**4. Clinical trials**

viral replication. By blocking AdV replication at one or more steps beyond the onset of E1A expression and before genome replication, digoxin and digitoxin manifest very prospective

Convallatoxin, a synthetic cardiotonic steroid, manifested a stronger activity versus AdV5 when compared with digoxin and digitoxin. In general, these three substances alter the cascade of AdV gene expression—an effect starting after initiation of early gene expression attaining a blocking of AdV DNA replication and of viral structural proteins. These findings open a novel approach of treating AdV infections and guide the development of novel antiviral therapies.

This compound inhibits selectively cellular binding sites (sialic acid-containing receptors) of several AdV serotypes. It was established that ADVs possess this cellular tropism. NMSO<sup>3</sup>

This substance markedly inhibits the AdV cystein protease, indispensable for the production

As a result of the studies carried out by G. Wadell, N. Arnberg and others in University of Umea in Sweden (2014–2017), O. Sterner and U. Ellervik (University of Lund, Sweden) synthesized the substance APD-209, announced as ADENOVIR (Pharma). It was noted that this substance with unknown structure for the publicity is considered as a new solution for the

Other Swedish authors [48] reported also that **analogues of 2-[2-(benzoylamino)benzoyl** 

In the search for discovery of efficient anti-AdV agents it was investigated the probable impact of silencing of a set of early, middle and late viral genes on the replication of AdV5 in vitro [49]. It was established that AdV replication was inhibited by siRNAs directed against AdV E1A, DNA polymerase, preterminal protein (pTR), IVa2, hexon, and protease genes. Besides, silencing of the early and middle genes was more effective in inhibiting AdV replication than the silencing of late genes, especially sharply manifested with effect on siRNA of the DNA polymerase gene. Besides, it was found that reducing the viral genome copy numbers (AdV DNA) is a more promising strategy than the reducing the number of proteins necessary for

Cyclic D,L-α-peptides, cycloferon, lactoferrin nitric oxide, doxovir, heterocyclic Schiff bases of aminohydroxyguanidine tosylate, PGD peptidomimetic molecules, some medical plant

potential as antivirals for the treatment of serious AdV infections.

 **(sulfated sialic acid derivative)**

**3.5. 2,4,5,7-tetranitro-9-fluorenone**

of infectious AdV virions [45, 46].

treatment of viral eye infections [47].

**3.6. ARD-209 (ADENOVIR)**

**3.7. Short interfering RNAs**

capsid formation.

substances (ref. in [17]).

could be used for the topical treatment of ocular AdV infections [43, 44].

**amino]benzoic acid** possess inhibitory effect on adenovirus replication.

**3.8. Other compounds inhibiting AdV replication in vitro**

**3.4. NMSO3**

20 Adenoviruses

Prophylaxis with effective antivirals versus AdV EKC would be particularly useful for preventing AdV transmission to the second eye as well as to the contact persons.

Cidofovir eye drops 1% prevent severe corneal opacities in EKC patients, dose-dependent local toxicity at frequent administration been registered [50, 51]. This anomalous nucleoside at concentration of 1% applied topically in a combination with 1% cyclosporine demonstrated therapeutic effect on patients with EKC in a controlled clinical pilot study [51]. No placebocontrolled randomized trials have been carried out on immunocompromised patients.

Controversial results were obtained with cidofovir the treatment of AdV infections in children undergoing bone marrow or stem cell transplantation [52]. Evidence was accumulated that as earlier AdV infection is detected for starting cidofovir treatment the better curative results were registered. Although cidofovir exhibits antiviral activity versus all AdV species, it possesses low oral bioavailability and significant toxicity (tubular necrosis) and does not confer long-term protection [53].

However, the lipid conjugate of cidofovir, brincyclovir (BCV; hexadecyloxy propyl-cidofovir; CMX001) is currently in Phase II clinical trial [25, 54], unfortunately manifesting a significant toxicity to the kidney and gastrointestinal tract.

The topical ganciclovir application against EKC [55] merits special attention. In a published clinical study, treatment with 0.15% GCV ophthalmic gel improved outcome of AdV conjunctivitis [56]. Three other clinical trials evaluating 0.15% GCV ophthalmic gel were organized, two of them finished: (1) Efficacy and Safety of GV 550 in Acute Adenovirus Keratoconjunctivitis (Clinical Trials.gov. trial NCT01156025) and (2) Efficacy and Safety of GV 550 in Acute Adenovirus Keratoconjunctivitis (a Clinicaltrialsregister.eu trial). Both included placebo and treatment groups on 40 persons each (in fact Phase II of clinical trial). In the third trial, Clinical Trials.gov trial NCT1533480 (A Placebo Controlled Comparison of Topical ZIRGAN Versus Genteal for the treatment of Adenovirus Conjunctivitis) which is currently in course, GCV is administered topically as 0.15% gel (ZIRGAN®) compared with 0.3% Hypromellose gel (Genteal gel®), serving as placebo (Phase IV).

On the base of the promising results with povidone-iodine (PVP-I), a microbicidal agent possessing also virucidal properties [57], topical ganciclovir and PVP-I combination drops have shown the most recent potential, but both therapeutics need to be investigated in larger scale studies [58].

The experimental data in vivo are in favor of GCV to be considered as an option for the treatment of AdV infections in immunocompromised patients.

Ribavirin efficacy for the treatment of AdV infections was very controversial [36, 59].

N-chlorotaurine (a week oxidant) manifested effectivity in phase II clinical trials with viral conjunctivitis [60].

During a severe outbreak of EKC caused by AdV 8 in 1972–1973 in Bulgaria abitylguanide was tested in two double-blind, randomized trials, carried out on total 349 patients (trial 1–151 patients; trial 2–198 patients) with virologically confirmed diagnosis.

Abitylguanide was applied as 1% eye drops (in saline). In each of the two trials, patients were divided in three groups: group I placebo (patients with symptomatic treatment), group II -abitylguanide 1% + symptomatic treatment, group III—patients treated with abitylguanide 1% only. Curative effect of abitylguanide was almost identical in group II and III in both trials. Moreover, the drug had a preventive effect on infection of the second eye. The abitylguanide treatment exerted a marked curative effect on the severity and duration of the disease: (1) more than twofold decrease in both trials in the number of patients with EKC form associated with keratitis; (2) five- and sixfold decrease in trial 1 an trial 2, respectively, in the incidence of severe keratitis; (3) two- and fivefold decrease in trial 1 and trial 2, respectively, in the number of patients with impaired vision; (4) twofold decrease of the healing time [61–63]. Effectivity toward AdV-induced EKC of the drug applied topically was confirmed in series of placebo controlled trials (not following the double-blind scheme) in three other ophthalmic clinics in the country, carried out in the second half of the 1980s. Pencheva et al. [64] in the Varna Medical Faculty registered marked decrease of the patients number with keratitis, twofold shortening of the healing time in abitylguanide treated patients, affection of the second eye—80% in the placebo group, and 22.6% in abitylguanide treated group.

(more precisely ocular AdV infections in laboratory animals); (4) application of methods for express diagnostic of ADV infections, in order earliest start of the respective treatment with anti-AdV chemotherapeutic agents. More detailed consideration of this topic was presented

Chemotherapy of Adenovirus Infections http://dx.doi.org/10.5772/intechopen.79160 23

The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, Sofia,

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[3] Grosso F, Stoilov P, Brown M, Cochrane A. Suppression of adenovirus replication bu

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[5] Strausberger R, Harel L, Levy Y, Amir J. A syndrome of transient encephalopathy associ-

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by Kaufman [66] and Luchs [67].

Address all correspondence to: galabov@microbio.bas.bg

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**Author details**

Angel S. Galabov

Bulgaria

**References**

In preliminary carried out study abitylguanide manifested a very high local tolerance (1, 2 and 3% eye drops in saline) tested in 21 volunteers (in rabbits—till 20% eye drop).

The pronounced effect of abitylguanide [65] in abovementioned trials on EKC patients served for the development and implementation in pharmaceutical industry of preparative ADENOSTATIN COLLYRIUM® (Pharmachim Ltd., Sofia) which clinical use marked favorable estimation by ophthalmologists in this country (tested in Japan, as well).

The clinical use of cardiotonic steroids as anti-AdV agents needs special consideration. As digitoxin has been associated with toxicity, the use of cardiac glycosides as antivirals would be short term, in contrast to the chronic use in patients with heart diseases. Having in mind that anti-AdV agents have to be used for the treatment of severe respiratory and disseminated diseases, these drugs seem more attractive as potential agents for the topical treatment of EKC and even for the prophylaxis of persons contact to EKC patients [3].

There is no doubt that chemotherapy of AdV infections occupies leading position as a tool for anti-etiological treatment. Therefore, the development of effective anti-AdV agents is especially a big task of the scientists and clinicians. The above-presented panorama of antivirals versus AdVs and AdV-caused infections shows that a lot of work is done for the realization of this problem. The author would like to mention the main directions that determined the development of antivirals and their implementation in the clinical practice: (1) discovery of the targets in virus growth cycle for chemotherapeutic attacks—a lot of "wide" places could be pointed in the AdVs; (2) attainment in the organic chemistry—modeling of new effective molecules with anti-AdV effects among anomalous nucleosides, end especially of non-nucleoside compounds ligands of AdV proteins; (3) development of adequate methodology for antiviral testing starting from the initial in vitro screening, and application of purified AdV structural and eventually nonstructural proteins as cell-free systems (approach contributed substantially for the successful development of anti-hepatitis C drugs; as concerns the in vivo testing, in the last years, several very convenient and adequate models were described and successfully used (more precisely ocular AdV infections in laboratory animals); (4) application of methods for express diagnostic of ADV infections, in order earliest start of the respective treatment with anti-AdV chemotherapeutic agents. More detailed consideration of this topic was presented by Kaufman [66] and Luchs [67].
