Adenovirus as a Vector and Oncolytic Virus

Abstract

Adenoviral vectors, both oncolytic viruses and gene delivery vectors, are among the earliest approved and commercialised vectors for gene therapy. Adenoviruses have high cytotoxicity and immunogenicity. Therefore, lentiviruses or adeno-associated viruses as viral vectors and herpes simplex virus as an oncolytic virus have recently drawn attention. Thus, adenoviral vectors are often considered relatively obsolete. However, their high cargo limit and transduction efficiency are significant advantages over newer viral vectors. This review provides an overview of the new-generation adenoviral vectors. In addition, we describe the modification of the fiber knob region that enhances affinity of adenoviral vectors for cancer cells and the utilisation of cancer-cell-specific promoters to suppress expression of unwanted transgenes in non-malignant tissues.

Keywords: adenoviral vector; adenovirus; midkine; oncolytic virus.

Figure 3

Combination of a chimeric adenovirus vector and midkine promoter. Because cluster of differentiation 46 (CD46) is also expressed in non-malignant cells, a safety device is required to prevent gene expression in these cells even if they are infected with an adenovirus serotype 5 F35 (AD5F35) vector. Safety is ensured by a conditionally replicating adenovirus (CRAD) that regulates genes necessary for adenovirus replication in the promoter region of midkine (A). The CRAD Ad5F35 vector as an oncolytic virus exhibits a remarkably potent oncolytic effect on cancer cells neighbouring primarily infected cells through secondary infection and replication (B). (A) is adapted from the data published by Nagaya et al., Anticancer Res, 2012 [95].

Figure 1

Genomic overview of each generation of adenoviral vectors. E1~E4, early regions 1–4; L1~L5, late regions 1–5; Ad5, adenovirus serotype 5; ITR, inverted terminal repeat; ψ, packaging signal.

Figure 2

Concept of the chimeric adenoviral vector, adenovirus serotype 5 F35 (Ad5F35). Ad5 infects cells via the coxsackie and adenovirus receptor (CAR), but CAR is poorly expressed in cancer cells. Ad35 infects via ubiquitously expressed cluster of differentiation 46 (CD46). Ad5 and Ad35 have no affinity for CD46 and CAR, respectively. Therefore, when the fiber knob region of Ad5 is converted to that of Ad35, it is possible for adenoviral vectors to infect via CD46.

Figure 4

Expression of midkine, coxsackie and adenovirus receptor (CAR), and cluster of differentiation 46 (CD46) in human bladder cancer cell lines (A) and the oncolytic effects of adenovirus serotype 5 F35 (Ad5F35)/Mkp-E1 against bladder cancer cell lines (B–D). This figure is adapted from the data published by Gotoh et al., Urology, 2013 [92].

Figure 5

Coxsackie and adenovirus receptor (CAR) and cluster of differentiation 46 (CD46) expressions in renal cell carcinoma (RCC) cell lines (A) and the oncolytic effects of Ad5F35/Mkp-E1 against these cells (B–D). Only low CAR mRNA expression was found, and Ad5F35/Mkp-E1 reduced the cell viability of RCC cell lines. However, little or no effect was observed with Ad5/Mkp-E1 (B–D). This figure is adapted from the data published by Nagaya et al., Anticancer Res. 2012 [95]. p < 0.05: *, p < 0.01: **, p < 0.001: ***.

Figure 6

Human codon-optimised Streptococcus pyogenes Cas9 gene (hCas9) was placed downstream of the midkine promoter (Mkp) and the enhanced green fluorescent protein (EGFP) gene inserted next to it as an expression marker (A). In PNT1A, which is a non-malignant cell line, hCas9 expression was inhibited. In the bladder cancer cells lines, hCas9 protein expression was confirmed after Ad5F35-Mkp-hCas9 infection (B). This figure is adapted from the data published by Matsunaga et al., Anticancer Res. 2021 [99].