Vasculature and microenvironmental gradients: the missing links in novel approaches to cancer therapy?

The usefulness of continuous administration of hypoxic cytotoxin combined with mild temperature hyperthermia, with reference to effects on quiescent tumour cell populations

To evaluate the usefulness of continuous administration of hypoxic cytotoxins in terms of targeting acute hypoxia in solid tumours and the significance of combination with mild temperature hyperthermia (MTH) (40 degrees C, 60 min), the cytotoxic effects of singly or continuously administered tirapazamine (TPZ) and TX-402 were examined in combination with or without MTH in vivo. Further, the effects were also analysed on total (=proliferating (P)+quiescent (Q)) and Q cell populations in solid tumours with the method for selectively detecting the Q cell response. C3H/He mice bearing SCC VII tumours received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) for 5 days to label all P cells. The tumour-bearing mice then received a single intra-peritoneal injection or 24 h continuous subcutaneous infusion of hypoxic cytotoxin, TPZ or TX-402, with or without MTH. On the other hand, to detect the changes in the hypoxic fraction (HF) in the tumours by MTH, another group of mice with or without MTH received a series of test doses of gamma-rays while alive or after tumour clamping. After each treatment, the tumour cells were isolated and incubated with a cytokinesis blocker (=cytochalasin-B) and the micronucleus (MN) frequency in cells without BrdU labelling (=Q cells) was determined using immunofluorescence staining for BrdU. The MN frequency in total tumour cells was determined from the tumours that were not pre-treated with BrdU. The sensitivity to TX-402 was slightly higher than that to TPZ in both total and Q tumour cells. Continuous administration elevated the sensitivity of both total and Q cells, especially total cells. MTH raised the sensitivity of Q cells more remarkably than that of total cells in both single and continuous administrations. It was thought to be probably because of the higher dose distribution of hypoxic cytotoxin in intermediately hypoxic areas derived mainly from chronic hypoxia through MTH. From the viewpoint of tumour control as a whole including both total and Q tumour cells, the continuous administration of hypoxic cytotoxin combined with MTH may be useful for sensitizing tumour cells in vivo.

The radiosensitivity of total and quiescent cell populations in solid tumors to 290 MeV/u carbon ion beam irradiation in vivo

PURPOSE

To clarify the radiosensitivity of intratumor total and quiescent (Q) cells in vivo to accelerated carbon ion beams compared with gamma-ray irradiation.

MATERIALS AND METHODS

SCC VII tumor-bearing mice received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) to label all intratumor proliferating (P) cells. Then they received 290 MeV/u carbon ions or gamma-rays. Immediately or 12 hours after the irradiation, the radiosensitivity of Q cells was assessed in terms of the micronucleus frequency using immunofluorescence staining for BrdU. That of the total (=P+Q) tumor cells was determined from the BrdU non-treated tumors based on the micronucleus frequency and clonogenic cell survival.

RESULTS

The apparent difference in radiosensitivity between total and Q cell populations under gamma-ray irradiation was markedly reduced with carbon ion beam, especially with a higher linear energy transfer (LET) value. Clearer repair in Q cells than total cells through delayed assay under gamma-ray irradiation was efficiently inhibited with carbon ion beams, especially with a higher LET.

CONCLUSION

In terms of tumor cell-killing effect as a whole, including intratumor Q cells, carbon ion beams, especially with higher LET values, were very useful for suppressing the dependency on the heterogeneity within solid tumors as well as depositing radiation dose precisely.

Imaging and Targeting of the Hypoxia-inducible Factor 1-active Microenvironment

Human solid tumors contain hypoxic regions that have considerably lower oxygen tension than normal tissues. They are refractory to radiotherapy and anticancer chemotherapy. Although more than half a century has passed since it was suggested that tumour hypoxia correlates with poor treatment outcomes and contributes to recurrence of cancer, no fundamental solution to this problem has been found. Hypoxia-inducible factor-1(HIF-1) is the main transcription factor that regulates the cellular response to hypoxia. It induces various genes, whose function is strongly associated with malignant alteration of the entire tumour. The cellular changes induced by HIF-1 are extremely important therapeutic targets of cancer therapy, particularly in therapy against refractory cancers. Therefore, targeting strategies to overcome the HIF-1-active microenvironment are important for cancer therapy. To Target HIF-1-active/ hypoxic tumor cells, we developed a fusion protein drug, PTD-ODD-Procaspase-3 that selectively induces cell death in HIF-1-active/hypoxic cells. The drug consists of the following three functional domains: the protein transduction domain (PTD), which efficiently delivers the fusion protein to hypoxic tumor cells, the ODD domain, which has a VHL-mediated protein destruction motif of human HIF-1α protein and confers hypoxia-dependent stabilization to the fusion proteins, and the human procaspase-3 proenzyme responsible for the cytocidal activity of the protein drug. In vivo imaging systems capable of monitoring HIF-1 activity in transplanted human cancer cells in mice are useful in evaluating the efficiency of these drugs and in study of HIF-1-active tumor cells.

Hypoxia-regulated p53 and its effect on radiosensitivity in cancer cells

PURPOSE

To determine the response of tumor suppressor p53 to hypoxia in different tumor cell lines and the involvement of p53 activity regulation in the effect of hypoxia on tumor cell sensitivity to radiation and hyperthermia.

MATERIALS AND METHODS

Three tumor cell lines with functional p53 were treated with chronic or cyclic hypoxia followed by radiation or hyperthermia to investigate p53 activity and cell survival. Flow cytometry was used to investigate the effect of hypoxia-induced cell cycle arrest on radiosensitivity in KHT-C (mouse fibrosarcoma) cells. Transient transfection was performed to determine the role of altered p53 activity in KHT-C and SCC VII (mouse squamous-cell carcinoma) radiosensitivity.

RESULTS

Aerobic radiosensitivity was decreased in KHT-C and SCC VII cells after in vitro chronic or cyclic hypoxia pretreatment, but in HT1080 cells, it was slightly increased after chronic hypoxia, and was unchanged after acute hypoxia pretreatment. Decreased radiosensitivity in hypoxia-pretreated KHT-C and SCC VII cells was unlikely due to hypoxia-induced cell cycle arrest, but rather seemed to be associated with increased expression of Mdm2 (mouse double minute-2) and decreased p53. Furthermore, hypoxia pretreatment inhibited the activation of p53 by radiation. Similar results were observed in hyperthermia treated KHT-C cells. Finally, decreased radiosensitivity was observed in both KHT-C and SCC VII cells transiently transfected with Mdm2 or anti-sense p53 cDNA.

CONCLUSION

We demonstrated that hypoxia may decrease tumor cell radiosensitivity through the suppression of p53 activity in some tumor cell lines. These results suggested the response of p53 to hypoxia can be cell type specific and contribute to radiosensitivity of hypoxic cells.

The HIF-1-active microenvironment: an environmental target for cancer therapy

Solid tumors possess unique microenvironments that are exposed to chronic hypoxic conditions, so-called tumor hypoxia. Although more than half a century has passed since it was suggested that tumor hypoxia correlated with bad treatment outcomes and contributed to the recurrence of cancer, no fundamental solution to this problem has yet been found. Hypoxia-inducible factor HIF-1 is the main transcription factor that regulates the cellular response to hypoxia. It induces various genes, whose function is strongly associated with the malignant alteration of the entire tumor. The cellular changes induced by HIF-1 are extremely important therapeutic targets of cancer therapy, particularly in the therapy against refractory cancers. Therefore targeting strategies to overcome the HIF-1-active microenvironment are important for cancer therapy.

Semiquantitative and quantitative dynamic contrast-enhanced magnetic resonance imaging measurements predict radiation response in cervix cancer

PURPOSE

To evaluate semiquantitative and quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) measurements in predicting the response to radiotherapy in cervix cancer.

METHODS AND MATERIALS

Patients with cervix cancer treated radically with chemoradiotherapy had DCE-MRI at three time points: before starting treatment, after 2 weeks of radiotherapy, and in the 5th week of radiotherapy. Semiquantitative measurements obtained from the signal intensity vs. time plots included arrival time of contrast, the slope and maximum slope of contrast uptake, time for peak enhancement, and the contrast enhancement ratio (CER). Pharmacokinetic modeling with a modeled vascular input function was used for the quantitative measurements volume transfer constant (K(trans)), rate constant (k(ep)), fraction plasma volume (fPV), and the initial area under gadolinium-time curve. The correlation of these measurements at each of the three time points with radiologic tumor response was investigated.

RESULTS

Thirteen patients had a total of 38 scans. There was no correlation between the DCE-MRI measurements and the corresponding tumor volumes. A statistically significant correlation with percentage tumor regression was shown with the pretreatment DCE-MRI semiquantitative parameters of peak time (p = 0.046), slope (p = 0.025), maximum slope (p = 0.046), and CER (p = 0.025) and the quantitative parameters K(trans) (p = 0.043) and k(ep) (p = 0.022). Second and third scan measurements did not show any correlation.

CONCLUSIONS

This is the first study to show that pretreatment DCE-MRI quantitative parameters predict the radiation response in cervix cancer. These measurements may allow a more meaningful comparison of DCE-MRI studies from different centers.

Proteins upregulated by mild and severe hypoxia in squamous cell carcinomas in vitro identified by proteomics

BACKGROUND

Solid malignant tumours are characterised by an inadequate vascular system, which can give rise to micro-regional hypoxic areas. As the negative impact of tumour hypoxia is believed largely to depend on dynamic changes in gene expression, it is important to identify the genes regulated by hypoxia to further enlighten the biology behind the cellular response to hypoxia. Previous studies have demonstrated that hypoxia has an impact not only on the gene transcription, but also on gene-specific mRNA translation. Therefore, proteomics is a suitable approach to understand the complexity of gene regulation under hypoxia at protein level. In this in vitro study we have studied the proteome of cells under intermediate hypoxia (1% O2) and anoxia and compared these to normoxic (21% O2) cells to identify proteins upregulated by mild and severe hypoxia.

MATERIALS AND METHODS

A human cervix cancer cell line (SiHa) and a human head and neck cancer cell line (FaDu(DD)) were used. Total cell lysate from hypoxic and normoxic cells was separated by 2-dimensional gel electrophoresis, and images were analysed using Quantity One software. Proteins from significant spots (difference in intensity by more than a factor 2) were identified by Liquid chromatography-mass spectrometry (LC-MS/MS). In order to confirm the hypoxic regulation of the identified proteins, immunoblotting and qPCR were employed when possible.

RESULTS

All together 32 spots were found to be upregulated in the hypoxic gels. Of these, 11 different proteins were successfully identified and largely confirmed by Western blotting and qPCR. Amongst these proteins are protein disulfide isomerase family A, member 6 (PDIA6) and dynein light chain roadblock-type 1 (DynLRB1). Both 2D gels and Western blots revealed that PDAI6 exhibited a cell line specific pattern; in FaDu(DD) there was upregulation at 1% and further upregulated at 0% compared to atmospheric air, whereas there was no upregulation in SiHa cells. DynLRB1 was found to be upregulated in FaDu(DD) at both 1% and 0% oxygen.

CONCLUSIONS

The upregulated proteins observed in this study are involved in different cellular processes, as regulators of both cell metabolism and stress response, and in cell migration and cell division. All of which may contribute to cell survival and adaptation during oxygen starvation.

Chemosensitivity of radioresistant cells in the multicellular spheroids of A549 lung adenocarcinoma

BACKGROUND

The relapse of cancer after radiotherapy is a clinical knotty problem. Previous studies have demonstrated that the elevation of several factors is likely in some way to lead to the development of treatment tolerance, so it is necessary to further explore the problem of re-proliferated radioresistant cells to chemotherapeutic agents. In the present study, we aimed to investigate the chemosensitivity of radioresistant cells originated from the multicellular spheroids of A549 lung adenocarcinoma.

METHODS

After irradiated with 25 Gy of 6 MV X-ray to A549 multicellular spheroids, whose 10th re-proliferated generations were employed as radioresistant cells, and the control groups were A549 parental cells and MCF7/VCR resistant cells. The chemo-sensitivity test was made by six kinds of chemotherapeutic drugs which were DDP, VDS, 5-Fu, HCP, MMC and ADM respectively, while verapamil (VPL) was used as the reversal agent. Then the treatment effect was evaluated by MTT assay, and the multidrug resistant gene expressions of mdr1 and MRP were measured by RT-PCR.

RESULTS

Both A549 parental cells and A549 derived radioresistant cells were resistant to DDP, but sensitive to VDS, 5-Fu, HCP, MMC and ADM. The inhibitory rates of VPL to these two types of cell were 98% and 25% respectively (P < 0.001). In addition, without drugs added, the absorbance value (A value) of A549 parental cells was 2-folds higher than that of their radioresistant cells (P < 0.001). As to the MCF7/VCR cells, they were resistant to DDP and VDS, but slight sensitive to MMC, ADM, 5-Fu, and HCP with 80% of inhibitory rate to VPL. The subsequent RT-PCR demonstrated that the Mdr1/beta2-MG and MRP/beta2-MG of all A549 cells were about 0 and 0.7 respectively, and those of MCF7/VCR cells were 35 and 4.36.

CONCLUSION

The chemosensitivity of A549 radioresistant cells had not changed markedly, and the decreased sensitivity to VPL could not be explained by the gene expression of mdr1 and MRP. It is possible that the changes in the cell membrane and decreased proliferate ability might be attributed to the resistance. Unlike multidrug resistance induced by chemotherapy, VPL may be not an ideal reverser to radioresistant cells. Therefore, the new biological strategy needs to be developed to treat recurring radioresistant tumor in combination with chemotherapy.

Blood supply in melanoma xenografts is governed by the morphology of the supplying arteries

Tumor blood supply was related to the morphology of the tumor microvasculature and the supplying arteries (SAs) of A-07-GFP and D-12-GFP melanoma xenografts growing in window chamber preparations in BALB/c nu/nu mice. Blood supply and morphologic parameters were determined from first-pass imaging movies and vascular maps recorded after a bolus of 155-kDa tetramethylrhodamine isothiocyanate-labeled dextran had been administered intravenously. Poorly supplied tumors showed microvascular networks that did not differ from those of well-supplied tumors in vessel tortuosity, diameter, and density. Conversely, the SAs of poorly supplied tumors were more tortuous and had a smaller diameter than those of well-supplied tumors, resulting in lower plasma velocities in the downstream tumor vessels. Consequently, the blood supply of A-07-GFP and D-12-GFP tumors was governed by the geometric resistance of the SAs rather than by the geometric resistance or the vessel density of the tumor microvasculature. The present study suggests that the SAs may represent an important target for physiological interventions of tumors and that it may be beneficial to focus on the tumor SAs rather than the tumor microvasculature when searching for novel therapeutic strategies for modifying tumor blood supply.

G3139, an anti-Bcl-2 antisense oligomer that binds heparin-binding growth factors and collagen I, alters in vitro endothelial cell growth and tubular morphogenesis

PURPOSE

We examined the effects of G3139 on the interaction of heparin-binding proteins [e.g., fibroblast growth factor 2 (FGF2) and collagen I] with endothelial cells. G3139 is an 18-mer phosphorothioate oligonucleotide targeted to the initiation codon region of the Bcl-2 mRNA. A randomized, prospective global phase III trial in advanced melanoma (GM301) has evaluated G3139 in combination with dacarbazine. However, the mechanism of action of G3139 is incompletely understood because it is unlikely that Bcl-2 silencing is the sole mechanism for chemosensitization in melanoma cells.

EXPERIMENTAL DESIGN

The ability of G3139 to interact with and protect heparin-binding proteins was quantitated. The effects of G3139 on the binding of FGF2 to high-affinity cell surface receptors and the induction of cellular mitogenesis and tubular morphogenesis in HMEC-1 and human umbilical vascular endothelial cells were determined.

RESULTS

G3139 binds with picomolar affinity to collagen I. By replacing heparin, the drug can potentiate the binding of FGF2 to FGFR1 IIIc, and it protects FGF from oxidation and proteolysis. G3139 can increase endothelial cell mitogenesis and tubular morphogenesis of HMEC-1 cells in three-dimensional collagen gels, increases the mitogenesis of human umbilical vascular endothelial cells similarly, and induces vessel sprouts in the rat aortic ring model.

CONCLUSIONS

G3139 dramatically affects the behavior of endothelial cells. There may be a correlation between this observation and the treatment interaction with lactate dehydrogenase observed clinically.

Multimodal optical imaging of microvessel network convective oxygen transport dynamics

Convective oxygen transport by microvessels depends on several parameters, including red blood cell flux and oxygen saturation. We demonstrate the use of intravital microscopy techniques to measure hemoglobin saturations, red blood cell fluxes and velocities, and microvessel cross-sectional areas in regions of microvascular networks containing multiple vessels. With these methods, data can be obtained at high spatial and temporal resolution and correlations between oxygen transport and hemodynamic parameters can be assessed. In vivo data are presented for a mouse mammary adenocarcinoma grown in a dorsal skinfold window chamber model.

Prevention of hypoxia by myoglobin expression in human tumor cells promotes differentiation and inhibits metastasis

As a tumor grows, it requires increased amounts of oxygen. However, the tumor blood vessels that form to meet this demand are functionally impaired, leading to regions of hypoxia within the tumor. Such hypoxia is one of the hallmarks of malignancy and is thought to promote a number of tumorigenic properties. Here, we sought to determine how tumors without hypoxia would progress by engineering A549 human lung carcinoma cells to ectopically express myoglobin (Mb), a multifunctional heme protein that specializes in oxygen transport, storage, and buffering. Mb expression prevented the hypoxic response in vitro and delayed tumor engraftment and reduced tumor growth following xenotransplantation into mice. Experimental tumors expressing Mb displayed reduced or no hypoxia, minimal HIF-1alpha levels, and a homogeneously low vessel density. Mb-mediated tumor oxygenation promoted differentiation of cancer cells and suppressed both local and distal metastatic spreading. These effects were primarily due to reduced tumor hypoxia, because they were not observed using point-mutated forms of myoglobin unable to bind oxygen and they were abrogated by expression of a constitutively active form of HIF-1alpha. Although limited to xenograft models, these data provide experimental proof of the concept that hypoxia is not just a side effect of deregulated growth but a key factor on which the tumor relies in order to promote its own expansion.

Mitochondrial reticulum network dynamics in relation to oxidative stress, redox regulation, and hypoxia

A single mitochondrial network in the cell undergoes constant fission and fusion primarily depending on the local GTP gradients and the mitochondrial energetics. Here we overview the main properties and regulation of pro-fusion and pro-fission mitodynamins, i.e. dynamins-related GTPases responsible for mitochondrial shape-forming, such as pro-fusion mitofusins MFN1, MFN2, and the inner membrane-residing long OPA1 isoforms, and pro-fission mitodynamins FIS1, MFF, and DRP1 multimers required for scission. Notably, the OPA1 cleavage into non-functional short isoforms at a diminished ATP level (collapsed membrane potential) and the DRP1 recruitment upon phosphorylation by various kinases are overviewed. Possible responses of mitodynamins to the oxidative stress, hypoxia, and concomitant mtDNA mutations are also discussed. We hypothesize that the increased GTP formation within the Krebs cycle followed by the GTP export via the ADP/ATP carrier shift the balance between fission and fusion towards fusion by activating the GTPase domain of OPA1 located in the peripheral intermembrane space (PIMS). Since the protein milieu of PIMS is kept at the prevailing oxidized redox potential by the TOM, MIA40 and ALR/Erv1 import-redox trapping system, redox regulations shift the protein environment of PIMS to a more reduced state due to the higher substrate load and increased respiration. A higher cytochrome c turnover rate may prevent electron transfer from ALR/Erv1 to cytochrome c. Nevertheless, the putative links between the mitodynamin responses, mitochondrial morphology and the changes in the mitochondrial bioenergetics, superoxide production, and hypoxia are yet to be elucidated, including the precise basis for signaling by the mitochondrion-derived vesicles.

Positron Emission Tomography Imaging of Hypoxia

Hypoxia imaging has applications in functional recovery in ischemic events such as stroke and myocardial ischemia, but especially in tumors in which hypoxia can be predictive of treatment response and overall prognosis. Recently there has been development of imaging agents utilizing positron emission tomography for non-invasive imaging of hypoxia. Many of these PET agents have come to the forefront of hypoxia imaging. Halogenated PET nitroimidazole imaging agents labeled with (18)F (t(1/2) = 110 m) and (124)I (t(1/2) = 110 m) have been under investigation for the last 25 years, with radiometal agents ((64)Cu-ATSM) being developed more recently. This review focuses on these positron emission tomography imaging agents for hypoxia.

The genomic analysis of lactic acidosis and acidosis response in human cancers

The tumor microenvironment has a significant impact on tumor development. Two important determinants in this environment are hypoxia and lactic acidosis. Although lactic acidosis has long been recognized as an important factor in cancer, relatively little is known about how cells respond to lactic acidosis and how that response relates to cancer phenotypes. We develop genome-scale gene expression studies to dissect transcriptional responses of primary human mammary epithelial cells to lactic acidosis and hypoxia in vitro and to explore how they are linked to clinical tumor phenotypes in vivo. The resulting experimental signatures of responses to lactic acidosis and hypoxia are evaluated in a heterogeneous set of breast cancer datasets. A strong lactic acidosis response signature identifies a subgroup of low-risk breast cancer patients having distinct metabolic profiles suggestive of a preference for aerobic respiration. The association of lactic acidosis response with good survival outcomes may relate to the role of lactic acidosis in directing energy generation toward aerobic respiration and utilization of other energy sources via inhibition of glycolysis. This “inhibition of glycolysis” phenotype in tumors is likely caused by the repression of glycolysis gene expression and Akt inhibition. Our study presents a genomic evaluation of the prognostic information of a lactic acidosis response independent of the hypoxic response. Our results identify causal roles of lactic acidosis in metabolic reprogramming, and the direct functional consequence of lactic acidosis pathway activity on cellular responses and tumor development. The study also demonstrates the utility of genomic analysis that maps expression-based findings from in vitro experiments to human samples to assess links to in vivo clinical phenotypes.

It is well recognized that tumor microenvironments play an important role in modulating tumor progression in human cancers. Although previous studies have highlighted the importance of hypoxia, there is limited knowledge on the effects of other components in tumor microenvironments. Therefore, we use gene expression to compare and analyze how cells respond to lactate, acidity, and hypoxia, as well as how these responses can be utilized to predict the clinical outcomes of patients with breast cancers. We uncover an unexpected association with better clinical outcome of the strong lactic acidosis and acidosis response in breast cancers as a result of their abilities to inhibit glycolysis and favor oxidative phosphorylation for energy generation. This effect is caused by not only the repression of the gene expression of glycolysis genes but also the inhibition of Akt activation of cells exposed to lactic acidosis and acidosis. In conclusion, we propose that lactic acidosis and acidosis to be considered as independent prognostic factors for human cancers.

Detection of different hypoxic cell subpopulations in human melanoma xenografts by pimonidazole immunohistochemistry

This study aimed at developing immunohistochemical assays for different subpopulations of hypoxic cells in tumors. BALB/c-nu/nu mice bearing A-07 or R-18 tumors were given a single dose of 90 mg/kg body weight or three doses (3 h apart) of 30 mg/kg body weight of pimonidazole hydrochloride intravenously. The fraction of pimonidazole-labeled cells was assessed in paraffin-embedded and frozen tumor sections and compared with the fraction of radiobiologically hypoxic cells. The staining pattern in paraffin-embedded sections indicated selective staining of chronically hypoxic cells. Frozen sections showed a staining pattern consistent with staining of both chronically and acutely/repetitively hypoxic cells. Fraction of pimonidazole-labeled cells in paraffin-embedded sections was lower than the fraction of radiobiologically hypoxic cells (single-dose and triple-dose experiment). In frozen sections, fraction of pimonidazole-labeled cells was similar to (single-dose experiment) or higher than (triple-dose experiment) fraction of radiobiologically hypoxic cells. Three different subpopulations of hypoxic cells could be quantified by pimonidazole immunohistochemistry: the fraction of cells that are hypoxic because of limitations in oxygen diffusion, the fraction of cells that are hypoxic simultaneously because of fluctuations in blood perfusion, and the fraction of cells that are exposed to one or more periods of hypoxia during their lifetime because of fluctuations in blood perfusion.

Insulin-like growth factor stimulation increases radiosensitivity of a pancreatic cancer cell line through endoplasmic reticulum stress under hypoxic conditions

Tumor hypoxia is an obstacle to radiotherapy. Radiosensitivity under hypoxic conditions is determined by molecular oxygen levels, as well as by various biological cellular responses. The insulin-like growth factor (IGF) signaling pathway is a widely recognized survival signal that confers radioresistance. However, under hypoxic conditions the role of IGF signaling in radiosensitivity is still poorly understood. Here, we demonstrate that IGF-II stimulation decreases clonogenic survival under hypoxic conditions in the pancreatic cancer cell lines AsPC-1 and Panc-1, and in the human breast cancer cell line MCF-7. IGF treatment under hypoxic conditions suppressed increased radiation sensitivity in these cell lines by pharmacologically inhibiting the phosphoinositide 3-kinase-mammalian target of rapamycin pathway, a major IGF signal-transduction pathway. Meanwhile, IGF-II induced the endoplasmic reticulum stress response under hypoxia, including increased protein levels of CHOP and ATF4, mRNA levels of CHOP, GADD34, and BiP, as well as splicing levels of XBP-1. The response was suppressed by inhibiting phosphoinositide 3-kinase and mammalian target of rapamycin activity. Overexpression of CHOP in AsPC-1 cells increased radiation sensitivity by IGF-II simulation under hypoxic conditions, whereas suppression of CHOP expression levels with small hairpin RNA or a dominant negative form of a proline-rich extensin-like receptor protein kinase in hypoxia decreased IGF-induced radiosensitivity. IGF-induced endoplasmic reticulum stress contributed to radiosensitization independent of cell cycle status. Taken together, IGF stimulation increased radiosensitivity through the endoplasmic reticulum stress response under hypoxic conditions.

Hyperthermia adds to chemotherapy

The hallmarks of hyperthermia and its pleotropic effects are in favour of its combined use with chemotherapy. Preclinical research reveals that for heat killing and synergistic effects the thermal dose is most critical. Thermal enhancement of drug cytotoxicity is accompanied by cellular death and necrosis without increasing its oncogenic potential. The induction of genetically defined stress responses can deliver danger signals to activate the host's immune system. The positive results of randomised trials have definitely established hyperthermia in combination with chemotherapy as a novel clinical modality for the treatment of cancer. Hyperthermia targets the action of chemotherapy within the heated tumour region without affecting systemic toxicity. In specific clinical settings regional hyperthermia (RHT) or hyperthermic perfusion has proved its value and deserve a greater focus and investigation in other malignancies. In Europe, more specialised centres should be created and maintained as network of excellence for hyperthermia in the field of oncology.

Clinical biomarkers for hypoxia targeting

Tumor hypoxia or a reduction of the tissue oxygen tension is a key microenvironmental factor for tumor progression and treatment resistance in solid tumors. Because hypoxic tumor cells have been demonstrated to be more resistant to ionizing radiation, hypoxia has been a focus of laboratory and clinical research in radiation therapy for many decades. It is believed that proper detection of hypoxic regions would guide treatment options and ultimately improve tumor response. To date, most clinical efforts in targeting tumor hypoxia have yielded equivocal results due to the lack of appropriate patient selection. However, with improved understanding of the molecular pathways regulated by hypoxia and the discovery of novel hypoxia markers, the prospect of targeting hypoxia has become more tangible. This chapter will focus on the development of clinical biomarkers for hypoxia targeting.

A novel triple-regulated oncolytic adenovirus carrying p53 gene exerts potent antitumor efficacy on common human solid cancers

Conditionally replicating adenoviruses (CRAd) can replicate specifically in cancer cells and lyse them. The CRAds were widely used in the preclinical and clinical studies of cancer therapy. We hypothesize that more precisely regulated replication of CRAds may further improve the vector safety profile and enhance its antitumor efficacy. Here, a triple-regulated CRAd carrying p53 gene expression cassette, SG600-p53, was engineered. In SG600-p53, the E1a gene with a deletion of 24 nucleotides within CR2 region is controlled under the human telomerase reverse transcriptase (hTERT) promoter, the E1b gene expression is directed by the hypoxia response element (HRE), whereas the p53 gene is controlled by the cytomegalovirus promoter. The precise triple-regulation endows SG600-p53 with enhanced antitumor potential and improved safety profile. The tumor-selective replication of this virus and its antitumor efficacy were characterized in several tumor cell lines in vitro and in xenograft models of human non-small cell lung cancer in nude mice. With the selective replication and oncolysis, it was found by ELISA assay that SG600-p53 expressed p53 efficiently in cancer cells. In NCI-H1299 tumor xenograft models, SG600-p53 displayed a tumor-selective killing capacity. At a dose of 2 x 10(9) plaque-forming units, SG600-p53 could completely inhibit the tumor growth and more effective than replication-defective Ad-p53. Histopathologic examination revealed that SG600-p53 administration resulted in cancer cell apoptosis. We concluded that the triple-regulated SG600-p53, as a more potent and safer antitumor therapeutic, could provide a new strategy for cancer biotherapy.

Changes in tumor hypoxia induced by mild temperature hyperthermia as assessed by dual-tracer immunohistochemistry

PURPOSE

To study the changes in hypoxia resulting from mild temperature hyperthermia (MTH) in a subcutaneous xenograft model using dual-tracer immunohistochemical techniques.

MATERIALS AND METHODS

HT29 tumors were locally heated at 41 degrees C. Changes in tumor hypoxia were investigated by pimonidazole and EF5. Pimonidazole was given 1h preheating, EF5 at various times during or after treatment, 1h later the animals were sacrificed. Blood vessels were identified by CD31 staining, and perfusion by Hoechst 33342 injected 1 min pre-sacrifice.

RESULTS

The overall hypoxic fraction was significantly decreased by MTH during and immediately after heating. However, MTH induced both increases and decreases in tumor hypoxia in different parts of the tumor. Specifically, MTH decreased hypoxia in the regions with relatively well-perfused blood vessels, but increased hypoxia in regions that were poorly perfused. At 24-h post heating, newly formed hypoxic regions surrounded previously-hypoxic foci, which in turn surrounded pimonidazole-stained debris. Quantitative analysis did not evince changes in tumor oxygenation due to MTH at 24h post-treatment.

CONCLUSION

In this xenograft model, the effect of MTH on tumor oxygenation was variable, both spatially and kinetically. Overall tumor oxygenation was improved during and after heating, but the effect was short-lived.

Responses of total and quiescent cell populations in solid tumors to carbon ion beam irradiation (290 MeV/u) in vivo

PURPOSE

The aim of this study was to clarify the radiosensitivity of intratumor total cells and quiescent (Q) cells in vivo to accelerated carbon ion beams compared with gamma-ray irradiation.

MATERIALS AND METHODS

Squamous cell carcinoma (SCC) VII tumor-bearing mice received continuous administration of 5-bromo-2'-deoxyuridine (BrdU) to label all intratumor proliferating (P) cells. They then were exposed to carbon ions (290 MeV/u) or gamma-rays. Immediately after and 12 h after irradiation, immunofluorescence staining for BrdU was used to assess the response of Q cells in terms of micronucleus frequency. The response of the total (P + Q) tumor cells was determined from the tumors not treated with BrdU.

RESULTS

The apparent difference in radiosensitivity between total and Q cell populations under gamma-ray irradiation was markedly reduced with carbon ion beams, especially with a higher linear energy transfer (LET) value. Clearer recovery in Q cells than in total cells through delayed assay under gamma-ray irradiation was efficiently inhibited by carbon ion beams, especially those with a higher LET.

CONCLUSION

In terms of the tumor cell-killing effect as a whole, including intratumor Q cells, carbon ion beams, especially with higher LET values, were extremely useful for suppressing the dependence on the heterogeneity within solid tumors as well as depositing the radiation dose precisely.

Hypoxia selects for androgen independent LNCaP cells with a more malignant geno- and phenotype

Hypoxia confers resistance to common cancer therapies, however, it has also has been shown to result in genetic alterations which may allow a survival advantage and increase the tumorigenic properties of cancer cells. Additionally, it may exert a selection pressure, allowing expansion of tumor cells with a more aggressive phenotype. To further assess the role of hypoxia in malignant progression in prostate cancer we exposed human androgen dependent prostate cancer cells (LNCaP) to cycles of chronic hypoxia and isolated a subline, LNCaP-H1. This article describes the partial characterization of this cell line. The LNCaP-H1 subline showed altered growth characteristics and exhibited androgen independent growth both in vitro and in vivo. Furthermore, these cells were resistant to mitochondrial-mediated apoptosis, probably since the endogenous levels of Bax was lower and Bcl-2 higher than in the parental LNCaP cells. Microarray analysis revealed that a complex array of pathways had differential gene expression between the 2 cell lines, with LNCaP-H1 cells exhibiting a genetic profile which suggests that they may be more likely metastasize to distant organs, especially bone. This was supported by an in vitro invasion assay, and an in vivo metastasis study. This study shows that hypoxia can select for androgen independent prostate cancer cells which have a survival advantage and are more likely to invade and metastasize.

Antiangiogenic therapy with mammalian target of rapamycin inhibitor RAD001 (Everolimus) increases radiosensitivity in solid cancer

PURPOSE

Radiotherapy exerts direct antivascular effects in tumors and also induces a proangiogenic stress response in tumor cells via the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway. Therefore, the combination of radiotherapy and antiangiogenic therapy with mTOR inhibitor RAD001 (Everolimus) might exert additive/synergistic effects on tumor growth.

EXPERIMENTAL DESIGN

Effects of radiation combined with mTOR inhibitor RAD001 were studied on proliferation of murine colon cancer CT-26, human pancreatic cancer L3.6pl, and human umbilical vascular endothelial cells in vitro. In vivo tumor growth of subcutaneous colon cancer CT 26 and orthotopic pancreatic cancer L3.6pl was assessed after fractionated radiotherapy (5 x 2 or 5 x 4 Gy) with or without the addition of the mTOR inhibitor RAD001. RAD001 (1.5 mg/kg/d) was administered until the end of experiments beginning before or after radiotherapy.

RESULTS

A single dose of 2 Gy reduced in vitro proliferation of L3.6pl (-16%), CT-26 (-70%), and human umbilical vascular endothelial cells (HUVEC; -72%). The mTOR inhibitor RAD001 (10 ng/mL) suppressed proliferation of HUVEC (-83%), L3.6pl (-8%), and CT-26 (-82%). Combination of even low concentrations of 0.01 ng/mL RAD001 and 0.25 Gy radiation significantly reduced proliferation of HUVECs (-57%), whereas additive effects of RAD001 and radiation on tumor cells were seen only at the highest concentrations tested. In vivo, RAD001 introduced before radiotherapy (5 x 2 Gy) improved tumor growth control in mice (L3.6pl: 326 mm(3) versus 1144 mm(3); CT-26: 210 mm(3) versus 636 mm(3); P < 0.05 versus control). RAD001 turned out to possess a dose-modifying effect on radiotherapy.

CONCLUSION

Endothelial cells seem to be most sensitive to combination of mTOR inhibition and radiotherapy. Additive tumor growth delay using the mTOR inhibitor RAD001 and radiotherapy in vivo therefore might rely on combined antiangiogenic and antivascular effects.

Tumor vascularity assessed by magnetic resonance imaging and intravital microscopy imaging

Gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is considered to be a useful method for characterizing the vascularity of tumors. However, detailed studies of experimental tumors comparing DCE-MRI-derived parametric images with images of the morphology and function of the microvascular network have not been reported. In this communication, we describe a novel MR-compatible mouse dorsal window chamber and report comparative DCE-MRI and intravital microscopy studies of A-07-GFP tumors xenografted to BALB/c nu/nu mice. Blood supply time (BST) images (i.e., images of the time from when arterial blood enters a tumor through the supplying artery until it reaches a vessel segment within the tumor) and morphologic images of the microvascular network were produced by intravital microscopy. Images of E.F (E is the initial extraction fraction of Gd-DTPA and F is perfusion) were produced by subjecting DCE-MRI series to Kety analysis. The E.F images mirrored the morphology (microvascular density) and the function (BST) of the microvascular networks well. Tumor regions showing high E.F values colocalized with tumor regions showing high microvascular density and low BST values. Significant correlations were found between E.F and microvascular density and between E.F and BST, both within and among tumors.

Solid tumor physiology and hypoxia-induced chemo/radio-resistance: novel strategy for cancer therapy: nitric oxide donor as a therapeutic enhancer

Hypoxia exists in solid tumor tissues due to abnormal vasculature, vascular insufficiency, treatment or malignancy related anemia, and low intratumor blood flow. Hypoxic status in solid tumor promotes accumulation of hypoxia-inducible factor-1 alpha which is promptly degraded by proteasomal ubiquitination under normoxic conditions. However, under hypoxic conditions, the ubiquitination system for HIF-1 alpha is inhibited by inactivation of prolyl hydroxylase which is responsible for hydroxylation of proline in the oxygen-dependent degradation domain of HIF-1 alpha. HIF-1 alpha is an important transcriptional factor that codes for hundreds of genes involved in erythropoiesis, angiogenesis, induction of glycolytic enzymes in tumor tissues, modulation of cancer cell cycle, cancer proliferation, and cancer metastasis. Hypoxia and accumulation of HIF-1 alpha in solid tumor tissues have been reported to associate with resistance to chemotherapy, radiotherapy, and immunotherapy and poor prognosis. Production of vascular endothelial growth factor (VEGF) in cancer cells is regulated by the activated HIF-1 mediated system. An increase in VEGF levels subsequently induces HIF-1 alpha accumulation and promotes tumor metastasis by angiogenesis. Recently, angiogenesis targeting therapy using humanized VEGF antibody and VEGF receptor tyrosine kinase inhibitors have been used in solid cancer therapy. Nitric oxide (NO) is a unique chemical gaseous molecule that plays a role as a chemical messenger involved in vasodilator, neurotransmitter, and anti-platelet aggregation. In vivo, NO is produced and released from three different isoforms of NO synthase (NOS) and from exogenously administered NO donors. In cancer science, NO has been mainly discussed as an oncogenic molecule over the past decades. However, NO has recently been noted in cancer biology associated with cancer cell apoptosis, cancer cell cycle, cancer progression and metastasis, cancer angiogenesis, cancer chemoprevention, and modulator for chemo/radio/immuno-therapy. The presence and activities of all the three isoforms of NOS and were detected in cancer tissue components such as cancer cells, tumor-associated macrophages, and vascular endothelium. Overexpression of iNOS in cancer tissues has been reported to associate with poor prognosis in patients with cancers. On the other hand, NO donors such as nitroglycerin have been demonstrated to improve the effects of cancer therapy in solid cancers. Nitroglycerin has been used safely for a long time as a potent vasodilator for the treatment of ischemic heart diseases or heart failure. Therefore, we think highly of clinical use of nitroglycerin as a novel cancer therapy in combination with anticancer drugs for improvement of cancer therapeutic levels. In this review article, we demonstrate the unique physiological characteristics of malignant solid tumors, several factors in solid tumors resulting in resistance for cancer therapies, and the effects of NO from NOS or exogenous NO-donating drugs on malignant cells. Furthermore, we refer to promising therapeutic roles of NO and NO-donating drugs for novel treatments in solid tumors.

Gene-viral cancer therapy using dual-regulated oncolytic adenovirus with antiangiogenesis gene for increased efficacy

Conditionally replicative adenovirus (CRAD) represents a promising approach for cancer therapy. Several CRADs controlled by the human telomerase reverse transcriptase promoter have been developed. However, because of their replicative capacity, the importance of cancer specificity for CRADs needs to be further emphasized. In this study, we have developed a novel dual-regulated CRAD, CNHK500-mE, which has its E1a and E1b gene controlled by the human telomerase reverse transcriptase promoter and the hypoxia response element, respectively. It also carries a mouse endostatin expression cassette controlled by the cytomegalovirus promoter. These properties allow for increased cancer cell targeting specificity and decreased adverse side effects. We showed that CNHK500-mE preferentially replicated in cancer cells. Compared with a replication-defective vector carrying the same endostatin expression cassette, CNHK500-mE-mediated transgene expression level was markedly increased via viral replication within cancer cells. In the nasopharyngeal tumor xenograft model, CNHK500-mE injection resulted in antitumor efficacy at day 7 after therapy. Three weeks later, it led to significant inhibition of xenograft tumor growth due to the combined effects of viral oncolytic therapy and antiangiogenesis gene therapy. Pathologic examination showed that most cancer cells were positive for adenoviral capsid protein and for apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling in the CNHK500-mE-treated tumor tissues, and the microvessels in these tumor tissues were diminished in quantity and abnormal in morphology. These results suggest that, as a potential cancer therapeutic agent, the CNHK500-mE is endowed with higher specificity to cancer cells and low cytotoxicity to normal cells.

The new vascular disrupting agent combretastatin-A1-disodium-phosphate (OXi4503) enhances tumour response to mild hyperthermia and thermoradiosensitization

PURPOSE

The aim of this study was to investigate the anti-cancer effect of the novel vascular disrupting agent (VDA), combretastatin-A1-disodium-phosphate (OXi4503), when combined with mild hyperthermia and/or radiation.

MATERIALS AND METHODS

A C3H mammary carcinoma was grown subcutaneously in the rear right foot of female CDF1 mice, and treated when a volume of 200 mm(3) was reached. OXi4503 was administered intra-peritoneally at variable doses. Hyperthermia was administered locally to the tumour-bearing foot using a thermostat-controlled water bath. Radiation treatment was performed locally using a conventional X-ray machine. Tumour response was assessed with either a tumour growth time or a tumour control assay.

RESULTS

The optimal delay between administration of 50 mg/kg of OXi4503 and hyperthermia was found to be 3 hours. The linear relationship between tumour growth time (TGT) and heating time at a specific temperature resulted in slope values between -0.003 days/min and 0.09 days/min at temperatures between 40 degrees C and 42.5 degrees C. When combined with OXi4503 this was significantly increased to 0.008 days/min and 0.03 days/min at temperatures between 39.5 degrees C and 41 degrees C, respectively. Above 41 degrees C, combined treatment did not result in significantly greater slope values. The radiation dose required to control 50% of the tumours (TCD50) was 52 Gy. Combining radiation with either heat treatment at 41.5 degrees C for 1 hour or OXi4503 reduced the TCD50 to 47 Gy and 41 Gy, respectively. Combining radiation with heat and OXi4503 further reduced the TCD50 to 37 Gy.

CONCLUSIONS

OXi4503 is a highly potent VDA, which is capable of significantly enhancing the anti-cancer effect of mild hyperthermia. Mild temperature thermoradiosensitization was also enhanced.

Chronic hypoxia decreases synthesis of homologous recombination proteins to offset chemoresistance and radioresistance

Hypoxic and/or anoxic tumor cells can have increased rates of mutagenesis and altered DNA repair protein expression. Yet very little is known regarding the functional consequences of any hypoxia-induced changes in the expression of proteins involved in DNA double-strand break repair. We have developed a unique hypoxic model system using H1299 cells expressing an integrated direct repeat green fluorescent protein (DR-GFP) homologous recombination (HR) reporter system to study HR under prolonged chronic hypoxia (up to 72 h under 0.2% O(2)) without bias from altered proliferation, cell cycle checkpoint activation, or severe cell toxicity. We observed decreased expression of HR proteins due to a novel mechanism involving decreased HR protein synthesis. Error-free HR was suppressed 3-fold under 0.2% O(2) as measured by the DR-GFP reporter system. This decrease in functional HR resulted in increased sensitivity to the DNA cross-linking agents mitomycin C and cisplatin but not to the microtubule-interfering agent, paclitaxel. Chronically hypoxic H1299 cells that had decreased functional HR were relatively radiosensitive [oxygen enhancement ratio (OER), 1.37] when compared with acutely hypoxic or anoxic cells (OER, 1.96-2.61). Using CAPAN1 cells isogenic for BRCA2 and siRNA to RAD51, we confirmed that the hypoxia-induced radiosensitivity was due to decreased HR capacity. Persistent down-regulation of HR function by the tumor microenvironment could result in low-fidelity DNA repair and have significant implications for response to therapy and genetic instability in human cancers.

N-myc augments death and attenuates protective effects of Bcl-2 in trophically stressed neuroblastoma cells

N-myc has proapoptotic functions, yet it acts as an oncogene in neuroblastoma. Thus, antiapoptotic mechanisms have to be operative in neuroblastoma cells that antagonize the proapoptotic effects of N-myc. We conditionally activated N-myc in SH-EP neuroblastoma cells subjected to the trophic stress of serum or nutrient deprivation while changing the expression of Bcl-2, survivin and FLIP(L), antiapoptotic molecules often overexpressed in poor prognosis neuroblastomas. Bcl-2 protected SH-EP cells from death during nutritional deprivation by activating energetically advantageous oxidative phosphorylation. N-myc overrode the metabolic protection provided by Bcl-2-induced oxidative phosphorylation by reestablishing the glycolytic phenotype and attenuated the antiapoptotic effect of Bcl-2 during metabolic stress. Survivin partially antagonized the growth suppressive function of N-myc in SH-EP neuroblastoma cells during serum deprivation whereas FLIP(L) did not. These findings advance our understanding of the functions of N-myc in neuroblastoma cells.

Interstitial permeability and elasticity in human cervix cancer

Malignant tumors are characterized by abnormalities of the vasculature and interstitium, which may impede the distribution of drugs and imaging agents. Here we describe a method for estimating tumor interstitial permeability and elasticity based on fitting a spatio-temporal fluid dynamic model to the time course of interstitial pressure (IFP) measurements. The model assumes that sudden insertion of the IFP measurement needle transiently perturbs the steady-state fluid balance, which recovers over time as a function of the vascular and interstitial hydraulic conductivities (L(p)S and K), the interstitial bulk modulus (E) and the extracellular, extravascular volume fraction (phi). Initial simulations showed that the time course of IFP recordings was mainly determined by K and E/phi. Mean values of K and E/phi in 60 newly diagnosed cervix cancers were 1.5 x 10(-7) (SE 2.2 x 10(-8)) cm(2)/mm Hg s and 2230 (SE 212) mm Hg, respectively. For comparison, K and E/phi were also measured in orthotopic ME-180 human cervix cancer xenografts and KHT-C fibrosarcomas in mice. K was higher in both of these tumors (7.0 x 10(-7) and 9.3 x 10(-7)) than in cervix cancer, and E/phi was lower (497 and 433). To our knowledge, these are the first measurements of interstitial permeability and elasticity in individual human cancers. Serial evaluation of these parameters may provide a means of clinically monitoring response to treatments that specifically target the tumor microenvironment.

Hypoxia and cancer

A major feature of solid tumours is hypoxia, decreased availability of oxygen, which increases patient treatment resistance and favours tumour progression. How hypoxic conditions are generated in tumour tissues and how cells respond to hypoxia are essential questions in understanding tumour progression and metastasis. Massive tumour-cell proliferation distances cells from the vasculature, leading to a deficiency in the local environment of blood carrying oxygen and nutrients. Such hypoxic conditions induce a molecular response, in both normal and neoplastic cells, that drives the activation of a key transcription factor; the hypoxia-inducible factor. This transcription factor regulates a large panel of genes that are exploited by tumour cells for survival, resistance to treatment and escape from a nutrient-deprived environment. Although now recognized as a major contributor to cancer progression and to treatment failure, the precise role of hypoxia signalling in cancer and in prognosis still needs to be further defined. It is hoped that a better understanding of the mechanisms implicated will lead to alternative and more efficient therapeutic approaches.

Hypoxia imaging with FAZA-PET and theoretical considerations with regard to dose painting for individualization of radiotherapy in patients with head and neck cancer

PURPOSE

To evaluate the role of hypoxia positron emission tomography (PET) using [18F]fluoroazomycin-arabinoside (FAZA) in head and neck cancer for radiation treatment planning using intensity-modulated radiotherapy and dose painting.

METHODS AND MATERIALS

Eighteen patients with advanced squamous cell head and neck cancer were included. Both FAZA-PET and axial CT were performed using mask fixation. The data were coregistered using software based on mutual information. Contours of tumor (primary gross tumor volume, GTV/CT-P) and lymph node metastases (GTV/CT-N) were outlined manually, and FAZA standardized uptake values (SUVs) were calculated automatically. The hypoxic subvolume (GTV/PET-FAZA) having at least 50% more FAZA uptake than background (mean SUV) neck muscle tissue was contoured automatically within GTV/CT-P (GTV/PET-FAZA-P) and GTV/CT-N (GTV/PET-FAZA-N).

RESULTS

The median GTV/PET-FAZA-P was 4.6 mL, representing 10.8% (range, 0.7-52%) of the GTV/CT-P. The GTV/PET-FAZA-P failed to correlate significantly with the GTV/CT-P (p = 0.06). The median GTV/PET-FAZA-N was 4.1 mL, representing 8.3% (range, 2.2-51.3%) of the GTV/CT-N. It was significantly correlated with the GTV/PET-N (p = 0.006). The GTV/PET-FAZA-P was located in a single confluent area in 11 of 18 patients (61%) and was diffusely dispersed in the whole GTV/CT-P in 4 of 18 patients (22%), whereas no hypoxic areas were identified in 3 of 18 patients (17%). The GTV/PET-FAZA-N was outlined as a single confluent region in 7 of 18 patients (39%), in multiple diffuse hypoxic regions in 4 of 18 patients (22%), and was not delineated in 7 of 18 patients (39%).

CONCLUSION

This study demonstrates that FAZA-PET imaging could be used for a hypoxia-directed intensity-modulated radiotherapy approach in head and neck cancer.

Inhibition of repair of radiation-induced damage by mild temperature hyperthermia, referring to the effect on quiescent cell populations

PURPOSE

We evaluated the usefulness of mild temperature hyperthermia (MTH) as an inhibitor of the repair of radiation-induced damage in terms of the responses of the total [= proliferating (P) + quiescent (Q)] and Q cell populations in solid tumors in vivo.

MATERIALS AND METHODS

SCC VII tumor-bearing mice received a continuous administration of 5-bromo-2'-deoxyuridine (BrdU) to label all P cells. They then underwent high-dose-rate (HDR) gamma-ray irradiation immediately followed by MTH or administration of caffeine or wortmannin; alternatively, they underwent reduced-dose rate gamma-ray irradiation simultaneously with MTH or administration of caffeine or wortmannin. Nine hours after the start of irradiation, the tumor cells were isolated and incubated with a cytokinesis blocker, and the micronucleus (MN) frequency in cells without BrdU labeling (= Q cells) was determined using immunofluorescence staining for BrdU. The MN frequency in the total tumor cell population was determined using tumors that were not pretreated with BrdU.

RESULTS

In both the total and Q-cell populations, especially the latter, MTH efficiently suppressed the reduction in sensitivity caused by leaving an interval between HDR irradiation and the assay and decreasing the irradiation dose rate, as well as the combination with wortmannin administration.

CONCLUSION

From the viewpoint of solid tumor control as a whole, including intratumor Q-cell control, MTH is useful for suppressing the repair of both potentially lethal and sublethal damage.

Dynamic contrast-enhanced magnetic resonance imaging of human melanoma xenografts with necrotic regions

PURPOSE

To investigate whether high-resolution images of necrotic regions in tumors can be derived from gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) series.

MATERIALS AND METHODS

E-13 human melanoma xenografts were used as preclinical models of human cancer. DCE-MRI was performed at a voxel size of 0.23 x 0.47 x 2.0 mm3 with the use of spoiled gradient recalled sequences. Tumor images of E . F (E is the initial extraction fraction of Gd-DTPA and F is blood perfusion) and lambda (the partition coefficient of Gd-DTPA, which is proportional to extracellular volume fraction) were produced by subjecting DCE-MRI series to Kety analysis, and these images were compared with histological preparations from the imaged slices.

RESULTS

Strong correlations were found between fraction of necrotic tissue and fraction of voxels with lambda > lambdaL for lambdaL values of 0.4 to 0.6. Binary lambda images differentiating between lambda values > lambdaL and lambda values < lambdaL were found to mirror necrotic regions well in tumors with large necroses. However, necrotic foci that were small compared with the voxel size were not detectable.

CONCLUSION

Clinically relevant images of necrotic tumor regions can be obtained for E-13 melanomas by subjecting Gd-DTPA-based DCE-MRI series to Kety analysis.

Tumor-specific positron emission tomography imaging in patients: [18F] fluorodeoxyglucose and beyond

Biochemical and molecular imaging of cancer using positron emission tomography (PET) plays an increasing role in the care of cancer patients. Most clinical work to date uses the glucose analogue [(18)F]fluorodeoxyglucose (FDG) to detect accelerated and aberrant glycolysis present in most tumors. Although clinical FDG PET has been used largely to detect and localize cancer, more detailed studies have yielded biological insights and showed the utility of FDG as a prognostic marker and as a tool for therapeutic response evaluation. As cancer therapy becomes more targeted and individualized, it is likely that PET radiopharmaceuticals other than FDG, aimed at more specific aspects of cancer biology, will also play a role in guiding cancer therapy. Clinical trials designed to test and validate new PET agents will need to incorporate rigorous quantitative image analysis and adapt to the evolving use of imaging as a biomarker and will need to incorporate cancer outcomes, such as survival into study design.

Prostate carcinoma cells selected by long-term exposure to reduced oxygen tension show remarkable biochemical plasticity via modulation of superoxide, HIF-1alpha levels, and energy metabolism

Cancer cells are able to tolerate levels of O(2) that are damaging or lethal to normal cells; we hypothesize that this tolerance is the result of biochemical plasticity which maintains cellular homeostasis of both energy levels and oxidation state. In order to examine this hypothesis, we used different O(2) levels as a selective agent during long-term culture of DU145 prostate cancer cells to develop three isogenic cell lines that grow in normoxic (4%), hyperoxic (21%), or hypoxic (1%) O(2) conditions. Growth characteristics and O(2) consumption differed significantly between these cell lines without changes in ATP levels or altered sensitivity to 2-deoxy-D-glucose, an inhibitor of glycolysis. O(2) consumption was significantly higher in the hyperoxic line as was the level of endogenous superoxide. The hypoxic cell line regulated the chemical gradient of the proton motive force (PMF) independent of the electrical component without O(2)-dependent changes in Hif-1alpha levels. In contrast, the normoxic line regulated Hif-1alpha without tight regulation of the chemical component of the PMF noted in the hypoxic cell line. From these studies, we conclude that selection of prostate cancer cells by long-term exposure to low ambient levels of O(2) resulted in cells with unique biochemical properties in which energy metabolism, reactive oxygen species (ROS), and HIF-1alpha levels are modulated to allow cell survival and growth. Thus, cancer cells exhibit remarkable biochemical plasticity in response to various O(2) levels.

Drug Resistance and the Solid Tumor Microenvironment

Resistance of human tumors to anticancer drugs is most often ascribed to gene mutations, gene amplification, or epigenetic changes that influence the uptake, metabolism, or export of drugs from single cells. Another important yet little-appreciated cause of anticancer drug resistance is the limited ability of drugs to penetrate tumor tissue and to reach all of the tumor cells in a potentially lethal concentration. To reach all viable cells in the tumor, anticancer drugs must be delivered efficiently through the tumor vasculature, cross the vessel wall, and traverse the tumor tissue. In addition, heterogeneity within the tumor microenvironment leads to marked gradients in the rate of cell proliferation and to regions of hypoxia and acidity, all of which can influence the sensitivity of the tumor cells to drug treatment. In this review, we describe how the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and discuss potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumor microenvironment.

Mechanism of action and preclinical antitumor activity of the novel hypoxia-activated DNA cross-linking agent PR-104

PURPOSE

Hypoxia is a characteristic of solid tumors and a potentially important therapeutic target. Here, we characterize the mechanism of action and preclinical antitumor activity of a novel hypoxia-activated prodrug, the 3,5-dinitrobenzamide nitrogen mustard PR-104, which has recently entered clinical trials.

EXPERIMENTAL DESIGN

Cytotoxicity in vitro was evaluated using 10 human tumor cell lines. SiHa cells were used to characterize metabolism under hypoxia, by liquid chromatography-mass spectrometry, and DNA damage by comet assay and gammaH2AX formation. Antitumor activity was evaluated in multiple xenograft models (PR-104 +/- radiation or chemotherapy) by clonogenic assay 18 h after treatment or by tumor growth delay.

RESULTS

The phosphate ester "pre-prodrug" PR-104 was well tolerated in mice and converted rapidly to the corresponding prodrug PR-104A. The cytotoxicity of PR-104A was increased 10- to 100-fold by hypoxia in vitro. Reduction to the major intracellular metabolite, hydroxylamine PR-104H, resulted in DNA cross-linking selectively under hypoxia. Reaction of PR-104H with chloride ion gave lipophilic cytotoxic metabolites potentially able to provide bystander effects. In tumor excision assays, PR-104 provided greater killing of hypoxic (radioresistant) and aerobic cells in xenografts (HT29, SiHa, and H460) than tirapazamine or conventional mustards at equivalent host toxicity. PR-104 showed single-agent activity in six of eight xenograft models and greater than additive antitumor activity in combination with drugs likely to spare hypoxic cells (gemcitabine with Panc-01 pancreatic tumors and docetaxel with 22RV1 prostate tumors).

CONCLUSIONS

PR-104 is a novel hypoxia-activated DNA cross-linking agent with marked activity against human tumor xenografts, both as monotherapy and combined with radiotherapy and chemotherapy.

Carbonic anhydrase 9 (CA9) expression in tumor cells enhances sensitivity to tirapazamine

PURPOSE

Carbonic anhydrase 9 (CA9) is over-expressed in many human solid tumors under conditions of low oxygen concentration and can be associated with a low probability of survival. In this study, stable CA9-expressing cell lines were established using the CA9 gene-defective human C33a cell line and the HeLa cell line to investigate the role of CA9 in response to ionizing radiation and hypoxia-selective cytotoxin, Tirapazamine (TPZ).

METHODS AND MATERIALS

Human CA9 cDNA or an empty vector was transfected into the C33a and HeLa cell lines and C33a-vector, C33a-CA9, HeLa-vector, and HeLa-CA9 cell lines were produced accordingly. Sensitivity of the C33a-vector/C33a-CA9 cells to ionizing radiation and TPZ was measured using clonogenic assays. The alkaline comet assay was used to measure single strand DNA breaks caused by TPZ in the C33a-vector, C33a-CA9, HeLa-vector, and HeLa-CA9 cell lines.

RESULTS

Radiation sensitivity, as determined with clonogenic survival assays, of C33a-vector/C33a-CA9 cells did not differ under either normoxic or hypoxic conditions. However, increased clonogenic sensitivity to TPZ was observed in C33a-CA9 cells under the hypoxic condition by 26% (95% CI 14-39%, P = 0.02 in comparison to the C33a-vector cells). The comet assay showed significantly greater DNA damage in the C33a-CA9 cells compared with that of the C33a-vector cells with the same treatment under hypoxic conditions, supporting the results of the clonogenic survival data. Because this difference in the amount of DNA damage was not observed for the hypoxic HeLa-CA9/HeLa-vector cell lines, both of which have induced CA9 expression by hypoxia, the enhanced sensitivity of C33a-CA9 cells to TPZ is considered to be due to the specific condition of CA9 over-expression.

CONCLUSION

Our results suggest the possibility that CA9 over-expression in tumors might be exploited to increase the treatment effects of TPZ.