Stem-like characteristics across sequentially temozolomide-adapted glioblastoma cell populations with increasing...

Acquired temozolomide (TMZ) resistance remains a major challenge in glioblastoma and may involve the emergence or enrichment of cancer stem cell (CSC)-like characteristics. However, whether stem-like characteristics differ across increasing levels of acquired TMZ resistance remains unclear. This study compared stem-like characteristics among parental TMZ-sensitive glioblastoma cells and two sequentially generated TMZ-adapted populations with different levels of acquired TMZ resistance.

Two TMZ-adapted glioblastoma cell populations (U87MG-T5 and U87MG-T67) were established through sequential TMZ exposure of parental U87MG cells. TMZ sensitivity was assessed by determining CC50 values, whereas proliferation was evaluated using population doubling time and viable cell counts. The mRNA expression levels of the aggressiveness-associated genes, vimentin and MMP2, were examined by qRT-PCR. Stem-like characteristics were assessed by measuring spheroid-forming capacity, sphere-initiating cell frequency, CD133 surface expression, and expression of OCT4 and SOX2. Both U87MG-T5 and U87MG-T67 exhibited lower TMZ sensitivity and slower proliferation than U87MG cells, with the most pronounced changes in U87MG-T67. Vimentin and MMP2 mRNA expressions were significantly higher in U87MG-T67, but not in U87MG-T5. Both adapted populations exhibited enhanced spheroid-forming capacity, increased sphere-initiating cell frequency, and higher proportion of CD133 positive cells than TMZ-sensitive cells. SOX2 mRNA expression was upregulated in U87MG-T5, whereas OCT4 mRNA expression was upregulated in U87MG-T67. Descriptive Western blot analysis showed that the SOX2 and OCT4 protein expressions appeared to be highest U87MG-T67.

Both U87MG-T5 and U87MG-T67 showed more pronounced CSC-like characteristics than parental U87MG cells, although they showed different patterns of SOX2 and OCT4 mRNA expression.