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 system10.
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 11 and thalidomide along with P-Gemox
was highly effective in treating ENKTL patients in a Phase II clinical
trial 33. 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” 34 Studies have utilized A549 cells to show
the effects of thalidomide on lung fibrosis 35–37. 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 transcriptome15,38. 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 6. Cytokine storm and
atherosclerosis are tightly connected in SARS-coV-2 39which 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 patients6,16. As SARS-coV-2 infection has a huge impact on the
hematopoietic system 40 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 41. 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 42. 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 43. Chronic
elevated stress levels have been reported in SARS and SARS-coV-2
patients even long after the outbreak 10. 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 inhibition44. 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 patient10.
The anti-inflammatory properties
of thalidomide and its analogs through reduction of IL-1β, TNF-α
expression and NF-κB inhibition are well established45. 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 46. Activation of IRF and ISRE
transcriptional targets in SARS-coV-2 affected lungs is in agreement
with previous studies reporting the SARS biology 47.
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 48,49.
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 45.
Remarkably, hydroxychloroquine, an FDA approved SLE drug is currently
being used in the management of critically ill SARS-coV-2 patients50. CC-220, another thalidomide analog shows very
promising results in phase I/II clinical trials against SLE51,52. CC-220 through suppression of Ikaros and Aiolos
expression 53, 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 39.
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) 54. There have been many reports
on COVID-19 patients develop blood clots 39, 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 55.
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.