Trans-membrane molecular water exchange based SS-DCE-MRI for quantitative proliferation evaluation of glioma

The Aquaporin 4 channel (AQP4), a water-selective membrane protein, plays several important roles in glioma fate determination, including tumor migration, proliferation, and therapy resistance. Currently, traditional biopsy is the sole method to characterize AQP4 expression levels in vivo but lacks spatial information. As strong intratumoral heterogeneity is common for glioma, this results in an incomplete picture of the regional distribution of AQP4. Herein, we describe a novel MRI method to make the AQP4 distribution visible in order to achieve whole-tumor AQP4 mapping.The key principle underlying this approach is to use the AQP4-regulated transmembrane water exchange, a MR measurable quantity, as a linear surrogate for AQP4 expression. For this purpose, we redesigned the dynamic-contrast-enhanced MRI, an old technique widely used in clinics on glioma and other diseases, to quantitatively characterize the intracellular water efflux rate (kio, an intrinsic property of the cell.We show that the AQP4-regulated pathway dominates kio in glioma cell cultures, rat glioma tumor, and eventually human glioma. Furthermore, we demonstrate the power of kio in accurately detecting the dynamic regulation of AQP4 in glioma proliferation stages and following treatment of Temozolomide and AQP4 inhibitor TGN020, and precisely revealing intratumor spatial heterogeneity of AQP4 expression in both the rat glioma model and human glioma (using stereotactic biopsy) in vivo. More importantly, we find that the lower-kio tumor subregions show higher fractions of stem-like slow cycling cells and therapy-resistance phenotypes, suggesting the potential value of the AQP4 map in evaluating therapy-resistance in glioma. In conculusion, we provide a novel way to achieve AQP4 molecular imaging in vivo. Rather than detecting AQP4 directly, we amplify the AQP4 signal by measuring the AQP4-regulated transmembrane water exchange with SS-DCE-MRI. With a customized MRI system for cell culture measurements in vitro and SS-DCE-MRI method for glioma modelsin vivo, we first demonstrated that the AQP4-regulated pathway dominates the kio in C6 and U87MG cell lines (in vitro), rat glioma model (C6, in vivo), and human glioma patients (in vivo). Furthermore, we exhibit the power of SS-DCE-MRI in precisely detecting the dynamic regulation of AQP4 in glioma proliferation stages and TMZ treatment in vitro and the intratumor spatial heterogeneity of AQP4 expression in both rat glioma model and human GBM in vivo. Collectively, transmembrane water exchange can be measured with clinically achievable SS-DCE-MRI without additional cost to patients and we expect this technique will significantly promote the intelligent managment and prognosis prediction of human glioma with future large-scale and multi-center validation.