Human Immunodeficiency Virus Type 1-Mediated Syncytium Formation Is Compatible with Adenovirus Replication and Facilitates Efficient Dispersion of Viral Gene Products andDe Novo-Synthesized Virus Particles

Abstract

Conditionally replicative adenovirus (CRAd) vectors are designed for specific oncolytic replication in tumor tissues with concomitant sparing of normal cells. As such, CRAds offer an unprecedented level of anticancer potential for malignancies that have been refractory to previous cancer gene therapy interventions. CRAd efficacy may, however, be compromised by inefficient dispersion of the replicating vector within the tumor tissue. To address this issue, we evaluated the utility of a fusogenic membrane glycoprotein (FMG), which induces the fusion of neighboring cellular membranes to form multinucleated syncytia. We hypothesized that the FMG-mediated syncytia would facilitate dispersion of the adenovirus (Ad) gene products and viral progeny. To test this, human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins, which induce syncytia in the presence of CD4+ target cells, were expressed by an Ad (Ad5HIVenv) in permissive (CD4-positive) and nonpermissive (CD4-negative) cell lines. After validating this Ad-FMG model, the efficiency of Ad replication in the presence or absence of syncytia was evaluated. The results demonstrated that syncytium formation was compatible with Ad replication and dramatically increased the dispersion of virus gene products within the cytoplasm of the syncytia as well as viral particles in the nuclei of the syncytial mass. Moreover, progeny virions were released more efficiently from syncytia compared with nonsyncytial cells. These data demonstrate the utility of FMGs as a dispersion agent and suggest that FMGs can improve the efficacy of CRAd gene therapy.

Syncytia formation affects the yield and cytotoxicity of an adenovirus expressing a fusogenic glycoprotein at a late stage of replication

“…4,6 However, a more recent report indicated that adenovirus DNA does not normally undergo internuclear spreading between 12h 24h 48h 72h 96h 5 days 6 days 7 days 12h 24h 48h 72h 96h 5 days 6 days 7 days Syncytia formation affects the yield and cytotoxicity S Guedan et al nuclei within a syncytium, suggesting that efficient adenovirus replication cannot occur without extracellular particle spread. 22 As a result, most nuclei within a syncytium would die without producing new viral particles, limiting the total virus production.…”

“…2,3 One possible method to enhance the efficacy of replicating adenovirus is arming the viruses with therapeutic transgenes. [4][5][6][7] In this respect, it has been previously shown that expression of FMGs efficiently kills tumoral cells by inducing cell-cell fusion and massive syncytia formation. [8][9][10][11] Various FMGs have been evaluated as a means to increase the potency of oncolytic viruses.…”

“…[8][9][10][11] Various FMGs have been evaluated as a means to increase the potency of oncolytic viruses. 4,6,[12][13][14][15][16] Expression of the HIV gp120 FMG by a replicative adenovirus enhanced viral release and facilitated dispersion of virus particles through a culture of tumor cells in vitro. 4 In addition, a more recent report demonstrated that coinjection of plasmid DNA encoding the hyperfusogenic form of the GALV envelope glycoprotein significantly enhanced the in vivo efficacy of the adenovirus therapy.…”

“…4,6,[12][13][14][15][16] Expression of the HIV gp120 FMG by a replicative adenovirus enhanced viral release and facilitated dispersion of virus particles through a culture of tumor cells in vitro. 4 In addition, a more recent report demonstrated that coinjection of plasmid DNA encoding the hyperfusogenic form of the GALV envelope glycoprotein significantly enhanced the in vivo efficacy of the adenovirus therapy. 6 However, despite the interest on generating a replicative adenovirus expressing the GALV glycoprotein, previous attempts to produce adenoviral vectors encoding the GALV fusogenic protein have proven difficult, possibly due to premature cell fusion precluding virus replication.…”

GALV expression enhances the therapeutic efficacy of an oncolytic adenovirus by inducing cell fusion and enhancing virus distribution

“…23 --25 Expression of the HIV gp120 fusogenic membrane glycoprotein by a replication-competent adenovirus enhanced virus release and facilitated dispersion of virus particles through a culture of HeLa --CD4 þ cells. 26 In a different strategy, coinjection of plasmid DNA encoding the gibbon-ape leukemia virus (GALV) envelope glycoprotein significantly enhanced the antitumor efficacy of the adenovirus therapy. 27 In addition, we have recently demonstrated that expression of the hyperfusogenic-form of the GALV by a replication-competent adenovirus enhanced tumor cell killing.…”