Commentary on STI talk, early entry inhibitor research, increase in viral replication seen in isolates in presence of NNRTIs

16 August 2000. Related: Conference reports, World AIDS 13 Durban 2000.

Reported by Mike Youle, MD for NATAP

www.natap.org

The political agenda for change is by far the most important aspect of this meeting.

Researchers have to some extent anticipated this and there appears to be a combination of acceptance that the first flush of excitement with HAART has been tempered by the rising incidence of side effects. On the other hand the economic imperative for those who can afford some therapy will drive strategies which examine intermittent, short term and low volume treatments.

Tony Fauci from the National Institutes for Health in Bethesda in a presentation reminiscent of a tele-novella heralded the importance of interruption of therapy (see also separate report below). Many in the audience, however, expressed concern that much like the ‘Hit hard – Hit early’ dictum which has now been discredited an early foray into this area, with sparse data (he presented less than double figure patient information) may drive a new treatment approach ahead of the science to support it. There will be further studies of this approach in the Late-breaker sessions.

[comment from Jules Levin, NATAP – In fact, in the Late Breaker sessions Mike Dybel of the NIH reported preliminary data on the 2 NIH studies – intermittent interruptions of a few days on therapy and a few days off therapy, and one month off therapy and 2 months on therapy – and was harshly criticized for presenting the data too soon. Many expressed concern that releasing preliminary data like this encourages patients to experiment with unproven treatment approaches and may put individuals at risk.]

So what more of the future approaches. In the sessions on New Antivirals and Targets, Guido Poli’s group showed data on the B-oligomer of pertussis toxin (PTX-B) which is a non-toxic derivative of the toxin which appear to act at some point around fusion of HIV to the cell surface [1]. It appears to be a selective inhibitor of R5 fusion and deactivates CCR5 in activated primary lymphocytes and macrophages. Whilst it does not block fusion of X4 viruses it blocked infection of cells with recombinant HIV-1 particles pseudo-typed with R5, X4 or even VZV-G envelopes. Taken together the results suggest that PTX-B inhibited entry of R5 viruses and the accumulation and replication of both R5 and X4 viruses. As one researcher said in the session on fusion inhibitors it is vital we have agents which cover all viral strains so as to avoid a requirement for even more different agents to achieve suppression.

This work was augmented by Stefano Rusconi from the University of Milan, Italy [2]. He and his co-workers had examined the two chemokine receptor blockers AOP-RANTES, against R5 virus and met-SDF-1beta, specifically directed against X4 viruses. The isolates used to test this combination therapy approach were from two primary HIV-1 infected patients who exhibited tropism for one or other receptor. In the experiments single isolates or a 50:50 combination were examined in the presence of one or both receptor-blockers. As one might have expected the combination of agents worked the most effectively with inhibition rates of >95% whilst the single agents were less successful with repression rates of only 30-60%. These experiments further point to the necessity of approaching receptor blockade with R5 and X4 targeted compounds.

A third presentation, given by Huang from a New York based group spanning industry and academia, gave some further hopes of a cheap and effective new therapy [3]. Human lysozyme is an enzyme known to act against bacterial and viral infections, tumours and to alter host immunity. It appears also to have an inherent anti-HIV activity and thus is hypothesized to be a possible new candidate drug against the virus.

In these experiments limited proteolysis of lysozyme was undertaken to produce ten fragments of the original. Each of these was examined for antiretroviral activity in an in vitro inhibition assay. One 18-amino acid fragment appeared to hold all of the activity of the complete enzyme with 50% inhibition concentrations of 58-68nM. Further trimming of this molecule resulted in HL-9 consisting of an amino acid sequence RAWVAWRNR that required this sequence for maximal action and was reduced in potency if the R’s were substituted for other amino acids. An elegant set of experiments characterized this as the optimal sequence for HIV suppression.

In addition to its antiretroviral activity this compound also inhibited the growth of cells infected by HHV-8 from AIDS patients with Kaposi’s sarcoma. This appears a promising candidate as a new anti-HIV agent and it is non-toxic derived from human protein and has potent activity against a broad range of HIV isolates.

A study which was not presented except in abstract form but which holds interest for the assessment of drug action in the brain came from Kings College London [4]. In an in vitro assay utilizing mixed population of cells (neurons, microglia, astrocytes and oligodendrocytes) as well as relevant neuro-transmitters was established to most nearly mimic the cerebral environment. In to this HIV infection with the standard lymphotrophic IIIB strain was accompanied an increase in microglia but no neuronal loss, whilst the macrophage tropic strain SF-2 resulted in a 35% reduction in neuronal levels. Both of these effects were blocked by the addition of physiologically achieved concentrations of abacavir and zidovudine giving further evidence of the activity of these drugs in a compartment often felt to not be as suppressed as outside the blood – brain barrier.

The most potentially worrying presentation related to drug therapy, in my view, came from a single case report by Chris Petropoulos from Virologic found during phenotypic drug susceptibility testing [5]. Using the Phenosense assay an up to 400% increase in viral replication was seen when isolates from the patient were put in the presence of non-nucleoside agents. Analysis of samples from the subject prior to the use of NNRTI’s suggested that novel genetic changes may have predisposed the virus to develop this phenotype. Clearly, apart from virus harbouring multiple mutations to zidovudine, the phenomenon of increase replication in the setting of antiretroviral agents has not been seen and with rising rates of resistance to NRTI’s this is a phenomenon that should be actively looked for in laboratories testing resistance routinely.

References:

Unless stated otherwise, references are to the Programme and Abstracts of the XIII International AIDS Conference, 9-14 July 2000, Durban, South Africa.

1. The B-oligomer of pertussis toxin inhibits HIV-1 replication at multiple stages; M Bukrinsky et al; The Picower Institute for Medical Research, Manhasset, NY; TuOrA404.
2. Combination of CCR5 and CXCR4 inhibitors in therapy of HIV-1 infection: in vitro studies in mixed virus infections; S. Rusconi et al; University of Milan, Ospedale Luigi Sacco, Istituto di Malattie Infettivee Tropicali, Milan, Italy; TuOrA408.
3. Identification, characterization and synthesis of lysozyme mimetics with potent anti-HIV activity; P. Huang et al; American Bio-Sciences, Boston, MA; TuOrA405.
4. First proof that NRTIs prevent HIV brain damage using an novel human brain tissue system; I. Everall, et al, Institute of Psychiatry, Kings Collge London, DeCrespigny Park, London; TuOrA407.
5. An HIV-1 Variant that shows dose-dependent stimulation of replication in the presence of Non-Nucleoside Reverse Transcriptase Inhibitors; C. Petropoulos et al, Virologic. Inc, South San Francisco, CA; TuOrPpA1148.