Does anyone know why it is possible to cure HCV, but not HIV? It was explained to me as a difference in the virus life cycle, but the explanation given me had some misconceptions that I would like to clarify.
A retrovirus is any virus belonging to the viral family Retroviridae. They are enveloped viruses possessing an RNA genome, and replicate via a DNA intermediate. Retroviruses rely on the enzyme reverse transcriptase to perform the reverse transcription of its genome from RNA into DNA, which can then be integrated into the host's genome with an integrase enzyme. The virus then replicates as part of the cell's DNA."
hepatitis C may be easier to treat in some ways than AIDS. That is because H.I.V. turns its RNA into DNA, which is incorporated into the chromosomes of cells it infects, making it hard to totally eliminate the virus. But hepatitis C virus does not do that, and the experience with interferon has shown that if the virus can be eliminated, patients can be cured.
Thanks for the input. I still don't see how the protease inhibitors and SOC can eliminate HCV but not HIV or HBV. I understand what you are saying, but not fully the mechanism by which HCV can be blocked from reproducing.
I assume there is something in the HCV life cycle that makes it vulnerable while the other two can find a mechanism that allows it to escape the drugs. HIV is significantly impacted by PIs but somehow finds a way to protect enough virions to keep going and survive long enough to mutate. Anyway, luckily for us this is an academic issue in our case.
As I see it the important thing is not that HCV is blocked from reproduction, it is that unlike most viruses HCV is sensitive to an interferon enhanced immune system. The PIs, which block the virus reproduction, can not do the job alone. They only speed up the process, so that the interferon will succeed in its job.
The way I understand viruses is that there is no cure by directly attacking the virus. Our immune system has to do the job. We can make the environment, ie our body, an unpleasant place for the virus, thereby helping the immune system in its effort to kill off the virus, and hopefully the virus will expire. Unfortunately, interferon and ribavirin do not only make the environment unpleasant for the hep C virus, but for us as well. Luckily, we are hardier than the hep C virus.
Also when the virus as with HIV and hep B has become a part of the DNA in the infected cells, I figure each infected cell must die for us to get rid of the disease. Apparently though, a small minority of chronic hep B patients are cured by interferon therapy.
Maybe the fact that HCV does not integrate into the cell DNA is the explanation why interferon works. Because of this HCV might be easier for the interferon enhanced immune system to kill.
In a nutshell...the PI`s stop the viruus from replcating somewhtt like the RIBA...and the PEG does the killing...BTW...PEG and RIBA were not designed for hepatitis...its just a fluke those drugs work...they wrere initally designed for cancer tx.
"I understand what you are saying, but not fully the mechanism by which HCV can be blocked from reproducing.
I assume there is something in the HCV life cycle that makes it vulnerable"
Interferon works in phases. Most of the virus is circulating in your bloodstream. The virus in your blood is the easiest to kill, because it doesn't live as long as the virus that is in liver cells. Also, it is out in the open, so to speak, and not hiding in cells.
The first phase of treatment lasts 1 to 2 days. This phase kills most of the virus circulating in your bloodstream. The action of Interferon in your bloodstream is simple. It mainly slows down the replication of the virus. In order for any life form to survive, it must live long enough to reproduce. By slowing down the rate of replication, the virus dies on its own without producing offspring.
Phase 2 lasts from day 2 through day 14. Interferon is now attacking the virus in your liver cells. This is a slow phase because the virus has trained the liver cells to look as though they aren't infected. The more your viral load drops, the more the interferon is able to see the the infected cells. The Hep C virus has turned the liver cells into virus reproduction factories. It teaches the liver cells how to make more copies of the virus. So now the action of interferon becomes more complicated. Interferon calls for help from other parts of your immune system. These other parts of your immune system degrade the RNA of the virus, interfere with the virus-making process and try to re-teach the liver cells how to behave normally.
Phase 3 lasts from day 14 through day 28, (and continues on through week 24). During this phase, interferon completely switches your immune system into full attack mode. Your immune system can now see which infected liver cells cannot be saved and starts to kill them. Interferon also encourages regeneration of liver cells, so as the infected cells are killed, new cells begin to grow in their place (this is how interferon may help reverse liver damage).
All of this activity takes place within 30 days. That's why your doctor expects to see a 2 log drop in your viral load within 12 weeks of treatment. It means that the interferon is sucessfully working on the virus that is actually in your liver (same with a 4 week RVR).
"I still don't see how the protease inhibitors and SOC can eliminate HCV but not HIV or HBV"
The protease of HCV, NS3, is responsible for blocking interferon. That's why protease inhibitors like Telepravir and Boceprevir, are being used for Hep C treatment. They block replication and help interferon.
"Can one not compare the effect of the PIs as making "everybody's" baseline viral load low and making "everybody" a rapid/quicker responder? No slow responders anymore. "
I suppose you can say that. But the PI's kill the wild type virus (which is the much larger number). You still need the interferon to kill the mutant type virus. And if somebody is interferon resistant, it's not going to work even if the PI lowered the viral load.
With all due respect.... we may have to re-define what we mean when we call people "non-responders". It appears that non-responders do indeed respond to Telaprevir triple therapy . Willy
"Based on these findings, the investigators stated, "In a population of patients who have failed previous [pegylated interferon/ribavirin] treatment, response rates 12 weeks after end of treatment were 52% overall in the T12/PR 24 arm: 73% in prior relapsers, 41% in prior non-responders."
(These were SVR 12 results and therefore not "official"-- Willy)
"Also I think HIV passes the brain/blood barrier, which HCV in most cases does not."
HCV RNA negative strand, which shows replication, was found in the brain tissue of 3 out of 12 Hep C patients in this study.
According to the prevailing hypothesis, circulating lymphocytes cross the blood-brain barrier carrying HCV to the central nervous system ...and the virus is then replicated in the macrophages and microglia in the brain as a separate compartment.
HEPATITIS C VIRUS NEUROINVASION: IDENTIFICATION OF INFECTED CELLS.
Wilkinson J, Radkowski M, Laskus T.
St. Joseph's Hospital and Medical Center, Phoenix, Arizona; Institute of Infectious Diseases, Warsaw Medical University, Warsaw, Poland.
Hepatitis C virus (HCV) infection is often associated with cognitive dysfunction and depression. HCV sequences and replicative forms were detected in autopsy brain tissue and cerebrospinal fluid from infected patients suggesting direct neuroinvasion. However, the phenotype of cells harboring HCV in brain remains unclear. We studied autopsy brain tissue from 12 HCV-infected patients, 6 of these patients were coinfected with HIV. Cryostat sections of frontal cortex and subcortical white matter were stained with monoclonal antibodies specific for microglia/macrophages (CD68), oligodendrocytes (CNPase), astrocytes (GFAP) and neurons (NeuN), separated by laser capture microscopy (LCM) and tested for the presence of positive and negative strand HCV RNA. Sections were also stained with antibodies to viral nonstructural protein 3 (NS3), separated by LCM and phenotyped by real-time PCR. Finally, sections were also double stained with antibodies specific for cell phenotype and HCV NS3. HCV RNA was detected in CD68-positive cells in 8 patients and negative strand HCV RNA, which is a viral replicative form, was found in 3 of these patients. HCV RNA was also found in astrocytes from 3 patients, but negative strand RNA was not detected in these cells. In double immunostaining, 83%-95% of cells positive for HCV NS3 were also CD68-positive, while 4% to 29% were GFAP-positive. NS3-positive cells were negative for neuron and oligodendrocyte phenotypic markers. In conclusion, HCV infects brain microglia/macrophages and to a lesser extent astrocytes. Our findings could explain the biological basis of neurocognitive abnormalities in HCV infection.
HIV can be inhibited as long as long as patients are put on a certain drug (forgot the name i learned in bio). the drug can even reduce the virus to UND for HIV, however, once the patient is off the drug, HIV returns bc my professor said it can hide during tx.
i asked my hepa about relapsed for HCV after tx, and she told me that relapse happens when people are reinfected. didn't mention anything about virus return from hiding in the body.
"But were they null responders, or were they "non-responders" because they were under-dosed, their dose was reduced or interrupted, etc?"
We will soon see, or at least better see. In the past it was virtually impossible to know exactly how and why people failed. Unless one had meticulous records of weekly viral loads, dosing records, etc it was a matter of supposition.
When the people who failed Prove 1 and Prove 2 (the SOC control arm "failures"; all geno 1 naives) were given the opportunity to be placed into rollover arms in which they were given triple therapy. We will be able to see all the classic groups of treatment failures (from null responder to relapsers) respond when given triple therapy. When they classify a person a null responder they will have fairly detailed records to prove it. It will then be followed up with detailed response rates to triple therapy given to the exact same people who had prior failed SOC.
Given the response rates of Prove 3 with past treatment failures I am hopeful that we will see null responders be converted into responders and perhaps even SVR success stories.
I am not trying to argue the point about interferon resistance but I would like to open up the possibility that even so called "null or non response" to SOC does not mean that one may not be able to be cured using protease or polymerase inhibitors (in conjunction with IFN & RBV) I think sometimes people attribute null response to interferon resistance. (I understand that presumably all interferon resistant people will be null responders (to current SOC) but that not all null responders are therefore interferon resistant. Does that sound right to you?)
I see that Rocker posted an article in which (it was claimed) that a Sherring-Plough 2nd generation PI in development was said to be 10X more powerful (in vitro) than existing PI's.(meaning Telaprevir and Boceprevir, presumably)
At some point the inhibitors may become effective enough that interferon (or RBV) will be dropped from treatment. That day may be here sooner than we think. Trials for such treatments may soon start several pharma's. Vertex had one planned on in 2009 I believe
By the way..... Vertex (well, actually Tibotech) will have a European trial which will utilize the SOC "lead in" before dosing Telaprevir on past treatment failures, null responders included. Figure over 18 months to get the trial started, dosed for a year and a 6 month wait for an "official" SVR PCR.
Reason why we are behind in a more effective cure for hepatitis is because all the research funds in the past have pumped into cancer cures ,,,(which there is none and will never be)..cancer is caused by the chemicals in our food and water...also all the cash went to AIDS cures.....its about time the new PI`s are on the way...
numerous cancers have been related to virus and bacteria small sample jc virus colon cancer hpv cervical hepatitis liver herpes type 8 karposi epstein bar to 4 types cancer non hodgkins and lymphomas stomach cancer bacteria at least 30 percent of all cancer related to this and list just keeps growing then there is a genectic component maybe 30 percent of cancer related to food and enviroment
"I see that Rocker posted an article in which (it was claimed) that a Sherring-Plough 2nd generation PI in development was said to be 10X more powerful (in vitro) than existing PI's.(meaning Telaprevir and Boceprevir, presumably) "
By adding ritonavir, an HIV anti-viral that strongly inhibits CYP3A, they boosted the bioavailability of Telaprevir more than that. But the issue then becomes one of possible toxicity.
Pharmacokinetic enhancement of the hepatitis C virus protease inhibitors VX-950 and SCH 503034 by co-dosing with ritonavir.
Kempf DJ, Klein C, Chen HJ, Klein LL, Yeung C, Randolph JT, Lau YY, Chovan LE, Guan Z, Hernandez L, Turner TM, Dandliker PJ, Marsh KC.
Global Pharmaceutical Research & Development Division Abbott, Abbott Park, IL, USA.
Inhibitors of hepatitis C virus (HCV) protease have shown marked antiviral activity in short-term clinical studies in HCV-infected individuals. The interaction of the investigational HCV protease inhibitors VX-950 and SCH 503034 with ritonavir, a potent inhibitor of cytochrome P450 3A, was studied in vitro and in vivo. In rat and human liver microsomes, the metabolism of VX-950 and SCH 503034 was strongly inhibited by the presence of 4 microM ritonavir. Upon co-dosing either VX-950 or SCH 503034 with ritonavir in rats, plasma exposure of the HCV protease inhibitors was increased by > 15-fold, and plasma concentrations 8 h after dosing were increased by > 50-fold. A human pharmacokinetic model of VX-950 co-administered with low-dose ritonavir suggested that improved efficacy and/or dosing convenience may be feasible by pharmacokinetic enhancement with ritonavir.
most viruses and viral infections are not linked to cancer.
In many cases it is likely that a combination of factors such as genetic make-up, exposure to a carcinogen, age, diet, the state of your immune system, etc, play a part to trigger a cell to become abnormal, and allow it to multiply 'out of control' into a cancer.
Some viruses are linked to certain cancers. For example, people with persistent infection with the hepatitis B virus or the hepatitis C virus have an increased risk of developing cancer of the liver. Another example is the link between the human papilloma virus (HPV virus) and cervical cancer. Most (possibly all) women who develop cervical cancer have been infected with a strain (sub-type) of the HPV virus at some point in their life. But, most viruses and viral infections are not linked to cancer.
As part of its long-term commitment to hepatitis C therapy, Schering-Plough also is developing SCH 900518 ("518"), a next-generation HCV protease inhibitor. A Phase IIa study with 518, known as the NEXT-1 study, is currently ongoing. The company said that 518 has been shown to be 10 times more potent in-vitro than other protease inhibitors currently in Phase III development and has the potential for once daily dosing. 518 also has shown decreased emergence of resistance in vitro. Given its pharmacokinetic (PK) profile, the company anticipates that 518 may be active against some HCV strains that are resistant to other protease inhibitors. Phase I proof of concept studies with 518 in treatment-naive patients and those who failed prior treatment, both as monotherapy and in combination with peginterferon (without ribavirin), demonstrated enhanced antiviral activity, with up to 4 log10 and 5 log10 decreases in circulating HCV, respectively.
Vertex has 2 second generation drugs in development but has refused to comment on their efficacy other than to say that they are "competitive". I'm sure that we will hear more about that fairly soon, but even a successful second generation compound will face a slow approval process. One thing that should speed approval process is that IF Vertex were to be approved....then would not that become the new SOC? IF so...... that would mean that the new "control arms" in in some studies (with TVR) might become 24 weeks instead of 48 weeks?
I was under the belief that the reason HCV is curable is that it spends more of its life cycle in the bloodstream and therefore more accessible when treated. It was not a well founded theory on my part, so thanks for the help in clarifying that and thank you all for the thoughtful input.
I hope that this helps some. Also included within the thread Jim included some other links that will be worthwhile.
I think I'll let the heavy hitters field the answer for you....at least in part. I'll have to read these also since I am trying to stay up on the issue. Thought I'd get them out here though to keep things moving.
Thanks for looking up the thread. I checked it out as well as other links in it and didn't really see anything which showed that 'people' are interferon resistant. I saw many references by those posting about intereferon resistance in reference to the host, but that was all. I've read numerous studies on interferon resistance and have never seen one that referred to the host as being interferon resistant. If there is a study which uses the definition in this context I'd really like to read it to see how the definiton is arrived at. Thanks again for the link.
I have not seen any studies that quantify interferon resistance, but Dr D did tell me that I should treat longer due to my age impacting my ability to react to interferon and stimulate my own immune system.
So it would not be interferon resistance in the strict sense of the word, but does say that our own ability to deliver interferon to the virus and the ability of our immune system to react to interferon and attack the virus play a strong role in the success of our treatment; perhaps as much or more of a role than the ability of HCV to resist interferon.
What is this is?? !! Is MK Andrews a doctor don´t think so is Cowriter a doctor dont think so, but if you didn´t know you sure as hell would thought they were when reading this litany.
No they are two amateur docs very knowledgeable I´m sure but still no docs.
We better hold on here a second are they speculating and mixing own thoughts with medical fact but not clearly telling what is what.
That could be dangerous in my opinion. I really would like to hear what Dr Dieterish dr Pearl , Shiffman , Jacobson or Bergs or any other heavy dr thinks about this kind of presentation (formulation) and which facts are correct and which are not !
We are all forum polices sometimes aint we, if I` m out in the blue here please police me right back.
MKAndrew has been researching (and speculating about) HCV for years. He's the first to admit that many of the speculations in his blog during the last 6 years have been dead ends - but he has a great talent for putting many of these issues into easily understood 'layman's' terms. At this point I value his opinion as much as I do many of the 'heavy' doctors.
I have always thought viral response to the interferon was pretty much as described here.I had thought it was more triphasic than biphasic..
"When patients chronically infected with hepatitis C virus (HCV) are placed on antiviral therapy with pegylated interferon (IFN)-alpha or IFN-alpha plus ribavirin (RBV), HCV RNA generally declines in a biphasic manner. However, a triphasic decline has been reported in a subset of patients. A triphasic decline consists of a first phase (1-2 days) with rapid virus load decline, followed by a "shoulder phase" (4-28 days) in which virus load decays slowly or remains constant, and a third phase of renewed viral decay. We show that by including the proliferation of both uninfected and infected cells, a viral kinetic model can account for a triphasic HCV RNA decay. The model predicts that a triphasic decline occurs only in patients in which a majority of hepatocytes are infected before therapy. The shoulder phase does not represent the intrinsic death rate of infected cells, but rather the third phase slope is close to the intrinsic death rate of infected cells when overall drug efficacy is close to 1. CONCLUSION: Triphasic responses can be predicted from a generalization of existent viral kinetic models through the inclusion of homeostatic proliferation of hepatocytes. This generalized model can also explain the viral kinetics seen in flat partial responders. Finally, the enhanced third phase in patients treated with IFN-alpha in combination with RBV versus patients treated with IFN-alpha alone can be explained by a mutagenic effect of RBV against HCV."
From the last line of the above post
"Finally, the enhanced third phase in patientsKidney diet - dialysis patients treated with IFN-alpha in combination with RBV versus patientsKidney diet - dialysis patients treated with IFN-alpha alone can be explained by a mutagenic effect of RBV against HCV."
Kind of goes hand and hand with coming into the third phase of viral decline at the opitmun ribavirin dosage..I'm convinced my rbv dosage increases at week 4 and 8 were as critical to my svr as the treatment extension was..
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