Targeted Photodynamic Virotherapy Armed with a Genetically Encoded Photosensitizer

Abstract

Photodynamic therapy (PDT) is a minimally invasive antitumor therapy that eradicates tumor cells through a photosensitizermediated cytotoxic effect upon light irradiation. However, systemic administration of photosensitizer often makes it difficult to avoid a photosensitive adverse effect. The red fluorescent protein KillerRed generates reactive oxygen species (ROS) upon green light irradiation. Here, we show the therapeutic potential of a novel tumor-specific replicating photodynamic viral agent (TelomeKiller) constructed using the human telomerase reverse transcriptase (hTERT) promoter. We investigated the lightinduced antitumor effect of TelomeKiller in several types of human cancer cell lines. Relative cell viability was investigated using an XTT assay. The in vivo antitumor effect was assessed using subcutaneous xenografted tumor and lymph node metastasis models. KillerRed accumulation resulted in ROS generation and apoptosis in light-irradiated cancer cells. Intratumoral injection of TelomeKiller efficiently delivered the KillerRed protein throughout the tumors and exhibited a long-lasting antitumor effect with repeated administration and light irradiation in mice. Moreover, intratumorally injected TelomeKiller could spread into the regional lymph node area and eliminate micrometastasis with limited-field laser irradiation. Our results suggest that KillerRed has great potential as a novel photosensitizer if delivered with a tumor-specific virus-mediated delivery system. TelomeKillerbased PDT is a promising antitumor strategy to efficiently eradicate tumor cells.

Reactive oxygen species generating systems meeting challenges of photodynamic cancer therapy

“…274, 278-280 On the other hand, reducing irradiance and/or fluence can achieve sub-lethal levels of ROS for mediating subtle cellular signaling. 277 The first developed RGP was the KillerRed, a homolog of GFP, anm2CP, by Lukyanov and coworkers.…”

Eradication of melanoma in vitro and in vivo via targeting with a Killer-Red-containing telomerase-dependent adenovirus

“…A telomerase-specific conditionally Killer-Redexpressing adenovirus has some advantages compared with conventional PDT: (a) the high tumor selectivity and prolonged accumulation of Killer-Red, which is achieved by using a telomerase-specific replicating adenovirus; (b) the dual effects mediated by Killer-Red-mediated cell death as well as virus-mediated cell death. 14 Since light in the yellow-green to orange wavelength range for excitation of Killer-Red has limited depth penetration, 8 cutaneous melanoma can be a good indication for Killer-Red-based PDT. We previously reported that intra-tumor injection of a telomerase-specific replication-competent adenovirus (OBP-301) eliminated lymph node metastasis of an orthotopic colorectal cancer model.…”

Bone and Soft-Tissue Sarcoma: A New Target for Telomerase-Specific Oncolytic Virotherapy

“…Another marker, KillerRed protein, is one of the brightest red fluorescent proteins, and is excited by a green laser with higher tissue-penetration ability [92]. We have generated a KillerRed-expressing oncolytic adenovirus, TelomeKiller, that permits the selective visualization of a variety of tumor cells, including sarcoma cells [93,94]. TelomeKiller may be a useful reagent for illuminating deep tumor tissues in FGS.…”