Outcome of liver cancer patients with SARS-CoV-2 infection: An International, Multicentre, Cohort Study.

BACKGROUND & AIMS: Information about the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in patients with liver cancer is lacking. This study characterizes the outcomes and mortality risk in this population. METHODS: Multicentre retrospective, cross-sectional, international study of liver cancer patients with SARS-CoV-2 infection registered between February and December 2020. Clinical data at SARS-CoV-2 diagnosis and outcomes were registered. RESULTS: Two hundred fifty patients from 38 centres were included, 218 with hepatocellular carcinoma (HCC) and 32 with intrahepatic cholangiocarcinoma (iCCA). The median age was 66.5 and 64.5 years, and 84.9% and 21.9% had cirrhosis in the HCC and iCCA cohorts respectively. Patients had advanced cancer stage at SARS-CoV-2 diagnosis in 39.0% of the HCC and 71.9% of the iCCA patients. After a median follow-up of 7.20 (IQR: 1.84-11.24) months, 100 (40%) patients have died, 48% of the deaths were SARS-CoV-2-related. Forty (18.4%) HCC patients died within 30-days. The death rate increase was significantly different according to the BCLC stage (6.10% [95% CI 2.24-12.74], 11.76% [95% CI 4.73-22.30], 20.69% [95% CI 11.35-31.96] and 34.52% [95% CI 17.03-52.78] for BCLC 0/A, B, C and D, respectively; p = .0017). The hazard ratio was 1.45 (95% CI 0.49-4.31; p = .5032) in BCLC-B versus 0/A, and 3.13 (95% CI 1.29-7.62; p = .0118) in BCLC-C versus 0/A in the competing risk Cox regression model. Nineteen out of 32 iCCA (59.4%) died, and 12 deaths were related to SARS-CoV-2 infection. CONCLUSIONS: This is the largest cohort of liver cancer patients infected with SARS-CoV-2. It characterizes the 30-day mortality risk of SARS-CoV-2 infected patients with HCC during this period.

Insuficiencia suprarrenal relativa en pacientes cirróticos / Adrenal insufficiency in cirrhotic patients

La insuficiencia suprarrenal relativa (ISR) es frecuente en pacientes cirróticos con sepsis grave, asociándose a un pobre pronóstico. Se desconoce su importancia en condiciones de enfermedad estable. El objetivo del trabajo ha sido evaluar la prevalencia de la ISR en una serie de pacientes cirróticos estables y su relación con el deterioro de la función hepática. Se determinó el impacto de la ISR en la supervivencia y se correlacionaron los niveles entre el cortisol basal en plasma y saliva en sujetos controles y cirróticos. Fueron incluidos 47 pacientes ambulatorios y 16 controles. La funcionalidad del eje hipotalámico-pituitario-suprarrenal se valoró mediante la prueba de estimulación con 250 μg de ACTH sintética EV, definiendo la ISR como delta cortisol < 9 μg/dl. Respecto al grado de deterioro de la función hepática, 22 tenían un Child-Pugh ≤ 8 y 25 pacientes = 9. La prevalencia de ISR fue de un 22%, siendo significativamente más elevada en aquellos con mayor deterioro de la función hepática (8/32 vs. 3/13, p < 0.05). Se observó correlación entre el cortisol salival y el plasmático basal (r = 0.6, p < 0.0004). Por último, la supervivencia fue más elevada en los pacientes sin ISR al año (97%) y a los tres años (91%) que aquellos que desarrollaron esta complicación (79 % y 51%, p < 0.05, respectivamente). En resumen, la prevalencia de ISR es elevada en los pacientes con cirrosis estable y se relaciona con un deterioro de la función hepática y una mayor mortalidad.

Relative adrenal insufficiency (RAI) is a common finding in cirrhotic patients with severe sepsis, and increased mortality. Its significance is unknown in stable conditions. The aim of this study was to evaluate the prevalence of RAI in stable cirrhotic patients at different stages of the disease. Also, the impact of RAI on the survival was evaluated and basal cortisol levels between plasma and saliva was correlated in control subjects and cirrhotic patients. Forty seven ambulatory patients and 16 control subjects were studied. RAI was defined as a serum cortisol increase of less than 9 μg/dl from baseline after the stimulation with 250 mg of synthetic ACTH. Twenty two had Child-Pugh ≤ 8 and 25 = 9. The prevalence of RAI in patients with stable cirrhosis was 22%. A higher incidence of RAI was observed in patients with a Child-Pugh = 9 (8/32) than in those with ≤ 8 (3/13, p < 0.05). A correlation between salivary cortisol and basal plasma cortisol (r = 0.6, p < 0.0004) was observed. Finally, survival at 1 year (97%) and 3 years (91%) was significantly higher without RAI than those who developed this complication (79% and 51%, p < 0.05, respectively). In summary, the prevalence of RAI is frequent in patients with stable cirrhosis and that it is related to the severity of liver diseaseand increased mortality.

Triggering HIV polyprotein processing by light using rapid photodegradation of a tight-binding protease inhibitor.

HIV protease (PR) is required for proteolytic maturation in the late phase of HIV replication and represents a prime therapeutic target. The regulation and kinetics of viral polyprotein processing and maturation are currently not understood in detail. Here we design, synthesize, validate and apply a potent, photodegradable HIV PR inhibitor to achieve synchronized induction of proteolysis. The compound exhibits subnanomolar inhibition in vitro. Its photolabile moiety is released on light irradiation, reducing the inhibitory potential by 4 orders of magnitude. We determine the structure of the PR-inhibitor complex, analyze its photolytic products, and show that the enzymatic activity of inhibited PR can be fully restored on inhibitor photolysis. We also demonstrate that proteolysis of immature HIV particles produced in the presence of the inhibitor can be rapidly triggered by light enabling thus to analyze the timing, regulation and spatial requirements of viral processing in real time.

Induced maturation of human immunodeficiency virus.

UNLABELLED: HIV-1 assembles at the plasma membrane of virus-producing cells as an immature, noninfectious particle. Processing of the Gag and Gag-Pol polyproteins by the viral protease (PR) activates the viral enzymes and results in dramatic structural rearrangements within the virion--termed maturation--that are a prerequisite for infectivity. Despite its fundamental importance for viral replication, little is currently known about the regulation of proteolysis and about the dynamics and structural intermediates of maturation. This is due mainly to the fact that HIV-1 release and maturation occur asynchronously both at the level of individual cells and at the level of particle release from a single cell. Here, we report a method to synchronize HIV-1 proteolysis in vitro based on protease inhibitor (PI) washout from purified immature virions, thereby temporally uncoupling virus assembly and maturation. Drug washout resulted in the induction of proteolysis with cleavage efficiencies correlating with the off-rate of the respective PR-PI complex. Proteolysis of Gag was nearly complete and yielded the correct products with an optimal half-life (t(1/2)) of ~5 h, but viral infectivity was not recovered. Failure to gain infectivity following PI washout may be explained by the observed formation of aberrant viral capsids and/or by pronounced defects in processing of the reverse transcriptase (RT) heterodimer associated with a lack of RT activity. Based on our results, we hypothesize that both the polyprotein processing dynamics and the tight temporal coupling of immature particle assembly and PR activation are essential for correct polyprotein processing and morphological maturation and thus for HIV-1 infectivity. IMPORTANCE: Cleavage of the Gag and Gag-Pol HIV-1 polyproteins into their functional subunits by the viral protease activates the viral enzymes and causes major structural rearrangements essential for HIV-1 infectivity. This proteolytic maturation occurs concomitant with virus release, and investigation of its dynamics is hampered by the fact that virus populations in tissue culture contain particles at all stages of assembly and maturation. Here, we developed an inhibitor washout strategy to synchronize activation of protease in wild-type virus. We demonstrated that nearly complete Gag processing and resolution of the immature virus architecture are accomplished under optimized conditions. Nevertheless, most of the resulting particles displayed irregular morphologies, Gag-Pol processing was not faithfully reconstituted, and infectivity was not recovered. These data show that HIV-1 maturation is sensitive to the dynamics of processing and also that a tight temporal link between virus assembly and PR activation is required for correct polyprotein processing.

In vitro analysis of human immunodeficiency virus particle dissociation: gag proteolytic processing influences dissociation kinetics.

Human immunodeficiency virus particles undergo a step of proteolytic maturation, in which the main structural polyprotein Gag is cleaved into its mature subunits matrix (MA), capsid (CA), nucleocapsid (NC) and p6. Gag proteolytic processing is accompanied by a dramatic structural rearrangement within the virion, which is necessary for virus infectivity and has been proposed to proceed through a sequence of dissociation and reformation of the capsid lattice. Morphological maturation appears to be tightly regulated, with sequential cleavage events and two small spacer peptides within Gag playing important roles by regulating the disassembly of the immature capsid layer and formation of the mature capsid lattice. In order to measure the influence of individual Gag domains on lattice stability, we established Förster's resonance energy transfer (FRET) reporter virions and employed rapid kinetic FRET and light scatter measurements. This approach allowed us to measure dissociation properties of HIV-1 particles assembled in eukaryotic cells containing Gag proteins in different states of proteolytic processing. While the complex dissociation behavior of the particles prevented an assignment of kinetic rate constants to individual dissociation steps, our analyses revealed characteristic differences in the dissociation properties of the MA layer dependent on the presence of additional domains. The most striking effect observed here was a pronounced stabilization of the MA-CA layer mediated by the presence of the 14 amino acid long spacer peptide SP1 at the CA C-terminus, underlining the crucial role of this peptide for the resolution of the immature particle architecture.

An unreported case of pancreatic panniculitis in a liver transplant patient.

Pancreatic panniculitis is an uncommon condition that can occur in association with pancreatic disease. Most of the cases reported to date were associated with acute or chronic pancreatitis and pancreas cancer. Recently, development has been described in kidney transplant patients and secondarily to allograft pancreatitis in a pancreas-kidney transplant recipient. Both findings suggest that immunological processes may be involved in the pathogenesis of this entity. We report for the first time a case of acute pancreatitis associated with pancreatic panniculitis in a patient who underwent a liver transplant 10 months before. A 69-year-old man with a history of epigastric pain of a few days of evolution was presented with painful subcutaneous nodules on both legs. Blood chemistry showed raised serum amylase and lipase levels. Ultrasonography and multislice CT scan were suggestive of an acute pancreatitis. A skin biopsy showed typical features of pancreatic panniculitis which included lobular panniculitis with lipocyte degeneration with ghost cells. The administration of octreotide resulted in both a rapid improvement of symptoms and a disappearance of skin lesions. Liver transplant specialists should be aware that the pancreatic panniculitis could be a manifestation ofpancreas disease in patients who have undergone l ver transplantation.

[Efficacy of the association of a single dose of hepatitis B hyperimmune gammaglobulin and entecavir in the prophylaxis of hepatitis B after liver transplantation: experience of a single center in Argentina]. / Eficacia de la asociación de una sola dosis de gamaglobulina hiperinmune anti-hepatitis B más entecavir en la profilaxis de la hepatitis B después del trasplante hepático: experiencia de un centro en la Argentina.

The present study reports the effectiveness of the association of a single dose of hepatitis B immunoglobulin (HBIg) associated to entecavir in the prophylaxis of hepatitis B in patients who have undergone liver transplantation. Six patients that had been transplanted because of hepatitis B liver disease were retrospectively evaluated. Three of them developed non-oncological complications related to liver cirrhosis, two had hepatocellular carcinoma and another one had fulminant HBV hepatitis. The mean follow-up was 22 months (range: 7-52 months). The 6 patients received entecavir as prophylactic treatment before transplantation. The pretransplant viral load was undetectable in all patients. HBsAg seroconversion was observed in four of the six patients. Three patients died during follow-up, two because of recurrent hepatocellular carcinoma, none of them had detectable HBV serum viral load. In a small series of patients we could demonstrate that a regimen with a single dose of gamma globulin entecavir is effective in the post-transplant management of patients with liver disease associated with HBV. Future studies will be able to demonstrate the effectiveness of specific gamma globulin-free regimens.

Eficacia de la asociación de una sola dosis de gamaglobulina hiperinmune anti-hepatitis B más entecavir en la profilaxis de la hepatitis B después del trasplante hepático: experiencia de un centro en la Argentina / [Efficacy of the association of a single dose of hepatitis B hyperimmune gammaglobulin and entecavir in the prophylaxis of hepatitis B after liver transplantation: experience of a single center in Argentina].

The present study reports the effectiveness of the association of a single dose of hepatitis B immunoglobulin (HBIg) associated to entecavir in the prophylaxis of hepatitis B in patients who have undergone liver transplantation. Six patients that had been transplanted because of hepatitis B liver disease were retrospectively evaluated. Three of them developed non-oncological complications related to liver cirrhosis, two had hepatocellular carcinoma and another one had fulminant HBV hepatitis. The mean follow-up was 22 months (range: 7-52 months). The 6 patients received entecavir as prophylactic treatment before transplantation. The pretransplant viral load was undetectable in all patients. HBsAg seroconversion was observed in four of the six patients. Three patients died during follow-up, two because of recurrent hepatocellular carcinoma, none of them had detectable HBV serum viral load. In a small series of patients we could demonstrate that a regimen with a single dose of gamma globulin entecavir is effective in the post-transplant management of patients with liver disease associated with HBV. Future studies will be able to demonstrate the effectiveness of specific gamma globulin-free regimens.

Maturation-dependent HIV-1 surface protein redistribution revealed by fluorescence nanoscopy.

Human immunodeficiency virus type 1 (HIV-1) buds from the cell as an immature particle requiring subsequent proteolysis of the main structural polyprotein Gag for morphological maturation and infectivity. Visualization of the viral envelope (Env) glycoprotein distribution on the surface of individual HIV-1 particles with stimulated emission depletion (STED) superresolution fluorescence microscopy revealed maturation-induced clustering of Env proteins that depended on the Gag-interacting Env tail. Correlation of Env surface clustering with the viral entry efficiency revealed coupling between the viral interior and exterior: Rearrangements of the inner protein lattice facilitated the alteration of the virus surface in preparation for productive entry. We propose that Gag proteolysis-dependent clustering of the sparse Env trimers on the viral surface may be an essential aspect of HIV-1 maturation.

Utilidad de la elastografía de transición (Fibroscan®) en la evaluación de la fibrosis hepática en pacientes con hepatopatía crónica / Usefulness of transient elastography (Fibroscan®) in the assessment of fibrosis in patients with chronic liver disease

El pronóstico de la enfermedad crónica hepática depende de la extensión y la progresión de la fibrosis hepática. Actualmente la biopsia hepática es la técnica de elección para determinar el grado de fibrosis, pero es una prueba invasiva, no exenta de complicaciones. Por ello, el desarrollo de marcadores no invasivos de fibrosis hepática se convirtió en una necesidad indiscutible. Se propuso la elastografìa por transición (Fibroscan®) para valorar la fibrosis hepática en pacientes con enfermedad crónica hepática, mediante la medición de la rigidez hepática. Nuestro objetivo fue evaluar la efectividad, la objetividad y la seguridad de esta técnica. Se estudiaron 68 pacientes a los que se les realizó una biopsia hepática en los 18 meses previos al estudio. Todos los procedimientos de elastografia y biopsia hepática fueron analizados por un mismo profesional (DA y MA, respectivamente). Para la valoración de la biopsia hepática se utilizó la escala METAVIR. El valor medio de rigidez en pacientes sin fibrosis o con fibrosis leve (F0-F1) y en los pacientes con fibrosis avanzada o cirrosis (F3-F4) fue 6.8 ± 3.0 kPa y 21.0 ± 15.1 kPa, respectivamente (con diferencia significativa, p < 0.01). Las áreas debajo de la curva ROC definieron los niveles de corte en cada grupo. Con independencia del diagnóstico etiológico de enfermedad hepática, hallamos una correlación positiva, en todos los pacientes, entre rigidez hepática medida por elastografìa y grado de fibrosis hepática en la biopsia. En conclusión, podemos considerar que el Fibroscan® es un método no invasivo, seguro, fácil y rápido, que lo convierte en la alternativa a la biopsia para identificar fibrosis significativa o cirrosis.

The prognosis and management of chronic liver disease largely depends on the extent and progression of liver fibrosis. Unfortunately, liver biopsy, an invasive and painful technique with several limitations, continues to be the gold standard for the staging and grading of fibrosis. Therefore, accurate noninvasive tests for liver injury are urgently needed. During the last years, transient elastography (Fibroscan®) has been proposed for the assessment of hepatic fibrosis in patients with chronic liver disease, by measuring liver stiffness. The aim of this study was to evaluate the effectiveness, objectivity and safety of this technique. We included 68 patients who underwent a liver biopsy in the last 18 months with a wide spectrum of chronic liver diseases. All procedures as well as the liver biopsies according to the METAVIR scoring system were analyzed by the same sonographer and the same specialist in pathology, respectively. Median value of stiffness with none or mild fibrosis (F0 and FI), and severe fibrosis or cirrhosis (F3 and F4) was 6.8 ± 3.0 kPa and 21.0 ± 15.1 kPa, respectively, with a significant difference between them (p < 0.01). The areas under the receiver operating characteristic curves showed the optimal liver stiffness cut-off values for each group. We found also a positive correlation between liver stiffness found by transient elastography and fibrosis stage on biopsy in all patients, independently of the liver disease etiology. Fibroscan® is an easy, quick to perform and safe non-invasive method, reliable for assessing liver fibrosis.

[Usefulness of transient elastography (Fibroscan®) in the assessment of fibrosis in patients with chronic liver disease]. / Utilidad de la elastografia de transición (Fibroscan®) en la evaluación de la fibrosis hepática en pacientes con hepatopatía crónica.

The prognosis and management of chronic liver disease largely depends on the extent and progression of liver fibrosis. Unfortunately, liver biopsy, an invasive and painful technique with several limitations, continues to be the gold standard for the staging and grading of fibrosis. Therefore, accurate noninvasive tests for liver injury are urgently needed. During the last years, transient elastography (Fibroscan®) has been proposed for the assessment of hepatic fibrosis in patients with chronic liver disease, by measuring liver stiffness. The aim of this study was to evaluate the effectiveness, objectivity and safety of this technique. We included 68 patients who underwent a liver biopsy in the last 18 months with a wide spectrum of chronic liver diseases. All procedures as well as the liver biopsies according to the METAVIR scoring system were analyzed by the same sonographer and the same specialist in pathology, respectively. Median value of stiffness with none or mild fibrosis (F0 and FI), and severe fibrosis or cirrhosis (F3 and F4) was 6.8 ± 3.0 kPa and 21.0 ± 15.1 kPa, respectively, with a significant difference between them (p < 0.01). The areas under the receiver operating characteristic curves showed the optimal liver stiffness cut-off values for each group. We found also a positive correlation between liver stiffness found by transient elastography and fibrosis stage on biopsy in all patients, independently of the liver disease etiology. Fibroscan® is an easy, quick to perform and safe non-invasive method, reliable for assessing liver fibrosis.

A SNAP-tagged derivative of HIV-1--a versatile tool to study virus-cell interactions.

Fluorescently labeled human immunodeficiency virus (HIV) derivatives, combined with the use of advanced fluorescence microscopy techniques, allow the direct visualization of dynamic events and individual steps in the viral life cycle. HIV proteins tagged with fluorescent proteins (FPs) have been successfully used for live-cell imaging analyses of HIV-cell interactions. However, FPs display limitations with respect to their physicochemical properties, and their maturation kinetics. Furthermore, several independent FP-tagged constructs have to be cloned and characterized in order to obtain spectral variations suitable for multi-color imaging setups. In contrast, the so-called SNAP-tag represents a genetically encoded non-fluorescent tag which mediates specific covalent coupling to fluorescent substrate molecules in a self-labeling reaction. Fusion of the SNAP-tag to the protein of interest allows specific labeling of the fusion protein with a variety of synthetic dyes, thereby offering enhanced flexibility for fluorescence imaging approaches.Here we describe the construction and characterization of the HIV derivative HIV(SNAP), which carries the SNAP-tag as an additional domain within the viral structural polyprotein Gag. Introduction of the tag close to the C-terminus of the matrix domain of Gag did not interfere with particle assembly, release or proteolytic virus maturation. The modified virions were infectious and could be propagated in tissue culture, albeit with reduced replication capacity. Insertion of the SNAP domain within Gag allowed specific staining of the viral polyprotein in the context of virus producing cells using a SNAP reactive dye as well as the visualization of individual virions and viral budding sites by stochastic optical reconstruction microscopy. Thus, HIV(SNAP) represents a versatile tool which expands the possibilities for the analysis of HIV-cell interactions using live cell imaging and sub-diffraction fluorescence microscopy.

Takotsubo Cardiomyopathy: A Cardiac Syndrome Mimicking Acute Myocardial Infarction in a Liver Transplant Recipient.

Takotsubo cardiomyopathy (TTC) is a rare clinical syndrome defined as a profound but reversible left ventricular dysfunction in the absence of coronary artery disease. We describe the clinical features and management of TC manifesting in the postoperative period in a patient undergoing liver transplantation. Two days after surgery, the patient developed clinical features of acute myocardial infarction. Ecochardiography revealed hypokinesis of the left ventricle. Coronary angiography revealed normal arteries without any stenosis or obstruction. The patient required vasopressor and inotropic support. The placement of intra-aortic balloon pump had a beneficial effect on the management of heart failure. The patient had a complete recovery of cardiac function 40 days after surgery. TC is a possible occurrence after liver transplant. Awareness of this condition is essential as early diagnosis and prompt management can save the patient's life.

Selective killing of human immunodeficiency virus infected cells by non-nucleoside reverse transcriptase inhibitor-induced activation of HIV protease.

BACKGROUND: Current antiretroviral therapy against human immunodeficiency virus (HIV-1) reduces viral load and thereby prevents viral spread, but it cannot eradicate proviral genomes from infected cells. Cells in immunological sanctuaries as well as cells producing low levels of virus apparently contribute to a reservoir that maintains HIV persistence in the presence of highly active antiretroviral therapy. Thus, accelerated elimination of virus producing cells may represent a complementary strategy to control HIV infection. Here we sought to exploit HIV protease (PR) related cytotoxicity in order to develop a strategy for drug induced killing of HIV producing cells. PR processes the viral Gag and Gag-Pol polyproteins during virus maturation, but is also implicated in killing of virus producing cells through off-target cleavage of host proteins. It has been observed previously that micromolar concentrations of certain non-nucleoside reverse transcriptase inhibitors (NNRTIs) can stimulate intracellular PR activity, presumably by enhancing Gag-Pol dimerization. RESULTS: Using a newly developed cell-based assay we compared the degree of PR activation displayed by various NNRTIs. We identified inhibitors showing higher potency with respect to PR activation than previously described for NNRTIs, with the most potent compounds resulting in ~2-fold increase of the Gag processing signal at 250 nM. The degree of enhancement of intracellular Gag processing correlated with the compound's ability to enhance RT dimerization in a mammalian two-hybrid assay. Compounds were analyzed for their potential to mediate specific killing of chronically infected MT-4 cells. Levels of cytotoxicity on HIV infected cells determined for the different NNRTIs corresponded to the relative degree of drug induced intracellular PR activation, with CC50 values ranging from ~0.3 µM to above the tested concentration range (10 µM). Specific cytotoxicity was reverted by addition of PR inhibitors. Two of the most active compounds, VRX-480773 and GW-678248, were also tested in primary human cells and mediated cytotoxicity on HIV-1 infected peripheral blood mononuclear cells. CONCLUSION: These data present proof of concept for targeted drug induced elimination of HIV producing cells. While NNRTIs themselves may not be sufficiently potent for therapeutic application, the results provide a basis for the development of drugs exploiting this mechanism of action.

HIV-1 Gag processing intermediates trans-dominantly interfere with HIV-1 infectivity.

Protease inhibitors (PI) act by blocking human immunodeficiency virus (HIV) polyprotein processing, but there is no direct quantitative correlation between the degree of impairment of Gag processing and virion infectivity at low PI concentrations. To analyze the consequences of partial processing, virus particles were produced in the presence of limiting PI concentrations or by co-transfection of wild-type proviral plasmids with constructs carrying mutations in one or more cleavage sites. Low PI concentrations caused subtle changes in polyprotein processing associated with a pronounced reduction of particle infectivity. Dissection of individual stages of viral entry indicated a block in accumulation of reverse transcriptase products, whereas virus entry, enzymatic reverse transcriptase activity, and replication steps following reverse transcription were not affected. Co-expression of low amounts of partially processed forms of Gag together with wild-type HIV generally exerted a trans-dominant effect, which was most prominent for a construct carrying mutations at both cleavage sites flanking the CA domain. Interestingly, co-expression of low amounts of Gag mutated at the CA-SP1 cleavage site also affected processing activity at this site in the wild-type virus. The results indicate that low amounts (<5%) of Gag processing intermediates can display a trans-dominant effect on HIV particle maturation, with the maturation cleavage between CA and SP1 being of particular importance. These effects are likely to be important for the strong activity of PI at concentrations achieved in vivo and also bear relevance for the mechanism of action of the antiviral drug bevirimat.