Author Archives: Dr. Alejandro Soza

POSITRON study

The results of the POSITRON study have been released by Gilead in a press release. This is a phase 3 trial of sofosbuvir + ribavirin for patients with hepatitis C virus infection with genotypes 2 and 3 who are intolerant or ineligible for interferon based treatments. Sofosbuvir is a nucleotide polymerase inhibitor, a kind of direct acting antiviral (DAA) for hepatitis C.

Patients were randomized in a 3 to 1 proportion to receive either sofosbuvir 400 mg QD + ribavirin twice daily (n=207) or placebo (n=71). Among those receiving sofosbuvir treatment, 15% were cirrhotic and 52% were infected with genotype 2 HCV. No patient in the placebo group achieved a sustained virological response at week 12 (SVR12), whereas 78% of treated patients achieved an SVR12. Strikingly all patients who received treatment became HCV RNA negative during treatment, so relapse accounted for all failures (no evidence for resistance).

Response rate was 91% for genotype 3 and 61% for genotype 3. Cirrhotics achieved an SVR of 15%.

We hope to see more details of this study in the upcoming meetings.

Reference

Positron Study – Gilead press release

Ledipasvir (GS-5885)

Ledipasvir, formerly known as GS-5885, is a new treatment for hepatitis C. It is a compound in clinical development by Gilead. Ledipasvir (GS-5885) is a drug that blocks NS5A, a viral protein critical for hepatitis C replication [cite]22314425[/cite].

Ledipasvir has been coformulated in a single pill with sofosbuvir. Very encouraging sustained virological response has been reported in interim reports of this combination, with an overall response of 100% in 25 patients, as recently presented at the Liver Meeting 2012 in Boston. More than 1000 patients have been treated with GS-5885 in phase 2 studies so far, with no signals of toxicity. The selected dose for further development is 90 mg QD.

Polymerase (NS5B) inhibitors

The HCV polymerase is viral protein that is key for the viral cycle [cite]22774409[/cite]. The polymerase is also known as NS5B (NS stands for non-structural). The complete name of the enzyme is RNA-dependent RNA polymerase.

The structure of the polymerase doesn´t change much across different HCV genotypes, so it is said that it has a highly conserved genomic structure.

The HCV polymerase is an obvious target for therapy, just as it has been demonstrated on other viruses such as the hepatitis B virus, HIV and herpes viruses. The tridimensional structure of the protein resembles a right hand, where besides the active catalytic site, several domains have been recognized: finger, palm and thumb. The catalytic site of the enzyme is located in the palm domain.

Polymerase inhibitors can be divided into nucleoside (or nucleotide) analogues and non-nucleoside analogues.

Nucleoside and nucleotide analogues (“nucs”)

Nucleoside and nucleotide analogues target the active site of the enzyme by mimicking its substrate and acting as chain terminators. Since the catalytic site of NS5B is highly conserved, these analogues are active against different HCV genotypes.

Additionally, as this site is critical for replication, single amino acidic changes in the active site lead to highly impaired replicative fitness, explaining why drugs targeting this site have a high genetic barrier to resistance.

Safety of this class has been questioned recently after one drug candidate belonging to this class was halted because of cardiac toxicity. It appears that this is not a class effect, as other nucleotide analogues have shown an excellent safety profile so far.

Nucleoside analogues:

  • Mericitabine, formerly RG-7128 (Roche).

Nucleotide analogues:

  • Sofosbuvir, formerly GS-7977 / PSI-7977 (Gilead).
  • VX-135 (Vertex).
  • IDX-184 and IDX-19368 (Idenix): On hold.
  • BMS-986094 (BMS): On hold, discontinued.

Non-nucleoside inhibitors (“non-nucs”)

Non-nucleoside inhibitors target different domains near the catalytic (active) site, producing an allosteric (indirect) inhibition by inducing conformational changes of the protein. At least five different binding sites have been described so far.

Aminoacidic substitutions at these sites are not critical for the functioning of the enzyme, so these compounds have a relatively low genetic barrier to resistance. A low genetic barrier to resistance means that it is easier that patients taking this medications will select resistant virus that will not be suppressed by the drug.  Being targeted to different sites, they can theoretically be used in combination with other nucleoside or non-nucleoside analogues.

Some non-nucleoside polymerase inhibitors:

  • ABT-333 and ABT-072 (Abbott).
  • BMS-791325 (BMS).
  • Tegobuvir, formerly GS-9190, and GS-9669 (Gilead).
  • Setrobuvir, formerly RG-77790 (Roche).
  • VX-222 (Vertex).

NS5A inhibitors

NS5A is an HCV viral protein with multiple functions. It is essential for viral replication. NS stands for non-structural.

Investigators at Bristol-Myers Squibb (BMS), using an elegant methodology known as chemical genetics approach, were able to identify the first NS5A inhibitor (BMS-790052, now known as daclatasvir) [cite]20410884[/cite]. This compound exhibitits pan-genotypic action with potent clinical effect of up to 3.6 log10 reduction after a single dose. Pan-genotypic means that the drug is effective against all HCV genotypes (1 to 6). Further clinical studies have shown very promising data regarding viral response when used in combination with peginterferon and ribavirin or in interferon-free combinations. A number of additional NS5A inhibitors are currently being developed.

As a class, NS5A exhibit a relatively low genetic barrier to resistance, with rapid selection of resistant associated variants [cite]21975800[/cite]. On the other side, NS5A have shown so far to be very safe and well tolerated [cite]21867941[/cite].

Some NS5A inhibitors:

  • GS-5885 (Gilead).
  • Daclatasvir, formerly BMS-790052 (BMS).
  • IDX-710 (Idenix).
  • ACH-2928 and ACH-3102 (Achillion).

 

Direct acting antivirals (DAA´s) for hepatitis C

Chronic hepatitis C affects more than 170 million individuals who are at risk of developing cirrhosis and hepatocellular carcinoma.

Despite that interferon based therapies for chronic hepatitis C have been the standard of care for more than two decades, there is still a very important gap between the needs and the response rates of conventional therapy.

More than 50% of patients harboring hepatitis C virus (HCV) genotype 1 do not respond to peginterferon and ribavirin. Moreover, there are several special groups of patients who have contraindications to interferon or ribavirin and a significant proportion of patients are forced to discontinue therapy due to the frequent side effects, such as anemia, neutropenia, fatigue, depression and flu-like symptoms.

This landscape is starting to change with the advent of new direct-acting antivirals, heralding a new era in hepatitis C treatment. In 2011, two protease inhibitors were approved for clinical use: Telaprevir and boceprevir.

DAA´s are oral drugs that block specific targets (enzymes or proteins) of the virus. HCV has structural and non-structural proteins. Among the most important HCV targets are NS3 (protease), NS5 and NS5B (polymerase), so the most clinically relevant DAA´s belong to the following categories:

Protease inhibitors

The hepatitis C protease is a key viral enzyme for the biological cycle of the virus. Protease inhibitors were the first anti-HCV small molecule agents developed. The currently approved oral therapies for hepatitis C boceprevir and telaprevir belong to this class.

The protease, also known as NS3 (NS stands for non-structural), processes the polyprotein, yielding several proteins needed for the replication complex of the virus, including NS4B, NS5A and NS5B. Furthermore, NS3 has an additional function in evading the host innate immunity, thus promoting viral replication and persistence in liver cells, so inhibiting this target has an additional beneficial effect restoring the host immunity.

The proof of principle study of the effect of the first HCV protease inhibitor in humans was published in 2003 with ciluprevir (BILN 2061). This drug was further discontinued because of myocardial toxicity in primates. A number of different protease inhibitors have been synthesized since then, being in different stages of clinical development. These drugs can be divided in two chemical classes: linear tetrapeptide α-ketoamide derivatives and macrocyclic compounds. During 2011, two of these drugs (boceprevir and telaprevir) have completed clinical development and were approved for clinical use in patients with genotype 1 infection. Some features of the two approved protease inhibitors are summarized in the following table:

Boceprevir Telaprevir
Commercial name Victrelis® Incivek®
Chemical structure Linear peptidomimetic Linear peptidomimetic
Dose 800 mg q8h 750 mg q8h
Presentation 200 mg capsules 375 mg tablets
Administration With food With a fatty food (21 g fat)
Half life 3.4 h 4 h
Elimination Bile 79%, urine 9% Bile 82%, urine 1%
Treatment duration (protease inhibitor) 24 to 44 weeks 12 weeks
Genotype Approved for genotype 1 HCV Approved for genotype 1 HCV
Phase 3 trials in treatment naïve patients SPRINT-2 ADVANCE
ILLUMINATE
SVR in naïve patients/Control* 63 – 66% / 38% 69 – 75% / 44%
Phase 3 trials in treatment experienced patients RESPOND-2 REALIZE
SVR in treatment experienced patients/Control* 59 – 66% / 21% 65% / 17%
Main side effects Anemia, disgeusia Anemia, skin rash, anal discomfort
Stopping rules > 100 IU/mL at week 12
Detectable at week 24 or 36		 > 1000 IU/mL at week 4 or 12
Detectable at week 24 or 36

 

* Basal characteristics of patients and trial designs are different. There are no head to head comparisons of boceprevir and telaprevir.

 

Second generation protease inhibitors

Several new compounds are at diverse stages of clinical development. Some of these include danoprevir (R7227/ITMN191), vaniprevir (MK-7009), MK-5172, BI201335, TMC435, narlaprevir (SCH900518), PHX1766, BMS-650032, ACH-1625, IDX320, ABT-450, GS-9256 and GS-9451. All target the active site of the NS3 protease and have shown a similar antiviral activity to boceprevir and telaprevir.

One of the strategies is boosting the protease inhibitor with low dose ritonavir, just as it has been used in HIV. Some of the potential advantages of these new compounds involve improved safety and tolerability profiles, pharmacokinetic advantages (i.e. once daily dosing) and different resistance profiles.

There are, nevertheless, side effects associated with these compounds, which include gastrointestinal symptoms (danoprevir, vaniprevir), bilirrubin elevation (TMC-435), ALT elevation and neutropenia (danoprevir).  Albeit some dissimilarity in the resistance profile of linear versus macrocyclic inhibitors exists, most compounds share resistance to the R155 variant. MK-5172, a macrocyclic compound is a possible exception, being active against variants containing the R155 mutation. This drug also seems to be active against genotype 3 isolates, and indeed seems to have pangenotypic antiviral activity.

Sofosbuvir (GS-7977)

Sofosbuvir is an oral antiviral against hepatitis C (DAA or direct acting antiviral). It belongs to a category of medications called nucleotide analogues. Sofosbuvir is currently not approved by the FDA, but it is actively being investigated in several clinical trials, nowadays in phase 3 studies. There is significant clinical interest in sofosbuvir, as it could be used as a backbone for interferon-free regimens for hepatitis C treatment.

Sofosbuvir, acts by inhibiting a key hepatitis C virus (HCV) enzyme called RNA polymerase (NS5B), acting as a chain terminator. This enzyme is critical for the replication of the virus.

Some features of sofsobuvir:

  • It is taken orally (by mouth) once daily in a dose of 400 mg QD.
  • Sofosbuvir has been shown so far to be safe and very well tolerated.
  • Sofosbuvir has a pangenotypic activity, meaning that it is active against all hepatitis C virus genotypes.
  • Sofosbuvir is potent inhibitor, with an IC50 in the picomolar range. IC50 refers to the concentration of the drug necessary for inhibiting HCV replication. If a drug has a low IC50, it means it is more potent.
  • Sofosbuvir has a high barrier to resistance. This means that the chance that using this medication results in selection of viral mutations that confer resistance to the medication is low. In order for selecting resistance mutants, the virus has to develop mutations in the active site of the HCV RNA polymerase. A mutation at this site will also decrease replication fitness of the virus, explaining this high barrier to resistance.
  • It has been co-formulated with an NS5A inhibitor (GS-5885) in a fixed dose single pill.

Sofosbuvir was developed by Pharmasset, and initially was known as PSI-7977. Pharmasset was acquired by Gilead in 2012, so the name of the drug changed to GS-7977, and now has the official name sofosbuvir.

Several studies, most published in abstract form, have shown impressive clinical results of using sofosbuvir in hepatitis C virus infected patients, including the Electron and the Proton studies. More recently, the Electron trial has been published in the New England Journal of Medicine [zotpressInText item="{NF73UMNJ}" format="%num%"].

Sofosbuvir is currently being evaluated in several phase 3 trials:

  • POSITRON: Sofosbuvir + ribavirin in interferon ineligible or intolerant patients with genotypes 2 and 3 for 12 weeks (results for Q4 2012).
  • FISSION: Sofosbuvir + ribavirin in treatment naive genotype 2 and 3 patients for 12 weeks (results for Q1 2013).
  • FUSION: Sofosbuvir + ribavirin in treatment experienced genotype 2 and 3 patients for 12 or 16 weeks (results for Q1 2013).
  • NEUTRINO: Sofosbuvir + peginterferon alfa 2a + ribavirin in treament naive patients with genotype 1, 4, 5 and 6 for 12 weeks (results for Q1 2013).
  • ION-1: Sofosbuvir + GS-5885 with or without ribavirin in treatment naive genotype 1 patients for 12 or 24 weeks (results for Q4 2014).

References

Discovery of a β-d-2′-deoxy-2′-α-fluoro-2′-β-C-methyluridine nucleotide prodrug (PSI-7977) for the treatment of hepatitis C virus. J Med Chem. 2010 Oct 14;53(19):7202-18.

Genotype and subtype profiling of PSI-7977 as a nucleotide inhibitor of hepatitis C virus. Antimicrob Agents Chemother. 2012 Jun;56(6):3359-68.

http://www.gilead.com/pr_1757156

[zotpressInTextBib style="Hepatology" sortby="default" sort="ASC"]

What is fatty liver?

Fatty liver

Obesity and overweight are the most common causes of fatty liver

What is fatty liver? Fatty liver refers to a liver disease characterized by accumulation of fatty acids and triglycerides in liver cells (hepatocytes). Alcohol is a common cause of fatty liver, and is a factor that should always be considered in a patient with fatty liver. In this article we will refer to fatty liver not associated with consumption of alcohol. Fat accumulation in hepatocytes can lead to liver inflammation, with the possibility of developing fibrosis and ultimately end up in chronic liver damage (or cirrhosis).

Nomenclature

Fatty liver is known in several ways:

  • Fatty liver: A general term. When it is not because alcohol is known as nonalcoholic fatty liver disease (NAFLD).
  • Liver steatosis: Accumulation of fat in the liver, synonymous of fatty liver.
  • Nonalcoholic steatohepatitis: When the accumulation of fat in the liver is also accompanied by an inflammatory process. Non-alcoholic steatohepatitis is abbreviated NASH.
  • Metabolic steatohepatitis: It has been proposed to call this disease metabolic steatohepatitis (MESH).

Causes

A critical step in fatty liver treatment is modifying eating habits, reducing caloric foods and excessive fat

The cause of the accumulation of fat in the liver are not known with certainty, but there are some mechanisms that have proved very important in the development of the disease:

  • Insulin resistance.
  • Oxidative stress.
  • Release of cytokines.

Epidemiology

The occurrence of fatty liver is extremely common. This disease is associated with the following risk factors:

  • Obesity.
  • Diabetes.
  • Hypercholesterolemia.
  • Hipertrigiceridemia.
  • Female sex.

However, it is increasingly common to find people with fatty liver without these risk factors. Not all people with fatty liver will develop complications or chronic liver damage.

In the general population, the prevalence of fatty liver is around 20 to 30%.

Clinical features

Fatty liver is often asymptomatic and only discovered after an ultrasound showing the liver more refractive (“bright”). The other way to get the diagnosis is through the discovery of elevated aminotransferases (transaminases) found in a routine blood test or some other reason. Some people complain of mild to moderate abdominal pain in the right upper quadrant (the area where the liver is located). Only a small percentage of patients develop symptoms of liver failure.

Diagnosis and evaluation

The diagnosis of fatty liver is based on the findings of liver biopsy. This shows fat accumulation in hepatocytes, and there may also be varying degrees of inflammation and fibrosis.

Although liver biopsy is the only test that ensures the diagnosis and is generally a low risk procedure, not all people with suspected diagnosis of fatty liver are subjected to this examination. It is customary to make a presumptive diagnosis of fatty liver disease in someone with suggestive images (ultrasound, CT or MRI). Liver biopsy is, however, the only test that differentiates between “simple steatosis” (fat accumulation) and ”steatohepatitis” (fat associated with inflammation and fibrosis).

Some people with fatty liver also have elevated transaminases or aminotransferases in the blood (SGOT and SGPT, also known as ALT and AST). In such cases it is important to rule out other causes of liver inflammation, such as infection by hepatitis B virus and hepatitis C, hemochromatosis and autoimmune hepatitis.

Prognosis and consequences

Most people with fatty liver will not develop severe disease consequences. Approximately 20% of the subjects may have some degree of hepatic fibrosis in the liver biopsy, which can lead to higher grades of the disease, including cirrhosis and liver cancer. Fatty liver is probably the most common cause of cryptogenic cirrhosis (cirrhosis with no clear cause).

Treatment

Treatment of fatty liver consists primarily in losing weight and increasing physical activity. Obesity and overweight, the main risk factors are modifiable through changes in lifestyle. Other recommendations include avoiding alcohol and unnecessary drug (medication) use.

In those who are in advanced stages of disease (inflammation or significant hepatic fibrosis) some drugs may help, such as antioxidants (vitamin E) or insulin-sensitizing agents. The use of pioglitazone, which has shown benefits normalizing aminotransferases and liver histology, is still somewhat controversial.

Hepatitis A

Hepatitis A virus infection

Hepatitis A is a disease caused by a virus which is transmitted by contamination of food. Hand washing and proper food hygiene is paramount for prevention of this infection

Hepatitis A is a disease which is characterized by acute inflammation of the liver caused by the hepatitis A virus. Its period of incubation (the time between the arrival of the virus in the body and the development of the disease) ranges between 15 and 49 days. The virus is transmitted by the ingestion of food contaminated with the virus, frequently raw seafood or raw vegetables that have been irrigated with fecally-contaminated water.

It is very common in children, although the majority do not show symptoms on contracting the virus. Those who develop symptoms (approximately 5% of children) show signs of nausea, choluria (dark urine) and jaundice (the yellowing colouring of the skin and eyes). Some 70% of adults show symptoms. Some of those affected, less than 1%, may develop fulminant liver failure, requiring a liver transplant. Nevertheless, in the majority of cases the disease runs its course without any lasting damage and the liver regenerates itself completely.

Hepatitis A is the hepatitis virus that most frequently attacks the liver, but also the most benign. It can only be contracted once, given that the body generates permanent defenses against the disease. There is no chronic hepatitis A, so this infection does not lead to cirrhosis. There is no specific antiviral treatment for hepatitis A. The infection is completely preventable via a safe and highly effective vaccine that should be routinely administered to children. Those people who live under the same roof can be given an immunoglobulin to prevent infection. This is administered in intra-muscular form and is only effective during the first two weeks of contact with the patient. It is only useful for those who have not had hepatitis A previously.

Apart from the vaccine and the immunoglobin, the principal prevention measures are an improvement in food hygiene, the universal availability of drinking water and avoiding consumption of vegetables that have been irrigated with fecally-contaminated water.

General considerations

  • Rest: Rest is useful to the extent that the person is in low spirits and is useful for avoiding the spread of the infection in schoolmates or workmate. Nowadays, the long periods of strict bed rest that were recommended years ago are no longer prescribed.
  • Diet: The diet should be light so as to reduce the nausea and vomiting that patients frequently suffer. The reduction of fat and fried food has this as its objective. During the recuperation phase it is important to moderately increase the consumption of high quality proteins (milk, eggs, meat) to help the regeneration the liver.
  • Symptoms of severity: There are two symptoms which indicate seriousness. The first is nausea and persistent vomiting, and secondly a certain drowsiness due to hepatic encephalopathy. The presence of these symptoms should lead to a doctor being called immediately.
  • Laboratory tests: Among the laborarory tests, the most important is the prothrombin time. If this is less than 60%, it may indicate seriousness. A bilirubin above 10 mg/dL is another indicator of severity. The diagnosis of this type of hepatitis is made via the IgM HAV (immunoglobin M of hepatitis A) in the blood. The transaminases refer to the level of the enzymes SGOT(AST) and SGPT(ALT) in the blood. Usually they are elevate above 1000 U/ml, but the degree of the elevation does not have a direct relation with the seriousness of the hepatitis. Billirubin is generally elevated, and this substance explains the yellow colouring of the skin and the eyes. The level of transaminase decreases gradually over the course of one or two months.
  • Course of the hepatitis: Some people may experience the reappearance of symptoms after an apparent recovery. This is not a sign of a bad prognosis. A small percentage of patients show symptoms of “cholestasic” hepatitis, which is manifested by intense pruritus (itching) of the skin and a marked yellow colour of the skin (due to billirubin elevation). On occasions corticoids are used for these cases. Hepatitis A generally lasts no more than six months. Chronic hepatitis due to hepatitis A virus infection does not exist.