The current pandemic of COVID-19 has taken 1.5 million lives and counting while causing many more people to fall ill. Many studies have shown that adverse outcomes are related to excessive levels of cytokines and pro-inflammatory factors.
Expression in lung autopsy tissue of COVID19 patients and healthy controls. Image Credit: https://www.biorxiv.org/content/10.1101/2020.12.01.404483v1.full.pdf
A new study published in the bioRxiv* pre-print server indicates that the topoisomerase 1 (Top1) is intimately related to the lethal inflammation associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in a large proportion of cases. It also shows that its inhibition by late treatment with a Top1 inhibitor called Topotecan (TPT) is effective in reducing morbidity and mortality, given at up to 4 days post-infection.
In most cases, severe COVID-19 presents with severe respiratory failure, often accompanied by shock and/or multi-organ failure. However, the infection itself has two phases, one with increasing viremia, and then rapidly increasing inflammation. Many clinical researchers have thus explored the feasibility and the effectiveness of inhibiting this hyper-inflammatory response to mitigate the severity of the disease.
While some have used single-cytokine inhibitors like IL-6R inhibitors, this may not serve because these trigger a cascade of inflammatory reactions and because this overlooks the interindividual variation in cytokine profiles.
SARS-CoV-2 Induces Transcription of Inflammatory Program
The current study first examined the role played by rapid induction of transcription in the activation of an inflammatory response. Chromatin factors acting on the DNA template might regulate the induction of such programs. If these factors are inhibited, they could simultaneously suppress several antiviral and anti-inflammatory pathways.
Earlier research on the host enzyme Top1 shows that it is an essential selective activator of inflammatory genes during viral and bacterial infections and co-infections. The inhibition of this enzyme could prevent mortality in animal models with inflammation-induced lethality. This suggests that epigenetic therapy to suppress the host reaction to SARS-CoV-2 might reduce mortality in this condition.
The current study first showed that with the progression of SARS-CoV-2 infection, there were alterations in the way chromatin associated with the active or inactive compartments, over large parts of the genome. These structural changes were associated with the epigenetic regulation of genes, resulting in transcriptional activity.
When Top1 expression was prevented, the pattern of transcription in these cells changed, with the selective inactivation of several infection-related genes.
Top1-dependent genes are highly inducible during SARS-CoV-2 infection as a result of chromatin and epigenetic changes that render their transactivation permissible.”
TPT Mitigates Severe Inflammation
They tested the impact of therapeutic TPT administration in hamsters, at 1 and 2 days post-infection. They found that TPT prevented the expression of inflammatory genes in the lungs of the infected hamsters, whereas the untreated lungs showed massive pneumonia and inflammatory damage.
In vivo studies showed that TPT at lower doses can still effectively prevent inflammatory activation and reduce the hyper-inflammatory response during COVID-19.
In the lungs of severely ill COVID-19 patients, the same genes that were suppressed by TPT in hamsters showed upregulation. This suggests that TPT administration may reverse the inflammatory gene expression induced by COVID-19.
Early inflammation is helpful to contain viral replication and dissemination within the body. Thus, they postulated, the anti-inflammatory effect of TPT should be induced during the phase of hyper-inflammation, which occurs in the later stages of infection.
They tested their hypothesis in mice engineered to express the human angiotensin I-converting enzyme 2 (ACE2) receptor under the cytokeratin 18 gene promoter (K18-hACE2), which mimic human infection and disease progression following SARS-CoV-2 infection. They administered TPT as early, intermediate and late therapy to infected mice, on days 1 and 2, days 3 and 4, or days 4 and 5 post-infection respectively.
They found that while early TPT did not affect the mortality or morbidity in the infected mice, intermediate treatment reduced the severity of illness but not the mortality. Late treatment with TPT suppressed both, reducing inflammatory gene expression in the lung as well.
What are the Implications?
TPT as well as other Top1 inhibitors like irinotecan are used in chemotherapy. Thus, they have multiple advantages: they are readily available and FDA-approved, inexpensive, sometimes found on the WHO list of essential medicines, and are manufactured in generic form throughout the world, making it easy to adopt their immediate use. These drugs thus form a very promising option for repurposing against SARS-CoV-2 morbidity and death.
We show that the host enzyme Topoisomerase-1 promotes transcriptional activation of pro-inflammatory genes during SARS-CoV-2 infection. We then demonstrate that Top1 inhibition limits the expression of inflammatory genes in the lungs of infected animals. Most importantly, Top1 inhibition decreases morbidity and morbidity in infected mice. The therapeutic effect can be achieved by drug administration 4-5 days following infection.”
Further studies are required to explore the mechanism underlying the observed increased chromatin segregation into smaller compartments, following SARS-CoV-2, similar to that which follows the depletion of the protein cohesion. Secondly, the suppressive effect of TPT is via transcriptional inactivation. However, the site of such action is unknown. The researchers hypothesize that it may act in both epithelial and immune cells, suppressing inducible transcription related to the inflammatory response.
The use of low doses, at about five times lower than that used in chemotherapy, along with their well-established toxicity profiles, implies their use in this viral infection will be related to little toxicity, particularly neutropenia. Their trials in COVID-19 patients will help to establish their safety further. Two clinical trials are slated to begin in January 2021, on the safety and efficacy of TPT, and pending their completion and analysis, off-label use should be discouraged.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.