Curvature-mediated rapid extravasation and penetration of nanoparticles against interstitial fluid pressure for improved drug delivery.

Elevated interstitial fluid pressure (IFP) within pathological tissues (e.g., tumors, obstructed kidneys, and cirrhotic livers) creates a significant hindrance to the transport of nanomedicine, ultimately impairing the therapeutic efficiency. Among these tissues, solid tumors present the most challenging scenario. While several strategies through reducing tumor IFP have been devised to enhance nanoparticle delivery, few approaches focus on modulating the intrinsic properties of nanoparticles to effectively counteract IFP during extravasation and penetration, which are precisely the stages obstructed by elevated IFP. Herein, we propose an innovative solution by engineering nanoparticles with a fusiform shape of high curvature, enabling efficient surmounting of IFP barriers during extravasation and penetration within tumor tissues. Through experimental and theoretical analyses, we demonstrate that the elongated nanoparticles with the highest mean curvature outperform spherical and rod-shaped counterparts against elevated IFP, leading to superior intratumoral accumulation and antitumor efficacy. Super-resolution microscopy and molecular dynamics simulations uncover the underlying mechanisms in which the high curvature contributes to diminished drag force in surmounting high-pressure differentials during extravasation. Simultaneously, the facilitated rotational movement augments the hopping frequency during penetration. This study effectively addresses the limitations posed by high-pressure impediments, uncovers the mutual interactions between the physical properties of NPs and their environment, and presents a promising avenue for advancing cancer treatment through nanomedicine.

Lymphangiogenesis guidance by paracrine and pericellular factors.

Lymphatic vessels are important for tissue fluid homeostasis, lipid absorption, and immune cell trafficking and are involved in the pathogenesis of several human diseases. The mechanisms by which the lymphatic vasculature network is formed, remodeled, and adapted to physiological and pathological challenges are controlled by an intricate balance of growth factor and biomechanical cues. These transduce signals for the readjustment of gene expression and lymphatic endothelial migration, proliferation, and differentiation. In this review, we describe several of these cues and how they are integrated for the generation of functional lymphatic vessel networks.

Design of in vitro biomimetic experimental system and simulation analysis for transvascular transport of nano-preparation.

Recently, the enhanced penetration and retention (EPR) effect of nano-preparations has been questioned. Whether the vascular endothelial cell gap (VECG) is the main transport pathway of nano-preparations has become a hot issue at present. Therefore, we propose an in vitro biomimetic experimental system that demonstrates the transvascular transport of nano-preparation. Based on the tumor growth process, the experimental system was used to simulate the change process of abnormal factors (vascular endothelial cell gap and interstitial fluid pressure (IFP)) in the tumor microenvironment. The influence of change in the abnormal factors on the enhanced penetration and retention effect of nano-preparation was explored, and simulation verification was performed. The results show that when the interstitial fluid pressure is close to the vascular fluid pressure (VFP), the transport of nano-preparation is obstructed, resulting in the disappearance of enhanced penetration and retention effect of the nano-preparation. This indicates that the pressure gradient between vascular fluid pressure and interstitial fluid pressure determines whether the enhanced penetration and retention effect of nano-preparations can exist.

Achieving deep intratumoral penetration and multimodal combined therapy for tumor through algal photosynthesis.

BACKGROUND: Elevated interstitial fluid pressure within tumors, resulting from impaired lymphatic drainage, constitutes a critical barrier to effective drug penetration and therapeutic outcomes. RESULTS: In this study, based on the photosynthetic characteristics of algae, an active drug carrier (CP@ICG) derived from Chlorella pyrenoidosa (CP) was designed and constructed. Leveraging the hypoxia tropism and phototropism exhibited by CP, we achieved targeted transport of the carrier to tumor sites. Additionally, dual near-infrared (NIR) irradiation at the tumor site facilitated photosynthesis in CP, enabling the breakdown of excessive intratumoral interstitial fluid by generating oxygen from water decomposition. This process effectively reduced the interstitial pressure, thereby promoting enhanced perfusion of blood into the tumor, significantly improving deep-seated penetration of chemotherapeutic agents, and alleviating tumor hypoxia. CONCLUSIONS: CP@ICG demonstrated a combined effect of photothermal/photodynamic/starvation therapy, exhibiting excellent in vitro/in vivo anti-tumor efficacy and favorable biocompatibility. This work provides a scientific foundation for the application of microbial-enhanced intratumoral drug delivery and tumor therapy.

Characterization of Microvascular Invasion in Hepatocellular Carcinoma Using Computational Modeling of Interstitial Fluid Pressure and Velocity.

BACKGROUND: Most solid tumors show increased interstitial fluid pressure (IFP), and this increased IFP is an obstacle to treatment. A noninvasive model for measuring IFP in hepatocellular carcinoma (HCC) is an unresolved issue. PURPOSE: To develop a noninvasive model to measure IFP and interstitial fluid velocity (IFV) in HCC and to characterize the microvascular invasion (MVI) status by using this model. STUDY TYPE: Retrospective. POPULATION: A total of 97 HCC patients (mean age 57.6 ± 10.9 years, 77.3% males), 53 of them with MVI and 44 of them without MVI. FIELD STRENGTH/SEQUENCE: A 3-T, three-dimensional spoiled gradient-recalled echo. ASSESSMENT: MVI was defined as microscopic vascular invasion of small vessels within the peritumoral liver tissue. The volumes of interest (VOIs) were manually delineated and enclosed the tumor lesion and healthy liver parenchyma, respectively. The extended Tofts model (ETM) was used to estimate permeability parameters from all the VOIs. Subsequently, the continuity partial differential equation (PDE) was implemented and IFP and IFV were acquired. STATISTICAL TESTS: Wilcoxon signed-ranks tests, histogram analysis, Mann-Whitney U test, Fisher's exact test, least absolute shrinkage and selection operator (LASSO) logistic regression, receiver operating characteristic (ROC) curve analysis with the area under the curve (AUC), Youden index, DeLong test, and Benjamini-Hochberg correction. A P value <0.05 was considered statistically significant. RESULTS: The HCC lesions exhibited elevated IFP and reduced IFV. There were no significant differences in any measured demographic and clinical features between the MVI-positive and MVI-negative groups, except for tumor size. Nine IFP histogram analysis-derived parameters and seven IFV histogram analysis-derived parameters could be used to characterize the MVI status. LASSO regression selected five features: IFP maximum, IFP 10th percentile, IFP 90th percentile, IFV SD, and IFV 10th percentile. The combination of these features showed the highest AUC (0.781) and specificity (77.3%). DATA CONCLUSION: A noninvasive IFP and IFV measurement model for HCC was developed. Specific IFP- and IFV-derived parameters exhibited significant association with the MVI status. EVIDENCE LEVEL: 3. TECHNICAL EFFICACY: Stage 2.

Thermal therapy induced fluid pressure and stress reductions in a solid tumor.

This paper presents an investigation on the interstitial fluid pressure and stress reductions in a vascularized solid tumor using a thermal therapy approach. The solid tumor is modeled as a fluid infiltrated poroelastic medium with a pressure source subjected to spatial heating. The distributions of temperature, interstitial fluid pressure, strains and stresses in a spherical tumor are obtained using a thermoporoelasticity theory in which the extracellular solid matrix and the interstitial fluid have different coefficient of thermal expansion (CTE). The numerical results for a solid tumor subjected to uniform spatial heating indicate that the CTE of the solid matrix of the tumor plays a crucial role in the reductions in the fluid pressure and effective stresses caused by the thermal therapy. The pore pressure and effective stresses are reduced when the CTE of the solid matrix is higher than that of the interstitial fluid. The reductions in fluid pressure and stresses may become significant depending on the difference between the CTEs of the solid matrix and interstitial fluid. The reductions reach the maximum at the tumor center and decrease with increasing radial distance from the tumor center. Finally, the thermally induced fluid flow is directed from the surface towards the center thereby potentially improving the microcirculation in the solid tumor.

Macro-scale models for fluid flow in tumour tissues: impact of microstructure properties.

Understanding the dynamics underlying fluid transport in tumour tissues is of fundamental importance to assess processes of drug delivery. Here, we analyse the impact of the tumour microscopic properties on the macroscopic dynamics of vascular and interstitial fluid flow. More precisely, we investigate the impact of the capillary wall permeability and the hydraulic conductivity of the interstitium on the macroscopic model arising from formal asymptotic 2-scale techniques. The homogenization technique allows us to derive two macroscale tissue models of fluid flow that take into account the microscopic structure of the vessels and the interstitial tissue. Different regimes were derived according to the magnitude of the vessel wall permeability and the interstitial hydraulic conductivity. Importantly, we provide an analysis of the properties of the models and show the link between them. Numerical simulations were eventually performed to test the models and to investigate the impact of the microstructure on the fluid transport. Future applications of our models include their calibration with real imaging data to investigate the impact of the tumour microenvironment on drug delivery.

Imaging acute effects of bevacizumab on tumor vascular kinetics in a preclinical orthotopic model of U251 glioma.

The effect of a human vascular endothelial growth factor antibody on the vasculature of human tumor grown in rat brain was studied. Using dynamic contrast-enhanced magnetic resonance imaging, the effects of intravenous bevacizumab (Avastin; 10 mg/kg) were examined before and at postadministration times of 1, 2, 4, 8, 12 and 24 h (N = 26; 4-5 per time point) in a rat model of orthotopic, U251 glioblastoma (GBM). The commonly estimated vascular parameters for an MR contrast agent were: (i) plasma distribution volume (vp ), (ii) forward volumetric transfer constant (Ktrans ) and (iii) reverse transfer constant (kep ). In addition, extracellular distribution volume (VD ) was estimated in the tumor (VD-tumor ), tumor edge (VD-edge ) and the mostly normal tumor periphery (VD-peri ), along with tumor blood flow (TBF), peri-tumoral hydraulic conductivity (K) and interstitial flow (Flux) and tumor interstitial fluid pressure (TIFP). Studied as % changes from baseline, the 2-h post-treatment time point began showing significant decreases in vp , VD-tumor, VD-edge and VD-peri , as well as K, with these changes persisting at 4 and 8 h in vp , K, VD-tumor, -edge and -peri (t-tests; p < 0.05-0.01). Decreases in Ktrans were observed at the 2- and 4-h time points (p < 0.05), while interstitial volume fraction (ve ; = Ktrans /kep ) showed a significant decrease only at the 2-h time point (p < 0.05). Sustained decreases in Flux were observed from 2 to 24 h (p < 0.01) while TBF and TIFP showed delayed responses, increases in the former at 12 and 24 h and a decrease in the latter only at 12 h. These imaging biomarkers of tumor vascular kinetics describe the short-term temporal changes in physical spaces and fluid flows in a model of GBM after Avastin administration.

Oscillatory interstitial fluid pressure and velocity in a solid tumor with partial surface fluid leakage.

This work investigates the interstitial fluid flow characteristics in a solid tumor with partial fluid leakage at the tumor surface subjected to oscillatory microvascular pressure. Solutions of the pore fluid pressure and velocity in a spherical tumor are obtained using the poroelasticity theory for small strains. It is found that partial fluid leakage at the tumor surface reduces the pore pressure drop and decreases the fluid velocity near the surface compared with those in a tumor with a fully leaking surface. Both the pore pressure and the fluid velocity decrease dramatically with an increase in the vascular frequency. The pore pressure at a vascular frequency of 1 Hz is two orders of magnitude smaller than the amplitude of the vascular pressure, and the fluid velocity at the same frequency is one order of magnitude smaller than that produced by the steady constant vascular pressure. The pore pressure amplitude may reach that of the vascular pressure under the steady state vascular pressure condition.

Morphology/Interstitial Fluid Pressure-Tunable Nanopomegranate Designed by Alteration of Membrane Fluidity under Tumor Enzyme and PEGylation.

Up to now, insufficient drug accumulation in tumor remains a major challenge for nanochemotherapy. However, the spherical nanocarriers with large diameter, which are beneficial for blood circulation and tumor extravasation, cannot travel deep in a tumor. Additionally, high tumor interstitial fluid pressure (IFP) in the tumor microenvironment may promote the efflux of the penetrable nanodrugs. Therefore, the size and shape of nanocarriers as well as the tumoral IFP can be regulated synchronously for improved tumor penetration and combined chemotherapy. Herein, a novel dual-functional polymer-polypeptide (Biotin-PEG2000-GKGPRQITITK) for both verified tumor targeting and responsiveness was synthesized to construct the "peel" of nanopomegranate-like nanovectors (DI-MPL), in which docetaxel-loaded micelles was encapsulated as "seeds". Interestingly, DI-MPL was endowed multi-abilities of tunable size/shape switch and controlled release of IFP alleviator imatinib (IM), which were developed with one and the same strategy-alteration of membrane fluidity under the cleavage of polymer-polypeptide and PEGylation. As a result, the peel of DI-MPL could turn into small pieces with the seed scattered out in response to matrix metalloproteinase-9 (MMP-9), making nanopomegranate (180 nm) switch into spheres/disks (40 nm), during which IM is released to reduce IFP synchronously. With prominent tumor penetration ability in both multicellular tumor spheroids (MCTS) and tumor tissue, DI-MPL exhibited optimal inhibition of MCTS growth and the enhanced chemotherapy in comparison to other preparations. Meanwhile, the improved penetrability of DI-MPL in tumor tissue was found to be related to the reduced IFP, which is achieved via inhibiting expression of phosphorylated platelet-derived growth factor receptor-ß (p-PDGFR-ß) by IM. Altogether, the bilateral adjusting strategies from nanocarrier size/shape and tumoral IFP with a single enzyme-responsive material could provide a potential combined chemotherapy to improve tumor penetration.

In silico investigations of intratumoral heterogeneous interstitial fluid pressure.

Recent preclinical studies have shown that interstitial fluid pressure (IFP) within tumors can be heterogeneous Andersen et al. (2019). In that study tumors of two xenograft models, respectively, HL-16 cervical carcinoma and Panc-1 pancreatic carcinoma, were investigated. Significant heterogeneity in IFP was reported and it was proposed that this was associated with division of tissue into compartments separated by thick connective tissue bands for the HL-16 tumors and with dense collagen-rich extracellular matrix for the Panc-1 tumors. The purpose of the current work is to explore these experimental observations by using in silico generated tumor models. We consider a mathematical multiphase model which accounts for tumor cells, fibroblasts and interstitial fluid. The model has been trained to comply with experimental in vitro results reported in Shieh et al. (2011) which has identified autologous chemotaxis, ECM remodeling, and cell-fibroblast interaction as drivers for invasive tumor cell behavior. The in silico model is informed with parameters that characterize the leaky intratumoral vascular network, the peritumoral lymphatics which collect the fluid, and the density of ECM as represented through the hydraulic conductivity of the interstitial space. Heterogeneous distribution of solid stress may result in heterogeneous compression of blood vessels and, thus, heterogeneous vascular density inside the tumor. To mimic this we expose the in silico tumor to an intratumoral vasculature whose net effect of density of blood vesssels and vessel wall conductivity is varied through a 2D Gaussian variogram constrained such that the resulting IFPs lie within the range as reported from the preclinical study. The in silico cervical carcinoma model illustrates that sparse ECM was associated with uniform intratumoral IFP in spite of heterogeneous microvascular network, whereas compartment structures resulted in more heterogeneous IFP. Similarly, the in silico pancreatic model shows that heterogeneity in the microvascular network combined with dense ECM structure prevents IFP to even out and gives rise to heterogeneous IFP. The computer model illustrates how a heterogeneous invasive front might form where groups of tumor cells detach from the primary tumor and form isolated islands, a behavior which is natural to associate with metastatic propensity. However, unlike experimental studies, the current version of the in silico model does not show an association between metastatic propensity and elevated IFP.

Fluid transport from the dental pulp revisited.

In the dental pulp surrounded by rigid dentinal walls, an increase in fluid volume will be followed by a rapid increase in interstitial fluid pressure. To maintain pressure homeostasis, a fluid drainage system is required. The dental pulp and apical periodontal ligament lack lymphatic vessels, and the questions are how the transport can take place inside the pulp and where the lymphatic vessels draining fluid from the apical periodontal ligament are located. The drainage of fluid within the pulp must be governed by a tissue pressure gradient (driving pressure) and the fluid is likely transported in loose connective tissue (gaps) surrounding vessels and nerve fibers. We suggest that aging of the pulp tissue characterized by fibrosis will reduce the draining capacity and make it more vulnerable to circulatory failure. When the fluid leaves the pulp, it will follow the nerve bundles and vessels through the periapical ligament into bone channels, where lymphatic vessels are found. In the mandibular canal, lymphatic vessels are localized and the fluid washout rate from the canal is slow, but chewing may speed it up by increasing the fluid pressure. In acute apical periodontitis, inflammatory mediators and bacterial components can be spread to regional lymph nodes via lymphatic vessels inside the jaw bone.

Stromal integrin α11-deficiency reduces interstitial fluid pressure and perturbs collagen structure in triple-negative breast xenograft tumors.

BACKGROUND: Cancer progression is influenced by a pro-tumorigenic microenvironment. The aberrant tumor stroma with increased collagen deposition, contractile fibroblasts and dysfunctional vessels has a major impact on the interstitial fluid pressure (PIF) in most solid tumors. An increased tumor PIF is a barrier to the transport of interstitial fluid into and within the tumor. Therefore, understanding the mechanisms that regulate pressure homeostasis can lead to new insight into breast tumor progression, invasion and response to therapy. The collagen binding integrin α11ß1 is upregulated during myofibroblast differentiation and expressed on fibroblasts in the tumor stroma. As a collagen organizer and a probable link between contractile fibroblasts and the complex collagen network in tumors, integrin α11ß1 could be a potential regulator of tumor PIF. METHODS: We investigated the effect of stromal integrin α11-deficiency on pressure homeostasis, collagen organization and tumor growth using orthotopic and ectopic triple-negative breast cancer xenografts (MDA-MB-231 and MDA-MB-468) in wild type and integrin α11-deficient mice. PIF was measured by the wick-in-needle technique, collagen by Picrosirius Red staining and electron microscopy, and uptake of radioactively labeled 5FU by microdialysis. Further, PIF in heterospheroids composed of MDA-MB-231 cells and wild type or integrin α11-deficient fibroblasts was measured by micropuncture. RESULTS: Stromal integrin α11-deficiency decreased PIF in both the orthotopic breast cancer models. A concomitant perturbed collagen structure was seen, with fewer aligned and thinner fibrils. Integrin α11-deficiency also impeded MDA-MB-231 breast tumor growth, but no effect was observed on drug uptake. No effects were seen in the ectopic model. By investigating the isolated effect of integrin α11-positive fibroblasts on MDA-MB-231 cells in vitro, we provide evidence that PIF regulation was mediated by integrin α11-positive fibroblasts. CONCLUSION: We hereby show the importance of integrin α11ß1 in pressure homeostasis in triple-negative breast tumors, indicating a new role for integrin α11ß1 in the tumor microenvironment. Our data suggest that integrin α11ß1 has a pro-tumorigenic effect on triple-negative breast cancer growth in vivo. The significance of the local microenvironment is shown by the different effects of integrin α11ß1 in the orthotopic and ectopic models, underlining the importance of choosing an appropriate preclinical model.

Activated Fibroblast Program Orchestrates Tumor Initiation and Progression; Molecular Mechanisms and the Associated Therapeutic Strategies.

: Neoplastic epithelial cells coexist in carcinomas with various non-neoplastic stromal cells, together creating the tumor microenvironment. There is a growing interest in the cross-talk between tumor cells and stromal fibroblasts referred to as carcinoma-associated fibroblasts (CAFs), which are frequently present in human carcinomas. CAF populations extracted from different human carcinomas have been shown to possess the ability to influence the hallmarks of cancer. Indeed, several mechanisms underlying CAF-promoted tumorigenesis are elucidated. Activated fibroblasts in CAFs are characterized as alpha-smooth muscle actin-positive myofibroblasts and actin-negative fibroblasts, both of which are competent to support tumor growth and progression. There are, however, heterogeneous CAF populations presumably due to the diverse sources of their progenitors in the tumor-associated stroma. Thus, molecular markers allowing identification of bona fide CAF populations with tumor-promoting traits remain under investigation. CAFs and myofibroblasts in wound healing and fibrosis share biological properties and support epithelial cell growth, not only by remodeling the extracellular matrix, but also by producing numerous growth factors and inflammatory cytokines. Notably, accumulating evidence strongly suggests that anti-fibrosis agents suppress tumor development and progression. In this review, we highlight important tumor-promoting roles of CAFs based on their analogies with wound-derived myofibroblasts and discuss the potential therapeutic strategy targeting CAFs.

Toward a noninvasive estimate of interstitial fluid pressure by dynamic contrast-enhanced MRI in a rat model of cerebral tumor.

PURPOSE: This study demonstrates a DCE-MRI estimate of tumor interstitial fluid pressure (TIFP) and hydraulic conductivity in a rat model of glioblastoma, with validation against an invasive wick-in-needle (WIN) technique. An elevated TIFP is considered a mark of aggressiveness, and a decreased TIFP a predictor of response to therapy. METHODS: The DCE-MRI studies were conducted in 36 athymic rats (controls and posttreatment animals) with implanted U251 cerebral tumors, and with TIFP measured using a WIN method. Using a model selection paradigm and a novel application of Patlak and Logan plots to DCE-MRI data, the MRI parameters required for estimating TIFP noninvasively were estimated. Two models, a fluid-mechanical model and a multivariate empirical model, were used for estimating TIFP, as verified against WIN-TIFP. RESULTS: Using DCE-MRI, the mean estimated hydraulic conductivity (MRI-K) in U251 tumors was (2.3 ± 3.1) × 10-5 (mm2 /mmHg-s) in control studies. Significant positive correlations were found between WIN-TIFP and MRI-TIFP in both mechanical and empirical models. For instance, in the control group of the fluid-mechanical model, MRI-TIFP was a strong predictor of WIN-TIFP (R2 = 0.76, p < .0001). A similar result was found in the bevacizumab-treated group of the empirical model (R2 = 0.93, p = .014). CONCLUSION: This research suggests that MRI dynamic studies contain enough information to noninvasively estimate TIFP in this, and possibly other, tumor models, and thus might be used to assess tumor aggressiveness and response to therapy.

Digesting a Path Forward: The Utility of Collagenase Tumor Treatment for Improved Drug Delivery.

Collagen and hyaluronan are the most abundant components of the extracellular matrix (ECM) and their overexpression in tumors is linked to increased tumor growth and metastasis. These ECM components contribute to a protective tumor microenvironment by supporting a high interstitial fluid pressure and creating a tortuous setting for the convection and diffusion of chemotherapeutic small molecules, antibodies, and nanoparticles in the tumor interstitial space. This review focuses on the research efforts to deplete extracellular collagen with collagenases to normalize the tumor microenvironment. Although collagen synthesis inhibitors are in clinical development, the use of collagenases is contentious and clinically untested in cancer patients. Pretreatment of murine tumors with collagenases increased drug uptake and diffusion 2-10-fold. This modest improvement resulted in decreased tumor growth, but the benefits of collagenase treatment are confounded by risks of toxicity from collagen breakdown in healthy tissues. In this review, we evaluate the published in vitro and in vivo benefits and limitations of collagenase treatment to improve drug delivery.

A Poroelasticity Theory Approach to Study the Mechanisms Leading to Elevated Interstitial Fluid Pressure in Solid Tumours.

Although the mechanisms responsible for elevated interstitial fluid pressure (IFP) in tumours remain obscure, it seems clear that high IFP represents a barrier to drug delivery (since the resulting adverse pressure gradient implies a reduction in the driving force for transvascular exchange of both fluid and macromolecules). R. Jain and co-workers studied this problem, and although the conclusions drawn from their idealized mathematical models offered useful insights into the causes of elevated IFP, they by no means gave a definitive explanation for this phenomenon. In this paper, we use poroelasticity theory to also develop a macroscopic mathematical model to describe the time evolution of a solid tumour, but focus our attention on the mechanisms responsible for the rise of the IFP, from that for a healthy interstitium to that measured in malignant tumours. In particular, we discuss a number of possible time scales suggested by our mathematical model and propose a tumour-dependent time scale that leads to results in agreement with experimental observations. We apply our mathematical model to simulate the effect of "vascular normalization" (as proposed by Jain in Nat Med 7:987-989, 2001) on the IFP profile and discuss and contrast our conclusions with those of previous work in the literature.

A Continuum Mechanics Model of Enzyme-Based Tissue Degradation in Cancer Therapies.

We propose a mathematical model to describe enzyme-based tissue degradation in cancer therapies. The proposed model combines the poroelastic theory of mixtures with the transport of enzymes or drugs in the extracellular space. The effect of the matrix-degrading enzymes on the tissue composition and its mechanical response are accounted for. Numerical simulations in 1D, 2D and axisymmetric (3D) configurations show how an injection of matrix-degrading enzymes alters the porosity of a biological tissue. We eventually exhibit numerically the main consequences of a matrix-degrading enzyme pretreatment in the framework of chemotherapy: the removal of the diffusive hindrance to the penetration of therapeutic molecules in tumors and the reduction of interstitial fluid pressure which improves transcapillary transport. Both effects are consistent with previous biological observations.

Imatinib increases oxygen delivery in extracellular matrix-rich but not in matrix-poor experimental carcinoma.

BACKGROUND: Imatinib causes increased turnover of stromal collagen, reduces collagen fibril diameter, enhances extracellular fluid turnover and lowers interstitial fluid pressure (IFP) in the human colonic carcinoma KAT-4/HT-29 (KAT-4) xenograft model. METHODS: We compared the effects of imatinib on oxygen levels, vascular morphology and IFP in three experimental tumor models differing in their content of a collagenous extracellular matrix. RESULTS: Neither the KAT4 and CT-26 colonic carcinoma models, nor B16BB melanoma expressed PDGF ß-receptors in the malignant cells. KAT-4 tumors exhibited a well-developed ECM in contrast to the other two model systems. The collagen content was substantially higher in KAT-4 than in CT-26, while collagen was not detectable in B16BB tumors. The pO2 was on average 5.4, 13.9 and 19.3 mmHg in KAT-4, CT-26 and B16BB tumors, respectively. Treatment with imatinib resulted in similar pO2-levels in all three tumor models but only in KAT-4 tumors did the increase reach statistical significance. It is likely that after imatinib treatment the increase in pO2 in KAT-4 tumors is caused by increased blood flow due to reduced vascular resistance. This notion is supported by the significant reduction observed in IFP in KAT-4 tumors after imatinib treatment. Vessel area varied between 4.5 and 7% in the three tumor models and was not affected by imatinib treatment. Imatinib had no effect on the fraction of proliferating cells, whereas the fraction of apoptotic cells increased to a similar degree in all three tumor models. CONCLUSION: Our data suggest that the effects of imatinib on pO2-levels depend on a well-developed ECM and provide further support to the suggestion that imatinib acts by causing interstitial stroma cells to produce a less dense ECM, which would in turn allow for an increased blood flow. The potential of imatinib treatment to render solid tumors more accessible to conventional treatments would therefore depend on the degree of tumor desmoplasia.

Metastatic pathway and the microvascular and physicochemical microenvironments of human melanoma xenografts.

BACKGROUND: Malignant melanoma of the skin can metastasize through blood vessels and lymphatics. The primary tumor develops a vascular microenvironment characterized by abnormal blood vessels and lymphatics and a physicochemical microenvironment characterized by low oxygen tension, regions with hypoxic tissue, and high interstitial fluid pressure (IFP). This study aimed at identifying relationships between the metastatic route of melanomas and characteristic features of the microvascular and physicochemical microenvironments of the primary tumor. METHODS: Two patient-derived xenograft (PDX) models (E-13, N-15) and four cell line-derived xenografts (CDX) models (C-10, D-12, R-18, T-22) of human melanoma were included in the study. Tumors were transplanted to an orthotopic site in BALB/c-nu/nu mice, and when the tumors had grown to a volume of 500-600 mm3, the IFP of the primary tumor was measured and the hypoxia marker pimonidazole was administered before the host mouse was euthanized. The primary tumor, lungs, and six pairs of lymph nodes were evaluated by examining hematoxylin/eosin-stained and immunostained histological preparations. The expression of angiogenesis-related genes was assessed by quantitative PCR. RESULTS: C-10, D-12, and E-13 tumors disseminated primarily by the hematogenous route and developed pulmonary metastases. These tumors showed high angiogenic activity and high expression of the F3 gene as well as ANGPT2 and TIE1, genes encoding proteins of the angiopoietin-tie system. N-15, R-18, and T-22 tumors disseminated mainly by the lymphogenous route and developed metastases in draining lymph nodes. These tumors had highly elevated IFP and showed high expression of NRP2, a gene encoding neuropilin-2. CONCLUSION: The primary metastatic route of orthotopic human melanoma xenografts and the development of lung and lymph node metastases are influenced significantly by the microvascular and physicochemical microenvironments of the primary tumor.