Selective Synergy of the Combination of Recombinant Methioninase With Cisplatinum and Ivermectin Which Eradicates Lung-Cancer Cells but Has No Synergy and Limited Effect on Normal Fibroblasts.

[BACKGROUND/AIM] Lung cancer remains one of the leading causes of cancer-related mortality worldwide due to its high incidence and poor prognosis. Although targeted therapies and immunotherapies have advanced, survival outcomes remain unsatisfactory for lung-cancer patients. Recombinant methioninase (rMETase), which targets methionine addiction, a fundamental and general hallmark of cancer, has demonstrated synergistic efficacy with chemotherapeutic agents in numerous cancer types. We have previously shown synergy of rMETase and ivermectin against pancreatic-, colon-, and breast-cancer cells. The present study aimed to investigate the synergistic efficacy of rMETase in combination with cisplatinum and ivermectin on lung-cancer cells compared to normal fibroblasts.

[MATERIALS AND METHODS] The human lung-adenocarcinoma cell line A549 and normal human-fibroblast cell strain Hs27 were seeded in 96-well plates (1,000 cells/well) containing Dulbecco's Modified Eagle's medium and incubated for 24 h. The cells were then treated for 72 h with rMETase (0.0625-8 U/ml), cisplatinum (0.25-32 μM), or ivermectin (1-128 μM). Cell viability was assessed using the WST-8 assay, and the 30% inhibitory concentration (IC) for each drug was calculated for both cell types. To evaluate synergy, both cell types were treated with each drug alone or in two-drug and three-drug combinations based on their respective IC values, and cell viability was measured. To assess the time-dependent effects of the triple-combination treatment, A549 lung-cancer cells and Hs27 fibroblasts were cultured under the same conditions and treated with the triple combination. Cell viability was then measured at 24, 48, 72, and 96 h after treatment initiation.

[RESULTS] The IC value of rMETase was 0.46 U/ml; cisplatinum was 0.33 μM; and ivermectin was 2.08 μM for A549 lung-cancer cells. For normal Hs27 fibroblasts the IC value for rMETase was 0.5 units/ml; for cisplatinum was 0.35 μM and for ivermectin was 6.4 μM. When these 3 agents were combined at their respective A549 IC concentrations, A549 cell viability was significantly reduced compared to monotherapy or dual combinations (<0.05), indicating synergy. In contrast, triple-combination-treatment using the A549 IC values or the Hs27 IC values, had minimal effect and no synergy on Hs27 normal fibroblasts, demonstrating selectivity for cancer cells. Furthermore, for A549 cells, the triple-combination therapy significantly decreased cell viability as early as 24 h after treatment initiation (<0.05), and essentially eradicated the lung-cancer cells with minimal effect on the normal fibroblasts during this time period.

[CONCLUSION] The present study demonstrated that the combination of rMETase, cisplatinum, and ivermectin exerts selective synergy on lung-cancer cells, which was not observed on normal fibroblasts. Moreover, the present combination therapy has a strong synergistic efficacy at early time points on the lung-cancer cells. Further studies are warranted to elucidate the underlying mechanisms of synergy of the present combination treatment selectively on cancer cells and to evaluate the efficacy and safety of the present treatment strategy.