SUMMARY

SARS-CoV-2 causes fatal infections by eliciting an over-exuberant immune response leading to injurious lung inflammation +/- a cytokine storm.  Patients may die from ARDS or survive with debilitating pulmonary fibrosis.  Interventions like hydroxychloroquine have been proposed as treatment modalities to modulate the intense host reaction and potentially improve respiratory outcomes despite lack of a direct antiviral effect. 

Plasma gelsolin (pGSN, an abundant, naturally-occurring, circulating protein depleted in severe inflammatory conditions) offers similar promise to hydroxychloroquine in aborting lung injury, and should be treated as a possible novel therapeutic agent in this time of crisis.  The recombinant human form (rhu-pGSN) has already been given safely to patients with mild community-acquired pneumonia (CAP). 

Since rhu-pGSN is a pathogen-indifferent Rx acting on host inflammatory responses, the microbial etiology of life-threatening CAP is not particularly relevant.  We hope to be able to fast track this product in this light.

 

Addressing Severe COVID19

Plasma gelsolin (pGSN) is an abundant normal blood protein which improves host defenses against microbial pathogens while simultaneously modulating the collateral damage inflicted by excessive inflammation.  It is a critical component of innate immunity which is depleted early in serious infections. Recombinant human (rhu)-pGSN imparts a survival advantage in animal models of pneumonia and sepsis irrespective of the specific etiology.

We propose that supplementation with rhu-pGSN as an adjunct to standard-of-care measures will prevent or limit organ injury (and mortality) in patients with severe coronavirus infections.

This strategy, rather than being a narrowly targeted pharmaceutical intervention, involves supplementing an evolutionarily conserved endogenous system designed to neutralize microbial pathogens, while simultaneously modulating the collateral damage inflicted by over-exuberant inflammation. This central regulator of the host response is an abundant blood protein component of innate immunity which is depleted early in serious infections and is efficacious in animal models of lung injury and sepsis. pGSN is sequestered in infected tissues, lowering its circulating levels.  Depletion of circulating pGSN depletes its organ-protective function, leading to multi-organ dysfunction syndrome (MODS), increased mortality and long-term morbidity in survivors. Similar pathophysiology underlies major sterile injuries.

 

Inhibition of systemic inflammatory response syndrome and/or cytokine storm

pGSN’s abundance protects distant organs by inactivating inflammatory mediators that escape the local infection site.  Actin exposure at local infection sites sequesters pGSN, depleting circulating levels. The extent that pGSN levels fall reflect the magnitude of tissue damage. Extensive infection (bacterial or viral) and massive injuries such as major trauma or extensive burns depress levels by as much as 90%(8).This depletion puts patients at risk for MODS and increased mortality.

The objective of pGSN supplementation is to restore pGSN’s immune-enhancing and inflammation-balancing functions sufficiently to impact the course of impending organ failure and mortality. Since pGSN’s beneficial effects are pathogen-indifferent, identifying the infectious etiology is not a therapeutic prerequisite. 

 

Enhanced Local Antimicrobial Action by Tissue Debridement and Macrophage Stimulation.

Pathogen invasion and host inflammation disrupt cell integrity, exposing cytoskeletal actin, comprising on average 10% of cellular protein, to the extracellular milieu.

As a result of actin exposure, the formation of biofilm containing actin filaments and other biopolymers such as DNA impedes the access of host defense cells as well as therapeutic agents to pathogens (2). pGSN dissolves biofilm by liquifying actin gels.  The liquification of highly viscous cystic fibrosis sputum exemplifies pGSN’s debridement function (2).

pGSN also enhances macrophage antimicrobial activity, increasing the phagocytosis and killing of Gram positive and negative bacteria by lung macrophages in vitro. Actin blocks macrophage scavenger receptors (MARCO and others) that mediate bacterial uptake. By debriding the actin, pGSN removes this inhibition, and increased binding and uptake is seen (3). Bacterial killing is separately enhanced by the induction of macrophage nitric oxide synthase 3(7).

 

pGSN’s Mechanisms Inform the Rationale for pGSN Supplementation.

Low pGSN concentrations accompanying injuries precede by hours to days the risk of adverse systemic complications such as MODS, providing a window of therapeutic opportunity (1). In a study of septic patients, pGSN levels more strongly predicted 28-day mortality than APACHE III scores. For every quartile reduction in pGSN, the odds of death increased 3.4-fold (6). Likewise, in a CDC-sponsored study of community-acquired pneumonia, patients with pGSN in the lowest quartile at the time of hospitalization experienced ~ 9x higher risk of death, ~2x higher risk of septic shock , and ~ 2x higher risk of respiratory failure(7).

In animal sepsis in vivo, administration of rhu-pGSN subcutaneously to mice and rats challenged with E. coli lipopolysaccharide endotoxin or subjected to cecal ligation-puncture significantly reduced their mortality in the absence of antibiotics (8-9). Mice given pGSN subcutaneously or by inhalation after highly lethal inocula of S. pneumonia had markedly diminished numbers of viable bacteria in their airways and significantly reduced mortality. The number of inflammation-inducing neutrophils was also considerably reduced, presumably in part as a result of enhanced bacterial clearance by alveolar macrophages (4). Rhu-pGSN has improved survival in both antibiotic-susceptible and -resistant infections; in surviving mice, rhu-pGSN reduced lung injury versus antibiotics alone.

In pneumonia caused by both bacteria and influenza, rhu-pGSN reduces mortality even when dosing is delayed until the animals are visibly sick (10-12). All of these results were obtained in the absence of antibiotic therapy.

pGSN therapy is a host-based, pathogen-indifferent intervention that can address concerns about antibiotic resistance in the empirical treatment of sepsis prior to culture results. pGSN administration diminishes the lethality of penicillin-resistant pneumococci in combination with penicillin, even though the antibiotic has no benefit on its own (10). pGSN enables meropenem to decrease the severity of antibiotic-resistant P. aeruginosa infection in myelosuppressed mice (12).

As evidence for pGSN’s systemic inflammation protective action, rhu-pGSN prevents increased lung vascular permeability caused by extensive burn injury in rats (13) and markedly diminishes a 2-deoxyglucose signal denoting systemic inflammation in mice challenged with P. aeruginosa (14).

 

Safety

As an endogenous protein, pGSN’s safety profile enhances the rationale for supplementation therapy in critically ill patients.  Attesting to pGSN’s safety considerations, toxicology studies in rodents and monkeys disclosed no safety signals. Inhalational and intravenous pGSN supplementation in four clinical trials has not caused any drug-related SAEs, including a recent study in hospitalized Community-Acquired Pneumonia patients in which gelsolin levels in patients were raised well above normal physiological concentrations (15).

BioAegis is already engaged in evaluating pGSN replacement in severe infection, specifically severe community-acquired pneumonia (sCAP) and have engaged leading infection experts to advise our clinical trial strategy. We have produced GMP-quality clinical supplies in a proprietary system, have been issued 40 patents including infection patents in China, and we have conducted a Phase 1b/2a clinical trial in pneumonia patients to obtain safety and pharmacokinetic data.

A key next step for this product is to initiate the next clinical trial and to scale up manufacturing to provide additional clinical supplies for these studies in more severely ill patients at risk for sepsis. This will move the program into Phase 2b to demonstrate proof of impact on clinical outcomes and to optimize cost of goods for clinical supplies and commercialization.

 

Use in Coronavirus Critical Care Patients

Given the scientific data we have identified previously, it is not unreasonable to believe that rhu-plasma gelsolin could have broad application to other lethal respiratory illnesses caused by SARS and Coronavirus.   Furthermore, it should have an important role in the future, as an immediate solution for fighting emerging infectious pathogens, for which vaccines and antibiotics have not yet been developed.

We are already engaged in evaluating pGSN replacement in severe infection, specifically severe community-acquired pneumonia(sCAP), including COVID19 and have engaged leading infection experts to advise our clinical trial strategy (16). In our clinical studies, endpoints to address the benefits of rhu-pGSN added to standard of care (SOC) would include MODS-free survival in high risk patients. A reduced incidence of MODS should lessen ICU time, frequency of intubation and days on a ventilator. Based on the expected effect size of pGSN supplementation, a blinded, randomized, standard of care-controlled clinical trial can be affordably powered for a primary outcome of ventilator-free survival (using either a Day-28-point prevalence or Kaplan-Meier analysis looking at time to event). Clinically meaningful secondary endpoints could include days in ICU, incidence of MOD, acute kidney injury- or dialysis-free survival, and hospital stay/costs.

 

CONCLUSION

Plasma gelsolin (pGSN, an abundant, naturally occurring, circulating protein depleted in severe inflammatory conditions) offers promise to abort lung injury, and should be treated as a possible novel therapeutic agent in this time of crisis.  The recombinant human form (rhu-pGSN) has already been given safely to patients with mild community-acquired pneumonia (CAP). 

Since rhu-pGSN is a pathogen-indifferent Rx acting on host inflammatory responses, the microbial etiology of life-threatening CAP is not particularly relevant.  Thus, it is likely to be effective not only in this current crisis but in other instances of viral and bacterial pneumonia which arise in the future.  We hope to be able to fast track this product in this light.

 

References:

1. Piktel, E., et al. Plasma gelsolin: indicator of inflammation and its potential as a diagnostic tool and therapeutic target. Int. J. Mol. Sci, 2018. 19: 2516 1-33.Walker, T., et al., Enhanced Pseudomonas aeruginosa biofilm development mediated by human neutrophils. Infection Immun, 2005. 73: p. 3693- 3701.
2. Vasconcellos, C., et al., Reduction in viscosity of cystic fibrosis sputum in vitro by gelsolin. Science, 1994. 263: p. 969-971.
3. Ordija, C., et al., Free actin impairs macrophage bacterial defenses via scavenger receptor MARCO interaction, with reversal by plasma gelsolin. Am J Physiol Lung Cell Mol Physiol, 2017. 312: p. L1018- L1028.
4. Yang, Z., et al., Plasma gelsolin improves lung host defense against pneumonia by enhancing macrophage NOS3 function. Am J Physiol Lung Cell Mol Physiol, 2015. 309: p. L11-16.
5. Lee, W. and R. Galbraith, The extracellular actin-scavenger system and actin toxicity. N Engl J Med, 1992. 326: p. 1335-1341. PMID:1314333 DOI:10.1056/NEJM199205143262006
6. Lee, P., et al., Plasma gelsolin depletion and circulating actin in sepsis — a pilot study. PLoS one, 2008. 3(11).
7. Self, W., et al., Low admission plasma gelsolin concentrations identify community-acquired pneumonia patients at high risk for severe outcomes. Clin Infect Dis, 2018. doi: 10.1093/cid/ciy1049
8. Lee, P.-S., et al., Plasma gelsolin is a marker and therapeutic agent in animal sepsis. Crit Care Med, 2007. 35: p. 849-855.
9. Cohen, T., et al., Therapeutic potential of plasma gelsolin administration in a rat model of sepsis. Cytokine, 2011. 54: p. 235-238.
10. Yang, Z., et al., Delayed Administration of Recombinant Plasma Gelsolin Improves Survival in a Murine Model of Penicillin-Susceptible and Penicillin-Resistant Pneumococcal Pneumonia.  The Journal of Infectious Diseases, Volume 220, Issue 9, 1 November 2019, Pages 1498–1502, https://doi.org/10.1093/infdis/jiz353
11. Yang et al, Delayed administration of recombinant plasma gelsolin improves survival in a murine model of severe influenza.  F1000 Research, 2019. 8: 1860.
12. DiNubile, M., et al.  Recombinant Human Plasma Gelsolin (rhu-pGSN) Improves Survival and Attenuates Lung Injury in a Murine Model of Multi-Drug Resistant Pseudomonas aeruginosa Pneumonia, manuscript submitted for publication, in review.
13. Rothenbach, P., et al., Recombinant plasma gelsolin infusion attenuates burn-induced pulmonary microvascular dysfunction. J Appl Physiol, 2003. 96: p. 25-31.
14. R. Bucki et al, Manuscript in preparation
15. https://clinicaltrials.gov/ct2/show/NCT03466073
16. Clinical Advisors List:
    1. Steven Opal, M.D., Professor of Medicine, Brown University School of Medicine; Chief, Infectious Disease Division, Memorial Hospital of RI
    1. Atul Malhotra, M.D., Division Chief, Pulmonary and Critical Care Medicine, Kenneth M. Moser Professor, Department of Medicine University of California-San Diego.
    1. Wesley Self, M.D., Associate Professor, Critical Care Medicine, Vanderbilt University Medical School, Co- Principal Investigator, EPIC Consortium.
    1. Richard Wunderink, MD., Professor, Critical Care and Pulmonary Medicine, Feinberg Northwestern University Medical School, Co-Principal Investigator, EPIC Consortium.
    1. James Bolognese, MStat., Senior Director, Strategic Consulting, Cytel Inc., Fellow of the American Statistical Association