Amino (hydroxyethoxymethyl) purine: a new well-absorbed prodrug of acyclovir

Amino Acid Ester Prodrugs of Acyclovir

Eighteen amino acid esters of the antiherpetic drug, acyclovir, were synthesized as potential prodrugs for oral administration. The esters were examined for in vitro antiviral activity against herpes simplex virus Type 1 (HSV-1). They were found to have less potency than the parent compound. Their efficiencies as prodrugs were evaluated in rats by measuring the urinary recovery of acyclovir. Ten prodrugs produced greater amounts of the parent drug in the urine. The L-amino acid esters were better prodrugs than the corresponding D- or D, L-isomers, suggesting the involvement of a stereoselective transporter. The L-valyl ester, 256U87, was the best prodrug. Sixty three per cent of its administered dose was excreted as acyclovir in the urine, a considerable improvement over acyclovir itself, for which this value was 19%. Since 256U87 was stable in aqueous solutions, its conversion to acyclovir in vivo was probably enzyme catalyzed. This L-valyl ester prodrug of acyclovir is now undergoing clinical evaluation.

Stability of some novel thymidine, 5-bromo-2'-deoxyuridine and 3'-azido-2'-3'-dideoxythymidine analogues

In the search of new prodrugs effective against herpes simplex virus series of thymidine, 5-bromo-2'-deoxyuridine esters with amino acid and peptide chains and 3'-azido-2',3'-dideoxythymidine derivatives have been synthesized and evaluated for antiviral activity. The chemical stability of some of them containing different residues was studied at pH 1 and 7.4 and temperature of 37 degrees C. An HPLC method was developed for quantification of the unchanged ester concentration. It was proved that esters with simple aliphatic straight side chain (containing alanyl-, glycyl-, or glycyl-glycyl-glycyl-residues) are relatively stable both at acidic and neutral media, 37 degrees C. Some of them undergo negligible hydrolysis with half lifes ranging between 6 and 23 h. In contrast, more complex esters with branched side chain (valyl-), with phenyl residue (phenylalanyl-), as well as containing thiazol ring are rather unstable especially at acidic conditions and undergo rapid hydrolysis resulting in the respective chemical precursor. The stability of the former group esters outlines them as suitable candidates for prodrugs: with higher lipophilicity facilitating po absorption, satisfying chemical stability and possibility to release the active moiety following enzymatic hydrolysis.

Chemistry and anti-herpes simplex virus type 1 evaluation of cycloSal-nucleotides of acyclic nucleoside analogues

The synthesis of different cycloSal-phosphotriesters of the acyclic nucleoside analogues acyclovir (ACV), penciclovir (PCV) and T-penciclovir (T-PCV) as potential new lipophilic, membrane-soluble pronucleotides is described. The introduction of the cycloSal moiety was achieved by using reactive cyclic chlorophosphane reagents. In addition to the cycloSal-PCV monophosphate (MP) phosphotriesters, a second derivative bearing an acetyl group at the second primary alcohol function was prepared. In hydrolysis studies the cycloSal-ACVMPs showed the expected range of hydrolytic stability dependent on the substituent in the masking group (8-17 h). In contrast, the cycloSal-PCVMP derivatives exhibited a 11- to 15-fold increase in hydrolytic lability as compared to the corresponding cycloSal-ACVMP derivatives. We demonstrated that the free primary alcohol group is responsible for this rate acceleration because cycloSal-OAc-PCVMP, in which the hydroxyl group was blocked by acetylation, did not show the aforementioned acceleration. Unexpectedly, the hydrolysis product was not PCVMP but according to NMR and mass spectrometry it was cycloPCVMP (cPCVMP). The title compounds were evaluated in vitro for their ability to inhibit herpes simplex virus type 1 (HSV-1) and thymidine kinase-negative (TK-) HSV-1 replication in Vero cells. The cycloSal-ACVMP compounds exhibited high antiviral activity in HSV-1-infected cells. More importantly, one derivative retained all activity from the wild-type virus strain in HSV-1/TK(-)-infected Vero cells. The PCV derivatives were markedly less active. The reason for the failure of the cycloSal-PCVMPs seems to be due to the formation of cPCVMP instead of the desired PCVMP.

Recognition and treatment of shingles

Varicella zoster virus (VZV) is responsible for a primary infection (varicella) followed by a latency, eventually resulting in herpes zoster (shingles). The replication cycle of VZV is normally interrupted after varicella. Consequently, VZV remains dormant in the organism. Reactivation occurs after viraemia, and the development of tissue alterations (skin and viscera) depends on the immunological status of the patient. Diagnosis of herpes zoster relies on clinical recognition and cytological and histological evaluations combined with immunohistochemistry and molecular biology techniques. Treatment of herpes zoster primarily relies upon antiviral drugs and incidentally on immunomodulating agents, specific immunoglobulins, antimicrobial agents, antiviral enzymes and corticosteroids. Drugs with a clinically relevant activity against varicella zoster virus infections include aciclovir, adenosine monophosphate, bromodeoxyuridine, desciclovir, fiacitabine, idoxuridine, interferon-alpha and vidarabine. Among them, aciclovir appears to be a first-line agent. Its efficacy has been well established by many clinical studies. Promising drugs for the future include famciclovir, penciclovir, valaciclovir and other molecules currently under investigation. Recent and promising improvements in antiviral drug development may increase patient compliance, cost-benefit ratios and therapeutic efficacy.

Desciclovir permeation of the human erythrocyte membrane by nonfacilitated diffusion

The mechanism of transport of desciclovir (DCV)--a structural analogue and prodrug of acyclovir (ACV) which provides an improved oral bioavailability of ACV--was investigated in human erythrocytes with a "papaverine-stop" assay. DCV influx was nonconcentrative, linearly dependent on DCV concentration (0.9 microM to 15 mM), insensitive (less than or equal to 20% inhibition) to nucleobases, nucleosides, or potent inhibitors of nucleoside transport, and occurred without permeant metabolism. However, DCV was a weak competitive inhibitor of the influx of adenine (Ki = 1.3 mM) and of 5-iodo-2'-deoxyuridine (Ki = 2.9 mM). permeants of the erythrocyte nucleobase and nucleoside carriers, respectively. This indicates that DCV has an affinity for both of these transporters, even though it appears not to be an effective permeant. We conclude that, in contrast to ACV which enters human erythrocytes primarily via the nucleobase carrier, DCV permeates these cells chiefly (greater than or equal to 80%) by nonfacilitated diffusion. This mechanistic difference in transport between ACV and DCV is attributed to differences in their desolvation energies and suggests an explanation for the differences in the oral bioavailability of ACV which is observed after the administration of these two "acyclic nucleosides."

Oral chemotherapy of fatal B virus (herpesvirus simiae) infection

Acyclovir and ganciclovir, which were only about 10-fold less effective against B virus than herpes simplex virus type 1 in VERO cells, were tested in vivo in B virus-infected rabbits. Untreated control rabbits became paralysed from 8 days and died from 10 days. Oral acyclovir at a dose rate of 500 mg/kg/day for 21 days prevented death; acyclovir prevented disease at 700 mg/kg/day. In B virus-infected humans such a high dose of acyclovir could not be given by mouth. Nevertheless, high dose oral acyclovir is suggested for immediate prophylaxis when monkey handlers have been exposed to potentially fatal B virus infection. Should signs or symptoms of disease occur then high dose intravenous acyclovir has been recommended. Since ganciclovir was found to be more effective than acyclovir, intravenous ganciclovir might be preferred for the treatment of established infection.

The prophylactic role of intravenous and long-term oral acyclovir after allogeneic bone marrow transplantation

Eighty-two patients were randomly allocated to receive intravenous acyclovir 5 mg kg-1 t.d.s. for 23 days followed by oral acyclovir 800 mg 6-hourly for 6 months or matching placebos after allogeneic bone marrow transplantation. Herpes simplex and varicella zoster virus infections were significantly reduced during the period of administration of acyclovir. No reduction in cytomegalovirus infection was demonstrated. The drug was not toxic.

Screening with a shell vial assay for antiviral activity against cytomegalovirus

An assay based on the shell vial cell culture (SVA) was devised to assess differences in fluorescence patterns of 8 cytomegalovirus (CMV) strains incubated in the presence or absence of three antiviral substances. The drug concentrations selected for in vitro testing were in the range of peak serum levels achievable in humans (ganciclovir 20 microM, acyclovir 80 microM, and phosphonoformic acid 300 microM). Four days after inoculation of the shell vials, the cell monolayer was fixed, stained with a mixture of monoclonal antibodies to early and late antigens of CMV, and reacted with antimouse fluorescein-labeled globulin. Twenty microM of ganciclovir in the media inhibited the formation of plaque-like foci and specific cytoplasmic fluorescence of laboratory strain AD169 and four clinical isolates. Two documented resistant strains exhibited partial inhibition at 20 microM, and a clinical isolate exhibited incomplete inhibition in three or four occasions. None of the strains was fully inhibited by 80 microM of acyclovir; however, different degrees of partial inhibition were observed. All isolates exhibited high-grade inhibition by 300 microM of phosphonoformic acid. The SVA can be used as a simple screening test for anti-CMV substances and as a screening of CMV resistance to ganciclovir prior to quantitative testing by the more complex plaque reduction assay.

Promising new antiviral drugs

We now have a basis for a more rational approach to rapid evaluation and development of antiviral drugs by screening for activity in vitro, testing for toxicity and efficacy in animals, and clinical testing in humans. Acyclovir is a prototype of this improved process. Interferon has a beneficial effect against CMV infection in renal transplant patients and has promising results in the treatment of papillomas and rhinovirus infections. It does not seem to be as effective against genital herpes or varicella zoster as acyclovir. Ribavirin is effective against respiratory syncytial virus infections and Lassa fever. Varicella-zoster virus is highly sensitive to bromovinyl deoxyuridine in vitro. Phosphonoformate is effective in herpes simplex in animals but of little clinical benefit topically in human recurrent A2 herpes. Zidovudine may decrease mortality rates and infectious complications in patients with acquired immunodeficiency syndrome. DHPG (9-(1,3-dihydroxy-2-propoxymethyl]guanine is useful in treatment of cytomegalovirus and infection in immunocompromised patients. The prodrug of acyclovir results in high blood levels of acyclovir and shows promise in the treatment of varicella-zoster infections. Many halogenated pyrimidine nucleoside analogs are being developed. Buciclovir is another acyclic guanosine analog effective against herpes simplex virus in vitro. 2'-nor-cyclic guanosine monophosphate has a broad antiviral spectrum of action. Interleukin-2 is being investigated. Combined therapies of two or more antiviral drugs or antiviral drugs and other treatments are being studied.

Herpes zoster associated encephalitis: clinical findings and acyclovir treatment

The clinical course of herpes zoster associated encephalitis (HZAE) with special emphasis on the treatment with acyclovir is described from the experience in 14 own patients and 47 review cases. Immunosuppression and dissemination involved increased risk of HZAE, whereas cranial zoster implied no or only a slightly increased risk. The symptoms were mainly disturbances of mental function and ataxia. Nuchal rigidity was noted in approximately one third of cases. The median duration from dermatomal lesion to HZAE was 15 days in immunosuppressed patients versus 5 days in non-immunosuppressed patients. Abnormal spinal fluid findings included mononuclear pleocytosis, occasionally with low glucose concentration. Protein was elevated in half of the patients. Serum sodium levels were often low. Brain CAT scans were generally normal and EEGs always abnormal. Recurrence of HZAE was noted in 2 patients. Treatment with acyclovir seemed to have a beneficial effect. The results, however, need cautious interpretation due to the heterogenous patient material. Two patients developed signs of HZAE while on treatment with desciclovir but recovered during ongoing therapy.

Human gastrointestinal absorption of acyclovir from tablet duodenal infusion and sipped solution

On two occasions at least 1 week apart, nine healthy male volunteers were administered in random order either 2 X 200 mg (1.8 mmol) acyclovir tablets or 400 mg of acyclovir in 500 ml of 5% dextrose solution which was infused at constant rate into the duodenum over 4 h. Six of the subjects subsequently sipped the same solution at the rate of 10.4 ml in each 5 min period for 4 h. Blood and urine were sampled over 24 h for each mode of administration. Acyclovir was assayed by radioimmunoassay. Mean areas under the plasma concentration-time curves (AUCs) +/- s.d. for tablet (T), intraduodenal infusion (I) and sipping (S) were, respectively: T = 14.7 +/- 5.1; I = 24.6 +/- 5.1; S = 28.4 +/- 9.5 (n = 6) mumol l-1 h. AUCs for I and S were significantly greater than that for T (2P less than 0.05). Mean apparent maximum plasma concentrations (Cmax) +/- s.d. were T = 3.8 +/- 1.5; I = 4.8 +/- 0.9; S = 5.1 +/- 1.5 mumol l-1. This trend to higher values for I and S was not significant. Mean apparent plasma disappearance half-lives (t1/2) +/- s.d. were respectively T = 2.3 +/- 0.4; I = 2.7 +/- 0.5; S = 3.0 +/- 0.2 h, I being significantly greater than T (2P less than 0.05), as was S greater than T (2P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Oral bromovinyldeoxyuridine therapy for herpes simplex and varicella-zoster virus infections in severely immunosuppressed patients: a preliminary clinical trial

Twenty-five patients with haematological diseases were treated orally with the highly potent and selective anti-herpes agent, bromovinyldeoxyuridine (BVDU), in a dosage of 7.5 mg/kg/day (divided over three or four doses a day) for 5 days for an intercurrent mucocutaneous herpesvirus infection. Of these 25 patients, 8 were severely granulocytopenic at the time of the viral infection, and 12 recently had undergone bone-marrow transplantation; 5 were under cytotoxic therapy for a lymphoproliferative disorder; 13 had herpes simplex virus type 1 (HSV-1); 1 had herpes simplex virus type 2 (HSV-2); and 11 had varicella-zoster virus (VZV) infection. In all but two patients, BVDU arrested progression of the HSV or VZV infection within 1-2 days after treatment was started. One of the two patients who failed to respond to BVDU had an HSV-2 infection. The other had an HSV-1 infection, which was highly sensitive to BVDU in vitro; BVDU may have failed in this patient because of incomplete drug intake or profuse diarrhoea, or both. The results of this preliminary uncontrolled clinical trial suggest that BVDU may be an effective and safe drug for the oral treatment of HSV-1 and VZV infections in severely immunosuppressed patients.

Acyclovir, oral, intravenous and combined with interferon for chronic HBeAg-positive hepatitis

Chronic hepatitis B patients with active viral replication were treated with acyclovir, either orally 800 mg 4 times daily, or intravenously 15 mg/kg twice daily; duration of treatment was 4 weeks. A second course of intravenous acyclovir (15 mg/kg twice daily for 2 weeks) was given to 5 patients in combination with intramuscular lymphoblastoid alpha-interferon treatment (2.5 MU/m2, once daily). Oral acyclovir had no detectable effect on DNA-polymerase or HBeAg. Intravenous acyclovir alone depressed HBV replication and HBeAg, followed by prolonged negativity of DNA-polymerase in 4 out of 11 patients. Combination therapy of acyclovir with interferon had a significantly greater fall in DNA-polymerase and HBeAg than acyclovir alone. Apart from thrombophlebitis, therapy with acyclovir was tolerated well provided fluid intake was more than 2 litres daily. The combination therapy of acyclovir with interferon appears the most promising for conversion of a state of active viral replication into virus latency.

An open study of human lymphoblastoid interferon and oral acyclovir in chronic hepatitis B virus infection

Ten patients were entered into an open study of interferon (IFN) 'induction' and oral acyclovir (ACV) 'maintenance' therapy. They received 5 Mega units (Mu)/m2 IFN by intramuscular injection daily for 3 days, followed by 7.5 Mu/m2 IFN daily for 7 days. IFN therapy was then discontinued and a 6-week course of oral ACV at a dose of 800 mg 4 times daily commenced. At 6 months, 2 patients had become HBeAg-negative and 1 had developed anti-HBe. Elimination of HBeAg in these patients was accompanied by return of serum liver function tests to normal. There was a statistically significant inhibition of DNA polymerase levels after the 1st week of IFN therapy, which then slowly increased to pretreatment values over 8 weeks. There were no significant adverse effects of ACV therapy, while fever, 'flu-like illness', fatigue, anorexia, and leucopenia were the main side-effects observed during the course of IFN which necessitated dose reduction in 7 patients. Combination therapy appears to effectively inhibit viral replication, although the 'maintenance' effect of oral ACV is minimal. A more effective drug to combine with IFN is needed.

Acyclovir enhances the antiviral effect of interferon in chronic hepatitis B

Patients with chronic hepatitis B with active viral replication had a significantly greater fall in DNA polymerase and hepatitis-Be antigen when treated with interferon and acyclovir together than when treated with either interferon or acyclovir alone. Apart from fatigue and thrombophlebitis, tolerance of the combination therapy was excellent. The combination therapy appears the most promising for conversion of a state of active viral replication into virus latency.

Evaluation of oral acyclovir therapy

Acyclovir is a specific antiviral agent. The triphosphate form inhibits viral DNA replication by competing for incorporation into the replicating DNA chain or by inhibiting viral DNA polymerase. Cells not infected with herpesvirus are generally unaffected. Oral acyclovir inhibits most herpes simplex virus types 1 and 2, and varicella-zoster virus at concentrations used clinically. Oral acyclovir has an average plasma half-life of three hours and is eliminated primarily by renal mechanisms. Peak plasma concentrations occur 1.5 to 2.5 hours after administration and the oral bioavailability is 15 to 30 percent. Acyclovir distributes into most body tissues, including vesicular fluid and the central nervous system. Oral acyclovir is effective treatment of initial and recurrent genital herpes and can suppress frequently recurring genital herpes in both immunocompetent and immunocompromised patients. It is also effective for acute herpes zoster in the immunocompetent and possibly immunocompromised patient. No role is established in either Epstein-Barr virus or cytomegalovirus infections. Oral acyclovir appears to be effective and relatively safe, nontoxic therapy when administered in doses of 1-4 g/d. Oral acyclovir represents a major therapeutic advance in the treatment of herpesvirus infections.