Y. Xing1,2, P. J. Li3, and P. Guo1,2; 1Tianjin University, Academy of Medical Engineering and Translational Medicine, Tianjin, China, 2Hangzhou Institute of Medicine (HIM), Chinese Academy of Sciences, Hangzhou, Zhejiang, China, 3Zhejiang cancer hospital, Hangzhou, Zhejiang, China
Purpose/Objective(s):Glioblastoma (GBM), a prevalent malignant brain tumor with 5-y survival rate under 10%, does not respond to the treatment of Depateux-m, a non-cleavable EGFR antibody-drug conjugate (ADC). This study aims to evaluate the pre-clinical efficacy and safety of radiotherapy combined with EGFR-MMAE, an enzyme-cleavable ADC in the treatment of GBM. Materials/
Methods: ADC target expression and internalization were characterized across five glioma cell lines: U87MG, A172, SNB19, U251, and T98G via flow cytometry. Fluorescence confocal microscopy further revealed that EGFR is pivotal in facilitating antibody endocytosis specifically in U87MG and SNB19 cell lines. To investigate therapeutic efficacy, orthotopic human GBM models were established with luciferase-tagged U87MG cells in nude mice, which were then divided into (1) control, (2) radiotherapy (RT), (3) EGFR-MMAE and (4) Combo (RT + EGFR-MMAE) groups. At 20 days post-inoculation with GBM tumors, EGFR-MMAE was administered at 5 mg/kg weekly, and the in vivo imaging system (IVIS) was used for weekly monitoring. Radiotherapy was delivered at a prescribed dose of 2 Gy per fraction (Gy/F), one fraction daily (F/D), for two consecutive weeks (W1-5), totaling an accumulated dose of 20 Gy. Following the 28-day treatment, the survival outcomes of the mice in each group were meticulously documented. Results: EGFR was found ubiquitously upregulated in five glioma cell lines, and it notably facilitated antibody endocytosis in U87MG and SNB19 cell lines. EGFR-MMAE demonstrated potent efficacies across these glioma cell lines, with half-maximal effective concentration (EC50) values ranging between 7.36 to 0.16ยตM. More importantly, the Combo group markedly suppressed tumor proliferation when compared to the other treatment groups. Survival analysis revealed median survival times for the control, radiotherapy alone, EGFR-MMAE alone, and the Combo groups as 39, 51.5, 55.5, and 69 days, respectively. The enhanced survival observed in the group treated with the Combo group was statistically significant in comparison to each of the other groups, indicating superior therapeutic index (Con vs. Combo: P<0.001; RT vs. Combo: P=0.0010; EGFR-MMAE vs. Combo: P<0.001). Conclusion: Our findings indicate that the combination therapy of radiotherapy and an enzyme-cleavable EGFR-MMAE exhibits promising preclinical efficacy against GBM, warranting further clinical investigation.
