Phase I trial of concurrent tirapazamine, cisplatin, and radiotherapy in patients with advanced head and neck cancer

Targeting hypoxia in solid and haematological malignancies

Tumour hypoxia is a known and extensively researched phenomenon that occurs in both solid and haematological malignancies. As cancer cells proliferate, demand for oxygen can outstrip supply reducing tumour oxygenation. In solid tumours this is contributed to by disorganized blood vessel development. Tumour hypoxia is associated with resistance to treatment, more aggressive disease behaviour and an increased likelihood of metastatic progression. It can be measured using both invasive and non-invasive methods to varying degrees of accuracy. The presence of hypoxia stimulates a complex cellular network of downstream factors including Hypoxia Inducible Factor 1 (HIF1), C-X-C motif chemokine 4 (CXCR4) and Hypoxia‐inducible glycolytic enzyme hexokinase‐2 (HK2) amongst many others. They work by affecting different mechanisms including influencing angiogenesis, treatment resistance, immune surveillance and the ability to metastasize all of which contribute to a more aggressive disease pattern. Tumour hypoxia has been correlated with poorer outcomes and worse prognosis in patients. The correlation between hypoxic microenvironments and poor prognosis has led to an interest in trying to therapeutically target this phenomenon. Various methods have been used to target hypoxic microenvironments. Hypoxia-activated prodrugs (HAPs) are drugs that are only activated within hypoxic environments and these agents have been subject to investigation in several clinical trials. Drugs that target downstream factors of hypoxic environments including HIF inhibitors, mammalian target of rapamycin (mTOR) inhibitors and vascular endothelial growth factor (anti-VEGF) therapies are also in development and being used in combination in clinical trials. Despite promising pre-clinical data, clinical trials of hypoxia targeting strategies have proven challenging. Further understanding of the effect of hypoxia and related molecular mechanisms in human rather than animal models is required to guide novel therapeutic strategies and future trial design. This review will discuss the currently available methods of hypoxia targeting and assessments that may be considered in planning future clinical trials. It will also outline key trials to date in both the solid and haemato-oncology treatment spheres and discuss the limitations that may have impacted on clinical success to date.

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.

A light-controlled multi-step drug release nanosystem targeting tumor hypoxia for synergistic cancer therapy

Hypoxia is a major obstacle for cancer therapy due to its association with cell proliferation, tumor distant metastasis, and treatment resistance. In this study, a hypoxia-activated bifunctional prodrug (CC5) was designed, synthesized and encapsulated by a photo-responsive ruthenium complex-derived polymer to yield a light-controlled multi-step drug release system (CC5-RuCa) for synergistic therapy against tumor hypoxia. Under NIR irradiation, CC5-RuCa not only generated ROS to kill the cancer cells in the exterior of the tumor but also released the prodrug CC5 with enhanced intratumoral penetration in the severe hypoxia region inside the tumor tissue. In vivo studies on MDA-MB-231 xenograft models revealed that CC5-RuCa with preferential accumulation in the tumor exhibited highly efficient tumor regression through the synergistic effect of photodynamic therapy and hypoxia-activated chemotherapy.

Novel semiconducting nano-agents incorporating tirapazamine for imaging guided synergistic cancer hypoxia activated photo-chemotherapy

For cancer treatment, the traditional monotherapy has the problems of low drug utilization rate, poor efficacy and easy recurrence of the cancer. Herein, nanoparticles (NPs) based on a novel semiconducting molecule (ITTC) are developed with excellent photostability, high photothermal conversion efficiency and good 1O2 generation ability. The chemotherapy of the hypoxia-activated prodrug tirapazamine (TPZ) was improved accordingly after oxygen consumption by the photodynamic therapy of ITTC NPs. Additionally, the metabolic process of ITTC NPs in vivo could be monitored in real time for fluorescence imaging guided phototherapy, which presented great passive targeting ability to the tumor site. Remarkably, both in vitro and in vivo experiments demonstrated that the combination of ITTC NPs and TPZ presented excellent synergistic tumor ablation through photothermal therapy, photodynamic therapy and hypoxia-activated chemotherapy with great potential for clinical applications in the future.

Reactions in Tirapazamine Induced by the Attachment of Low-Energy Electrons: Dissociation Versus Roaming of OH

Tirapazamine (TPZ) has been tested in clinical trials on radio-chemotherapy due to its potential highly selective toxicity towards hypoxic tumor cells. It was suggested that either the hydroxyl radical or benzotriazinyl radical may form as bioactive radical after the initial reduction of TPZ in solution. In the present work, we studied low-energy electron attachment to TPZ in the gas phase and investigated the decomposition of the formed TPZ- anion by mass spectrometry. We observed the formation of the (TPZ-OH)- anion accompanied by the dissociation of the hydroxyl radical as by far the most abundant reaction pathway upon attachment of a low-energy electron. Quantum chemical calculations suggest that NH2 pyramidalization is the key reaction coordinate for the reaction dynamics upon electron attachment. We propose an OH roaming mechanism for other reaction channels observed, in competition with the OH dissociation.

Methodological Development of Combination Drug and Radiotherapy in Basic and Clinical Research

Newer technical improvements in radiation oncology have been rapidly implemented in recent decades, allowing an improved therapeutic ratio. The development of strategies using local and systemic treatments concurrently, mainly targeted therapies, has however plateaued. Targeted molecular compounds and immunotherapy are increasingly being incorporated as the new standard of care for a wide array of cancers. A better understanding of possible prior methodology issues is therefore required and should be integrated into upcoming early clinical trials including individualized radiotherapy-drug combinations. The outcome of clinical trials is influenced by the validity of the preclinical proofs of concept, the impact on normal tissue, the robustness of biomarkers and the quality of the delivery of radiation. Herein, key methodological aspects are discussed with the aim of optimizing the design and implementation of future precision drug-radiotherapy trials.

Biomarker driven treatment of head and neck squamous cell cancer

Abstract

Treatment modalities of head and neck squamous cell cancer include surgery, radiation, chemotherapy, targeted agents and immune checkpoint inhibition. Treatment is often toxic and can affect long-term function and quality of life. In this context, identification of biomarker data that can help tailor therapy on an individualized basis and reduce treatment-related toxicity would be highly beneficial. A variety of predictive biomarkers have been discovered and are already utilized in clinical practice, while many more are being explored. We will review p16 overexpression as a surrogate biomarker in HPV-associated head and neck cancer and plasma EBV DNA as a biomarker in nasopharyngeal carcinoma, the two established biomarkers currently utilized in clinical practice. We will also examine novel predictive biomarkers that are in clinical development and may shape the future landscape of targeted head and neck cancer therapy. These emerging biomarkers include the tyrosine kinases and their signaling pathway, immune checkpoint biomarkers, tumor suppressor abnormalities, and molecular predictors of hypoxia-targeted therapy. We will also look at futuristic biomarkers including detection of circulating DNA from clinical specimens and rapid tumor profiling. We will highlight the ongoing effort that will see a shift from prognostic to predictive biomarker development in head and neck cancer with the goal of delivering individualized cancer therapy.

Trial registration

N/A.

Molecular targeting of hypoxia in radiotherapy

Hypoxia (low O₂) is an essential microenvironmental driver of phenotypic diversity in human solid cancers. Hypoxic cancer cells hijack evolutionarily conserved, O₂- sensitive pathways eliciting molecular adaptations that impact responses to radiotherapy, tumor recurrence and patient survival. In this review, we summarize the radiobiological, genetic, epigenetic and metabolic mechanisms orchestrating oncogenic responses to hypoxia. In addition, we outline emerging hypoxia- targeting strategies that hold promise for individualized cancer therapy in the context of radiotherapy and drug delivery.

Hypoxic tumor microenvironment: Opportunities to develop targeted therapies

In recent years, there has been great progress in the understanding of tumor biology and its surrounding microenvironment. Solid tumors create regions with low oxygen levels, generally termed as hypoxic regions. These hypoxic areas offer a tremendous opportunity to develop targeted therapies. Hypoxia is not a random by-product of the cellular milieu due to uncontrolled tumor growth; rather it is a constantly evolving participant in overall tumor growth and fate. This article reviews current trends and recent advances in drug therapies and delivery systems targeting hypoxia in the tumor microenvironment. In the first part, we give an account of important physicochemical changes and signaling pathways activated in the hypoxic microenvironment. This is then followed by various treatment strategies including hypoxia-sensitive signaling pathways and approaches to develop hypoxia-targeted drug delivery systems.

Hypoxia-activated prodrugs: paths forward in the era of personalised medicine

Tumour hypoxia has been pursued as a cancer drug target for over 30 years, most notably using bioreductive (hypoxia-activated) prodrugs that target antineoplastic agents to low-oxygen tumour compartments. Despite compelling evidence linking hypoxia with treatment resistance and adverse prognosis, a number of such prodrugs have recently failed to demonstrate efficacy in pivotal clinical trials; an outcome that demands reflection on the discovery and development of these compounds. In this review, we discuss a clear disconnect between the pathobiology of tumour hypoxia, the pharmacology of hypoxia-activated prodrugs and the manner in which they have been taken into clinical development. Hypoxia-activated prodrugs have been evaluated in the manner of broad-spectrum cytotoxic agents, yet a growing body of evidence suggests that their activity is likely to be dependent on the coincidence of tumour hypoxia, expression of specific prodrug-activating reductases and intrinsic sensitivity of malignant clones to the cytotoxic effector. Hypoxia itself is highly variable between and within individual tumours and is not treatment-limiting in all cancer subtypes. Defining predictive biomarkers for hypoxia-activated prodrugs and overcoming the technical challenges of assaying them in clinical settings will be essential to deploying these agents in the era of personalised cancer medicine.

F-18 fluoromisonidazole for imaging tumor hypoxia: imaging the microenvironment for personalized cancer therapy

Hypoxia in solid tumors is one of the seminal mechanisms for developing aggressive trait and treatment resistance in solid tumors. This evolutionarily conserved biological mechanism along with derepression of cellular functions in cancer, although resulting in many challenges, provide us with opportunities to use these adversities to our advantage. Our ability to use molecular imaging to characterize therapeutic targets such as hypoxia and apply this information for therapeutic interventions is growing rapidly. Evaluation of hypoxia and its biological ramifications to effectively plan appropriate therapy that can overcome the cure-limiting effects of hypoxia provides an objective means for treatment selection and planning. Fluoromisonidazole (FMISO) continues to be the lead radiopharmaceutical in PET imaging for the evaluation, prognostication, and quantification of tumor hypoxia, one of the key elements of the tumor microenvironment. FMISO is less confounded by blood flow, and although the images have less contrast than FDG-PET, its uptake after 2 hours is an accurate reflection of inadequate regional oxygen partial pressure at the time of radiopharmaceutical administration. By virtue of extensive clinical utilization, FMISO remains the lead candidate for imaging and quantifying hypoxia. The past decade has seen significant technological advances in investigating hypoxia imaging in radiation treatment planning and in providing us with the ability to individualize radiation delivery and target volume coverage. The presence of widespread hypoxia in the tumor can be effectively targeted with a systemic hypoxic cell cytotoxin or other agents that are more effective with diminished oxygen partial pressure, either alone or in combination. Molecular imaging in general and hypoxia imaging in particular will likely become an important in vivo imaging biomarker of the future, complementing the traditional direct tissue sampling methods by providing a snap shot of a primary tumor and metastatic disease and in following treatment response and will serve as adjuncts to personalized therapy.

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.

Correlation of p16 status, hypoxic imaging using [18F]-misonidazole positron emission tomography and outcome in patients with loco-regionally advanced head and neck cancer

INTRODUCTION

We investigated the relationship between hypoxia, human papillomavirus (HPV) status and outcome in head and neck squamous cell carcinoma.

METHODS

Patients with stage III and IV head and neck squamous cell carcinoma treated on phase I and II chemoradiation trials with 70-Gy radiation combined with tirapazamine/cisplatin or cisplatin/fluorouracil (5FU), hypoxic imaging using [18F]-misonidazole positron emission tomography and known HPV status (by p16 immunohistochemistry) were included in this sub-study. Separate analyses were conducted to consider the impact of tirapazamine on HPV-negative tumours in the phase II trial.

RESULTS

Both p16-positive oropharyngeal tumours and p16-negative head and neck squamous cell carcinoma tumours had a high prevalence of tumour hypoxia; 14/19 (74%) and 35/44 (80%), respectively. The distribution of hypoxia (primary, nodal) was similar. On phase II, trial patients with p16-negative hypoxic tumours had worse loco-regional control with cisplatin and 5FU compared with tirapazamine and cisplatin (P < 0.001) and worse failure-free survival (hazard ratio = 5.18; 95% confidence interval, 1.98-13.55; P = 0.001). Only 1 out of 14 p16-positive patients on the phase II trial experienced loco-regional failure.

CONCLUSION

Hypoxia, as assessed by [18F]-misonidazole positron emission tomography, is frequently present in both p16-positive and negative head and neck cancer. Further research is required to determine whether hypoxic imaging can be used to predict benefit from hypoxia-targeting therapies in patients with p16-negative tumours.

Specific recommendations for accurate and direct use of PET-CT in PET guided radiotherapy for head and neck sites

PURPOSE

To provide specific experience-based guidance and recommendations for centers wishing to develop, validate, and implement an accurate and efficient process for directly using positron emission tomography-computed tomography (PET-CT) for the radiotherapy planning of head and neck cancer patients.

METHODS

A PET-CT system was modified with hard-top couch, external lasers and radiotherapy immobilization and indexing devices and was subject to a commissioning and quality assurance program. PET-CT imaging protocols were developed specifically for radiotherapy planning and the image quality and pathway tested using phantoms and five patients recruited into an in-house study. Security and accuracy of data transfer was tested throughout the whole data pathway. The patient pathway was fully established and tested ready for implementation in a PET-guided dose-escalation trial for head and neck cancer patients.

RESULTS

Couch deflection was greater than for departmental CT simulator machines. An area of high attenuation in the couch generated image artifacts and adjustments were made accordingly. Using newly developed protocols CT image quality was suitable to maintain delineation and treatment accuracy. Upon transfer of data to the treatment planning system a half pixel offset between PET and CT was observed and corrected. By taking this into account, PET to CT alignment accuracy was maintained below 1 mm in all systems in the data pathway. Transfer of structures delineated in the PET fusion software to the radiotherapy treatment planning system was validated.

CONCLUSIONS

A method to perform direct PET-guided radiotherapy planning was successfully validated and specific recommendations were developed to assist other centers. Of major concern is ensuring that the quality of PET and CT data is appropriate for radiotherapy treatment planning and on-treatment verification. Couch movements can be compromised, bore-size can be a limitation for certain immobilization techniques, laser positioning may affect setup accuracy and couch deflection may be greater than scanners dedicated to radiotherapy. The full set of departmental commissioning and routine quality assurance tests applied to radiotherapy CT simulators must be carried out on the PET-CT scanner. CT image quality must be optimized for radiotherapy planning whilst understanding that the appearance will differ between scanners and may affect delineation. PET-CT quality assurance schedules will need to be added to and modified to incorporate radiotherapy quality assurance. Methods of working for radiotherapy and PET staff will change to take into account considerations of both parties. PET to CT alignment must be subject to quality control on a loaded and unloaded couch preferably using a suitable emission phantom, and tested throughout the whole data pathway. Data integrity must be tested throughout the whole pathway and a system included to verify that delineated structures are transferred correctly. Excellent multidisciplinary team communication and working is vital, and key staff members on both sides should be specifically dedicated to the project. Patient pathway should be clearly devised to optimize patient care and the resources of all departments. Recruitment of a cohort of patients into a methodology study is valuable to test the quality assurance methods and pathway.

The clinical importance of assessing tumor hypoxia: relationship of tumor hypoxia to prognosis and therapeutic opportunities

Tumor hypoxia is a well-established biological phenomenon that affects the curability of solid tumors, regardless of treatment modality. Especially for head and neck cancer patients, tumor hypoxia is linked to poor patient outcomes. Given the biological problems associated with tumor hypoxia, the goal for clinicians has been to identify moderately to severely hypoxic tumors for differential treatment strategies. The "gold standard" for detecting and characterizing of tumor hypoxia are the invasive polarographic electrodes. Several less invasive hypoxia assessment techniques have also shown promise for hypoxia assessment. The widespread incorporation of hypoxia information in clinical tumor assessment is severely impeded by several factors, including regulatory hurdles and unclear correlation with potential treatment decisions. There is now an acute need for approved diagnostic technologies for determining the hypoxia status of cancer lesions, as it would enable clinical development of personalized, hypoxia-based therapies, which will ultimately improve outcomes. A number of different techniques for assessing tumor hypoxia have evolved to replace polarographic pO2 measurements for assessing tumor hypoxia. Several of these modalities, either individually or in combination with other imaging techniques, provide functional and physiological information of tumor hypoxia that can significantly improve the course of treatment. The assessment of tumor hypoxia will be valuable to radiation oncologists, surgeons, and biotechnology and pharmaceutical companies who are engaged in developing hypoxia-based therapies or treatment strategies.

Phase I study of weekly nab-paclitaxel + weekly cetuximab + intensity-modulated radiation therapy (IMRT) in patients with stage III-IVB head and neck squamous cell carcinoma (HNSCC)

BACKGROUND

There is a clinical need to improve the efficacy of standard cetuximab + concurrent intensity-modulated radiation therapy (IMRT) for patients with locally and/or regionally advanced HNSCC. Taxanes have radiosensitizing activity against HNSCC, and nab-paclitaxel may offer therapeutic advantage in comparison with other taxanes.

PATIENTS AND METHODS

This was a single-institution phase I study with a modified 3 + 3 design. Four dose levels (DLs) of weekly nab-paclitaxel were explored (30, 45, 60, and 80 mg/m(2)), given with standard weekly cetuximab (450 mg/m(2) loading dose followed by 250 mg/m(2) weekly) and concurrent IMRT (total dose, 70 Gy).

RESULTS

Twenty-five eligible patients (20 M, 5 F) enrolled, with median age 58 years (range, 46-84 years). Primary tumor sites were oropharynx, 19 (10 human papillomavirus [HPV] pos, 8 HPV neg, 1 not done); neck node with unknown primary, 2; larynx 2; and oral cavity and maxillary sinus, 1 each. Seven patients had received prior induction chemotherapy. Maximum tolerated dose (MTD) was exceeded at DL4 (nab-paclitaxel, 80 mg/m(2)) with three dose-limiting toxicities (DLTs) (grade 3 neuropathy, grade 3 dehydration, with grade 3 mucositis grade 3 anemia) among five assessable patients. There was only one DLT (grade 3 supraventricular tachycardia) among six patients at DL3 (nab-paclitaxel, 60 mg/m(2)), and this was deemed the MTD. Among 23 assessable patients, the most common ≥ g3 AEs were lymphopenia 100%, functional mucositis 65%, and pain in throat/oral cavity 52%. At a median follow-up of 33 months, 2-year failure-free survival (FFS) is 65% [95% confidence interval (CI) 42% to 81%] and 2-year overall survival (OS) is 91% (95% CI 69-97).

CONCLUSION

The recommended phase II dose for nab-paclitaxel is 60 mg/m(2) weekly when given standard weekly cetuximab and concurrent IMRT. This regimen merits further study as a nonplatinum alternative to IMRT + cetuximab alone.

CLINICALTRIALSGOV ID

NCT00736619.

Phase III randomized trial of weekly cisplatin and irradiation versus cisplatin and tirapazamine and irradiation in stages IB2, IIA, IIB, IIIB, and IVA cervical carcinoma limited to the pelvis: a Gynecologic Oncology Group study

PURPOSE

This prospective, randomized phase III intergroup trial of the Gynecologic Oncology Group and National Cancer Institute of Canada Clinical Trials Group was designed to test the effectiveness and safety of adding the hypoxic cell sensitizer tirapazamine (TPZ) to standard cisplatin (CIS) chemoradiotherapy in locally advanced cervix cancer.

PATIENTS AND METHODS

Patients with locally advanced cervix cancer were randomly assigned to CIS chemoradiotherapy versus CIS/TPZ chemoradiotherapy. Primary end point was progression-free survival (PFS). Secondary end points included overall survival (OS) and tolerability.

RESULTS

PFS was evaluable in 387 of 402 patients randomly assigned over 36 months, with enrollment ending in September 2009. Because of the lack of TPZ supply, the study did not reach its original target accrual goal. At median follow-up of 28.3 months, PFS and OS were similar in both arms. Three-year PFS for the TPZ/CIS/RT and CIS/RT arms were 63.0% and 64.4%, respectively (log-rank P = .7869). Three-year OS for the TPZ/CIS/RT and CIS/RT arms were 70.5% and 70.6%, respectively (log-rank P = .8333). A scheduled interim safety analysis led to a reduction in the starting dose for the TPZ/CIS arm, with resulting tolerance in both treatment arms.

CONCLUSION

TPZ/CIS chemoradiotherapy was not superior to CIS chemoradiotherapy in either PFS or OS, although definitive commentary was limited by an inadequate number of events (progression or death). TPZ/CIS chemoradiotherapy was tolerable at a modified starting dose.

Role of positron emission tomography/computed tomography (PET/CT) in head and neck cancer

Positron emission tomography/computed tomography (PET/CT) has an important role in the diagnosis and treatment of head and neck cancer. The technique can aid in the detection of an unknown primary tumor, assist in locoregional staging, evaluate for distant metastases or second primary tumors, and be a component of restaging and tumor surveillance. This article reviews the basic principles, pitfalls, and uses of PET/CT in head and neck cancer, as well as potential future applications.

PR-104 a bioreductive pre-prodrug combined with gemcitabine or docetaxel in a phase Ib study of patients with advanced solid tumours

Background

The purpose of this phase Ib clinical trial was to determine the maximum tolerated dose (MTD) of PR-104 a bioreductive pre-prodrug given in combination with gemcitabine or docetaxel in patients with advanced solid tumours.

Methods

PR-104 was administered as a one-hour intravenous infusion combined with docetaxel 60 to 75 mg/m² on day one given with or without granulocyte colony stimulating factor (G-CSF) on day two or administrated with gemcitabine 800 mg/m² on days one and eight, of a 21-day treatment cycle. Patients were assigned to one of ten PR-104 dose-levels ranging from 140 to 1100 mg/m² and to one of four combination groups. Pharmacokinetic studies were scheduled for cycle one day one and ¹⁸F fluoromisonidazole (FMISO) positron emission tomography hypoxia imaging at baseline and after two treatment cycles.

Results

Forty two patients (23 females and 19 males) were enrolled with ages ranging from 27 to 85 years and a wide range of advanced solid tumours. The MTD of PR-104 was 140 mg/m² when combined with gemcitabine, 200 mg/m² when combined with docetaxel 60 mg/m², 770 mg/m² when combined with docetaxel 60 mg/m² plus G-CSF and ≥770 mg/m² when combined with docetaxel 75 mg/m² plus G-CSF. Dose-limiting toxicity (DLT) across all four combination settings included thrombocytopenia, neutropenic fever and fatigue. Other common grade three or four toxicities included neutropenia, anaemia and leukopenia. Four patients had partial tumour response. Eleven of 17 patients undergoing FMISO scans showed tumour hypoxia at baseline. Plasma pharmacokinetics of PR-104, its metabolites (alcohol PR-104A, glucuronide PR-104G, hydroxylamine PR-104H, amine PR-104M and semi-mustard PR-104S1), docetaxel and gemcitabine were similar to that of their single agents.

Conclusions

Combination of PR-104 with docetaxel or gemcitabine caused dose-limiting and severe myelotoxicity, but prophylactic G-CSF allowed PR-104 dose escalation with docetaxel. Dose-limiting thrombocytopenia prohibited further evaluation of the PR104-gemcitabine combination. A recommended dose was identified for phase II trials of PR-104 of 770 mg/m² combined with docetaxel 60 to 75 mg/m² both given on day one of a 21-day treatment cycle supported by prophylactic G-CSF (NCT00459836).

Hypoxia in head and neck squamous cell carcinoma

Hypoxia is a common feature in most of the solid tumors including head and neck squamous cell carcinoma (HNSCC). Hypoxia reflects the imbalance between oxygen consumption by the rapidly proliferating cancer cells and the insufficient oxygen delivery due to poor vascularization and blood supply. The hypoxic microenvironment in the HNSCC contributes to the development of aggressive carcinoma phenotype with high metastatic rate, resistance to therapeutic agents, and higher tumor recurrence rates, leading to low therapeutic efficiency and poor outcome. To overcome the therapeutic resistance due to hypoxia and improving the prognosis of the HNSCC patients, many approaches have been examined in laboratory studies and clinical trials. In this short paper, we discuss the mechanisms involved in the resistance of radiotherapy and chemotherapy in hypoxic condition. We also exploit the molecular mechanisms employed by the HNSCC cells to adapt the hypoxic condition and their tumorigenic role in head and neck, as well as the strategies to overcome hypoxia-induced therapeutic resistance.

Imaging hypoxia in gliomas

Hypoxia plays a central role in tumour development, angiogenesis, growth and resistance to treatment. Owing to constant developments in medical imaging technology, significant advances have been made towards in vitro and in vivo imaging of hypoxia in a variety of tumours, including gliomas of the central nervous system. The aim of this article is to review the literature on imaging approaches currently available for measuring hypoxia in human gliomas and provide an insight into recent advances and future directions in this field. After a brief overview of hypoxia and its importance in gliomas, several methods of measuring hypoxia will be presented. These range from invasive monitoring by Eppendorf polarographic O(2) microelectrodes, positron electron tomography (PET) tracers based on 2-nitroimidazole compounds [(18)F-labelled fluoro-misonidazole ((18)F-MISO) or 1-(2-[((18))F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP-170)], (64)Cu-ATSM Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) or (99m)Tc- and (68)Ga-labelled metronidazole (MN) agents to advanced MRI methods, such as blood oxygenation level dependent (BOLD) MRI, oxygen-enhanced MRI, diffusion-weighted MRI (DWI-MRI), dynamic contrast-enhanced MRI (DCE-MRI) and (1)H-magnetic resonance spectroscopy.

Is there a role for tirapazamine in the treatment of cervical cancer?

INTRODUCTION

Cervical cancer is the second-most common malignancy in women worldwide. Cisplatin was introduced as a radiosensitizer in 1999 to improve chances of survival. Tumor cell hypoxia, however, remains a major limiting factor in the treatment of solid tumors with chemotherapy and radiation. There has since been significant interest in the use of bioreductive agents to overcome the hypoxia and improve survival. The addition of tirapazamine (TPZ) to conventional chemoradiation protocols in the management of cervical cancer held promise in the initial Phase I and II clinical trials in delaying recurrence and improving survival. However, GOG recently announced early closure of the Phase III trial of tirapazamine in cervical cancer due to a lack of increased survival.

AREAS COVERED

This article covers the definition of hypoxic tumor cells, the markers of tumor hypoxia, methods for measuring hypoxia as well as the pharmacologic action of tirapazamine in hypoxic media. Furthermore, it critically evaluates TPZ's role in cervical cancer treatment and the drawbacks to the GOG study. The authors review all clinical trials published to date with special emphasis on cervical cancer. A systematic review of the literature was also undertaken with PubMed and Ovid.

EXPERT OPINION

Despite the promising results from early clinical trials, it has been shown that the addition of tirapazamine appears to confer no benefits on progression-free or overall survival in patients with cervical cancer. Success in the future will require smaller randomized trials with biologic targets that have acceptable toxicity and efficacy.

Targeting tumor perfusion and oxygenation to improve the outcome of anticancer therapy

Radiotherapy and chemotherapy are widespread clinical modalities for cancer treatment. Among other biological influences, hypoxia is a main factor limiting the efficacy of radiotherapy, primarily because oxygen is involved in the stabilization of the DNA damage caused by ionizing radiations. Radiobiological hypoxia is found in regions of rodent and human tumors with a tissue oxygenation level below 10 mmHg at which tumor cells become increasingly resistant to radiation damage. Since hypoxic tumor cells remain clonogenic, their resistance to the treatment strongly influences the therapeutic outcome of radiotherapy. There is therefore an urgent need to identify adjuvant treatment modalities aimed to increase tumor pO(2) at the time of radiotherapy. Since tumor hypoxia fundamentally results from an imbalance between oxygen delivery by poorly efficient blood vessels and oxygen consumption by tumor cells with high metabolic activities, two promising approaches are those targeting vascular reactivity and tumor cell respiration. This review summarizes the current knowledge about the development and use of tumor-selective vasodilators, inhibitors of tumor cell respiration, and drugs and treatments combining both activities in the context of tumor sensitization to X-ray radiotherapy. Tumor-selective vasodilation may also be used to improve the delivery of circulating anticancer agents to tumors. Imaging tumor perfusion and oxygenation is of importance not only for the development and validation of such combination treatments, but also to determine which patients could benefit from the therapy. Numerous techniques have been developed in the preclinical setting. Hence, this review also briefly describes both magnetic resonance and non-magnetic resonance in vivo methods and compares them in terms of sensitivity, quantitative or semi-quantitative properties, temporal, and spatial resolutions, as well as translational aspects.

Enhanced antitumor efficacy of cisplatin by tirapazamine-transferrin conjugate

Combination of tirapazamine (TPZ) with cisplatin has been studied extensively in clinical trial for tumor therapy. However, in phase III clinical trial, the combination therapy did not show overall survival improvement in patients. To decrease the side effects and increase the efficacy of the combination therapy, TPZ was conjugated with transferrin (Tf-G-TPZ) for targeted delivery and co-administered with cisplatin. In vitro toxicity study showed that the combination of Tf-G-TPZ with cisplatin induced substantially higher cytotoxicity of tumor cells than the combination of TPZ and cisplatin. After Tf-G-TPZ was intravenously injected into tumor-bearing mice, its total accumulation in tumor was 2.3 fold higher than that of the unmodified TPZ, suggesting transferrin-mediated target delivery of TPZ into the tumor tissue. With the increased accumulation of Tf-G-TPZ in tumor, the synergistic anti-tumor effects of Tf-G-TPZ and cisplatin were also enhanced as showed by the 53% tumor inhibition rate. Meanwhile, the side effects such as body weight lost were not significantly increased. Therefore, Tf-G-TPZ holds great promise to a better substitute for TPZ in the combination therapy with cisplatin.

Correlation of Ataxia-Telangiectasia-Mutated (ATM) gene loss with outcome in head and neck squamous cell carcinoma

OBJECTIVES

Ataxia-Telangiectasia-Mutated (ATM) gene loss has been associated with poor prognosis and treatment resistance in head and neck squamous cell carcinomas (HNSCC). We investigated the relationship between ATM loss detected by fluorescence in-situ hybridisation (FISH) with patient outcome, and its relationship with Human Papillomavirus (HPV)/p16(INK4A) status.

MATERIAL AND METHODS

Copy number of the ATM gene and chromosome 11 were determined by FISH and HPV status was determined using p16(INK4A) immunohistochemistry in 87 paraffin embedded tumour samples from patients with HNSCC treated with chemoradiation at a single institution. ATM loss was correlated with patient outcome as both a continuous and dichotomous variable.

RESULTS

Of 73 evaluable patients, 44 (60.3%) demonstrated loss of the ATM gene. There was no correlation between ATM loss (defined as a mean ratio of ATM: chromosome 11<0.75) and overall survival (OS, p=0.67) or time to locoregional failure (TTLRF, p=0.72). Similarly, when evaluated as a continuous variable there was no significant relationship between ATM loss and patient outcome (OS, p=0.89; TTLRF, p=0.21). No significant relationship was found between p16(INK4A) status and ATM loss, for patient outcome. We found 35.6% (n=26) of patients demonstrated polysomy of chromosome 11 (defined as the presence of a mean >2.5 copies of chromosome 11) which was significantly associated with p16(INK4A) negative status (p=0.0004), but did not influence outcome.

CONCLUSIONS

ATM loss is a frequent event in HNSCC, however it does not impact outcome after treatment with chemoradiation. Polysomy of chromosome 11 was significantly associated with p16(INK4A) negative status but also lacks prognostic significance.

Phase 1 study of tirapazamine in combination with radiation and weekly cisplatin in patients with locally advanced cervical cancer

INTRODUCTION

Hypoxia is an adverse prognostic factor in locoregionally advanced cervical cancer treated with radiation. The aim of this phase I study was to develop a well-tolerated regimen that added tirapazamine to the standard regimen of radiation and weekly low-dose cisplatin.

METHODS

Eligible patients had previously untreated carcinoma of the cervix, stages IB2 to IVA. The starting schedule was radiotherapy (45-50.4 Gy external beam radiation followed by brachytherapy), with concomitant weekly intravenous cisplatin, 40 mg/m on weeks 1 to 6 and weekly intravenous tirapazamine, 290 mg/m in weeks 1 to 5.

RESULTS

Eleven patients were enrolled. The median age was 52 years (range, 31-65 years). Ten patients had squamous cell carcinoma and 1 patient had adenocarcinoma; 5 patients had stage 1B2 disease, 1 had stage IIA, 3 had stage IIB-3, 1 had stage IIIB, and 1 had stage IVA. The first 2 patients on dose level 1 experienced a dose-limiting toxicity (DLT): 1 experienced grade 3 alanine amino transferase elevation and grade 4 pulmonary embolism, and 1 experienced grade 3 ototoxicity. Doses were decreased to dose level -1 with a 30-mg/m dose of cisplatin and a 260-mg/m dose of tirapazamine. Three patients were treated without any DLTs. Six patients were then treated on dose level -1a: a 35-mg/m dose of cisplatin and a 260-mg/m doses of tirapazamine with 2 DLTs--grade 3 neutropenia with dose omission and grade 4 pulmonary embolism with major hemodynamic compromise. Three of 10 evaluable patients have experienced locoregional failure.

CONCLUSIONS

The combination of weekly tirapazamine and cisplatin with radiation for locally advanced cervical cancer was associated with more toxicity than anticipated with the recommended dose level being tirapazamine 260 mg/m and cisplatin 30 mg/m. Further study of this weekly schedule is not warranted.

Radionuclide imaging of perfusion and hypoxia

PURPOSE

We present a review of radionuclide imaging of tumour vascular physiology as it relates to angiogenesis. We focus on clinical trials in human subjects using PET and SPECT to evaluate tumour physiology, in particular blood flow and hypoxia.

METHODS

A systematic review of literature based on MEDLINE searches updated in February 2010 was performed.

RESULTS

Twenty-nine studies were identified for review: 14 dealt with (15)O-water PET perfusion imaging, while 8 dealt with (18)F-fluoromisonidazole PET hypoxia imaging. Five used SPECT methods. The studies varied widely in technical quality and reporting of methods.

CONCLUSIONS

A subset of radionuclide methods offers accurate quantitative scientific observations on tumour vascular physiology of relevance to angiogenesis and its treatment. The relationship between cellular processes of angiogenesis and changing physiological function remains poorly defined. The promise of quantitative functional imaging at high specificity and low administered dose sustains interest in radionuclide methods.

The contribution of cetuximab in the treatment of recurrent and/or metastatic head and neck cancer

Recurrent and/or metastatic squamous cell carcinoma of the head and neck (HNSCC) continues to be a source of significant morbidity and mortality worldwide. Agents that target the epidermal growth factor receptor (EGFR) have demonstrated beneficial effects in this setting. Cetuximab, a monoclonal antibody against the EGFR, improves locoregional control and overall survival when used as a radiation sensitizer in patients with locoregionally advanced HNSCC undergoing definitive radiation therapy with curative intent. Cetuximab is also active as monotherapy in patients whose cancer has progressed on platinum-containing therapy. In the first-line setting for incurable HNSCC, cetuximab added to platinum-based chemotherapy significantly improves overall survival compared with standard chemotherapy alone. These positive results have had a significant impact on the standard of care for advanced HNSCC. In this review, we will discuss the mechanism of action, clinical data and common toxicities that pertain to the use of cetuximab in the treatment of advanced incurable HNSCC.

Tirapazamine, cisplatin, and radiation versus cisplatin and radiation for advanced squamous cell carcinoma of the head and neck (TROG 02.02, HeadSTART): a phase III trial of the Trans-Tasman Radiation Oncology Group

PURPOSE

Promising results in a randomized phase II trial with the hypoxic cytotoxin tirapazamine (TPZ) combined with cisplatin (CIS) and radiation led to this phase III trial.

PATIENTS AND METHODS

Patients with previously untreated stage III or IV (excluding T1-2N1 and M1) squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx, or larynx were randomly assigned to receive definitive radiotherapy (70 Gy in 7 weeks) concurrently with either CIS (100 mg/m(2)) on day 1 of weeks 1, 4, and 7 or CIS (75 mg/m(2)) plus TPZ (290 mg/m(2)/d) on day 1 of weeks 1, 4, and 7 and TPZ alone (160 mg/m(2)/d) on days 1, 3, and 5 of weeks 2 and 3 (TPZ/CIS). The primary end point was overall survival (OS). The planned sample size was 850, estimated to result in 334 deaths, which would provide 90% power to detect a difference in 2-year survival rates of 60% v 70% for CIS versus TPZ/CIS, respectively (hazard ratio = 0.69).

RESULTS

Eight hundred sixty-one patients were accrued from 89 sites in 16 countries. In an intent-to-treat analysis, the 2-year OS rates were 65.7% for CIS and 66.2% for TPZ/CIS (TPZ/CIS--CIS: 95% CI, -5.9% to 6.9%). There were no significant differences in failure-free survival, time to locoregional failure, or quality of life as measured by Functional Assessment of Cancer Therapy-Head and Neck.

CONCLUSIONS

We found no evidence that the addition of TPZ to chemoradiotherapy, in patients with advanced head and neck cancer not selected for the presence of hypoxia, improves OS.

Hypoxia-inducible factor-1 as a therapeutic target in endometrial cancer management

In the Western world, endometrial cancer (EC) is the most common malignant tumor of the female genital tract. Solid tumors like EC outgrow their vasculature resulting in hypoxia. Tumor hypoxia is important because it renders an aggressive phenotype and leads to radio- and chemo-therapy resistance. Hypoxia-inducible factor-1alpha (HIF-1alpha) plays an essential role in the adaptive cellular response to hypoxia and is associated with poor clinical outcome in EC. Therefore, HIF-1 could be an attractive therapeutic target. Selective HIF-1 inhibitors have not been identified. A number of nonselective inhibitors which target signaling pathways upstream or downstream HIF-1 are known to decrease HIF-1alpha protein levels. In clinical trials for the treatment of advanced and/or recurrent EC are the topoisomerase I inhibitor Topotecan, mTOR-inhibitor Rapamycin, and angiogenesis inhibitor Bevacizumab. Preliminary data shows encouraging results for these agents. Further work is needed to identify selective HIF-1 inhibitors and to translate these into clinical trials.

[Radiotherapy, chemotherapy and target therapy for treatment of head and neck cancer : new developments]

Approximately 60% of patients initially treated for squamous cell cancer of the upper gastrointestinal tract suffer from advanced tumor disease (UICC stages III and IV). Multimodal strategies lead to overall survival rates of up to 50%. Recent studies show indications that the risk of distant metastases after induction chemotherapy (CT) is less than after primary radiotherapy (RT) or radiochemotherapy (RCT). Hyperfractionation or accelerated radiation with concomitant boost shows superior results compared to classic RT. Intensity-modulated radiotherapy (IMRT) is a new method for better adjusted dose distribution. Targeted therapy with specific antibodies against biological targets, such as epidermal growth factor receptor (EGFR), showed superiority over RT but the comparison to classic RCT is still pending. Targeted therapy against vascular endothelial growth factor (VEGR) showed antiangiogenetic effects on tumors. In cases of non-resectability or distant metastases, palliative CT and target therapy are recommended. Reirradiation or IMRT offer increased locoregional tumor control at the expense of higher toxicity. Overall, advances in research on tumor biology offer increasingly more prognostic factors and markers for customized individual targeted therapy and CT.

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.

Current concepts of management in radiotherapy for head and neck squamous-cell cancer

Radiotherapy plays a key role in the management of early stage and locally advanced head and neck squamous-cell carcinomas (HNSCC) either alone or, more frequently combined with surgery and/or chemotherapy. Several approaches have been developed to improve its efficacy while maintaining acceptable toxicities, such as altered fractionated radiotherapy or concomitant chemoradiotherapy which have both improved the anti-tumor efficacy of radiotherapy. Of particular interest is concomitant chemoradiotherapy (CT-RT) which is the most commonly used approach in locally advanced disease. Taxanes and platinum-based induction chemotherapy could constitute an option in the treatment of locally advanced HNSCC and it's contribution before concomitant RT-CT is currently under investigation. More recently, epidermal growth factor receptor (EGFr) molecular targeting with cetuximab combined with radiotherapy has been successfully tested in a large randomized trial and this combination constitutes a new option, especially for patients with medical co-morbidities. Finally management of treatment related acute or late toxicity remains an important issue and in the last decade major achievements have been obtained in this field especially using intensity modulated radiotherapy (IMRT).

Brain tumor hypoxia: tumorigenesis, angiogenesis, imaging, pseudoprogression, and as a therapeutic target

Hypoxia is implicated in many aspects of tumor development, angiogenesis, and growth in many different tumors. Brain tumors, particularly the highly aggressive glioblastoma multiforme (GBM) with its necrotic tissues, are likely affected similarly by hypoxia, although this involvement has not been closely studied. Invasion, apoptosis, chemoresistance, resistance to antiangiogenic therapy, and radiation resistance may all have hypoxic mechanisms. The extent of the influence of hypoxia in these processes makes it an attractive therapeutic target for GBM. Because of their relationship to glioma and meningioma growth and angiogenesis, hypoxia-regulated molecules, including hypoxia inducible factor-1, carbonic anhydrase IX, glucose transporter 1, and vascular endothelial growth factor, may be suitable subjects for therapies. Furthermore, other novel hypoxia-regulated molecules that may play a role in GBM may provide further options. Emerging imaging techniques may allow for improved determination of hypoxia in human brain tumors to better focus therapeutic treatments; however, tumor pseudoprogression, which may be prompted by hypoxia, poses further challenges. An understanding of the role of hypoxia in tumor development and growth is important for physicians involved in the care of patients with brain tumors.

Prospective trial incorporating pre-/mid-treatment [18F]-misonidazole positron emission tomography for head-and-neck cancer patients undergoing concurrent chemoradiotherapy

PURPOSE

To report the results from a prospective study of a series of locoregionally advanced head-and-neck cancer patients treated with platinum-based chemotherapy and intensity-modulated radiotherapy and to discuss the findings of their pre-/mid-treatment [(18)F]-misonidazole ((18)F-FMISO) positron emission tomography (PET) scans.

METHODS AND MATERIALS

A total of 28 patients agreed to participate in this study. Of these 28 patients, 20 (90% with an oropharyngeal primary cancer) were able to undergo the requirements of the protocol. Each patient underwent four PET scans: one pretreatment fluorodeoxyglucose PET/computed tomography scan, two pretreatment (18)F-FMISO PET/computed tomography scans, and a third (18)F-FMISO PET (mid-treatment) scan performed 4 weeks after the start of chemoradiotherapy. The (18)F-FMISO PET scans were acquired 2-3 h after tracer administration. Patients were treated with 2-3 cycles of platinum-based chemotherapy concurrent with definitive intensity-modulated radiotherapy.

RESULTS

A heterogeneous distribution of (18)F-FMISO was noted in the primary and/or nodal disease in 90% of the patients. Two patients had persistent detectable hypoxia on their third mid-treatment (18)F-FMISO PET scan. One patient experienced regional/distant failure but had no detectable residual hypoxia on the mid-treatment (18)F-FMISO PET scan.

CONCLUSION

Excellent locoregional control was observed in this series of head-and-neck cancer patients treated with concurrent platinum-based chemotherapy and intensity-modulated radiotherapy despite evidence of detectable hypoxia on the pretreatment (18)F-FMISO PET/computed tomography scans of 18 of 20 patients. In this prospective study, neither the presence nor the absence of hypoxia, as defined by positive (18)F-FMISO findings on the mid-treatment PET scan, correlated with patient outcome. The results of this study have confirmed similar results reported previously.

Clinical biomarkers of angiogenesis inhibition

INTRODUCTION

An expanding understanding of the importance of angiogenesis in oncology and the development of numerous angiogenesis inhibitors are driving the search for biomarkers of angiogenesis. We review currently available candidate biomarkers and surrogate markers of anti-angiogenic agent effect.

DISCUSSION

A number of invasive, minimally invasive, and non-invasive tools are described with their potential benefits and limitations. Diverse markers can evaluate tumor tissue or biological fluids, or specialized imaging modalities.

CONCLUSIONS

The inclusion of these markers into clinical trials may provide insight into appropriate dosing for desired biological effects, appropriate timing of additional therapy, prediction of individual response to an agent, insight into the interaction of chemotherapy and radiation following exposure to these agents, and perhaps most importantly, a better understanding of the complex nature of angiogenesis in human tumors. While many markers have potential for clinical use, it is not yet clear which marker or combination of markers will prove most useful.

Molecular imaging of hypoxia

Hypoxia, a condition of insufficient O2 to support metabolism, occurs when the vascular supply is interrupted, as in stroke or myocardial infarction, or when a tumor outgrows its vascular supply. When otherwise healthy tissues lose their O2 supply acutely, the cells usually die, whereas when cells gradually become hypoxic, they adapt by up-regulating the production of numerous proteins that promote their survival. These proteins slow the rate of growth, switch the mitochondria to glycolysis, stimulate growth of new vasculature, inhibit apoptosis, and promote metastatic spread. The consequence of these changes is that patients with hypoxic tumors invariably experience poor outcome to treatment. This has led the molecular imaging community to develop assays for hypoxia in patients, including regional measurements from O2 electrodes placed under CT guidance, several nuclear medicine approaches with imaging agents that accumulate with an inverse relationship to O2, MRI methods that measure either oxygenation directly or lactate production as a consequence of hypoxia, and optical methods with NIR and bioluminescence. The advantages and disadvantages of these approaches are reviewed, along with the individual strategies for validating different imaging methods. Ultimately the proof of value is in the clinical performance to predict outcome, select an appropriate cohort of patients to benefit from a hypoxia-directed treatment, or plan radiation fields that result in better local control. Hypoxia imaging in support of molecular medicine has become an important success story over the last decade and provides a model and some important lessons for development of new molecular imaging probes or techniques.

Novel imaging approaches to head and neck cancer

An inadequate supply of oxygen, hypoxia, is an important factor contributing to resistance to treatment in a number of tumor types, including head and neck cancer. Novel imaging methods have been applied to studies of this important prognostic factor. Mammalian cells need oxygen to live but O2 also participates in the cytotoxic effects of ionizing radiation. Hypoxia is often the result of abnormal blood vessels supplying the tumor, increased diffusion distances to tumor cells, and reduced O2 transport capacity of the blood. Its consequences are mediated by a series of hypoxia-initiated genomic changes activating angiogenesis, glycolysis, and other processes that enable tumor cells to survive or escape the O2-deficient environment. Hypoxia has been shown to be important in overall diminished therapeutic response, malignant progression, increased probability of recurrence, locoregional spread, and distant metastases. Strategies are being developed to surmount the cure-limiting consequences of hypoxia, but methods are needed to select patients most likely to benefit from these new treatments. Even though hypoxia is a common tumor phenotype, it is by no means universal and is often heterogeneous within an individual patient. This review considers the biology of hypoxia, its consequences with respect to treatment, methods for measuring oxygenation in tissues, modern techniques for imaging of regional hypoxia, and how information about the oxygenation status of tumors might impact treatment.

Hypoxia positron emission tomography imaging with 18f-fluoromisonidazole

The importance of hypoxia in disease pathogenesis and prognosis is gathering increasing clinical significance and having a greater impact on patient management and outcome. Previous efforts to evaluate hypoxia have included the invasive assessment of hypoxia with immunohistologic and histographic oxygen probes. The emergence of new radiotracers has allowed noninvasive assessment of hypoxia, with the most extensively investigated and validated positron emission tomography radiotracer of hypoxia to date being (18)F-fluoromisonodazole ((18)F-FMISO). This review discusses the relevance and biology of hypoxia in cells and organ systems, and reviews the laboratory and clinical applications of (18)F-FMISO in oncology and noncancer disease states.

Homologous recombination is the principal pathway for the repair of DNA damage induced by tirapazamine in mammalian cells

Tirapazamine (3-amino-1,2,4-benzotriazine-1,4-dioxide) is a promising hypoxia-selective cytotoxin that has shown significant activity in advanced clinical trials in combination with radiotherapy and cisplatin. The current study aimed to advance our understanding of tirapazamine-induced lesions and the pathways involved in their repair. We show that homologous recombination plays a critical role in repair of tirapazamine-induced damage because cells defective in homologous recombination proteins XRCC2, XRCC3, Rad51D, BRCA1, or BRCA2 are particularly sensitive to tirapazamine. Consistent with the involvement of homologous recombination repair, we observed extensive sister chromatid exchanges after treatment with tirapazamine. We also show that the nonhomologous end-joining pathway, which predominantly deals with frank double-strand breaks (DSB), is not involved in the repair of tirapazamine-induced DSBs. In addition, we show that tirapazamine preferentially kills mutants both with defects in XPF/ERCC1 (but not in other nucleotide excision repair factors) and with defects in base excision repair. Tirapazamine also induces DNA-protein cross-links, which include stable DNA-topoisomerase I cleavable complexes. We further show that gamma H2AX, an indicator of DNA DSBs, is induced preferentially in cells in the S phase of the cell cycle. These observations lead us to an overall model of tirapazamine damage in which DNA single-strand breaks, base damage, and DNA-protein cross-links (including topoisomerase I and II cleavable complexes) produce stalling and collapse of replication forks, the resolution of which results in DSB intermediates, requiring homologous recombination and XPF/ERCC1 for their repair.

The cellular adaptations to hypoxia as novel therapeutic targets in childhood cancer

Exposure of tumour cells to reduced levels of oxygen (hypoxia) is a common finding in adult tumours. Hypoxia induces a myriad of adaptive changes within tumour cells which result in increased anaerobic glycolysis, new blood vessel formation, genetic instability and a decreased responsiveness to both radio and chemotherapy. Hypoxia correlates with disease stage and outcome in adult epithelial tumours and increasingly it is becoming apparent that hypoxia is also important in paediatric tumours. Despite its adverse effects upon tumour response to treatment hypoxia offers several avenues for new drug development. Bioreductive agents already exist, which are preferentially activated in areas of hypoxia, and thus have less toxicity for normal tissue. Additionally the adaptive cellular response to hypoxia offers several novel targets, including vascular endothelial growth factor (VEGF), carbonic anhydrase, and the central regulator of the cellular response to hypoxia, hypoxia inducible factor-1 (HIF-1). Novel agents have emerged against all of these targets and are at various stages of clinical and pre-clinical development. Hypoxia offers an exciting opportunity for new drug development that can include paediatric tumours at an early stage.