Radionuclide imaging of perfusion and hypoxia

Radionuclide imaging and therapy directed towards the tumor microenvironment: a multi-cancer approach for personalized medicine

Targeted radionuclide theranostics is becoming more and more prominent in clinical oncology. Currently, most nuclear medicine compounds researched for cancer theranostics are directed towards targets expressed in only a small subset of cancer types, limiting clinical applicability. The identification of cancer-specific targets that are (more) universally expressed will allow more cancer patients to benefit from these personalized nuclear medicine–based interventions. A tumor is not merely a collection of cancer cells, it also comprises supporting stromal cells embedded in an altered extracellular matrix (ECM), together forming the tumor microenvironment (TME). Since the TME is less genetically unstable than cancer cells, and TME phenotypes can be shared between cancer types, it offers targets that are more universally expressed. The TME is characterized by the presence of altered processes such as hypoxia, acidity, and increased metabolism. Next to the ECM, the TME consists of cancer-associated fibroblasts (CAFs), macrophages, endothelial cells forming the neo-vasculature, immune cells, and cancer-associated adipocytes (CAAs). Radioligands directed at the altered processes, the ECM, and the cellular components of the TME have been developed and evaluated in preclinical and clinical studies for targeted radionuclide imaging and/or therapy. In this review, we provide an overview of the TME targets and their corresponding radioligands. In addition, we discuss what developments are needed to further explore the TME as a target for radionuclide theranostics, with the hopes of stimulating the development of novel TME radioligands with multi-cancer, or in some cases even pan-cancer, application.

Non-conventional and Investigational PET Radiotracers for Breast Cancer: A Systematic Review

Breast cancer is one of the most common malignancies in women, with high morbidity and mortality rates. In breast cancer, the use of novel radiopharmaceuticals in nuclear medicine can improve the accuracy of diagnosis and staging, refine surveillance strategies and accuracy in choosing personalized treatment approaches, including radioligand therapy. Nuclear medicine thus shows great promise for improving the quality of life of breast cancer patients by allowing non-invasive assessment of the diverse and complex biological processes underlying the development of breast cancer and its evolution under therapy. This review aims to describe molecular probes currently in clinical use as well as those under investigation holding great promise for personalized medicine and precision oncology in breast cancer.

In vivo evaluation of percutaneous carbon dioxide treatment for improving intratumoral hypoxia using 18F-fluoromisonidazole PET-CT

Carbon dioxide (CO₂) treatment is reported to have an antitumor effect owing to the improvement in intratumoral hypoxia. Previous studies were based on histological analysis alone. In the present study, the improvement in intratumoral hypoxia by percutaneous CO₂ treatment in vivo was determined using ¹⁸F-fluoromisonidazole positron emission tomography-computed tomography (¹⁸F-FMISO PET-CT) images. Twelve Japanese nude mice underwent implantation of LM8 tumor cells in the dorsal subcutaneous area 2 weeks before percutaneous CO₂ treatment and ¹⁸F-FMISO PET-CT scans. Immediately after intravenous injection of ¹⁸F-FMISO, CO₂ and room air were administered transcutaneously in the CO₂-treated group (n=6) and a control group (n=6), respectively; each treatment was performed for 10 minutes. PET-CT was performed 2 h after administration of ¹⁸F-FMISO. ¹⁸F-FMISO tumor uptake was quantitatively evaluated using the maximum standardized uptake value (SUV_max), tumor-to-liver ratio (TLR), tumor-to-muscle ratio (TMR), metabolic tumor volume (MTV) and total lesion glycolysis (TLG). Mean ± standard error of the mean (SEM) of the tumor volume was not significantly different between the two groups (CO₂-treated group, 1.178±0.450 cm³; control group, 1.368±0.295 cm3; P=0.485). Mean ± SEM of SUV_max, TLR, MTV (cm3) and TLG were significantly lower in the CO₂-treated group compared with the control group (0.880±0.095 vs. 1.253±0.071, P=0.015; 1.063±0.147361 vs. 1.455±0.078, P=0.041; 0.353±0.139 vs. 1.569±0.438, P=0.015; 0.182±0.070 vs. 1.028±0.338, P=0.015), respectively. TMR was not significantly different between the two groups (4.520±0.503 vs. 5.504±0.310; P=0.240). In conclusion, ¹⁸F-FMISO PET revealed that percutaneous CO₂ treatment improved intratumoral hypoxia in vivo. This technique enables assessment of the therapeutic effect in CO₂ treatment by imaging, and may contribute to its clinical application.

Can the Efficacy of [18F]FDG-PET/CT in Clinical Oncology Be Enhanced by Screening Biomolecular Profiles?

Positron Emission Tomography (PET) is a functional imaging modality widely used in clinical oncology. Over the years the sensitivity and specificity of PET has improved with the advent of specific radiotracers, increased technical accuracy of PET scanners and incremental experience of Radiologists. However, significant limitations exist—most notably false positives and false negatives. Additionally, the accuracy of PET varies between cancer types and in some cancers, is no longer considered a standard imaging modality. This review considers the relative influence of macroscopic tumour features such as size and morphology on 2-Deoxy-2-[¹⁸F]fluoroglucose ([¹⁸F]FDG) uptake by tumours which, though well described in the literature, lacks a comprehensive assessment of biomolecular features which may influence [¹⁸F]FDG uptake. The review aims to discuss the potential influence of individual molecular markers of glucose transport, glycolysis, hypoxia and angiogenesis in addition to the relationships between these key cellular processes and their influence on [¹⁸F]FDG uptake. Finally, the potential role for biomolecular profiling of individual tumours to predict positivity on PET imaging is discussed to enhance accuracy and clinical utility.

Enhanced Application of 18F-FDG PET/CT in Bladder Cancer by Adding Early Dynamic Acquisition to a Standard Delayed PET Protocol

PURPOSE

We investigated the value of early dynamic (ED) PET for the detection and characterization of bladder cancer.

METHODS

Fifty-two bladder cancer patients were prospectively enrolled. The study protocol was composed of ED, whole-body (WB, 60 minutes after injection), and additional delayed (AD, 120 minutes after injection) PET acquisition. Early dynamic PET was acquired for 10 minutes and reconstructed as 5 frames at 2-minute intervals. A focal radiotracer accumulation confined to the bladder wall was considered as PET positive and referred for further quantitative measurement. SUVmax on ED (SUVmax, SUVmax, SUVmax, SUVmax, and SUVmax for 5 frames), WB (SUVmax), and AD PET (SUVmax) were measured. PET results were correlated with bladder cancer pathology variables.

RESULTS

The sensitivities of ED, WB, and AD PET for bladder cancer were 84.6%, 57.7%, and 61.2%, respectively. The sensitivity of ED PET was significantly higher than that of WB (P = 0.002) and AD PET (P = 0.008). On ED PET, SUVmax was significantly correlated with muscle invasiveness, histological grade, and pathological tumor size (P = 0.018, P = 0.030, and P = 0.030). On WB and AD PET, only pathological tumor size showed significant positive correlation with SUVmax and SUVmax (P = 0.043 and P = 0.007).

CONCLUSIONS

Early dynamic PET can help to detect and characterize bladder cancer.

Intra-arterially infused carbon dioxide-saturated solution for sensitizing the anticancer effect of cisplatin in a rabbit VX2 liver tumor model

The present study aimed to evaluate the efficacy of an intra-arterially infused carbon dioxide (CO2)-saturated solution in sensitizing the anticancer effect of cisplatin in a rabbit VX2 liver tumor model. Forty VX2 liver tumor-bearing Japanese white rabbits were randomly divided into four groups and infused via the proper hepatic artery with a saline solution (control group), CO2-saturated solution (CO2 group), cisplatin solution (cisplatin group), or CO2-saturated solution and cisplatin solution (combined group). The tumor volume (TV) and the relative tumor volume (RTV), RTV = (TV on day 3 or 7)/(TV on day 0) x 100, were calculated using contrast-enhanced computed tomography. Hypoxia-inducible factor-1α (HIF‑1α) and carbonic anhydrase IX (CA IX) staining were used to evaluate cellular hypoxia. Cleaved caspase-3 and cleaved caspase-9 were analyzed to assess tumor apoptosis. The mean RTV on days 3 and 7 were 202.6±23.7 and 429.2±94.8%, respectively, in the control group; 172.2±38.1 and 376.5±61.1% in the CO2 group; 156.1±15.1 and 269.6±45.2% in the cisplatin group; and 118.3±28.1 and 210.3±55.1% in the combined group. RTV was significantly lower in the CO2 group than in the control group (day 3; P<0.05), and in the combined group than in the cisplatin group (days 3 and 7; P<0.05). HIF-1α and CA IX suppression, and increased cleaved caspase-3 and cleaved caspase-9 expression, were detected in the CO2 and combined groups, compared with the other two groups. An intra-arterially infused CO2-saturated solution inhibits liver VX2 tumor growth and sensitizes the anticancer effect of cisplatin.

Whole-body PET/CT evaluation of tumor perfusion using generator-based 62Cu-ethylglyoxal bis(thiosemicarbazonato)copper(II): validation by direct comparison to 15O-water in metastatic renal cell carcinoma

This study was undertaken to demonstrate the feasibility of whole-body (62)Cu-ethylglyoxal bis(thiosemicarbazonato)copper(II) ((62)Cu-ETS) PET/CT tumor perfusion imaging in patients with metastatic renal carcinoma and to validate (62)Cu-ETS as a quantitative marker of tumor perfusion by direct comparison with (15)O-water perfusion imaging.

METHODS

PET/CT imaging of 10 subjects with stage IV renal cell cancer was performed after intravenous administration of (15)O-water (10-min dynamic list-mode study) with the heart and at least 1 tumor in the PET field of view, followed 10 min later by intravenous (62)Cu-ETS (6-min list-mode study). Whole-body (62)Cu imaging was then performed from 6 to 20 min at 2-3 min/bed position. Blood flow (K1) was quantified with both agents for normal and malignant tissues in the 21.7-cm dynamic field of view. The required arterial input functions were derived from the left atrium and, in the case of (62)Cu-ETS, corrected for partial decomposition of the agent by blood with data from an in vitro analysis using a sample of each patient's blood. This imaging protocol was repeated at an interval of 3-4 wk after initiation of a standard clinical treatment course of the antiangiogenic agent sunitinib.

RESULTS

All subjects received the scheduled (62)Cu-ETS doses for the dynamic and subsequent whole-body PET/CT scans, but technical issues resulted in no baseline (15)O-water data for 2 subjects. Direct comparisons of the perfusion estimates for normal tissues and tumor metastases were made in 18 paired baseline and treatment studies (10 subjects; 8 baseline studies, 10 repeated studies during treatment). There was an excellent correlation between the blood flow estimates made with (62)Cu-ETS and (15)O-water for normal tissues (muscle, thyroid, myocardium) and malignant lesions (pulmonary nodules, bone lesions); the regression line was y = 0.85x + 0.15, R(2) = 0.83, for the 88 regions analyzed.

CONCLUSION

(62)Cu-ETS provided high-quality whole-body PET/CT images, and (62)Cu-ETS measures of blood flow were highly and linearly correlated with (15)O-water-derived K1 values (mL(-1) ⋅ min(-1) ⋅ g). This tracer is suitable for use as a PET tracer of tumor perfusion in patients with metastatic renal cell carcinoma.

Hypoxia, blood flow and metabolism in squamous-cell carcinoma of the head and neck: correlations between multiple immunohistochemical parameters and PET

Background

The relationship between the uptake of [¹⁸F]fluoroerythronitroimidazole ([¹⁸F]FETNIM), blood flow ([¹⁵O]H₂O) and 2-[¹⁸F]fluoro-2-deoxyglucose ([¹⁸F]FDG) and immunohistochemically determined biomarkers was evaluated in squamous-cell carcinomas of the head and neck (HNSCC).

Methods

[¹⁸F]FETNIM and [¹⁸F]FDG PET were performed on separate days on 15 untreated patients with HNSCC. Hypoxia imaging with [¹⁸F]FETNIM was coupled with measurement of tumor blood flow using [¹⁵O]H₂O. Uptake of [¹⁸F]FETNIM was measured as tumor-to-plasma ratio (T/P) and fractional hypoxic volume (FHV), and that of [¹⁸F]FDG as standardized uptake value (SUV) and the metabolically active tumor volume (TV). Tumor biopsies were cut and stained for GLUT-1, Ki-67, p53, CD68, HIF-1α, VEGF_sc-152, CD31 and apoptosis. The expression of biomarkers was correlated to PET findings and patient outcome.

Results

None of the PET parameters depicting hypoxia and metabolism correlated with the expression of the biomarkers on a continuous scale. When PET parameters were divided into two groups according to median values, a significant association was detected between [¹⁸F]FDG SUV and p53 expression (p =0.029) using median SUV as the cut-off. There was a significant association between tumor volume and the amount of apoptotic cells (p =0.029). The intensity of VEGF stained cells was associated with [¹⁸F]FDG SUV (p =0.036). Patient outcome was associated with tumor macrophage content (p =0.050), but not with the other biomarkers. HIF-1α correlated with GLUT-1 (r_s =0.553, p =0.040) and Ki-67 with HIF-1α (r_s =506, p =0.065). p53 correlated inversely with GLUT-1 (r_s = −618, p =0.019) and apoptosis with Ki-67 (r_s = −638, p =0.014).

Conclusions

A high uptake of [¹⁸F]FDG expressed as SUV is linked to an aggressive HNSCC phenotype: the rate of apoptosis is low and the expressions of p53 and VEGF are high. None of the studied biomarkers correlated with perfusion and hypoxia as evaluated with [¹⁵O]H₂O-PET and [¹⁸F]FETNIM-PET. Increased tumor metabolism evaluated with PET may thus signify an aggressive phenotype, which should be taken into account in the management of HNSCC.

Modeling of nanotherapeutics delivery based on tumor perfusion

Heterogeneities in the perfusion of solid tumors prevent optimal delivery of nanotherapeutics. Clinical imaging protocols to obtain patient-specific data have proven difficult to implement. It is challenging to determine which perfusion features hold greater prognostic value and to relate measurements to vessel structure and function. With the advent of systemically administered nanotherapeutics, whose delivery is dependent on overcoming diffusive and convective barriers to transport, such knowledge is increasingly important. We describe a framework for the automated evaluation of vascular perfusion curves measured at the single vessel level. Primary tumor fragments, collected from triple-negative breast cancer patients and grown as xenografts in mice, were injected with fluorescence contrast and monitored using intravital microscopy. The time to arterial peak and venous delay, two features whose probability distributions were measured directly from time-series curves, were analyzed using a Fuzzy C-mean (FCM) supervised classifier in order to rank individual tumors according to their perfusion characteristics. The resulting rankings correlated inversely with experimental nanoparticle accumulation measurements, enabling modeling of nanotherapeutics delivery without requiring any underlying assumptions about tissue structure or function, or heterogeneities contained within. With additional calibration, these methodologies may enable the study of nanotherapeutics delivery strategies in a variety of tumor models.

Clinical imaging of tumor angiogenesis

Angiogenesis is an integral part of tumor growth and invasion. This has led to the emergence of several antiangiogenic therapies and stimulated efforts to accurately evaluate the extent of angiogenesis before and in response to anticancer treatment. The most commonly used approach has been the assessment of new vessel formation in histological samples. However, it is becoming apparent that this is insufficient for a full understanding of tumor physiology and for in vivo guidance of cancer management. Imaging has the potential to provide noninvasive and repeatable assessment of the angiogenic process. Imaging approaches use a variety of modalities and are aimed at either assessment of the functional integrity of tumor vasculature or assessment of its molecular status. This review summarizes the aims and methods of clinical tumor angiogenesis imaging, including present technologies and ones that will be developed within the next 5-10 years.

PET Tracers for Clinical Imaging of Breast Cancer

Molecular imaging of breast cancer has undoubtedly permitted a substantial development of the overall diagnostic accuracy of this malignancy in the last years. Accurate tumour staging, design of individually suited therapies, response evaluation, early detection of recurrence and distant lesions have also evolved in parallel with the development of novel molecular imaging approaches. In this context, positron emission tomography (PET) can be probably seen as the most interesting molecular imaging technology with straightforward clinical application for such purposes. Dozens of radiotracers for PET imaging of breast cancer have been tested in laboratory animals. However, in this review we shall focus mainly in the smaller group of PET radiopharmaceuticals that have lead through into the clinical setting. PET imaging can be used to target general metabolic phenomena related to tumoural transformation, including glucose metabolism and cell proliferation, but can also be directed to specific hormone receptors that are characteristic of the breast cancer cell. Many other receptors and transport molecules present in the tumour cells could also be of interest for imaging. Furthermore, molecules related with the tumour microenvironment, tumour induced angiogenesis or even hypoxia could also be used as molecular biomarkers for breast cancer imaging.

Evaluation of breast tumor blood flow with dynamic first-pass 18F-FDG PET/CT: comparison with angiogenesis markers and prognostic factors

The purpose of this study was to prospectively evaluate the relationship between tumor blood flow and glucose metabolism as evaluated by dynamic first-pass (18)F-FDG PET and by proliferation and endothelial pathologic markers in the setting of newly diagnosed breast cancer.

METHODS

Forty patients were prospectively included. Biopsy samples of each tumor were used to assess the Ki67 index of proliferation and immunostaining for CD34 (a panendothelial cell marker) and CD105 (a proliferation-related endothelial cell marker). All patients underwent (18)F-FDG PET/CT at least 1 wk after sample biopsy and before any treatment. A dynamic 2-min acquisition was performed immediately after intravenous injection of a 5 MBq/kg dose of (18)F-FDG; tumor blood flow was then calculated using a single-compartment kinetic model. A static acquisition was performed 90 min after injection for quantification of delayed (18)F-FDG tumor uptake (standardized uptake value maximal index [SUV(max)]), reflecting tumor metabolism.

RESULTS

Pathologic and PET/CT data were available for all patients. The SUV(max) measured on delayed PET images correlated strongly and positively with the expression of Ki67 (r = +0.69; P < 0.0001). In contrast, there was no significant correlation between SUV(max) and endothelial markers (CD34 and CD105). Tumor blood flow correlated positively with the expression of CD34 and CD105 (P = 0.016 and P = 0.007, respectively) and with the expression of Ki67 (P = 0.028). By logistic regression analysis, only expression of Ki67 remained an independent predictor of high (supramedian) SUV(max); CD105 score and histopathologic grade 3 were independently associated with a high (supramedian) tumor blood flow level.

CONCLUSION

Tumor blood flow quantified by dynamic first-pass (18)F-FDG PET/CT is significantly associated with tumor angiogenesis as evaluated by immunohistochemistry in the setting of breast cancer, whereas tumor metabolism appears to be more associated with markers of proliferation. Thus, determination of tumor blood flow and metabolism with a single injection of (18)F-FDG could be an exciting alternative to more complex and less available techniques.

Targeting angiogenesis in ovarian cancer

Results of standard chemotherapy in ovarian cancer are hampered by the development of drug resistance leading to disease recurrence. This prompted interest in the development of therapies targeting critical pathways responsible for tumor progression. Angiogenesis is a key process that enables ovarian cancer growth and metastasis in the peritoneal space. Its regulation relies on signaling mechanisms initiated by the vascular endothelial growth factor, the platelet-derived growth factor, the fibroblast growth factor, angiopoietins, and others. These pathways are not only important to the modulation of the tumor microenvironment and vasculature, but also control cancer cell proliferation and survival. In this review, we discuss preclinical evidence supporting the rationale for inhibiting these pathways and provide an overview for the clinical development of agents targeting them. Clinical trials evaluating such agents alone and in combination with chemotherapy are ongoing. Early clinical results position antiangiogenic therapy at the forefront of change to the standard treatment of difficult to treat ovarian cancer.

MR evaluation of response to targeted treatment in cancer cells

The development of molecular technologies, together with progressive sophistication of molecular imaging methods, has allowed the further elucidation of the multiple mutations and dysregulatory effects of pathways leading to oncogenesis. Acting against these pathways by specifically targeted agents represents a major challenge for current research efforts in oncology. As conventional anatomically based pharmacological endpoints may be inadequate to monitor the tumor response to these targeted treatments, the identification and use of more appropriate, noninvasive pharmacodynamic biomarkers appear to be crucial to optimize the design, dosage and schedule of these novel therapeutic approaches. An aberrant choline phospholipid metabolism and enhanced flux of glucose derivatives through glycolysis, which sustain the redirection of mitochondrial ATP to glucose phosphorylation, are two major hallmarks of cancer cells. This review focuses on the changes detected in these pathways by MRS in response to targeted treatments. The progress and limitations of our present understanding of the mechanisms underlying MRS-detected phosphocholine accumulation in cancer cells are discussed in the light of gene and protein expression and the activation of different enzymes involved in phosphatidylcholine biosynthesis and catabolism. Examples of alterations induced in the MRS choline profile of cells exposed to different agents or to tumor environmental factors are presented. Current studies aimed at the identification in cancer cells of MRS-detected pharmacodynamic markers of therapies targeted against specific conditional or constitutive cell receptor stimulation are then reviewed. Finally, the perspectives of present efforts addressed to identify enzymes of the phosphatidylcholine cycle as possible novel targets for anticancer therapy are summarized.