Abstract 2687: The combination of temozolomide and minocycline for the treatment of glioblastoma
Authors: Arriaga Marco A. , Garcia-Rodriguez Natasha , Ramirez Andrea , Chew Sue Anne 
Published: April 2023

Glioblastoma multiforme (GBM) is the most prevalent and aggressive form of malignant brain tumor and accounts for 49.1% of all central nervous system tumors. Current methods of therapy remain minimally successful as survival rate remains low (only 6.8% of patients surviving 5 years post-diagnosis). Thus, there is a great need to design alternative treatment methods for patients with GBM. Temozolomide (TMZ) is a chemotherapeutic treatment and a first line treatment option for GBM as it has been shown to increase survival time. Minocycline (MINO) is commonly used for its antibiotic properties but has also been proven to have antiangiogenic effects for GBM treatment. The objective of this study was to investigate the additive effects of MINO and TMZ in both GBM (U87) and human umbilical vein endothelial cells (HUVEC) for the treatment of GBM. We hypothesized that the combination of MINO and TMZ will result in lower cell viability and higher protein levels of apoptosis and autophagy markers) compared to the drugs alone and therefore, will be more effective at treating GBM. In this study, U87 and HUVEC cells were treated with MINO and TMZ alone or in combination and a MTT assay was used to determine cell viability by measuring absorbance (570 nm) with a microplate reader. The IC50 values of the drugs were determined from the dose-response curves using GraphPad to compare the sensitivity of each cell line to the drugs. Protein levels of apoptosis (Cas3, PARP) and autophagy (LC3B) markers were determined after treatment of U87 cells with MINO and TMZ alone or in combination using immunoblotting. β-actin was used as a loading control and 0.5% dimethyl sulfoxide was used as a positive autophagy control. Protein bands were detected and visualized with enhanced chemiluminescence reagents. The IC50 of MINO and TMZ were found to be 1688 µM and 1913 µM in U87 cells, and 247 µM and 1162 µM in HUVEC cells, respectively. Although glioma cells result in autophagy and apoptosis when exposed to MINO, MINO’s anti-angiogenic effect may have resulted in heightened sensitivity in HUVEC cells. U87 cells exposed to MINO (1000 µM) resulted in a cell viability of 61% and TMZ (1200 µM) resulted in 60%, while the combination of both drugs resulted in 43% cell viability. HUVEC cells exposed to MINO (200 µM) resulted in a cell viability of 64% and TMZ (30 µM) resulted in 84%, while the combination of both drugs resulted in 44% cell viability, resulting in additive effects for both cell lines. Preliminary results for protein expression analysis show similar expression of apoptotic and autophagy markers in samples with individual and combined drug treatments. In conclusion, this study demonstrated that the combination of MINO and TMZ resulted in additive effects compared to each drug alone and thus, the dual delivery of both drugs from a local delivery system may be a promising therapy for GBM.

Citation Format: Marco A. Arriaga, Natasha Garcia-Rodriguez, Andrea Ramirez, Sue Anne Chew. The combination of temozolomide and minocycline for the treatment of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2687.