Enhanced Anti-Tumor Activity in Mice with Temozolomide-Resistant Human Glioblastoma Cell Line-Derived Xenograft Using SN-38-Incorporated Polymeric Microparticle

Glioblastoma multiforme (GBM) has remained one of the most lethal and challenging cancers to treat. Previous studies have shown encouraging results when irinotecan was used in combination with temozolomide (TMZ) for treating GBM. However, irinotecan has a narrow therapeutic index: a slight dose increase in irinotecan can induce toxicities that outweigh its therapeutic benefits. SN-38 is the active metabolite of irinotecan that accounts for both its anti-tumor efficacy and toxicity. In our previous paper, we showed that SN-38 embedded into 50:50 biodegradable poly[(d,l)-lactide-co-glycolide] (PLGA) microparticles (SMPs) provides an efficient delivery and sustained release of SN-38 from SMPs in the brain tissues of rats. These properties of SMPs give them potential for therapeutic application due to their high efficacy and low toxicity. In this study, we tested the anti-tumor activity of SMP-based interstitial chemotherapy combined with TMZ using TMZ-resistant human glioblastoma cell line-derived xenograft models. Our data suggest that treatment in which SMPs are combined with TMZ reduces tumor growth and extends survival in mice bearing xenograft tumors derived from both TMZ-resistant and TMZ-sensitive human glioblastoma cell lines. Our findings demonstrate that combining SMPs with TMZ may have potential as a promising strategy for the treatment of GBM.

WNK2 Inhibits Autophagic Flux in Human Glioblastoma Cell Line

Autophagy is a cell-survival pathway with dual role in tumorigenesis, promoting either tumor survival or tumor death. WNK2 gene, a member of the WNK (with no lysine (K)) subfamily, acts as a tumor suppressor gene in gliomas, regulating cell migration and invasion; however, its role in autophagy process is poorly explored. The WNK2-methylated human glioblastoma cell line A172 WT (wild type) was compared to transfected clones A172 EV (empty vector), and A172 WNK2 (WNK2 overexpression) for the evaluation of autophagy using an inhibitor (bafilomycin A1—baf A1) and an inducer (everolimus) of autophagic flux. Western blot and immunofluorescence approaches were used to monitor autophagic markers, LC3A/B and SQSTM1/p62. A172 WNK2 cells presented a significant decrease in LC3B and p62 protein levels, and in LC3A/B ratio when compared with control cells, after treatment with baf A1 + everolimus, suggesting that WNK2 overexpression inhibits the autophagic flux in gliomas. The mTOR pathway was also evaluated under the same conditions, and the observed results suggest that the inhibition of autophagy mediated by WNK2 occurs through a mTOR-independent pathway. In conclusion, the evaluation of the autophagic process demonstrated that WNK2 inhibits the autophagic flux in glioblastoma cell line.