Discussion
SARS-coV-2 infection causes surge in a number of pathways related to
inflammation, cytokine signaling, leukocyte and lymphocyte activation,
innate and adaptive immune response marking the phenomenon of “cytokine
storm”. As the whole immune system is affected during the SARS-coV-2
infection, immunomodulators would be highly beneficial in treating the
symptoms. A COVID-19 patient with pneumonia was treated successfully
with thalidomide and low dose glucocorticoid. There was a significant
decrease in the inflammatory cytokines including IL1-, IL-6 and IFN-ϒ
and increase in the CD4+ and CD8+ T cells and NK cells. Thalidomide
reduced the severity of many COVID-19 symptoms such as lung lesions,
exudation due to its pleiotropic effects on the human system .
Hemophagocytic syndrome, a
hyperinflammatory disorder is also another condition in which cytokine
storm occurs. It is frequently present with extranodal natural killer/T
cell lymphoma (ENKTL). Thalidomide was effective in suppressing the
cytokine storm through inhibition of NF-κB based transcription of IFN-ϒ
and TNF genes and thalidomide along with P-Gemox was highly effective in
treating ENKTL patients in a Phase II clinical trial . Comparison of
SARS-coV-2 expression profiles with drug signatures through enrichment
analysis revealed striking actions of thalidomide and lenalidomide in
A549 and endothelial cells. The results suggest that thalidomide and
lenalidomide could reverse the devastating effects of SARS-coV-2
infections on immune system. We selected A549, an adenocarcinomic human
alveolar basal epithelial cell line to test our hypothesis that
thalidomide would be effective against the cytokine storms. The A549
cell line is an appropriate model for testing cytokine storm targeting
drugs since a previous study established this model by infecting the
cells with influenza A/H1N1 virus (PR-8) or nonstructural protein 1
(NS1) plasmid to test the mechanisms behind inflammatory
cytokines/chemokines mediated “cytokine storm” Studies have utilized
A549 cells to show the effects of thalidomide on lung fibrosis . A
limitation of this study is that only 978 genes called “landmark
genes” are profiled in the iLINCS drug signatures. However, the
profiles are highly reproducible and represent the whole transcriptome .
Our models of A549 and HUVEC effectively capture the effects of
thalidomide in lungs as well as endothelium.
It is also emerging that SARS-coV-2 infections perturb vascular plexus
significantly and there is a substantial increase in the growth of new
blood vessels and evidence of intussusceptive angiogenesis with
overexpression of angiogenesis and hypoxia genes in the lungs of
COVID-19 patients . Cytokine storm and atherosclerosis are tightly
connected in SARS-coV-2 which is consistent with our analysis revealing
the enrichment of atherosclerosis in the SARS-coV-2 signatures (Figure
6). Thalidomide is a renowned modulator of vascular system, and it is
known to transcriptionally or functionally target various genes (Table
S1) up-regulated genes in the lungs of COVID-19 patients . As SARS-coV-2
infection has a huge impact on the hematopoietic system affecting the
myeloid cell maturation, we meta-analyzed the effects of thalidomide and
its derivatives on PBMC, bone marrow cells as well as lymphoma cells.
Thalidomide and lenalidomide exhibited attenuation of cytokine signaling
and inflammation in addition to its anti-angiogenic action (Figure 3A).
The drugs affected most of the
pathways up-regulated in SARS-coV-2 affected lungs and PBMC (Figure 1A,
3A) in A549 cells, mandating direct investigations in SARS-coV-2
infected models.
COVID-19 coincides with a strong neuro-endocrine modulation because the
disease devastates functions of the organs, and naturally the reciprocal
communication between the organs of the endocrine stress system gets a
set-back . ACE2 is expressed along the hypothalamus, pituitary and
adrenal (HPA) axis which is implicated in the stress response and
adrenal glands has the highest concentration of virus particles next to
lung . A high expression of ACE2 in brain is believed to be the reason
for the possible infection of the central nervous system in SARS
patients . Chronic elevated stress levels has been reported in SARS and
SARS-coV-2 patients even long after the outbreak . Notably, thalidomide
is also known for its neuro-endocrine modulation properties. Thalidomide
modulates CNS by reducing the generation of pro-inflammatory cytokines
such as IL-1, IL-6, IL-8 and TNF-α through NF-κB inhibition . There was
a down-regulation of genes involved in circadian wake cycle (Figure 1B,
S2) including PER3 in the PBMC of COVID-19 patients hinting on the
possible sleep disturbances in SARS-coV-2 patients. Thalidomide being a
well-known antiemetic and sedative action on the neuroendocrine axis
would relax the patients which is supported by the report that
thalidomide was effective in treating the anxiety and digestive symptoms
in the COVID-19 patient .
The anti-inflammatory properties
of thalidomide and its analogs through reduction of IL-1β, TNF-α
expression and NF-κB inhibition are well established . SARS-coV-2
infections showing elevated NF-κB signaling and rampage activation of
immune response. Unlike other RNA viruses, SARS-coV-2 suppresses TNF
receptor-associated factors 3 (TRAF3) activation, inhibiting NF-κB and
IRFs, leading to suppression of early pro-inflammatory and antiviral
responses. Whereas later stages of the infection show an enhanced
expression of IRF targets in the lungs with an activation of IL-1, IL-6
and TNF-α expression and inhibition of type I interferon signaling .
Activation of IRF and ISRE transcriptional targets in SARS-coV-2
affected lungs is in agreement with previous studies reporting the SARS
biology . Thalidomide inhibited LCK activity affecting STAT1
phosphorylation, cytokine mediated signaling, NF- κB signaling,
osteoclast differentiation and MAPK signaling through modulation of
various upstream activators and downstream effectors. Lenalidomide, in
addition, suppressed leukocyte differentiation, TLR signaling along with
IRF activation in A549 and lymphoma cells. The effects of thalidomide
and lenalidomide observed in our study are consistent with the previous
studies where thalidomide and lenalidomide has been shown to inhibit IRF
and STAT1 phosphorylation resulting in the downregulation of interferon
expression and TLR signaling .
The expression profile of SARS-coV-2 infected lungs, PBMC as well as
A549 cells show resemblance with profiles of lymphoma, multiple myeloma
and SLE. Therefore, drugs which are effective in treating SLE, lymphoma
and multiple myeloma might be effective against SARS-coV-2 infection.
Thalidomide and its derivatives show impressive efficacy in treating
multiple myeloma and certain forms of lymphoma . Remarkably,
hydroxychloroquine, an FDA approved SLE drug is currently being used in
the management of critically ill SARS-coV-2 patients . CC-220, another
thalidomide analog shows very promising results in phase I/II clinical
trials against SLE . CC-220 through suppression of Ikaros and Aiolos
expression , transcription factors which are essential for
differentiation of leukocyte and NK cells thus modulating the innate
immune system. As innate immune system pathways are deregulated in
SARS-coV-2 infected lung and PBMC, further studies are warranted to
investigate the efficacy and safety of CC-220 in treating COVID-19
Any treatment strategy with thalidomide and its analogs including
repurposing thalidomide for COVID-19, should consider
thalidomide-induced adverse effects including neuropathy and venous
thromboembolism (VTE) . There have been many reports on COVID-19
patients develop blood clots , a dangerous issue which might be
aggravated with the use of thalidomide and lenalidomide. In addition,
lenalidomide might cause cytokine release syndrome in chronic
lymphocytic leukemia patient . Therefore, a very careful dosage regimen
has to be followed with all these drugs as serious adverse effects have
been observed during dose escalation earlier.