Dynamic contrast-enhanced magnetic resonance imaging of tumor interstitial fluid pressure

Hydraulic conductivity of human cancer tissue: A hybrid study

Background

Elevated tumor tissue interstitial fluid pressure (IFP) is an adverse biomechanical biomarker that predicts poor therapy response and an aggressive phenotype. Advances in functional imaging have opened the prospect of measuring IFP non-invasively. Image-based estimation of the IFP requires knowledge of the tissue hydraulic conductivity (K), a measure for the ease of bulk flow through the interstitium. However, data on the magnitude of K in human cancer tissue are not available.

Methods

We measured the hydraulic conductivity of tumor tissue using modified Ussing chambers in surgical resection specimens. The effect of the tumor microenvironment (TME) on K was investigated by quantifying the collagen content, cell density, and fibroblast density of the tested samples using quantitative immune histochemistry. Also, we developed a computational fluid dynamics (CFD) model to evaluate the role of K on interstitial fluid flow and drug transport in solid tumors.

Results

The results show that the hydraulic conductivity of human tumor tissues is very limited, ranging from approximately 10-15 to 10-14 m2/Pa∙s. Moreover, K values varied significantly between tumor types and between different samples from the same tumor. A significant inverse correlation was found between collagen fiber density and hydraulic conductivity values. However, no correlation was detected between K and cancer cell or fibroblast densities. The computational model demonstrated the impact of K on the interstitial fluid flow and the drug concentration profile: higher K values led to a lower IFP and deeper drug penetration.

Conclusions

Human tumor tissue is characterized by a very limited hydraulic conductivity, representing a barrier to effective drug transport. The results of this study can inform the development of realistic computational models, facilitate non-invasive IFP estimation, and contribute to stromal targeting anticancer therapies.

Deep GRU-CNN Model for COVID-19 Detection From Chest X-Rays Data

In the current era, data is growing exponentially due to advancements in smart devices. Data scientists apply a variety of learning-based techniques to identify underlying patterns in the medical data to address various health-related issues. In this context, automated disease detection has now become a central concern in medical science. Such approaches can reduce the mortality rate through accurate and timely diagnosis. COVID-19 is a modern virus that has spread all over the world and is affecting millions of people. Many countries are facing a shortage of testing kits, vaccines, and other resources due to significant and rapid growth in cases. In order to accelerate the testing process, scientists around the world have sought to create novel methods for the detection of the virus. In this paper, we propose a hybrid deep learning model based on a convolutional neural network (CNN) and gated recurrent unit (GRU) to detect the viral disease from chest X-rays (CXRs). In the proposed model, a CNN is used to extract features, and a GRU is used as a classifier. The model has been trained on 424 CXR images with 3 classes (COVID-19, Pneumonia, and Normal). The proposed model achieves encouraging results of 0.96, 0.96, and 0.95 in terms of precision, recall, and f1-score, respectively. These findings indicate how deep learning can significantly contribute to the early detection of COVID-19 in patients through the analysis of X-ray scans. Such indications can pave the way to mitigate the impact of the disease. We believe that this model can be an effective tool for medical practitioners for early diagnosis.

Noninvasive Molecular Imaging of the Enhanced Permeability and Retention Effect by 64Cu-Liposomes: In vivo Correlations with 68Ga-RGD, Fluid Pressure, Diffusivity and 18F-FDG

Background

The accumulation of liposome encapsulated chemotherapy in solid cancers is dependent on the presence of the enhanced permeability and retention (EPR) effect. Positron emission tomography (PET) imaging with a liposome encapsulated radioisotope, such as liposome encapsulated Cu-64 (⁶⁴Cu-liposome) may help to identify tumors with high liposome accumulation, and thereby stratify patients based on expected benefit from liposomal chemotherapy. However, intravenous administration of liposomes without a cytotoxic content is complicated by the accelerated blood clearance (ABC) phenomenon for succeeding therapeutic liposome dosing. Alternative markers for assessing the tumor’s EPR level are therefore warranted.

Materials and Methods

To increase our understanding of EPR variations and to ultimately identify an alternative marker for the EPR effect, we investigated the correlation between ⁶⁴Cu-liposome PET/CT (EPR effect) and ⁶⁸Ga-RGD PET/CT (neoangiogenesis), ¹⁸F-FDG PET/CT (glycolysis), diffusion-weighted MRI (diffusivity) and interstitial fluid pressure in two experimental cancer models (CT26 and COLO 205).

Results

⁶⁴Cu-liposome and ⁶⁸Ga-RGD SUV_max displayed a significant moderate correlation, however, none of the other parameters evaluated displayed significant correlations. These results indicate that differences in neoangiogenesis may explain some EPR variability, however, as correlations were only moderate and not observed for SUV_mean, ⁶⁸Ga-RGD is probably insufficient to serve as a stand-alone surrogate marker for quantifying the EPR effect and stratifying patients.

Dual inhibition of PFKFB3 and VEGF normalizes tumor vasculature, reduces lactate production, and improves chemotherapy in glioblastoma: insights from protein expression profiling and MRI

Rationale: Tumor vascular normalization (TVN) is emerging to enhance the efficacy of anticancer treatment in many cancers including glioblastoma (GBM). However, a common and severe challenge being currently faced is the transient TVN effect, hampering the sustained administration of anticancer therapy during TVN window. Additionally, the lack of non-contrast agent-based imaging biomarkers to monitor TVN process postpones the clinical translation of TVN strategy. In this study, we investigated whether dual inhibition of VEGF and the glycolytic activator PFKFB3 could reinforce the TVN effect in GBM. Dynamic contrast-enhanced-magnetic resonance imaging (DCE-MRI) and intravoxel incoherent motion (IVIM)-MRI were performed to monitor TVN process and to identify whether IVIM-MRI is a candidate or complementary imaging biomarker for monitoring TVN window without exogenous contrast agent administration. Methods: Patient-derived orthotopic GBM xenografts in mice were established and treated with bevacizumab (BEV), 3PO (PFKFB3 inhibitor), BEV+3PO dual therapy, or saline. The vascular morphology, tumor hypoxia, and lactate level were evaluated before and at different time points after treatments. Doxorubicin was used to evaluate chemotherapeutic efficacy and drug delivery. Microarray of angiogenesis cytokines and western blotting were conducted to characterize post-treatment molecular profiling. TVN process was monitored by DCE- and IVIM-MRI. Correlation analysis of pathological indicators and MRI parameters was further analyzed. Results: Dual therapy extended survival and delayed tumor growth over each therapy alone, concomitant with a decrease of cell proliferation and an increase of cell apoptosis. The dual therapy reinforces TVN effect, thereby alleviating tumor hypoxia, reducing lactate production, and improving the efficacy and delivery of doxorubicin. Mechanistically, several angiogenic cytokines and pathways were downregulated after dual therapy. Notably, dual therapy inhibited Tie1 expression, the key regulator of TVN, in both endothelial cells and tumor cells. DCE- and IVIM-MRI data showed that dual therapy induced a more homogenous and prominent TVN effect characterized by improved vascular function in tumor core and tumor rim. Correlation analysis revealed that IVIM-MRI parameter D* had better correlations with TVN pathological indicators compared with the DCE-MRI parameter Ktrans. Conclusions: Our results propose a rationale to overcome the current limitation of BEV monotherapy by integrating the synergistic effects of VEGF and PFKFB3 blockade to enhance chemotherapy efficacy through a sustained TVN effect. Moreover, we unveil IVIM-MRI parameter D* has much potential as a complementary imaging biomarker to monitor TVN window more precisely without exogenous contrast agent injection.

Towards noninvasive estimation of tumour pressure by utilising MR elastography and nonlinear biomechanical models: a simulation and phantom study

The solid and fluid pressures of tumours are often elevated relative to surrounding tissue. This increased pressure is known to correlate with decreased treatment efficacy and potentially with tumour aggressiveness and therefore, accurate noninvasive estimates of tumour pressure would be of great value. We present a proof-of-concept method to infer the total tumour pressure, that is the sum of the fluid and solid parts, by examining stiffness in the peritumoural tissue with MR elastography and utilising nonlinear biomechanical models. The pressure from the tumour deforms the surrounding tissue leading to changes in stiffness. Understanding and accounting for these biases in stiffness has the potential to enable estimation of total tumour pressure. Simulations are used to validate the method with varying pressure levels, tumour shape, tumour size, and noise levels. Results show excellent matching in low noise cases and still correlate well with higher noise. Percent error remains near or below 10% for higher pressures in all noise level cases. Reconstructed pressures were also calculated from experiments with a catheter balloon embedded in a plastisol phantom at multiple inflation levels. Here the reconstructed pressures generally match the increases in pressure measured during the experiments. Percent errors between average reconstructed and measured pressures at four inflation states are 17.9%, 52%, 23.2%, and 0.9%. Future work will apply this method to in vivo data, potentially providing an important biomarker for cancer diagnosis and treatment.

A novel filter for accurate estimation of fluid pressure and fluid velocity using poroelastography

Fluid pressure and fluid velocity carry important information for cancer diagnosis, prognosis and treatment. Recent work has demonstrated that estimation of these parameters is theoretically possible using ultrasound poroelastography. However, accurate estimation of these parameters requires high quality axial and lateral strain estimates from noisy ultrasound radio frequency (RF) data. In this paper, we propose a filtering technique combining two efficient filters for removal of noise from strain images, i.e., Kalman and nonlinear complex diffusion filters (NCDF). Our proposed filter is based on a novel noise model, which takes into consideration both additive and amplitude modulation noise in the estimated strains. Using finite element and ultrasound simulations, we demonstrate that the proposed filtering technique can significantly improve image quality of lateral strain elastograms along with fluid pressure and velocity elastograms. Technical feasibility of the proposed method on an in vivo set of data is also demonstrated. Our results show that the CNRe of the lateral strain, fluid pressure and fluid velocity as estimated using the proposed technique is higher by at least 10.9%, 51.3% and 334.4% when compared to the results obtained using a Kalman filter only, by at least 8.9%, 27.6% and 219.5% when compared to the results obtained using a NCDF only and by at least 152.3%, 1278% and 742% when compared to the results obtained using a median filter only for all SNRs considered in this study.

Functional intratumoral lymphatics in patient-derived xenograft models of squamous cell carcinoma of the uterine cervix: implications for lymph node metastasis

Studies of cell line-derived human tumor xenografts have suggested that the lymphatics seen in immunohistochemical preparations from non-peripheral regions of tumors are nonfunctional. In this investigation, lymphangiogenesis, hemangiogenesis, and lymph node metastasis were studied in patient-derived xenograft (PDX) models of carcinoma of the uterine cervix. Lymph vessel density (LVD) and blood vessel density (BVD) were measured in immunohistochemical preparations. The expression of angiogenesis-related genes was investigated by quantitative PCR. Lymphatic functionality was assessed with the ferritin assay, and tumor interstitial fluid pressure (IFP) was measured with a Millar catheter. The PDX models mirrored the angiogenesis and aggressiveness of the donor patients' tumors, and two highly aggressive models developed functional lymphatics within the tumor mass. Tumors with functional intratumoral lymphatics showed low IFP, high LVD, high BVD, high expression of a large number of angiogenesis-related genes, and high incidence of lymph node metastases. LVD correlated with BVD, and lymph node metastasis was associated with high LVD and high BVD. Nine angiogenesis-related genes associated with the development of functional intratumoral lymhatics were identified. High expression of these genes, high LVD, and high BVD may be important biomarkers for poor outcome in cervix carcinoma.

Dynamic contrast-enhanced MRI of the microenvironment of pancreatic adenocarcinoma xenografts

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with poor outcome. Resistance to treatment is associated with impaired vascularity, extensive hypoxia, and interstitial hypertension. In this study, the potential of dynamic contrast-enhanced (DCE)-MRI as a method for assessing the microvascular density (MVD), the fraction of hypoxic tissue, and the interstitial fluid pressure (IFP) of PDACs was investigated.

MATERIAL AND METHODS

Intramuscular BxPC-3, Capan-2, MIAPaCa-2, and Panc-1 PDAC xenografts were used as preclinical models of human PDACs. DCE-MRI with Gd-DOTA as contrast agent was conducted with a 7.05-T scanner, and the DCE-MRI series were analyzed voxelwise by using the Tofts pharmacokinetic model. Tumor MVD and hypoxia were measured in histological preparations by using pimonidazole as a hypoxia marker and CD31 as a marker of endothelial cells. IFP was measured with a Millar catheter.

RESULTS

K^trans (the volume transfer constant of Gd-DOTA) increased with increasing MVD and decreased with increasing hypoxic fraction, but was not associated with IFP. Any association between v_e (the fractional distribution volume of Gd-DOTA) and MVD, hypoxic fraction, or IFP could not be detected.

CONCLUSIONS

This study shows that DCE-MRI is a useful modality for assessing important features of the microenvironment of PDAC xenografts and thus provides the basis for future preclinical and clinical DCE-MRI investigations of PDAC.

Lymph node metastasis and the physicochemical micro-environment of pancreatic ductal adenocarcinoma xenografts

Pancreatic ductal adenocarcinoma (PDAC) patients develop lymph node metastases early and have a particularly poor prognosis. The poor prognosis has been shown to be associated with the physicochemical microenvironment of the tumor tissue, which is characterized by desmoplasia, abnormal microvasculature, extensive hypoxia, and highly elevated interstitial fluid pressure (IFP). In this study, we searched for associations between lymph node metastasis and features of the physicochemical microenvironment in an attempt to identify mechanisms leading to metastatic dissemination and growth. BxPC-3 and Capan-2 PDAC xenografts were used as preclinical models of human PDAC. In both models, lymph node metastasis was associated with high IFP rather than high fraction of hypoxic tissue or high microvascular density. Seven angiogenesis-related genes associated with high IFP-associated lymph node metastasis were detected by quantitative PCR in each of the models, and these genes were all up-regulated in high IFP/highly metastatic tumors. Three genes were mutual for the BxPC-3 and Capan-2 models: transforming growth factor beta, angiogenin, and insulin-like growth factor 1. Further comprehensive studies are needed to determine whether there is a causal relationship between the up-regulation of these genes and high IFP and/or high propensity for lymph node metastasis in PDAC.

A numerical framework for interstitial fluid pressure imaging in poroelastic MRE

A numerical framework for interstitial fluid pressure imaging (IFPI) in biphasic materials is investigated based on three-dimensional nonlinear finite element poroelastic inversion. The objective is to reconstruct the time-harmonic pore-pressure field from tissue excitation in addition to the elastic parameters commonly associated with magnetic resonance elastography (MRE). The unknown pressure boundary conditions (PBCs) are estimated using the available full-volume displacement data from MRE. A subzone-based nonlinear inversion (NLI) technique is then used to update mechanical and hydrodynamical properties, given the appropriate subzone PBCs, by solving a pressure forward problem (PFP). The algorithm was evaluated on a single-inclusion phantom in which the elastic property and hydraulic conductivity images were recovered. Pressure field and material property estimates had spatial distributions reflecting their true counterparts in the phantom geometry with RMS errors around 20% for cases with 5% noise, but degraded significantly in both spatial distribution and property values for noise levels > 10%. When both shear moduli and hydraulic conductivity were estimated along with the pressure field, property value error rates were as high as 58%, 85% and 32% for the three quantities, respectively, and their spatial distributions were more distorted. Opportunities for improving the algorithm are discussed.

Decline of Tumor Vascular Function as Assessed by Dynamic Contrast-Enhanced Magnetic Resonance Imaging Is Associated With Poor Responses to Radiation Therapy and Chemotherapy

PURPOSE

To investigate whether changes in the volume transfer coefficient (K(trans)) in a growing tumor could be used as a surrogate marker for predicting tumor responses to radiation therapy (RT) and chemotherapy (CT).

METHODS AND MATERIALS

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was consecutively performed on tumor-bearing mice, and temporal and spatial changes of K(trans) values were measured along with tumor growth. Tumor responses to RT and CT were studied before and after observed changes in K(trans) values with time.

RESULTS

Dynamic changes with an initial increase and subsequent decline in K(trans) values were found to be associated with tumor growth. When each tumor was divided into core and peripheral regions, the K(trans) decline was greater in core, although neither vascular structure or necrosis could be linked to this spatial difference. Tumor responses to RT were worse if applied after the decline of K(trans), and there was less drug distribution and cell death in the tumor core after CT.

CONCLUSION

The K(trans) value in growing tumors, reflecting the changes of tumor microenvironment and vascular function, is strongly associated with tumor responses to RT and CT and could be a potential surrogate marker for predicting the tumor response to these treatments.

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.

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.

High interstitial fluid pressure is associated with tumor-line specific vascular abnormalities in human melanoma xenografts

Purpose

Interstitial fluid pressure (IFP) is highly elevated in many solid tumors. High IFP has been associated with low radiocurability and high metastatic frequency in human melanoma xenografts and with poor survival after radiation therapy in cervical cancer patients. Abnormalities in tumor vascular networks have been identified as an important cause of elevated tumor IFP. The aim of this study was to investigate the relationship between tumor IFP and the functional and morphological properties of tumor vascular networks.

Materials and Methods

A-07-GFP and R-18-GFP human melanomas growing in dorsal window chambers in BALB/c nu/nu mice were used as preclinical tumor models. Functional and morphological parameters of the vascular network were assessed from first-pass imaging movies and vascular maps recorded after intravenous bolus injection of 155-kDa tetramethylrhodamine isothiocyanate-labeled dextran. IFP was measured in the center of the tumors using a Millar catheter. Angiogenic profiles of A-07-GFP and R-18-GFP cells were obtained with a quantitative PCR array.

Results

High IFP was associated with low growth rate and low vascular density in A-07-GFP tumors, and with high growth rate and high vascular density in R-18-GFP tumors. A-07-GFP tumors showed chaotic and highly disorganized vascular networks, while R-18-GFP tumors showed more organized vascular networks with supplying arterioles in the tumor center and draining venules in the tumor periphery. Furthermore, A-07-GFP and R-18-GFP cells differed substantially in angiogenic profiles. A-07-GFP tumors with high IFP showed high geometric resistance to blood flow due to high vessel tortuosity. R-18-GFP tumors with high IFP showed high geometric resistance to blood flow due to a large number of narrow tumor capillaries.

Conclusions

High IFP in A-07-GFP and R-18-GFP human melanoma xenografts was primarily a consequence of high blood flow resistance caused by tumor-line specific vascular abnormalities.

Interstitial fluid pressure correlates with intravoxel incoherent motion imaging metrics in a mouse mammary carcinoma model

The effective delivery of a therapeutic drug to the core of a tumor is often impeded by physiological barriers, such as the interstitial fluid pressure (IFP). There are a number of therapies that can decrease IFP and induce tumor vascular normalization. However, a lack of a noninvasive means to measure IFP hinders the utilization of such a window of opportunity for the maximization of the treatment response. Thus, the purpose of this study was to investigate the feasibility of using intravoxel incoherent motion (IVIM) diffusion parameters as noninvasive imaging biomarkers for IFP. Mice bearing the 4T1 mammary carcinoma model were studied using diffusion-weighted imaging (DWI), immediately followed by wick-in-needle IFP measurement. Voxelwise analysis was conducted with a conventional monoexponential diffusion model, as well as a biexponential model taking IVIM into account. There was no significant correlation of IFP with either the median apparent diffusion coefficient from the monoexponential model (r = 0.11, p = 0.78) or the median tissue diffusivity from the biexponential model (r = 0.30, p = 0.44). However, IFP was correlated with the median pseudo-diffusivity (D(p)) of apparent vascular voxels (r = 0.76, p = 0.02) and with the median product of the perfusion fraction and pseudo-diffusivity (f(p)D(p)) of apparent vascular voxels (r = 0.77, p = 0.02). Although the effect of IVIM in tumors has been reported previously, to our knowledge, this study represents the first direct comparison of IVIM metrics with IFP, with the results supporting the feasibility of the use of IVIM DWI metrics as noninvasive biomarkers for tumor IFP.

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.

Assessment of tumor radioresponsiveness and metastatic potential by dynamic contrast-enhanced magnetic resonance imaging

PURPOSE

It has been suggested that gadolinium diethylene-triamine penta-acetic acid (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may provide clinically useful biomarkers for personalized cancer treatment. In this preclinical study, we investigated the potential of DCE-MRI as a noninvasive method for assessing the radioresponsiveness and metastatic potential of tumors.

METHODS AND MATERIALS

R-18 melanoma xenografts growing in BALB/c nu/nu mice were used as experimental tumor models. Fifty tumors were subjected to DCE-MRI, and parametric images of Ktrans (the volume transfer constant of Gd-DTPA) and ve (the fractional distribution volume of Gd-DTPA) were produced by pharmacokinetic analysis of the DCE-MRI series. The tumors were irradiated after the DCE-MRI, either with a single dose of 10 Gy for detection of radiobiological hypoxia (30 tumors) or with five fractions of 4 Gy in 48 h for assessment of radioresponsiveness (20 tumors). The host mice were then euthanized and examined for lymph node metastases, and the primary tumors were resected for measurement of cell survival in vitro.

RESULTS

Tumors with hypoxic cells showed significantly lower Ktrans values than tumors without significant hypoxia (p<0.0001, n=30), and Ktrans decreased with increasing cell surviving fraction for tumors given fractionated radiation treatment (p<0.0001, n=20). Tumors in metastasis-positive mice had significantly lower Ktrans values than tumors in metastasis-negative mice (p<0.0001, n=50). Significant correlations between ve and tumor hypoxia, radioresponsiveness, or metastatic potential could not be detected.

CONCLUSIONS

R-18 tumors with low Ktrans values are likely to be resistant to radiation treatment and have a high probability of developing lymph node metastases. The general validity of these observations should be investigated further by studying preclinical tumor models with biological properties different from those of the R-18 tumors.

Assessment of tumor hypoxia and interstitial fluid pressure by gadomelitol-based dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND AND PURPOSE

Extensive hypoxia and high interstitial fluid pressure (IFP) in the primary tumor may cause resistance to radiation treatment and promote metastatic spread. The potential of gadomelitol-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in assessing the extent of hypoxia and the level of interstitial hypertension in tumors was investigated in this preclinical study.

MATERIALS AND METHODS

Twenty-three A-07 tumors were subjected to DCE-MRI and subsequent measurement of IFP and fraction of pimonidazole-positive hypoxic tissue (HF(Pim)). Parametric tumor images of K(trans), v(e), and V(b)(Tofts) (Tofts model) and of K(i) and V(b)(Patlak) (Patlak model) were produced by pharmacokinetic analyses of the DCE-MRI series.

RESULTS

There was no correlation between IFP and HF(Pim) in the tumors. K(trans) and K(i) decreased significantly with increasing HF(Pim), whereas V(b)(Tofts) and V(b)(Patlak) increased significantly with increasing IFP.

CONCLUSION

Information on both the extent of hypoxia and the level of interstitial hypertension in A-07 tumors can be derived from a single DCE-MRI series by using gadomelitol as contrast agent.

Phenomenological model of interstitial fluid pressure in a solid tumor

Tumor interstitial fluid pressure (TIFP) has the potential to predict tumor response to nonsurgical cancer treatments, including radiation therapy. At present the only quantitative measures available are of limited use, since they are invasive and yield only point measurements. We present the mathematical framework for a quantitative, noninvasive measure of TIFP. The model describes the distribution of interstitial fluid pressure in three distinct tumor regions: vascularized tumor rim, central tumor region, and normal tissue. A relationship between the TIFP and the fluid flow velocity at the periphery of a tumor is presented. This model suggests that a measure of fluid flow rate from a tumor into normal tissue reflects TIFP. We demonstrate that the acquisition of serial images of a tumor after the injection of a contrast agent can provide a noninvasive and potentially quantitative measure of TIFP.

MRI & MRS assessment of the role of the tumour microenvironment in response to therapy

MRI and MRS techniques are being applied to the characterisation of various aspects of the tumour microenvironment and to the assessment of tumour response to therapy. For example, kinetic parameters describing tumour blood vessel flow and permeability can be derived from dynamic contrast-enhanced MRI data and have been correlated with a positive tumour response to antivascular therapies. The ongoing development and validation of noninvasive, high-resolution anatomical/molecular MR techniques will equip us with the means to detect specific tumour biomarkers early on, and then to monitor the efficacy of cancer treatments efficiently and reliably, all within a clinically relevant time frame. Reliable tumour microenvironment imaging biomarkers will provide obvious advantages by enabling tumour-specific treatment tailoring and potentially improving patient outcome. However, for routine clinical application across many disease types, such imaging biomarkers must be quantitative, robust, reproducible, sufficiently sensitive and cost-effective. These characteristics are all difficult to achieve in practice, but image biomarker development and validation have been greatly facilitated by an increasing number of pertinent preclinical in vivo cancer models. Emphasis must now be placed on discovering whether the preclinical results translate into an improvement in patient care and, therefore, overall survival.

Non-invasive imaging of combretastatin activity in two tumor models: Association with invasive estimates

INTRODUCTION

The efficacy of the vascular disrupting agent combretastatin A-4 phosphate (CA4P) depends on several factors including tumor size, nitric oxide level, interstitial fluid pressure, and vascular permeability. These factors vary among tumor types. The aim of this study was to investigate all these factors in two tumor models that respond differently to CA4P.

MATERIAL AND METHODS

Mice bearing C3H mammary carcinomas or KHT sarcomas (200 to 800 mm(3)) were intraperitoneally injected with CA4P (100 mg/kg). Tumor size and the effect of a nitric oxide inhibitor nitro-L-arginine (NLA) administered intravenously were evaluated by necrotic fraction histologically assessed at 24 hours. Interstitial fluid pressure (IFP) was measured using the wick-in-needle technique, and vascular characteristics were assessed with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

RESULTS

Initial necrotic fraction was about 10% in both tumor models at 200 mm(3), but only increased significantly with tumor size in the C3H mammary carcinoma. In this tumor, CA4P significantly induced further necrosis by about 15% at all sizes, but in the KHT tumor, the induced necrotic fraction depended on tumor size. For both tumor types, NLA with CA4P significantly increased necrotic fraction above that for each drug alone. CA4P significantly decreased IFP in all tumors except in the 800 mm(3) C3H tumor, which had an initially non-significant lower value. Interstitial volume estimated by DCE-MRI increased in all groups, except the 800 mm(3) C3H tumors. DCE-MRI vascular parameters showed different initial characteristics and general significant reductions following CA4P treatment.

CONCLUSIONS

Both tumor models showed differences in all factors before treatment, and in their response to CA4P. Perfusion and permeability as estimated by DCE-MRI play a central role in the CA4P response, and interstitial volume and IFP seemed related. These factors may be of clinical value in the planning of CA4P treatments.

Tumors exposed to acute cyclic hypoxic stress show enhanced angiogenesis, perfusion and metastatic dissemination

Clinical studies have shown that patients with highly hypoxic primary tumors may have poor disease-free and overall survival rates. Studies of experimental tumors have revealed that acutely hypoxic cells may be more metastatic than normoxic or chronically hypoxic cells. In the present work, causal relations between acute cyclic hypoxia and metastasis were studied by periodically exposing BALB/c nu/nu mice bearing A-07 human melanoma xenografts to a low oxygen atmosphere. The hypoxia treatment consisted of 12 cycles of 10 min of 8% O(2) in N(2) followed by 10 min of air for a total of 4 hr, began on the first day after tumor cell inoculation and was given daily until the tumors reached a volume of 100 mm(3). Twenty-four hours after the last hypoxia exposure, the primary tumors were subjected to dynamic contrast-enhanced magnetic resonance imaging for assessment of blood perfusion before being resected and processed for immunohistochemical examinations of microvascular density and expression of proangiogenic factors. Mice exposed to acute cyclic hypoxia showed increased incidence of pulmonary metastases, and the primary tumors of these mice showed increased blood perfusion, microvascular density and vascular endothelial growth factor-A (VEGF-A) expression; whereas, the expression of interleukin-8, platelet-derived endothelial cell growth factor and basic fibroblast growth factor was unchanged. The increased pulmonary metastasis was most likely a consequence of hypoxia-induced VEGF-A upregulation, which resulted in increased angiogenic activity and blood perfusion in the primary tumor and thus facilitated tumor cell intravasation and hematogenous transport into the general circulation.

Dynamic contrast-enhanced magnetic resonance imaging of human cervical carcinoma xenografts: pharmacokinetic analysis and correlation to tumor histomorphology

BACKGROUND AND PURPOSE

Biomarkers that can predict the outcome of treatment accurately are needed for treatment individualization in advanced carcinoma of the uterine cervix. The potential of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was investigated in the present preclinical study.

MATERIALS AND METHODS

CK-160 and TS-415 human cervical carcinoma xenografts were subjected to DCE-MRI at 1.5T using a spatial resolution of 0.23×0.47×2.0mm(3). Parametric images of K(trans) (the volume transfer constant of Gd-DTPA) and v(e) (the extravascular extracellular volume fraction) were produced by pharmacokinetic analysis of the DCE-MRI data and compared with the histomorphology of the imaged tissue.

RESULTS

Analysis of small homogeneous tumor regions showed that K(trans), but not v(e), differed significantly between parenchymal tissue, connective tissue, and necrotic tissue, consistent with the vascularity of these compartments. However, strong correlations between K(trans) and the fractional volume of the compartments could not be detected for larger tumor regions, primarily because the majority of the voxels represented a chaotic mixture of parenchymal, connective, and necrotic tissue.

CONCLUSION

The potential of DCE-MRI in providing detailed information on the histomorphology of cervical carcinoma is limited, mainly because the tumor tissue shows significant morphological heterogeneity at the subvoxel level.

Associations between radiocurability and interstitial fluid pressure in human tumor xenografts without hypoxic tissue

PURPOSE

The interstitial fluid pressure (IFP) of the primary tumor is an independent prognostic parameter for cervical cancer patients treated with radiation therapy. The aim of this preclinical study was to investigate whether tumor radiocurability may be associated with IFP through hypoxia-independent mechanisms.

EXPERIMENTAL DESIGN

Small A-07 and R-18 melanoma xenografts without hypoxic tissue were used as preclinical tumor models. IFP was measured by using the wick-in-needle method. Radiation dose resulting in 50% local tumor control (TCD(50)), cell density, cell tumorigenicity, plating efficiency in vitro, mitotic index, fraction of Ki67-positive cells, vascular endothelial growth factor-A (VEGF-A) concentration, and radiation-induced endothelial cell apoptosis were assessed in tumors with low and high IFP.

RESULTS

TCD(50) was found to be higher for tumors with high IFP than for tumors with low IFP by factors of 1.13 +/- 0.03 (A-07; P < 0.0001) and 1.10 +/- 0.03 (R-18; P < 0.0001). In the A-07 line, tumors with high IFP showed a larger number of clonogenic cells and a higher rate of cell proliferation than tumors with low IFP. In the R-18 line, tumors with high IFP showed a higher concentration of VEGF-A and a lower endothelial cell apoptotic index after irradiation than tumors with low IFP.

CONCLUSIONS

The radiation resistance of normoxic tumor tissue with highly elevated IFP may be an indirect consequence of increased tumor cell clonogenicity as well as increased VEGF-A expression, possibly caused by hypertension-induced modifications of signaling pathways regulating cell proliferation, cell survival, and/or angiogenesis.

Radiocurability is associated with interstitial fluid pressure in human tumor xenografts

Interstitial fluid pressure (IFP) has been shown to be an independent prognostic parameter for disease-free survival in cervical carcinoma patients treated with radiation therapy. However, the underlying mechanisms are not fully understood. The main aims of this study were to investigate whether tumor radiocurability may be associated with IFP and, if so, to identify possible mechanisms. Human melanoma xenografts transplanted intradermally or in window chamber preparations in BALB/c nu/nu mice were used as preclinical tumor models. Radiation dose resulting in 50% local tumor control was higher by a factor of 1.19 +/- 0.06 in tumors with IFP > or = 9 mm Hg than in tumors with IFP < or = 7 mm Hg. Tumor IFP was positively correlated to vessel segment length and vessel tortuosity and was inversely correlated to vessel density. Compared with tumors with low IFP, tumors with high IFP showed high resistance to blood flow, high frequency of Po(2) fluctuations, and high fractions of acutely hypoxic cells, whereas the fraction of radiobiologically hypoxic cells and the fraction of chronically hypoxic cells did not differ between tumors with high and tumors with low IFP. IFP showed a significant correlation to the fraction of acutely hypoxic cells, probably because both parameters were determined primarily by the microvascular resistance to blood flow. Therefore, the observed association between tumor radiocurability and IFP was most likely an indirect consequence of a strong relationship between IFP and the fraction of acutely hypoxic cells.

Human cervical carcinoma xenograft models for studies of the physiological microenvironment of tumors

OBJECTIVE

To establish and characterize experimental tumor models of advanced squamous cell carcinoma of the uterine cervix.

METHODS

Permanent cell lines (CK-160 and TS-415) were established from pelvic lymph node metastases of two cervical carcinoma patients. Xenografted tumors were initiated by inoculating 5 x 10(5) cells into the gastrocnemius muscle of BALB/c nu/nu mice. The tumors were characterized with respect to histological appearance, fraction of necrotic tissue (NF), pimonidazole hypoxic fraction (HF(Pim)), interstitial fluid pressure (IFP), extracellular pH (pH(e)), metastatic propensity, and radiation sensitivity.

RESULTS

The xenografted tumors reflected the donor patients' tumors in histological appearance, metastatic propensity, and radiation sensitivity and showed significant intertumor heterogeneity in growth rate, NF, HF(Pim), IFP, and pH(e).

CONCLUSIONS

CK-160 and TS-415 xenografts possess properties making them relevant models for studies of the physiological microenvironment of cervical carcinoma and its influence on metastatic dissemination and response to treatment.