Adeno-associated virus-mediated cancer gene therapy: current status

Abstract

Gene therapy is one of the frontiers of modern medicine. Adeno-associated virus (AAV)-mediated gene therapy is becoming a promising approach to treat a variety of diseases and cancers. AAV-mediated cancer gene therapies have rapidly advanced due to their superiority to other gene-carrying vectors, such as the lack of pathogenicity, the ability to transfect both dividing and non-dividing cells, low host immune response, and long-term expression. This article reviews and provides up to date knowledge on AAV-mediated cancer gene therapy.

Keywords: Adeno-associated virus; Cancer; Cancer gene therapy; Gene vehicle.

Fig. 1. Structure of the AAV-2 subunit and comparison with related structures

(a) Experimental electron density for AAV-2. Phases for this 3-Å resolution electron density map are independent of the AAV-2 model, having been obtained by symmetry averaging and extension from a CPV model at 15-Å resolution. Density is clear and allows an unambiguous fitting of the chemical sequence throughout VP3. (b) Ribbon drawing of the AAV-2 subunit. The locations of the neighboring symmetry axes are shown. The β-barrel is on the inner surface of the capsid (pink) with strands of the two sheets labeled conventionally as A, B, I, D, and G, and C, H, E, and F. Loops are labeled according to the flanking strands—e.g., GH loop. Regions where the sequence differs greatest between the AAV serotypes are colored purple [122]. (c) Comparison of the backbones of AAV-2 (red) and canine parvovirus (cyan). The loop structure, which is responsible for many of the viral-host interactions differs substantially between AAV-2 and canine parvovirus, is largely absent from insect densoviruses (not shown). Reprinted with permission from ref 6.

Fig. 2. The AAV/HSV-tk and GCV suicide gene system

The AAV vector carrying an HSV-tk gene is constructed using RC and helper plasmids, and AAV/HSV is then transduced into the target cells. Cell killing is subsequently achieved by inhibiting the cell cycle and promoting cell apoptosis as systemically-administered GCV is converted to a GCV triphosphate.

Fig. 3. Effect of antiangiogenic gene therapy and paclitaxel on metastasis of orthotopically transplanted human breast cancer cells (intervention model)

MDA-MB-231-luc cells were transplanted into mammary fat pads of female, athymic mice. Whole body images were obtained on a weekly basis after intraperitoneally administration of luciferin in a Xenogen system (a). Luminescence signals from the primary tumors were too strong and were overlapping with the signals originating from the metastatic sites. Therefore, the primary tumors were shielded (lower half) to reveal tumor metastasis to lungs and lymph nodes (days 21 and 42). Intensity of signals is shown at the bottom. On day 42, mice were killed and brachial lymph nodes and lung tissues were removed for ex vivo imaging. C, adeno-associated virus (AAV)-LacZ; E, AAV-P125A-endostatin; T, paclitaxel; T+E, combination treatment; LN, lymph node. Panel (b) shows relative luciferase-positive pixels from the metastatic sites. Each value is a mean of five animals ± s.d. Panel (c) shows the histopathology of lungs. The lung tissues were stained with hematoxylin and eosin stain and the black arrow shows the tumor that has metastasized to the lungs (×200). **Denotes statistical significance (P<0.02). Reprinted with permission from ref 105.

Fig. 4. Detailed analysis of retinal function and structure in patients with choroideremia

(A) Pre-surgery and (B) 6 months post-surgery analysis of patient 1 showing a shift in the cloud of variable fixation (blue dots; B, white arrow) into the area of retina exposed to vector (dotted white line), but away from the area of surviving autofluorescent retinal pigment epithelium (white solid line) that was not exposed to vector. The increase in retinal sensitivity also correlated anatomically with the region of surviving retina exposed to AAV.REP1 (C, dotted line) and residual outer retina identified with optical coherence tomography scanning (D, green arrow). The thin fovea and injection site can be seen on either side of the residual retina (green arrow). Green dot (L) is the mean center of all fixation points. ETDRS=Early Treatment for Diabetic Retinopathy Study (a standard vision test). AAV=adeno-associated virus. REP1=Rab escort protein 1. Reprinted with permissions from ref 39.