Quantitative changes of metabolic and bioenergetic parameters in experimental tumors during fractionated irradiation

Bioluminescence Imaging Applications in Cancer: A Comprehensive Review

Bioluminescence imaging (BLI), an optical preclinical imaging modality, is an invaluable imaging modality due to its low-cost, high throughput, fast acquisition times, and functional imaging capabilities. BLI is being extensively used in the field of cancer imaging, especially with the recent developments in genetic-engineering, stem cell, and gene therapy treatments. The purpose of this paper is to provide a comprehensive review of the principles, developments, and current status of BLI in cancer research. This paper covers the fundamental BLI concepts including BLI reporters and enzyme-substrate systems, data acquisition, and image characteristics. It reviews the studies discussing the use of BLI in cancer research such as imaging tumor-characteristic phenomena including tumorigenesis, metastasis, cancer metabolism, apoptosis, hypoxia, and angiogenesis, and response to cancer therapy treatments including chemotherapy, radiotherapy, immunotherapy, gene therapy, and stem cell therapy. The key advantages and disadvantages of BLI compared to other common imaging modalities are also discussed.

Glycolysis-related gene induction and ATP reduction during fractionated irradiation. Markers for radiation responsiveness of human tumor xenografts

BACKGROUND AND PURPOSE

Lactate was previously shown to be a prognostic but not a predictive pre-therapeutic marker for radiation response of tumor xenografts. We hypothesize that metabolic changes during fractionated irradiation may restrict the predictiveness of lactate regarding tumor radiosensitivity.

MATERIALS AND METHODS

Tumor xenografts were generated in nude mice by implanting 4 head and neck squamous cell carcinoma lines with different sensitivities to fractionated irradiation. Tumors were irradiated with up to 15 fractions of 2 Gy over a period of 3 weeks, and ATP and lactate levels were measured in vital tumor areas with induced metabolic bioluminescence imaging. Corresponding changes in mRNA expression of glycolysis-related genes were determined by quantitative RT-PCR.

RESULTS

Lactate content decreased significantly in 3 out of 4 cell lines in the course of irradiation showing no correlation with cell line-specific radiosensitivity. Radiation-induced changes in ATP levels and glycolysis-related mRNA expression, however, only occurred in radiosensitive or intermediately radioresistant xenografts, whereas these parameters remained unchanged in radioresistant tumors.

CONCLUSION

Sensitivity-related differences in the transcriptional response of tumors to radiotherapy may be exploited in the clinic for better individualization of tumor treatment.

Radiation-induced changes in microcirculation and interstitial fluid pressure affecting the delivery of macromolecules and nanotherapeutics to tumors

The immature, chaotic microvasculature of most solid tumors can present a significant impediment to blood-borne delivery, uneven distribution, and compromised penetration of macromolecular anticancer drugs and diagnostic agents from tumor microvessels across the interstitial space to cancer cells. To reach viable tumor cells in relevant concentrations, macromolecular agents are confronted with several barriers to vascular, transvascular, and interstitial transport. Amongst those (1) heterogeneous and poor blood supply, (2) distinctly reduced or even abolished hydrostatic and oncotic pressure gradients across the microvessel wall abrogating the convective transport from the vessel lumen into the interstitial space (impairment of transvascular transport), and (3) impediment of convective transport within the interstitial compartment due to elevated interstitial fluid pressure (IFP) (resulting from hyperpermeable blood vessels coupled with non-functional lymphatics) and a dense structure of the interstitial matrix are the major mechanisms hindering drug delivery. Upon irradiation, changes in these barrier functions are inconclusive so far. Alterations in vascular transport properties following fractionated radiation up to 40 Gy are quite inconsistent in terms of direction, extent, and time course. Total doses above 45 Gy can damage tumor microvessels, additionally impeding vascular delivery. Vascular permeability for macromolecules might be enhanced up to a total dose of 45 Gy. However, this effect is counteracted/abolished by the elevated IFP in solid tumors. When assessing IFP during fractionated radiotherapy in patient tumors, inconsistent alterations have been observed, both in direction and extent. From these data it is concluded that modulations in vascular, transvascular, and interstitial transport by irradiation of solid tumors are rather unclear so far. Translation of experimental data into the clinical setting thus needs to be undertaken with especial care.

Changes in the fraction of total hypoxia and hypoxia subtypes in human squamous cell carcinomas upon fractionated irradiation: evaluation using pattern recognition in microcirculatory supply units

BACKGROUND AND PURPOSE

Evaluate changes in total hypoxia and hypoxia subtypes in vital tumor tissue of human head and neck squamous cell carcinomas (hHNSCC) upon fractionated irradiation.

MATERIALS AND METHODS

Xenograft tumors were generated from 5 hHNSCC cell lines (UT-SCC-15, FaDu, SAS, UT-SCC-5 and UT-SCC-14). Hypoxia subtypes were quantified in cryosections based on (immuno-)fluorescent marker distribution patterns of Hoechst 33342 (perfusion), pimonidazole (hypoxia) and CD31 (endothelium) in microcirculatory supply units (MCSUs). Tumors were irradiated with 5 or 10 fractions of 2 Gy, 5×/week.

RESULTS

Upon irradiation with 10 fractions, the overall fraction of hypoxic MCSUs decreased in UT-SCC-15, FaDu and SAS, remained the same in UT-SCC-5 and increased in UT-SCC-14. Decreases were observed in the proportion of chronically hypoxic MCSUs in UT-SCC-15, in the fraction of acutely hypoxic MCSUs in UT-SCC-15 and SAS, and in the percentage of hypoxemically hypoxic MCSUs in SAS tumors. After irradiation with 5 fractions, there were no significant changes in hypoxia subtypes. Changes in the overall fraction of hypoxic MCSUs were comparable to corresponding alterations in the proportions of acutely hypoxic MCSUs. There was no correlation between radiation resistance (TCD(50)) and any of the investigated hypoxic fractions upon fractionated irradiation.

CONCLUSIONS

This study shows that there are large alterations in the fractions of hypoxia subtypes upon irradiation that can differ from changes in the overall fraction of hypoxic MCSUs.

Hypoxia and Ionizing Radiation: Changes in Adhesive Properties and Cell Adhesion Molecule Expression in MG-63 Three-Dimensional Tumor Spheroids

The effects of chemically induced hypoxia and ionizing radiation on the adhesive properties of MG-63 human osteosarcoma three-dimensional spheroids were investigated. Hypoxia was induced by addition of CoCl2 to small, nonhypoxic spheroids and verified by HIF-1alpha expression. In addition, the possible role of important cell adhesion molecules involved in tumor dissemination in inducing adhesive changes were also studied. In particular, two key integrins (i.e., the alpha chain of the fibronectin receptor, alpha5, and the alpha chain of the collagen receptor, alpha2), an important member of the immunoglobulin superfamily (CD54 or ICAM-1) and the strategic molecule CD44 (H-CAM, the principal receptor for hyaluronan) were examined. Because of the important role of fibronectin in adhesive processes, variations in this extracellular matrix component were also examined. The results seem to indicate that CoCl2-induced hypoxia greatly increases adhesion of MG-63 spheroids to both tissue culture plates and plates coated with fibronectin or collagen when compared to controls, while ionizing radiation induces a great decrease in this attachment. Furthermore, chemically induced hypoxia also partially inhibits the effects of ionizing radiation. The data also show that these adhesive changes are accompanied by concomitant variations in the expression of alpha5 and alpha2 integrins, CD44, and CD54 and fibronectin.

Temporal Dynamics of1H-NMR-Visible Metabolites during Radiation-Induced Apoptosis in MG-63 Human Osteosarcoma Spheroids

The metabolic changes that occur as a function of time in MG-63 osteosarcoma three-dimensional tumor spheroids undergoing radiation-induced apoptosis were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of MG-63 spheroids collected at 24, 48 and 72 h after exposure to 5 Gy of ionizing radiation were compared to the spectra of their respective controls. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. Apoptosis was verified by both staining of spheroid DNA with the Hoechst 33258 dye and determination of caspase 3 enzyme activity at the three times examined. The results demonstrate that, as the percentage of apoptosis rises with time after exposure to ionizing radiation, the metabolic changes that take place in MG-63 spheroids follow very precise temporal dynamics. In particular, significant time-related increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis, were observed. In addition, temporal variations were also observed in choline-containing metabolites, reduced glutathione (GSH), glutamine/glutamate, taurine, alanine, creatine/phosphocreatine and lactate. These data show that in addition to CH(2) and CH(3) lipids, other metabolites can also be extremely useful in a deeper understanding of the temporal dynamics of radiation-induced apoptosis. This comprehension is particularly important in spheroids, a cell model of great complexity that resembles in vivo tumors much more closely than monolayer cultures. Ultimately, it is hoped that such studies can help to evaluate the outcome of radiotherapy protocols more accurately.

Increases in 1H-NMR mobile lipids are not always associated with overt apoptosis: evidence from MG-63 human osteosarcoma three-dimensional spheroids exposed to a low dose (2 Gy) of ionizing radiation

The metabolic changes that occur in MG-63 osteosarcoma three-dimensional tumor spheroids exposed to 2 Gy of ionizing radiation, a dose that is comparable to radiation therapy, were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of control and exposed MG-63 spheroids were compared. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. The spectra of whole MG-63 spheroids as well as the perchloric acid extracts of these systems were evaluated. Cell damage was also examined by lactate dehydrogenase release and changes in cell growth. No cell damage was observed, but numerous metabolic changes took place in spheroids after exposure to ionizing radiation. In particular, significant increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis and also present in MG-63 spheroids undergoing overt apoptosis, were observed in spheroids irradiated with 2 Gy. However, the chromatin dye Hoechst 33258 and DNA fragmentation assays showed no overt apoptosis up to 7 days after irradiation with this low dose. Thus it is evident that increases in mobile lipids do not always indicate actual cell death. A detailed analysis of the other metabolic changes observed appears to suggest that the cell death program was initiated but not completed. In fact, the completely different behavior of two important cellular defense mechanisms, reduced glutathione and taurine, in spheroids irradiated with 2 Gy and in those undergoing overt apoptosis seems to indicate that these systems are protecting spheroids from actual cell death. In addition, these data also suggest that (1)H-NMR can be used to examine the effects of low doses of ionizing radiation in spheroids, a cell model of great complexity that closely resembles tumors in vivo. The importance of this possibility in relation to reaching the ultimate goal of a better evaluation of the outcome of radiotherapy protocols should not be ignored.

Dose-response relationship between probability of pathologic tumor control and glucose metabolic rate measured with FDG PET after preoperative chemoradiotherapy in locally advanced non-small-cell lung cancer

PURPOSE

To determine the dose-response relationship between the probability of tumor control on the basis of pathologic tumor response (pTCP) and the residual metabolic rate of glucose (MRglc) in response to preoperative chemoradiotherapy in locally advanced non-small-cell lung cancer and to define the level of residual MRglc that corresponds to pTCP 50% and pTCP > or = 95%.

METHODS AND MATERIALS

Quantitative dynamic 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography was performed to measure regional MRglc at the primary lesion before and 2 weeks after preoperative chemoradiotherapy in an initial group of 13 patients with locally advanced NSCLC. A simplified kinetic method was developed subsequently from the initial dynamic study and used in the subsequent 16 patients. The preoperative radiotherapy programs consisted of (1) a split course of 42 Gy in 28 fractions within a period of 28 days using a twice-daily treatment schedule for Stage IIIA(N2) NSCLC (n = 18) and (2) standard once-daily radiation schedule of 45-63 Gy in 25-35 fractions during a 5-7-week period (n = 11). The preoperative chemotherapy regimens included two cycles of cisplatin, vinblastine, and 5-fluorouracil (n = 24), cisplatin and etoposide (n = 2), and cisplatin, Taxol, and 5-fluorouracil (n = 3). Patients free of tumor progression after preoperative chemoradiotherapy underwent surgery. The degree of residual MRglc measured 2 weeks after preoperative chemoradiotherapy and 2 weeks before surgery was correlated with the pathologic tumor response. The relationship between MRglc and pTCP was modeled using logistic regression.

RESULTS

Of 32 patients entered into the study, 29 (16 men and 13 women; 30 lesions) were evaluated for the correlation between residual MRglc and pathologic tumor response. Three patients did not participate in the second study because of a steady decline in general condition. The median age was 60 years (range 42-78). One of the 29 patients had two separate lesions, and MRglc was measured in each separately. The tumor histologic types included squamous cell carcinoma (n = 9), adenocarcinoma (n = 13), large cell carcinoma (n = 6), and poorly differentiated carcinoma (n = 2). The extent of the primary and nodal disease was as follows: Stage IIB (T3N0M0), Pancoast tumor (n = 2); Stage IIIA, T2-T3N2M0 (n = 18); Stage IIIB: T1-T3N3M0 (n = 5) and T4N0M0 (n = 2); a second lesion, T1 (n = 1); and localized stump recurrence (n = 2). A pathologically complete response was obtained in 14 (47%) of the 30 lesions. The remaining 16 lesions had residual cancer. The mean baseline value of the maximal MRglc was 0.333 +/- 0.087 micromol/min/g (n = 16), and it was reduced to 0.0957 +/- 0.059 micromol/min/g 2 weeks after chemoradiotherapy (p = 0.011). The correlation between residual MRglc and pTCP was made using an increment value of 0.02 micromol/min/g between the maximal and minimal values of MRglc. A pathologically complete response was obtained in 6 of 6 patients with residual MRglc of < or = 0.050 micromol/min/g, 3 of 4 with < or = 0.070, 4 of 7 with < or = 0.090, 0 of 4 with < or = 0.110, 1 of 3 with < or = 0.130, and 0 of 6 with > or = 0.130 micromol/min/g. The fitted logistic model showed that residual MRglc corresponding to pTCP 50% and pTCP > or = 95% was 0.076 and < or = 0.040 micromol/min/g, respectively.

CONCLUSION

The correlation between the gradient of residual MRglc after chemoradiotherapy and pTCP is an inverse dose-response relationship. Residual MRglc of 0.076 and < or = 0.040 micromol/min/g, representing pTCP 50% and pTCP > or = 95%, respectively, may be useful surrogate markers for the tumor response to radiotherapy or chemoradiotherapy in lung cancer.

Effects of hyperbaric oxygen and normobaric carbogen on the radiation response of the rat rhabdomyosarcoma R1H

PURPOSE

Hypoxic tumor cells are an important factor of radioresistance. Hyperbaric oxygen (HBO) and normobaric carbogen (95% oxygen, 5% carbon dioxide) increase the oxygen delivery to tumors. This study was performed to explore changes of tumor oxygenation during a course of fractionated irradiation and to determine the effectiveness of normobaric carbogen and HBO during the final phase of the radiation treatment.

METHODS AND MATERIALS

Experiments were performed on the rhabdomyosarcoma R1H growing on WAG/Rij rats. After 20 X-ray fractions of 2 Gy within 4 weeks, oxygen partial pressure (pO2) was measured using the Eppendorf oxygen electrode under ambient conditions, with normobaric carbogen or HBO at a pressure of 240 kPa. Following the 4-week radiation course, a top-up dose of 10-50 Gy was applied in 2-10 fractions of 5 Gy with or without hyperoxygenation.

RESULTS

HBO but not carbogen significantly increased the median pO2 in irradiated tumors. The radiation doses to control 50% of tumors were 38.0 Gy, 29.5 Gy, and 25.0 Gy for air, carbogen, and HBO, respectively. Both high oxygen content gas inspirations led to significantly improved tumor responses with oxygen enhancement ratios (OERs) of 1.3 for normobaric carbogen and 1.5 for HBO (air vs. carbogen: p = 0.044; air vs. HBO: p = 0.02; carbogen vs. HBO: p = 0.048).

CONCLUSION

Both normobaric carbogen and HBO significantly improved the radiation response of R1H tumors. HBO appeared to be more effective than normobaric carbogen, both with regard to tumor oxygenation and response to irradiation.

Simultaneous administration of glucose and hyperoxic gas achieves greater improvement in tumor oxygenation than hyperoxic gas alone

PURPOSE

To test the feasibility of hyperglycemic reduction of oxygen consumption combined with oxygen breathing (O(2)), to improve tumor oxygenation.

METHODS AND MATERIALS

Fischer-344 rats bearing 1 cm R3230Ac flank tumors were anesthetized with Nembutal. Mean arterial pressure, heart rate, tumor blood flow ([TBF], laser Doppler flowmetry), pH, and pO(2) were measured before, during, and after glucose (1 or 4 g/kg) and/or O(2).

RESULTS

Mean arterial pressure and heart rate were unaffected by treatment. Glucose at 1 g/kg yielded maximum blood glucose of 400 mg/dL, no change in TBF, reduced tumor pH (0.17 unit), and 3 mm Hg pO(2) rise. Glucose at 4 g/kg yielded maximum blood glucose of 900 mg/dL, pH drop of 0.6 unit, no pO(2) change, and reduced TBF (31%). Oxygen tension increased by 5 mm Hg with O(2). Glucose (1 g/Kg) + O(2) yielded the largest change in pO(2) (27 mm Hg); this is highly significant relative to baseline or either treatment alone. The effect was positively correlated with baseline pO(2), but 6 of 7 experiments with baseline pO(2) < 10 mm Hg rose above 10 mm Hg after combined treatment.

CONCLUSION

We demonstrated the feasibility of combining hyperglycemia with O(2) to improve tumor oxygenation. However, some cell lines are not susceptible to the Crabtree effect, and the magnitude is dependent on baseline pO(2). Additional or alternative manipulations may be necessary to achieve more uniform improvement in pO(2).

A comparison of the potential therapeutic gain of p(66)/Be neutrons and d(14)/Be neutrons

PURPOSE

To determine the relationship between photon sensitivity and neutron sensitivity and between neutron RBE and photon resistance for two neutron modalities (with mean energies of 6 and 29 MeV) using human tumor cell lines spanning a wide range of radiosensitivities, the principal objective being whether or not a neutron advantage can be demonstrated.

METHODS AND MATERIALS

Eleven human tumor cell lines with mean photon inactivation doses of 1.65-4. 35 Gy were irradiated with 0-5.0 Gy of p(66)/Be neutrons (mean energy of 29 MeV) at Faure, S.A. and the same plating was irradiated on the same day with 0-10.0 Gy of Cobalt-gamma-rays. Twelve human tumor cell lines, many of which were identical with the above selection, and spanning mean photon inactivation doses of 1.75-4.08 Gy, were irradiated with 0-4 Gy of d(14)/Be neutrons (mean energy of 6 MeV) and with 0-10 Gy of 240 kVp X-rays at the Essen Klinikum. Cell survival was determined by the clonogenic assay, and data were fitted to the linear quadratic equation.

RESULTS

1. Using the mean inactivation dose, a significant correlation was found to exist between neutron sensitivity and photon sensitivity. However, this correlation was more pronounced in the Faure beam (r(2) = 0.89, p </= 0.0001) than in the Essen beam (r(2) = 0.65, p = 0.0027). 2. No significant relationship could be established between neutron RBE and photon resistance for both modalities (p = 0.69 and p = 0.07, respectively). 3. Using alpha-coefficients as a criterion, the neutron sensitivity for the Faure beam correlated with photon sensitivity (p = 0.001), but this did not apply to the Essen beam (p = 0.27). 4. The neutron RBE for the Essen beam derived from alpha-coefficients showed a steep increase with photon resistance (p = 0.003). In the Faure beam there was no increase of RBE with photon resistance (p = 0.494).

CONCLUSION

Radiobiological differences between high-energy and low-energy neutrons are particularly apparent in the dependence of the neutron RBE on photon sensitivity. The increase of RBE with photon resistance is more pronounced in the low-energy Essen neutrons than in the high-energy Faure neutrons. An RBE advantage is indicated for photon-resistant cell lines and this is particularly apparent in the low-dose range using alpha-coefficients as compared to the mean inactivation dose. The clinical application of low-energy neutrons may be more restricted because of poor penetration and lack of skin sparing. However, these neutrons discriminate better between photon-sensitive and photon-resistant cells giving an RBE range of 2-6 and a mean RBE of 4.1, than high-energy neutrons where the RBE range is 1.6-3.5 and the mean RBE is 2.4. From the radiobiological point of view it, therefore, appears that the clinical potential of low-energy neutrons is considerably underrated.