Background. Oncolytic strain S. pyogenes GUR (type emm111), a throat isolate from a scarlet fever patient has been used clinically to treat cancer patients in the former Soviet Union for more than 20 years. In order to understand the role of M-protein in the oncolytic activity of the strain the emm knock-out mutant (strain GURSA1) was created.
Methods. GAS strains were studied for oncolytic activity in vitro towards rat glioma C6, hepatoma 22a and pancreatic cancer PANC02 cell lines. To evaluate the safety of the studied strains we performed experiments on normal human fibroblasts. For cytotoxicity evaluation, we used the MTT assay, trypan blue assay and the xCELLigence system. Differences between the groups were analyzed using Mann–Whitney U-test.
Results. Reliable difference in the cytotoxic activity of the strains was observed during the experiments. S. pyogenes GURSA1 demonstrated weaker oncolytic activity in comparison with S. pyogenes GUR (Table 1). Both strains do not have a statistically significant cytotoxic effect on normal human fibroblasts.
Table 1. Cell viability index (%) 4 hours after streptococci exposure
|
|
S. pyogenes GUR |
S. pyogenes GURSA1 |
|
Glioma C6 |
18,6±2,6* |
63,5±8,4* |
|
Hepatoma 22a |
45,0±9,1* |
67,4±4,2* |
|
PANC02 |
32,7±2,7* |
114,3±5,1* |
|
Fibroblasts |
95,7±8,4 |
102,8±5,3 |
* p < 0.05 between the strains (n=3)
Conclusions. M-protein plays a significant role in oncolytic activity of S. pyogenes GUR. Additional studies are required to understand the mechanisms underlying this effect.
This research was funded by the Ministry of Science and Higher Education of the Russian Federation, grant number №075-15-2020-902 (16.11.2020).