Tropism-Modification Strategies for Targeted Gene Delivery Using Adenoviral Vectors

Abstract

Achieving high efficiency, targeted gene delivery with adenoviral vectors is a long-standing goal in the field of clinical gene therapy. To achieve this, platform vectors must combine efficient retargeting strategies with detargeting modifications to ablate native receptor binding (i.e. CAR/integrins/heparan sulfate proteoglycans) and “bridging” interactions. “Bridging” interactions refer to coagulation factor binding, namely coagulation factor X (FX), which bridges hepatocyte transduction in vivo through engagement with surface expressed heparan sulfate proteoglycans (HSPGs). These interactions can contribute to the off-target sequestration of Ad5 in the liver and its characteristic dose-limiting hepatotoxicity, thereby significantly limiting the in vivo targeting efficiency and clinical potential of Ad5-based therapeutics. To date, various approaches to retargeting adenoviruses (Ad) have been described. These include genetic modification strategies to incorporate peptide ligands (within fiber knob domain, fiber shaft, penton base, pIX or hexon), pseudotyping of capsid proteins to include whole fiber substitutions or fiber knob chimeras, pseudotyping with non-human Ad species or with capsid proteins derived from other viral families, hexon hypervariable region (HVR) substitutions and adapter-based conjugation/crosslinking of scFv, growth factors or monoclonal antibodies directed against surface-expressed target antigens. In order to maximize retargeting, strategies which permit detargeting from undesirable interactions between the Ad capsid and components of the circulatory system (e.g. coagulation factors, erythrocytes, pre-existing neutralizing antibodies), can be employed simultaneously. Detargeting can be achieved by genetic ablation of native receptor-binding determinants, ablation of “bridging interactions” such as those which occur between the hexon of Ad5 and coagulation factor X (FX), or alternatively, through the use of polymer-coated “stealth” vectors which avoid these interactions. Simultaneous retargeting and detargeting can be achieved by combining multiple genetic and/or chemical modifications.

Gene-Directed Enzyme Prodrug Cancer Therapy

“…This drawback causes ex vivo and intratumoral protocols to be preferably chosen for viral GDEPT because systemic administration can cause severe side effects [113]. In order to redirect the tropism of viruses to specifically target tumor cells, some attempts have been made to change the mechanism of virus internalization and create a "retargeted transduction" viral vector [114]. For example, Morrison et al used a hydrophilic polymer, N-(2-hydroxypropyl) methacrylamide (HPMA), to shield the viral capsid, followed by "recoating" of the virus by chemical conjugation of the murine epidermal growth factor [115].…”

Safety and Efficacy of VCN-01, an Oncolytic Adenovirus Combining Fiber HSG-Binding Domain Replacement with RGD and Hyaluronidase Expression

“…Different capsid modifications are being explored to avoid liver transduction and to expose specific ligands for tumor cells (5). The mutation of the putative heparan sulfateglycosaminoglycans (HSG) binding domain KKTK, located in the fiber shaft, abrogates liver transduction in mice, rats, and nonhuman primates (6)(7)(8).…”

Localization of neutralization epitopes on adenovirus fiber knob from species C

“…CAR, CD46 and DSG2) and thus determines the AdV infection and tissue tropism (Arnberg, 2012). Therefore, knob-exchanged Ad5 vectors may have altered infection patterns and biodistribution that result in reduced transduction and pose a health security risk (Coughlan et al, 2010). Characterization of serotype-specific neutralization epitopes on the fiber knob will add to our understanding of humoral immune responses to AdVs and will contribute to the construction of novel and more desirable capsid-modified rAd5 vectors.…”