
viruses(3) and have originated as human
pathogens by animal-to-human-host
switching(4). The two SARS viruses are
derived from viruses enzootic in bats for which a rich reservoir exists
in Asian countries and in particular in
China(5). As of January 27, 2021, there
are >100 million confirmed cases and >2
million related deaths related to COVID-19 according to the Johns
Hopkins Coronavirus Resource Center
(https://coronavirus.jhu.edu/map.html). Currently, multiple vaccine
candidates have entered into clinical trials, some of them have already
been approved by health authorities and recently vaccination has been
started in several countries (6-9).
However, in addition to prophylactic vaccines SARS-CoV-2-specific
therapies for treatment of infected patients are urgently needed.
Accordingly, several antiviral drugs, among them remdesivir,
hydroxychloroquine, lopinavir and interferons, have been evaluated for
treatment of COVID-19 but so far with limited clinical
success(10,
11). Convalescent plasma treatment is
another possibility for treatment of severe
COVID-19(12) and achieved FDA approval
for treatment of critically ill patients but there are limitations to
its production(13). In addition, first
monoclonal SARS-CoV-2-specific antibodies have been developed, showed
first promising results in experimental animal
models(14) and reduced viral loads in
patients(15). Therefore, a huge unmet
need for SARS-CoV-2-specific treatment strategies remains.
The SARS-CoV-2 viral genome is a single-stranded positive RNA (+ssRNA)
of almost 30 kb, encoding at least 5 open reading frames (ORFs). The
first ORF (ORF1a/b) occupies about 70% of the entire genome and encodes
16 nonstructural proteins (nsp1-16). The remaining 30% of the genome
encodes 4 major structural proteins necessary for virion assembly: spike
(S), membrane (M), envelope (E), nucleocapsid
(N)(16-18).
Gene expression in general and viral gene expression in infectious
diseases can be suppressed through the mechanism of RNA interference
(RNAi) for therapeutic purposes(19-23).
The RNAi approach is based on negative regulation of gene expression at
the post-transcriptional level and therefore highly
specific(24,
25). Hence, the main advantage of the
RNAi strategy over most other therapeutic approaches is its specificity
but the technology has also limitations among them how to enhance
specific targeting of and efficient transportation into infected cells.
In this study we screened a panel of SARS-CoV-2-specific siRNAs for
their potential to silence SARS-CoV-2 gene expression. The most potent
silencing siRNA was then modified to enhance siRNA stability and
formulated with a novel non-toxic peptide dendrimer KK-46 as vehicle for
efficient siRNA delivery into the target cells. Finally we show in anin vivo model of SARS-CoV-2 infection in Syrian
hamsters(26) that topical treatment by
inhalation of the modified siRNA-peptide dendrimer formulation has the
potential to reduce viral replication and to ameliorate
SARS-CoV-2-induced lung inflammation.