Modification of Tryptanthrin Enhances Drug Activity in Glioblastoma Cells

Introduction
Glioblastoma (GBM) is the most aggressive adult brain tumour, with a poor prognosis and limited therapeutic approaches. We recently showed ARHGAP12 regulates cell morphology and contributes to tumour recurrence, with co-expression of ARHGAP29 linked to reduced survival after treatment. As Glycogen Synthase Kinase 3 (GSK-3) signalling regulates this, we hypothesised that targeting ARHGAP12 in combination with migrastatic drugs could enhance GBM cell migration inhibition. Previous investigations showed that tryptanthrin-6-oxime enhanced anti-migratory and anti-invasive efficacy in U251-derived GBM cell lines compared to tryptanthrin. Because tryptanthrin-6-oxime significantly reduced invasion in U251 control cells and ARHGAP12 kd cells, a derivative, tryptanthrin-6-oxime O-acetate (T6OA), was synthesised to enhance migrastatic activity and determine whether temozolomide (TMZ) cytotoxicity could be improved.

Method
Cell viability of control U251-NT and ARHGAP12 kd cells treated with T6OA, TMZ or their combination was determined using MTT assays. Calculated cytotoxic IC50 and migrastatic IC25 concentrations were used in 2D scratch and 3D spheroid invasion assays, followed by immunofluorescence microscopy.

Results
T6OA-treated MTT assays gave IC50 and IC25 values of 16.96 μM and 0.43 μM in U251-NT cells, and 14.15 μM and 4.26 μM in ARHGAP12 kd cells. Untreated scratch and spheroid invasion assays showed greater migration of ARHGAP12 kd cells; however, U251-NT cells migrated more efficiently from the spheroid core in 3D compared with kd cells.

Conclusion
Both U251 cell lines had lower IC50 and IC25 values than those previously obtained for tryptanthrin-6-oxime (U251-NT: IC50 57.68 μM, IC25 42.93 μM; ARHGAP12 kd cells: IC50 51.88 μM, IC25 31.28 μM), suggesting further modification of tryptanthrin increased potency. Potentiation of TMZ activity following the addition of anti-migratory drugs suggests T6OA combined with TMZ presents a promising approach in advancing therapeutic GBM intervention.