Comparison of HSV-1 thymidine kinase-dependent and -independent inhibition of replication-competent adenoviral vectors by a panel of drugs

Abstract

Replication-competent adenoviral vectors hold the promise to be more efficient gene delivery vehicles than their replicationdeficient counterparts, but they are also associated with a higher risk for adverse effects, especially in light of the fact that there is no established effective therapy for serious, disseminated adenovirus infection. To assess whether the therapeutic options to inhibit adenoviral replication can be enhanced by expressing a suicide gene, we examined the antiadenoviral effects of 15 drugs against wild-type adenovirus type 5 (Ad5) and an Ad5-based replication-competent vector expressing herpes simplex virus-1 thymidine kinase (HSV-tk) (Ad.OW34) using a real-time polymerase chain reaction -based assay and flow cytometry. Ad5 and Ad.OW34 were highly susceptible to the fluorinated pyrimidine analogs 5-fluoro-2 0 -deoxyuridine (FUdR), 5-fluorouridine (FUR), and trifluorothymidine (TFT), with a mean 50% inhibitory concentration (IC 50 ) ranging from 0.12 to 0.32 mM. The mean IC 50 of ribavirin and cidofovir (CDV) for Ad5, the most frequently used drugs to treat adenovirus disease, was 6.87 and 3.19 mM, respectively. In contrast to Ad5, the Ad.OW34 vector was susceptible to (E)-5-(2-bromovinyl)-2 0 -deoxyuridine (BVdU, IC 50 0.09 mM), ganciclovir (GCV, IC 50 0.19 mM), and acyclovir (ACV, IC 50 32.04 mM). Additionally, we demonstrated in an animal model that Ad.OW34 vector replication can be inhibited significantly by GCV, CDV, and TFT by 35.2, 7.7, and 3.7-fold, respectively, compared to untreated animals. The observed antiadenoviral effects were primarily not through cell killing, since the in vitro 50% cytotoxic concentrations (CC 50 ) were more than 1000 times higher than the antiadenoviral IC 50 of the drugs examined, even in cells stably expressing HSV-tk. Since for HSV-tk-dependent inhibition of adenoviral vectors, stability of HSV-tk expression is crucial, we examined Ad.OW34 vector stability, by passaging the vector 10 times serially in the presence of 10 mM GCV. The HSV-tk/GCV system neither changed the susceptibility of Ad.OW34 to GCV significantly nor detectable vector rearrangements occurred, suggesting that the system might be suitable as a fail-safe mechanism to stop adenoviral vector replication.

Synergy between expression of fusogenic membrane proteins, chemotherapy and facultative virotherapy in colorectal cancer

“…23,24 However, this effect is negatively affected by the virostatic effect of the chemotherapeutics. 41,42 As we observed in our tumor model a slightly enhanced antineoplastic effect when just combining the oncolytic vectors with FOLFOX, in the triple therapy the transcomplementation approach improved chemotherapy to some extent independently of the FMG expression. Third, without using chemotherapy, several groups reported previously that the intratumoral expression of FMG enhances the efficacy of virotherapy.…”

Enhanced killing of pancreatic cancer cells by expression of fusogenic membrane glycoproteins in combination with chemotherapy

“…However, because oncolytic adenoviruses can enhance the efficacy of chemotherapeutic agents (20), as also observed in both of our tumor models, this transcomplementation approach might improve chemotherapy by itself independently of the FMG expression. On the other hand, chemotherapeutic agents will also inhibit viral replication (56,57). Furthermore, without using chemotherapy, several groups reported previously that the intratumoral expression of FMGs enhances the efficacy of virotherapy (24,58).…”

In vitro analysis of cidofovir and genetically engineered TK expression as potential approaches for the intervention of ColoAd1-based treatment of cancer

“…In an in vitro Therapeutic interventions for ColoAd1 M Bauzon et al study comparing CDV with RBV, CDV anti-Ad activity was significantly better than that of RBV, 8 and similar observations on a limited set of clinical isolates have also been reported. [9][10][11] The antiviral activity of CDV to ColoAd1 was tested along with its parent viruses, Ad11p and Ad3 (Figures 2a-c).…”

“…13 The choice of incorporating the HSV-TK gene into the virus as a safety valve is based on several parameters. As shown earlier by others, 8 the HSV-TK gene, when incorporated and expressed from a replicating viral genome, can be a highly effective means for restricting virus replication and spread when the pro-drug GCV is administered to therapeutic levels. GCV and related agents, widely used in the treatment of HSV infection in humans, are poor substrates for the mammalian nucleoside monophosphate kinase, but can be converted 1000-fold more efficiently to the monophosphate by the HSV-TK gene.…”