Engineered Methioninase-expressing Tumor-targeting A1-R Inhibits Syngeneic-Cancer Mouse Models by Depleting Tumor Methionine.

Background/aim: We previously developed A1-R, which selectively targets and kills tumors. In the present study, we established recombinant methioninase (rMETase)-producing A1-R (A1-R-rMETase), by transfer of the gene, to target methionine addiction of syngeneic-cancer mouse models.

Materials And Methods: A plasmid containing the gene was extracted from METase-producing recombinant and inserted into A1-R using electroporation. Lewis Lung Carcinoma (LLC) cells (10) were injected subcutaneously in male C57BL/6 mice aged 4-6 weeks. We determined that 10 A1-R-rMETase administered iv was a safe dosage in C57BL/6 mice and was used for efficacy studies on LLC tumors in C57BL/6 mice. Tumor size was measured with calipers three times per week for 3 weeks. On day 22, tumor methionine levels were measured using HPLC in the control mice injected with phosphate-buffered saline (PBS) and the mice injected with A1-R-rMETase.

Results: The mean LLC tumor size of each group on day 22 was as follows: PBS control: 741.5 mm; mice injected with A1-R: 566.3 mm (=0.370); and mice injected with A1-R-rMETase: 198.8 mm (=0.0003 control and =0.0117 A1-R). The mice injected with A1-R-rMETase showed a significantly lower mean tumor methionine level than mice injected with PBS (5.9 nM/mg protein 11.1 nM/mg protein, =0.0095). A1-R-rMETase grew continuously in the tumors but not in the liver or spleen.

Conclusion: Tumor-targeting A1-R engineered to express the gene, inhibited LLC tumor growth in a syngeneic mouse model and reduced the methionine level in the tumor. A1-R-rMETase combines the tumor targeting and killing capability of A1-R plus rMETase which targets the methionine addiction of cancer.