Other AAV-mediated gene therapies
The negative signaling associated with programmed death-1 (PD-1) contributes to tumor evasion. Investigators delivered the extracellular domain of murine PD-1 to a tumor site using AAV vectors and obtained high antitumor efficacy [84]. Since the Fas/Fas ligand (FasL) system involves apoptosis of tumor cells, AAV-mediated transduction of human FasL genes in human laryngeal carcinoma Hep2-bearing nude mice causes obvious suppression of tumor growth and prolonged survival rates (60% vs 0% in control untreated mice) [85]. Administration of the AAV-based central cell-binding domain and C-terminal heparin-binding domain (CBD-Hep II) recombinant polypeptide of human fibronectin suppresses the growth and spontaneous metastasis of breast carcinoma, and prolongs the survival of tumor-bearing mice [86]. Prostate apoptosis response-4 (Par-4) is the tumor-suppressor protein that results in cell apoptosis in tumor cells not in normal cells. A study showed that expression of AAV/Par-4 induced rapid cell death in the HepG2 hepatocarcinoma model [87].
AAV3-mediated expression of the pyruvate dehydrogenase E1 alpha subunit gene can also result in the apoptosis of liver cancer cells [15]. Tumor necrosis factor (TNF) related apoptosis-inducing ligand (TRAIL) receptor 2 (also called death receptor 5, DR5) is usually expressed in tumor cell lines but not in normal cells. Investigators have demonstrated that an AAV-based anti-DR5 mouse-human chimeric antibody can markedly inhibit tumor growth in vitro and in vivo [88]. Survivin is an apoptosis protein. The binding of heat shock protein 90 (Hsp90) to survivin can inhibit the degradation of survivin by the ubiquitin-proteasome system. Since survivin Lys-79~Leu-87 is the binding site for Hsp90, the identical 9-amino acid peptide, named shepherdin, was constructed. AAV-mediated NT4-Ant-shepherdin, consisting of a cell-penetrating peptide (Ant), the signal peptide of neurotrophin-4 (NT4) and shepherdin, can significantly suppress the growth of the lung cancer cell line A549 by inducing apoptosis [89]. Telomerase is made of the catalytic subunit of human telomerase reverse transcriptase (hTERT) and telomerase RNA (hTR). Overexpression of a 27 kDa C-terminal polypeptide of hTERT (hTERTC27) carried by recombinant AAV can prevent the growth of human U87-MG glioblastoma cells in nude mice by increasing necrosis, apoptosis and neutrophil infiltration, and by decreasing microvascular density [90].