Human telomerase reverse-transcriptase promoter-controlled and herpes simplex virus thymidine kinase-armed adenoviruses for renal cell carcinoma treatment

Therapeutic strategies for targeting telomerase in cancer

Telomere and telomerase play important roles in abnormal cell proliferation, metastasis, stem cell maintenance, and immortalization in various cancers. Therefore, designing of drugs targeting telomerase and telomere is of great significance. Over the past two decades, considerable knowledge regarding telomere and telomerase has been accumulated, which provides theoretical support for the design of therapeutic strategies such as telomere elongation. Therefore, the development of telomere-based therapies such as nucleoside analogs, non-nucleoside small molecules, antisense technology, ribozymes, and dominant negative human telomerase reverse transcriptase are being prioritized for eradicating a majority of tumors. While the benefits of telomere-based therapies are obvious, there is a need to address the limitations of various therapeutic strategies to improve the possibility of clinical applications. In this study, current knowledge of telomere and telomerase is discussed, and therapeutic strategies based on recent research are reviewed.

A Double Fail-Safe Approach to Prevent Tumorigenesis and Select Pancreatic β Cells from Human Embryonic Stem Cells

The transplantation of human embryonic stem cell (hESC)-derived insulin-producing β cells for the treatment of diabetes is finally approaching the clinical stage. However, even with state-of-the-art differentiation protocols, a significant percentage of undefined non-endocrine cell types are still generated. Most importantly, there is the potential for carry-over of non-differentiated cell types that may produce teratomas. We sought to modify hESCs so that their differentiated progeny could be selectively devoid of tumorigenic cells and enriched for cells of the desired phenotype (in this case, β cells). Here we report the generation of a modified hESC line harboring two suicide gene cassettes, whose expression results in cell death in the presence of specific pro-drugs. We show the efficacy of this system at enriching for β cells and eliminating tumorigenic ones both in vitro and in vivo. Our approach is innovative inasmuch as it allows for the preservation of the desired cells while eliminating those with the potential to develop teratomas.

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hESCs were engineered with suicide genes for safety and differentiation efficiency

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One cassette is exclusively expressed in teratogenic cells (safety)

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Another is selectively excised out in hESC-derived pancreatic β cells (selectivity)

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Our strategy allows for hESC-derived tumors to be prevented or ablated in vivo

Induced prodrug activation by conditional protein degradation

Enzyme prodrug therapies hold potential as a targeted treatment option for cancer patients. However, off-target effects can be detrimental to patient health and represent a safety concern. This concern can be alleviated by including a failsafe mechanism that can abort the therapy in healthy cells. This feature can be included in enzyme prodrug therapies by use of conditional degradation tags, which degrade the protein unless stabilized. We call this process Degradation-Directed Enzyme Prodrug Therapy (DDEPT). Herein, we use traceless shielding (TShld), a mechanism that degrades a protein of interest unless it is rescued by the addition of rapamycin, to test this concept. We demonstrated that TShld rapidly yielded only native protein products within 1h after rapamycin addition. The rapid protection phenotype of TShld was further adapted to rescue yeast cytosine deaminase, a prodrug converting enzyme. As expected, cell viability was adversely affected only in the presence of both 5-fluorocytosine (5-FC) and rapamycin. We believe that the DDEPT system can be easily combined with other targeting strategies to further increase the safety of prodrug therapies.

Construction of a novel vector expressing Survivin-shRNA and fusion suicide gene yCDglyTK and its application in inhibiting proliferation and migration of colon cancer cells

Despite progress achieved in cancer chemotherapy in recent decades, adverse effects remain a limiting factor for a number of patients with colorectal cancer, suggesting the requirement for novel therapeutic strategies. Gene therapy appears to be a promising strategy for treating cancer. The present study aimed to investigate the anti-tumor effect of a combined gene therapy, using Survivin downregulation by RNAi and a fusion suicide gene yCDglyTK therapy system. A triple-gene vector expressing Survivin-targeted small hairpin RNA (Survivin-shRNA) and fusion suicide gene yCDglyTK was constructed, and administered to HCT116 cells. Survivin expression decreased significantly and yCDglyTK fusion gene expression was confirmed by both reverse transcription-quantitative polymerase chain reaction and western blot analysis. Introduction of Survivin-shRNA into yCDglyTK/prodrug system eradicated colon cancer cells and induced apoptosis more effectively. Furthermore, this therapeutic system is able to inhibit the migration of HCT116 cells. These results indicate that the recombinant plasmid may serve as a novel gene therapy approach to treat colorectal carcinoma.

Triterpene-loaded microemulsion using Coix lacryma-jobi seed extract as oil phase for enhanced antitumor efficacy: preparation and in vivo evaluation

Ganoderma lucidum triterpene-loaded microemulsions (TMEs) using Coix lacryma-jobi (adlay) seed oil as oil phase were prepared, characterized, and evaluated for enhanced antitumor activity. Ternary phase diagrams for the TMEs were constructed and the optimal preparation was developed. Transmission electron microscopy and dynamic light scattering showed that this formulation had a well defined spherical shape, a homogeneous distribution, a small size, and a narrow polydispersity index. The drug-loading rate was determined to be 9.87% by ultraviolet spectrophotometry, and acceptable stability under various stimulations in vitro was confirmed. Importantly, the TME formulation showed a significantly greater antiproliferative effect towards human lung carcinoma (A549) cells and murine lung tumor (Lewis) cells in comparison with suspension formulations containing triterpene and adlay seed oil as a positive control. The half-maximal inhibitory concentration of the TMEs was about 0.62 mg crude drug per mL, being 2.5-fold improved relative to that of the corresponding suspension formulation, but no significant cytotoxicity was observed for the bare microemulsion in A549 cells and Lewis cells. In vivo, the TME formulation showed markedly enhanced antitumor efficacy in a xenograft model of Lewis lung cancer after intragastric administration. Compared with cyclophosphamide, the TME formulation showed similar antitumor activity but less general toxicity. These results indicate the feasibility of using a microemulsion to increase the solubility of triterpene and adlay. TMEs hold promise as an efficient drug delivery system for the treatment of lung cancer.