MRI-guided dynamic risk assessment in cervical cancer based on tumor hypoxia at diagnosis and volume response at brachytherapy

BACKGROUND AND PURPOSE

Improvements in treatment outcome for patients with locally advanced cervical cancer (LACC) require a better classification of patients according to their risk of recurrence. We investigated whether an imaging-based approach, combining pretreatment hypoxia and tumor response during therapy, could improve risk classification.

MATERIAL AND METHODS

Ninety-three LACC patients with T2-weigthed (T2W)-, dynamic contrast enhanced (DCE)- and diffusion weighted (DW)-magnetic resonance (MR) images acquired before treatment, and T2W- and, for 64 patients, DW-MR images, acquired at brachytherapy, were collected. Pretreatment hypoxic fraction (HFpre) was determined from DCE- and DW-MR images using the consumption and supply-based hypoxia (CSH)-imaging method. Volume regression at brachytherapy was assessed from T2W-MR images and combined with HFpre. In 17 patients with adequate DW-MR images at brachytherapy, the apparent diffusion coefficient (ADC), reflecting tumor cell density, was calculated. Change in ADC during therapy was combined with volume regression yielding functional regression as explorative response measure. Endpoint was disease free survival (DFS).

RESULTS

HFpre was the strongest predictor of DFS, but a significant correlation with outcome was found also for volume regression. The combination of HFpre and volume regression showed a stronger association with DFS than HFpre alone. Patients with disease recurrence were selected to either the intermediate- or high-risk group with a 100 % accuracy. Functional regression showed a stronger correlation to HFpre than volume regression.

CONCLUSION

The combination of pretreatment hypoxia and volume regression at brachytherapy improved patient risk classification. Integration of ADC with volume regression showed promise as a new tumor response parameter.

Prostate cancer radiogenomics reveals proliferative gene expression programs associated with distinct MRI-based hypoxia levels

BACKGROUND AND PURPOSE

The biology behind individual hypoxia levels in patient tumors is poorly understood. Here, we used radiogenomics to identify associations between magnetic resonance imaging (MRI)-based hypoxia levels and biological processes derived from gene expression data in prostate cancer.

MATERIALS AND METHODS

For 85 prostate cancer patients, MRI-based hypoxia images were constructed by combining diffusion-weighted images reflecting oxygen consumption and supply. The ability to differentiate hypoxia levels in these images was verified by comparison with matched biopsy sections stained for the hypoxia marker pimonidazole. For MRI-defined hypoxia levels, corresponding hypoxic fractions were calculated and correlated with biopsy gene expression profiles. Biological processes were predicted by gene set enrichment analysis (GSEA) and validated by immunohistochemistry (Ki67 proliferation marker, reactive stroma grade) and RT-PCR (MYC).

RESULTS

Genes with correlation between expression level and hypoxic fraction were identified for 56 MRI-based hypoxia levels. At all levels, GSEA identified proliferation as the predominant biological process enriched among the correlating genes. Two independent proliferative gene signatures were developed. The Peak1 signature, upregulated at moderate/severe hypoxia, reflected MYC upregulation and high Ki67-proliferation index of cancer cells in pimonidazole-positive regions. The Peak2 signature, upregulated at mild to non-hypoxic levels, was associated with fibroblast gene signature and reactive stroma grade. High scores of both Peak1 and Peak2 indicated elevated risk of biochemical recurrence in multiple cohorts.

CONCLUSION

Radiogenomics identified two gene expression programs activated at different hypoxia levels, reflecting proliferation of cancer cells and stroma cells. Genes involved in these programs could be candidate targets for intervention.

MRI Assessment of Changes in Tumor Vascularization during Neoadjuvant Anti-Angiogenic Treatment in Locally Advanced Breast Cancer Patients

Anti-VEGF (vascular endothelial growth factor) treatment improves response rates, but not progression-free or overall survival in advanced breast cancer. It has been suggested that subgroups of patients may benefit from this treatment; however, the effects of adding anti-VEGF treatment to a standard chemotherapy regimen in breast cancer patients are not well studied. Understanding the effects of the anti-vascular treatment on tumor vasculature may provide a selection of patients that can benefit. The aim of this study was to study the vascular effect of bevacizumab using clinical dynamic contrast-enhanced MRI (DCE-MRI). A total of 70 women were randomized to receive either chemotherapy alone or chemotherapy with bevacizumab for 25 weeks. DCE-MRI was performed at baseline and at 12 and 25 weeks, and in addition 25 of 70 patients agreed to participate in an early MRI after one week. Voxel-wise pharmacokinetic analysis was performed using semi-quantitative methods and the extended Tofts model. Vascular architecture was assessed by calculating the fractal dimension of the contrast-enhanced images. Changes during treatment were compared with baseline and between the treatment groups. There was no significant difference in tumor volume at any point; however, DCE-MRI parameters revealed differences in vascular function and vessel architecture. Adding bevacizumab to chemotherapy led to a pronounced reduction in vascular DCE-MRI parameters, indicating decreased vascularity. At 12 and 25 weeks, the difference between the treatment groups is severely reduced.

Exploring Hypoxia in Prostate Cancer With T2-weighted Magnetic Resonance Imaging Radiomics and Pimonidazole Scoring

BACKGROUND/AIM

Radiomics involves high throughput extraction of mineable precise quantitative imaging features that serve as non-invasive prognostic or predictive biomarkers. High levels of hypoxia are associated with a poorer prognosis in prostate cancer and limit radiation therapy efficacy. Most patients with prostate cancer undergo magnetic resonance imaging (MRI) as a part of their diagnostics, and T2 imaging is the most utilised imaging method. The aim of this study was to determine whether hypoxia in prostate tumors could be identified using a radiomics model extracted from T2-weighted MR images.

MATERIALS AND METHODS

Eighty eight intermediate or high-risk prostate cancer patients were evaluated. Prior to radical prostatectomy, all patients received pimonidazole (PIMO). PIMO hypoxic scores were assigned in whole-mount sections from prostatectomy specimens by an experienced pathologist who was blinded to MRI. The region of interest used for radiomics analysis included the prostatic index tumor. Radiomics extraction yielded 165 features using a special evaluation version of RadiomiX [RadiomiX Research Toolbox version 20180831 (OncoRadiomics SA, Liège, Belgium)] for non-clinical use. Multivariable logistic regression with Elastic Net regularization was utilised using 10 times repeated 10-fold cross-validation to select the best model hyperparameters, optimizing for area under the receiver operating characteristic curve (AUC).

RESULTS

The average (out of sample) performance based on the repeated cross validation using the ONESE model yielded an AUC of 0.60±0.2. Shape-based features were the most prominent in the model.

CONCLUSION

The development of a radiomics hypoxia model using T2 weighted MR images, standard in the staging of prostate cancer, is possible.

Targeted Therapy on the Screen: Do We Hit the Target?

A phase II trial, investigating whether the antidiabetic drug metformin could reduce hypoxia in cervical cancer, used imaging to preselect patients and test the biological hypothesis behind the drug effect. This trial design would be of importance for the implementation of targeted treatment in the clinic. See related article by Han et al., p. 5263.

Incorporating cross-voxel exchange for the analysis of dynamic contrast-enhanced imaging data: pre-clinical results

Tumours exhibit abnormal interstitial structures and vasculature function often leading to impaired and heterogeneous drug delivery. The disproportionate spatial accumulation of a drug in the interstitium is determined by several microenvironmental properties (blood vessel distribution and permeability, gradients in the interstitial fluid pressure). Predictions of tumour perfusion are key determinants of drug delivery and responsiveness to therapy. Pharmacokinetic models allow for the quantification of tracer perfusion based on contrast enhancement measured with non-invasive imaging techniques. An advanced cross-voxel exchange model (CVXM) was recently developed to provide a comprehensive description of tracer extravasation as well as advection and diffusion based on cross-voxel tracer kinetics (Sinnoet al2021). Transport parameters were derived from DCE-MRI of twenty TS-415 human cervical carcinoma xenografts by using CVXM. Tracer velocity flows were measured at the tumour periphery (mean 1.78-5.82μm.s^-1) pushing the contrast outward towards normal tissue. These elevated velocity measures and extravasation rates explain the heterogeneous distribution of tracer across the tumour and its accumulation at the periphery. Significant values for diffusivity were deduced across the tumours (mean 152-499μm².s^-1). CVXM resulted in generally smaller values for the extravasation parameterKext(mean 0.01-0.04 min^-1) and extravascular extracellular volume fractionve(mean 0.05-0.17) compared to the standard Tofts parameters, suggesting that Toft model underestimates the effects of inter-voxel exchange. The ratio of Tofts' extravasation parameters over CVXM's was significantly positively correlated to the cross-voxel diffusivity (P< 0.0001) and velocity (P= 0.0005). Tofts' increasedvemeasurements were explained using Sinnoet al(2021)'s theoretical work. Finally, a scan time of 15 min renders informative estimations of the transport parameters. However, a duration as low as 7.5 min is acceptable to recognize the spatial variation of transport parameters. The results demonstrate the potential of utilizing CVXM for determining metrics characterizing the exchange of tracer between the vasculature and the tumour tissue. Like for many earlier models, additional work is strongly recommended, in terms of validation, to develop more confidence in the results, motivating future laboratory work in this regard.

Risk of recurrence after chemoradiotherapy identified by multimodal MRI and 18F-FDG-PET/CT in locally advanced cervical cancer

BACKGROUND AND PURPOSE

MRI, applying dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) sequences, and 18F-fluorodeoxyglucose (18F-FDG) PET/CT provide information about tumor aggressiveness that is unexploited in treatment of locally advanced cervical cancer (LACC). We investigated the potential of a multimodal combination of imaging parameters for classifying patients according to their risk of recurrence.

MATERIALS AND METHODS

Eighty-two LACC patients with diagnostic MRI and FDG-PET/CT, treated with chemoradiotherapy, were collected. Thirty-eight patients with MRI only were included for validation of MRI results. Endpoints were survival (disease-free, cancer-specific, overall) and tumor control (local, locoregional, distant). K^trans, reflecting vascular function, apparent diffusion coefficient (ADC), reflecting cellularity, and standardized uptake value (SUV), reflecting glucose uptake, were extracted from DCE-MR, DW-MR and FDG-PET images, respectively. By applying an oxygen consumption and supply-based method, ADC and K^trans parametric maps were voxel-wise combined into hypoxia images that were used to determine hypoxic fraction (HF).

RESULTS

HF showed a stronger association with outcome than the single modality parameters. This association was confirmed in the validation cohort. Low HF identified low-risk patients with 95% precision. Based on the 50th SUV-percentile (SUV₅₀), patients with high HF were divided into an intermediate- and high-risk group with high and low SUV₅₀, respectively. This defined a multimodality biomarker, HF/SUV₅₀. HF/SUV₅₀ increased the precision of detecting high-risk patients from 41% (HF alone) to 57% and showed prognostic significance in multivariable analysis for all endpoints.

CONCLUSION

Multimodal combination of MR- and FDG-PET/CT-images improves classification of LACC patients compared to single modality images and clinical factors.

miR-200a/b/-429 downregulation is a candidate biomarker of tumor radioresistance and independent of hypoxia in locally advanced cervical cancer

Many patients with locally advanced cervical cancer experience recurrence within the radiation field after chemoradiotherapy. Biomarkers of tumor radioresistance are required to identify patients in need of intensified treatment. Here, the biomarker potential of miR-200 family members was investigated in this disease. Also, involvement of tumor hypoxia in the radioresistance mechanism was determined, using a previously defined 6-gene hypoxia classifier. miR-200 expression was measured in pre-treatment tumor biopsies of an explorative cohort (n=90) and validation cohort 1 (n=110) by RNA sequencing. Publicly available miR-200 data of 79 patients were included for validation of prognostic significance. A score based on expression of the miR-200a/b/-429 (miR-200a, miR-200b and miR-429) cluster showed prognostic significance in all cohorts. The score was significant in multivariate analysis of central pelvic recurrence. No association with distant recurrence or hypoxia status was found. Potential miRNA target genes were identified from gene expression profiles and showed enrichment of genes in extracellular matrix organization and cell adhesion. miR-200a/b/-429 overexpression had a pronounced radiosensitizing effect in tumor xenografts, whereas the effect was minor in vitro. In conclusion, miR-200a/b/-429 downregulation is a candidate biomarker of central pelvic recurrence and seems to predict cell-adhesion-mediated tumor radioresistance independent of clinical markers and hypoxia.

MRI Distinguishes Tumor Hypoxia Levels of Different Prognostic and Biological Significance in Cervical Cancer

Tumor hypoxia levels range from mild to severe and have different biological and therapeutical consequences but are not easily assessable in patients. Here we present a method based on diagnostic dynamic contrast enhanced (DCE) MRI that reflects a continuous range of hypoxia levels in patients with tumors of cervical cancer. Hypoxia images were generated using an established approach based on pixel-wise combination of DCE-MRI parameters ν _e and K ^trans, representing oxygen consumption and supply, respectively. Using two tumor models, an algorithm to retrieve surrogate measures of hypoxia levels from the images was developed and validated by comparing the MRI-defined levels with hypoxia levels reflected in pimonidazole-stained histologic sections. An additional indicator of hypoxia levels in patient tumors was established on the basis of expression of nine hypoxia-responsive genes; a strong correlation was found between these indicator values and MRI-defined hypoxia levels in 63 patients. Chemoradiotherapy outcome of 74 patients was most strongly predicted by moderate hypoxia levels, whereas more severe or milder levels were less predictive. By combining gene expression profiles and MRI-defined hypoxia levels in cancer hallmark analysis, we identified a distribution of levels associated with each hallmark; oxidative phosphorylation and G₂-M checkpoint were associated with moderate hypoxia, epithelial-to-mesenchymal transition, and inflammatory responses with significantly more severe levels. At the mildest levels, IFN response hallmarks together with HIF1A protein expression by IHC appeared significant. Thus, our method visualizes the distribution of hypoxia levels within patient tumors and has potential to distinguish levels of different prognostic and biological significance. SIGNIFICANCE: These findings present an approach to image a continuous range of hypoxia levels in tumors and demonstrate the combination of imaging with molecular data to better understand the biology behind these different levels.

Abstract A03: Vascular function affected fundamentally different by different antiangiogenic agents

The purpose of this preclinical study was to investigate the effect of two antiangiogenic agents, properdistatin and sunitinib, on the morphology and function of tumor vasculature. Properdistatin is a novel peptide derived from the thrombospondin-1 domain of the plasma protein properdin. Properdistatin treatment has been shown to inhibit angiogenesis and tumor growth in breast cancer xenografts. Sunitinib is a tyrosine kinase inhibitor that interacts with several receptors including vascular endothelial growth factor receptors 1-3, and platelet-derived growth factor receptors α-β. Sunitinib treatment has been shown to inhibit angiogenesis and tumor growth in a number of tumor models, and has been approved clinically for several indications.

A-07 human melanoma xenografts grown in dorsal window chambers or as intradermal flank tumors were used as preclinical tumor model. In window chamber tumors, morphologic parameters of tumor vascular networks were assessed from high-resolution transillumination images, and blood supply time and plasma velocities were assessed from first-pass imaging movies recorded after a bolus of 155kDa tetramethylrhodamine isothiocyanate-labeled dextran had been administered intravenously. In flank tumors, parametric images of ADC and Ktrans were produced from diffusion weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced MRI (DCE-MRI). Tumor hypoxia and necrosis were assessed from immunohistochemical preparations of the imaged tissue, and tumor interstitial fluid pressure (IFP) was assessed with probe measurement.

Properdistatin treatment reduced the density of small-diameter vessels, reduced blood supply time, and increased plasma velocities, whereas sunitinib treatment did not alter blood supply time, reduced overall vessel density, induced tumor hypoxia and necrosis, and did not alter tumor IFP. Sunitinib-treated flank tumors showed reduced Ktrans values corresponding to a decrease in vessel density, and increased ADC values corresponding to induction of tumor necrosis.

In conclusion, properdistatin treatment improved vascular function, whereas sunitinib treatment did not improve vascular function but induced tumor hypoxia and necrosis in A-07 tumors. This data demonstrates that different antiangiogenic agents may affect vascular function fundamentally different in the same tumor model. DW-MRI and DCE-MRI were sensitive to the sunitinib-induced changes in the tumor microenvironment, demonstrating that these MR-techniques may be used to identify tumors where antiangiogenic treatment does not improve vascular function.

Citation Format: Jon-Vidar Gaustad, Trude G. Simonsen, Tord Hompland, Lise Mari K. Andersen, Einar K. Rofstad. Vascular function affected fundamentally different by different antiangiogenic agents. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr A03.

Short-term pretreatment DCE-MRI in prediction of outcome in locally advanced cervical cancer

BACKGROUND AND PURPOSE

Several investigators have indicated that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has the potential to provide biomarkers for personalized treatment of cervical carcinoma. However, some clinical studies have suggested that treatment failure is associated with low tumor signal enhancement, whereas others have reported associations between high signal enhancement and poor outcome. The purpose of this investigation was to clear up these conflicting reports and to provide a method for identifying biomarkers that easily can be implemented in routine DCE-MRI diagnostics.

METHODS

The study involved 85 patients (FIGO stage IB through IVA) treated with concurrent chemoradiotherapy. Low-enhancing tumor volume (LETV) and low-enhancing tumor fraction (LETF), defined as the volume and fractional volume of low-enhancing voxels, respectively, were calculated from signal intensities recorded within 1 min after contrast administration by using two methods reported to give conflicting conclusions.

RESULTS

Multivariate analysis involving tumor volume, lymph node status, FIGO stage, and LETV or LETF revealed that LETV and LETF provided independent prognostic information on treatment outcome, independent of the method of calculation.

CONCLUSION

Low signal enhancement is associated with poor prognosis in cervical carcinoma, and biomarkers predicting poor outcome can be provided by short-term DCE-MRI without advanced image analysis.

DW-MRI in assessment of the hypoxic fraction, interstitial fluid pressure, and metastatic propensity of melanoma xenografts

Background

Cancer patients with primary tumors showing extensive hypoxia and highly elevated interstitial fluid pressure (IFP) have poor prognosis. The potential of diffusion-weighted magnetic resonance imaging (DW-MRI) in assessing the hypoxic fraction, IFP, and metastatic propensity of tumors was investigated in this study.

Methods

A-07 and R-18 melanoma xenografts were used as general models of human cancer. DW-MRI was performed at 1.5 T, and maps of the apparent diffusion coefficient (ADC) were produced with in-house-made software developed in Matlab. Pimonidazole was used as a hypoxia marker. Tumor cell density and hypoxic fraction were assessed by quantitative analysis of histological sections. IFP was measured with a Millar catheter. Metastatic propensity was determined by examining tumor-bearing mice for pulmonary micrometastases post mortem.

Results

ADC decreased with increasing tumor cell density, independent of whether the A-07 and R-18 data were analyzed separately or together. In the A-07 line, ADC decreased with increasing hypoxic fraction and increasing IFP and was lower in metastatic than in nonmetastatic tumors, and in the R-18 line, ADC decreased with increasing hypoxic fraction. There was a strong inverse correlation between ADC and hypoxic fraction as well as between ADC and IFP across the two tumor lines, primarily because low ADC as well as high hypoxic fraction and high IFP were associated with high cell density.

Conclusion

Low ADC is a potentially useful biomarker of poor prognosis in cancer, since low ADC is mainly a consequence of high cell density, and high cell density may lead to increased hypoxia and interstitial hypertension and, therefore, increased microenvironment-associated metastasis.

Connective tissue of cervical carcinoma xenografts: associations with tumor hypoxia and interstitial fluid pressure and its assessment by DCE-MRI and DW-MRI

Abstract Background. A high fraction of stroma in malignant tissues is associated with tumor progression, metastasis, and poor prognosis. Possible correlations between the stromal and physiologic microenvironments of tumors and the potential of dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) magnetic resonance imaging (MRI) in quantification of the stromal microenvironment were investigated in this study. Material and methods. CK-160 cervical carcinoma xenografts were used as preclinical tumor model. A total of 43 tumors were included in the study, and of these tumors, 17 were used to search for correlations between the stromal and physiologic microenvironments, 11 were subjected to DCE-MRI, and 15 were subjected to DW-MRI. DCE-MRI and DW-MRI were carried out at 1.5 T with a clinical MR scanner and a slotted tube resonator transceiver coil constructed for mice. Fraction of connective tissue (CTFCol) and fraction of hypoxic tissue (HFPim) were determined by immunohistochemistry. A Millar SPC 320 catheter was used to measure tumor interstitial fluid pressure (IFP). Results. CTFCol showed a positive correlation to IFP and an inverse correlation to HFPim. The apparent diffusion coefficient assessed by DW-MRI was inversely correlated to CTFCol, whereas no correlation was found between DCE-MRI-derived parameters and CTFCol. Conclusion. DW-MRI is a potentially useful method for characterizing the stromal microenvironment of tumors.

Magnetic resonance imaging identifies early effects of sunitinib treatment in human melanoma xenografts

BACKGROUND

Antiangiogenic treatment may change the tumor microenvironment and hence influence the effect of conventional therapies. The potential of diffusion weighted magnetic resonance imaging (DW-MRI) and dynamic contrast enhanced MRI (DCE-MRI) in assessing microenvironmental effects of sunitinib treatment was investigated in this preclinical study.

METHODS

Sunitinib-treated and untreated A-07 tumors were subjected to DW-MRI and DCE-MRI, and parametric images of ADC and Ktrans were produced. Microvascular density, hypoxic fraction, and necrotic fraction were assessed from immunohistochemical preparations, and tumor interstitial fluid pressure (IFP) was assessed with probe measurement.

RESULTS

Sunitinib-treated tumors showed reduced microvascular density, increased hypoxic fraction, increased necrotic fraction, increased ADC, and reduced Ktrans, but did not differ from untreated tumors in growth rate and IFP.

CONCLUSIONS

Sunitinib treatment affected the tumor microenvironment without affecting tumor size. DW-MRI and DCE-MRI were sensitive to the sunitinib-induced changes in the tumor microenvironment.

Dynamic contrast-enhanced magnetic resonance imaging of the metastatic potential of tumors: a preclinical study of cervical carcinoma and melanoma xenografts

BACKGROUND

Gadolinium diethylene-triamine penta-acetic acid (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has been suggested to be a useful non-invasive method for providing biomarkers for personalized cancer treatment. In this preclinical study, we investigated whether Gd-DTPA-based DCE-MRI may have the potential to differentiate between poorly and highly metastatic tumors.

MATERIAL AND METHODS

CK-160 cervical carcinoma and V-27 melanoma xenografts were used as tumor models. Fifty-six tumors were imaged, and parametric images of K(trans) (the volume transfer constant of Gd-DTPA) and v(e) (the fractional distribution volume of Gd-DTPA) were produced by pharmacokinetic analysis of the DCE-MRI series. The host mice were examined for lymph node metastases immediately after the DCE-MRI.

RESULTS

Highly metastatic tumors showed lower values for median K(trans) than poorly metastatic tumors (p = 0.00033, CK-160; p < 0.00001, V-27). Median v(e) was lower for highly than for poorly metastatic V-27 tumors (p = 0.047), but did not differ significantly between metastatic and non-metastatic CK-160 tumors (p > 0.05).

CONCLUSION

This study supports the clinical attempts to establish DCE-MRI as a method for providing biomarkers for tumor aggressiveness and suggests that tumors showing low K(trans) and low ve values may have high probability of lymphogenous metastatic dissemination.

Assessment of the interstitial fluid pressure of tumors by dynamic contrast-enhanced magnetic resonance imaging with contrast agents of different molecular weights

BACKGROUND

Cancer patients showing highly elevated interstitial fluid pressure (IFP) in the primary tumor may benefit from particularly aggressive treatment. There is some evidence that gadolinium diethylene-triamine penta-acetic acid (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may be a useful non-invasive method for providing information on the IFP of tumors. The purpose of this preclinical study was to investigate whether any association between DCE-MRI-derived parametric images and tumor IFP can be strengthened by using MR contrast agents with higher molecular weights than that of Gd-DTPA.

MATERIAL AND METHODS

A-07 human melanoma xenografts were used as preclinical models of human cancer. Three contrast agents were compared: Gd-DTPA (0.55 kDa), P846 (3.5 kDa), and gadomelitol (6.5 kDa). A total of 46 tumors were subjected to DCE-MRI and subsequent measurement of IFP. Parametric images of K(trans) (the volume transfer constant of the contrast agent) and v(e) (the fractional distribution volume of the contrast agent) were produced by pharmacokinetic analysis of the DCE-MRI series.

RESULTS

Significant inverse correlations were found between median K(trans) and IFP for Gd-DTPA (p = 0.0076; R(2) = 0.46; n = 14) and P846 (p = 0.0042; R(2) = 0.45; n = 16), whereas there was no correlation between median K(trans) and IFP for gadomelitol (p > 0.05; n = 16). Significant correlation between median v(e) and IFP was not found for any of the contrast agents (p > 0.05 for Gd-DTPA, P846, and gadomelitol).

CONCLUSION

K(trans) images, but not v(e) images, derived by pharmacokinetic analysis of DCE-MRI data for low-molecular-weight contrast agents may provide information on the IFP of tumors. Any association between K(trans) and IFP cannot be expected to be improved by using contrast agents with higher molecular weights than those of Gd-DTPA and P846.

Interstitial fluid pressure and associated lymph node metastasis revealed in tumors by dynamic contrast-enhanced MRI

Elevated interstitial fluid pressure (IFP) in tumors can cause metastatic dissemination and treatment resistance, but its study poses a challenge because of a paucity of noninvasive imaging strategies. In this study, we address this issue by reporting the development of a noninvasive tool to assess tumor IFP and interstitial hypertension-induced lymph node metastasis. Using mouse xenograft models of several types of human cancer, we used gadolinium diethylene-triamine penta-acetic acid (Gd-DTPA) as a contrast agent for dynamic contrast-enhanced MRI (DCE-MRI). Immediately after Gd-DTPA administration, a high-signal-intensity rim was observed in the tumor periphery, which moved outward with time. Assuming the velocity of Gd-DTPA to be equal to the fluid flow velocity, we used a simple model of peritumoral interstitial fluid flow to calculate the fluid flow velocity at the tumor surface (v(0)) based on the rim movement. Significant positive correlations were found between v(0) and IFP in all tumor xenografts. Moreover, the primary tumors of metastasis-positive mice displayed higher IFP and v(0) than the primary tumors of metastasis-negative mice. Findings were confirmed in cervical cancer patients with pelvic lymph node metastases, where we found v(0) to be higher compared with patients without lymph node involvement (P < 0.00001). Together, these findings establish that Gd-DTPA-based DCE-MRI can noninvasively visualize tumor IFP, and they reveal the potential for v(0) determined by this method to serve as a novel general biomarker of tumor aggressiveness.

Preclinical evaluation of Gd-DTPA and gadomelitol as contrast agents in DCE-MRI of cervical carcinoma interstitial fluid pressure

BACKGROUND

High interstitial fluid pressure (IFP) in the primary tumor is associated with poor disease-free survival in locally advanced cervical carcinoma. A noninvasive assay is needed to identify cervical cancer patients with highly elevated tumor IFP because these patients may benefit from particularly aggressive treatment. It has been suggested that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with gadolinium diethylene-triamine penta-acetic acid (Gd-DTPA) as contrast agent may provide useful information on the IFP of cervical carcinomas. In this preclinical study, we investigated whether DCE-MRI with contrast agents with higher molecular weights (MW) than Gd-DTPA would be superior to Gd-DTPA-based DCE-MRI.

METHODS

CK-160 human cervical carcinoma xenografts were subjected to DCE-MRI with Gd-DTPA (MW of 0.55 kDa) or gadomelitol (MW of 6.5 kDa) as contrast agent before tumor IFP was measured invasively with a Millar SPC 320 catheter. The DCE-MRI was carried out at a spatial resolution of 0.23 × 0.23 × 2.0 mm³ and a time resolution of 14 s by using a 1.5-T whole-body scanner and a slotted tube resonator transceiver coil constructed for mice. Parametric images were derived from the DCE-MRI recordings by using the Tofts iso-directional transport model and the Patlak uni-directional transport model.

RESULTS

When gadomelitol was used as contrast agent, significant positive correlations were found between the parameters of both pharmacokinetic models and tumor IFP. On the other hand, significant correlations between DCE-MRI-derived parameters and IFP could not be detected with Gd-DTPA as contrast agent.

CONCLUSION

Gadomelitol is a superior contrast agent to Gd-DTPA in DCE-MRI of the IFP of CK-160 cervical carcinoma xenografts. Clinical studies attempting to develop DCE-MRI-based assays of the IFP of cervical carcinomas should involve contrast agents with higher MW than Gd-DTPA.

Microenvironment-associated lymph node metastasis of human cervical carcinoma xenografts

BACKGROUND

The prognosis is particularly poor for patients with advanced squamous cell carcinoma of the uterine cervix when the primary tumor has developed severe physiological abnormalities. The impact of the physiological microenvironment of the primary tumor on lymph node metastasis was investigated in this preclinical study.

MATERIAL AND METHODS

Xenografted tumors of two human cervical carcinoma lines (CK-160 and TS-415) transplanted into BALB/c nu/nu mice were included in the study. The fraction of radiobiologically hypoxic cells (HF(Rad)), interstitial fluid pressure (IFP), and extracellular pH (pH(e)) were measured in 22 CK-160 tumors and 16 TS-415 tumors and related to the metastatic status of the host mice.

RESULTS

In CK-160, HF(Rad) was significantly higher in the metastatic than in the nonmetastatic tumors, whereas the metastatic and nonmetastatic tumors did not differ significantly in IFP or pH(e). In TS-415, IFP was significantly higher in the tumors that metastasized than in those that did not metastasize, whereas the tumors of the metastasis-positive and metastasis-negative mice did not differ significantly in HF(Rad) or pH(e).

CONCLUSION

Lymph node metastasis is associated with abnormalities in the physiological microenvironment of the primary tumor in cervical carcinoma xenografts, and tumor line-specific mechanisms are probably involved.

Assessment of hypoxia and radiation response in intramuscular experimental tumors by dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND AND PURPOSE

Studies of intradermal melanoma xenografts have suggested that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may be a useful method for assessing the extent of hypoxia in tumors. Because the microvascular network of tumors is influenced significantly by the site of growth, we challenged this possibility in the present work by studying relationships between DCE-MRI-derived parameters and hypoxia in intramuscular melanoma xenografts.

MATERIALS AND METHODS

Intramuscular R-18, U-25, and V-27 tumors were subjected to DCE-MRI and measurement of the fraction of radiobiologically hypoxic cells (HF(Rad)). Parametric images of K(trans) and v(e) were produced by pharmacokinetic analysis, and K(trans) and v(e) were related to HF(Rad) in individual tumors.

RESULTS

K(trans) decreased with increasing HF(Rad). The correlations between K(trans) and HF(Rad) were similar for the three tumor lines and were highly significant (P<0.00001). There was no correlation between v(e) and HF(Rad). However, v(e) decreased significantly with increasing cell survival after single dose irradiation.

CONCLUSION

Intramuscular melanoma xenografts show similar inverse correlations between K(trans) and HF(Rad) as intradermal tumors, which support the current clinical attempts to establish DCE-MRI as a method for detecting hypoxia and defining therapeutic targets in tumors.

Second-harmonic generation in collagen as a potential cancer diagnostic parameter

The fibrillar collagen network in tumor and normal tissues is different due to remodeling of the extracellular matrix during the malignant process. Collagen type I fibers have the crystalline and noncentrosymmetric properties required for generating the second-harmonic signal. The content and structure of collagen were studied by imaging the second-harmonic generation (SHG) signal in frozen sections from three tumor tissues, osteosarcoma, breast carcinoma, and melanoma, and were compared with corresponding normal tissues, bone/femur, breast, and dermis/skin. The collagen density was measured as the percentage of pixels containing SHG signal in tissue images, and material parameters such as the second-order nonlinear optical susceptibility given by the d22 coefficient and an empirical anisotropy parameter were used to characterize the collagen structure. Generally, normal tissues had much more collagen than tumor tissues. In tumor tissues, a cap of collagen was seen at the periphery, and further into the tumors, the distribution of collagen was sparse and heterogeneous. The difference in structure was reflected in the two times higher d22 coefficient and lower anisotropy values in normal tissues compared with tumor tissues. Together, the differences in the collagen content, distribution, and structure show that collagen signature is a promising diagnostic marker.

Quantification of the second-order nonlinear susceptibility of collagen I using a laser scanning microscope

Characteristic changes in the organization of fibrillar collagen can potentially serve as an early diagnostic marker in various pathological processes. Tissue types containing collagen I can be probed by pulsed high-intensity laser radiation, thereby generating second harmonic light that provides information about the composition and structure at a microscopic level. A technique was developed to determine the essential second harmonic generation (SHG) parameters in a laser scanning microscope setup. A rat-tail tendon frozen section was rotated in the xy-plane with the pulsed laser light propagating along the z-axis. By analyzing the generated second harmonic light in the forward direction with parallel and crossed polarizer relative to the polarization of the excitation laser beam, the second-order nonlinear optical susceptibilities of the collagen fiber were determined. Systematic variations in SHG response between ordered and less ordered structures were recorded and evaluated. A 500 microm-thick z-cut lithiumniobate (LiNbO(3)) was used as reference. The method was applied on frozen sections of malignant melanoma and normal skin tissue. Significant differences were found in the values of d(22), indicating that this parameter has a potential role in differentiating between normal and pathological processes.