Chemical sensitizers for hypoxic cells: a decade of experience in clinical radiotherapy

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.

The measurement and modification of hypoxia in colorectal cancer: overlooked but not forgotten

Tumour hypoxia is the inevitable consequence of a tumour's rapid growth and disorganized, inefficient vasculature. The compensatory mechanisms employed by tumours, and indeed the absence of oxygen itself, hinder the ability of all treatment modalities. The clinical consequence is poorer overall survival, disease-free survival, and locoregional control. Recognizing this, clinicians have been attenuating the effect of hypoxia, primarily with hypoxic modification or with hypoxia-activated pro-drugs, and notable success has been demonstrated. However, in the case of colorectal cancer (CRC), there is a general paucity of knowledge and evidence surrounding the measurement and modification of hypoxia, and this is possibly due to the comparative inaccessibility of such tumours. We specifically review the role of hypoxia in CRC and focus on the current evidence for the existence of hypoxia in CRC, the majority of which originates from indirect positron emission topography imaging with hypoxia selective radiotracers; the evidence correlating CRC hypoxia with poorer oncological outcome, which is largely based on the measurement of hypoxia inducible factor in correlation with clinical outcome; the evidence of hypoxic modification in CRC, of which no direct evidence exists, but is reflected in a number of indirect markers; the prognostic and monitoring implications of accurate CRC hypoxia quantification and its potential in the field of precision oncology; and the present and future imaging tools and technologies being developed for the measurement of CRC hypoxia, including the use of blood-oxygen-level-dependent magnetic resonance imaging and diffuse reflectance spectroscopy.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Targeting Hypoxia: Revival of Old Remedies

Tumour hypoxia is significantly correlated with patient survival and treatment outcomes. At the molecular level, hypoxia is a major driving factor for tumour progression and aggressiveness. Despite the accumulative scientific and clinical efforts to target hypoxia, there is still a need to find specific treatments for tumour hypoxia. In this review, we discuss a variety of approaches to alter the low oxygen tumour microenvironment or hypoxia pathways including carbogen breathing, hyperthermia, hypoxia-activated prodrugs, tumour metabolism and hypoxia-inducible factor (HIF) inhibitors. The recent advances in technology and biological understanding reveal the importance of revisiting old therapeutic regimens and repurposing their uses clinically.

Therapeutic Modification of Hypoxia

Regions of reduced oxygenation (hypoxia) are a characteristic feature of virtually all animal and human solid tumours. Numerous preclinical studies, both in vitro and in vivo, have shown that decreasing oxygen concentration induces resistance to radiation. Importantly, hypoxia in human tumours is a negative indicator of radiotherapy outcome. Hypoxia also contributes to resistance to other cancer therapeutics, including immunotherapy, and increases malignant progression as well as cancer cell dissemination. Consequently, substantial effort has been made to detect hypoxia in human tumours and identify realistic approaches to overcome hypoxia and improve cancer therapy outcomes. Hypoxia-targeting strategies include improving oxygen availability, sensitising hypoxic cells to radiation, preferentially killing these cells, locating the hypoxic regions in tumours and increasing the radiation dose to those areas, or applying high energy transfer radiation, which is less affected by hypoxia. Despite numerous clinical studies with each of these hypoxia-modifying approaches, many of which improved both local tumour control and overall survival, hypoxic modification has not been established in routine clinical practice. Here we review the background and significance of hypoxia, how it can be imaged clinically and focus on the various hypoxia-modifying techniques that have undergone, or are currently in, clinical evaluation.

ZIF-Based Nanoparticles Combine X-Ray-Induced Nitrosative Stress with Autophagy Management for Hypoxic Prostate Cancer Therapy

Although reactive oxygen species (ROS)-mediated tumor treatments are predominant in clinical applications, ROS-induced protective autophagy promotes cell survival, especially in hypoxic tumors. Herein, X-ray triggered nitrite (NO₂ ^- ) is used for hypoxic prostate cancer therapy by inhibiting autophagy and inducing nitrosative stress based on an electrophilic zeolitic imidazole framework (ZIF-82-PVP). After internalization of pH-responsive ZIF-82-PVP nanoparticles, electrophilic ligands and Zn²⁺ are delivered into cancer cells. Electrophilic ligands can not only consume GSH under hypoxia but also capture low-energy electrons derived from X-rays to generate NO₂ ^- , which inhibits autophagy and further elevates lethal nitrosative stress levels. In addition, dissociated Zn²⁺ specifically limits the migration and invasion of prostate cancer cells through ion interference. In vitro and in vivo results indicate that ZIF-82-PVP nanoparticles under X-ray irradiation can effectively promote the apoptosis of hypoxic prostate cancer cells. Overall, this nitrosative stress-mediated tumor therapy strategy provides a novel approach targeting hypoxic tumors.

Hypoxia and its therapeutic possibilities in paediatric cancers

In tumours, hypoxia-a condition in which the demand for oxygen is higher than its availability-is well known to be associated with reduced sensitivity to radiotherapy and chemotherapy, and with immunosuppression. The consequences of hypoxia on tumour biology and patient outcomes have therefore led to the investigation of strategies that can alleviate hypoxia in cancer cells, with the aim of sensitising cells to treatments. An alternative therapeutic approach involves the design of prodrugs that are activated by hypoxic cells. Increasing evidence indicates that hypoxia is not just clinically significant in adult cancers but also in paediatric cancers. We evaluate relevant methods to assess the levels and extent of hypoxia in childhood cancers, including novel imaging strategies such as oxygen-enhanced magnetic resonance imaging (MRI). Preclinical and clinical evidence largely supports the use of hypoxia-targeting drugs in children, and we describe the critical need to identify robust predictive biomarkers for the use of such drugs in future paediatric clinical trials. Ultimately, a more personalised approach to treatment that includes targeting hypoxic tumour cells might improve outcomes in subgroups of paediatric cancer patients.

Hypoxia, metabolism, and the circadian clock: new links to overcome radiation resistance in high-grade gliomas

Radiotherapy is the cornerstone of treatment of high-grade gliomas (HGGs). It eradicates tumor cells by inducing oxidative stress and subsequent DNA damage. Unfortunately, almost all HGGs recur locally within several months secondary to radioresistance with intricate molecular mechanisms. Therefore, unravelling specific underlying mechanisms of radioresistance is critical to elucidating novel strategies to improve the radiosensitivity of tumor cells, and enhance the efficacy of radiotherapy. This review addresses our current understanding of how hypoxia and the hypoxia-inducible factor 1 (HIF-1) signaling pathway have a profound impact on the response of HGGs to radiotherapy. In addition, intriguing links between hypoxic signaling, circadian rhythms and cell metabolism have been recently discovered, which may provide insights into our fundamental understanding of radioresistance. Cellular pathways involved in the hypoxic response, DNA repair and metabolism can fluctuate over 24-h periods due to circadian regulation. These oscillatory patterns may have consequences for tumor radioresistance. Timing radiotherapy for specific times of the day (chronoradiotherapy) could be beneficial in patients with HGGs and will be discussed.

Hypoxia Imaging and Adaptive Radiotherapy: A State-of-the-Art Approach in the Management of Glioma

Severe hypoxia [oxygen partial pressure (pO₂) below 5–10 mmHg] is more frequent in glioblastoma multiforme (GBM) compared to lower-grade gliomas. Seminal studies in the 1950s demonstrated that hypoxia was associated with increased resistance to low–linear energy transfer (LET) ionizing radiation. In experimental conditions, the total radiation dose has to be multiplied by a factor of 3 to achieve the same cell lethality in anoxic situations. The presence of hypoxia in human tumors is assumed to contribute to treatment failures after radiotherapy (RT) in cancer patients. Therefore, a logical way to overcome hypoxia-induced radioresistance would be to deliver substantially higher doses of RT in hypoxic volumes delineated on pre-treatment imaging as biological target volumes (BTVs). Such an approach faces various fundamental, technical, and clinical challenges. The present review addresses several technical points related to the delineation of hypoxic zones, which include: spatial accuracy, quantitative vs. relative threshold, variations of hypoxia levels during RT, and availability of hypoxia tracers. The feasibility of hypoxia imaging as an assessment tool for early tumor response to RT and for predicting long-term outcomes is discussed. Hypoxia imaging for RT dose painting is likewise examined. As for the radiation oncologist's point of view, hypoxia maps should be converted into dose-distribution objectives for RT planning. Taking into account the physics and the radiobiology of various irradiation beams, preliminary in silico studies are required to investigate the feasibility of dose escalation in terms of normal tissue tolerance before clinical trials are undertaken.

Overcoming Radioresistance: Small Molecule Radiosensitisers and Hypoxia-activated Prodrugs

The role of hypoxia in radiation resistance is well established and many approaches to overcome hypoxia in tumours have been explored, with variable success. Two small molecule strategies for targeting hypoxia have dominated preclinical and clinical efforts. One approach has been the use of electron-affinic nitroheterocycles as oxygen-mimetic sensitisers. These agents are best exemplified by the 5-nitroimidazole nimorazole, which has limited use in conjunction with radiotherapy in head and neck squamous cell carcinoma. The second approach seeks to leverage tumour hypoxia as a tumour-specific address for hypoxia-activated prodrugs. These prodrugs are selectively activated by reductases under hypoxia to release cytotoxins, which in some instances may diffuse to kill surrounding oxic tumour tissue. A number of these hypoxia-activated prodrugs have been examined in clinical trial and the merits and shortcomings of recent examples are discussed. There has been an evolution from delivering DNA-interactive cytotoxins to molecularly targeted agents. Efforts to implement these strategies clinically continue today, but success has been elusive. Several issues have been identified that compromised these clinical campaigns. A failure to consider the extravascular transport and the micropharmacokinetic properties of the prodrugs has reduced efficacy. One key element for these 'targeted' approaches is the need to co-develop biomarkers to identify appropriate patients. Hypoxia-activated prodrugs require biomarkers for hypoxia, but also for appropriate activating reductases in tumours, as well as markers of intrinsic sensitivity to the released drug. The field is still evolving and changes in radiation delivery and the impact of immune-oncology will provide fertile ground for future innovation.

Preparation, Characterization, and In Vitro pH-sensitivity Evaluation of Superparamagnetic Iron Oxide Nanoparticle- Misonidazole pH-sensitive Liposomes

Background:

The use of Misonidazole (MISO), the first and a potential hypoxic tumor cell radiosensitizer, has been limited by peripheral neurotoxicity, thus discouraging phase III clinical trials.

Objective:

To develop a targeted drug delivery and tracing System with pH-sensitive liposomes (SpHLs) and Superparamagnetic Iron Oxide Nanoparticles (SPIONs) to counter MISO-related adverse effects and to enable tracing under magnetic resonance.

Methods:

SPION-MISO-SpHLs were prepared by a reverse evaporation and freeze-thawing method. HPLC and phenanthroline spectrophotometry were established for MISO and Fe determination. The characterization and in vitro pH-sensitivity of SPION-MISO-SpHLs were evaluated.

Results:

The maximal entrapment efficiencies of MISO and SPIONs in SPION-MISO-SpHLs were 30.2% and 23.7%, respectively. The cumulative release rates of MISO and SPIONs were respectively 2.49 and 2.47 times higher in pH 5.5 than in pH 7.4 buffer. The mean particle size of SPION-MISOSpHLs was 950 nm. The zeta potential was -58.9 mV in pH 7.4 buffer and 36.3 mV in pH 5.5 buffer. SEM imaging showed that SPION-MISO-SpHLs had similar spherical morphologies. SPIONs were packed in the center of liposomes and were well dispersed in a TEM graph. Magnetization curve showed that SPION-MISO-SpHLs retained superparamagnetic properties. SPION-MISO-SpHLs were compared with MISO+SPION+blank liposome in hypoxia and control groups of A549 cells. MISO and SPION concentrations in culture medium showed significant differences between the same concentration groups (P < 0.0001) and at different times (P < 0.0001).

Conclusion:

SPION-MISO-SpHLs possess pH-dependent release ability and superparamagnetism, and thus provides a system for targeted delivery and tracing under magnetic resonance.

Binding preference of nitroimidazolic radiosensitizers to nucleobases and nucleosides probed by electrospray ionization mass spectrometry and density functional theory

Nitroimidazolic radiosensitizers are used in radiation therapy to selectively sensitize cancer cells deprived of oxygen, and the actual mechanism of radiosensitization is still not understood. Selecting five radiosensitizers (1-methyl-5-nitroimidazole, ronidazole, ornidazole, metronidazole, and nimorazole) with a common 5-nitroimidazolic ring with different substitutions at N1 and C2 positions of the imidazole moiety, we investigate here their binding to nucleobases (A, T, G, and C) and nucleosides (As, Td, Gs, and Cd) via the positive electrospray ionization mass spectrometry experiments. In addition, quantum chemical calculations at the M062x/6-311+G(d,p) level of theory and basis set were used to determine binding energies of the proton bound dimers of a radiosensitizer and a nucleobase. The positive electrospray ionization leads to the formation of proton bound dimers of all radiosensitizers except 1-methyl-5-nitroimidazole in high abundance with C and smaller abundance with G. Ronidazole and metronidazole formed less abundant dimers also with A, while no dimers were observed to be formed at all with T. In contrast to the case of the nucleoside Td, the dimer intensity is as high as that with Cd, while the abundance of the dimer with Gs is smaller than that of the former. The experimental results are consistent with the calculations of binding energies suggesting proton bound dimers with C and G to be the strongest bound ones. Finally, a barrier-free proton transfer is observed when protonated G or C approaches the nitroimidazole ring.

Next-Generation Hypoxic Cell Radiosensitizers: Nitroimidazole Alkylsulfonamides

Innovations in the field of radiotherapy such as stereotactic body radiotherapy, along with the advent of radio-immuno-oncology, herald new opportunities for classical oxygen-mimetic radiosensitizers. The role of hypoxic tumor cells in resistance to radiotherapy and in suppression of immune response continues to endorse tumor hypoxia as a bona fide, yet largely untapped, drug target. Only nimorazole is used clinically as a radiosensitizer, and there is a dearth of new radiosensitizers in development. Here we present a survey of novel nitroimidazole alkylsulfonamides and document their cytotoxicity and ability to radiosensitize anoxic tumor cells in vitro. We use a phosphate prodrug approach to increase aqueous solubility and to improve tumor drug delivery. A 2-nitroimidazole and a 5-nitroimidazole analogue demonstrated marked tumor radiosensitization in either ex vivo assays of surviving clonogens or tumor regrowth delay.

GBM radiosensitizers: dead in the water…or just the beginning?

The finding that most GBMs recur either near or within the primary site after radiotherapy has fueled great interest in the development of radiosensitizers to enhance local control. Unfortunately, decades of clinical trials testing a wide range of novel therapeutic approaches have failed to yield any clinically viable radiosensitizers. However, many of  the previous radiosensitizing strategies were not based on clear pre-clinical evidence, and in many cases blood-barrier penetration was not considered. Furthermore, DNA repair inhibitors have only recenly arrived in the clinic, and likely represent potent agents for glioma radiosensitization. Here, we present recent progress in the use of small molecule DNA damage response inhibitors as GBM radiosensitizers. In addition, we discuss the latest progress in targeting hypoxia and oxidative stress for GBM radiosensitization.

Clinical Advances of Hypoxia-Activated Prodrugs in Combination With Radiation Therapy

With the increasing incidence of cancer worldwide, the need for specific, effective therapies is ever more urgent. One example of targeted cancer therapeutics is hypoxia-activated prodrugs (HAPs), also known as bioreductive prodrugs. These prodrugs are inactive in cells with normal oxygen levels but in hypoxic cells (with low oxygen levels) undergo chemical reduction to the active compound. Hypoxia is a common feature of solid tumors and is associated with a more aggressive phenotype and resistance to all modes of therapy. Therefore, the combination of radiation therapy and bioreductive drugs presents an attractive opportunity for synergistic effects, because the HAP targets the radiation-resistant hypoxic cells. Hypoxia-activated prodrugs have typically been precursors of DNA-damaging agents, but a new generation of molecularly targeted HAPs is emerging. By targeting proteins associated with tumorigenesis and survival, these compounds may result in greater selectivity over healthy tissue. We review the clinical progress of HAPs as adjuncts to radiation therapy and conclude that the use of HAPs alongside radiation is vastly underexplored at the clinical level.

Defining the hypoxic target volume based on positron emission tomography for image guided radiotherapy - the influence of the choice of the reference region and conversion function

BACKGROUND

Hypoxia imaged by positron emission tomography (PET) is a potential target for optimization in radiotherapy. However, the implementation of this approach with respect to the conversion of intensities in the images into oxygenation and radiosensitivity maps is not straightforward. This study investigated the feasibility of applying two conversion approaches previously derived for ¹⁸F-labeled fluoromisonidazole (¹⁸F-FMISO)-PET images for the hypoxia tracer ¹⁸F-flortanidazole (¹⁸F-HX4).

MATERIAL AND METHODS

Ten non-small-cell lung cancer patients imaged with ¹⁸F-HX4 before the start of radiotherapy were considered in this study. PET image uptake was normalized to a well-oxygenated reference region and subsequently linear and non-linear conversions were used to determine tissue oxygenations maps. These were subsequently used to delineate hypoxic volumes based partial oxygen pressure (pO₂) thresholds. The results were compared to hypoxic volumes segmented using a tissue-to-background ratio of 1.4 for ¹⁸F-HX4 uptake.

RESULTS

While the linear conversion function was not found to result in realistic oxygenation maps, the non-linear function resulted in reasonably sized sub-volumes in good agreement with uptake-based segmented volumes for a limited range of pO₂ thresholds. However, the pO₂ values corresponding to this range were significantly higher than what is normally considered as hypoxia. The similarity in size, shape, and relative location between uptake-based sub-volumes and volumes based on the conversion to pO₂ suggests that the relationship between uptake and pO₂ is similar for ¹⁸F-FMISO and ¹⁸F-HX4, but that the model parameters need to be adjusted for the latter.

CONCLUSIONS

A non-linear conversion function between uptake and oxygen partial pressure for ¹⁸F-FMISO-PET could be applied to ¹⁸F-HX4 images to delineate hypoxic sub-volumes of similar size, shape, and relative location as based directly on the uptake. In order to apply the model for e.g., dose-painting, new parameters need to be derived for the accurate calculation of dose-modifying factors for this tracer.

Tumor hypoxia and reoxygenation: the yin and yang for radiotherapy

Tumor hypoxia, a common feature occurring in nearly all human solid tumors is a major contributing factor for failures of anticancer therapies. Because ionizing radiation depends heavily on the presence of molecular oxygen to produce cytotoxic effect, the negative impact of tumor hypoxia had long been recognized. In this review, we will highlight some of the past attempts to overcome tumor hypoxia including hypoxic radiosensitizers and hypoxia-selective cytotoxin. Although they were (still are) a very clever idea, they lacked clinical efficacy largely because of ‘reoxygenation’ phenomenon occurring in the conventional low dose hyperfractionation radiotherapy prevented proper activation of these compounds. Recent meta-analysis and imaging studies do however indicate that there may be a significant clinical benefit in lowering the locoregional failures by using these compounds. Latest technological advancement in radiotherapy has allowed to deliver high doses of radiation conformally to the tumor volume. Although this technology has brought superb clinical responses for many types of cancer, recent modeling studies have predicted that tumor hypoxia is even more serious because ‘reoxygenation’ is low thereby leaving a large portion of hypoxic tumor cells behind. Wouldn’t it be then reasonable to combine hypoxic radiosensitizers and/or hypoxia-selective cytotoxin with the latest radiotherapy? We will provide some preclinical and clinical evidence to support this idea hoping to revamp an enthusiasm for hypoxic radiosensitizers or hypoxia-selective cytotoxins as an adjunct therapy for radiotherapy.

Nanoparticles for radiooncology: Mission, vision, challenges

Cancer is one of the leading non-communicable diseases with highest mortality rates worldwide. About half of all cancer patients receive radiation treatment in the course of their disease. However, treatment outcome and curative potential of radiotherapy is often impeded by genetically and/or environmentally driven mechanisms of tumor radioresistance and normal tissue radiotoxicity. While nanomedicine-based tools for imaging, dosimetry and treatment are potential keys to the improvement of therapeutic efficacy and reducing side effects, radiotherapy is an established technique to eradicate the tumor cells. In order to progress the introduction of nanoparticles in radiooncology, due to the highly interdisciplinary nature, expertise in chemistry, radiobiology and translational research is needed. In this report recent insights and promising policies to design nanotechnology-based therapeutics for tumor radiosensitization will be discussed. An attempt is made to cover the entire field from preclinical development to clinical studies. Hence, this report illustrates (1) the radio- and tumor-biological rationales for combining nanostructures with radiotherapy, (2) tumor-site targeting strategies and mechanisms of cellular uptake, (3) biological response hypotheses for new nanomaterials of interest, and (4) challenges to translate the research findings into clinical trials.

Synthesis and Biological Evaluation of Iodoglucoazomycin (I-GAZ), an Azomycin-Glucose Adduct with Putative Applications in Diagnostic Imaging and Radiotherapy of Hypoxic Tumors

Iodoglucoazomycin (I-GAZ; N-(2-iodo-3-(6-O-glucosyl)propyl)-2-nitroimidazole), a non-glycosidic nitroimidazole-6-O-glucose adduct, was synthesized, radioiodinated, and evaluated as a substrate of glucose transporter 1 (GLUT1) for radiotheranostic (therapy+diagnostic) management of hypoxic tumors. Nucleophilic iodination of the nosylate synthon of I-GAZ followed by deprotection afforded I-GAZ in 74 % overall yield. I-GAZ was radioiodinated via 'exchange' labeling using [(123/131) I]iodide (50-70 % RCY) and then purified by Sep-Pak™ (>96 % RCP). [(131) I]I-GAZ was stable in 2 % ethanolic solution in sterile water for 14 days when stored at 5 °C. In cell culture, I-GAZ was found to be nontoxic to EMT-6 cells at concentrations <0.5 mm, and weakly radiosensitizing (SER 1.1 at 10 % survival of EMT-6 cells; 1.2 at 0.1 % survival in MCF-7 cells). The hypoxic/normoxic uptake ratio of [(123) I]I-GAZ in EMT-6 cells was 1.46 at 2 h, and under normoxic conditions the uptake of [(123) I]I-GAZ by EMT-6 cells was unaltered in the presence of 5 mm glucose. The biodistribution of [(131) I]I-GAZ in EMT-6 tumor-bearing Balb/c mice demonstrated rapid clearance from blood and extensive renal and hepatic excretion. Tumor/blood and tumor/muscle ratios reached ∼3 and 8, respectively, at 4 h post-injection. Regression analysis of the first order polynomial plots of the blood and tumor radioactivity concentrations supported a perfusion-excretion model with low hypoxia-dependent binding. [(131) I]I-GAZ was found to be stable in vivo, and did not deiodinate.

(18)F-fluoromisonidazole positron emission tomography can predict pathological necrosis of brain tumors

PURPOSE

Tumor necrosis is one of the indicators of tumor aggressiveness. (18)F-fluoromisonidazole (FMISO) is the most widely used positron emission tomography (PET) tracer to evaluate severe hypoxia in vivo. Because severe hypoxia causes necrosis, we hypothesized that intratumoral necrosis can be detected by FMISO PET in brain tumors regardless of their histopathology. We applied FMISO PET to various types of brain tumors before tumor resection and evaluated the correlation between histopathological necrosis and FMISO uptake.

METHODS

This study included 59 brain tumor patients who underwent FMISO PET/computed tomography before any treatments. According to the pathological diagnosis, the brain tumors were divided into three groups: astrocytomas (group 1), neuroepithelial tumors except for astrocytomas (group 2), and others (group 3). Two experienced neuropathologists evaluated the presence of necrosis in consensus. FMISO uptake in the tumor was evaluated visually and semi-quantitatively using the tumor-to-normal cerebellum ratio (TNR).

RESULTS

In visual analyses, 26/27 cases in the FMISO-positive group presented with necrosis, whereas 28/32 cases in the FMISO-negative group did not show necrosis. Mean TNRs with and without necrosis were 3.49 ± 0.97 and 1.43 ± 0.42 (p < 0.00001) in group 1, 2.91 ± 0.83 and 1.44 ± 0.20 (p < 0.005) in group 2, and 2.63 ± 1.16 and 1.35 ± 0.23 (p < 0.05) in group 3, respectively. Using a cut-off value of TNR = 1.67, which was calculated by normal reference regions of interest, we could predict necrosis with sensitivity, specificity, and accuracy of 96.7, 93.1, and 94.9 %, respectively.

CONCLUSIONS

FMISO uptake within the lesion indicated the presence of histological micro-necrosis. When we used a TNR of 1.67 as the cut-off value, intratumoral micro-necrosis was sufficiently predictable. Because the presence of necrosis implies a poor prognosis, our results suggest that FMISO PET could provide important information for treatment decisions or surgical strategies of any type of brain tumor.

Optimizing hypoxia detection and treatment strategies

Clinical studies using Eppendorf needle sensors have invariably documented the resistance of hypoxic human tumors to therapy. These studies first documented the need for individual patient measurement of hypoxia, as hypoxia varied from tumor to tumor. Furthermore, hypoxia in sarcomas and cervical cancer leads to distant metastasis or local or regional spread, respectively. For various reasons, the field has moved away from direct needle sensor oxygen measurements to indirect assays (hypoxia-inducible factor-related changes and bioreductive metabolism) and the latter can be imaged noninvasively. Many of hypoxia's detrimental therapeutic effects are reversible in mice but little treatment improvement in hypoxic human tumors has been seen. The question is why? What factors cause human tumors to be refractory to antihypoxia strategies? We suggest the primary cause to be the complexity of hypoxia formation and its characteristics. Three basic types of hypoxia exist, encompassing various diffusional (distance from perfused vessel), temporal (on or off cycling), and perfusional (blood flow efficiency) limitations. Surprisingly, there is no current information on their relative prevalence in human tumors and even animal models. This is important because different hypoxia subtypes are predicted to require different diagnostic and therapeutic approaches, but the implications of this remain unknown. Even more challenging, no agreement exists for the best way to measure hypoxia. Some results even suggest that hypoxia is unlikely to be targetable therapeutically. In this review, the authors revisit various critical aspects of this field that are sometimes forgotten or misrepresented in the recent literature. As most current noninvasive imaging studies involve PET-isotope-labeled 2-nitroimidazoles, we emphasize key findings made in our studies using 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetamide (EF5) and F-18-labeled EF5. These show the importance of differentiating hypoxia subtypes, optimizing drug pharmacology, ensuring drug and isotope stability, identifying key biochemical and physiological variables in tumors, and suggesting therapeutic strategies that are most likely to succeed.

Texaphyrins: a new approach to drug development

The texaphyrins are prototypical metal-coordinating expanded porphyrins. They represent a burgeoning class of pharmacological agents that show promise for an array of medical applications. Currently, two different water-soluble lanthanide texaphyrins, namely motexafin gadolinium ( Gd-Tex , 1) and motexafin lutetium ( Lu-Tex , 2), are involved in multi-center clinical trials for a variety of indications. The first of these agents, XCYTRIN® (motexafin gadolinium) Injection, is being evaluated as a potential X-ray radiation enhancer in a randomized Phase III clinical trial in patients with brain metastases. The second, in various formulations, is being evaluated as a photosensitizer for use in: (i) the photodynamic treatment of recurrent breast cancer (LUTRIN® Injection; now in Phase IIb clinical trials); (ii) photoangioplastic reduction of atherosclerosis involving peripheral and coronary arteries (ANTRIN® Injection; now in Phase II and Phase I clinical trials, respectively); and (iii) light-based age-related macular degeneration (OPTRIN™ Injection; currently under Phase II clinical evaluation), a vision-threatening disease of the retina. In this article, these developments, along with fundamental aspects of the underlying chemistry are reviewed.

Hypoxic modification of radiotherapy in squamous cell carcinoma of the head and neck--a systematic review and meta-analysis

BACKGROUND

The importance of tumour hypoxia for the outcome of radiotherapy has been under investigation for decades. Numerous clinical trials modifying the hypoxic radioresistance in squamous cell carcinoma of the head and neck (HNSCC) have been conducted, but most have been inconclusive, partly due to a small number of patients in the individual trial. The present meta-analysis was, therefore, performed utilising the results from all clinical trials addressing the specific question of hypoxic modification in HNSCC undergoing curative intended primary radiotherapy alone.

METHODS

A systematic review of published and unpublished data identified 4805 patients with HNSCC treated in 32 randomized clinical trials, applying, normobaric oxygen or carbogen breathing (5 trials); hyperbaric oxygen (HBO) (9 trials); hypoxic radiosensitizers (17 trials) and HBO and radiosensitizer (1 trial). The trials were analysed with regard to the following endpoints: loco-regional control (32 trials), disease specific survival (30 trials), overall survival (29 trials), distant metastases (12 trials) and complications to radiotherapy (23 trials).

RESULTS

Overall hypoxic modification of radiotherapy in head and neck cancer did result in a significant improved therapeutic benefit. This was most dominantly observed when using the direct endpoint of loco-regional control with an odds ratio (OR) of 0.71, 95% cf.l. 0.63-0.80; p<0.001), but this was almost mirrored in the disease specific survival (OR: 0.73, 95% cf.l. 0.64-0.82; p<0.001), and to a lesser extent in the overall survival (OR: 0.87, 95% cf.l. 0.77-0.98; p=0.03). The risk of distant metastases was not significantly influenced although it appears to be less in the tumours treated with hypoxic modification (OR: 0.87, 95% cf.l. 0.69-1.09; p=0.22), whereas the radiation related late complications were not influenced by the overall use of hypoxic modifications (OR: 1.00, 95% cf.l. 0.82-1.23; p=0.96). The improvement in loco-regional control was found to be independent of the type of hypoxic modification. The trials have used different fractionation schedules, including large doses per fraction, which may result in relatively more hypoxia and greater benefit. However, analysis of HNSCC trials using conventional fractionation only, showed that the significant effect of hypoxic modification was maintained.

CONCLUSION

The meta-analysis thus demonstrates that there is level 1a evidence in favour of adding hypoxic modification to radiotherapy of squamous cell carcinomas of the head and neck.

Dose prescription and optimisation based on tumour hypoxia

INTRODUCTION. Tumour hypoxia is an important factor that confers radioresistance to the affected cells and could thus decrease the tumour response to radiotherapy. The development of advanced imaging methods that quantify both the extent and the spatial distribution of the hypoxic regions has created the premises to devise therapies that target the hypoxic regions in the tumour. MATERIALS AND METHODS. The present study proposes an original method to prescribe objectively dose distributions that focus the radiation dose to the radioresistant tumour regions and could therefore spare adjacent normal tissues. The effectiveness of the method was tested for clinically relevant simulations of tumour hypoxia that take into consideration dynamics and heterogeneity of oxygenation. RESULTS AND DISCUSSION. The results have shown that highly heterogeneous dose distributions may lead to significant improvements of the outcome only for static oxygenations. In contrast, the proposed method that involves the segmentation of the dose distributions and the optimisation of the dose prescribed to each segment to account for local heterogeneity may lead to significantly improved local control for clinically-relevant patterns of oxygenation. The clinical applicability of the method is warranted by its relatively easy adaptation to functional imaging of tumour hypoxia obtained with markers with known uptake properties.

Hypoxia-specific Inhibition of Recovery from Radiation Damage by a Novel 2-nitroimidazole with a Theophylline Side Chain

A novel 2-nitroimidazole with a theophylline side-chain, 7-(4'-(2-nitroimidazol-1-yl)-butyl)-theophylline, (NITP) was as efficient a hypoxic-cell radiosensitizer as misonidazole. However, if cells were irradiated with NITP under hypoxic conditions and then exposed to the drug under aerobic conditions, a much larger radiosensitizing effect was observed, partly because of a reduction in the size of the shoulder of the survival curve. There was little effect of NITP on the radiosensitivity of well oxygenated cells, even with post-irradiation drug contact. Split-dose survival curves showed that the drug inhibited recovery from radiation damage only when the cells were irradiated under hypoxia but not when irradiations were under oxic conditions. A reduction in the size of the shoulder of the survival curve should allow the hypoxic-cell radiosensitizing efficiency of NITP to be maintained with low doses of radiation used in multifraction cancer radiotherapy. Bifunctional drugs containing both electron-affinic and repair inhibiting groups may represent a new approach to the synthesis of hypoxic-cell targeted adjuncts to radiotherapy.

Hypoxic tumor cell radiosensitization through nitric oxide

Hypoxia is a principal signature of the tumor microenvironment and is considered to be the most important cause of clinical radioresistance and local failure. Oxygen is so far the best radiosensitizer, but tumor oxygenation protocols are compromised by its metabolic consumption and therefore limited diffusion inside tumors. Many chemical radiosensitizers can selectively target hypoxic tumor cells, but their systemic toxicity compromises their adequate clinical use. NO is an efficient hypoxic radiosensitizer, as it may mimic the effects of oxygen on fixation of radiation-induced DNA damage, but the required levels cannot be obtained in vivo because of vasoactive complications. Our laboratory explored whether this problem may be overcome by endogenous production of NO inside tumors. We demonstrated that iNOS, activated by pro-inflammatory cytokines, is capable of radiosensitizing tumor cells through endogenous production of NO, at non-toxic extracellular concentrations. We observed that this radiosensitizing effect is transcriptionally controlled by hypoxia and by NF-kappaB. Tumor-associated immune cells may contribute to the iNOS-mediated radiosensitization by the generation of pro-inflammatory cytokines and NO, which may diffuse towards bystander tumor cells. Our findings indicate a rationale for combining immunostimulatory and radiosensitizing strategies in the future.

Hypoxic radiosensitization: adored and ignored

Since observations from the beginning of the last century, it has become well established that solid tumors may contain oxygen-deficient hypoxic areas and that cells in such areas may cause tumors to become radioresistant. Identifying hypoxic cells in human tumors has improved by the help of new imaging and physiologic techniques, and a substantial amount of data indicates the presence of hypoxia in many types of human tumors, although with a considerable heterogeneity among individual tumors. Controlled clinical trials during the last 40 years have indicated that this source of radiation resistance can be eliminated or modified by normobaric or hyperbaric oxygen or by the use of nitroimidazoles as hypoxic radiation sensitizers. More recently, attention has been given to hypoxic cytotoxins, a group of drugs that selectively or preferably destroys cells in a hypoxic environment. An updated systematic review identified 10,108 patients in 86 randomized trials designed to modify tumor hypoxia in patients treated with curative attempted primary radiation therapy alone. Overall modification of tumor hypoxia significantly improved the effect of radiotherapy, with an odds ratio of 0.77 (95% CI, 0.71 to 0.86) for the outcome of locoregional control and with an associated significant overall survival benefit (odds ratio = 0.87; 95% CI, 0.80 to 0.95). No significant influence was found on the incidence of distant metastases or on the risk of radiation-related complications. Ample data exist to support a high level of evidence for the benefit of hypoxic modification. However, hypoxic modification still has no impact on general clinical practice.

Review: implications of in vitro research on the effect of radiotherapy and chemotherapy under hypoxic conditions

As it is now well established that human solid tumors frequently contain a substantial fraction of cells that are hypoxic, more and more in vitro research is focusing on the impact of hypoxia on the outcome of radiotherapy and chemotherapy. Indeed, the efficacy of irradiation and many cytotoxic drugs relies on an adequate oxygen supply. Consequently, hypoxic regions in solid tumors often contain viable cells that are intrinsically more resistant to treatment with radiotherapy or chemotherapy. Moreover, efforts have been made to exploit hypoxia as a potential difference between malignant and normal tissues.Nowadays, a body of evidence indicates that oxygen deficiency clearly influences some major intracellular pathways such as those involved in cell proliferation, cell cycle progression, apoptosis, cell adhesion, and others. Obviously, when investigating the effects of radiotherapy or chemotherapy or both combined under hypoxic conditions, it is essential to consider the influences of hypoxia itself on the cell. In this review, we first focus on the effects of hypoxia per se on some critical biological pathways. Next, we sketch an overview of preclinical and clinical research on radiotherapy, chemotherapy, and chemoradiation under hypoxic conditions.

Radiosensitization by the combination of SR-2508 and paclitaxel in hypoxic human tumor cells in vitro

The two radiosensitizers SR-2508 (etanidazole) and paclitaxel (taxol) have different dose-limiting toxicities in humans. Combination of the two radiosensitizers may increase radiosensitization without increasing toxicity. This study was carried out to determine the synergistic radiosensitizing effect of combination of SR-2508 and paclitaxel in two hypoxic human tumor cell lines: a breast carcinoma (MCF-7) and a carcinoma cervicis (HeLa). The 3-(4,5 dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay was used to determine the number of surviving cells. Cell cycle was evaluated by flow cytometry. Cell viability was measured by the ability of single cells to form colonies in vitro. Our data demonstrated that the radiosensitization produced by the two radiosensitizers was additive in hypoxic HeLa cells while held in the G(1) phase of the cell cycle. On the other hand, there was no synergistic radiosensitizing effect in hypoxic MCF-7 cells by combination of the two drugs. Our results suggested that the synergistic radiosensitizing effect of SR-2508 and paclitaxel may be tumor-dependent and that breast cancer may not be a good candidate. This study may provide a new combination of radiosensitizers in radiotherapy for cervical carcinoma.

Rationale for the treatment of cancer with sodium selenite

Epidemiological studies conducted during several decades of the last century have demonstrated the importance of sufficient nutritional supply of selenium (Se) for human health. More importantly, low blood Se levels were found to be associated with an increased incidence and mortality from various types of cancers. Recently, attention of researchers was drawn to the relationship between free radical generation, known otherwise as oxidative stress, and carcinogenesis. It was therefore thought that antioxidants should be beneficial for prevention and inhibition of different malignancies. However, there appeared to be a paradox, because tumor growth is associated with tissue hypoxia that is accompanied by the formation of reductive rather than oxidative free radicals. Various organic and inorganic Se compounds, generally considered to be antioxidants, produced mixed results when tested in animal models and human subjects. Amongst them, sodium selenite has been shown to be the most effective in an in vitro and in vivo carcinogenesis studies. As recently demonstrated, selenite is not an antioxidant, but possesses oxidizing properties in the presence of specific substrates. Thus selenite is capable of oxidizing polythiols to corresponding disulfides, but does not react with monothiols. Such polythiols associated with cancer membrane-bound proteins appear under the reducing conditions of hypoxic tumor tissue. These thiol groups can, in turn, initiate a disulfide exchange reaction with plasma proteins, predominantly with fibrinogen, to form an insoluble and protease-resistant fibrin-like polymer. As the result, tumor cells become surrounded by a coat which masks specific tumor antigens thus allowing cancer cells to escape immune recognition and elimination by natural killer (NK) cells. Selenite by virtue of oxidizing cell membrane thiols, can prevent the formation of the coat and consequently makes cancer cells vulnerable to the immune surveillance and destruction. In addition, selenite may directly activate NK cells, as well as inhibit angiogenesis without undesirable decrease in the oxidative potential of cellular environment. It is, therefore, postulated that sodium selenite, in view of its relative low toxicity, might become a drug of choice for many types of cancer including leukemia.

Effects of hypoxic cell radiosensitizer doranidazole (PR-350) on the radioresponse of murine and human tumor cells in vitro and in vivo

We have investigated the radiosensitizing effect of doranidazole, a hypoxic cells radiosensitizer, using SCCVII tumor cells of C3H mice and CFPAC-1 and MIA PaCa-2 human pancreatic tumor cells. The radiosensitivity of hypoxic SCCVII cells in vitro increased with 1 mM doranidazole by a factor of 1.34 and 1.68, when determined by clonogenic survival and micronucleus (MN) formation, respectively. The radiation-induced growth delay of SCCVII tumors was significantly enhanced and the TCD(50/120) was reduced by a factor of 1.33 when 200 mg/kg doranidazole was injected, i.v., 20 min prior to tumor irradiation. The in vivo-in vitro excision assay showed that radiosensitivity of SCCVII cells in vivo increased by a factor of 1.47 with 200 mg/kg doranidazole. The radiation-induced growth delay of CFPAC-1 xenografts in nude mice was significantly enhanced and the TCD(50/90) was reduced by a factor of 1.30 by 200 mg/kg doranidazole. On the other hand, 200 mg/kg of doranidazole exerted no influence on the radiation-induced growth delay in MIA PaCa-2 xenografts. The tumor oxygenation status, as determined with an oxygen sensitive needle probe and the immunohistological study using pimonidazole, indicated that MIA PaCa-2 tumors are better oxygenated than CFPAC-1 tumors. The relatively well-oxygenated status in MIA PaCa-2 tumor may account for the lack of radiosensitization by doranidazole. It is concluded that the magnitude of radiosensitization of tumors by doranidazole is dependent on the oxygenation status of the tumors and that doranidazole may be useful in increasing the response of hypoxic human pancreatic tumor to IORT.

Clinical studies of hypoxia modification in radiotherapy

Hypoxic modification has been the subject of investigations in clinical radiation oncology since the early 60s. To date, this has not yet resulted in a treatment that has been widely accepted. Logistics and technical difficulties limit the routine use of hyperbaric oxygen in radiotherapy. The nitroimidazoles have not gained general acceptance, initially because of their toxicity and later because of doubts about the effectiveness of the newer generation of less toxic drugs. Nevertheless, there is good evidence from these studies that improving clinical outcome by hypoxic modulation is an achievable goal. Newer approaches including combinations of radiotherapy with tirapazamine, erythropoietin, and carbogen and nicotinamide (ARCON) are currently in phase III trial. For these new strategies to be successful, it is important that the proper patient categories are selected. Various methods to assess tumor oxygenation are now becoming available in the clinic. These potential predictive assays must be incorporated and validated in current and future large-scale clinical trials. Modifiers that target other aspects of tumor biology may also have indirect effects on tumor oxygenation. These aspects require further study in preclinical and early clinical settings.

How to overcome (and exploit) tumor hypoxia for targeted gene therapy

Tumor hypoxia has long been recognized as a critical issue in oncology. Resistance of hypoxic areas has been shown to affect treatment outcome after radiation, chemotherapy, and surgery in a number of tumor sites. Two main strategies to overcome tumor hypoxia are to increase the delivery of oxygen (or oxygen-mimetic drugs), and exploiting this unique environmental condition of solid tumors for targeted therapy. The first strategy includes hyperbaric oxygen breathing, the administration of carbogen and nicotinamide, and the delivery of chemical radiosensitizers. In contrast, bioreductive drugs and hypoxia-targeted suicide gene therapy aim at activating cytotoxic agents at the tumor site, while sparing normal tissue from damage. The cellular machinery responds to hypoxia by activating the expression of genes involved in angiogenesis, anaerobic metabolism, vascular permeability, and inflammation. In most cases, transcription is initiated by the binding of the transcription factor hypoxia-inducible factor (HIF) to hypoxia responsive elements (HREs). Hypoxia-targeting for gene therapy has been achieved by utilizing promoters containing HREs, to induce selective and efficient transgene activation at the tumor site. Hypoxia-targeted delivery and prodrug activation may add additional levels of selectivity to the treatment. In this article, the latest developments of cancer gene therapy of the hypoxic environment are discussed, with particular attention to combined protocols with ionizing radiation. Ultimately, it is proposed that by adopting specific transgene activation and molecular amplification systems, resistant hypoxic tumor tissues may be effectively targeted with gene therapy.

Evaluation of the effect of routine packed red blood cell transfusion in anemic cervix cancer patients treated with radical radiotherapy

PURPOSE

It is well established that anemia predicts diminished radiocurability in cervix cancer. However, the therapeutic benefit of measures to correct the anemia remains controversial. The objective of this study was to determine the impact of routine transfusion in patients with hemoglobin level (hb-l) < or =11 g/dl.

METHODS AND MATERIALS

Since 1985, it has been departmental policy to attempt to correct hb-l < or =11 g/dl before and/or during radiotherapy by red blood cell transfusion (RBCT) in patients undergoing radical radiotherapy for primary cervix cancer. To assess the benefit of RBCT, the charts of 204 patients (FIGO: IB-IV) treated until 1997 were reviewed. Parameters analyzed for their impact on disease-specific survival (DSS), pelvic control (PC), and metastases-free survival (MFS) included pretreatment hb-l, treatment hb-l, stage, tumor size, and lymph node status. To determine any differences in outcome according to type of anemia, a separate analysis was performed, grouping patients by cause of anemia (tumor vs. other medical illness related).

RESULTS

Each of the parameters tested was significantly correlated with the end points studied in univariate analysis. Patients whose hb-l were corrected (18.5%) had an outcome that did not differ significantly from that of nontransfused patients, whereas DSS, PC, and MFS (all: p < 0.001) were significantly decreased in nonresponders to RBCT. Subgroup analysis showed no impact of hb-l in patients with other medical illness-related anemia (n = 12). In multivariate analysis treatment, but not pretreatment, hb-l remained predictive for DSS, PC, and MFS. Persistent anemia was associated with a significantly increased risk of death (relative risk: 2.1) and pelvic failure (relative risk: 2.4) compared with nontransfused patients. If only patients with tumor anemia were considered, the respective risks increased (2.7; 3.6). None of the patients with other causes of anemia recurred, whether or not their hb-l was maintained. Assessment of the therapeutic gain in patients who responded to RBCT showed improved PC (p = 0.02) and a trend toward increased DSS (p = 0.06), but no effect on MFS after adjustment for tumor size and lymph node status.

CONCLUSION

Treatment hb-l, in addition to tumor size and lymph node status, independently predicted outcome. Although our final multivariate analysis showed a therapeutic benefit for patients whose hb-l was corrected, the response to RBCT was disappointing. Results of our subgroup analysis suggest that the cause of anemia in patients with cervical cancer warrants in-depth investigation.

Therapeutic and imaging capacity of tumor-localizing radiosensitive Mn-porphyrin KADT-F10 for SCCVII tumors in C3H /He mice

A tumor localizing radiation sensitizer, KADT-F10, in which two molecules of nitroimidazole fluorinate, KU2280, are bound to side chain residues of a tumor localizing Mn-porphyrin was synthesized and evaluated. Suppression of tumor growth was significantly higher in a group of mice in which a total 50mg/kg KADT-F10 was administered before radiotherapy at 50 Gly (A: n=7) than in a group of mice in which radiotherapy alone was done (B: n=7). In group B, all mice died within 73 days after radiotherapy, while in group A, the tumor disappeared in five of seven mice, and three of seven mice completely recovered 120 days after radiotherapy. Clear magnetic resonance images of SCCVII tumor were obtained 1.5h after KADTF-10 administration.

Phase I trial of the hypoxic cell cytotoxin tirapazamine with concurrent radiation therapy in the treatment of refractory solid tumors

PURPOSE

Patients with refractory solid tumors were treated with the combination of fractionated radiation therapy and multiple-dose intravenous tirapazamine to determine the toxicities and maximum tolerated dose of tirapazamine when given concurrently with radiation therapy.

METHODS

Patients received radiation therapy in accordance with standard treatment practice in relation to fraction size and number of fractions for their particular cancer. In all cases, the course of radiation therapy exceeded the time of tirapazamine administration. Initially, tirapazamine was administered 5 days per week for 2 weeks for a total of 10 doses. After the first 8 patients, the schedule was changed to 3 times per week (Monday, Wednesday, Friday) for 4 weeks for a total of 12 doses. Between 3 and 6 patients were treated at each dose level.

RESULTS

A total of 43 patients were treated in the study between 1991 and 1995. All patients were 18 years old or older, had a Karnofsky performance status of > or = 60% and had adequate hematologic, hepatic, and renal function. Dose escalation began at 9 mg/m(2)/dose and was increased using a modified Fibonacci schema. The maximum tolerated dose was not reached and dose escalation was stopped at 260 mg/m(2) because of other data that became available suggesting 330 mg/m(2) was associated with dose-limiting toxicity (1, 2).

CONCLUSION

Tirapazamine in doses of up to 260 mg/m(2) times 12 doses can be given safely with fractionated radiation therapy. This dose appears to result in adequate plasma exposure (2) for radiation sensitization, and this schedule is being tested in a Phase II trial by the Radiation Therapy Oncology Group to determine if tirapazamine is a radiation enhancer in the clinic.

[Radiation sensitizing agents for hypoxic cells: past, present and future]

Hypoxic cells are present in rodent and xenografted human tumours and it has been known for a long time that the absence of oxygen in tumours is a factor of resistance against ionising radiation. The dose modifying role of oxygen (oxygen enhancement ratio) has been largely studied in experimental models. For pO2 values of 2 mmHg, the relative radiosensitivity of tumour cells is intermediate between the maximum sensitivity observed in air and the minimal one observed in hypoxia. The measurement of tumour pO2 in patients (polarographic technique) has demonstrated the presence of low values (< 10 mmHg) in many different tumour sites (ENT, uterine cervix, breast, melanoma, etc). In order to sensitise hypoxic tumours, imidazole have been used in patients, but most of the results were negative. New methods have been developed in the combination of bioreductive drugs of cytotoxic cells to radiotherapy. In this article, we will describe the clinical results obtained in patients with radiosensitising chemical agents.

The clinical radiobiology of brachytherapy

The unique geometrical features of brachytherapy, together with the wide variety of temporal patterns of dose delivery, result in important interactions between physics and radiobiology. These interactions exert a major influence on the way in which brachytherapy treatments should be evaluated, both in absolute and comparative terms. This article reviews the main physical and radiobiological aspects of brachytherapy and considers examples of their influence on specific types of treatment. The issues relating to the optimization of high dose rate brachytherapy are presented, together with the implications of multiphasic repair kinetics for low dose-rate and pulsed high dose rate brachytherapy. The opportunities for application of radiobiological principles to improve various brachytherapy techniques, together with the integration of brachytherapy with teletherapy, are also outlined. Equations for the numerical evaluation of brachytherapy treatments are presented in the Appendices.

A randomized double-blind phase III study of nimorazole as a hypoxic radiosensitizer of primary radiotherapy in supraglottic larynx and pharynx carcinoma. Results of the Danish Head and Neck Cancer Study (DAHANCA) Protocol 5-85

PURPOSE

A multicenter randomized and balanced double-blind trial with the objective of assessing the efficacy and tolerance of nimorazole given as a hypoxic radiosensitizer in conjunction with primary radiotherapy of invasive carcinoma of the supraglottic larynx and pharynx.

PATIENTS AND TREATMENT

Between January 1986 and September 1990, 422 patients (414 eligible) with pharynx and supraglottic larynx carcinoma were double-blind randomized to receive the hypoxic cell radiosensitizer nimorazole, or placebo, in association with conventional primary radiotherapy (62-68 Gy, 2 Gy per fraction, five fractions per week). The median observation time was 112 months.

RESULTS

Univariate analysis showed that the outcome (5-year actuarial loco-regional tumor control) was significantly related to T-classification (T1-T2 48% versus T3-T4 36%, P = 0.0008), neck-nodes (N- 53% versus N+ 33%), pre-irradiation hemoglobin (Hb) concentration (high 46% versus low 37%, P = 0.02) and sex (females 51% versus males 38%, P = 0.03). Overall the nimorazole group showed a significantly better loco-regional control rate than the placebo group (49 versus 33%, P = 0.002). A similar significant benefit of nimorazole was observed for the end-points of final loco-regional control (including surgical salvage) and cancer-related deaths (52 versus 41%, P = 0.002). This trend was also found in the overall survival but to a lesser, non-significant extent (26 versus 16%, 10-year actuarial values, P = 0.32). Cox multivariate regression analysis showed the most important prognostic parameters for loco-regional control to be positive neck nodes (relative risk 1.84 (1.38-2.45)), T3-T4 tumor (relative risk 1.65 (1.25-2.17)) and nimorazole (relative risk 0.69 (0.52-0.90)). The same parameters were also significantly related to the probability of dying from cancer. The compliance to radiotherapy was good and 98% of the patients received the planned dose. Late radiation-related morbidity was observed in 10% of the patients, irrespective of nimorazole treatment. Drug-related side-effects were minor and tolerable with transient nausea and vomiting being the most frequent complications.

CONCLUSION

Nimorazole significantly improves the effect of radiotherapeutic management of supraglottic and pharynx tumors and can be given without major side-effects.