Herboxidiene and EGFR expression in A172 glioblastoma cells

Glioblastoma carries a five-year survival of about 10%, and EGFR amplification is one of the molecular criteria that define the disease in the 2021 WHO classification of central nervous system tumours. SF3b inhibitors, which displace the U2 snRNP from the intron branch point, suppress EGFR expression in lung adenocarcinoma cells by causing retention of EGFR intron 2. We asked whether the same route operates in glioblastoma, using A172 cells, which express wild-type EGFR together with an in-frame tandem duplication of exons 18–26. Herboxidiene inhibited A172 proliferation: DMSO-treated cultures reached 2.32 ± 0.61 times their day 0 reading by day 3, whereas every herboxidiene concentration from 0.125 to 1 µM held the cultures at or below their starting value and differed from the vehicle on days 2 and 3 (Dunnett, p < 0.05). RT-PCR across EGFR exons 2–3 showed no intron 2-retained product at any concentration; instead the spliced product decreased relative to ACTB, to 0.43 of the vehicle value at 0.125 µM, without deepening further up to 1 µM. EGFR protein fell, but the two forms behaved differently: the 170 kDa wild-type band was no longer detectable from 0.13 µM, whereas the 190 kDa duplicated form persisted at every concentration and declined only gradually, to 0.30 of the vehicle value at 1 µM. RT-PCR of CDKN1B (p27) showed retention of introns 1 and 2 at 0.5 µM in A172 and in A549 lung adenocarcinoma cells. In A172 cells, therefore, herboxidiene suppresses EGFR expression without the intron 2 retention seen in lung adenocarcinoma lines, and the growth inhibition is not accounted for by loss of EGFR alone.

The proliferation data are the mean ± SD of three series; the RT-PCR and western blot experiments were each performed once, without replicates or statistical testing, and should be read as preliminary.