Molecular Imaging of Extracellular Tumor pH to Reveal Effects of Locoregional Therapy on Liver Cancer Microenvironment

Abstract

Purpose: To establish magnetic resonance (MR)-based molecular imaging paradigms for the noninvasive monitoring of extracellular pH (pH e ) as a functional surrogate biomarker for metabolic changes induced by locoregional therapy of liver cancer.Experimental Design: Thirty-two VX2 tumor-bearing New Zealand white rabbits underwent longitudinal imaging on clinical 3T-MRI and CT scanners before and up to 2 weeks after complete conventional transarterial chemoembolization (cTACE) using ethiodized oil (lipiodol) and doxorubicin. MR-spectroscopic imaging (MRSI) was employed for pH e mapping. Multiparametric MRI and CT were performed to quantify tumor enhancement, diffusion, and lipiodol coverage of the tumor posttherapy. In addition, incomplete cTACE with reduced chemoembolic doses was applied to mimic undertreatment and exploit pH e mapping to detect viable tumor residuals. Imaging findings were correlated with histopathologic markers indicative of metabolic state (HIF-1a, GLUT-1, and LAMP-2) and viability (proliferating cell nuclear antigen and terminal deoxynucleotidyl-transferase dUTP nick-end labeling).Results: Untreated VX2 tumors demonstrated a significantly lower pH e (6.80 AE 0.09) than liver parenchyma (7.19 AE 0.03, P < 0.001). Upregulation of HIF-1a, GLUT-1, and LAMP-2 confirmed a hyperglycolytic tumor phenotype and acidosis. A gradual tumor pH e increase toward normalization similar to parenchyma was revealed within 2 weeks after complete cTACE, which correlated with decreasing detectability of metabolic markers. In contrast, pH e mapping after incomplete cTACE indicated both acidic viable residuals and increased tumor pH e of treated regions. Multimodal imaging revealed durable tumor devascularization immediately after complete cTACE, gradually increasing necrosis, and sustained lipiodol coverage of the tumor.Conclusions: MRSI-based pH e mapping can serve as a longitudinal monitoring tool for viable tumors. As most liver tumors are hyperglycolytic creating microenvironmental acidosis, therapy-induced normalization of tumor pH e may be used as a functional biomarker for positive therapeutic outcome.

Impact of the acidic environment on gene expression and functional parameters of tumors in vitro and in vivo

“…Lamp2 has been described to be overexpressed in aggressive tumors and to be upregulated in acidosis-adapted tumor cells [ 34 ]. This protein has been proposed as a histologic marker for pathologic correlation with in vivo pH e mapping [ 46 ]. However, in our study Lamp2 was found to be upregulated only in Walker-256 cells and in AT1 tumors (Figs.…”

A high‐throughput imaging platform to characterize extracellular pH in organotypic three‐dimensional in vitro models of liver cancer

“…Three well studied and characterized human hepatic cancer cell lines with varying growth characteristics were used: HepG2 (ATCC, Gaithersburg, MD; catalog no HB‐8065, ), Huh7 (CLS Cell Lines Services, Eppelheim, Germany; catalog no 300156/p7178_HuH7, ), and SNU475 (ATCC; catalog no CRL‐2236, ). Additionally, we used a human hepatocyte cell line derived from primary normal liver cells infected with SV40 large T‐antigen, THLE2 (ATCC; catalog no CRL‐10149, ), and a metastatic liver cancer cell line, VX2 (ATCC; catalog no CRL‐6503, ), which was derived from a sarcoma of a female New Zealand White rabbit, commonly used in a translational rabbit liver cancer model 21,24 . All experiments were performed in mycoplasma‐free cells and human cell lines have been authenticated using short tandem repeat genotype profiling within three years prior to experimental use.…”

“…Therefore, imaging of tumor metabolism in the TME serves as a predictive biomarker for individual susceptibility to oncological treatments. Additionally, it may enable earlier and more sensitive monitoring of tumor response to therapy that precedes morphological changes measurable with conventional anatomical imaging 11 …”

<p>Glucometabolic Reprogramming in the Hepatocellular Carcinoma Microenvironment: Cause and Effect</p>

“…54 Recently scientists have proposed using high-resolution pH mapping to monitor pH e in HCC, which could be a biomarker for metabolic changes and monitoring tumor aggressiveness and therapeutic outcome. [55][56][57] Tumor acidosis is the consequence of lactate and H + ions accumulation, which are produced by glycolysis and oxidative metabolism. Most tumor cells, also called as glycolytic tumor cells, prefer glycolysis rather than OXPHOS, leading to increases in lactate and H + production.…”