Using positron emission tomography with [(18)F]FDG to predict tumor behavior in experimental colorectal cancer

Non-invasive MRI tumor imaging and synergistic anticancer effect of HSP90 inhibitor and glycolysis inhibitor in RIP1-Tag2 transgenic pancreatic tumor model

PURPOSES

To utilize non-invasive MRI imaging for real-time testing the synergistic effects of HSP90 inhibitor and glycolysis inhibitor for pancreatic cancer therapy in spontaneous pancreatic cancer mouse model.

MATERIAL AND METHODS

Transgenic RIP1-Tag2 spontaneous pancreatic cancer mice were treated with geldanamycin (GA, 5 mg/kg) and /or 3-Bromo-pyruvate (3-BrPA, 5 mg/kg) from 8 to 12 weeks of age. Non-invasive MRI imaging measured and calculated the total tumor mass and volumes in real-time and compared to ex vivo tumors size. Serum VEGF levels were measured by ELISA. HSP 90 client protein levels (AKT and VEGF) were measured by western blots.

RESULTS

RIP-Tag2 transgenic mice developed pancreatic tumors from 8 to 12 weeks of age. Non-invasive MRI imaging detected primary tumors in pancreas and metastasis in intestine and mesenterium with minimal resolution of 20 mm(3). VEGF, AKT, hexokinase II, and Hsp90 were expressed in the pancreatic cancer tissues from RIP1-Tag2 transgenic mice. Combination of GA and 3-BrPA decreased serum VEGF levels by 70% compared to control group. Non-invasive MRI imaging showed that combination of GA and 3-BrPA inhibited pancreatic tumor and metastasis by more than 90% and significantly prolonged life span of RIP1-Tag2 transgenic pancreatic cancer mice. The synergistic effect of geldanamycin and 3-BrPA is through inhibition of two different pathways on HSP90 for its client protein degradation and on HK II for energy metabolism.

CONCLUSION

Non-invasive MRI imaging revealed synergistic effects of Hsp90 inhibitors and glycolysis inhibitors, which may provide a new therapeutic option for pancreatic cancer therapy.

Is FDG-PET scan in patients with early stage Hodgkin lymphoma of any value in the implementation of the involved-node radiotherapy concept and dose painting?

BACKGROUND AND PURPOSE

To evaluate the input of FDG-PET data in the implementation of the involved-node radiotherapy concept and dose painting.

MATERIALS AND METHODS

Patients with early-stage Hodgkin lymphoma treated with combined modality treatments. First, patients underwent a PET/CT before chemotherapy in the treatment position using a head and shoulder immobilization mask. Second, all patients had a CT simulation for treatment planning. The CT simulation was coregistered with the prechemotherapy CT and FDG-PET scan. All prechemotherapy volumes were superimposed on the CT simulation. The initially involved lymph node areas to be irradiated were delineated on the CT simulation scan. Chemotherapy-induced shrinkage rates of the tumor masses visible on CT scan and on FDG-PET were determined and compared.

RESULTS

Before chemotherapy, FDG-PET-avid areas represented 25% of the total volume on CT. After chemotherapy, the influence of initial FDG-PET data on the delineation of involved-node radiotherapy fields was significant and was due to the fact that in 36% of the patients, FDG-PET helped pinpoint lymph nodes that were undetected on CT. After chemotherapy, the rates of tumor volume shrinkage on CT and FDG-PET were similar. This finding suggests similar chemosensitivity for FDG-PET-avid and non-avid areas. There was no correlation between initial FDG-PET-avid volumes and the clinical outcome.

CONCLUSION

Prechemotherapy FDG-PET data are essential for correctly implementing the involved-node radiotherapy concept but seem to be of minimal value for applying the concept of dose painting.

Radioimmunoguided surgery (RIGS), PET/CT image-guided surgery, and fluorescence image-guided surgery: Past, present, and future

(125)I-labeled anti-TAG-72 antibodies were applied in radioimmunoguided surgery (RIGS) to remove gross and occult tumors. It is challenging to handle (125)I-labeled materials. PET/CT image-guided surgery utilizes (18)FDG to monitor the biochemical activity of the tumor and to integrate pre- and postoperative imaging for complete tumor removal. PET/CT image-guided surgery only detects later stage disease. Fluorescence image-guided surgery using anti-TAG-72 antibodies may provide opportunities for intraoperative cancer detection of both gross and occult tumors.

FDG-PET scan in patients with clinically and/or radiologically suspicious colorectal cancer recurrence but normal CEA

Background

Although frequently used for tumor surveillance, the sensitivity of carcinoembryonic antigen (CEA) to detect recurrent colorectal cancer (CRC) is not optimal. Fluorine 18-fluoro-2-deoxy-glucose-positron emission tomography (¹⁸F FDG-PET) scans promise to improve recurrent CRC detection. We aimed to review PET scans of patients with clinically and/or radiologically suspicious tumor recurrence but normal CEA.

Methods

A retrospective review of an electronic database of 308 patients with CRC who had PET scans was performed. Only PET studies of patients with normal CEAs and suspected tumor recurrence who had pathological verification were selected for further analysis. Thirty-nine patients met the inclusion criteria.

Results

PET was positive in 26 patients (67%) and normal in 13 (33%). Histopathologic evidence of tumor recurrence was seen in 27 of the 39 patients (69%). When correlated with histopathology, PET was true positive in 22 patients, false positive in 4, true negative in 8 and false negative in 5. Overall, the accuracy of PET was 76.9%, negative predictive value (NPV) was 61.5%, and positive predictive value (PPV) was 84.6%. PPV value of PET for liver metastases was 88.8% compared to 73.3% for local recurrence. In two patients with confirmed recurrence, CEA became positive 2 months after PET scan indicating earlier detection of disease with PET. The false positive PET findings were mainly in the bowel and were secondary to acute/chronic inflammation and granulation tissue. In 3 patients with false negative PET, histopathology was consistent with mucinous adenocarcinoma.

Conclusion

PET yields high PPV for recurrent CRC, particularly for liver metastases, in spite of normal CEA levels and should be considered early in the evaluation of patients with suspected tumor recurrence.

Promise and Progress for Functional and Molecular Imaging of Response to Targeted Therapies

Biomarkers to predict or monitor therapy response are becoming essential components of drug developer's armamentaria. Molecular and functional imaging has particular promise as a biomarker for anticancer therapies because it is non-invasive, can be used longitudinally and provides information on the whole patient or tumor. Despite this promise, molecular or functional imaging endpoints are not routinely incorporated into clinical trial design. As the costs of clinical trials and drug development become prohibitively more expensive, the need for improved biomarkers has become imperative and thus, the relatively high cost of imaging is justified. Imaging endpoints, such as Diffusion-Weighted MRI, DCE-MRI and FDG-PET have the potential to make drug development more efficient at all phases, from discovery screening with in vivo pharmacodynamics in animal models through the phase III enrichment of the patient population for potential responders. This review focuses on the progress of imaging responses to new classes of anti-cancer therapies targeted against PI3 kinase/AKT, HIF-1alpha and VEGF. The ultimate promise of molecular and functional imaging is to theragnostically predict response prior to commencement of targeted therapy.

Assessment of quantitative FDG PET data in primary colorectal tumours: which parameters are important with respect to tumour detection?

PURPOSE

The impact of quantitative parameters on the differentiation of primary colorectal tumours from normal colon tissue was assessed. Dynamic PET data (DPET) were acquired, and compartment and non-compartment modelling applied. The discriminant power of single parameters and the combination of PET parameters was assessed. All lesions were confirmed by histology.

METHODS

FDG DPET studies were acquired in 22 patients with colorectal tumours prior to surgery. Five of these patients also had liver metastases at the time of the PET study. The SUV 56-60 min p.i. was included in the evaluation. A two-tissue compartment model was applied and the parameters k1-k4 as well as the fractional blood volume (VB) were obtained. The FDG influx was calculated from the compartment data. Non-compartment modelling was used to calculate the fractal dimension (FD) of the time-activity data.

RESULTS

FD, SUV, influx and k3 were the most important single parameters for lesion differentiation. The highest accuracy was achieved for FD (88.78%). The overall tracer uptake was mainly dependent on k3 and not on k1 or VB. The support vector machines (SVM) algorithm was used to predict the classification based on the combination of individual PET parameters. The overall accuracy was 97.3%, with only one false positive case and no false negative results. The analysis of the subgroup of five patients with primary tumours and synchronous metastases revealed no significant differences for the individual PET parameters. However, VB tended to be lower while k1 and k2 were higher in patients with synchronous metastases. The SVM classification analysis predicted the presence of metastases based on the PET data of the primary tumour in three of five patients.

CONCLUSION

Quantitative FDG PET studies provide very accurate data for the differentiation of primary colorectal tumours from normal tissue. The use of quantitative data has the advantage that the detection of a colorectal tumour is not primarily dependent on the individual assessment and experience of the physician evaluating the FDG PET data only visually. The results suggest that the presence of metastatic lesions may be predicted by analysis of the dynamic PET data of the corresponding primary tumour. Further studies are needed to assess this aspect in detail.

Correlation of GLUT-1 overexpression, tumor size, and depth of invasion with 18F-2-fluoro-2-deoxy-D-glucose uptake by positron emission tomography in colorectal cancer

We investigated the wide variability of 18F-2-fluoro-2-deoxy-D: -glucose (FDG) uptake, semiquantified as standardized uptake value (SUV), in positron emission tomography (PET) scanning, in 20 patients with colorectal cancer (CRC), including 1 with synchronous hepatic metastasis. The sensitivity of PET in CRC diagnosis was 100%, with a mean SUV of 8.0 (3.1-11.9). Tumor size and depth of invasion were associated with higher SUVs (P=.0004, .042, respectively). Strong glucose transporter-1 (GLUT-1) expression had significantly positive correlation with the SUV (r=.619, P=.003). GLUT-1 expression revealed positive staining in 17 (85%) of the 20 primary lesions. The central part of the tumor, thought to be relatively hypoxic, had stronger GLUT-1 expression and a higher SUV than the periphery, in both the primary tumor and hepatic metastatic foci. Our data suggest that the SUVs of FDG uptake in PET may be a noninvasive biomarker for advanced CRC, indicative of a large hypoxic tumor with deep invasion.

Molecular targeting of the lymphovascular system for imaging and therapy

Progress toward targeting cancer cells is a multi-disciplinary endeavor. In addition to the surgical and oncology specialties, radiologists collaborate with mathematicians, computer scientists, and physicists, in a constant effort to incrementally improve upon the current imaging modalities. Recently, radiologists have formed collaborations with molecular biologists and chemists in order to develop molecular agents that target cancer cells via receptor-substrate or specific physiochemical interactions. In this review, we summarize selected efforts toward molecular targeting of the lymphovascular system. Standard imaging modalities, positron emission tomography, single photon emission tomography, and ultrasound, are reviewed as well as, the targeted introduction of substances for endolymphatic therapy. We also review the current status of sentinel lymph node mapping with radiocolloids and the application of molecular targeting for the development of a radiopharmaceutical specifically designed for sentinel lymph node mapping.

Glucose uptake inhibitor sensitizes cancer cells to daunorubicin and overcomes drug resistance in hypoxia

PURPOSE

A high-rate glycolysis is a fundamental property of solid tumors and is associated with an over-expression of glucose transporters and glycolytic enzymes. We hypothesize that over-expression of glucose transporters in tumors prevents apoptosis, promotes cancer cell survival, and confers drug resistance. Inhibition of glucose transporter will preferentially sensitize the anticancer effects of chemotherapeutic drugs to overcome drug resistance in hypoxia.

METHODS

Glucose transporter expressions were detected in cancer tissues and NCI 60 cancer cells with immunostaining and DNA microarray. Glucose uptake was measured with 3H-2-deoxy-glucose. Cytotoxicity of daunorubicin (DNR) in combination of glucose inhibitor was detected by MTS assay under hypoxic condition. Early stage apoptosis was monitored with Annexin V-FITC staining.

RESULTS

Immunostaining showed that GLUT1 was significantly increased in hypoxic regions of the human colon and breast tumors. The expression profiles of all glucose transporters in NCI 60 cancer cells exhibited distinct expression patterns. Phloretin exhibited more than 60% glucose uptake inhibition. Hypoxia conferred two to fivefold higher drug resistance in SW620 and K562 to DNR. Inhibition of glucose uptake by phloretin sensitized cancer cells to DNR for its anticancer activity and apoptosis to overcome drug resistance only under hypoxia.

CONCLUSION

Cancer cells heavily rely on glucose transporters for glucose uptake to facilitate a high-rate glycolysis under hypoxia for their survival and drug resistance. Combination of glucose transporter inhibitors and chemotherapeutic drugs may provide a preferential novel therapeutic strategy to overcome drug resistance in hypoxia.

Hypoxia in relation to vasculature and proliferation in liver metastases in patients with colorectal cancer

PURPOSE

To investigate hypoxia measured by pimonidazole binding, glucose transporter 1 (GLUT1) and carbonic anhydrase IX (CA-IX) expression, proliferation, and vascularity in liver metastases of colorectal cancer and to compare GLUT1 and CA-IX expression in corresponding primary tumors.

METHODS AND MATERIALS

Twenty-five patients with liver metastases of colorectal cancer, planned for metastasectomy, were included. The hypoxia marker pimonidazole and proliferation marker iododeoxyuridine were administered before surgery. After immunofluorescent staining of the frozen metastases, pimonidazole binding, vascularity, and proliferation were analyzed quantitatively. Thirteen paraffin-embedded primary tumors were stained immunohistochemically for GLUT1 and CA-IX expression, which was analyzed semiquantitatively in primary tumors and corresponding liver metastases.

RESULTS

In liver metastases, pimonidazole binding showed a pattern consistent with diffusion-limited hypoxia. The mean pimonidazole-positive fraction was 0.146; the mean distance from vessels to pimonidazole-positive areas was 80 microm. When expressed, often co-localization was observed between pimonidazole binding and GLUT1 or CA-IX expression, but microregional areas of mismatch were also observed. No correlation between the level of pimonidazole binding and GLUT1 or CA-IX expression was observed. In some patients, a large fraction (up to 30%) of proliferating cells was present in pimonidazole-stained areas. Expression of CA-IX in primary tumors and metastases showed a significant correlation, which was absent for GLUT1 expression.

CONCLUSIONS

Compared with other tumor types, liver metastases of colorectal cancer contain large amounts of hypoxic cells. The lack of correlation with pimonidazole binding brings into question the value of GLUT1 and CA-IX as endogenous markers of hypoxia.

Factors influencing [F-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) uptake in melanoma cells: the role of proliferation rate, viability, glucose transporter expression and hexokinase activity

Using human (SK-MEL 23, SK-MEL 24 and G361) and murine (B16) melanoma cell lines, the coregulatory potential of the uptake of the positron emission tomography (PET) tracer, [Fluorine-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) has been investigated in relationship to tumor characteristics. Comparative studies among the four melanoma cell lines demonstrated that the lowest FDG uptake in SK-MEL 24 corresponded strongly to the data for DT (population doubling time) and MTT (tetrazolium salt) cell viability as well as hexokinase (HK) activity, but was not related to the glucose transporter 1 (GLUT 1) expression level. Furthermore, the FDG uptake in each melanoma cell line measured by cell cycle kinetics was significantly positively correlated to both the proliferation index (PI=S/G2M phase fractions) and the cell viability, though with one exception relating to the PI of the lowest FDG uptake cell line, SK-MEL 24. No positive correlation was found between the expression of GLUT 1 and FDG uptake in any individual cell line. However, the HK activities in SK-MEL 23 and 24 showed considerable positive relationships with FDG uptake. Our present study suggests that both the proliferation rate and the cell viability of melanoma cells may be key factors for FDG uptake and that HK activity, rather than GLUT 1 expression, seems to be a major factor.

Factors influencing [F-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) accumulation in melanoma cells: is FDG a substrate of multidrug resistance (MDR)?

In order to specify the influence of multidrug-resistance (MDR) on the accumulation of the PET tracer, F-18 FDG ([Fluorine-18] 2-fluoro-2-deoxy-D-glucose, in melanoma cells, both the MDR function and expression of two human melanoma cell lines SK-MEL 23 and 24, were evaluated. The effects of MDR modulators on FDG accumulation and efflux were also investigated. A functional analysis using representative MDR fluorescent substrates and inhibitors clarified the following characteristics: 1) SK-MEL 23 possesses a highly active function of MRP, but not P-gp. 2) SK-MEL 24 possesses weak functions of both MRP and P-gp. Western blot analysis using monoclonal antibodies for MDR expression demonstrated an exceedingly high MRP expression of SK-MEL 23 and only slight P-gp and MRP expression of SK-MEL 24, corresponding to the functional data. The efflux inhibition assay using F-18 FDG revealed a considerable retention of FDG in SK-MEL 23 in the presence of the MRP inhibitor probenecid. It was also found that the P-gp inhibitor verapamil depressed the FDG efflux of SK-MEL 24. Our present in vitro study suggests that FDG may be a substrate of MDR in some melanoma cells and further MDR may be one of the important factors affecting FDG-PET melanoma imaging.

Dependence of FDG uptake on tumor microenvironment

PURPOSE

To investigate the factors affecting the (18)F-fluorodeoxyglucose ((18)F-FDG) uptake in tumors at a microscopic level, by correlating it with tumor hypoxia, cellular proliferation, and blood perfusion.

METHODS AND MATERIALS

Nude mice bearing Dunning prostate tumors (R3327-AT) were injected with (18)F-FDG and pimonidazole, bromodeoxyuridine, and, 1 min before sacrifice, with Hoechst 33342. Selected tumor sections were imaged by phosphor plate autoradiography, while adjacent sections were used to obtain the images of the spatial distribution of Hoechst 33342, pimonidazole, and bromodeoxyuridine. The images were co-registered and analyzed on a pixel-by-pixel basis.

RESULTS

Statistical analysis of the data obtained from these tumors demonstrated that (18)F-FDG uptake was positively correlated with pimonidazole staining intensity in each data set studied. Correlation of FDG uptake with bromodeoxyuridine staining intensity was always negative. In addition, FDG uptake was always negatively correlated with the staining intensity of Hoechst 33342.

CONCLUSIONS

For the Dunning prostate tumors studied, FDG uptake was always positively correlated with hypoxia and negatively correlated with both cellular proliferation and blood flow. Therefore, for the tumor model studied, higher FDG uptake is indicative of tumor hypoxia, but neither blood flow nor cellular proliferation.

Molecular and cellular regulation of glucose transporter (GLUT) proteins in cancer

Malignant cells are known to have accelerated metabolism, high glucose requirements, and increased glucose uptake. Transport of glucose across the plasma membrane of mammalian cells is the first rate-limiting step for glucose metabolism and is mediated by facilitative glucose transporter (GLUT) proteins. Increased glucose transport in malignant cells has been associated with increased and deregulated expression of glucose transporter proteins, with overexpression of GLUT1 and/or GLUT3 a characteristic feature. Oncogenic transformation of cultured mammalian cells causes a rapid increase of glucose transport and GLUT1 expression via interaction with GLUT1 promoter enhancer elements. In human studies, high levels of GLUT1 expression in tumors have been associated with poor survival. Studies indicate that glucose transport in breast cancer is not fully explained by GLUT1 or GLUT3 expression, suggesting involvement of another glucose transporter. Recently, a novel glucose transporter protein, GLUT12, has been found in breast and prostate cancers. In human breast and prostate tumors and cultured cells, GLUT12 is located intracellularly and at the cell surface. Trafficking of GLUT12 to the plasma membrane could therefore contribute to glucose uptake. Several factors have been implicated in the regulation of glucose transporter expression in breast cancer. Hypoxia can increase GLUT1 levels and glucose uptake. Estradiol and epidermal growth factor, both of which can play a role in breast cancer cell growth, increase glucose consumption. Estradiol and epidermal growth factor also increase GLUT12 protein levels in cultured breast cancer cells. Targeting GLUT12 could provide novel methods for detection and treatment of breast and prostate cancer.

Why do cancers have high aerobic glycolysis?

If carcinogenesis occurs by somatic evolution, then common components of the cancer phenotype result from active selection and must, therefore, confer a significant growth advantage. A near-universal property of primary and metastatic cancers is upregulation of glycolysis, resulting in increased glucose consumption, which can be observed with clinical tumour imaging. We propose that persistent metabolism of glucose to lactate even in aerobic conditions is an adaptation to intermittent hypoxia in pre-malignant lesions. However, upregulation of glycolysis leads to microenvironmental acidosis requiring evolution to phenotypes resistant to acid-induced cell toxicity. Subsequent cell populations with upregulated glycolysis and acid resistance have a powerful growth advantage, which promotes unconstrained proliferation and invasion.

Single group study to evaluate the feasibility and complications of radiofrequency ablation and usefulness of post treatment position emission tomography in lung tumours

BACKGROUND

There is genuine need to develop interventional treatment options for management of lung tumors. Radiofrequency ablation (RFA) is one such alternative being promoted to treat lung tumors recently. Larger studies should help define RFA's further development. Furthermore fluorodeoxyglucose positron emission tomography (PET) has been reported to be an accurate indicator of treatment response in variety of tumors. This study focuses on the evaluating the feasibility of RFA and usefulness of PET scan in lung tumors after RFA procedure.

PATIENTS AND METHODS

Between November 1999 and May 2002, 50 patients with primary or metastasis pulmonary tumors underwent RFA procedure. The electrode was guided to the target areas using computerized tomography (CT). Tumors smaller than 3.5 cm were given single RFA, while tumors larger than 3.5 cm received RFA to multiple sites. Maximum 4 lesions or 6 target areas were treated during one operating procedure. Whole body and/or lung PET images were acquired; identical site CT images and chest X-ray were taken 1 week before and after RFA.

RESULTS

Of the 50 patients, 17 had single lesions while rest had multiple lesions. Tumors smaller than 3.5 cm were completely dissipated after RFA. In tumors larger than 3.5 cm, the part within 3.5 cm diameter dissipated. While CT showed that tumor image became larger 1 to 2 weeks after RFA procedure. PET demonstrated tumor destruction in 70% cases, compared to 38% in CT.

CONCLUSION

The present study shows RFA to be safe and effective treatment option for lung tumors. PET is superior to CT in evaluation the effectiveness of RFA treatment shortly after the procedure.

Analysis of gene expression profiles of hepatocellular carcinomas with regard to 18F-fluorodeoxyglucose uptake pattern on positron emission tomography

PURPOSE

18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET) scan has been found to reflect tumour aggressiveness and prognosis in various types of cancer. In this study, the gene expression profiles of hepatocellular carcinomas (HCCs) were evaluated to determine whether HCCs with high 18F-FDG uptake have more aggressive biological potential than those with low uptake.

METHODS

Surgical specimens were obtained from ten patients with HCC (six males and four females, age range 38-68 years). The tumour samples were divided into two groups based on the 18F-FDG PET scan findings: high 18F-FDG uptake (n=4) and low 18F-FDG uptake (n=6).

RESULTS

The pathological tumour grade was closely correlated with the 18F-FDG uptake pattern: HCCs with high 18F-FDG uptake were pathologically Edmondson-Steiner grade III, while those with low uptake were either grade II or grade II with a focal area of grade III. The total RNA was extracted from the frozen tissues of all HCCs (n=10) and adjacent non-cancerous tissue (n=7). The gene expression profiles were evaluated using an oligoDNA microarray. The HCCs with high 18F-FDG uptake showed increased expression of 11 genes--including vascular cell adhesion molecule-1, vinexin beta and core 1 UDP-galactose:N-acetylgalactosamine-alpha-R-beta 1,3-galactosyltransferase and the natural killer cell inhibitory receptor--compared to those with low uptake (p<0.005). Nine genes, including regulator of mitotic spindle assembly 1, grb2-related adaptor protein and beta-1,3-n-acetylglucosaminyltransferase, were repressed.

CONCLUSION

Gene expression is closely related to cell survival, cell-to-cell adhesion or cell spreading; therefore, HCCs with high 18F-FDG uptake appear to have more aggressive biological properties than those with low uptake.

Surgical management of hepatic malignancy

Over the past twenty-five years, hepatic resection has evolved from a high risk, resource-intensive procedure with limited application to a safe and commonly performed operation with broad indications. This period has seen dramatic improvements in perioperative outcome, including reductions in mortality, blood loss, transfusion rates, and hospital stay. These improved perioperative results are largely responsible for the emergence of hepatic resection as a viable and effective treatment option for selected patients with 1 degree and 2 degrees hepatobiliary malignancy. Continued advances in imaging technology, along with a heightened awareness of the clinical and tumor-related variables that dictate outcome, have allowed better preoperative assessment of disease extent and improved patient selection. Advances in other areas, such as minimally invasive and ablative techniques, have increased the treatment options and have had some impact on the approach to patients with malignant hepatobiliary disease; however, resection remains the most effective therapy. Although the long term results after resection are better than with other modalities, recurrence rates remain high, and further improvements in survival will require more effective systemic agents. As better adjuvant and neo-adjuvant therapies emerge, the results of resection are likely to improve and the indications for its application perhaps will extend to patients currently considered to have unresectable disease.

Molecular targeting of angiogenesis

The majority of pharmacological approaches for the treatment of solid tumors suffer from poor selectivity, thus limiting dose escalation (i.e., the doses of drug which are required to kill tumor cells cause unacceptable toxicities to normal tissues). The situation is made more dramatic by the fact that the majority of anticancer drugs accumulate preferentially in normal tissues rather than in neoplastic sites, due to the irregular vasculature and to the high interstitial pressure of solid tumors. One avenue towards the development of more efficacious and better tolerated anti-cancer drugs relies on the targeted delivery of therapeutic agents to the tumor environment, thus sparing normal tissues. Molecular markers which are selectively expressed in the stroma and in neo-vascular sites of aggressive solid tumors appear to be particularly suited for ligand-based tumor targeting strategies. Tumor blood vessels are accessible to agents coming from the bloodstream, and their occlusion may result in an avalanche of tumor cell death. Furthermore, endothelial cells and stromal cells are genetically more stable than tumor cells and can produce abundant markers, which are ideally suited for tumor targeting strategies. This review focuses on recent advances in the development of ligands for the selective targeting of tumor blood vessels and new blood vessels in other angiogenesis-related diseases.

Cancer metabolism: facts, fantasy, and fiction

The concept of a glycolytic cancer cell was introduced by Warburg over 70 years ago. This perception has since become the rationale that drives a considerable proportion of basic research on cancer, and it influences the current strategies for the diagnosis, monitoring, and treatment of cancer. Here we review the data from the last 40 years on this issue. We conclude that there is no evidence that cancer cells are inherently glycolytic, but that some tumours might indeed be glycolytic in vivo as a result of their hypoxic environment.

Bioluminescence Detection of Cells Having Stabilized p53 in Response to a Genotoxic Event

Inactivation of p53 is one of the most frequent molecular events in neoplastic transformation. Approximately 60% of all human tumors have mutations in both p53 alleles. Wild-type p53 activity is regulated in large part by the proteosome-dependent degradation of p53, resulting in a short p53 half-life in unstressed and untransformed cells. Activation of p53 by a variety of stimuli, including DNA damage induced by genotoxic drugs or radiation, is accomplished by stabilization of wild-type p53. The stabilized and active p53 can result in either cell-cycle arrest or apoptosis. Surprisingly, the majority of tumor-associated, inactivating p53 mutations also result in p53 accumulation. Thus, constitutive elevation of p53 levels in cells is a reliable measure of p53 inactivation, whereas transiently increased p53 levels reflect a recent genotoxic stress. In order to facilitate noninvasive imaging of p53 accumulation, we here describe the construction of a p53-luciferase fusion protein. Induction of DNA damage in cells expressing the fusion protein resulted in a time-dependent accumulation of the fusion that was noninvasively detected using bioluminescence imaging and validated by Western blot analysis. The p53-Luc protein retains p53 function because its expression in HCT116 cells lacking functional p53 resulted in activation of p21 expression as well as induction of apoptosis in response to a DNA damaging event. Employed in a transgenic animal model, the proposed p53-reporter fusion protein will be useful for studying p53 activation in response to exposure to DNA-damaging carcinogenic agents. It could also be used to study p53 stabilization as a result of inactivating p53 mutations. Such studies will further our understanding of p53's role as the "guardian of the genome" and its function in tumorigenesis.

A Novel Polyacrylamide Magnetic Nanoparticle Contrast Agent for Molecular Imaging using MRI

A novel polyacrylamide superparamagnetic iron oxide nanoparticle platform is described which has been synthetically prepared such that multiple crystals of iron oxide are encapsulated within a single polyacrylamide matrix (PolyAcrylamide Magnetic [PAM] nanoparticles). This formulation provides for an extremely large T2 and T2* relaxivity of between 620 and 1140 sec(-1) mM(-1). Administration of PAM nanoparticles into rats bearing orthotopic 9L gliomas allowed quantitative pharmacokinetic analysis of the uptake of nanoparticles in the vasculature, brain, and glioma. Addition of polyethylene glycol of varying sizes (0.6, 2, and 10 kDa) to the surface of the PAM nanoparticles resulted in an increase in plasma half-life and affected tumor uptake and retention of the nanoparticles as quantified by changes in tissue contrast using MRI. The flexible formulation of these nanoparticles suggests that future modifications could be accomplished allowing for their use as a targeted molecular imaging contrast agent and/or therapeutic platform for multiple indications.

Evaluation of (E)-2'-deoxy-2'-(fluoromethylene)cytidine on the 9L rat brain tumor model using MRI

(E)-2'-deoxy-2'-(fluoromethylene)cytidine (FMdC), was evaluated as a potential treatment for malignant gliomas using the rat 9L brain tumor model. FMdC was shown to be an effective inhibitor of cell proliferation in cultured 9L cells with an EC(50) of 40 ng/ml. In vitro studies also revealed that this compound significantly inhibited incorporation of [(3)H]thymidine in 9L cells. In vivo therapeutic efficacy of FMdC was evaluated in rats harboring intracerebral 9L tumors which were treated daily with 15 mg/kg, i.p. Treatment response was quantified from changes in tumor growth rates as assessed from sequential magnetic resonance imaging (MRI) tumor volume measurements. In vivo tumor cell kill in individual animals was calculated by fitting tumor volume data with an iterative computer routine. It was estimated that therapeutically responsive rats treated with FMdC daily produced a >/= 0.1 log kill per therapeutic dose which resulted in a significant reduction in tumor growth rate. In addition, localized (1)H-MRS of intracerebral 9L tumors revealed changes in metabolite levels which correlated with therapeutic response. These results provide evidence supporting the use of FMdC in clinical trials for the treatment of malignant gliomas and reveals that MR can play an important role in the pre-clinical evaluation of novel compounds using orthotopic tumor models.

Noninvasive real-time imaging of apoptosis

Strict coordination of proliferation and programmed cell death (apoptosis) is essential for normal physiology. An imbalance in these two opposing processes results in various diseases including AIDS, neurodegenerative disorders, myelodysplastic syndromes, ischemiareperfusion injury, cancer, autoimmune disease, among others. Objective and quantitative noninvasive imaging of apoptosis would be a significant advance for rapid and dynamic screening as well as validation of experimental therapeutic agents. Here, we report the development of a recombinant luciferase reporter molecule that when expressed in mammalian cells has attenuated levels of reporter activity. In cells undergoing apoptosis, a caspase-3-specific cleavage of the recombinant product occurs, resulting in the restoration of luciferase activity that can be detected in living animals with bioluminescence imaging. The ability to image apoptosis noninvasively and dynamically over time provides an opportunity for high-throughput screening of proapoptotic and antiapoptotic compounds and for target validation in vivo in both cell lines and transgenic animals.

Enhancement of the relative uptake of 18F-FDG in mouse fibrosarcoma by rolipram

The effect of rolipram, a selective phosphodiesterase type 4 inhibitor, on the uptake of 18F-fluorodeoxyglucose (18F-FDG) in tumor tissue was examined in mice transplanted with NFSa fibrosarcoma. The uptake indexes of 18F-FDG in the heart, skeletal muscle and brain remarkably decreased after treatment with 3 mg/kg of rolipram (heart: 13%, skeletal muscle: 14%, brain: 31%), but fibrosarcoma tissue showed only a 50% reduction in the uptake index of 18F-FDG. The tumor/muscle ratio of radioactivity 30 min after 18F-FDG injection was consequently enhanced from 1.9 to 6.5 by rolipram. This indicates the possible use of rolipram to enhance the sensitivity of tumor detection, as well as characterization of tumors in 18F-FDG PET.

Magnetic resonance imaging in cancer research

Non-invasive assessment of antineoplastic response and correlation of the location, magnitude and duration of transgene expression in vivo would be particularly useful for evaluating cancer gene therapy protocols. This review presents selected examples of how magnetic resonance (MR) has been used to assess therapeutic efficacy by non-invasive quantitation of cell kill, to detect a therapeutic response prior to a change in tumour volume and to detect spatial heterogeneity of the tumour response and quantitate transgene expression. In addition, applications of the use of bioluminescence imaging (BLI) for the evaluation of treatment efficacy and in vivo transgene expression are also presented. These examples provide an overview of areas in which imaging of animal tumour models can contribute towards improving the evaluation of experimental therapeutic agents.

It's not just about anatomy: in vivo bioluminescence imaging as an eyepiece into biology

Among the newly described tools that enable analyses of cellular and molecular events in living animals, in vivo bioluminescence imaging (BLI) offers important opportunities for investigating a wide variety of disease processes. BLI utilizes luciferase as an internal biological light source that can be genetically programmed to noninvasively "report" the presence or activation of specific biological events. Applications of BLI have included the use of luciferase to demonstrate expression of cell- and tissue-specific promoters, label cell populations, guide detection by other imaging modalities, and detect protein-protein interaction. These applications of BLI technology have allowed quantitative measurements of tumor burden and treatment response, immune cell trafficking, and detection of gene transfer. Spatiotemporal information can be rapidly obtained in the context of whole biological systems in vivo, which can accelerate the development of experimental therapeutic strategies. This paper provides a review of the biological applications in which in vivo BLI has been utilized to nondestructively monitor biological processes in intact small animal models, and highlights some of the advancements that will increase the versatility of BLI as a molecular imaging tool.