Non-invasive assessment of human tumour hypoxia with 123I-iodoazomycin arabinoside: preliminary report of a clinical study

Optimized Carbohydrate-Based Nanogel Formulation to Sensitize Hypoxic Tumors

Solid tumors are often poorly vascularized, which impairs oxygen supply and drug delivery to the cells. This often leads to genetic and translational adaptations that promote tumor progression, invasion, metastasis, and resistance to conventional chemo-/radiotherapy and immunotherapy. A hypoxia-directed nanosensitizer formulation of a hypoxia-activated prodrug (HAP) was developed by encapsulating iodoazomycin arabinofuranoside (IAZA), a 2-nitroimidazole nucleoside-based HAP, in a functionally modified carbohydrate-based nanogel, facilitating delivery and accrual selectively in the hypoxic head and neck and prostate cancer cells. Although IAZA has been reported as a clinically validated hypoxia diagnostic agent, recent studies have pointed to its promising hypoxia-selective anti-tumor properties, which make IAZA an excellent candidate for further exploration as a multimodal theranostic of hypoxic tumors. The nanogels are composed of a galactose-based shell with an inner core of thermoresponsive (di(ethylene glycol) methyl ethyl methacrylate) (DEGMA). Optimization of the nanogels led to high IAZA-loading capacity (≅80-88%) and a slow time-controlled release over 50 h. Furthermore, nanoIAZA (encapsulated IAZA) displayed superior in vitro hypoxia-selective cytotoxicity and radiosensitization in comparison to free IAZA in the head and neck (FaDu) and prostate (PC3) cancer cell lines. The acute systemic toxicity profile of the nanogel (NG1) was studied in immunocompromised mice, indicating no signs of toxicity. Additionally, growth inhibition of subcutaneous FaDu xenograft tumors was observed with nanoIAZA, demonstrating that this nanoformulation offers a significant improvement in tumor regression and overall survival compared to the control.

Blood-Brain Barrier, Cell Junctions, and Tumor Microenvironment in Brain Metastases, the Biological Prospects and Dilemma in Therapies

Brain metastasis is the most commonly seen brain malignancy, frequently originating from lung cancer, breast cancer, and melanoma. Brain tumor has its unique cell types, anatomical structures, metabolic constraints, and immune environment, which namely the tumor microenvironment (TME). It has been discovered that the tumor microenvironment can regulate the progression, metastasis of primary tumors, and response to the treatment through the particular cellular and non-cellular components. Brain metastasis tumor cells that penetrate the brain–blood barrier and blood–cerebrospinal fluid barrier to alter the function of cell junctions would lead to different tumor microenvironments. Emerging evidence implies that these tumor microenvironment components would be involved in mechanisms of immune activation, tumor hypoxia, antiangiogenesis, etc. Researchers have applied various therapeutic strategies to inhibit brain metastasis, such as the combination of brain radiotherapy, immune checkpoint inhibitors, and monoclonal antibodies. Unfortunately, they hardly access effective treatment. Meanwhile, most clinical trials of target therapy patients with brain metastasis are always excluded. In this review, we summarized the clinical treatment of brain metastasis in recent years, as well as their influence and mechanisms underlying the differences between the composition of tumor microenvironments in the primary tumor and brain metastasis. We also look forward into the feasibility and superiority of tumor microenvironment-targeted therapies in the future, which may help to improve the strategy of brain metastasis treatment.

Hypoxia and its Modification in Bladder Cancer: Current and Future Perspectives

Radiotherapy plays an essential role in the curative treatment of muscle-invasive bladder cancer (MIBC). Hypoxia affects the response to MIBC radiotherapy, limiting radiocurability. Likewise, hypoxia influences MIBC genetic instability and malignant progression being associated with metastatic disease and a worse prognosis. Hypoxia identification in MIBC enables treatment stratification and the promise of improved survival. The most promising methods are histopathological markers such as necrosis; biomarkers of protein expression such as HIF-1α, GLUT-1 and CAIX; microRNAs; and novel mRNA signatures. Although hypoxia modification can take different forms, the gold standard remains carbogen and nicotinamide, which improve local control rates in bladder preservation and absolute overall survival with no significant increase in late toxicity. This is an exciting time for evolving therapies such as bioreductive agents, novel oxygen delivery techniques, immunotherapy and poly (ADP-ribose) polymerase 1 (PARP) inhibitors, all in development and representing upcoming trends in MIBC hypoxia modification. Whatever the future holds for hypoxia-modified radiotherapy, there is no doubt of its importance in MIBC. mRNA signatures provide an ideal platform for the selection of those with hypoxic tumours but are yet to qualified and integrated into the clinic. Future interventional trials will require biomarker stratification to ensure optimal treatment response to improve outcomes for patients with MIBC.

Short-Term Environmental Conditioning Enhances Tumorigenic Potential of Triple-Negative Breast Cancer Cells

Tumor microenvironments expose cancer cells to heterogeneous, dynamic environments by shifting availability of nutrients, growth factors, and metabolites. Cells integrate various inputs to generate cellular memory that determines trajectories of subsequent phenotypes. Here we report that short-term exposure of triple-negative breast cancer cells to growth factors or targeted inhibitors regulates subsequent tumor initiation. Using breast cancer cells with different driver mutations, we conditioned cells lines with various stimuli for 4 hours before implanting these cells as tumor xenografts and quantifying tumor progression by means of bioluminescence imaging. In the orthotopic model, conditioning a low number of cancer cells with fetal bovine serum led to enhancement of tumor-initiating potential, tumor volume, and liver metastases. Epidermal growth factor and the mTORC1 inhibitor ridaforolimus produced similar but relatively reduced effects on tumorigenic potential. These data show that a short-term stimulus increases tumorigenic phenotypes based on cellular memory. Conditioning regimens failed to alter proliferation or adhesion of cancer cells in vitro or kinase signaling through Akt and ERK measured by multiphoton microscopy in vivo, suggesting that other mechanisms enhanced tumorigenesis. Given the dynamic nature of the tumor environment and time-varying concentrations of small-molecule drugs, this work highlights how variable conditions in tumor environments shape tumor formation, metastasis, and response to therapy.

Hypoxia Mediates Tumor Malignancy and Therapy Resistance

Hypoxia is a hallmark of the tumor microenvironment and contributes to tumor malignant phenotypes. Hypoxia-inducible factor (HIF) is a master regulator of intratumoral hypoxia and controls hypoxia-mediated pathological processes in tumors, including angiogenesis, metabolic reprogramming, epigenetic reprogramming, immune evasion, pH homeostasis, cell migration/invasion, stem cell pluripotency, and therapy resistance. In this book chapter, we reviewed the causes and types of intratumoral hypoxia, hypoxia detection methods, and the oncogenic role of HIF in tumorigenesis and chemo- and radio-therapy resistance.

Pharmacokinetics and Scintigraphic Imaging of the Hypoxia-Imaging Agent [123I]IAZA in Healthy Adults Following Exercise-Based Cardiac Stress †

The objective of this work is to evaluate the potential effect of cardiac stress exercise on the accumulation of [¹²³I]IAZA, a radiopharmaceutical used to image focal tissue hypoxia, in otherwise normal myocardium in healthy volunteers, and to determine the impact of exercise on [¹²³I]IAZA pharmacokinetics. The underlying goal is to establish a rational basis and a baseline for studies of focal myocardial hypoxia in cardiac patients using [¹²³I]IAZA. Three healthy male volunteers ran the ‘Bruce’ treadmill protocol, a clinically-accepted protocol designed to expose myocardial ischemia in patients. The ‘Bruce’ criterion heart rate is 85% of [220–age]. Approximately one minute before reaching this level, [¹²³I]IAZA (5.0 mCi/0.85 mg) was administered as a slow (1–3 min) single intravenous (i.v.) injection via an indwelling venous catheter. The volunteer continued running for an additional 1 min before being transferred to a gamma camera. Serum samples were collected from the arm contralateral to the administration site at pre-determined intervals from 1 min to 45 h post injection and were analyzed by radio HPLC. Pharmacokinetic (PK) parameters were derived for [¹²³I]IAZA and total radioactivity (total[¹²³I]) using compartmental and noncompartmental analyses. Whole-body planar scintigraphic images were acquired from 0.75 to 24 h after dosing. PK data and scintigraphic images were compared to previously published [¹²³I]IAZA data from healthy volunteers rest. Following exercise stress, both [¹²³I]IAZA and total[¹²³I] exhibited bi-exponential decline profiles, with rapid distribution phases [half-lives (t_1/2α) of 1.2 and 1.4 min, respectively], followed by slower elimination phases [t_1/2β of 195 and 290 min, respectively]. Total body clearance (CL_TB) and the steady state volume of distribution (V_ss) were 0.647 L/kg and 185 mL/min, respectively, for [¹²³I]IAZA and 0.785 L/kg and 135 mL/min, respectively, for total[¹²³I]. The t_1/2β, CL_TB and V_ss values were comparable to those reported previously for rested volunteers. The t_1/2α was approximately 4-fold shorter for [¹²³I]IAZA and approximately 3-fold shorter for total[¹²³I] under exercise relative to rested subjects. The heart region was visualized in early whole body scintigraphic images, but later images showed no accumulated radioactivity in this region, and no differences from images reported for rested volunteers were apparent. Minimal uptake of radiotracer in myocardium and skeletal muscle was consistent with uptake in non-stressed myocardium. Whole-body scintigrams for [¹²³I]IAZA in exercise-stressed healthy volunteers were indistinguishable from images of non-exercised volunteers. There was no evidence of hypoxia-dependent binding in exercised but otherwise healthy myocardium, supporting the conclusion that exercise stress at Bruce protocol intensity does not induce measurable myocardial hypoxia. Effects of exercise on PK parameters were minimal; specifically, the t_1/2α was shortened, reflecting increased cardiac output associated with exercise. It is concluded that because [¹²³I]IAZA was not metabolically bound in exercise-stressed myocardium, a stress test will not create elevated myocardial background that would mask regions of myocardial perfusion deficiency. [¹²³I]IAZA would therefore be suitable for the detection of viable, hypoxic myocardium in patients undergoing stress-test-based diagnosis.

The chemistry and radiochemistry of hypoxia-specific, radiohalogenated nitroaromatic imaging probes

Hypoxia is prevalent in many solid tumors. Hypoxic tumors tend to exhibit rapid growth and aberrant vasculature, which lead to oxygen (O2) depletion and impaired drug delivery. The reductive environment in hypoxic tumors alters cellular metabolism, which can trigger transcriptional responses; induce genetic alterations; promote invasion, metastasis, resistance to radiotherapy and chemotherapy, tumor progression, and recurrence; and leads to poor local control and reduced survival rates. Therefore, exploiting the reductive microenvironment in hypoxic tumors by delivering electron-affinic, O2-mimetic radioactive drugs that bioreductively activate selectively in the hypoxic microenvironment offers a logical approach to molecular imaging of focal hypoxia. Because these agents also radiosensitize hypoxic cells, they provide an innovative approach to the therapy management of such tumors. To date, nuclear imaging of hypoxic tumor has proven to be clinically effective, whereas chemical radiosensitization by these compounds has not been helpful. The current review provides an insight into the chemistry, radiochemistry, and purification strategies for selected nitroaromatics that directly exploit the bioreductive environment in hypoxic cells. Both experimental and calculated single-electron reduction potentials of electron-affinic compounds, nitroimidazoles in particular, correlate with in vitro radiosensitizing properties, making them preferred choices for use as radiopharmaceuticals for diagnostic imaging and as sensitizers to enhance the killing effects of low-energy-transfer x-rays (O2-mimetic radiosensitization). Extensive research and careful drug design have led to the development of several potentially useful hypoxia-targeting drugs, for example, [(18)F]FAZA, [(18)F]FMISO, [(18)F]EF5, and [(123)I]IAZA, that accrue selectively in hypoxic cells. These molecular probes are now globally used in clinical hypoxia imaging, including cancer. Future innovative developments must, however, consider hypoxia-selective molecular processes and the physicochemical properties of the drugs that dictate their biodistribution, hypoxia-selective accumulation, pharmacokinetics, clearance, biochemical behavior, and metabolism. This will facilitate their ultimate transformation to effective molecular theranostics, leading to improved multimodal management of cancer.

Hypoxia imaging agents labeled with positron emitters

Imaging hypoxia using positron emission tomography (PET) is of great importance for therapy of cancer. [(18)F]Fluoromisonidazole (FMISO) was the first PET agent for hypoxia imaging, and various radiolabeled nitroimidazole derivatives such as [(18)F]fluoroerythronitroimidazole (FETNIM), [(18)F]1-α-D: -(2-deoxy-2-fluoroarabinofuranosyl)-2-nitroimidazole (FAZA), [(18)F]2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide (EF-5), and [(18)F]fluoroetanidazole (FETA) have been developed successively. To overcome the high cost of cyclotron installation, (68)Ga-labeled nitroimidazole derivatives also have been developed. Another important hypoxia imaging agent is (64)Cu-diacetyl-bis(N (4)-methylthiosemicarbazone) ((64)Cu-ATSM), which can distribute in cancer tissue rapidly due to high lipophilicity. However, its application is limited due to high cost of radionuclide production. Although various hypoxia imaging agents have been reported and tested, hypoxia PET images still have to be improved, because of the low blood flow in hypoxic tissues and resulting low uptake of the agents.

Stroma targeting nuclear imaging and radiopharmaceuticals

Malignant transformation of tumor accompanies profound changes in the normal neighboring tissue, called tumor stroma. The tumor stroma provides an environment favoring local tumor growth, invasion, and metastatic spreading. Nuclear imaging (PET/SPECT) measures biochemical and physiologic functions in the human body. In oncology, PET/SPECT is particularly useful for differentiating tumors from postsurgical changes or radiation necrosis, distinguishing benign from malignant lesions, identifying the optimal site for biopsy, staging cancers, and monitoring the response to therapy. Indeed, PET/SPECT is a powerful, proven diagnostic imaging modality that displays information unobtainable through other anatomical imaging, such as CT or MRI. When combined with coregistered CT data, [(18)F]fluorodeoxyglucose ([(18)F]FDG)-PET is particularly useful. However, [(18)F]FDG is not a target-specific PET tracer. This paper will review the tumor microenvironment targeting oncologic imaging such as angiogenesis, invasion, hypoxia, growth, and homing, and also therapeutic radiopharmaceuticals to provide a roadmap for additional applications of tumor imaging and therapy.

Imaging tumour physiology and vasculature to predict and assess response to heat

The vascular supply of tumours and the tumour microenvironment both play an important role when tumours are treated with hyperthermia. Blood flow is one of the major vehicles by which heat is dissipated thus the vascular supply will influence the ability to heat the tumour. It also influences the type of microenvironment that exists within tumours, and it is now well-established that cells existing in areas of oxygen deficiency, nutrient deprivation and acidic conditions are more sensitive to the effect of hyperthermia. The vascular supply and microenvironment are also affected by hyperthermia. In general, mild heat temperatures transiently improve blood flow and oxygenation, while higher hyperthermia temperatures cause vascular collapse and so increase the adverse microenvironmental conditions. Being able to image these vascular and microenvironmental parameters both before and after heating will help in our ability to predict and assess response. Here we review the various techniques that can be applied to supply this information, especially using non-invasive imaging approaches.

Molecular imaging of hypoxia with radiolabelled agents

Tissue hypoxia results from an inadequate supply of oxygen (O₂) that compromises biological functions. Structural and functional abnormalities of the tumour vasculature together with altered diffusion conditions inside the tumour seem to be the main causes of tumour hypoxia. Evidence from experimental and clinical studies points to a role for tumour hypoxia in tumour propagation, resistance to therapy and malignant progression. This has led to the development of assays for the detection of hypoxia in patients in order to predict outcome and identify patients with a worse prognosis and/or patients that would benefit from appropriate treatments. A variety of invasive and non-invasive approaches have been developed to measure tumour oxygenation including oxygen-sensitive electrodes and hypoxia marker techniques using various labels that can be detected by different methods such as positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), autoradiography and immunohistochemistry. This review aims to give a detailed overview of non-invasive molecular imaging modalities with radiolabelled PET and SPECT tracers that are available to measure tumour hypoxia.

Phase II study of tirapazamine, cisplatin, and etoposide and concurrent thoracic radiotherapy for limited-stage small-cell lung cancer: SWOG 0222

PURPOSE

A SWOG pilot study (S0004) showed that tirapazamine (TPZ) when combined with concurrent chemoradiotherapy yielded a promising median survival of 22 months in limited-stage small-cell lung cancer (LSCLC). We report results of the phase II study designed to confirm this result.

PATIENTS AND METHODS

The concurrent phase consisted of two cycles of cisplatin, etoposide, and once-daily radiation to 61 Gy. TPZ was given at 260 mg/m(2) on days 1, 29, and at 160 mg/m(2) on days 8, 10, 12, 36, 38, and 40. Consolidation consisted of two cycles of cisplatin and etoposide. Complete responders received prophylactic cranial irradiation. Results were considered promising if the median survival time was at least 21 months and of no further interest if < or = 14 months.

RESULTS

S0222 was closed early due to a report of excess toxicity for TPZ in a head and neck cancer trial elsewhere. Of planned 85 patients, 69 were accrued. In 68 assessable patients, 17 (25%) had grade 3 to 4 esophagitis and eight (12%) had grade 3 febrile neutropenia during the concurrent phase. There were three possible treatment-related deaths, two in concurrent phase (one progressive disease not otherwise specified within 30 days, one pericardial effusion) and one in consolidation phase (esophageal hemorrhage). At a median follow-up of 35 months, median progression-free survival was 11 months (95% CI, 10 to 13 months) and median overall survival was 21 months (95% CI, 17 to 33 months).

CONCLUSION

S0222 showed acceptable levels of toxicity and similar promising median survival as S0004. Further study of hypoxia-targeted therapy is warranted in LSCLC.

Radiosynthesis of [(131)I]IAZGP via nucleophilic substitution and its biological evaluation as a hypoxia marker - is specific activity a factor influencing hypoxia-mapping ability of a hypoxia marker?

INTRODUCTION

The hypoxia marker IAZGP, 1-(6-deoxy-6-iodo-beta-d-galactopyranosyl)-2-nitroimidazole, has been labeled with (123)I/(124)I/(125)I/(131)I via iodine-radioiodine exchange, which gives the radiotracer in a specific activity of 10-90 MBq/micromol. We synthesized the same radiotracer possessing several hundred to thousand times higher specific activity (high-SA IAZGP) via nucleophilic substitution and compared its biological behavior with that of conventionally produced IAZGP (low-SA IAZGP) to determine if specific activity is a factor influencing cell uptake kinetics, biodistribution and intratumor microregional localization of the radiotracer.

METHODS

High-SA [(131)I]IAZGP was prepared by substitution of the tosyl functionality with [(131)I]iodide. In vitro uptake of high- and low-SA [(131)I]IAZGP by HCT8 and HT29 cells was assessed in normoxic and hypoxic conditions. Biodistribution and intratumor localization of high- and low-SA [(131)I]IAZGP were determined by injection into HT29 tumor-bearing mice.

RESULTS

The nucleophilic substitution reaction proceeded efficiently in acetonitrile at 150 degrees C, giving the final product in an average yield of 42% and an average specific activity of 30 GBq/micromol. In vitro, high-SA [(131)I]IAZGP was incorporated into the tumor cells with similar kinetics and oxygen dependence to low-SA [(131)I]IAZGP. In HT29 tumor-bearing mice, biodistributions of high- and low-SA [(131)I]IAZGP were equivalent. Ex vivo autoradiography revealed heterogeneous intratumor localization of high-SA [(131)I]IAZGP corresponding closely to distributions of other exogenous and endogenous hypoxia markers. Comparable microregional distribution patterns were observed with low-SA [(131)I]IAZGP.

CONCLUSIONS

Radiolabeled IAZGP produced via nucleophilic substitution is validated as an exogenous hypoxia marker. Specific activity does not appear to influence the in vivo hypoxia-mapping ability of the radiotracer.

Applications of nitroimidazole in vivo hypoxia imaging in ischemic stroke

BACKGROUND AND PURPOSE

Nitroimidazole imaging is a promising contender for noninvasive in vivo mapping of brain hypoxia after stroke. However, there is a dearth of knowledge about the behavior of these compounds in the various pathophysiologic situations encountered in ischemic stroke. In this article we report the findings from a systematic review of the literature on the use of the nitroimidazoles to map hypoxia after stroke.

SUMMARY OF REVIEW

We describe the characteristics of nitroimidazoles as imaging tracers, their pharmacology, and results of both animal and clinical studies during and after focal cerebral ischemia. Findings in brain tumors are also presented to the extent that they enlighten results in stroke. Early results from application of kinetic modeling for quantitative measurement of tracer binding are briefly discussed.

CONCLUSIONS

Based on this literature review, nitroimidazole hypoxia imaging agents are of considerable interest in stroke because they appear, both in animal models and in humans, to specifically detect the severely hypoxic viable tissue, but not the reperfused nor the necrotic tissue. To fully realize this potential in stroke, however, formal validation by concurrent measurement of tissue oxygen tension, together with development of novel ligands with faster distribution kinetics, faster clearance from normal tissue, and well-defined trapping mechanisms, are important goals for future investigations.

Advances in methods for assessing tumor hypoxia in vivo: implications for treatment planning

Tumor hypoxia and its downstream effects have remained of considerable interest for decades due to its negative impact on response to various cancer therapies and promotion of metastasis. Diagnosing hypoxia non-invasively can provide a significant advancement in cancer treatment and is the dire necessity for implementing specific targeted therapies now emerging to treat different aspects of cancer. A variety of techniques are being proposed to do so. However, none of them has yet been established in the clinical arena. This review summarizes the methods currently available to assess tumor hypoxia in vivo and their respective advantages and shortcomings. It also points out the impedances that need to be overcome to establish any particular method in the clinic, along with a broad overview of requirements for further advancement in this sphere of cancer research.

Hypoxia: importance in tumor biology, noninvasive measurement by imaging, and value of its measurement in the management of cancer therapy

PURPOSE

The Cancer Imaging Program of the National Cancer Institute convened a workshop to assess the current status of hypoxia imaging, to assess what is known about the biology of hypoxia as it relates to cancer and cancer therapy, and to define clinical scenarios in which in vivo hypoxia imaging could prove valuable.

RESULTS

Hypoxia, or low oxygenation, has emerged as an important factor in tumor biology and response to cancer treatment. It has been correlated with angiogenesis, tumor aggressiveness, local recurrence, and metastasis, and it appears to be a prognostic factor for several cancers, including those of the cervix, head and neck, prostate, pancreas, and brain. The relationship between tumor oxygenation and response to radiation therapy has been well established, but hypoxia also affects and is affected by some chemotherapeutic agents. Although hypoxia is an important aspect of tumor physiology and response to treatment, the lack of simple and efficient methods to measure and image oxygenation hampers further understanding and limits their prognostic usefulness. There is no gold standard for measuring hypoxia; Eppendorf measurement of pO(2) has been used, but this method is invasive. Recent studies have focused on molecular markers of hypoxia, such as hypoxia inducible factor 1 (HIF-1) and carbonic anhydrase isozyme IX (CA-IX), and on developing noninvasive imaging techniques.

CONCLUSIONS

This workshop yielded recommendations on using hypoxia measurement to identify patients who would respond best to radiation therapy, which would improve treatment planning. This represents a narrow focus, as hypoxia measurement might also prove useful in drug development and in increasing our understanding of tumor biology.

Expression of hypoxic-inducible factor 1α predicts metastasis-free survival after radiation therapy alone in stage IIIB cervical squamous cell carcinoma

PURPOSE

Hypoxia-inducible factor-1alpha (HIF-1alpha) is an intrinsic marker of tumor hypoxia. It has been considered that the hypoxic status reduces radiosensitivity, but the role of HIF-1alpha in advanced cervical carcinoma is still unclear. The objective of this study was to clarify the impact of HIF-1alpha, human papillomavirus (HPV), and other molecular factors, such as p53, bax, bcl-2, and their correlations on the outcome of patients with Stage IIIB cervical carcinoma in radiation therapy.

METHODS AND MATERIALS

We analyzed 38 patients with FIGO Stage IIIB squamous cell carcinoma of the cervix treated with radiation therapy alone. All patients received the combination therapy of external beam irradiation and low-dose-rate intracavity brachytherapy. The tumor expressions of HIF-1alpha, p53, bax, and bcl-2 were examined by immunohistochemical staining of the pretreatment paraffin embedded specimens. HPV infection was also detected by polymerase chain reaction. The effects of these parameters on clinical outcomes were analyzed by univariate analysis.

RESULTS

Of 38 patients, high expression of HIF-1alpha, p53, bax, and bcl-2 were seen in 17 (45%), 22 (58%), 15 (39%), and 15 (39%) patients, respectively, and 28 patients (74%) showed positive infection with HPV. There was a significant positive correlation between high HIF-1alpha expression and disease recurrence (p < 0.05). Furthermore, HIF-1alpha had a significant correlation with the recurrence-free survival rate (p = 0.04). No statistical correlation was noted between high HIF-1alpha expression and the local control rate (p = 0.17), whereas the HIF-1alpha status predicted distant metastasis with strong significance (p = 0.03). Conversely, other factors demonstrated no impact on the clinical outcome.

CONCLUSIONS

The present results suggest that HIF-1alpha is an important prognostic factor, especially for predicting future metastasis after radiation therapy for patients with Stage IIIB squamous cell carcinoma of the cervix.

Phase I Study of Tirapazamine Plus Cisplatin/Etoposide and Concurrent Thoracic Radiotherapy in Limited-Stage Small Cell Lung Cancer (S0004)

PURPOSE

To determine the feasibility and a recommended phase II dose of tirapazamine when combined with chemoradiotherapy in limited-stage small cell lung cancer (LSCLC).

EXPERIMENTAL DESIGN

Concurrent chemoradiotherapy consisted of two cycles of cisplatin, etoposide, and once-daily radiation to 61 Gy. Tirapazamine (260 mg/m2) was given 1 h before cisplatin with planned dose escalation to 330 mg/m2 in the absence of dose-limiting toxicity, defined as > or =33% esophagitis (grade 3 or above). Consolidation therapy consisted of two cycles of tirapazamine (330 mg/m2), cisplatin, and etoposide. Complete responders received prophylactic cranial irradiation.

RESULTS

Thirty patients were enrolled at the 260 mg/m2 tirapazamine dose. All had performance status of 0-1. By comparison with S9713, a predecessor Southwest Oncology Group study in LSCLC that used the same concurrent chemoradiotherapy without tirapazamine, the present trial showed a higher rate of grade 3-4 esophagitis (34% versus 22%), vomiting (34% versus 23%), and febrile neutropenia (7% versus 2%). The consolidation phase was relatively well tolerated, with grade 4 neutropenia in 44% and febrile neutropenia in 5% of patients. There were two treatment-related deaths: one from neutropenic fever and one from respiratory infection. The overall response rate was 80%, and the median survival was 22 months.

CONCLUSIONS

Protocol-defined dose-limiting toxicity was observed at the initial tirapazamine dose, precluding dose escalation. Compared with S9713, the addition of tirapazamine increased the incidence of vomiting, neutropenia, and febrile neutropenia, although the overall toxicity profile remained acceptable. In view of the observed favorable survival, further study of tirapazamine in LSCLC is warranted.

Molecular imaging: The latest generation of contrast agents and tissue characterization techniques

Molecular Imaging technologies will have a profound impact on both basic research and clinical imaging in the near future. As the field covers many different specialties and scientific disciplines it is not possible to review all in a single article. In the current article we will turn our attention to those modalities that are either currently in use or in development for the medical imaging clinic.

A survey on histological image analysis-based assessment of three major biological factors influencing radiotherapy: proliferation, hypoxia and vasculature

Image analysis is a rapidly evolving field with growing applications in science and engineering. In cancer research, it has played a key role in advancing techniques of major diagnostic importance, minimising human intervention and providing vital clinical information. Especially in the field of tissue microscopy, the use of computers for the automated analysis of histological sections is becoming increasingly important. This paper presents an overview of various image analysis methodologies and summarises developments in this field, with great emphasis given on the assessment of three major biological factors known to influence the outcome of radiotherapy: proliferation, vasculature and hypoxia. A brief introduction followed by a survey is provided in each of these areas.

Non-invasive PET and SPECT imaging of tissue hypoxia using isotopically labeled 2-nitroimidazoles

The measurement of pathologically low levels of tissue pO2 is an important diagnostic goal for determining the prognosis of many clinically important diseases including cardiovascular insufficiency, stroke and cancer. A class of bioreductively activated drugs, typified by the 2-nitroimidazoles, has excellent potential for application to this goal. Such drugs bind to cells at a rate which is maximal under conditions of severe hypoxia (e.g. less than 0.05% oxygen) and is inhibited, with Michaelis-Menten kinetics, as a function of increasing oxygen concentration. A number of detection possibilities exist for the drug adducts, including invasive assays which can measure drug adducts in tissue sections at cell-to-cell resolution. Use of such agents in non-invasive assays is important and, to this end, a number of drugs have been conjugated with radioactive isotopes suitable for detection by Nuclear Medicine techniques. In contrast with the invasive assays, resolution and contrast is much more limited with the non-invasive assays. Thus, there are many factors contributing to the balance of pros and cons for the non-invasive vs. invasive use of 2-nitroimidazole drugs as hypoxia detectors. These factors will be summarized in this review, with emphasis on compounds suitable for clinical use. PET (positron emission tomography) imaging with 18F-labeled EF5 (a drug in current clinical trials using invasive assays) will be described.

Monitoring of response to radiation therapy for human tumor xenografts using 99mTc-HL91 (4,9-diaza-3,3,10,10-tetramethyldodecan-2,11-dione dioxime)

PURPOSE

Oxygenation status of tumor tissue is an important factor to discriminate it with respect to its radiosensitivity. 99mTc-4,9-diaza-3,3,10,10-tetramethyldodecan-2,11-dione dioxime (99mTc-HL91) is retained in hypoxic tissues, making it possible to use it as hypoxic imaging agent. We evaluated if the accumulation of 99mTc-HL91 in tumors could aid in the prediction of sensitivity of radiation therapy of cancers.

METHODS

Human tumors (the gastric cancer cell line: MKN45, the epidermoid carcinoma cell line: KB-31, and the lung adenocarcinoma cell line: HLC) were xenografted into the thigh of athymic mice and irradiated with a 4 MV linear accelerator. Tumor growth was measured and 99mTc-HL91 uptakes in tumors were determined by serial imaging, biodistribution, and autoradiography.

RESULTS

99mTc-HL91 uptake (ratio of ROItumor to ROIwhole body) in HLC ranged from 1.1 to 8.0%, and it did not show any response to radiation therapy. Major variations were observed in 99mTc-HL91 accumulation in MKN45 and KB-31; from 0.7 to 4.7%, and from 1.0 to 7.3%, respectively. Some tumors responded to radiotherapy, while others did not. Tumor response was not dependent on the 99mTc-HL91 uptake, tumor size or radiation dose. Comparing 99mTc-HL91 uptake in tumors before (B) and after (A) their radiation, uptake (B) was always smaller than uptake (A) for HLC, and they did not respond to irradiation at all. For MKN45 and KB-31, tumors responded to radiation when their uptake (A) was not higher than uptake (B). In contrast, the tumors continued to grow when their uptake (A) was higher than uptake (B). Sequential 99mTc-HL91 imaging of KB-31 and their autoradiography indicated that tumors whose 99mTc-HL91 uptakes was increased post irradiation were composed of mainly hypoxic cells. On the other hand, many viable areas were observed in tumors when the increase in 99mTc-HL91 uptake was relatively small.

CONCLUSION

99mTc-HL91 uptake in tumors did not always relate to their sensitivities to radiation therapy. Sequential 99mTc-HL91 imagings post irradiation showed that the increase in 99mTc-HL91 uptake in tumors predicted a poor response to radiation therapy, and that a decrease or no change suggested that radiation therapy would be effective. Monitoring by 99mTc-HL91 imaging is a good tool to predict the radiosentivities of tumors.

99mTc-labeling studies of a modified metronidazole and its biodistribution in tumor bearing animal models

A cysteine-based bifunctional chelating agent viz. N-(2'-hydroxybenzyl)-cysteine with a free carboxylic acid group (CAA) was synthesized. Bearing in mind the affinity of localization of nitroimidazoles in hypoxic tissues, this bifunctional chelating agent was coupled to metronidazole (MNZ). The (99m)Tc labeling studies of the novel agent (MNZCAA) thus obtained, was carried out and the radiolabeled product was subsequently purified. The complexation yield under optimized condition was approximately 85%. Biodistribution studies carried out in Swiss mice bearing 'barcl-95' tumors showed selective accumulation of the injected activity in the tumor (1.70%/g at 30 min p.i.) with renal as well as hepatobiliary clearance. High tumor/muscle ratio (14.7 at 3 h post-injection) of the novel agent indicates considerable promise towards further evaluation.

Nuclear medicine imaging to predict response to radiotherapy: a review

PURPOSE

To review available literature on positron emission tomography (PET) and single photon emission computerized tomography (SPECT) for the measurement of tumor metabolism, hypoxia, growth factor receptor expression, and apoptosis as predictors of response to radiotherapy.

METHODS AND MATERIALS

Medical literature databases (Pubmed, Medline) were screened for available literature and critically analyzed as to their scientific relevance.

RESULTS

Studies on 18F-fluorodeoxyglucose PET as a predictor of response to radiotherapy in head-and-neck carcinoma are promising but need confirmation in larger series. 18F-fluorothymine is stable in human plasma, and preliminary clinical data obtained with this marker of tumor cell proliferation are promising. For imaging tumor hypoxia, novel, more widely available radiopharmaceuticals with faster pharmacokinetics are mandatory. Imaging of ongoing apoptosis and growth factor expression is at a very early stage, but results obtained in other domains with radiolabeled peptides appear promising. Finally, for most of the tracers discussed, validation against a gold standard is needed.

CONCLUSION

Optimization of the pharmacokinetics of relevant radiopharmaceuticals as well as validation against gold-standard tests in large patient series are mandatory if PET and SPECT are to be implemented in routine clinical practice for the purpose of predicting response to radiotherapy.

Tumor hypoxia and blood vessel detection: an image analysis technique for simultaneous tumor hypoxia grading and blood vessel detection in tissue sections

We have developed a multistage image analysis technique for the simultaneous segmentation of blood vessels and hypoxic regions in dual-stained tumor tissue sections. The algorithm, which is integrated in a task-oriented image analysis system developed on-site, initially uses the K-nearest neighbor classification rule in order to label the image pixels. Classification is based on a training set selected from manually drawn regions corresponding to the areas of interest. If the output image contains a significant number of misclassified pixels, the user has the option to apply a series of specific problem-designed routines (texture analysis, fuzzy c-means clustering, and edge detection) in order to improve the final segmentation result. Validation experiments indicate that the algorithm can robustly detect these biological features, even in tissue sections with a very low quality of staining. This approach has also been combined with other image analysis based procedures in order to objectively obtain quantitative measurements of potential clinical interest.

Correlations between in vivo tumor weight, oxygen pressure, 31P NMR spectroscopy, hypoxic microenvironment marking by beta-D-iodinated azomycin galactopyranoside (beta-D-IAZGP), and radiation sensitivity

PURPOSE

The purpose of this study is to evaluate the amount of hypoxic fraction in a rodent tumor by means of polarographic oxygen electrode, phosphorus-31 magnetic resonance spectroscopy (31P-MRS), and a newly synthesized hypoxic marker, beta-D-iodinated azomycin galactopyranoside (beta-D-IAZGP). We also investigated the radiosensitivity for tumors of different weights.

METHODS AND MATERIALS

Murine mammary carcinoma cells, FM3A, were subcutaneously implanted into the back of 5-week-old male C3H/He mice. beta-D-IAZGP radiolabeled with 123I or with 125I was injected intravenously into tumor-bearing mice, and marker distribution was measured by nuclear medicine procedures. Radiosensitivity of the tumor was measured by the in vivo/in vitro clonogenic assay. Tumor oxygenation status was also measured directly by polarographic oxygen electrodes and indirectly estimated from 31P-MR spectra.

RESULTS

Higher accumulation of 123I-beta-D-IAZGP was observed in the tumors than in normal tissues at 24 h after administration. As to biodistribution of 125I-beta-D-IAZGP, the tumor/blood ratio varied widely, but correlated significantly with tumor weight. Mean oxygen pressure (pO2) values and ratios of nucleoside triphosphate beta to inorganic phosphate (beta-ATP/Pi) and of phosphocreatine to inorganic phosphate (PCr/Pi) decreased significantly with the increase in tumor volume. As tumor volume increased, the surviving fraction of cells from tumors irradiated in vivo increased significantly.

CONCLUSIONS

The increase in tumor volume was significantly correlated with a reduction in mean pO2, a decrease in the ratios of beta-ATP/Pi or PCr/Pi, an increase in uptake of beta-D-IAZGP, and an increase in radioresistance. Because the uptake of beta-D-IAZGP can be measured noninvasively by nuclear medicine techniques, it could be clinically useful for monitoring hypoxia in human tumors.

Microwave-assisted (radio)halogenation of nitroimidazole-based hypoxia markers

Microwave-assisted radiohalogenation for the production of short-lived radiopharmaceuticals has now been applied to the synthesis and radiolabelling of azomycin nucleosides. (Radio)halogens were incorporated either by nucleophilic substitution of a leaving group or by halogen-halogen exchange, in the synthesis of IAZA, IAZP and FAZA. A comparison of conventional labelling and microwave-assisted labelling procedures reflects a clear advantage of the microwave technique.

Tumor control probability for selective boosting of hypoxic subvolumes, including the effect of reoxygenation

PURPOSE

To study the effect on tumor control probability of selectively boosting the dose to hypoxic subvolumes.

METHODS AND MATERIALS

A Monte Carlo model was developed that separates the tumor into two compartments, one of which receives a primary dose, and one of which receives a higher boost dose. During radiation delivery, each compartment consists of three clonogen subpopulations: those that are well oxygenated, those that are temporarily hypoxic (geometrically transient hypoxia), and those that are permanently hypoxic (geometrically stable hypoxia). The spatial location of temporary hypoxia within the tumor volume varies over time, whereas, the spatial location of permanent hypoxia does not. The effect of reoxygenation was included. Clonogen proliferation was not included in the model.

RESULTS

A modest boost dose (120%-150% of the primary dose) increases tumor control probability to that found in the absence of permanent hypoxia. The entire hypoxic subvolume need not be included to obtain a significant benefit. However, only tumors with a geometrically stable hypoxic volume will have an improved control rate.

CONCLUSIONS

Tumors with an identifiable geometrically stable hypoxic volume will have an improved control rate if the dose to the hypoxic volume is escalated. Further work is required to determine the spatiotemporal evolution of the hypoxic volumes before and during the course of radiotherapy.

Hypoxia imaging in brain tumors

Assessment of the oxygenation status of brain tumors has been studied increasingly with imaging techniques in light of recent advances in oncology. Tumor oxygen tension is a critical factor influencing the effectiveness of radiation and chemotherapy and malignant progression. Hypoxic tumors are resistant to treatment, and prognostic value of tumor oxygen status is shown in head and neck tumors. Strategies increasing the tumor oxygenation are being investigated to overcome the compromising [figure: see text] effect of hypoxia on tumor treatment. Administration of nicotinamide and inhalation of various high oxygen concentrations have been implemented. Existing methods for assessment of tissue oxygen level are either invasive or insufficient. Accurate and noninvasive means to measure tumor oxygenation are needed for treatment planning, identification of patients who might benefit from oxygenation strategies, and assessing the efficacy of interventions aimed to increase the radiosensitivity of tumors. Of the various imaging techniques used to assess tissue oxygenation, MR spectroscopy and MR imaging are widely available, noninvasive, and clinically applicable techniques. Tumor hypoxia is related closely to insufficient blood flow through chaotic and partially nonfunctional tumor vasculature and the distance between the capillaries and the tumor cells. Information on characteristics of tumor vasculature such as blood volume, perfusion, and increased capillary permeability can be provided with MR imaging. MR imaging techniques can provide a measure of capillary permeability based on contrast enhancement and relative cerebral blood volume estimates using dynamic susceptibility MR imaging. Blood oxygen level dependent contrast MR imaging using gradient echo sequence is intrinsically sensitive to changes in blood oxygen level. Animal models using blood oxygen level-dependent contrast imaging reveal the different responses of normal and tumor vasculature under hyperoxia. Normobaric hyperoxia is used in MR studies as a method to produce MR contrast in tissues. Increased T2* signal intensity of brain tissue has been observed using blood oxygen level-dependent contrast MR imaging. Dynamic blood oxygen level-dependent contrast MR imaging during hyperoxia is suggested to image tumor oxygenation. Quantification of cerebral oxygen saturation using blood oxygen level-dependent MR imaging also has been reported. Quantification of cerebral blood oxygen saturation using MR imaging has promising clinical applications; however, technical difficulties have to be resolved. Blood oxygen level dependent MR imaging is an emerging technique to evaluate the cerebral blood oxygen saturation, and it has the potential and versatility to assess oxygenation status of brain tumors. Upon improvement and validation of current MR techniques, better diagnostic, prognostic, and treatment monitoring capabilities can be provided for patients with brain tumors.

Nuclear medicine applications in molecular imaging

With the emergence of the new field of molecular imaging, there is an increasing demand for development of sensitive and safe novel imaging agents that can be rapidly translated from small animal models into patients. Nuclear medicine and positron emission tomography (PET) techniques have the ability to detect and serially monitor a variety of biologic and pathophysiologic processes, usually with tracer quantities of radiolabeled peptides, drugs, and other molecules at doses free of pharmacologic side effects, unlike the current generation of intravenous agents required for magnetic resonance (MR) and computed tomography (CT) scanning. In this article, we will review a representative sampling of the wide array of radiopharmaceuticals developed specifically for nuclear medicine radionuclide imaging that have been approved for clinical use, and those in pre-clinical trials. We will also review the existing strategies used to select the appropriate biologic markers and targets for radionuclide labeling that have been employed in the development of novel radiotracers and the imaging of small animals with new microSPECT (single photon emission computed tomography) technologies.