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Kinchington D, Schinazi RF, eds. ($99.00.) Humana Press, 2000. ISBN 0 896 03561 1.
This is an interesting collection of techniques used to search for compounds active against a variety of different viruses, and also to identify mutations in viral genes conveying resistance to antivirals. Although antiviral compounds were discovered and described in research laboratories more than 60 years ago, their widespread clinical application has only come of age during the past 20–30 years. Over the past decade, a rational application of antivirals has started—that is, they are used after the viruses to be attacked have been investigated and found to be susceptible to particular compounds.
This volume deals with a variety of assays used to determine the antiviral activity of compounds against several viruses of clinical importance (hepatitis viruses, herpesviruses, human immunodeficiency viruses (HIV), influenza viruses, and papilloma viruses). The introductory chapter on antiviral compounds is very comprehensive but could have been slightly longer. Very interesting is the chapter on laboratory safety considerations, also outlining differences in hazards and risk evaluations carried out for various microorganisms in the USA, the EC, and the UK.
For hepatitis B virus (HBV) several cell bound assays (Hep AD38 assay, and cell line 2.2.15 assay) are described, the importance of which cannot be overestimated. Systems have been found that allow limited replication of HBVs in vitro, in which compounds inhibiting different steps of the HBV replication cycle (be it at reverse transcription, DNA synthesis, or other steps) can be investigated. Some of the assays are still very research orientated, whereas others lend themselves to application in specially equipped clinical laboratories. A high throughput assay for hepatitis C virus (HCV) helicase activity is presented that might be of interest to test for anti-HCV compounds; however, no practical examples for antivirals used against HCV are given. For herpesviruses, conventional plaque reduction assays and other antiviral activity assays are presented. Of interest is an assay that allows the measurement of the inhibition of TPA stimulated EBV antigen synthesis in cells. Furthermore, assays are described for monitoring the drug resistance of herpes simplex viruses, particularly against aciclovir, but also derivatives thereof (for example, ganciclovir) and phosphonoformic acid (PFA). Strains resistant to these drugs emerge in immunocompromised patients and their detection and monitoring are of great clinical importance.
Cell culture based and biochemical assays (targeting the viral enzymes reverse transcriptase (RT), protease, and integrase) are presented for HIV. The detection of specific mutations conveying drug resistance against AZT, ddC, ddl, d4T, 3TC and others can be facilitated by a reverse hybridisation assay (line probe assay; LiPA), whereby polymerase chain reaction (PCR) amplicons of the HIV RT gene are hybridised against a panel of specific immobilised oligonucleotide probes. This assay, which is described in full, gives very good results for recognising known mutations, but is limited in its power to recognise mutations in general. Because HIV genes are highly diverse, laboratories have started to sequence the amplicons of RT and protease genes of clinical isolates to obtain all mutations of the genes that might be important for the development of drug resistance. Large numbers of mutations associated with drug resistance, which are not detectable by LiPA, have been identified in this way. The sequencing procedure is of particular relevance for the evaluation of HIV protease gene mutations. Unfortunately, a precise procedure to carry out these increasingly important tests, in a manner that can be adapted to specially equipped routine laboratories, have only been alluded to and not described in detail.
Although papillomaviruses (HPV) are important human pathogens and their replication inhibition is of great potential preventative value, the tests described for assaying for DNA binding and helicase activities of the E1 protein of HPV are not put in a firm context of testing for antivirals, and their clinical importance is not made clear. Similarly, the methods described to characterise influenza viruses, which are mutant in their sensitivity to neuraminidase inhibitors (for example, 4-guanidino-neu5ac2en), are not put into a strong clinical context. The principle and potential of so called antisense oligonucleotides as possible antiviral therapeutics is only mentioned briefly, but no tests to evaluate them are identified.
Overall, I found the methods described well and in detail, but the introductory paragraphs of chapters were short on background information. In contrast, the annotations of individual authors about possible pitfalls and problems of methods, as well as ways to overcome them, are very helpful. More examples on clinical applications for which, after all, these methods are important would have been beneficial. Most references are up to date up to about 1996. Given the increasing importance of antiviral testing in clinical settings this book is timely in addressing the topic.
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