Foscarnet therapy for ganciclovir-resistant cytomegalovirus retinitis in patients with AIDS

Drug interactions in people with HIV treated with antivirals for other viral illnesses

INTRODUCTION

Background: People with HIV (PWH) have benefited tremendously from effective antiretroviral(ARV) treatments. However, PWH are at increased risk for other viral infections transmitted in the same way as HIV (such as hepatitis C and MPox) or that are opportunistic (e.g. cytomegalovirus). These coinfections contribute significantly to morbidity and mortality among PWH and require effective treatments to optimize patient outcomes. However, their management is complicated by drug-drug interactions (DDIs) with ARVs.

AREAS COVERED

Metabolism pathways and DDIs between approved ARVs and selected antiviral agents used for the treatment of common and clinically relevant viral coinfections are discussed. Literature review included search of published papers, conference abstracts (IAS, CROI, IDWeek, EACS, Glasgow) as well as unpublished data from approved drug prescribing information and regulatory submissions sourced from PubMed, Google, and Google Scholar available between June 30 1981 through June 1, 2024.

EXPERT OPINION

Management of drug interactions is essential for maintaining efficacy and safety of ARV and other co-administered antiviral therapies. Longer acting agents are now available for treatment of HIV and this lengthens the period during which drug interactions may occur. Emerging novel nanoparticle-carrier targeted hepatitis C and HIV treatments may mitigate, if not eliminate, their propensity for drug-drug interactions.

Safety considerations with current and emerging antiviral therapies for cytomegalovirus infection in transplantation

Introduction: Human cytomegalovirus (HCMV) is a major contributor of morbidity and mortality, and its management is essential for the successful outcome of solid organ and hematopoietic stem cell transplantation. Areas covered: This review discusses the safety profiles of currently available and emerging antiviral drugs and the other strategies for HCMV prevention and treatment after transplantation. Expert opinion: Strategies for management of HCMV rely largely on the use of antiviral agents that inhibit viral DNA polymerase (ganciclovir/valganciclovir, foscarnet, and cidofovir/brincidofovir) and viral terminase complex (letermovir), with different types and degrees of adverse effects. An investigational agent, maribavir, exerts its anti-CMV effect through UL97 inhibition, and its safety profile is under clinical evaluation. In choosing the antiviral medication to use, it is important to consider these safety profiles in addition to overall efficacy. In addition to antiviral drugs, reduction of immunosuppression is often generally needed in the management of HCMV infection, but with a potential risk of allograft rejection or graft-versus-host disease. The use of HCMV-specific or non-specific intravenous immunoglobulins remains debated, while adoptive HCMV-specific T cell therapy remains investigational, and associated with unique set of adverse effects.

Antiviral Therapies for Herpesviruses: Current Agents and New Directions

PURPOSE

The objective of this review was to summarize the recent literature describing the current burden of disease due to herpesviruses in the antiviral and transplant era; describe mechanisms of action of antiviral agents and the development of resistance; summarize the literature of recent antiviral agents brought to market as well as agents under development; and to present literature on future strategies for herpesvirus therapeutics.

METHODS

An extensive search of the medical literature related to antiherpesviral therapy was conducted to compose this narrative review. Literature searches were performed via PubMed and ultimately 137 articles were included as most relevant to the scope of this article.

FINDINGS

Herpesviruses are a family of DNA viruses that are ubiquitous throughout human populations and share the feature of establishing lifelong infections in a latent phase with the potential of periodic reactivation. With the exception of herpes simplex virus, varicella zoster virus, and Epstein-Barr virus, which have a significant disease burden in individuals with normal immune function, the morbidity and mortality of the remaining viruses are primarily associated with the immunocompromised host. Over the last half-century, several agents have been tested in large randomized, placebo-controlled trials that have resulted in safe and effective antiviral agents for the treatment of many of these infections.

IMPLICATIONS

With increasing use of antiherpesviral agents for extended periods, particularly in immunocompromised hosts, the emergence of resistant viruses has necessitated the development of newer agents with novel targets and better side-effect profiles.

Intracellular Metabolism of 3′-Azido-3′-Deoxythymidine in the Presence of Ganciclovir or Foscarnet

Comparisons were made between the intracellular phosphorylation of 3′-Azido-3′-deoxythymidine (AZT) alone and in combination with ganciclovir (GCV) or foscarnet (PFA) in lymphocytes, uninfected fibroblasts and CMV-infected fibroblasts. The effects of AZT and the combinations of AZT with GCV or PFA on cellular dNTP pools were also examined. The phosphorylation of AZT was not altered by the presence of GCV or PFA in lymphocytes, and neither AZT nor the combinations of AZT with GCV or PFA changed the levels of cellular dNTP pools in these cells. AZT was phosphorylated to a greater extent in lymphocytes when compared to fibroblasts, but the proportion of AZT di- and triphosphates was greater in fibroblasts. The infection of fibroblasts with CMV enhanced AZT phosphorylation and increased the levels of cellular dNTP pools. GCV caused a specific reduction in AZT phosphorylation in CMV-infected fibroblasts, with a seven-fold drop in AZT triphosphate compared to AZT alone. GCV did not affect AZT phosphorylation in uninfected fibroblasts, nor did GCV reduce the dTTP pool compared to AZT alone. The effects of GCV upon AZT phosphorylation in CMV-infected cells may shed light on the antagonistic effects of GCV upon the anti-HIV activity of AZT, and are of importance for the development of effective combination therapies for the treatment of AIDS patients infected with CMV.

The use of antiviral drugs during the neonatal period

Parenteral therapy of viral infections of the newborn and infant began with vidarabine (adenine arabinoside) for the treatment of neonatal herpes simplex virus (HSV) infections in the early 1980s. Acyclovir has become the treatment of choice for neonatal HSV infections and a variety of other herpesvirus infections. Ganciclovir is beneficial for the treatment of congenital cytomegalovirus (CMV) infections involving the central nervous system (CNS). This article reviews the use of acyclovir and ganciclovir in the treatment of neonatal HSV and congenital CMV infections. A brief summary precedes a detailed discussion of available established and alternative therapeutics.

Antisense approach for the treatment of cytomegalovirus infection

Human cytomegalovirus (HCMV) is the most common viral opportunistic infection in patients suffering with acquired immunodeficiency virus (AIDS). HCMV is a systemic infection that may infect several sites in the body, including the retina, gastrointestinal tract, lungs, liver, and central nervous system. Retinitis is the most frequent manifestation of HCMV infection, occurring in 15-40% of all patients. HCMV is progressive and destroys the retina, eventually leading to blindness. Although, there are several drugs available to treat this disease, they are often of limited efficacy and have significant side-effects. Antisense oligonucleotides represent a novel alternative to the currently available drugs. Due to their high affinity and specificity to target the HCMV RNAs, interest in antisense technology to treat HCMV infections has been intense during the past few years. Two antisense drugs are currently in clinical trials, ISIS 2922 (Formivirsen) and GEM 132.

Antiviral therapies in children: has their time arrived?

The increase in the number and classes of antiviral agents that has occurred since the 1980s is remarkable. The rapid expansion in therapeutic options for previously untreatable illnesses challenges clinicians to gain familiarity and experience with these new drugs, especially with regard to their use in children. This article describes the clinical utilities, pharmacokinetics, and adverse effects of these new drugs to empower practitioners to use them appropriately.

Emerging therapies for herpes viral infections (types 1 – 8)

There are eight members of the herpesviridae family: herpes simplex virus-1 (HSV-1), HSV-2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, human herpes virus-6, human herpes virus-7 and human herpes virus-8. The diseases caused by viruses of the herpesviridae family are treated with and managed by systemic and topical antiviral therapies and immunomodulating drugs. Because these viruses establish a latent state in hosts, antiherpetic agents, such as nucleoside analogues, only control symptoms of disease or prevent outbreaks, and cannot cure the infections. There is a need for treatments that require less frequent dosing, can be taken even when lesions are more advanced than the first signs or symptoms, and can treat resistant strains of the viruses without the toxicities of existing therapies. Immunomodulating agents, such as resiquimod, can act on the viruses indirectly by inducing host production of cytokines, and can thereby reduce recurrences of herpes. The new helicase primase inhibitors, which are the first non-nucleoside antiviral compounds, are being investigated for treatment of HSV disease, including infections resistant to existing therapy.

Clinical and biologic aspects of human cytomegalovirus resistance to antiviral drugs

The emergence of human cytomegalovirus (HCMV) drug resistant strains is a life-threatening condition in immunocompromised individuals with active HCMV infection. HCMV drug resistance represented a major problem in patients with acquired immunodeficiency syndrome until the recent introduction of highly active antiretroviral combination therapy, which dramatically decreased the incidence in this clinical setting. However, HCMV resistance to antiviral drugs is now an emerging problem in the transplantation setting. The molecular mechanisms of HCMV drug resistance have been elucidated and rely on the selection during treatment of HCMV strains harboring mutations in two key viral genes: UL97 coding for a viral phosphotransferase and UL54 coding for the viral DNA polymerase.

Mutations in the UL97 ORF of ganciclovir-resistant clinical cytomegalovirus isolates differentially affect GCV phosphorylation as determined in a recombinant vaccinia virus system

Mutations in the human cytomegalovirus (HCMV) UL97 phosphotransferase have been associated with ganciclovir (GCV) resistance due to an impairment of GCV monophosphorylation. Vaccinia virus recombinants (rVV) were generated that encoded different HCMV UL97 proteins (pUL97) with mutations previously detected in resistant HCMV clinical isolates at codons 460, 520, 592, 594, 595, 598 and 607. These rVVs allowed quantification of GCV phosphorylation catalyzed by the different mutated pUL97s. When compared to rVV-UL97 wild type, mean levels of residual intracellular GCV phosphorylation differed by a factor of 10 for the mutated UL97 proteins ranging from 5.2 to 51.8%. Mutations M460V (located in a UL97 region homologous to domain VIb of protein kinases) and H520Q (located in a cytomegalovirus-specific, functionally critical domain) were responsible for the lowest levels of residual GCV phosphorylation (9.3 and 5.2%). Mutations in a region homologous to the domain IX had a lower impact on GCV phosphorylation (15.8-51.8%). The relevance of pUL97 mutation G598S in inducing GCV resistance was demonstrated for the first time.

Engineered RNase P ribozymes inhibit gene expression and growth of cytomegalovirus by increasing rate of cleavage and substrate binding

We have previously employed an in vitro (genetic) selection procedure to select RNase P ribozyme variants for their activity in cleaving a mRNA substrate from a pool of ribozymes containing randomized sequences. In this study, one of the variants was used to target the overlapping region of the mRNAs encoding the major transcription regulatory proteins, IE1 and IE2, of human cytomegalovirus (HCMV). The ribozyme variant exhibited an enhanced substrate binding and rate of chemical cleavage, and was at least 25 times more efficient in cleaving the target mRNA in vitro than the ribozyme derived from the wild-type sequence. Our results provide the first direct evidence that a point mutation at nucleotide 86 of RNase P catalytic RNA from Escherichia coli (A(86)-->C(86)) increases the rate of chemical cleavage while another mutation at nucleotide 205 (G(205)-->C(205)) enhances substrate binding of the ribozyme. Moreover, the variant was also more effective in inhibiting IE1 and IE2 expression and HCMV growth in cultured cells. A reduction of more than 97% in IE1 and IE2 expression and a reduction of 3000-fold in viral growth were observed in cells expressing the variant. Thus, RNase P ribozyme variant is highly effective in inhibiting HCMV gene expression and growth. Our results provide the direct evidence that increasing the rate of chemical cleavage and substrate-binding affinity of the ribozymes should lead to an improvement of their anti-HCMV efficacy. Moreover, our data also suggest that highly effective anti-HCMV ribozyme variants can be developed using genetic engineering approaches including in vitro selection.

Separation methods for antiviral phosphorus-containing drugs

Among antiviral drugs, phosphorus-containing compounds, foscarnet and cidofovir, present adverse effects including renal toxicity. Since their main therapeutic target is the treatment of CMV retinitis, which needs lifelong maintenance therapy, accurate analytical methods are required for drug monitoring. According to the high hydrophilic property of the two compounds, ion pair reversed-phase HPLC methods were proposed for their separation in drug formulations and biological samples. Their lack of UV absorption at wavelengths above 205 nm does not allow the use of this detection technique for biological fluids. Electrochemical detection methods (coulometry and amperometry) led to a quantification limit of 15 microM for foscarnet. Fluorescent derivatives obtained by modification of cidofovir cytosine nucleus with alpha-haloketones offered advantage over UV detection and allowed to reach a detection limit of 5 ng/ml, making possible investigations on the drug time-course in biological fluids.

Foscarnet therapy for ganciclovir-resistant cytomegalovirus retinitis after stem cell transplantation: effective monitoring of CMV infection by quantitative analysis of CMV mRNA

We report three pediatric patients with ganciclovir-resistant cytomegalovirus (CMV) retinitis who were successfully treated with foscarnet. The patients were recipients of hematopoietic stem cell transplantation (SCT) from HLA-mismatched donors. Because these patients had developed or experienced progressive CMV retinitis during ganciclovir therapy, they received foscarnet therapy at 60 mg/kg every 8 h. Their retinitis resolved promptly after initiating foscarnet therapy, suggesting foscarnet's effectiveness in treating ganciclovir-resistant CMV infection. The amount of CMV mRNA was quantitatively measured using an NASBA technique, which amplified the beta2.7 transcripts specific for CMV replication. This technique was useful for monitoring disease activity in a more rapid and sensitive manner than the PCR assay for CMV DNA.

Changing therapeutic paradigms in CMV retinitis in AIDS

Cytomegalovirus (CMV) retinitis is a common ocular complication of immunosuppression. The management of CMV retinitis has been continuously evolving over the last decade. The mainstay of therapy remains ganciclovir and foscarnet. However, increasing resistance and ongoing toxicities to these agents remain a challenge. Additional frequently utilised agents include cidofovir and fomivirsen. The advent of highly active antiretroviral therapy (HAART) has allowed the restoration of immunocompetency to many patients previously challenged by CMV infection. In some circumstances, HAART has even eliminated the need for ongoing antiviral therapy. This paper reviews the current treatment modalities, including their toxicities and dosing recommendations.

The thymidylate synthase inhibitor ZD1694 potently inhibits murine and human cytomegalovirus replication in quiescent fibroblasts

Tomudex (ZD1694) is a quinazoline-based folate analog and a powerful inhibitor of cellular thymidylate synthase and is approved in Europe for use in oncology. Here the first evidence of its activity against murine and human cytomegalovirus (MCMV and HCMV) is reported. ZD1694 irreversibly inhibited the replication and DNA synthesis of both viruses in quiescent fibroblasts. The corresponding 50% effective concentrations were 0.006 and 0.002 microM respectively, whereas the 50% cytotoxic concentration was >10 microM for both murine and human quiescent fibroblasts. A similar antiviral effect was observed against two ganciclovir-resistant HCMV strains isolated from AIDS patients. Taken as a whole these results demonstrate that cellular thymidylate synthase plays an essential role in viral replication and that ZD1694 merits further investigation as anticytomegaloviral agent.

Antiviral properties of a series of 1,6-naphthyridine and 7, 8-dihydroisoquinoline derivatives exhibiting potent activity against human cytomegalovirus

A series of 1,6-naphthyridine (L. Chan, H. Jin, T. Stefanac, J. F. Lavallee, G. Falardeau, W. Wang, J. Bedard, S. May, and L. Yuen, J. Med. Chem. 42:3023-3025, 1999) and isoquinoline (L. Chan, H. Jin, T. Stefanac, W. Wang, J. F. Lavallee, J. Bedard, and S. May, Bioorg. Med. Chem. Lett. 9:2583-2586, 1999) analogues exhibiting a high level of anti-human cytomegalovirus (HCMV) activity were investigated in a series of studies aimed at better understanding the mechanism of action of some representatives of this class of compounds. In vitro antiviral profiling revealed that these compounds were active against a narrow spectrum of viruses, essentially the human herpesviruses and type 2 rhinovirus. In HCMV assays, a 39- to 223-fold lower 50% inhibitory concentration was obtained for compound A1 than for ganciclovir against strains AD 169 and Towne. In addition, ganciclovir, foscarnet, cidofovir, and BDCRB (2-bromo-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole)-resistant HCMV strains remained susceptible to 1,6-naphthyridines and 7, 8-dihydroisoquinolines tested in this study, supporting the view that a novel mechanism of action could be involved. Drug combination studies showed a small but significant synergistic antiviral effect between compound B2 and ganciclovir. Cytotoxicity profiling of representative compounds under various cell growth conditions indicated a generally similar cytotoxic effect, relative to ganciclovir, in log-phase growing cells. However, in stationary cells, a relatively higher level of toxicity was observed than that for control compound. Effect of time of drug addition showed that the anti-HCMV activity of compound A1, ganciclovir, and cidofovir was lost at approximately the same time (72 h postinfection), indicating that the compound was affecting events at the early and late stage of virus replication. This interpretation is also supported by reduction of de novo synthesis of pp65 tegument protein and lack of any effect of the compound on viral adsorption. A reduction of the HCMV enhancer-promoter-directed luciferase expression was also observed in a stably transfected cell line when compound A1 was present at relatively high concentrations.

A standardized plaque reduction assay for determination of drug susceptibilities of cytomegalovirus clinical isolates

Twelve laboratories collaborated in formulating and testing a standardized plaque reduction assay for cytomegalovirus (CMV) cell-associated clinical isolates. Four characterized and plaque-purified CMV strains, as well as six coded clinical isolates obtained after antiviral therapy, were distributed and tested. Good agreement was obtained for four of the clinical isolates, but a broad distribution of results was obtained for two isolates. Analysis of these results indicates the problems associated with clinical isolates, including the large genetic variability and the highly cell-associated phenotype. This collaborative effort, by addressing these problems, represents a significant step toward the development of a standardized assay.

Comparison of human cytomegalovirus DNA polymerase activity for ganciclovir-resistant and -sensitive clinical strains

Previously, we found that a ganciclovir (GCV)-resistant clinical human cytomegalovirus (HCMV) isolate had an amino acid substitution at codon 501 (Leu --> Phe) in the delta-region C of the DNA polymerase gene. DNA polymerases have now been (partially) purified from both the GCV-resistant and sensitive parental strains and the activity of DNA polymerase and 3'-5' exonuclease compared. With respect to DNA polymerase activity, the Michaelis constant (Km) and maximum velocity (Vmax) of the GCV-resistant strain for the DNA template were lower than those of the GCV-sensitive strain. With respect to 3'-5' exonuclease activity, the Km and Vmax of the GCV-resistant strain for the DNA substrate in the presence of ammonium sulfate were lower than those of the GCV-sensitive strain, while being similar in the absence of ammonium sulfate. Although the polymerase activity of the two strains showed almost the same sensitivity for the different polymerase inhibitors, the 3'-5' exonuclease activity of the GCV-resistant strain was more resistant to these inhibitors than that of the GCV-sensitive strain.

Effect of desferrioxamine (DFO) and calcium trinatrium diethylenetriaminepentaacetic acid (DTPA) on rat cytomegalovirus replication in vitro and in vivo

Cytomegalovirus (CMV) infection is a major problem in the immunosuppressed patient. It is thought that besides direct CMV induced cell lysis, immunological damage is part of CMV pathogenesis. New antiviral drugs, which combine immunomodulating and antiviral qualities, could be beneficial. Recently, it has been described that desferrioxamine (DFO) and calcium trinatrium diethylenetriaminepentaacetic acid (DTPA) exhibit both properties. In this report the antiviral effects of both compounds against rat CMV (RCMV) are described in vitro and in vivo using a generalised and local infection model. In vitro, both compounds exhibited a significant antiviral effect, DTPA being more potent than DFO. However, in the generalised infection model no effect was seen on mortality, morbidity or presence of virus in internal organs. In rats infected subcutaneously in the hind paw, no effect was seen locally on paw thickness, presence of viral antigens and inflammatory response. In addition, these rats suffered from a generalised infection of low magnitude at 15 days post infection, although both DFO and DTPA were able to lower the level of viral replication. In conclusion, our data indicate that despite in vitro activity, in vivo usage of DFO or DTPA for acute CMV infection is not warranted.

Comparative tolerability of therapies for cytomegalovirus retinitis

Cytomegalovirus (CMV) retinitis is a potentially sight-threatening complication of advanced HIV infection. The acute infection can be controlled with one of several therapies, including intravenous ganciclovir, foscarnet or cidofovir, slow release ganciclovir intraocular implants or serial intraocular injections of ganciclovir or foscarnet. The initial induction course of therapy is typically followed by lifelong maintenance therapy. In addition to the aforementioned treatments, oral ganciclovir and intravitreal fomivirsen injections are other options for maintenance therapy. The choice of agent must take into consideration factors such as comparative short and long term toxicity of the agents, route of administration and the possible need for indwelling catheters, administration time, cost and protection afforded against systemic dissemination of CMV infection. Possible drug interactions and additive toxicities of other agents needed for the management of the underlying HIV infection must also be taken into consideration. These factors can affect the tolerability of therapy as well as the quality of life of the patient. Relapse or progression of CMV retinitis may be caused by either inadequate drug concentrations at the site of the infection or by drug resistance. This may necessitate either an increase in drug dosage, a change in route of administration or a change to an alternative agent. All of these approaches can increase the risk of toxicity of the therapy. With the initiation of highly active antiretroviral therapy and partial reconstitution of the immune system, some patients have been able to successfully discontinue anti-CMV maintenance therapy, thereby decreasing long term drug toxicity. Determination of the patient predictors of success of this approach is an active area of research.

Treatment of recurrent cytomegalovirus retinitis with the ganciclovir implant

PURPOSE

To evaluate preoperative characteristics and outcome of the treatment of recurrent cytomegalovirus (CMV) retinitis with the ganciclovir implant.

METHODS

Records of 54 patients with acquired immunodeficiency syndrome and active, previously treated CMV retinitis who received a ganciclovir implant in one (n = 31) or both (n = 23) eyes were reviewed. Entry criteria included prior insertion and removal of an indwelling catheter or failure to respond to tolerated doses of ganciclovir and foscarnet. Preoperative factors that might correlate with outcome were analyzed, including demographic factors, duration of human immunodeficiency virus disease and CMV retinitis, indications for surgery, prior anti-CMV treatment, and extent of retinitis.

RESULTS

Forty-six patients completed 1 month of follow-up and were analyzed for outcome. Thirty-one (67.4%) had inactive retinitis at 1 month vs 15 (32.6%) with active retinitis, and they received a mean of 23.5 +/- 22.9 weeks of preoperative ganciclovir vs 58.0 +/- 52.0 weeks in patients with active retinitis (P = .003). Involvement of more than 25% of retinal area by CMV retinitis was also correlated with activity at 1 month (P < .001). Patients who received implants because of lack of venous access had a median time to progression of 8.0 +/- 3.0 months vs 2.0 +/- 1.2 months for patients who had inadequate response or intolerance to intravenous medication (P = .073). Patients with 6 months or less vs more than 6 months of preoperative ganciclovir treatment had progression at a median time of 8.0 +/- 1.7 months vs 2.0 +/- 0.3 months, respectively (P = .016).

CONCLUSION

Longer duration of preoperative ganciclovir or larger area of CMV retinitis correlates with lower success of ganciclovir implant therapy for recurrent retinitis.

A high throughput colorimetric cell proliferation assay for the identification of human cytomegalovirus inhibitors

A colorimetric assay based on the cleavage of the tetrazolium salt WST-1 has been developed for human cytomegalovirus (HCMV) antiviral susceptibility testing and adapted to a microtiter plate format. Optimal conditions were determined and the standard routine assay was calibrated with a viral input of 0.05-0.10 plaque forming unit (p.f.u.)/cell with a density of 2000 cells/well in a 96-well microtiter plate for an incubation period of 7 days. Ganciclovir (9-(2-hydroxy-1(hydroxymethyl) ethyoxymethyl) guanine; DHPG), and cidofovir ((S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine; HPMPC) were used as positive control test compounds to validate the assay. The effective EC50 concentration values obtained with the two antiviral compounds in the present assay were in good agreement with plaque reduction assay results performed in parallel experiments. This method presents the advantage of being easy and rapid to perform, reliable, reproducible, and convenient for use in a high throughput screening capacity.

Genetic analysis of a ganciclovir-resistant human cytomegalovirus mutant

We isolated a ganciclovir (GCV)-resistant human cytomegalovirus (HCMV) from a laboratory strain, AD169, and analysed the mutant. Attempts were also made to identify directly the mutated gene. The 50% inhibitory concentration (IC50) of GCV for the mutant strain was five times higher than that of the wild-type strain. The mutant strain showed similar sensitivity to phosphonoacetic acid and cidofovir as the wild-type strain. These data suggest mutation in the UL97 gene encoding for the phosphotransferase that phosphorylates GCV. Molecular analysis of the mutant strain revealed that a single base substitution of adenine by cytosine occurred at the 1796 nucleotide position of the UL97 gene region, resulting in the substitution of lysine by threonine at codon 599 in the UL97 gene product. Marker transfer experiment confirmed that this mutation conferred HCMV resistance to GCV. The mutation at codon 599 was easily identified by means of RsaI digestion of the selected PCR product.

Cidofovir in the treatment of cytomegaloviral disease

OBJECTIVE

To review the clinical pharmacology and microbiology of cidofovir in the therapy of cytomegalovirus (CMV) disease.

DATA SOURCES

Pertinent literature was identified via a MEDLINE search (October 1986-February 1997), and data from abstracts presented at recent scientific meetings were also included; unpublished information was provided by the manufacturer.

STUDY SELECTION

Antiviral activity data were included if widely accepted methodology was used. All clinical data currently available from human studies were also included.

DATA SYNTHESIS

Cidofovir is similar to ganciclovir in mechanism of action; however, cidofovir does not require viral enzymes for activation. Although the half-life of cidofovir in plasma is only 2.6 hours, the intracellular half-life may be much longer, allowing efficacy with biweekly maintenance dosing. In vitro, cidofovir appears to be equally or more effective than the other agents currently available for the treatment of CMV. In vivo, cidofovir appears to be effective in delaying the progression of CMV retinitis, although no clinical trials to date have directly compared cidofovir with either ganciclovir or foscarnet. Current intravenous dose recommendations are 5 mg/kg once weekly for two doses (induction), and then 5 mg/kg once every other week (maintenance). Since cidofovir is cleared almost entirely by the kidneys, dosage adjustments must be made in patients with impaired renal function. Disadvantages of cidofovir primarily include its risks of adverse drug reactions, such as nephrotoxicity, which is likely to occur in up to 50% of patients if appropriate preventative measures are not taken. Neutropenia and constitutional reactions to probenecid are also commonly encountered during the course of cidofovir therapy.

CONCLUSIONS

Cidofovir is the first acyclic phosphonate nucleoside antiviral agent to be approved for general use in the US. In addition to delaying the progression of CMV retinitis, cidofovir may provide some protective benefits to patients at risk for developing the disease and may be active against certain strains of virus resistant to other currently available therapies. Another advantage of cidofovir is its infrequent dosage schedule, which may prove beneficial in patients who are not compliant with daily intravenous dosing regimens. When determining the appropriate treatment for a patient with CMV retinitis, the benefits of using cidofovir must be weighed carefully against the risk of potentially serious adverse effects.

Cytomegalovirus polymerase chain reaction viraemia in patients receiving ganciclovir maintenance therapy for retinitis

OBJECTIVES

To determine whether recurrence of polymerase chain reaction (PCR) viraemia during maintenance ganciclovir for cytomegalovirus (CMV) retinitis correlates with (i) CMV disease at a new anatomical site, (ii) progression of the presenting retinitis, or (iii) acquisition of genetic changes in gene UL97 associated with resistance to ganciclovir.

DESIGN

A previously described cohort of 45 patients presenting with first episode retinitis was followed clinically using ophthalmoscopy and serial tests for PCR viraemia for a median of 7 months. CMV viral load and genetic markers of ganciclovir resistance were measured in PCR-positive samples.

METHODS

PCR amplification of the glycoprotein B region of CMV and quantitative competitive PCR assays were employed. Genetic changes in UL97 were identified by sequencing/point mutation assay.

RESULTS

PCR viraemia correlated significantly with new episodes of CMV disease (P=0.011) and a trend was seen for the association with progression of retinitis (P=0.07). Amongst the 14 patients PCR-positive during maintenance ganciclovir, 10 (71%) had genetic markers of resistance. None of these patients became PCR-negative in blood after reinduction ganciclovir therapy compared with three out of four without markers of resistance (P=0.022).

CONCLUSIONS

CMV PCR viraemia correlated strongly with the development of new episodes of CMV disease. Most patients with progression of retinitis remained PCR-negative in blood, consistent with therapeutic failure due to poor intraocular penetration of ganciclovir. However, the minority who were PCR-positive in blood may have reinfected their eye, and frequently had markers of ganciclovir resistance. The implications of these findings for the management of patients with CMV disease are discussed.

The Cys607-->Tyr change in the UL97 phosphotransferase confers ganciclovir resistance to two human cytomegalovirus strains recovered from two immunocompromised patients

Two ganciclovir (GCV)-resistant human cytomegalovirus (HCMV) strains recovered from an AIDS patient (strain VR4990) and a heart transplant recipient (strain VR5474) showed a Cys607-->Tyr change in the UL97-encoded phosphotransferase. No amino acid substitutions were observed in the viral DNA polymerase. Marker transfer experiments showed marked reduction in GCV phosphorylation and drug susceptibility of the recombinant HCMV strain VR4990rec2-1-1. These results further extend the region of the carboxy-terminal domain of the UL97 phosphotransferase involved in GCV substrate recognition.

Thiazolo[4,5-d]pyrimidines. Part II. Synthesis and anti-human cytomegalovirus activity in vitro of certain acyclonucleosides and acyclonucleotides derived from the guanine analogue 5-aminothiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione

The synthesis and in vitro antiviral activity of certain hydroxyalkoxymethyl, hydroxyalkyl, hydroxyalkenyl and phosphonoalkenyl derivatives of the guanine congener 5-aminothiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione are reported. The compounds of this study were selected for their structural similarity to acyclonucleosides with known anti-herpesvirus activity. 5-Amino-3-[(Z)-4-hydroxy-2-buten-1-yl]thiazolo[4,5-d]pyrimidine-2, 7(3H,6H)- dione was the only member of the series to display significant in vitro activity against human cytomegalovirus (HCMV); however, this compound did not inhibit other herpesviruses, human immunodeficiency virus type 1 or murine cytomegalovirus. It was found to have a cytotoxicity profile similar to that of ganciclovir (DHPG). The antiviral effect was found to be sensitive to the initial viral input and the time of addition during the virus replication cycle. Significantly, the compound was found to have equal anti-HCMV activity, against standard virus strains, to DHPG, but also showed potent activity against DHPG-resistant virus strains, except for a strain mutated in the UL97 (phosphotransferase) gene.

What clinicians need to know about antiviral drugs and viral resistance

The development of safe and effective antiviral therapies for the management of a variety of viral infections has expanded tremendously in recent years. Treatment is now possible for serious and potentially life-threatening infections with herpesviruses, respiratory viruses such as influenza A and respiratory syncytial virus, and the human immunodeficiency virus. The increased availability and use of antiviral drugs, however, has led to the emergence of drug-resistant viruses, especially in immunocompromised hosts. With this review, the major antiviral agents are presented with a description of the mechanisms of action, the evolution of drug resistance, and the need for in vitro antiviral susceptibility testing.

Cytomegalic colitis after total colectomy in ulcerative colitis: report of a case

A 58-year-old man with ulcerative colitis underwent total colectomy and ileorectal anastomosis. Steroid suppositories were administered postoperatively, and he had had no exacerbation in the residual rectum for 12 years. He suddenly presented with frequent bloody stools and anal pain. An intensive intravenous regimen of prednisolone was ineffective. Cytomegalic inclusion bodies were identified in biopsy specimens. Administration of ganciclovir reduced the ulcers remarkably. The clinical course suggested that this deterioration was caused by cytomegalovirus infection from the beginning. Cytomegalovirus colitis should be recognized as an exacerbating factor, even in ulcerative colitis patients who have undergone surgery, especially when the residual bowel inflammation is resistant to steroid therapy.

Herpesvirus resistance to antiviral drugs: a review of the mechanisms, clinical importance and therapeutic options

During the past decade, potent agents against herpes simplex virus (HSV) types 1 and 2, varicella zoster virus (VZV), and cytomegalovirus (CMV) have become available. The increasing clinical use of acyclovir, ganciclovir, and foscarnet has been associated with the emergence of drug-resistant herpesvirus strains. Resistance to acyclovir or ganciclovir most frequently results from deficient intracellular phosphorylation of these agents which is required for drug activation. Resistance to foscarnet is due to viral DNA polymerase mutants that permit viral replication despite the presence of the drug. In immunocompetent patients, herpesvirus resistance is rare and generally does not correlate with clinical outcome. In contrast, in immunocompromised hosts, resistance of HSV, VZV, and CMV is increasingly detected, and may be associated with disease refractory to antiviral therapy. Foscarnet treatment has been used with some clinical benefit in patients with acyclovir-resistant HSV or VZV, or ganciclovir-resistant CMV. For therapy of resistant mucocutaneous HSV disease, topical trifluorothymidine, and topical or intravenous cidofovir (HPMPC) have yielded encouraging results that warrant further investigation. Improved methods for detection of herpesvirus resistance, and validation of alternative therapy for patients with documented resistance are required to reduce the clinical impact of drug-resistant herpesviruses.

Patterns of resistance and sensitivity to antiviral compounds of drug-resistant strains of human cytomegalovirus selected in vitro

Drug-resistant human cytomegalovirus (HCMV) strains were selected in human embryonic lung (HEL) fibroblasts under pressure of the (S)-3-hydroxy-2-phosphonylmethoxypropyl (HPMP) derivatives of cytosine (HPMPC) and adenine (HPMPA), the 2-phosphonylmethoxyethyl (PME) derivative of 2,6-diaminopurine (PMEDAP), ganciclovir (GCV), acyclovir (ACV), and foscarnet (PFA). Drug susceptibility profiles of the different drug-resistant (i.e., GCVr, HPMPCr, HPMPAr, PFAr, ACVr, and PMEDAPr) strains were determined in HEL cells. A considerable degree of cross-resistance against GCV, HPMPC, and HPMPA occurred with GCVr, HPMPCr, and HPMPAr strains. No changes in susceptibility to 9-(2-phosphonylmethoxyethyl)adenine (PMEA), PMEDAP, ACV, or PFA were detected for the HPMPCr, HPMPAr, and GCVr strains when compared to the wild-type virus. On the other hand, a significant degree of cross-resistance was noted with the PMEDAPr, PFAr, and ACVr strains against PMEA, PMEDAP, PFA, and ACV. NO differences in susceptibility to HPMPC, HPMPA and GCV were observed for the ACVr, PFAr, and PMEDAPr strains relative to the wild type. The drug susceptibility profiles of the different resistant strains point to a common mechanism of HCMV resistance to PFA and the PME derivatives that is different from the mechanism of HCMV resistance to the HPMP derivatives.

Single amino acid changes in the DNA polymerase confer foscarnet resistance and slow-growth phenotype, while mutations in the UL97-encoded phosphotransferase confer ganciclovir resistance in three double-resistant human cytomegalovirus strains recovered from patients with AIDS

Three human cytomegalovirus (HCMV) strains (VR4760, VR4955, and VR5120) showing double resistance to ganciclovir (GCV) and foscarnet (PFA) were isolated from three patients with AIDS who underwent multiple sequential courses of therapy with GCV and PFA (A. Sarasini, F. Baldanti, M. Furione, E. Percivalle, R. Brerra, M. Barbi, and G. Gerna, J. Med. Virol., 47:237-244, 1995). We previously demonstrated that the three strains were genetically unrelated and that each of them was present as a single viral population in vivo. Thus, in each of the three cases, a single viral strain was resistant to both GCV and PFA. In the present paper, we report the characterization of the molecular bases of the double resistance and demonstrate that the PFA resistance is associated with a slower replication of HCMV strains in cell cultures. Sequencing of the UL97 and UL54 genes, GCV anabolism assays, and marker transfer experiments showed that GCV resistance was due to single amino acid changes in the UL97 gene product (VR4760, Met-460 --> Ile; VR4955, Ala-594 --> Val; VR5120, Leu595 --> Ser), while single amino acid changes in domain II of the DNA polymerase (VR4760 and VR5120, Val-715 --> Met; VR4955, Thr-700 --> Ala) were responsible for both the PFA resistance and the slow-growth phenotype. Thus, in these three cases, double resistance to GCV and PFA was not due to a single mutation conferring cross-resistance or to the presence of a mixture of strains with different drug susceptibilities. The HCMV DNA polymerase recombinant strains carrying the mutations conferring PFA resistance were sensitive to GCV and (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC). In addition, the same UL54 mutations were responsible for the slow growth of the clinical isolates, since the recombinant strains showed a marked delay in immediate-early antigen plaque formation and a reduction of infectious virus yield compared with AD169, from which they were derived. These results may have some important implications for the successful isolation, propagation, and characterization of PFA-resistant strains from clinical samples containing mixed viral populations.

A foveal-sparing pattern of cytomegalovirus retinitis in the acquired immunodeficiency syndrome

PURPOSE

We describe the clinical course of 12 eyes of 10 patients in whom recurrent cytomegalovirus (CMV) retinitis exhibited a foveal-sparing pattern.

METHODS

We retrospectively reviewed the case records and photographic charts of 10 patients (12 eyes) with the acquired immunodeficiency syndrome (AIDS), in whom recurrent CMV retinitis exhibited a foveal-sparing pattern within 1500 mm of the foveola.

RESULTS

The site of primary retinitis was temporal in 10 eyes of nine patients in whom it was known. The median number of recurrences up to the observation of foveal-sparing retinitis was two (range one to eight), and five patients had active CMV retinitis despite treatment for at least two continuous months. Once established, the median rate of progression in a non-foveal vector was 2.3 times faster than toward the fovea, and the median time to reduction in acuity to < 6/30 (or death) was 11 to 14 weeks. Three eyes of three patients retained 6/30 or better acuity up to death. Foveal CMV retinitis ultimately reduced acuity to < 6/30 in five eyes. Six eyes suffered retinal detachment, involving the fovea in five, and being the primary reason for acuity of < 6/30 in four. Four patients suffered dose-limiting toxicity.

CONCLUSION

Foveal-sparing CMV retinitis arises in patients with recurrent CMV retinitis resistant to treatment ('clinically resistant'), particularly that which has arisen temporally. Despite its foveolar proximity, and ultimate significant loss of function, the pattern of progression allows for preservation of useful foveal vision for longer periods than would have been expected.

A sensitive and specific polymerase chain reaction-based assay for the diagnosis of cytomegalovirus retinitis

PURPOSE

To develop a sensitive and specific laboratory assay for the diagnosis of cytomegalovirus retinitis.

METHOD

We used a polymerase chain reaction-based assay for detection of cytomegalovirus DNA in vitreous samples. We attempted to detect cytomegalovirus DNA in 19 vitreous samples from patients with the acquired immunodeficiency syndrome (AIDS) who had untreated cytomegalovirus retinitis and in 40 vitreous samples from patients with AIDS who had been treated with systemic ganciclovir or foscarnet, or both. We also attempted to detect cytomegalovirus DNA in vitreous samples from 54 immunocompetent patients, including 32 with retinal detachment or macular hole, 11 with vitreous inflammation, and 11 with vitreous hemorrhage. Additionally, we attempted to detect cytomegalovirus DNA in 15 vitreous samples from patients with AIDS who had vitreoretinal inflammation not caused by cytomegalovirus.

RESULTS

Cytomegalovirus DNA was detected in 18 of 19 eyes with untreated cytomegalovirus retinitis. We detected cytomegalovirus DNA in 19 of 40 vitreous samples from patients with previously treated cytomegalovirus retinitis. Cytomegalovirus DNA was not detected in any of 69 patients who did not have a clinical diagnosis of cytomegalovirus retinitis. Thus, the assay had an estimated sensitivity of 95% in detecting untreated cytomegalovirus retinitis and a sensitivity of 48% in detecting cytomegalovirus retinitis that had been treated with systemic ganciclovir or foscarnet, or both. The assay did not give false-positive results in patients with vitreous hemorrhage or vitreous inflammation. Most important, the assay did not give false-positive results in AIDS patients with vitreous inflammation from causes other than cytomegalovirus retinitis.

CONCLUSION

We have developed a sensitive and specific diagnostic assay that will assist in the diagnosis of cytomegalovirus retinitis.

Viral sensitivity testing in patients with cytomegalovirus retinitis clinically resistant to foscarnet or ganciclovir

PURPOSE

Resistance to antiviral therapy is a potential cause of progression of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome. We investigated the results of viral sensitivity testing in a series of patients with clinically resistant retinitis who had positive results of blood or urine cytomegalovirus cultures.

METHODS

All patients with newly diagnosed cytomegalovirus retinitis between January 1990 and December 1991 were prospectively studied. Blood and urine cultures for cytomegalovirus were obtained in a nonrandomized subgroup of this group. The results of in vitro sensitivity to foscarnet and ganciclovir, determined by a DNA hybridization assay, were then analyzed in seven patients with clinically resistant cytomegalovirus retinitis and whose blood or urine culture results, or both, were positive for cytomegalovirus while on a treatment regimen.

RESULTS

Foscarnet-resistant cytomegalovirus (ID50 > 300 microM) was isolated from two patients, one of whom was being treated with foscarnet. Ganciclovir-resistant cytomegalovirus (ID 50 > 6.0 microM) was isolated from four patients, three of whom were being treated with ganciclovir. Foscarnet- and ganciclovir-resistant cytomegalovirus occurred with previous ganciclovir therapy in one patient. Clinical improvement occurred in three patients whose change in therapy was based on viral sensitivity testing. In general, prolonged therapy with one drug was associated with a progressive increase in the ID 50 for that drug.

CONCLUSIONS

Viral resistance to foscarnet or ganciclovir may explain refractory cytomegalovirus retinitis in some patients.

Quantitation of human cytomegalovirus glycoprotein H gene in cells using competitive PCR and a rapid fluorescence-based detection system

A technique is described for quantitation of the human cytomegalovirus (HCMV) glycoprotein H (gH) gene in cells using a quantitative-competitive polymerase chain reaction (QC-PCR). Two recombinant DNA molecules, differing in size due to a 92-bp deletion within the HCMV gH sequence, were used in co-amplification studies to construct a standard curve from which the copy number of the gH gene present in clinical samples could be interpolated. The use of primers labeled with a fluorescent dye allowed direct detection of the amplified products by measuring the amount of fluorescence emitted by each specific PCR fragment with an automated DNA sequencer coupled to a software program. This system was validated subsequently using bronchoalveolar lavage cells obtained from immunocompromised patients and found to be highly sensitive and reproducible over a range of 5-50,000 HCMV gH copies. This rapid procedure could easily be applied to study the pathogenesis of HCMV infection, identify the patients at high risk of developing HCMV disease, and monitor the effects of antiviral therapy at the molecular level.