The reverse Warburg effect and 18F-FDG uptake in non-small cell lung cancer A549 in mice: a pilot study

Imaging assessment of toxicity related to immune checkpoint inhibitors

In recent years, a wide range of cancer immunotherapies have been developed and have become increasingly important in cancer treatment across multiple oncologic diseases. In particular, immune checkpoint inhibitors (ICIs) offer promising options to improve patient outcomes. However, a major limitation of these treatments consists in the development of immune-related adverse events (irAEs) occurring in potentially any organ system and affecting up to 76% of the patients. The most frequent toxicities involve the skin, gastrointestinal tract, and endocrine system. Although mostly manageable, potentially life-threatening events, particularly due to neuro-, cardiac, and pulmonary toxicity, occur in up to 30% and 55% of the patients treated with ICI-monotherapy or -combination therapy, respectively. Imaging, in particular computed tomography (CT), magnetic resonance imaging (MRI), and 2-deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT), plays an important role in the detection and characterization of these irAEs. In some patients, irAEs can even be detected on imaging before the onset of clinical symptoms. In this context, it is particularly important to distinguish irAEs from true disease progression and specific immunotherapy related response patterns, such as pseudoprogression. In addition, there are irAEs which might be easily confused with other pathologies such as infection or metastasis. However, many imaging findings, such as in immune-related pneumonitis, are nonspecific. Thus, accurate diagnosis may be delayed underling the importance for adequate imaging features characterization in the appropriate clinical setting in order to provide timely and efficient patient management. ¹⁸F-FDG-PET/CT and radiomics have demonstrated to reliably detect these toxicities and potentially have predictive value for identifying patients at risk of developing irAEs. The purpose of this article is to provide a review of the main immunotherapy-related toxicities and discuss their characteristics on imaging.

Innovative strategies for photodynamic therapy against hypoxic tumor

Photodynamic therapy (PDT) is applied as a robust therapeutic option for tumor, which exhibits some advantages of unique selectivity and irreversible damage to tumor cells. Among which, photosensitizer (PS), appropriate laser irradiation and oxygen (O₂) are three essential components for PDT, but the hypoxic tumor microenvironment (TME) restricts the O₂ supply in tumor tissues. Even worse, tumor metastasis and drug resistance frequently happen under hypoxic condition, which further deteriorate the antitumor effect of PDT. To enhance the PDT efficiency, critical attention has been received by relieving tumor hypoxia, and innovative strategies on this topic continue to emerge. Traditionally, the O₂ supplement strategy is considered as a direct and effective strategy to relieve TME, whereas it is confronted with great challenges for continuous O₂ supply. Recently, O₂-independent PDT provides a brand new strategy to enhance the antitumor efficiency, which can avoid the influence of TME. In addition, PDT can synergize with other antitumor strategies, such as chemotherapy, immunotherapy, photothermal therapy (PTT) and starvation therapy, to remedy the inadequate PDT effect under hypoxia conditions. In this paper, we summarized the latest progresses in the development of innovative strategies to improve PDT efficacy against hypoxic tumor, which were classified into O₂-dependent PDT, O₂-independent PDT and synergistic therapy. Furthermore, the advantages and deficiencies of various strategies were also discussed to envisage the prospects and challenges in future study.

Effect of Glut-1 and HIF-1α double knockout by CRISPR/CAS9 on radiosensitivity in laryngeal carcinoma via the PI3K/Akt/mTOR pathway

Hypoxic resistance is the main obstacle to radiotherapy for laryngeal carcinoma. Our previous study indicated that hypoxia-inducible factor 1α (HIF-1α) and glucose transporter 1 (Glut-1) double knockout reduced tumour biological behaviour in laryngeal carcinoma cells. However, their radioresistance mechanism remains unclear. In this study, cell viability was determined by CCK8 assay. Glucose uptake capability was evaluated by measurement of ¹⁸ F-fluorodeoxyglucose radioactivity. A tumour xenograft model was established by subcutaneous injection of Tu212 cells. Tumour histopathology was determined by haematoxylin and eosin staining, immunohistochemical staining, and TUNEL assays. Signalling transduction was evaluated by Western blotting. We found that hypoxia induced radioresistance in Tu212 cells accompanied by increased glucose uptake capability and activation of the PI3K/Akt/mTOR pathway. Inhibition of PI3K/Akt/mTOR activity abolished hypoxia-induced radioresistance and glucose absorption. Mechanistic analysis revealed that hypoxia promoted higher expressions of HIF-1α and Glut-1. Moreover, the PI3K/Akt/mTOR pathway was a positive mediator of HIF-1α and/or Glut-1 in the presence of irradiation. HIF-1α and/or Glut-1 knockout significantly reduced cell viability, glucose uptake and PI3K/Akt/mTOR activity, all of which were induced by hypoxia in the presence of irradiation. In vivo analysis showed that knockout of HIF-1α and/or Glut-1 also inhibited tumour growth by promoting cell apoptosis, more robustly compared with the PI3K inhibitor wortmannin, particularly in tumours with knockout of both HIF-1α and Glut-1. HIF-1α and/or Glut-1 knockout also abrogated PI3K/Akt/mTOR signalling transduction in tumour tissues, in a manner similar to wortmannin. HIF-1α and/or Glut-1 knockout facilitated radiosensitivity in laryngeal carcinoma Tu212 cells by regulation of the PI3K/Akt/mTOR pathway.

ATG4B Inhibitor UAMC-2526 Potentiates the Chemotherapeutic Effect of Gemcitabine in a Panc02 Mouse Model of Pancreatic Ductal Adenocarcinoma

Resistance against anti-cancer therapy is one of the major challenges during treatment of multiple cancers. Gemcitabine is a standard first-line chemotherapeutic drug, yet autophagy is highly activated in the hypoxic microenvironment of solid tumors and enhances the survival of tumor cells against gemcitabine chemotherapy. Recently, we showed the add-on effect of autophagy inhibitor UAMC-2526 to prevent HT-29 colorectal tumor growth in CD1^-/- Foxn1nu mice treated with oxaliplatin. In this study, we aimed to investigate the potential beneficial effects of UAMC-2526 in a syngeneic Panc02 mouse model of pancreatic ductal adenocarcinoma (PDAC). Our data showed that UAMC-2526 combined with gemcitabine significantly reduced tumor growth as compared to the individual treatments. However, in contrast to in vitro experiments with Panc02 cells in culture, we were unable to detect autophagy inhibition by UAMC-2526 in Panc02 tumor tissue, neither via western blot analysis of autophagy markers LC3 and p62, nor by transmission electron microscopy. In vitro experiments revealed that UAMC-2526 enhances the potential of gemcitabine to inhibit Panc02 cell proliferation without obvious induction of cell death. Altogether, we conclude that although the combination treatment of UAMC-2526 with gemcitabine did not inhibit autophagy in the Panc02 mouse model, it has a beneficial effect on tumor growth inhibition.

Likely Common Role of Hypoxia in Driving 18F-FDG Uptake in Cancer, Myocardial Ischemia, Inflammation and Infection

First introduced in 1976, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) has become an indispensable tool for diagnosis and prognostic evaluation of tumors, heart disease, as well as other conditions, including inflammation and infection. Because ¹⁸F-FDG can accurately reflect the glucose metabolism level of organs and tissues, it is known as a "century molecule" and is currently the main agent for PET imaging. The degree of ¹⁸F-FDG uptake by cells is related to both the rate of glucose metabolism and glucose transporter expression. These, in turn, are strongly influenced by hypoxia, in which cells meet their energy needs through glycolysis, and ¹⁸F-FDG uptake increased due to hypoxia. ¹⁸F-FDG uptake is a complex process, and hypoxia may be one of the fundamental driving forces. The correct interpretation of ¹⁸F-FDG uptake in PET imaging can help clinics make treatment decisions more accurately and effectively. In this article, we review the application of ¹⁸F-FDG PET in tumors, myocardium, and inflammation. We discuss the relationship between ¹⁸F-FDG uptake and hypoxia, the possible mechanism of ¹⁸F-FDG uptake caused by hypoxia, and the associated clinical implications.

Hypoxia and the Tumor Microenvironment

Hypoxia is an important feature of the tumor microenvironment, and is closely associated with cell proliferation, angiogenesis, metabolism and the tumor immune response. All these factors can further promote tumor progression, increase tumor aggressiveness, enhance tumor metastatic potential and lead to poor prognosis. In this review, these effects of hypoxia on tumor biology will be discussed, along with their significance for tumor detection and treatment.

HRD1 attenuates the high uptake of [18F]FDG in hepatocellular carcinoma PET imaging

INTRODUCTION

Due to individual deviations in tumor tissue uptake, the role of [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography (PET) in hepatocellular carcinoma (HCC) diagnosis is limited. β-Hydroxy β-methylglutaryl-CoA reductase degradation 1 (HRD1) plays a key role in clearing misfolded proteins. This study is aimed to investigate the role and mechanism of HRD1 in [18F]FDG uptake for the diagnosis of HCC.

METHODS

HRD1 expression level was detected using immunohistochemical (IHC) staining in 9 HCC patients. [18F]FDG PET/CT scans were conducted before treatment. [18F]FDG uptakes in HRD1 overexpressed and knockdown transgenic models were measured by γ-counter and microPET imaging. The GLUT1-HRD1 complex was examined by co-immunoprecipitation and IHC assays. GLUT1 expression in different cell lines, xenograft models and HCC patients was evaluated by Western blot and IHC assays.

RESULTS

HRD1 was highly expressed in the HCC tumors of patients with low [18F]FDG uptake, while the HRD1 expression was obviously low in the higher [18F]FDG uptake group. Both in vitro and in vivo studies found that HRD1 significantly inhibited [18F]FDG uptake in HCC Huh7 cell lines and animal models. Furthermore, the co-location and interaction of HRD1 with GLUT1 were detected, and the results also indicate that HRD1 could induce the degradation of GLUT1 in vitro and in vivo.

CONCLUSION

HRD1 inhibits the high uptake of [18F]FDG in HCC tumor cells by inducing degradation of GLUT1, which leads to decreased diagnostic efficiency of [18F]FDG PET imaging for HCC.

ADVANCES IN KNOWLEDGE

This study suggests that HRD1 inhibits the high uptake of [18F]FDG in HCC tumor by inducing degradation of GLUT1.

IMPLICATIONS FOR PATIENT CARE

HCC diagnosis with [18F]FDG PET should be accompanied by determination of HRD1 expression, and patients with high tumor HRD1 expression might be unsuitable for [18F]FDG PET.

Glycolysis-Related Genes Serve as Potential Prognostic Biomarkers in Clear Cell Renal Cell Carcinoma

Metabolic rearrangement is a marker of cancer that has been widely studied in recent years. One of the major metabolic characteristics of tumor cells is the high levels of glycolysis, even under aerobic conditions, a phenomenon that is called the "Warburg effect." We investigated the expression and copy number variation (CNV) frequency of all glycolysis-related genes in multiple cancer types and found many differentially expressed genes, particularly in clear cell renal cell carcinoma (ccRCC). Single nucleotide variants (SNVs) showed that the overall average mutation frequency for all genes was low. The purpose of this study was to establish a predictive model by studying glycolysis-related genes in ccRCC. We compared the expression of glycolysis-related genes in 539 ccRCC tissues and 72 normal renal tissues from The Cancer Genome Atlas dataset and identified 17 upregulated and 26 downregulated genes. Pathway analysis revealed that PSAT1 and SDHB could activate the cell cycle, RPIA could activate the DNA damage response, and HK3 could activate apoptosis and EMT signaling, while PDK2 could inhibit apoptosis. The results of the drug sensitivity analysis suggested that some of these differentially expressed genes were positively correlated with drug sensitivity. Thirteen genes were selected from the gene coexpression network and the LASSO regression analysis. The Kaplan-Meier overall survival curves showed that the expression of upregulated genes in ccRCC patients was associated with lower overall survival. We established a predictive model consisting of 13 genes (RPIA, G6PD, PSAT1, ENO2, HK3, IDH1, PDK4, PGM2, PGK1, FBP1, OGDH, SUCLA2, and SUCLG2). This predictive model correlated well with the development and progression of ccRCC. Thus, it is of great value in the diagnosis and prognostic evaluation of ccRCC and may aid the identification of potential prognostic biomarkers and drug targets.

Human Bone Marrow Mesenchymal Stem Cells Modified Hybrid Baculovirus-Adeno-Associated Viral Vectors Targeting 131I Therapy of Hypopharyngeal Carcinoma

Hypopharyngeal carcinoma is one of the most aggressive subtypes of squamous cell carcinoma of the head and neck. Although significant progress has been made in surgical techniques, radiotherapy, and chemotherapy, the prognosis is still poor. Mesenchymal stem cells (MSCs) have attracted substantial attention as tumor-targeted cellular carriers for cancer gene therapy. We have previously shown that recombinant baculovirus-adeno-associated vectors (BV-AAV) possessed high efficiency for multi-gene coexpression in human bone marrow MSCs (BMSCs) and BV-AAV-engineered BMSCs could effectively target hypopharyngeal cancer tissues in vivo. However, it was not clear whether BV-AAV-engineered BMSCs as cellular vehicles, mediating the expression of the sodium iodide symporter (NIS), would be effective in controlling the growth of hypopharyngeal carcinoma by radioiodine therapy. We constructed a hybrid BV-AAV containing the Luc-P2A-eGFP fusion or NIS sequence to modify BMSCs (BMSCs-Bac-Luc-P2A-eGFP or BMSCs-Bac-NIS). The ¹²⁵I uptake of BMSCs-Bac-NIS was analyzed by an automatic gamma counter in vitro and micro-single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging in vivo. The value of radioiodine therapy for hypopharyngeal carcinoma was evaluated by measuring tumor volume, glucose metabolism (via 2-deoxy-2-[¹⁸F] glucose [¹⁸F-FDG] positron emission tomography/CT), and proliferation of tumor cells. We demonstrated that ¹²⁵I uptake of BMSCs-Bac-NIS persists over long-term in vitro (at least 8 h). Radioactive uptake could be detected by SPECT/CT 1 h after ¹²⁵I injection in the BMSCs-Bac-NIS group, showing that this strategy allows for the tracking of real-time migration and transgene expression of BMSCs. Radioiodine therapy resulted in a significant reduction in tumor growth (386.93 ± 249.23 mm³ vs 816.56 ± 213.87 mm³ in controls), increased survival, and decreased SUVmax of ¹⁸F-FDG. The hybrid BV-AAV that can provide a variety of genes and regulatory elements, as a novel gene therapy strategy opens the prospect of NIS-mediated radionuclide therapy of hypopharyngeal carcinoma after MSC-mediated gene delivery.

The Effect of Carbogen Breathing on 18F-FDG Uptake in Non-Small-Cell Lung Cancer

It has been reported that ¹⁸F-FDG uptake is higher in hypoxic cancer cells than in well-oxygenated cells. We demonstrated that ¹⁸F-FDG uptake in lung cancer would be affected by high concentration oxygen breathing. Methods. Overnight fasted non-small-cell lung cancer A549 subcutaneous (s.c.) xenografts bearing mice (n = 10) underwent ¹⁸F-FDG micro-PET scans, animals breathed room air on day 1, and same animals breathed carbogen (95% O₂ + 5% CO₂) on the subsequent day. In separated studies, autoradiography and immunohistochemical staining visualization of frozen section of A549 s.c. tumors were applied, and to compare between carbogen-breathing mice and those with air breathing, a combination of ¹⁸F-FDG and hypoxia marker pimonidazole was injected 1 h before animal sacrifice, and ¹⁸F-FDG accumulation was compared with pimonidazole binding and glucose transporter 1 (GLUT-1) expression. Results. PET studies revealed that tumor ¹⁸F-FDG uptake was significantly decreased in carbogen-breathing mice than those with air breathing (P < 0.05). Ex vivo studies confirmed that carbogen breathing significantly decreased hypoxic fraction detected by pimonidazole staining, referring to GLUT-1 expression, and significantly decreased ¹⁸F-FDG accumulation in tumors. Conclusions. High concentration of O₂ breathing during ¹⁸F-FDG uptake phase significantly decreases ¹⁸F-FDG uptake in non-small-cell lung cancer A549 xenografts growing in mice.

Cancer-associated fibroblasts modify lung cancer metabolism involving ROS and TGF-β signaling

Lung cancer is a major public health problem due to its high incidence and mortality rate. The altered metabolism in lung cancer is key for the diagnosis and has implications on both, the prognosis and the response to treatments. Although Cancer-associated fibroblasts (CAFs) are one of the major components of the tumor microenvironment, little is known about their role in lung cancer metabolism. We studied tumor biopsies from a cohort of 12 stage IIIA lung adenocarcinoma patients and saw a positive correlation between the grade of fibrosis and the glycolysis phenotype (Low PGC-1α and High GAPDH/MT-CO1 ratio mRNA levels). These results were confirmed and extended to other metabolism-related genes through the in silico data analysis from 73 stage IIIA lung adenocarcinoma patients available in TCGA. Interestingly, these relationships are not observed with the CAFs marker α-SMA in both cohorts. To characterize the mechanism, in vitro co-culture studies were carried out using two NSCLC cell lines (A549 and H1299 cells) and two different fibroblast cell lines. Our results confirm that a metabolic reprogramming involving ROS and TGF-β signaling occurs in lung cancer cells and fibroblasts independently of α-SMA induction. Under co-culture conditions, Cancer-Associated fibroblasts increase their glycolytic ability. On the other hand, tumor cells increase their mitochondrial function. Moreover, the differential capability among tumor cells to induce this metabolic shift and also the role of the basal fibroblasts Oxphos Phosphorylation (OXPHOS) function modifying this phenomenon could have implications on both, the diagnosis and prognosis of patients. Further knowledge in the mechanism involved may allow the development of new therapies.

How to Modulate Tumor Hypoxia for Preclinical In Vivo Imaging Research

Tumor hypoxia is related with tumor aggressiveness, chemo- and radiotherapy resistance, and thus a poor clinical outcome. Therefore, over the past decades, every effort has been made to develop strategies to battle the negative prognostic influence of tumor hypoxia. For appropriate patient selection and follow-up, noninvasive imaging biomarkers such as positron emission tomography (PET) radiolabeled ligands are unprecedentedly needed. Importantly, before being able to implement these new therapies and potential biomarkers into the clinical setting, preclinical in vivo validation in adequate animal models is indispensable. In this review, we provide an overview of the different attempts that have been made to create differential hypoxic in vivo cancer models with a particular focus on their applicability in PET imaging studies.

High expression of synthesis of cytochrome c oxidase 2 and TP53-induced glycolysis and apoptosis regulator can predict poor prognosis in human lung adenocarcinoma

Synthesis of cytochrome c oxidase 2 (SCO2) and TP53-induced glycolysis and apoptosis regulator (TIGAR) are 2 p53-mediated proteins that can play a regulatory role in cancer energy metabolism. However, no study has examined the association of SCO2 and TIGAR with the prognosis of patients with lung adenocarcinoma (AC). In our study, the expression of SCO2 and TIGAR proteins in lung AC was detected, and the potential relation to prognosis was evaluated, aiming to take a further view of lung AC progression. Quantum dots-based immunofluorescence histochemistry staining was performed to observe the expression of p53, SCO2, and TIGAR in 75 specimens of lung AC. Of these, 51 (68.0%) showed high expression of SCO2, and 59 (78.7%) showed high expression of TIGAR. High TIGAR expression was significantly associated with a history of smoking (P = .017) and being male (P = .006). The correlation between high SCO2 expression and age also was significant (P = .042). Moreover, high TIGAR expression was positively correlated with high SCO2 expression (P = .019; r_s = 0.271). High expression of the SCO2 and TIGAR proteins predicted poorer survival and a higher mortality rate (P = .024 and .030, respectively). High expression of SCO2 and TIGAR proteins is significantly associated with lung AC progression, suggesting their potential use as prognostic markers and therapeutic targets.

Revisit 18F-fluorodeoxyglucose oncology positron emission tomography: "systems molecular imaging" of glucose metabolism

¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography has become an important tool for detection, staging and management of many types of cancer. Oncology application of ¹⁸F-FDG bases on the knowledge that increase in glucose demand and utilization is a fundamental features of cancer. Pasteur effect, Warburg effect and reverse Warburg effect have been used to explain glucose metabolism in cancer. ¹⁸F-FDG accumulation in cancer is reportedly microenvironment-dependent, ¹⁸F-FDG avidly accumulates in poorly proliferating and hypoxic cancer cells, but low in well perfused (and proliferating) cancer cells. Cancer is a heterogeneous and complex “organ” containing multiple components, therefore, cancer needs to be investigated from systems biology point of view, we proposed the concept of “systems molecular imaging” for much better understanding systems biology of cancer.

This article revisits ¹⁸F-FDG uptake mechanisms, its oncology applications and the role of ¹⁸F-FDG PET for “systems molecular imaging”.

miR-125b regulates differentiation and metabolic reprogramming of T cell acute lymphoblastic leukemia by directly targeting A20

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematopoietic malignancy. Although it has been reported that overexpression of miR-125b leads to T-ALL development, the underlying mechanisms of miR-125b action are still unclear. The goal of this study is to delineate the role of miR-125b in T-ALL development. We found that miR-125b is highly expressed in undifferentiated leukemic T cells (CD4-negative) while its expression is low in differentiated T cells (CD4-positive). Overexpression of miR-125b increased the CD4-negative population in T cells, whereas depletion of miR-125b by miR-125b-sponge decreased the CD4-negative cell population. We identified that A20 (TNFAIP3) is a direct target of miR-125b in T cells. Overexpression of miR-125b also increased glucose uptake and oxygen consumption in T cells through targeting A20. Furthermore, restoration of A20 in miR-125b-overexpressing cells decreased the CD4-negative population in T cell leukemia, and decreased glucose uptake and oxygen consumption to the basal level of T cells transfected with vector. In conclusion, our data demonstrate that miR-125b regulates differentiation and reprogramming of T cell glucose metabolism via targeting A20. Since both de-differentiation and dysregulated glucose metabolism contribute to the development of T-cell leukemia, these findings provide novel insights into the understanding and treatment of T-ALL.

Cancer-associated fibroblasts enhance tumor 18F-FDG uptake and contribute to the intratumor heterogeneity of PET-CT

Purpose: Elevated glucose uptake is a hallmark of cancer. Fluorodeoxyglucose (FDG) uptake was believed to indicate the aggressiveness of tumors and the standardized uptake value (SUV) is a well-known measurement for FDG uptake in positron emission tomography-computed tomography (PET/CT). However, the SUV is variable due to the heterogeneity of tumors. Methods: 126 patients with colorectal cancer underwent ¹⁸F-FDG PET/CT scanning before surgery between Jan 2011 and April 2016. Cancer-associated fibroblast (CAF) densities were calculated with the inForm Advanced image analysis software and were comparatively analyzed between patients with high and low maximum SUV (SUVmax-high and SUVmax-low). Glucose uptake was evaluated in induced and isolated CAFs and CAF-cocultured colon cancer HCT116 cells. Moreover, micro-PET/CT was performed on xenografted tumors and autoradiography was performed in the AOM/DSS induced colon cancer model. Results: CAFs were glycolytic, evidenced by glucose uptake and upregulated HK2 expression. Compared to non-activated fibroblasts (NAFs), CAFs were more dependent on glucose and sensitive to a glycolysis inhibitor. CAFs increased the SUVmax in xenograft tumors and spontaneous colon cancers. Moreover, multivariate analysis revealed that the SUVmax was only associated with tumor size among conventional parameters in colon cancer patients (126 cases, p = 0.009). Besides tumor size, the CAF density was the critical factor associated with SUVmax and outcome, which was 2.27 ± 0.74 and 1.68 ± 0.45 in the SUVmax-high and the SUVmax-low groups, respectively (p = 0.014). Conclusion: CAFs promote tumor progression and increase SUVmax of ¹⁸F-FDG, suggesting CAFs lead to the intratumor heterogeneity of the SUV and the SUVmax is a prognostic marker for cancer patients.

The Use of PET Imaging for Prognostic Integrin α2β1 Phenotyping to Detect Non-Small Cell Lung Cancer and Monitor Drug Resistance Responses

PURPOSE: Growing evidence has demonstrated that aberrant expression of integrin α2β1 might contribute to the invasion, metastasis and drug resistance of non-small cell lung cancer (NSCLC). Thus, the integrin α2β1 targeting ⁶⁸Ga-DOTA-A2B1 tracer was validated in NSCLC in contrast to accumulation of the clinically used ¹⁸F-FDG PET tracer to see if ⁶⁸Ga-DOTA-A2B1-PET imaging can offer a valuable and critical diagnostic imaging criterion for the identification of phenotypes of aggressive lung cancer.

METHODS: To verify the prognostic value of integrin α2β1, several quantitative and functional in vitro assays were validated in different NSCLC cell lines (CL1-0, CL1-5, A549 and selected A549⁺⁺ cells). Positron emission tomography (PET) imaging studies using both standard ¹⁸F-FDG and a newly developed ⁶⁸Ga-labeled integrin α2β1 (⁶⁸Ga-DOTA-A2B1) tracer were sequentially performed on mice with lung tumor xenografts in different anatomic locations (subcutaneous, orthotopic and osseous) to validate the targeting capability of the ⁶⁸Ga-DOTA-A2B1 tracers. Treatment responses were monitored by injecting animals with metastatic bone tumors with 5 mg/kg doxorubicin. All in vivo treatment responses in each treatment subgroup were monitored with a PET imaging system to evaluate the up-regulation of integrin expression at the earliest stage of treatment (6 h).

RESULTS: The PET and computed tomography (CT) images from NSCLC xenograft animals unambiguously demonstrated accumulation of the integrin tracer ⁶⁸Ga-DOTA-A2B1 in the tumor lesions at all locations. The average tumor uptake and tumor-to-normal (T/N) ratio were 2.51 ± 0.56 %ID/g and T/N = 2.82, 3.40 ± 0.42 %ID/g and T/N = 1.52, and 1.58 ± 0.108 %ID/g and T/N = 2.31 in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). The xenograft tumors were all clearly visible. In contrast, the accumulation of ¹⁸F-FDG reached 3.6 ± 0.76 %ID/g, 1.39 ± 0.075 %ID/g and 3.78 ± 0.73 %ID/g in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). However, due to the high background uptake by normal tissue, the T/N values were less than or close to 1, making the tumors almost indistinguishable in the PET imaging analysis. Furthermore, ⁶⁸Ga-DOTA-A2B1-PET imaging of the treated osseous tumor model demonstrated more than 19% tracer uptake in A549 lesions (1.72 ± 0.95 %ID/g vs. pretreatment 1.44 ± 0.12 %ID/g,p = 0. 015) 6 h post-treatment with doxorubicin. The elevated intensity of tracer uptake was in accordance with the results of in vitroWestern blot and ex vivo integrin staining, demonstrating elevated integrin α2β1 expression.

CONCLUSION: In this study, integrin α2β1 was identified as a biomarker of aggressive malignant NSCLC. Thus, efforts should be devoted to validating integrin α2β1 as a potential target for non-invasive diagnosis and as a predictive marker for monitoring treatment responses using a preclinical PET imaging system.

Mismatched intratumoral distribution of [18F] fluorodeoxyglucose and 3'-deoxy-3'-[18F] fluorothymidine in patients with lung cancer

In a mouse model of human lung cancer, intratumoral distribution between 3′-deoxy-3′-[¹⁸F] fluorothymidine (¹⁸F-FLT) and [¹⁸F] fluorodeoxyglucose (¹⁸F-FDG) was mutually exclusive. ¹⁸F-FLT primarily accumulated in proliferating cancer cells, whereas ¹⁸F-FDG accumulated in hypoxic cancer cells. The aim of the present study was to evaluate these preclinical findings in patients with lung cancer. A total of 55 patients with solitary pulmonary lesion were included in the present study. Patients underwent ¹⁸F-FLT positron emission tomography-computed tomography (PET/CT) and ¹⁸F-FDG PET/CT scan with a 3-day interval. The final diagnosis was based on histological examination. Among the 55 cases, a total of 24 cases were confirmed as malignant lesions. Mismatched ¹⁸F-FLT- and ¹⁸F-FDG-accumulated regions were observed in 19 cases (79%) and matched in 5 (21%). Among the 31 benign lesions, ¹⁸F-FLT and ¹⁸F-FDG were mismatched in 12 cases (39%) and matched in 19 (61%). The difference in intratumoral distribution of ¹⁸F-FLT and ¹⁸F-FDG between malignant and benign lesions was statistically significant (P<0.05). The results of the present study indicate that a mismatch in intratumoral distribution of ¹⁸F-FLT and ¹⁸F-FDG may be a feature of patients with lung cancer. Increased ¹⁸F-FDG accumulation may serve as an indicator of tumor hypoxia, whereas regions with increased ¹⁸F-FLT uptake may be associated with an increased rate of cancer cell proliferation in patients with lung cancer.

Cytoplasmic GPER translocation in cancer-associated fibroblasts mediates cAMP/PKA/CREB/glycolytic axis to confer tumor cells with multidrug resistance

Multiple drug resistance is a challenging issue in the clinic. There is growing evidence that the G-protein-coupled estrogen receptor (GPER) is a novel mediator in the development of multidrug resistance in both estrogen receptor (ER)-positive and -negative breast cancers, and that cancer-associated fibroblasts (CAFs) in the tumor microenvironment may be a new agent that promotes drug resistance in tumor cells. However, the role of cytoplasmic GPER of CAFs on tumor therapy remains unclear. Here we first show that the breast tumor cell-activated PI3K/AKT (phosphoinositide 3-kinase/AKT) signaling pathway induces the cytoplasmic GPER translocation of CAFs in a CRM1-dependent pattern, and leads to the activation of a novel estrogen/GPER/cAMP/PKA/CREB signaling axis that triggers the aerobic glycolysis switch in CAFs. The glycolytic CAFs feed the extra pyruvate and lactate to tumor cells for augmentation of mitochondrial activity, and this energy metabolically coupled in a 'host-parasite relationship' between catabolic CAFs and anabolic cancer cells confers the tumor cells with multiple drug resistance to several conventional clinical treatments including endocrine therapy (tamoxifen), Her-2-targeted therapy (herceptin) and chemotherapy (epirubicin). Moreover, the clinical data from 18F-fluorodeoxyglucose positron emission tomography/computed tomography further present a strong association between the GPER/cAMP/PKA/CREB pathway of stromal fibroblasts with tumor metabolic activity and clinical treatment, suggesting that targeting cytoplasmic GPER in CAFs may rescue the drug sensitivity in patients with breast cancer. Thus, our data define novel insights into the stromal GPER-mediated multiple drug resistance from the point of reprogramming of tumor energy metabolism and provide the rationale for CAFs as a promising target for clinical therapy.

Metabolic coupling in urothelial bladder cancer compartments and its correlation to tumor aggressiveness

Monocarboxylate transporters (MCTs) are vital for intracellular pH homeostasis by extruding lactate from highly glycolytic cells. These molecules are key players of the metabolic reprogramming of cancer cells, and evidence indicates a potential contribution in urothelial bladder cancer (UBC) aggressiveness and chemoresistance. However, the specific role of MCTs in the metabolic compartmentalization within bladder tumors, namely their preponderance on the tumor stroma, remains to be elucidated. Thus, we evaluated the immunoexpression of MCTs in the different compartments of UBC tissue samples (n = 111), assessing the correlations among them and with the clinical and prognostic parameters. A significant decrease in positivity for MCT1 and MCT4 occurred from normoxic toward hypoxic regions. Significant associations were found between the expression of MCT4 in hypoxic tumor cells and in the tumor stroma. MCT1 staining in normoxic tumor areas, and MCT4 staining in hypoxic regions, in the tumor stroma and in the blood vessels were significantly associated with UBC aggressiveness. MCT4 concomitant positivity in hypoxic tumor cells and in the tumor stroma, as well as positivity in each of these regions concomitant with MCT1 positivity in normoxic tumor cells, was significantly associated with an unfavourable clinicopathological profile, and predicted lower overall survival rates among patients receiving platinum-based chemotherapy. Our results point to the existence of a multi-compartment metabolic model in UBC, providing evidence of a metabolic coupling between catabolic stromal and cancer cells' compartments, and the anabolic cancer cells. It is urgent to further explore the involvement of this metabolic coupling in UBC progression and chemoresistance.

(18)F-fluoromisonidazole PET reveals spatial and temporal heterogeneity of hypoxia in mouse models of human non-small-cell lung cancer

AIM

To noninvasively observe dynamic changes in tumor hypoxia in mouse models of human non-small-cell lung cancer (NSCLC) using (18)F-fluoromisonidazole PET.

MATERIALS & METHODS

Nude mice with NSCLC H460 and A549 subcutaneous xenografts were coinjected intravenously with (18)F-fluoromisonidazole and the hypoxia marker pimonidazole, and observed by serial PET scans. After sacrifice, the tumor distribution of (18)F-fluoromisonidazole and pimonidazole was compared by digital autoradiography and microscopy, respectively.

RESULTS

The NSCLC hypoxic microenvironment was spatially heterogeneous. Serial PET scans over 48 h revealed an apparent change in the intratumoral distribution of (18)F-fluoromisonidazole.

CONCLUSION

The tumor hypoxic microenvironment is spatially and temporally heterogeneous, and hypoxic cancer cells have a shorter life span when growing in vivo. Therefore, the concept of hypoxic resistance and hypoxia-targeting therapy of macroscopic tumors should be revisited.

Is carbonic anhydrase IX a validated target for molecular imaging of cancer and hypoxia?

The presence of hypoxia is a general feature of most solid malignancies, and hypoxia is considered as one of major factors for anticancer therapy failure. Carbonic anhydrase IX (CAIX) has been reported to be an endogenous hypoxia marker, CAIX monoclonal antibodies, their segments and inhibitors are developed for CAIX imaging. However, growing evidence indicates that CAIX expression under hypoxia condition may be cancer cell lines or cancer-type dependent. Here we review the current literature on CAIX and discuss the advantage and limitation of CAIX as a target for tumor hypoxia imaging. Accordingly, CAIX would be unreliable as a universal target for cancer and tumor hypoxia visualization.