BIOM-14. TRANSMEMBRANE WATER EFFLUX RATE (<i>K</i>IO) IS AN MRI-DETECTABLE BIOMARKER TO EVALUATE THE EFFICIENCY OF TTFIELDS TREATMENT ON GLIOBLASTOMA

Abstract BACKGROUND Tumor Treating Fields (TTFields) has emerged as an effective treatment modality for Glioblastoma, shown to improve both OS and PFS. Yet how to monitor response to TTFields remains unclear. In this study, we proposed using transmembrane water efflux rate (kio), a non-invasive biomarker detectable in conventional MRI and reflecting cell membrane permeability, to assess the treatment efficiency of TTFields. METHODS U-87 MG human glioblastoma cell line were treated with TTFields at frequency of 200 kHz and varying field strengths of 0 V/cm, 0.8 V/cm, 1.2 V/cm and 1.6 V/cm using the inovitro system from Novocure. The measurement of kio was performed on a 0.5 T benchtop MRI system (Pure Devices GmbH) using a home-developed filter-exchange imaging (FEXI) sequence. Cell membrane morphology were quantitatively analysed using scanning electron microscopy. Patients with newly diagnosed glioblastoma (ndGBM) who underwent DCE-MRI before and after TTFields treatment were identified and the change of FEXI-kio value were analysed. RESULTS In the same frequency, the effect of TTFields on cancer cell proliferation is dependent on intensity, manifested a decrease in cell growth rate under high electric field intensity. As the TTFields electric field intensity increased, the cell membrane permeability (kio) also increased, exhibits a significant negative correlation with glioblastoma cell growth rate (p=0.031). Scanning electron microscopy reveals that TTFields can induce significant cell membrane pores, and the total surface area of membrane pores correlates significantly positively with FEXSY-kio index. DCE-MRI data obtained from 4 ndGBM before and after TTFields therapy showed that the FEXI-kio value is increased after TTFields treatment. CONCLUSION This study demonstrated that TTFields increases membrane permeability by inducing cell membrane holes, and kio is a promising non-invasive MRI biomarker to evaluate the efficiency of TTFields treatment.