Tipranavir: A Protease Inhibitor for HIV Salvage Therapy

α-pyrones and their hydroxylated analogs as promising scaffolds against Mycobacterium tuberculosis

Tuberculosis ranks as the leading cause of global human mortality from a single infectious agent. To address the uprising issues of drug resistance, intense research efforts have been directed towards drug discovery. However, it is a long and economically challenging process that is often associated with high failure rates. Therefore, it seems prudent to take forward the core scaffolds that have already acclaimed clinical relevance. In this direction, hydroxylated α-pyrone scaffold has received US FDA approval for human use against HIV. Interestingly, literature review reveals the potential applicability of α-pyrones in TB drug discovery. On one hand, α-pyrones play a vital role in the cell wall of Mycobacterium tuberculosis and on the other hand natural α-pyrones display appreciable anti-TB activity. This review aims to rekindle the interest of researchers toward α-pyrone as a new anti-TB drug that may possibly tackle drug resistance and open a dual frontier in TB and HIV drug discovery.

α-pyrones: Small molecules with versatile structural diversity reflected in multiple pharmacological activities-an update

The investigations in the chemistry and biology of α-pyrone (2-pyrone) are of vital importance as they constitute an essential pharmacophore in many naturally occurring and biologically active synthetic agents. They are a promising class of biorenewable platform chemicals that provide access to an array of chemical products and intermediates. Literature survey reveals that a simple change in the substitution pattern on the 2-pyrone ring system often leads to diverse biological activities. In this review, we present a brief overview of 2-pyrone pharmacophore followed by highlighting their pharmacological properties and potential applicability till date. Particular attention is focused on the distinctive chemotherapeutic activities of 2-pyrones as anti-HIV, anti-TB and anti-cancer agents followed by their potential role against neurodegeneration, hypercholesterolemia, microbial infections, chronic obstructive lung disease, inflammation, antinociception and immunomodulation. Since 2005, when 2-pyrones came in limelight, their detailed pharmacological activities have been well documented. This review has mainly been prepared on the basis of original reports published in recent two decades with an aim to attract the attention of researchers towards this versatile scaffold for future endeavors that may lead to the development of potential drug candidates against above diseases.

A review of the toxicity of HIV medications

Antiretroviral therapy has changed human immunodeficiency virus (HIV) infection from a near-certainly fatal illness to one that can be managed chronically. More patients are taking antiretroviral drugs (ARVs) for longer periods of time, which naturally results in more observed toxicity. Overdose with ARVs is not commonly reported. The most serious overdose outcomes have been reported in neonates who were inadvertently administered supratherapeutic doses of HIV prophylaxis medications. Typical ARV regimens include a "backbone" of two nucleoside reverse transcriptase inhibitors (NRTI) and a "base" of either a protease inhibitor (PI) or nonnucleoside reverse transcriptase inhibitor. New classes of drugs called entry inhibitors and integrase inhibitors have also emerged. Older NRTIs were associated with mitochondrial toxicity, but this is less common in the newer drugs, emtricitabine, lamivudine, and tenofovir. Mitochondrial toxicity results from NRTI inhibition of a mitochondrial DNA polymerase. Mitochondrial toxicity manifests as myopathy, neuropathy, hepatic failure, and lactic acidosis. Routine lactate assessment in asymptomatic patients is not indicated. Lactate concentration should be obtained in patients taking NRTIs who have fatigue, nausea, vomiting, or vague abdominal pain. Mitochondrial toxicity can be fatal and is treated by supportive care and discontinuing NRTIs. Metabolic cofactors like thiamine, carnitine, and riboflavin may be helpful in managing mitochondrial toxicity. Lipodystrophy describes changes in fat distribution and lipid metabolism that have been attributed to both PIs and NRTIs. Lipodystrophy consists of loss of fat around the face (lipoatrophy), increase in truncal fat, and hypertriglyceridemia. There is no specific treatment of lipodystrophy. Clinicians should be able to recognize effects of chronic toxicity of ARVs, especially mitochondrial toxicity.

Review article: drug hepatotoxicity

BACKGROUND

Drug toxicity is the leading cause of acute liver failure in the United States. Further understanding of hepatotoxicity is becoming increasingly important as more drugs come to market.

AIMS

(i) To provide an update on recent advances in our understanding of hepatotoxicity of select commonly used drug classes. (ii) To assess the safety of these medications in patients with pre-existing liver disease and in the post-liver transplant setting. (iii) To review relevant advances in toxicogenomics which contribute to the current understanding of hepatotoxic drugs.

METHODS

A Medline search was performed to identify relevant literature using search terms including 'drug toxicity, hepatotoxicity, statins, thiazolidinediones, antibiotics, antiretroviral drugs and toxicogenomics'.

RESULTS

Amoxicillin-clavulanic acid is one of the most frequently implicated causes of drug-induced liver injury worldwide. Statins rarely cause clinically significant liver injury, even in patients with underlying liver disease. Newer thiazolidinediones are not associated with the degree of liver toxicity observed with troglitazone. Careful monitoring for liver toxicity is warranted in patients who are taking antiretrovirals, especially patients who are co-infected with hepatitis B and C. Genetic polymorphisms among enzymes involved in drug metabolism and HLA types may account for some of the differences in individual susceptibility to drug hepatotoxicity.

CONCLUSIONS

Drug-induced hepatotoxicity will remain a problem that carries both clinical and regulatory significance as long as new drugs continue to enter the market. Future results from ongoing multicentre collaborative efforts may help contribute to our current understanding of hepatotoxicity associated with drugs.

Drug-induced liver disease in 2006

PURPOSE OF REVIEW

To identify the key publications of 2006 dealing with drug-induced liver injury.

RECENT FINDINGS

When given in therapeutic doses over 14 days, acetaminophen produced significant asymptomatic elevations in alanine aminotransferase among healthy volunteers, suggesting that subclinical injury may be more common than previously thought. Acute liver failure in children was shown to differ in several important respects from that seen in adults, notably a much lower incidence of acetaminophen toxicity with nearly half of all cases being indeterminate in origin. The first cases of hepatotoxicity with telithromycin, a new class of ketolide antibiotic, were described along with reports suggesting liver injury from ezetimibe among other agents. The potential for chronic injury to develop after acute drug-induced liver injury was analyzed in a large Swedish database; 5-6% of cases were judged to become chronic, with drugs causing cholestatic injury predominating. Among well described hepatotoxins, new reports appeared with highly active antiretroviral therapy agents, herbal therapies and several antibiotics. Finally, the safe use of pravastatin and pioglitazone was demonstrated in patients with chronic liver disease in controlled clinical trials.

SUMMARY

Drug-induced liver injury remains an important concern for many existing drugs as well as for agents in development.

Tipranavir: a new protease inhibitor for the treatment of antiretroviral-experienced HIV-infected patients

Tipranavir (TPV) is a novel non-peptidic protease inhibitor (PI). It binds strongly and selectively to the HIV-1 protease, is orally administered twice daily, boosted with low doses of ritonavir, and shows a favourable resistance profile. In the two registrational trials, named RESIST 1 and 2, TPV/ritonavir 500/200 mg b.i.d., along with an optimised antiretroviral backbone, provided better virologic responses than controls receiving standard of care ritonavir-boosted PI-based regimens. A total of 21 mutations at 16 protease codons have been shown to impact on TPV susceptibility and response rates. The TPV mutation score includes L10V, I13V, K20M/R/V, L33F, E35G, M36I, K43T, M46L, I47V, I54A/M/V, Q58E, H69K, T74P, V82L/T, N83D and I84V. Viruses containing eight or more of these mutations are generally resistant to the drug. TPV use is associated with an excess of grade 3/4 liver enzyme elevations compared with other ritonavir-boosted PIs, and the potential for drug-drug interactions is relevant and must be considered when prescribing TPV.

Clinical trials for heavily pretreated patients: update in 2006

PURPOSE OF REVIEW

To report on recent clinical studies in highly experienced patients with multiple exposures and failures to therapies using new drugs - either new drugs with a different resistance profile or a new class of drugs.

RECENT FINDINGS

The major concern in a situation of salvage therapy is the capacity to build an antiretroviral regimen with sufficient potency to circumvent the intensity of viral replication and resistance of the virus. New drugs represent the major weapon in that fight. Several drugs have been developed in the past few years that have allowed a change in the paradigm for salvage therapy. They belong either to the old class of protease inhibitors but have been designed to target resistant viruses (tipranavir, darunavir), or to a new class such as fusion inhibitors, entry co-receptor inhibitors or integrase inhibitors.

SUMMARY

Due to their potency and their ability to combine in a salvage regimen, the new drugs have allowed us to revisit the paradigm for managing treatment failure. Until recently it was estimated that one log drop in viral load was acceptable as the primary endpoint in salvage studies. Recent results now suggest that undetectability of the viral load has become a realistic target.