Pharmacokinetics, absorption, distribution and disposition of [125I]-defibrotide following intravenous or oral administration in the rat

Defibrotide mitigates endothelial cell injury induced by plasmas from patients with COVID-19 and related vasculopathies

Background and objectives

COVID-19 progression is characterized by systemic small vessel arterial and venous thrombosis. Microvascular endothelial cell (MVEC) activation and injury, platelet activation, and histopathologic features characteristic of acute COVID-19 also describe certain thrombotic microangiopathies, including atypical hemolytic-uremic syndrome (aHUS), thrombotic thrombocytopenic purpura (TTP), and hematopoietic stem cell transplant (HSCT)-associated veno-occlusive disease (VOD). We explored the effect of clinically relevant doses of defibrotide, approved for HSCT-associated VOD, on MVEC activation/injury.

Methods

Human dermal MVEC were exposed to plasmas from patients with acute TMAs or acute COVID-19 in the presence and absence of defibrotide (5 μg/ml) and caspase 8, a marker of EC activation and apoptosis, was assessed. RNAseq was used to explore potential mechanisms of defibrotide activity.

Results

Defibrotide suppressed TMA plasma-induced caspase 8 activation in MVEC (mean 60.2 % inhibition for COVID-19; p = 0.0008). RNAseq identified six major cellular pathways associated with defibrotide's alteration of COVID-19-associated MVEC changes: TNF-α signaling; IL-17 signaling; extracellular matrix (ECM)-EC receptor and platelet receptor interactions; ECM formation; endothelin activity; and fibrosis. Communications across these pathways were revealed by STRING analyses. Forty transcripts showing the greatest changes induced by defibrotide in COVID-19 plasma/MVEC cultures included: claudin 14 and F11R (JAM), important in maintaining EC tight junctions; SOCS3 and TNFRSF18, involved in suppression of inflammation; RAMP3 and transgelin, which promote angiogenesis; and RGS5, which regulates caspase activation and apoptosis.

Conclusion

Our data, in the context of a recent clinical trial in severe COVID-19, suggest benefits to further exploration of defibrotide and these pathways in COVID-19 and related endotheliopathies.

The use of defibrotide in blood and marrow transplantation

Hepatic veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) is a potentially life-threatening complication of conditioning during hematopoietic stem cell transplantation (HSCT) or chemotherapy without HSCT, with a historically reported mean incidence of 13.7% post-HSCT. Typical symptoms of VOD/SOS may include hyperbilirubinemia, painful hepatomegaly, weight gain, and ascites. Defibrotide, a polydisperse mixture of predominantly single-stranded polydeoxyribonucleotides, is currently the only therapy approved to treat hepatic VOD/SOS with pulmonary/renal dysfunction (ie, multiorgan dysfunction/multiorgan failure [MOD/MOF]) following HSCT in the United States and to treat severe hepatic VOD/SOS post-HSCT in the European Union. In preclinical and human studies, defibrotide has demonstrated profibrinolytic, antithrombotic, anti-inflammatory, and angio-protective actions, thus promoting an anticoagulant phenotype of the endothelium that protects and stabilizes the function of endothelial cells. In a phase 3, historically controlled, multicenter trial in adults and children with VOD/SOS and MOD/MOF (defibrotide: n = 102; controls treated before defibrotide availability: n = 32), defibrotide resulted in significantly greater day +100 survival following HSCT (38.2%) vs controls (25.0%; propensity analysis-estimated between-group difference: 23%; P = .0109). The most common adverse events (AEs) were hypotension and diarrhea; rates of common hemorrhagic AEs were similar in the defibrotide and historical control group (64% and 75%, respectively). In a phase 3 prophylaxis trial, defibrotide was found to lower incidence of VOD/SOS in children (not an approved indication) and reduce the incidence of graft-versus-host disease. This review describes the development and clinical applications of defibrotide, focusing on its on-label use in patients with VOD/SOS and MOD/MOF after HSCT.

Defibrotide in the treatment of hepatic veno-occlusive disease

Hepatic veno-occlusive disease (VOD), also known as sinusoidal obstruction syndrome (SOS), represents the most frequent complication in patients in early phase following hematopoietic stem-cell transplantation (HSCT). In its severe form, VOD/SOS can be associated with multiorgan failure and with a mortality rate >80% by day +100. Defibrotide (DF) (a mixture of 90% single-stranded phosphodiester oligonucleotides and 10% double-stranded phosphodiester oligonucleotides derived from controlled depolarization of porcine intestinal mucosal DNA) has been proposed for the treatment of SOS due to its ability to restore thrombo-fibrinolytic balance and protect endothelial cells. The present review highlights why the mechanisms of action of DF allow its successful use in the prevention and treatment of SOS following HSCT.

Pharmacokinetic profile of defibrotide in patients with renal impairment

Hepatic veno-occlusive disease, also called sinusoidal obstruction syndrome (VOD/SOS), is an unpredictable, potentially life-threatening complication of hematopoietic stem cell transplant conditioning. Severe VOD/SOS, generally associated with multiorgan dysfunction (pulmonary or renal dysfunction), may be associated with >80% mortality. Defibrotide, recently approved in the US, has demonstrated efficacy treating hepatic VOD/SOS with multiorgan dysfunction. Because renal impairment is prevalent in patients with VOD/SOS, this Phase I, open-label, two-part study in adults examined the effects of hemodialysis and severe or end-stage renal disease (ESRD) on defibrotide pharmacokinetics (PK). Part 1 compared defibrotide PK during single 6.25 mg/kg doses infused with and without dialysis. Part 2 assessed defibrotide plasma PK after multiple 6.25 mg/kg doses in nondialysis-dependent subjects with severe/ESRD versus healthy matching subjects. Among six subjects enrolled in Part 1, percent ratios of least-squares mean and 90% confidence intervals (CIs) on dialysis and nondialysis days were 109.71 (CI: 97.23, 123.78) for maximum observed plasma concentration (C_max); 108.39 (CI: 97.85, 120.07) for area under the concentration–time curve to the time of the last quantifiable plasma concentration (AUC_0–t); and 109.98 (CI: 99.39, 121.70) for AUC extrapolated to infinity (AUC_0–∞). These ranges were within 80%–125%, indicating no significant effect of dialysis on defibrotide exposure/clearance. In Part 2, defibrotide exposure parameters in six subjects with severe/ESRD after multiple doses (AUC_0–t, 113 µg·h/mL; AUC over dosing interval, 113 µg·h/mL; C_max, 53.8 µg/mL) were within 5%–8% of parameters after the first dose (AUC_0–t, 117 µg·h/mL; AUC_0–∞, 118 µg·h/mL; C_max, 54.9 µg/mL), indicating no accumulation. Defibrotide peak and extent of exposures in those with severe/ESRD were ~35%–37% and 50%–60% higher, respectively, versus controls, following single and multiple doses. One adverse event (vomiting, possibly drug-related) was reported. These findings support defibrotide prescribing guidance stating no dose adjustment is necessary for hemodialysis or severe/ESRD.

What is going on between defibrotide and endothelial cells? Snapshots reveal the hot spots of their romance

Defibrotide (DF) has received European Medicines Agency authorization to treat sinusoidal obstruction syndrome, an early complication after hematopoietic cell transplantation. DF has a recognized role as an endothelial protective agent, although its precise mechanism of action remains to be elucidated. The aim of the present study was to investigate the interaction of DF with endothelial cells (ECs). A human hepatic EC line was exposed to different DF concentrations, previously labeled. Using inhibitory assays and flow cytometry techniques along with confocal microscopy, we explored: DF-EC interaction, endocytic pathways, and internalization kinetics. Moreover, we evaluated the potential role of adenosine receptors in DF-EC interaction and if DF effects on endothelium were dependent of its internalization. Confocal microscopy showed interaction of DF with EC membranes followed by internalization, though DF did not reach the cell nucleus even after 24 hours. Flow cytometry revealed concentration, temperature, and time dependent uptake of DF in 2 EC models but not in other cell types. Moreover, inhibitory assays indicated that entrance of DF into ECs occurs primarily through macropinocytosis. Our experimental approach did not show any evidence of the involvement of adenosine receptors in DF-EC interaction. The antiinflammatory and antioxidant properties of DF seem to be caused by the interaction of the drug with the cell membrane. Our findings contribute to a better understanding of the precise mechanisms of action of DF as a therapeutic and potential preventive agent on the endothelial damage underlying different pathologic situations.

Defibrotide: properties and clinical use of an old/new drug

The drug named defibrotide (DFT) has been studied for many years. It has been shown to possess many activities: profibrinolytic, antithrombotic-thrombolytic, antiischemic (heart, liver, kidney, skin, brain), antishock, antiatherosclerotic, antirejection and anti-angiogenic. The previously displayed activities, as antithrombotic, profibrinolytic and anti-inflammatory, suggested its use in vascular disorders, as in the treatment of peripheral obliterative arterial disease and in thrombophlebitis. Some years after, the use of DFT in hepatic veno-occlusive disease has been also proposed. Even if DFT was considered for long time a multi-target drug, now it could be considered on the whole as a drug able to protect endothelium against activation. The present work reviews the more important experimental and clinical studies performed to detect DFT effects.

Use of defibrotide in the treatment and prevention of veno-occlusive disease

Hepatic veno-occlusive disease (VOD) is one of the most important complications of high-dose chemotherapy and stem cell transplantation. VOD is a clinical syndrome characterized by jaundice, hepatic enlargement and fluid retention typically seen by day +30 after transplantation. Severe VOD is complicated by multiorgan failure and a high mortality rate approaching 100%. Defibrotide (DF) is a novel agent with both antithrombotic and fibrinolytic properties that has emerged as an effective therapy for severe VOD. In Phase II studies, treatment of severe VOD has resulted in complete responses of 30-60% and survival past day 100 ranging between 32-50%. A Phase III, historically controlled study of DF for treatment of severe VOD has recently been completed and results are awaited with interest. In addition, DF may be effective prophylaxis for VOD in high-risk patients. This review will focus on a summary of the pharmacology of DF and the clinical evidence for its use in VOD.

Extending the lifetime of anticoagulant oligodeoxynucleotide aptamers in blood

We have investigated (123)I and (125)I DNA aptamer analogs of anticoagulant DNA aptamers to thrombin exosite 1 and exosite 2 for thrombus imaging potential. Two severe problems are rapid clearance from circulating blood and blood nuclease. With aptamers (unlike antisense) the nucleotide analogs used in polymerase chain reaction-selection cycles also must be used in the radiotracer. We investigated 3'-biotin-streptavidin (SA) bioconjugates of the aptamers to alleviate these problems. Blood nuclease assays and biodistribution analysis were used in the mouse and rabbit. We found that 3'-biotin protected the aptamers significantly from blood nuclease in vitro, but it did not slow in vivo clearance. In contrast, the 3'-biotin-SA bioconjugates were resistant to blood nuclease in vitro and were also longer-lived (10-20 times) in vivo. Bioconjugate aptamers retained affinity for thrombin. Two solutions emerge: 1) In noncirculating blood (within a thrombus) 3'-biotin extends aptamer lifetime, whereas 2) in circulating blood (the transport medium), where more aggressive clearance is encountered, 3'-SA extends aptamer lifetime.

Pharmacokinetics, absorption, distribution and disposition of [125I]-oligotide following intravenous or oral administration in the rat

Oligotide (O) was labelled with 125I. The radiolabelled compound ([125I]-Oligotide ([125I]-O)) retained the biological activity of parent O. Following single intravenous administration the half lives of radioactivity associated with O and/or O related components in plasma were 9-10 min and 9-10 h for alpha and beta phases respectively. Following single oral administration the half life of radioactivity associated with O and/or O related components in plasma was 11.45-12.76 h for beta fase. Following multiple oral administration once daily for 7 days, the half life of radioactivity associated with O and/or O related components following the 7th dose was 10-12 h for beta phase. The areas under plasma total radioactivity versus time curves were dose-dependent. Following single intravenous administration the major proportion of the administered dose was excreted via urine, while following single oral administration excretion via urine and faeces accounted for similar proportions of the administered dose. Following both single and oral administration the levels of radioactive components derived from [125I]-O in organs examined were generally highest in highly perfused organs.

Study on pharmacokinetics of radioactive labelled defibrotide after oral or intravenous administration in rats

Defibrotide (D) was labelled with 125I or with 32P. The radiolabelled compounds ([125I]-Defibrotide ([125I]-D), [32P]-Defibrotide ([32P]-D) retained the same profibrinolytic activity, in vitro, as the parent drug, suggesting that the labelling procedures had not modified the pharmacological properties of D and hence that its chemical structure was not affected significantly. After single intravenous or oral administration of [125I]-D or [32P]-D the pharmacokinetic parameters for the two labels were generally in good agreement (75%). t 1/2 alpha was in the range of minutes while t 1/2 beta was in the range of hours. Bioavailability, following single oral administration of [125I]-D or [32P]-D, was in the range of 58-70%. These data suggest that D, in spite of its macromolecular nature, is absorbed, after oral administration, fairly well.