Physiologic Mechanisms of Therapeutic Resistance: Blood Flow and Hypoxia

Hypoxia signaling and oxygen metabolism in cardio-oncology

Cardio-oncology is a rapidly growing field in cardiology that focuses on the management of cardiovascular toxicities associated with cancer-directed therapies. Tumor hypoxia is a central driver of pathologic tumor growth, metastasis, and chemo-resistance. In addition, conditions that mimic hypoxia (pseudo-hypoxia) play a causal role in the pathogenesis of numerous types of cancer, including renal cell carcinoma. Therefore, therapies targeted at hypoxia signaling pathways have emerged over the past several years. Though efficacious, these therapies are associated with significant cardiovascular toxicities, ranging from hypertension to cardiomyopathy. This review focuses on oxygen metabolism in tumorigenesis, the role of targeting hypoxia signaling in cancer therapy, and the relevance of oxygen metabolism in cardio-oncology. This review will specifically focus on hypoxia signaling mediated by hypoxia-inducible factors and the prolyl hydroxylase oxygen-sensing enzymes, the cardiovascular effects of specific cancer targeted therapies mediated on VEGF and HIF signaling, hypoxic signaling in cardiovascular disease, and the role of oxygen in anthracycline cardiotoxicity. The implications of these therapies on myocardial biology and cardiac function are discussed, underlining the fine balance of hypoxia signaling in cardiac homeostasis. Understanding these cardiovascular toxicities will be important to optimize treatment for cancer patients while mitigating potentially severe cardiovascular side effects.

Response prediction of neoadjuvant chemoradiation therapy in locally advanced rectal cancer using CT-based fractal dimension analysis

OBJECTIVES

There are individual variations in neo-adjuvant chemoradiation therapy (nCRT) in patients with locally advanced rectal cancer (LARC). No reliable modality currently exists that can predict the efficacy of nCRT. The purpose of this study is to assess if CT-based fractal dimension and filtration-histogram texture analysis can predict therapeutic response to nCRT in patients with LARC.

METHODS

In this retrospective study, 215 patients (average age: 57 years (18-87 years)) who received nCRT for LARC between June 2005 and December 2016 and underwent a staging diagnostic portal venous phase CT were identified. The patients were randomly divided into two datasets: a training set (n = 170), and a validation set (n = 45). Tumor heterogeneity was assessed on the CT images using fractal dimension (FD) and filtration-histogram texture analysis. In the training set, the patients with pCR and non-pCR were compared in univariate analysis. Logistic regression analysis was applied to identify the predictive value of efficacy of nCRT and receiver operating characteristic analysis determined optimal cutoff value. Subsequently, the most significant parameter was assessed in the validation set.

RESULTS

Out of the 215 patients evaluated, pCR was reached in 20.9% (n = 45/215) patients. In the training set, 7 out of 37 texture parameters showed significant difference comparing between the pCR and non-pCR groups and logistic multivariable regression analysis incorporating clinical and 7 texture parameters showed that only FD was associated with pCR (p = 0.001). The area under the curve of FD was 0.76. In the validation set, we applied FD for predicting pCR and sensitivity, specificity, and accuracy were 60%, 89%, and 82%, respectively.

CONCLUSION

FD on pretreatment CT is a promising parameter for predicting pCR to nCRT in patients with LARC and could be used to help make treatment decisions.

KEY POINTS

• Fractal dimension analysis on pretreatment CT was associated with response to neo-adjuvant chemoradiation in patients with locally advanced rectal cancer. • Fractal dimension is a promising biomarker for predicting pCR to nCRT and may potentially select patients for individualized therapy.

Pre-treatment with Bifidobacterium infantis and its specific antibodies enhance targeted radiosensitization in a murine model for lung cancer

PURPOSE

The hypoxic microenvironments of solid tumours are complex and reduce the susceptibility of cancer cells to chemo- and radiotherapy. Conventional radiosensitisers have poor specificity, unsatisfactory therapeutic effects, and significant side effects. Anaerobic bacteria colonise and destroy hypoxic areas of the tumour and consequently enhance the effects of radiation.

METHODS

In this study, we treated a Lewis lung carcinoma transplant mouse model with Bifidobacterium infantis (Bi) combined with its specific monoclonal antibody (mAb) and radiotherapy (RT) to investigate its ability to radiosensitise the tumour. The tumour metabolism and hypoxia in the tumour tissue were monitored by micro-¹⁸F-FDG and ¹⁸F-FMISO PET/CT imaging. Immunohistochemistry was used to detect phosphorylated histone (γ-H2AX), proliferation (Ki-67), platelet endothelial cell adhesion molecules (CD31), tumour necrosis factor-α (TNF-α), hypoxia-inducible factor-1α (HIF-1α), and glucose transporter 1 (Glut-1) levels.

RESULTS

Tumour growth was slowed and survival time was markedly prolonged in mice subjected to the combination of B. infantis, specific antibody, and radiotherapy. Levels of HIF-1α, Glut-1, Ki-67, and CD31 expression, as well as uptake of FDG and FMISO, were the lowest in the combination-treated mice. In contrast, γ-H2AX and TNF-α expression levels were elevated and hypoxia in tumour tissue was reduced compared with controls.

CONCLUSION

In conclusion, our data indicated that the curative effect of radiotherapy for lung cancer was enhanced by pre-treating mice with a combination of B. infantis and its specific monoclonal antibody.

Tumor radiomic features complement clinico-radiological factors in predicting long-term local control and laryngectomy free survival in locally advanced laryngo-pharyngeal cancers

OBJECTIVE

To study if pre-treatment CT texture features in locally advanced squamous cell carcinoma of laryngo-pharynx can predict long-term local control and laryngectomy free survival (LFS).

METHODS

Image texture features of 60 patients treated with chemoradiation (CTRT) within an ethically approved study were studied on contrast-enhanced images using a texture analysis research software (TexRad, UK). A filtration-histogram technique was used where the filtration step extracted and enhanced features of different sizes and intensity variations corresponding to a particular spatial scale filter (SSF): SSF = 0 (without filtration), SSF = 2 mm (fine texture), SSF = 3-5 mm (medium texture) and SSF = 6 mm (coarse texture). Quantification by statistical and histogram technique comprised mean intensity, standard-deviation, entropy, mean positive pixels, skewness and kurtosis. The ability of texture analysis to predict LFS or local control was determined using Kaplan-Meier analysis and multivariate cox model.

RESULTS

Median follow-up of patients was 24 months (95% CI:20-28). 39 (65%) patients were locally controlled at last follow-up. 10 (16%) had undergone salvage laryngectomy after CTRT. For both local control & LFS, threshold optimal cut-off values of texture features were analyzed. Medium filtered-texture feature that were associated with poorer laryngectomy free survival were entropy ≥4.54, (p = 0.006), kurtosis ≥4.18; p = 0.019, skewness ≤-0.59, p = 0.001, and standard deviation ≥43.18; p = 0.009). Inferior local control was associated with medium filtered features entropy ≥4.54; p 0.01 and skewness ≤ - 0.12; p = 0.02. Using fine filters, entropy ≥4.29 and kurtosis ≥-0.27 were also associated with inferior local control (p = 0.01 for both parameters). Multivariate analysis showed medium filter entropy as an independent predictor for LFS and local control (p < 0.001 & p = 0.001).

CONCLUSION

Medium texture entropy is a predictor for inferior local control and laryngectomy free survival in locally advanced laryngo-pharyngeal cancer and this can complement clinico-radiological factors in predicting prognosticating these tumors.

ADVANCES IN KNOWLEDGE

Texture features play an important role as a surrogate imaging biomarker for predicting local control and laryngectomy free survival in locally advanced laryngo-pharyngeal tumors treated with definitive chemoradiation.

FAM175B promotes apoptosis by inhibiting ATF4 ubiquitination in esophageal squamous cell carcinoma

FAM175B is a reported regulator of p53 and suppresses tumorigenesis in numerous types of cancer, but very little is known about its function in esophageal squamous cell carcinomas (ESCCs), almost 70% of which exhibit mutations in p53. Here, we report that FAM175B expression is downregulated in high-grade intraepithelial neoplasia (t = 2.44, P = 0.031) and ESCC (t = 5.664, P < 0.001) tissues relative to that in adjacent normal esophageal tissues. Exogenous expression of FAM175B in ESCC cells resulted in a decrease in proliferation rate, inhibition of colony formation, and an increase in apoptosis rate. Knockdown of FAM175B produced the opposite results. Furthermore, confocal microscopy and coimmunoprecipitation assay showed that Activating transcription factor 4 (ATF4) colocalized and interacted with FAM175B. Ubiquitination assays revealed that FAM175B inhibited ubiquitin-dependent ATF4 degradation and elevated ATF4 protein level. Finally, luciferase reporter experiments further clarified that FAM175B promoted CHOP expression in an ATF4-dependent manner. Accordingly, the proapoptotic activity of FAM175B was significantly rescued by treatment with si-ATF4 and the CHOP inhibitor 4-PBA. In summary, FAM175B inhibited ATF4 ubiquitination and promoted ESCC cell apoptosis in a p53-independent manner. FAM175B expression loss may be an early diagnostic biomarker in ESCC patients.

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

Redox-Responsive Manganese Dioxide Nanoparticles for Enhanced MR Imaging and Radiotherapy of Lung Cancer

In this study, we synthesized manganese dioxide nanoparticles (MnO₂ NPs) stabilized with biocompatible polymers (polyvinylpyrrolidone and polyacrylic acid) and analyzed their effect on non-small cell lung cancer (NSCLC) cells with or without gefitinib resistance in vitro. MnO₂ NPs showed glutathione (GSH)-responsive dissolution and subsequent enhancement in magnetic resonance (MR) imaging. Of note, treatment with MnO₂ NPs induced significant cytotoxic effects on NSCLC cells, and additional dose-dependent therapeutic effects were obtained upon X-ray irradiation. Normal cells treated with MnO₂ NPs were viable at the tested concentrations. In addition, increased therapeutic efficacy could be achieved when the cells were treated with MnO₂ NPs in hypoxic conditions. Therefore, we conclude that the use of MnO₂ NPs in MR imaging and combination radiotherapy may be an efficient strategy for the imaging and therapy of NSCLC.

CT texture analysis in patients with locally advanced rectal cancer treated with neoadjuvant chemoradiotherapy: A potential imaging biomarker for treatment response and prognosis

PURPOSE

To evaluate the association of computed tomography (CT) texture features of locally advanced rectal cancer with neoadjuvant chemoradiotherapy (CRT) response and disease-free survival (DFS).

METHODS AND FINDINGS

The institutional review board approved this retrospective study. 95 patients who received neoadjuvant CRT, followed by surgery, for locally advanced rectal cancer were included. Texture features (entropy, uniformity, kurtosis, skewness, and standard deviation) were assessed in pretreatment CT images and obtained without filtration and with Laplacian of Gaussian spatial filter of various filter values (1.0, 1.5, 2.0, and 2.5). Dworak pathologic grading was used for treatment response assessment. Independent t-test was used to compare each texture feature between the treatment responder and non-responder groups. DFS was assessed with Kaplan-Meier method, and differences were compared with log-rank test. Cox proportional hazards models were constructed to predict prognosis based on stage, age, and each texture feature. Treatment responders (n = 32) showed significantly lower entropy, higher uniformity, and lower standard deviation in no filtration, fine (1.0), and medium (1.5) filter values. Entropy, uniformity, and standard deviation without filtration showed significant difference in DFS in Kaplan-Meier analysis (P = 0.015, 0.025, and 0.038). Homogeneous texture features (≤ 6.7 for entropy, > 0.0118 for uniformity, and ≤ 28.06 for standard deviation) were associated with higher DFS. Entropy, uniformity, and standard deviation were independent texture features in predicting DFS (P = 0.017, 0.03, and 0.036).

CONCLUSIONS

Homogeneous texture features are associated with better neoadjuvant CRT response and higher DFS in patients with locally advanced rectal cancer.

Hypoxia: A Double-Edged Sword in Cancer Therapy

Hypoxia is a common feature of malignant tumors. There is an interactive connection between hypoxia and chemoresistance, radioresistance, invasiveness, and angiogenesis. Therefore, tumor hypoxia has been considered as a validated target for treating cancer. This review focuses on the role of hypoxia on chemoresistance and radioresistance. In addition, we address several approaches targeting tumor hypoxia, known as hypoxia-targeted therapy.

Hybrid Manganese Dioxide Nanoparticles Potentiate Radiation Therapy by Modulating Tumor Hypoxia

Hypoxia in the tumor microenvironment (TME) mediates resistance to radiotherapy and contributes to poor prognosis in patients receiving radiotherapy. Here we report the design of clinically suitable formulations of hybrid manganese dioxide (MnO₂) nanoparticles (MDNP) using biocompatible materials to reoxygenate the TME by reacting with endogenous H₂O₂ MDNP containing hydrophilic terpolymer-protein-MnO₂ or hydrophobic polymer-lipid-MnO₂ provided different oxygen generation rates in the TME relevant to different clinical settings. In highly hypoxic murine or human xenograft breast tumor models, we found that administering either MDNP formulation before radiotherapy modulated tumor hypoxia and increased radiotherapy efficacy, acting to reduce tumor growth, VEGF expression, and vascular density. MDNP treatment also increased apoptosis and DNA double strand breaks, increasing median host survival 3- to 5-fold. Notably, in the murine model, approximately 40% of tumor-bearing mice were tumor-free after a single treatment with MDNPs plus radiotherapy at a 2.5-fold lower dose than required to achieve the same curative treatment without MDNPs. Overall, our findings offer a preclinical proof of concept for the use of MDNP formulations as effective radiotherapy adjuvants. Cancer Res; 76(22); 6643-56. ©2016 AACR.

Hypoxia-inducible factor-1alpha suppressing apoptosis and increasing tolerance of lung cancer cells to chemotherapy

In order to construct plasmid of hypoxia-inducible factor-1alpha (HIF-1alpha), and transfect into human lung cancer cells A549, the change in sensitivity of lung cancer cells A549 to chemotherapy was observed. HIF-1alpha mRNA structure region was amplified by RT-PCR and inserted into plasmid pcDNA3. The expression plasmid pcDNA3/HIF-1alpha was transfected into A549 with Lipofec-tAMINE2000. The expression of HIF-1alpha protein was detected by Western blot. After A549 cells were transfected with HIF-1alpha prior to addition of 5-Fu, the growth activity was measured by growth curve, apoptosis was detected by flow cytometry at 48 h, and the levels of caspase3 and MDR-1 were determined by Western blot. The results showed that the constructed expression plasmid was analyzed with restriction enzymes and gel electrophoresis. Two DNA lanes at 2.55 kb and 5.4 kb respectively were found, which were consistent with that expected. The growth rate in 5-Fu group was significantly inhibited, and the apoptosis index and caspase3 activity were increased significantly as compared with control group. After HIF-1alpha being transfected into A549, the activity of MDR-1 was increased and the effect of 5-Fu was weakened. In conclusion, HIF-1alpha can promote chemoresistance by increasing the activation of MDRI and suppressing apoptosis during lung cancer cells A549 induced with 5-Fu.

Swedish lung cancer radiation study group: the prognostic value of anaemia, thrombocytosis and leukocytosis at time of diagnosis in patients with non-small cell lung cancer

There is a need to improve the prognostic and predictive indicators in non-small cell lung cancer (NSCLC). At present, the main focus is on genetic predictive markers while the prognostic value of the standard blood variables related to haematopoiesis has been subjected to relatively limited attention. To study the prognostic potential of haemoglobin (Hgb), platelet (Plt) and white blood cell (WBC) levels at time of diagnosis in NSCLC patients, 835 NSCLC patients, stage I-IV, who received radiotherapy with curative intention (>50 Gy), were included in the study. WBC, Plt, Hgb, gender, age at diagnosis, stage, surgery and first-line chemotherapy were studied in relation to overall survival. For patients with Hgb < 110 g/L and Hgb ≥ 110 g/L), the median survival was 11.2 and 14.5 months, respectively (p = 0.0032). For WBC > 9.0 × 10(9)/L and < 9.0 × 10(9)/L, the median survival was 11.6 and 15.4 months, respectively (p < 0.0001). For Plt > 350 × 10(9)/L and <350 × 10(9)/L, the median survival was 11.2 and 14.9 months, respectively (p < 0.0001). The median survival in patients with pathological results in all three markers was half of that in patients with normal levels of all three markers (8.0 and 16.0 months, respectively (p < 0.0001). The level of the three studied haematological biomarkers corresponds significantly to outcome in NSCLC. These results indicate that standard haematological variables may be used as guidance for the clinician in the decision-making regarding treatment intensity and patient information.

Structure based antibody-like peptidomimetics

Biologics such as monoclonal antibodies (mAb) and soluble receptors represent new classes of therapeutic agents for treatment of several diseases. High affinity and high specificity biologics can be utilized for variety of clinical purposes. Monoclonal antibodies have been used as diagnostic agents when coupled with radionuclide, immune modulatory agents or in the treatment of cancers. Among other limitations of using large molecules for therapy the actual cost of biologics has become an issue. There is an effort among chemists and biologists to reduce the size of biologics which includes monoclonal antibodies and receptors without a reduction of biological efficacy. Single chain antibody, camel antibodies, Fv fragments are examples of this type of deconstructive process. Small high-affinity peptides have been identified using phage screening. Our laboratory used a structure-based approach to develop small-size peptidomimetics from the three-dimensional structure of proteins with immunoglobulin folds as exemplified by CD4 and antibodies. Peptides derived either from the receptor or their cognate ligand mimics the functions of the parental macromolecule. These constrained peptides not only provide a platform for developing small molecule drugs, but also provide insight into the atomic features of protein-protein interactions. A general overview of the reduction of monoclonal antibodies to small exocyclic peptide and its prospects as a useful diagnostic and as a drug in the treatment of cancer are discussed.

Hypoxia stabilizes microtubule networks and decreases tumor cell chemosensitivity to anticancer drugs through Egr-1

The hypoxic environment of solid tumor causes the tumor cells survive and which could protect them from death by facilitating resistance to therapy. Here, we provide evidence that hypoxia can increase tumor cell viability and proliferation through an Egr-1-dependant pathway. Hypoxia protected the microtubules from disassembly, and Egr-1 was colocalized with microtubules in different cell cycle stages. Knockdown of Egr-1 with its siRNA overcame the protection effect of hypoxia and increased the sensitivity of tumor cells to vinblastine under hypoxic conditions. Our results suggest a novel approach for increasing the sensitivity of tumor cells to chemotherapeutics that target microtubule assembly.

Combined optical imaging and mammography of the healthy breast: optical contrast derived from breast structure and compression

In this paper, we report new progress in developing the instrument and software platform of a combined X-ray mammography/diffuse optical breast imaging system. Particularly, we focus on system validation using a series of balloon phantom experiments and the optical image analysis of 49 healthy patients. Using the finite-element method for forward modeling and a regularized Gauss-Newton method for parameter reconstruction, we recovered the inclusions inside the phantom and the hemoglobin images of the human breasts. An enhanced coupling coefficient estimation scheme was also incorporated to improve the accuracy and robustness of the reconstructions. The recovered average total hemoglobin concentration (HbT) and oxygen saturation (SO2) from 68 breast measurements are 16.2 microm and 71%, respectively, where the HbT presents a linear trend with breast density. The low HbT value compared to literature is likely due to the associated mammographic compression. From the spatially co-registered optical/X-ray images, we can identify the chest-wall muscle, fatty tissue, and fibroglandular regions with an average HbT of 20.1+/-6.1 microm for fibroglandular tissue, 15.4+/-5.0 microm for adipose, and 22.2+/-7.3 microm for muscle tissue. The differences between fibroglandular tissue and the corresponding adipose tissue are significant (p < 0.0001). At the same time, we recognize that the optical images are influenced, to a certain extent, by mammographical compression. The optical images from a subset of patients show composite features from both tissue structure and pressure distribution. We present mechanical simulations which further confirm this hypothesis.

The role of hypoxia in vascular injury and repair

Although the terms ischemia and hypoxia are often used interchangeably, they represent distinct processes that result in different modulatory effects at the cellular level. Hypoxia is a reduction in oxygen delivery below tissue demand, whereas ischemia is a lack of perfusion, characterized not only by hypoxia but also by insufficient nutrient supply. Hypoxia can be either acute or chronic, and both are centrally regulated by hypoxia-inducible factor, a transcription factor that governs the expression of key response genes such as vascular endothelial growth factor and erythropoietin. Whereas severe chronic hypoxia can cause cell death, less-severe hypoxia can protect against subsequent damage, a phenomenon known as hypoxic conditioning. Several important processes are characterized by hypoxia, including ischemia-reperfusion, tumor growth and progression, inflammation, myocardial ischemia, and a number of ocular pathologies.

Selective ETAR antagonist atrasentan inhibits hypoxia-induced breast cancer cell invasion

Tumour hypoxia, being widespread in solid tumours, is related to an increased risk of invasion and metastasis as well as to resistance to chemotherapy and radiotherapy. Hypoxia-inducible factor-1alpha (HIF-1alpha) has emerged as the key regulator of the cellular response to hypoxia. In primary breast cancers, HIF-1alpha is overexpressed, and high levels of HIF-1alpha predict for early relapse and increased metastasis. The endothelin (ET) axis, comprising the peptides ET-1, -2, -3 and their receptors A (ETAR) and B (ETBR), is another regulatory system of major relevance in human breast cancer. However, little is known about the interaction of HIF-1alpha and the ET axis in breast carcinomas. Therefore, we analysed expression of HIF-1alpha and the ET axis in 600 breast cancer tissue samples by immunohistochemistry, observing a significant correlation between expression of HIF-1alpha and ET-1 (P<0.001). In vitro, hypoxia was found to double ET-1 secretion of MCF-7 breast cancer cells (203.5% of controls; P<0.001), thereby promoting an invasive phenotype. Of note, real-time PCR analysis revealed that the increase of ET-1 was not due to enhanced transcription of the ET-1 gene. In invasion assays, breast cancer cell invasiveness was strongly increased by hypoxia (150.0% of controls; P=0.007). Most important, this increase was completely inhibited by the selective ETAR antagonist atrasentan. In conclusion, we provide evidence for a relevant interaction between hypoxia and the ET axis in breast cancer cells. Our data suggest that tumour hypoxia induces breast carcinoma invasiveness by releasing intracellularly stored ET-1. However, induction of invasiveness may be inhibited by selective ETAR antagonism, thus emphasising the promising status of the ET axis as a therapeutic target in breast cancer.

Hypoxia, drug therapy and toxicity

Hypoxia is defined as a decrease in available oxygen reaching the tissues of the body. It is linked to the pathology of cancer, cardiovascular disease, and stroke, the leading causes of death in the United States. Cells under hypoxic stress either induce an adaptive response that includes increasing the rates of glycolysis and angiogenesis or undergo cell death by promoting apoptosis or necrosis. The ability of cells to maintain a balance between adaptation and cell death is regulated by a family of transcription factors called the hypoxia inducible factors (HIF). HIF1, the most widely studied HIF, is essential for regulating the expression of a battery of hypoxia-responsive genes involved in the adaptive and cell death responses. The ability of HIF1 to balance these 2 responses likely lies in the regulation of HIF1alpha stability and transcriptional activity by post-translational hydroxylation and its ability to respond to other cellular factors including key metabolites and growth factors. Targeting HIF1 signaling for therapeutics, therefore, requires an understanding of how these various signals converge upon HIF1 and regulate its role in maintaining the balance between adaptation and cell death. In addition, one must understand how this balance can be perturbed during toxicant-induced tissue damage. This review will summarize our current understanding of hypoxia signaling as it applies to drug therapy and toxicity and describe how these processes can influence the HIF-mediated balance between adaptation and cell death.

Anemia may influence the outcome of patients undergoing neo-adjuvant treatment of rectal cancer

BACKGROUND

We hypothesized that anemia could represent one of the major factors influencing the outcome of patients undergoing neo-adjuvant treatment of rectal cancer.

PATIENTS AND METHODS

This analysis included all the consecutive patients who underwent neo-adjuvant treatment (chemotherapy and/or radiotherapy) before surgery for rectal cancer in three oncology/radiotherapy departments from June 1996 to December 2003.

RESULTS

Three hundred and seventeen patients were eligible for our analysis. Median age at diagnosis was 64 years (range 26-88 years); male/female ratio was 184/133. Two hundred and eighty-five patients (89.9%) were diagnosed with adenocarcinoma, while 32/317 (10.1%) with mucinous adenocarcinoma. Neo-adjuvant treatments carried out were as follows: radiotherapy alone in 75/317 patients (23.7%), radiotherapy plus chemotherapy in 242/317 patients (76.3%). At univariate and multivariate analysis, only the hemoglobin (Hb) level (group 1: < or=12 g/dl versus group 2: >12 g/dl) resulted in a significant factor for disease-free survival. The role of the Hb level seemed to be confirmed further by the clinical downstaging obtained in approximately 55% of patients in group 2, in comparison with 35% of the patients achieving a significant downstaging in group 1.

CONCLUSION

Our results indicated that anemia could represent an important parameter able to influence the outcome in patients receiving neo-adjuvant treatment of rectal cancer.

Erythropoietin administration during primary treatment for locally advanced cervical carcinoma is associated with poor response to radiation

The purpose of this study was to determine whether the use of recombinant erythropoietin (r-EPO) during treatment for locally invasive carcinoma of the cervix affects recurrence rates, disease-free survival, and overall survival. Retrospective analysis of outcomes of patients with locally advanced cervical cancer treated with radiation and concurrent chemotherapy between January 1997 and July 2004 was performed. Recurrence rates, disease-free survival, and overall survival were calculated using SPSS statistical software. Throughout P < 0.05 was considered significant. Of 68 patients included in this study, 18 patients received erythropoietin during treatment and 50 did not. Patient age, stage, hemoglobin at presentation, and average weekly hemoglobin (AWH) were similar in both groups of patients. The recurrence rate among patients who received r-EPO was 61% compared with 30% among patients who did not receive r-EPO (P = 0.014). Eight of 18 patients (44%) who received r-EPO were alive at last known follow-up compared to 36 of 50 (72%) who did not receive the medication (P = 0.045). Disease-free survival and overall survival were significantly shorter in patients who received r-EPO during treatment (P = 0.028, 0.032). The administration of r-EPO during primary treatment of patients with locally advanced cervical cancer is associated with increased recurrence rate, increased risk of death due to disease, and decreased disease-free and overall survivals.

"Translating" tumor hypoxia: unfolded protein response (UPR)-dependent and UPR-independent pathways

Poor oxygenation (hypoxia) is present in the majority of human tumors and is associated with poor prognosis due to the protection it affords to radiotherapy and chemotherapy. Hypoxia also elicits multiple cellular response pathways that alter gene expression and affect tumor progression, including two recently identified separate pathways that strongly suppress the rates of mRNA translation during hypoxia. The first pathway is activated extremely rapidly and is mediated by phosphorylation and inhibition of the eukaryotic initiation factor 2alpha. Phosphorylation of this factor occurs as part of a coordinated endoplasmic reticulum stress response program known as the unfolded protein response and activation of this program is required for hypoxic cell survival and tumor growth. Translation during hypoxia is also inhibited through the inactivation of a second eukaryotic initiation complex, eukaryotic initiation factor 4F. At least part of this inhibition is mediated through a Redd1 and tuberous sclerosis complex 1/2-dependent inhibition of the mammalian target of rapamycin kinase. Inhibition of mRNA translation is hypothesized to affect the cellular tolerance to hypoxia in part by promoting energy homeostasis. However, regulation of translation also results in a specific increase in the synthesis of a subset of hypoxia-induced proteins. Consequently, both arms of translational control during hypoxia influence gene expression and phenotype. These hypoxic response pathways show differential activation requirements that are dependent on the level of oxygenation and duration of hypoxia and are themselves highly dynamic. Thus, the severity and duration of hypoxia can lead to different biological and therapeutic consequences.

Hypoxia and anemia: factors in decreased sensitivity to radiation therapy and chemotherapy?

Hypoxia is a common feature of solid tumors that occurs across a wide variety of malignancies. Hypoxia and anemia (which contributes to tumor hypoxia) can lead to ionizing radiation and chemotherapy resistance by depriving tumor cells of the oxygen essential for the cytotoxic activities of these agents. Hypoxia may also reduce tumor sensitivity to radiation therapy and chemotherapy through one or more indirect mechanisms that include proteomic and genomic changes. These effects, in turn, can lead to increased invasiveness and metastatic potential, loss of apoptosis, and chaotic angiogenesis, thereby further increasing treatment resistance. Investigations of the prognostic significance of pretreatment tumor oxygenation status have shown that hypoxia (oxygen tension [pO(2)] value < or =10 mmHg) is associated with lower overall and disease-free survival, greater recurrence, and less locoregional control in head and neck carcinoma, cervical carcinoma, and soft-tissue sarcoma. In view of the deleterious effect of hypoxia on standard cancer treatment, a variety of hypoxia- and anemia-targeted therapies have been studied in an effort to improve therapeutic effectiveness and patient outcomes. Early evidence from experimental and clinical studies suggests the administration of recombinant human erythropoietin (rHuEPO) may enhance the effectiveness of radiation therapy and chemotherapy by increasing hemoglobin levels and ameliorating anemia in patients with disease- or treatment-related anemia. However, further research is needed in the area of hypoxia-related treatment resistance and its reversal.

The impact of anaemia on outcome in cancer

Anaemia is not an inconsequential side effect of cancer and its treatment should not be ignored. Current practice for anaemia management varies and its role in influencing outcome in cancer patients is under recognized. As a common complication of cancer, anaemia is prevalent in virtually all tumour types to varying degrees. Predictive factors for anaemia include baseline haemoglobin concentration, decrease in haemoglobin concentration within the first month of treatment, tumour type, duration of treatment and prior blood transfusions. Interest in the prognostic significance of anaemia in cancer patients has generated extensive clinical research. Data is now published in a wide range of tumour types confirming that anaemia is a negative prognostic indicator of outcome (e.g. survival, disease-free recurrence and local relapse), with the strongest association in patients receiving radiotherapy. The association has also been documented in patients undergoing chemotherapy and chemoradiation. A retrospective meta-analysis has shown an overall 65% increased risk of death associated with anaemia in cancer patients. The impact of anaemia as an independent prognostic factor for outcome may be mediated by several factors, however the emerging consensus is on the central role of tumour hypoxia. It has been nearly 50 years since R. Thomlinson and L. Gray (British Journal of Cancer 1955, 9: 539) first documented the existence of hypoxia in tumours and it is now well accepted that tumour hypoxia protects tumour cells from therapeutic damage directly by reducing the availability of oxygen-free radicals which are necessary for optimal impact of radiotherapy, certain chemotherapeutic agents and photodynamic therapy. The indirect effects include the impact of hypoxia on gene expression, which affects genetic stability, proliferation kinetics and cellular metabolism. There has been an emergence of preclinical and circumstantial data over recent years that are suggestive of the ability to correct the negative effect of anaemia on outcome by the use of repeated blood transfusions or recombinant human erythropoietin. This has led to some attempts to measure the impact on survival in cancer patients of treating anaemia, but early attempts have served to underline the complexity of the relationship and have produced unexpected results.

Impact of anemia in patients with head and neck cancer treated with radiation therapy

Locoregional recurrence remains a major obstacle to achieving a cure of locally advanced head and neck cancers, despite multimodality therapy. Multiple studies report that a low hemoglobin (Hgb) before or during radiation therapy is an important risk factor for poor locoregional disease control and survival. Anemia is common in the head and neck cancer population and is suspected to contribute to intratumoral hypoxia with resultant radioresistance. Although having a low Hgb level has been shown to be detrimental, it is unclear as to exactly what the threshold should be for low Hgb (studies in this area have used thresholds ranging from 9-14.5 g/dL). Quality-of-life studies suggest that correction of moderately severe anemia may result in significant gains. Optimal Hgb levels for improving outcomes may vary across and within tumor types, and this is an area that requires further evaluation. However, the correction of anemia may be a worthwhile strategy for radiation oncologists to improve local control and survival. This article reviews the impact of anemia on outcomes after radiotherapy of head and neck cancers.

Tissue oxygen tension measurements in the Shionogi model of prostate cancer using 19F MRS and MRI

OBJECTIVES

To investigate changes in tumour tissue oxygenation throughout the tumour growth-regression-relapse cycle in an androgen-dependent animal tumour model.

MATERIALS AND METHODS

19F T1 relaxometry of Perfluoro-15-Crown-5-Ether was used to measure in vivo partial oxygen pressure (pO2) of Shionogi tumours on a 2.35-T MR scanner. Perfluoro-15-Crown-5-Ether was administered as an emulsion injected intravenously or as a neat compound injected directly into the tumour. Non-localized, tumour 19F T1 measurements, made at multiple time points throughout the tumour cycle, were translated into pO2 levels.

RESULTS

No correlation between tumour size and pO2 values was found. Values of pO2 for growing tumours (50 +/- 30 torr) were significantly lower than for regressing and relapsing tumours after 9 days post-castration (70 +/- 10 torr, p<0.05). Maximum pO2 values (90 +/- 30 torr) were reached between fifth and eighth day post-castration, when tumour pO2 was significantly higher than both pre-castration (p<0.001) and after 9 days post-castration (p<0.05).

CONCLUSION

We demonstrate that longitudinal pO2 measurements in vivo are feasible. Values of pO2 for growing androgen-dependent tumours were significantly lower than for regressing and relapsing androgen-independent tumours. These results have potential clinical importance in optimizing the timing of chemotherapy and/or radiotherapy of hormone dependent tumours.

Preclinical and clinical studies: A preview of potential future applications of erythropoietic agents

Understanding the tissue distribution of erythropoietin receptors and cellular actions of erythropoietic agents may facilitate the development of wider applications for these compounds. Erythropoietin receptors have been identified in the central nervous system (CNS), retina, heart, vascular endothelium, kidney, lung, liver, gastrointestinal and reproductive tracts, and erythroid bone marrow precursors. Potential benefits of erythropoietic agents in several therapeutic areas may result from actions other than hematopoiesis stimulation. Their hematopoietic effects may also have broader applications in treating anemia of the elderly and non-chemotherapy (CT)-related anemia in patients with cancer. Furthermore, because hypoxic tumor cells tend to be more resistant to radiation therapy (RT) and some forms of CT, and more aggressive than normoxic cells, increased oxygenation resulting from anemia correction may increase RT and CT sensitivity, possibly impacting treatment outcomes. However, clinical studies addressing this hypothesis have conflicting results. Preliminary evidence suggests erythropoietin has CNS neuroprotective effects, including potential clinical benefits in ischemic stroke. In addition, data suggest that erythropoietin (epoetin alfa) may attenuate declines in cognitive function during CT for early-stage breast cancer. Erythropoietin may have benefits in retinal disease, peripheral neuropathy, and myocardial ischemia. Thus, accumulating evidence suggests that erythropoietic agents may have clinical utility outside CT-related anemia.

Beneficial and ominous aspects of the pleiotropic action of erythropoietin

The primary function of the glycoprotein hormone erythropoietin (Epo) is to promote red cell production by inhibiting apoptosis of erythrocytic progenitors in hemopoietic tissues. However, functional Epo receptors (Epo-R) have recently been demonstrated in various nonhemopoietic tissues indicating that Epo is a more pleiotropic viability and growth factor. Herein, in vitro and in vivo effects of Epo in the brain and the cardiovascular system are reviewed. In addition, the therapeutic impact of Epo in oncology is considered, including the question of whether Epo might promote tumor growth. Convincing evidence is available that Epo acts as a neurotrophic and neuroprotective factor in the brain. Epo prevents neuronal cells from hypoxia-induced and glutamate-induced cell death. Epo-R is expressed by neurons and glia cells in specific regions of the brain. Epo supports the survival of neurons in the ischemic brain. The neuroprotective potential of Epo has already been confirmed in a clinical trial on patients with acute stroke. With respect to the vasculature, Epo acts on both endothelial and smooth muscle cells. Epo promotes angiogenesis and stimulates the production of endothelin and other vasoactive mediators. In addition, Epo-R is expressed by cardiomyocytes. The role of Epo as a myocardial protectant is at the focus of present research. Epo therapy in tumor patients is practiced primarily to maintain the hemoglobin concentration above the transfusion trigger and to reduce fatigue. In addition, increased tumor oxygenation may improve the efficacy of chemotherapy and radiotherapy. However, tumor cells often express Epo-R. Therefore, careful studies are required to fully exclude that recombinant human Epo (rHuEpo) promotes tumor growth.

Detection and treatment of minimal residual disease in high-risk neuroblastoma

Intensive, myeloablative therapy supported by autologous hematopoietic stem-cell transplantation (AHSCT) has improved the outcome for children with high-risk neuroblastoma. However, >50% of patients develop recurrent neuroblastoma, often from minimal residual disease (MRD). Immunocytological and reverse transcriptase polymerase chain reaction (RT-PCR) for genes highly expressed in neuroblastoma both can detect small amounts of MRD in blood and bone marrow, and detection of MRD at certain levels during therapy has prognostic value. Radionucleotide scans using meta-iodobenzaguanidine (MIBG) imaging allows sensitive detection of neuroblastoma in patients, but whether or not all MIBG-positive disease detected after AHSCT will progress remains to be defined and is complicated by use of post-AHSCT therapy. Selective removal of tumor cells from marrow or blood stem cells harvested for AHSCT could decrease recurrence by preventing infusion of tumorigenic cells with AHSCT. Treating MRD after AHSCT with the differentiation-inducing retinoid 13-cis-retinoic acid significantly /improved EFS of high-risk neuroblastoma patients. Randomized clinical trials in the Children's Oncology Group are testing the value of purging blood stem cells and also whether post-AHSCT therapy with an anti-GD2 monoclonal antibody (combined with cytokines) improves outcome over use of 13-cis-retinoic acid alone. New approaches to treating neuroblastoma MRD that are in early clinical trials include the cytotoxic retinoid fenretinide and the hu14.18-IL2 immunocytokine. It is anticipated that testing novel approaches to treating neuroblastoma MRD will be the subject of future phase-III randomized trials.

Overcoming the hypoxic barrier to radiation therapy with anaerobic bacteria

The low level of oxygenation within tumors is a major cause of radiation treatment failures. We theorized that anaerobic bacteria that can selectively destroy the hypoxic regions of tumors would enhance the effects of radiation. To test this hypothesis, we used spores of Clostridium novyi-NT to treat transplanted tumors in mice. The bacteria were found to markedly improve the efficacy of radiotherapy in several of the mouse models tested. Enhancement was noted with external beam radiation derived from a Cs-137 source, systemic radioimmunotherapy with an I-131-conjugated monoclonal antibody, and a previously undescribed form of experimental brachytherapy using plaques loaded with I-125 seeds. C. novyi-NT spores added little toxicity to the radiotherapeutic regimens, and the combination resulted in long-term remissions in a significant fraction of animals.

New Insights Into Erythropoietin and Epoetin Alfa: Mechanisms of Action, Target Tissues, and Clinical Applications

Recombinant human erythropoietin (epoetin alfa) has proven beneficial for the treatment of various anemias. The mechanism of action of endogenous erythropoietin and the therapeutic use of epoetin alfa to stimulate red blood cell production and improve the quality of life in cancer patients are reviewed here. Epoetin alfa may also attenuate the cognitive dysfunction associated with cancer therapy. Interestingly, functional endogenous erythropoietin receptor signaling pathways have been demonstrated in numerous nonerythropoietic tissues. Of particular importance, epoetin alfa confers neurotrophic and neuroprotective effects in cultured neurons and in several animal models for neurologic disease. In one clinical trial, epoetin alfa appeared to limit functional and histologic damage in patients with stroke. Therefore, in cancer patients receiving chemotherapy, the beneficial effects of epoetin alfa could be mediated not only through enhanced erythrocyte production but also via direct effects on the nervous system. Further investigation into the nonerythropoietic effects of epoetin alfa could broaden its clinical utility for patients with cancer and also provide new therapies for various neurologic disorders.

Once-weekly dosing of epoetin-alpha increases hemoglobin and improves quality of life in anemic cancer patients receiving radiation therapy either concomitantly or sequentially with chemotherapy

BACKGROUND

The current study was performed to prospectively evaluate the effectiveness, clinical outcomes, and safety of once-weekly (QW) recombinant human erythropoietin (r-HuEPO [epoetin-alpha]) in anemic cancer patients with nonmyeloid malignancies who were receiving radiation therapy (RT) concomitantly or sequentially with chemotherapy (CT).

METHODS

A total of 777 anemic patients (hemoglobin [Hb] < or = 11 g/dL) were enrolled in this multicenter, open-label, nonrandomized, 16-week study. Patients initially received epoetin-alpha at a dose of 40,000 units (U) subcutaneously QW, escalating to a dose of 60,000 U QW if the Hb increased to < or = 1 g/dL after 4 weeks. Endpoints were changes in hematologic and quality of life (QOL) parameters.

RESULTS

Among the 442 patients evaluable for hematologic response, the mean increase in Hb from baseline to the time of final evaluation was 1.9 +/- 1.8 g/dL (P < 0.05). An increase in Hb of > or = 2 g/dL, in the absence of blood transfusions, occurred in 68.3% of patients (278 of 407 patients) who were on the study for > or = 30 days. The overall response rate (Hb increase > or = 2 g/dL or Hb > or = 12 g/dL in the absence of blood transfusions) was 74.0% (301 of 407 patients). In 359 patients who were evaluable for QOL assessment, epoetin-alpha therapy was found to significantly (P < 0.05) improve mean Linear Analog Scale Assessment (LASA) scores for energy level, ability to perform daily activities, and overall QOL from baseline to the time of final evaluation. QW epoetin-alpha therapy was found to be well tolerated.

CONCLUSIONS

Treatment with QW epoetin-alpha was found to increase Hb levels, decrease transfusion requirements, and improve functional status and QOL in anemic patients with nonmyeloid malignancies who were receiving RT concomitantly or sequentially with CT. Clinical benefits and the safety profile of QW epoetin-alpha in this setting appear to be similar to those observed in anemic cancer patients receiving CT.

Carbon dioxide reactivity of computed tomography functional parameters in rabbit VX2 soft tissue tumour

Tumour blood flow is one of the important factors limiting the efficacy of radiation therapy (hypoxic radioresistance), chemotherapy (drug delivery) and thermal therapy (heat dissipation) in treating cancer. The modification of tumour blood flow has been an area of intense investigation. In the current study, the arterial carbon dioxide tension (PaCO2) was changed in order to investigate the tumour vascular response to carbon dioxide. Functional maps of blood flow, blood volume and mean transit time were generated at four PaCO2 levels in VX2 tumour in the rabbit thigh and normal soft tissue. The PaCO2 levels investigated were normocapnia (PaCO2 = 40.9 +/- 1.2 mmHg), hypocapnia (27.2 +/- 2.3 and 33.5 +/- 2.3 mmHg) and hypercapnia (54.9 +/- 4.4 mmHg). The carbon dioxide reactivity of the global tumour blood flow and mean transit time showed significant differences between normocapnia and the two levels of hypocapnia, but not between normocapnia and hypercapnia. The average fractional change of blood flow from normocapnia for the two levels of hypocapnia was -0.41 +/- 0.06 and -0.29 +/- 0.08, respectively (P < 0.05). In the case of mean transit time the fractional change was +0.39 +/- 0.30 and +0.23 +/- 0.24, respectively (P < 0.05). The fractional change of blood volume from normocapnia, however, was not significantly different at any capnic level, as was the case with respect to each of the functional parameters in normal tissue. The ability to reduce blood flow and increase mean transit time through hypocapnia has significant implications in thermal therapy, since heat dissipation is a major factor in limiting the effectiveness of treatment.

Impact of tumor hypoxia and anemia on radiation therapy outcomes

Local recurrence remains a major obstacle to achieving cure of many locally advanced solid tumors treated with definitive radiation therapy. The microenvironment of solid tumors is hypoxic compared with normal tissue, and this hypoxia is associated with decreased radiosensitivity. Recent preclinical data also suggest that intratumoral hypoxia, particularly in conjunction with an acid microenvironment, may be directly or indirectly mutagenic. Investigations of the prognostic significance of the pretreatment oxygenation status of tumors in patients with head and neck or cervical cancer have demonstrated that increased hypoxia, typically designated in these studies as pO(2) levels below 2.5-10 mm Hg, is associated with decreased local tumor control and lower rates of disease-free and overall survival. Hypoxia-directed therapies in the radiation oncology setting include treatment using hyperbaric oxygen, fluosol infusion, carbogen breathing, and electron-affinic and hypoxic-cell sensitizers. These interventions have shown the potential to increase the effectiveness of curative-intent radiation therapy, demonstrating that the strategy of overcoming hypoxia may be a viable and important approach. Anemia is common in the cancer population and is suspected to contribute to intratumoral hypoxia. A review of the literature reveals that a low hemoglobin level before or during radiation therapy is an important risk factor for poor locoregional disease control and survival, implying that a strong correlation could exist between anemia and hypoxia (ultimately predicting for a poor outcome). While having a low hemoglobin level has been shown to be detrimental, it is unclear as to exactly what the threshold for "low" should be (studies in this area have used thresholds ranging from 9-14.5 g/dl). Optimal hemoglobin and pO(2) thresholds for improving outcomes may vary across and within tumor types, and this is an area that clearly requires further evaluation. Nonetheless, the correction of anemia may be a worthwhile strategy for radiation oncologists to improve local control and survival.

Biology of erythropoietin

Hypoxia induces tissue-specific gene products such as erythropoietin (EPO) and vascular endothelial growth factor (VEGF), which improve the peripheral O2 supply, and glucose transporters and glycolytic enzymes, which adapt cells to reduced O2 availability. EPO has been the fountainhead in research on pO2-dependent synthesis of proteins. The EPO gene enhancer (like the flanking DNA-elements of several other pO2-controlled genes) contains a consensus sequence (CGTG) that binds the trans-acting dimeric hypoxia-inducible factor 1 (HIF-1alpha/beta). The alpha-subunit of HIF-1 is rapidly degraded by the proteasome under normoxic conditions, but it is stabilized on occurrence of hypoxia. HIF-1 DNA-binding is also increased by insulin, and by interleukin-1 and tumor necrosis factor. Thus, in some aspects there is synergy in the cellular responses to hypoxia, glucose deficiency and inflammation. In viewing clinical medicine recombinant human EPO (rHu-EPO) has become the mainstay of treatment for renal anemia. Endogenous EPO and rHu-EPO are similar except for minor differences in the pattern of their 4 carbohydrate chains. RHu-EPO is also administered to patients suffering from non-renal anemias, such as in autoimmune diseases or malignancies. The correction of anemia in patients with solid tumors is not merely considered a palliative intervention. Hypoxia promotes tumor growth. However, the benefits of the administration of rHu-EPO to tumor patients with respect to its positive effects on tumor oxygenation, tumor growth inhibition and support of chemo- and radiotherapy is still debatable ground.

Imaging and quantitation of the hypoxic cell fraction of viable tumor in an animal model of intracerebral high grade glioma using [18F]fluoromisonidazole (FMISO)

We have demonstrated that FMISO uptake is significantly higher in tumor tissue in the C6 intracerebral glioma rat model compared to normal brain, and that there is persisting hypoxia in gliomas independent of tumor size. FMISO uptake was observed homogeneously throughout viable glioma tissue in tumor sizes ranging from 2mm to almost 1cm. Quantitation of uptake of FMISO showed a tumor/brain ratio of 1.9 and a tumor/blood ratio of 2.6 at 2 hours post injection.

The negative impact of anemia on radiotherapy and chemoradiation outcomes

In cancer patients, anemia is common and has been found to impair quality of life and reduce locoregional disease control conferred by radiotherapy. The prognostic importance of anemia in the radiation oncology setting may be related to a reduction of molecular oxygen levels, thereby attenuating radiation-induced damage and ultimate cell death. Substantially higher doses of radiation are required to eradicate malignant cells under the hypoxic conditions commonly identified in solid tumors. Consistent with this, patients with hypoxic solid tumors have been found to have shorter postradiation disease-free survival rates relative to patients with well-oxygenated tumors. An attempt to enhance intratumoral oxygenation via correction of anemia, a highly prevalent but modifiable condition, is therefore a reasonable approach to optimize radiotherapy and chemoradiation outcomes. Clinical studies investigating recombinant human erythropoietin (epoetin alfa) as an adjunct to radiotherapy have demonstrated its ability to increase and maintain hemoglobin (Hb) levels during the course of radiotherapy. In a study involving anemic patients undergoing chemoradiation for head and neck cancer, epoetin alfa extended locoregional control and survival to rates reported for patients with normal pretreatment Hb levels. Given the high prevalence and prognostic significance of anemia during radiotherapy, strategies that safely and effectively increase Hb levels may be of value for optimizing radiotherapy and chemoradiation outcomes.

Hypoxia inhibits G1/S transition through regulation of p27 expression

Mammalian cellular responses to hypoxia include adaptive metabolic changes and a G1 cell cycle arrest. Although transcriptional regulation of metabolic genes by the hypoxia-induced transcription factor (HIF-1) has been established, the mechanism for the hypoxia-induced G1 arrest is not known. By using genetically defined primary wild-type murine embryo fibroblasts and those nullizygous for regulators of the G1/S checkpoint, we observed that the retinoblastoma protein is essential for the G1/S hypoxia-induced checkpoint, whereas p53 and p21 are not required. In addition, we found that the cyclin-dependent kinase inhibitor p27 is induced by hypoxia, thereby inhibiting CDK2 activity and forestalling S phase entry through retinoblastoma protein hypophosphorylation. Reduction or absence of p27 abrogated the hypoxia-induced G1 checkpoint, suggesting that it is a key regulator of G1/S transition in hypoxic cells. Intriguingly, hypoxic induction of p27 appears to be transcriptional and through an HIF-1-independent region of its proximal promoter. This demonstration of the molecular mechanism of hypoxia-induced G1/S regulation provides insight into a fundamental response of mammalian cells to low oxygen tension.

Tumor oximetry: demonstration of an enhanced dynamic mapping procedure using fluorine-19 echo planar magnetic resonance imaging in the Dunning prostate R3327-AT1 rat tumor

PURPOSE

We have developed an enhanced approach to measuring regional oxygen tension (pO(2)) dynamics in tumors. The technique is demonstrated in a group of 8 Dunning prostate rat tumors (R3327-AT1) with respect to respiratory challenge.

METHODS AND MATERIALS

Hexafluorobenzene was injected directly into the tumors of anesthetized rats. (19)F nuclear magnetic resonance echo planar imaging relaxometry was performed to obtain maps of regional tumor oxygenation under baseline conditions and when the inhaled gas was changed to oxygen or carbogen.

RESULTS

Sequential pO(2) maps required 8 min, with a typical precision of 1-3 torr at 30-100 individual regions across a tumor. When rats breathed 33% oxygen, distinct heterogeneity was observed for baseline oxygenation in each tumor with pO(2) values ranging from hypoxic to greater than 100 torr. Larger tumors showed significantly lower baseline pO(2). Respiratory challenge with oxygen or carbogen produced significant increases in tumor oxygenation with a close correlation between the response to each gas at individual locations. Regions of both small and large tumors responded to respiratory challenge, but the rate was generally much faster in initially well-oxygenated regions.

CONCLUSIONS

Regional pO(2) was assessed quantitatively and the response of multiple individual tumor regions observed simultaneously with respect to interventions.

Spectroscopic diffuse optical tomography for the quantitative assessment of hemoglobin concentration and oxygen saturation in breast tissue

Near-infrared (NIR) spectroscopic diffuse tomography has been used to map the hemoglobin concentration and the hemoglobin oxygen saturation quantitatively in tissuelike phantoms and to determine average values in vivo. A series of phantom calibrations were performed to achieve quantitatively accurate images of the absorption and the reduced scattering coefficients at multiple optical wavelengths. A least-squares fit was applied to absorption-coefficient images at multiple NIR wavelengths to obtain hemoglobin images of the concentration and the hemoglobin oxygen saturation. Objects of varying hemoglobin concentration and oxygen saturation within highly scattering media were localized and imaged to within 15% of their actual values. The average hemoglobin concentration and oxygen saturation of breast tissue was measured in vivo for two women volunteers. The potential application for the diagnosis of breast tumors is discussed.

Increase of ceramide and induction of mixed apoptosis/necrosis by N-(4-hydroxyphenyl)- retinamide in neuroblastoma cell lines

BACKGROUND

The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR or fenretinide) is toxic to myeloid leukemia and cervical carcinoma cell lines, probably in part due to its ability to increase levels of reactive oxygen species (ROS). We have studied the effects of 4-HPR on neuroblastoma cell lines. Since neuroblastomas commonly relapse in bone marrow, a hypoxic tissue compartment, and many chemotherapeutic agents are antagonized by hypoxia, our purpose was to study in these cell lines several factors influencing 4-HPR-induced cytotoxicity, including induced levels of ROS, effects of physiologic hypoxia and antioxidants, levels of ceramide, and the mechanism of cell death.

METHODS

ROS generation was measured by carboxydichlorofluorescein diacetate fluoresence. Ceramide was quantified by radiolabeling and thin-layer chromatography. Immunoblotting was used to assess p53 protein levels. Apoptosis (programmed cell death) and necrosis were analyzed by nuclear morphology and internucleosomal DNA fragmentation patterns. Cytotoxicity was measured by a fluorescence-based assay employing digital imaging microscopy in the presence or absence of the pancaspase enzyme inhibitor BOC-d-fmk. Statistical tests were two-sided.

RESULTS/CONCLUSIONS

In addition to increasing ROS, 4-HPR (2.5-10 microM) statistically significantly increased the level of intracellular ceramide (up to approximately 10-fold; P<.001) in a dose-dependent manner in two neuroblastoma cell lines, one of which is highly resistant to alkylating agents and to etoposide. Cell death induced by 4-HPR was reduced but not abrogated by hypoxia in the presence or absence of an antioxidant, N-acetyl-L-cysteine. Expression of p53 protein was not affected by 4-HPR. Furthermore, the pan-caspase enzyme inhibitor BOC-d-fmk prevented apoptosis, but not necrosis, and only partially decreased cytotoxicity induced by 4-HPR, indicating that 4-HPR induced both apoptosis and necrosis in neuroblastoma cells.

IMPLICATIONS

4-HPR may form the basis for a novel, p53-independent chemotherapy that operates through increased intracellular levels of ceramide and that retains cytotoxicity under reduced oxygen conditions.

Exploring the mechanistic aspects of mitomycin antibiotic bioactivation in Chinese hamster ovary cells overexpressing NADPH:cytochrome C (P-450) reductase and DT-diaphorase

We have directly demonstrated the involvement of human NADPH: cytochrome c (P-450) reductase in the aerobic/hypoxic differential toxicity of mitomycin C and porfiromycin in living cells by varying only this enzyme in a transfected cell line. In the same manner, we have implicated rat DT-diaphorase in the aerobic and hypoxic activation of mitomycin C, but found only a minor role for this enzyme in the aerobic activation of porfiromycin. DT-Diaphorase does not cause the production of an aerobic/hypoxic differential toxicity by mitomycin C, but rather activates this agent through an oxygen insensitive pathway. The evidence suggests that DT-diaphorase activates mitomycin C more effectively than porfiromycin, with porfiromycin being preferentially activated through a one-electron reductive pathway. The therapeutic potential of mitomycin antibiotics in the treatment of cancer can be envisioned to be enhanced for those tumors containing elevated levels of the bioreductive enzymes. However, cytogenetic heterogeneity within the tumor cell population and the various environmental factors which impact on bioreductive enzyme function, including pH and oxygen tension, may subvert this approach. Moreover, if high tumor levels of a drug activating enzyme reflect high levels in the normal tissues of the patient, normal tissue damage may also be enhanced with possibly no improvement in the therapeutic ratio. Approaches utilizing gene therapy, whereby a specific bioreductive catalyst is introduced into the tumor cell population via a targeting vehicle to activate a particular prodrug, may be more effective in that not only will the prodrug of choice be specifically activated in the tumor, but the source of the catalyst, be it bacterial, rodent, or human, will not be important. In fact, in the case of DT-diaphorase and mitomycin C, the rat form of the enzyme could be advantageous because it is more effective in activating mitomycin C than is the human form of this enzyme. Assuming targeted gene delivery to malignant cells, a non-host enzyme which is more effective at activating mitomycin C than the analogous host enzyme might also result in less drug activation in normal tissue and, hence, less normal tissue toxicity.

Radioresistance, chemoresistance, and apoptosis resistance. The past, present, and future

A wide variety of cancer therapy resistance mechanisms are available, with perhaps surprising overlap between causes of chemotherapy and radiation resistance. As previously discussed, most of the widely used chemotherapeutic agents and gamma-radiation utilize apoptosis as the common death pathway, thereby making apoptosis and the ability to manipulate apoptosis of integral importance to the future of cancer therapy. This is evidenced by the information explosion on this topic in the last 5 years. Obviously much remains to be learned. However, with the aforementioned cooperation of the oncology team and a greater understanding of the molecular mechanisms behind cancer and cancer therapy resistance, response rates, survival times, the quality of life of patients enduring antineoplastic therapies, and the importance of comparative oncology can only increase. We look forward to the findings in the coming years on this incredibly clinically relevant topic with great fondness and uncertainty.