Depletion of telomerase RNA inhibits growth of gastrointestinal tumors transplanted in mice

Aim: To explore effects of Telomerase RNA-targeting phosphorothioate antisense oligodeoxynucleotides (PS-ASODN) on growth of human gastrointestinal stromal tumors transplanted in mice.

Methods: A SCID mouse model for transplantation of human gastrointestinal stromal tumors (GISTs) was established using tumor cells from a patient who was diagnosed with GIST and consequently had been treated with imatinib. GIST cells cultured for 10 passages were used for inoculation into mice. Transfection of PS-ASODN was carried out with Lipotap Liposomal Transfection Reagent. GISTs that subsequently developed in SCID mice were subjected to intra-tumoral injection once daily from day 7 to day 28 post-inoculation, and mice were divided into the following four groups according to treatment: PS-ASODN group (5.00 μmoL/L of oligonucleotide, each mouse received 0.2 mL once daily); imatinib group (0.1 mg/g body weight); Liposome negative control group (0.01 mL/g); and saline group (0.01 mL/g). On day 28, the mice were sacrificed, and tumor attributes including weight and longest and shortest diameters were measured. Tumor growth was compared between treatment groups, and Telomerase activity was measured by enzyme-linked immunosorbent assay. Apoptosis was examined by flow cytometry. Real-time polymerase chain reaction was used to detect expression of the mRNA encoding the Apoptosis inhibition B-cell leukemia/lymphoma 2 (Bcl-2) gene.

Results: In the PS-ASODN group, tumor growth was inhibited by 59.437%, which was markedly higher than in the imatinib group (11.071%) and Liposome negative control group (2.759%) [tumor inhibition = (mean tumor weight of control group--mean tumor weight of treatment group)/(mean tumor weight of control group) × 100%]. Telomerase activity was significantly lower (P < 0.01) in the PS-ASODN group (0.689 ± 0.158) compared with the imatinib group (1.838 ± 0.241), Liposome negative control group (2.013 ± 0.273), and saline group (2.004 ± 0.163). Flow cytometry revealed that the Apoptosis rate of tumor cells treated with PS-ASODN was 20.751% ± 0.789%, which was higher (P < 0.01) than that of the imatinib group (1.163% ± 0.469%), Liposome negative control group (1.212% ± 0.310%), and saline group (1.172% ± 0.403%). Expression of Bcl-2 mRNA in the transplanted GISTs was markedly downregulated (P < 0.01) in the PS-ASODN group (7.245 ± 0.739) compared with the imatinib group (14.153 ± 1.618) and Liposome negative control group (16.396 ± 1.351).

Conclusion: PS-ASODN can repress GIST growth, mediated perhaps by inhibition of Telomerase activity and downregulation of Bcl-2 expression.