Lowering of tumoral interstitial fluid pressure by prostaglandin E(1) is paralleled by an increased uptake of (51)Cr-EDTA

Integrated in silico and 3D in vitro model of macrophage migration in response to physical and chemical factors in the tumor microenvironment

Macrophages are abundant in the tumor microenvironment (TME), serving as accomplices to cancer cells for their invasion. Studies have explored the biochemical mechanisms that drive pro-tumor macrophage functions; however the role of TME interstitial flow (IF) is often disregarded. Therefore, we developed a three-dimensional microfluidic-based model with tumor cells and macrophages to study how IF affects macrophage migration and its potential contribution to cancer invasion. The presence of either tumor cells or IF individually increased macrophage migration directedness and speed. Interestingly, there was no additive effect on macrophage migration directedness and speed under the simultaneous presence of tumor cells and IF. Further, we present an in silico model that couples chemokine-mediated signaling with mechanosensing networks to explain our in vitro observations. In our model design, we propose IL-8, CCL2, and β-integrin as key pathways that commonly regulate various Rho GTPases. In agreement, in vitro macrophage migration remained elevated when exposed to a saturating concentration of recombinant IL-8 or CCL2 or to the co-addition of a sub-saturating concentration of both cytokines. Moreover, antibody blockade against IL-8 and/or CCL2 inhibited migration that could be restored by IF, indicating cytokine-independent mechanisms of migration induction. Importantly, we demonstrate the utility of an integrated in silico and 3D in vitro approach to aid the design of tumor-associated macrophage-based immunotherapeutic strategies.

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 α11β1 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 α11β1 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 α11β1 in pressure homeostasis in triple-negative breast tumors, indicating a new role for integrin α11β1 in the tumor microenvironment. Our data suggest that integrin α11β1 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 α11β1 in the orthotopic and ectopic models, underlining the importance of choosing an appropriate preclinical model.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5449-z) contains supplementary material, which is available to authorized users.

Inhibition of integrin αVβ6 changes fibril thickness of stromal collagen in experimental carcinomas

Background

Chemotherapeutic efficacy can be improved by targeting the structure and function of the extracellular matrix (ECM) in the carcinomal stroma. This can be accomplished by e.g. inhibiting TGF-β1 and -β3 or treating with Imatinib, which results in scarcer collagen fibril structure in xenografted human KAT-4/HT29 (KAT-4) colon adenocarcinoma.

Methods

The potential role of α_Vβ₆ integrin-mediated activation of latent TGF-β was studied in cultured KAT-4 and Capan-2 human ductal pancreatic carcinoma cells as well as in xenograft carcinoma generated by these cells. The monoclonal α_Vβ₆ integrin-specific monoclonal antibody 3G9 was used to inhibit the α_Vβ₆ integrin activity.

Results

Both KAT-4 and Capan-2 cells expressed the α_Vβ₆ integrin but only KAT-4 cells could utilize this integrin to activate latent TGF-β in vitro. Only when Capan-2 cells were co-cultured with human F99 fibroblasts was the integrin activation mechanism triggered, suggesting a more complex, fibroblast-dependent, activation pathway. In nude mice, a 10-day treatment with 3G9 reduced collagen fibril thickness and interstitial fluid pressure in KAT-4 but not in the more desmoplastic Capan-2 tumors that, to achieve a similar effect, required a prolonged 3G9 treatment. In contrast, a 10-day direct inhibition of TGF-β1 and -β3 reduced collagen fibril thickness in both tumor models.

Conclusion

Our data demonstrate that the α_Vβ₆-directed activation of latent TGF-β plays a pivotal role in modulating the stromal collagen network in carcinoma, but that the sensitivity to α_Vβ₆ inhibition depends on the simultaneous presence of alternative paths for latent TGF-β activation and the extent of desmoplasia.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0249-7) contains supplementary material, which is available to authorized users.

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 β-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.

Recapitulation of complex transport and action of drugs at the tumor microenvironment using tumor-microenvironment-on-chip

Targeted delivery aims to selectively distribute drugs to targeted tumor tissues but not to healthy tissues. This can address many clinical challenges by maximizing the efficacy but minimizing the toxicity of anti-cancer drugs. However, a complex tumor microenvironment poses various barriers hindering the transport of drugs and drug delivery systems. New tumor models that allow for the systematic study of these complex environments are highly desired to provide reliable test beds to develop drug delivery systems for targeted delivery. Recently, research efforts have yielded new in vitro tumor models, the so called tumor-microenvironment-on-chip, that recapitulate certain characteristics of the tumor microenvironment. These new models show benefits over other conventional tumor models, and have the potential to accelerate drug discovery and enable precision medicine. However, further research is warranted to overcome their limitations and to properly interpret the data obtained from these models. In this article, key features of the in vivo tumor microenvironment that are relevant to drug transport processes for targeted delivery were discussed, and the current status and challenges for developing in vitro transport model systems were reviewed.

Targeting tumor microenvironment: crossing tumor interstitial fluid by multifunctional nanomedicines

Introduction: The genesis of cancer appears to be a complex matter, which is not simply based upon few genetic abnormalities/alteration. In fact, irregular microvasculature and aberrant interstitium of solid tumors impose significant pathophysiologic barrier functions against cancer treatment modalities, hence novel strategies should holistically target bioelements of tumor microenvironment (TME). In this study, we provide some overview and insights on TME and important strategies used to control the impacts of such pathophysiologic barriers.

Methods: We reviewed all relevant literature for the impacts of tumor interstitium and microvasculature within the TME as well as the significance of the implemented strategies.

Results: While tumorigenesis initiation seems to be in close relation with an emergence of hypoxia and alterations in epigenetic/genetic materials, large panoplies of molecular events emerge as intricate networks during oncogenesis to form unique lenient TME in favor of tumor progression. Within such irregular interstitium, immune system displays defective surveillance functionalities against malignant cells. Solid tumors show multifacial traits with coadaptation and self-regulation potentials, which bestow profound resistance against the currently used conventional chemotherapy and immunotherapy agents that target solely one face of the disease.

Conclusion: The cancerous cells attain unique abilities to form its permissive microenvironment, wherein (a) extracellular pH is dysregulated towards acidification, (b) extracellular matrix (ECM) is deformed, (c) stromal cells are cooperative with cancer cells, (d) immune system mechanisms are defective, (e) non-integrated irregular microvasculature with pores (120-1200 nm) are formed, and (h) interstitial fluid pressure is high. All these phenomena are against cancer treatment modalities. As a result, to control such abnormal pathophysiologic traits, novel cancer therapy strategies need to be devised using multifunctional nanomedicines and theranostics.

Analysis on the current status of targeted drug delivery to tumors

Targeted drug delivery to tumor sites is one of the ultimate goals in drug delivery. Recent progress in nanoparticle engineering has certainly improved drug targeting, but the results are not as good as expected. This is largely due to the fact that nanoparticles, regardless of how advanced they are, find the target as a result of blood circulation, like the conventional drug delivery systems do. Currently, the nanoparticle-based drug delivery to the target tumor tissues is based on wrong assumptions that most of the nanoparticles, either PEGylated or not, reach the target by the enhanced permeation and retention (EPR) effect. Studies have shown that so-called targeting moieties, i.e., antibodies or ligands, on the nanoparticle surface do not really improve delivery to target tumors. Targeted drug delivery to tumor sites is associated with highly complex biological, mechanical, chemical and transport phenomena, of which characteristics vary spatiotemporally. Yet, most of the efforts have been focused on design and surface manipulation of the drug carrying nanoparticles with relatively little attention to other aspects. This article examines the current misunderstandings and the main difficulties in targeted drug delivery.

Interstitial Fluid and Lymph Formation and Transport: Physiological Regulation and Roles in Inflammation and Cancer

The interstitium describes the fluid, proteins, solutes, and the extracellular matrix (ECM) that comprise the cellular microenvironment in tissues. Its alterations are fundamental to changes in cell function in inflammation, pathogenesis, and cancer. Interstitial fluid (IF) is created by transcapillary filtration and cleared by lymphatic vessels. Herein we discuss the biophysical, biomechanical, and functional implications of IF in normal and pathological tissue states from both fluid balance and cell function perspectives. We also discuss analysis methods to access IF, which enables quantification of the cellular microenvironment; such methods have demonstrated, for example, that there can be dramatic gradients from tissue to plasma during inflammation and that tumor IF is hypoxic and acidic compared with subcutaneous IF and plasma. Accumulated recent data show that IF and its convection through the interstitium and delivery to the lymph nodes have many and diverse biological effects, including in ECM reorganization, cell migration, and capillary morphogenesis as well as in immunity and peripheral tolerance. This review integrates the biophysical, biomechanical, and biological aspects of interstitial and lymph fluid and its transport in tissue physiology, pathophysiology, and immune regulation.

Increased fibrosis and interstitial fluid pressure in two different types of syngeneic murine carcinoma grown in integrin β3-subunit deficient mice

Stroma properties affect carcinoma physiology and direct malignant cell development. Here we present data showing that α_Vβ₃ expressed by stromal cells is involved in the control of interstitial fluid pressure (IFP), extracellular volume (ECV) and collagen scaffold architecture in experimental murine carcinoma. IFP was elevated and ECV lowered in syngeneic CT26 colon and LM3 mammary carcinomas grown in integrin β₃-deficient compared to wild-type BALB/c mice. Integrin β₃-deficiency had no effect on carcinoma growth rate or on vascular morphology and function. Analyses by electron microscopy of carcinomas from integrin β₃-deficient mice revealed a coarser and denser collagen network compared to carcinomas in wild-type littermates. Collagen fibers were built from heterogeneous and thicker collagen fibrils in carcinomas from integrin β₃-deficient mice. The fibrotic extracellular matrix (ECM) did not correlate with increased macrophage infiltration in integrin β₃-deficient mice bearing CT26 tumors, indicating that the fibrotic phenotype was not mediated by increased inflammation. In conclusion, we report that integrin β₃-deficiency in tumor stroma led to an elevated IFP and lowered ECV that correlated with a more fibrotic ECM, underlining the role of the collagen network for carcinoma physiology.

How to improve exposure of tumor cells to drugs: promoter drugs increase tumor uptake and penetration of effector drugs

Solid tumors are characterized by an abnormal architecture and composition that limit the uptake and distribution of antitumor drugs. Over the last two decades, drugs have been identified that improve the tumor uptake and distribution of drugs that have direct antitumor effects. We propose to refer to these drugs as promoter drugs, and as effector drugs to drugs that have direct antitumor effects. Some promoter drugs have received regulatory approval, while others are in active clinical development. This review gives an overview of promoter drugs, by classifying them according to their mechanism of action: promoter drugs that modulate tumor blood flow, modify the barrier function of tumor vessels, induce tumor cell killing, and overcome stromal barriers. Eventually, we discuss those that we feel are the main conclusions to be drawn from promoter drug research that has been performed so far, and suggest areas of future investigation to improve the efficacy of promoter drugs in cancer therapy.

The peptide AF-16 decreases high interstitial fluid pressure in solid tumors

BACKGROUND

The high interstitial fluid pressure (IFP) in solid tumors restricts the access to nutrients, oxygen and drugs.

MATERIAL AND METHODS

We investigated the ability of the peptide AF-16, involved in water and ion transfer through cell membranes, to lower the IFP in two different solid rat mammary tumors, one chemically induced, slowly growing, and the other transplantable, and rapidly progressing having high cellularity. AF-16 was administered either in the tumor capsule, intranasally or intravenously. The IFP was measured by a miniature fiber optic device.

RESULTS

AF-16 significantly lowered the IFP in both the slowly and the rapidly progressing tumors, whether administrated locally or systemically. The AF-16 induced IFP reduction was maximal after 90 min, lasted at least 3 h, and returned to pretreatment levels in less than 24 h. Topical AF-16 transiently reduced the IFP in the DMBA tumors from 17.7 ± 4.2 mmHg to 8.6 ± 2.1 mmHg.

CONCLUSION

We conclude that AF-16 transiently and reversibly lowered the high IFP in solid tumors during a few hours, which might translate into improved therapeutic efficacy.

Intratumoral drug delivery with nanoparticulate carriers

Stiff extracellular matrix, elevated interstitial fluid pressure, and the affinity for the tumor cells in the peripheral region of a solid tumor mass have long been recognized as significant barriers to diffusion of small-molecular-weight drugs and antibodies. However, their impacts on nanoparticle-based drug delivery have begun to receive due attention only recently. This article reviews biological features of many solid tumors that influence transport of drugs and nanoparticles and properties of nanoparticles relevant to their intratumoral transport, studied in various tumor models. We also discuss several experimental approaches employed to date for enhancement of intratumoral nanoparticle penetration. The impact of nanoparticle distribution on the effectiveness of chemotherapy remains to be investigated and should be considered in the design of new nanoparticulate drug carriers.

Enzymatic depletion of tumor hyaluronan induces antitumor responses in preclinical animal models

Hyaluronan (HA) is a glycosaminoglycan polymer that often accumulates in malignancy. Megadalton complexes of HA with proteoglycans create a hydrated connective tissue matrix, which may play an important role in tumor stroma formation. Through its colloid osmotic effects, HA complexes contribute to tumor interstitial fluid pressure, limiting the effect of therapeutic molecules on malignant cells. The therapeutic potential of enzymatic remodeling of the tumor microenvironment through HA depletion was initially investigated using a recombinant human HA-degrading enzyme, rHuPH20, which removed HA-dependent tumor cell extracellular matrices in vitro. However, rHuPH20 showed a short serum half-life (t(1/2) < 3 minutes), making depletion of tumor HA in vivo impractical. A pegylated variant of rHuPH20, PEGPH20, was therefore evaluated. Pegylation improved serum half-life (t(1/2) = 10.3 hours), making it feasible to probe the effects of sustained HA depletion on tumor physiology. In high-HA prostate PC3 tumors, i.v. administration of PEGPH20 depleted tumor HA, decreased tumor interstitial fluid pressure by 84%, decreased water content by 7%, decompressed tumor vessels, and increased tumor vascular area >3-fold. Following repeat PEGPH20 administration, tumor growth was significantly inhibited (tumor growth inhibition, 70%). Furthermore, PEGPH20 enhanced both docetaxel and liposomal doxorubicin activity in PC3 tumors (P < 0.05) but did not significantly improve the activity of docetaxel in low-HA prostate DU145 tumors. The ability of PEGPH20 to enhance chemotherapy efficacy is likely due to increased drug perfusion combined with other tumor structural changes. These results support enzymatic remodeling of the tumor stroma with PEGPH20 to treat tumors characterized by the accumulation of HA.

Effects of freezing on intratumoral drug transport

Efficacy of many novel therapeutic agents are impaired by hindered interstitial diffusion in tumor. In the context of overcoming this drug delivery barrier, a hypothesis was postulated that freeze/thaw (F/T) may induce favorable changes of tumor tissue microstructure to facilitate the interstitial diffusion. This hypothesis may also be relevant to develop a mechanistically derived chemotherapeutic strategy for cryo-treated tumors. In the present study, this hypothesis was tested by characterizing the effects of F/T on the interstitial diffusion using an in vitro engineered tumor model (ET). The diffusion coefficients of FITC-labeled dextran was measured within the frozen/thawed and unfrozen ETs. The results showed that the diffusion coefficients increased after F/T but the extent of increase was dependent on the size of dextran. This implies that the combination of cryosurgery and chemotherapy should be designed considering the biophysical changes of tissues after freeze/thaw and the diffusion characteristics of drug molecules.

Combined anti-angiogenic therapy targeting PDGF and VEGF receptors lowers the interstitial fluid pressure in a murine experimental carcinoma

Elevation of the interstitial fluid pressure (IFP) of carcinoma is an obstacle in treatment of tumors by chemotherapy and correlates with poor drug uptake. Previous studies have shown that treatment with inhibitors of platelet-derived growth factor (PDGF) or vascular endothelial growth factor (VEGF) signaling lowers the IFP of tumors and improve chemotherapy. In this study, we investigated whether the combination of PDGFR and VEGFR inhibitors could further reduce the IFP of KAT-4 human carcinoma tumors. The tumor IFP was measured using the wick-in-needle technique. The combination of STI571 and PTK/ZK gave an additive effect on the lowering of the IFP of KAT-4 tumors, but the timing of the treatment was crucial. The lowering of IFP following combination therapy was accompanied by vascular remodeling and decreased vascular leakiness. The effects of the inhibitors on the therapeutic efficiency of Taxol were investigated. Whereas the anti-PDGF and anti-VEGF treatment did not significantly inhibit tumor growth, the inhibitors enhanced the effect of chemotherapy. Despite having an additive effect in decreasing tumor IFP, the combination therapy did not further enhance the effect of chemotherapy. Simultaneous targeting of VEGFR and PDGFR kinase activity may be a useful strategy to decrease tumor IFP, but the timing of the inhibitors should be carefully determined.

High‐dose, short‐term, anti‐inflammatory treatment with dexamethasone reduces growth and augments the effects of 5‐fluorouracil on dimethyl‐α‐benzanthracene‐induced mammary tumors in rats

OBJECTIVE

To evaluate the effects of dexamethasone (DXM) alone or in combination with 5-fluorouracil (5-FU) on dimethyl-alpha-benzanthracene (DMBA)-induced mammary tumors in rats.

MATERIAL AND METHODS

Female Sprague-Dawley rats were divided into 4 groups receiving: 1) saline (controls), 2) DXM (3 mg/kg), 3) 5-FU (1.5 mg/kg) and 4) DXM and 5-FU combined. The drugs were given i.p. every day for 4 days. Interstitial fluid pressure (Pif) and tumor growth were determined in all tumors on days 1, 5 and 7 using the "wick-in-the needle" technique and by external size measurements, respectively. Vessel density and inflammatory cell infiltration of tumor tissue were analyzed by immunohistochemistry.

RESULTS

DXM treatment significantly retarded tumor growth and reduced Pif. Treatment with a combination of DXM and 5-FU reduced tumor size significantly more than any of the agents alone (p<0.01-0.001). Enhanced uptake of 5-FU by DXM treatment was demonstrated by microdialysis. There were no differences in the density of CD31-positive vessels after DXM or 5-FU treatment, but inflammatory cell infiltration of tumor tissue was significantly reduced after DXM treatment.

CONCLUSIONS

Our data suggest that DXM may be beneficial as an adjuvant to chemotherapy in the treatment of mammary cancer by increasing the uptake of 5-FU in the tumor.

Imaging intratumoral convection: pressure-dependent enhancement in chemotherapeutic delivery to solid tumors

PURPOSE

Low-molecular weight (LMW) chemotherapeutics are believed to reach tumors through diffusion across capillary beds as well as membrane transporters. Unexpectedly, the delivery of these agents seems to be augmented by reductions in tumor interstitial fluid pressure, an effect typically associated with high-molecular weight molecules that reach tumors principally through convection. We investigated the hypothesis that improved intratumoral convection can alter tumor metabolism and enhance the delivery of a LMW chemotherapeutic agent to solid tumors.

EXPERIMENTAL DESIGN

For this purpose, we applied 31P/19F magnetic resonance spectroscopy (MRS) and magnetic resonance spectroscopic imaging (MRSI) to examine the influence of type I collagenase on tumor bioenergetics and the delivery of 5-fluorouracil (5FU) to HT29 human colorectal tumors grown s.c. in mice.

RESULTS

Collagenase effected a 34% reduction in tumor interstitial fluid pressure with an attendant disintegration of intratumoral collagen. Neither mice-administered collagenase nor controls receiving PBS showed changes in (31)phosphorus MRS-measured tumor bioenergetics; however, a time-dependent increase in the content of extracellular inorganic phosphate (Pi(e)) was observed in tumors of collagenase-treated animals. (31)Phosphorus MRSI showed that this increase underscored a more homogeneous distribution of Pi(e) in tumors of experimental mice. (19)Fluorine MRS showed that these changes were associated with a 50% increase in 5FU uptake in tumors of experimental versus control animals; however, this increase resulted in an increase in 5FU catabolites rather than fluoronucleotide intermediates that are required for subsequent cytotoxicity.

CONCLUSIONS

These data indicate that the modulation of convective flow within tumors can improve the delivery of (LMW) chemotherapeutics and show the potential role for noninvasive imaging of this process in vivo.

Paclitaxel encapsulated in cationic liposomes increases tumor microvessel leakiness and improves therapeutic efficacy in combination with Cisplatin

PURPOSE

Paclitaxel encapsulated in cationic liposomes (EndoTAG-1) is a vascular targeting formulation for the treatment of solid tumors. It triggers intratumoral microthrombosis, causing significant inhibition of tumor perfusion and tumor growth associated with endothelial cell apoptosis. Here, we quantified the effects of repeated EndoTAG-1 therapy on tumor microvascular leakiness with respect to leukocyte-endothelial cell interactions, the targeting property of cationic liposomes, and the therapeutic combination with conventional cisplatin chemotherapy.

EXPERIMENTAL DESIGN

Using dorsal skinfold chamber preparations in Syrian Golden hamsters, in vivo fluorescence microscopy experiments were done after repeated EndoTAG-1 treatment of A-Mel-3 tumors. Controls received glucose, paclitaxel alone, or cationic liposomes devoid of paclitaxel. Extravasation of rhodamine-labeled albumin was measured to calculate microvessel permeability, and intratumoral leukocyte-endothelial cell interactions were quantified. Subcutaneous tumor growth was evaluated after combination therapy followed by histologic analysis.

RESULTS

Microvascular permeability was significantly increased only after treatment with EndoTAG-1, whereas intratumoral leukocyte-endothelial cell interactions were not affected by any treatment. In separate skinfold chamber experiments, fluorescently labeled cationic liposomes kept their targeting property for tumor endothelial cells after repeated EndoTAG-1 treatment and no signs of extravasation were observed. Subcutaneous A-Mel-3 tumor growth was significantly inhibited by the combination of cisplatin and EndoTAG-1.

CONCLUSIONS

These data show that vascular targeting with EndoTAG-1 increases tumor microvessel leakiness probably due to vascular damage. This mechanism is not mediated by inflammatory leukocyte-endothelial cell interactions. Manipulating the blood-tumor barrier by repeated tumor microvessel targeting using EndoTAG-1 can effectively be combined with tumor cell-directed conventional cisplatin chemotherapy.

Interstitial fluid pressure, vascularity and metastasis in ectopic, orthotopic and spontaneous tumours

Background

High tumour interstitial fluid pressure (IFP) has been adversely linked to poor drug uptake in patients, and to treatment response following radiotherapy in cervix cancer patients. In this study we measured IFP values in a selection of murine and xenograft models, spontaneously arising or transplanted either intramuscularly (i/m) or orthotopically and analysed their relationship to tumour vascularity and metastatic spread.

Methods

KHT-C murine fibrosarcoma, ME180 and SiHa human cervix carcinoma were grown either intramuscularly (i/m), sub-cutaneously (s/c) or orthotopically. Polyoma middle-T (MMTV-PyMT) transgenic spontaneous mammary tumours were studied either as spontaneous tumours or following orthotopic or i/m transplantation. IFP was measured in all tumours using the wick-in-needle method. Spontaneous metastasis formation in the lungs or lymph nodes was assessed in all models. An immunohistochemical analysis of tumour hypoxia, vascular density, lymphatic vascular density and proliferation was carried out in ME180 tumours grown both i/m and orthotopically. Blood flow was also assessed in the ME180 model using high-frequency micro-ultrasound functional imaging.

Results

Tumour IFP was heterogeneous in all the models irrespective of growth site: KHT-C i/m: 2–42 mmHg, s/c: 1–14 mmHg, ME180: i/m 5–68 mmHg, cervix 4–21 mmHg, SiHa: i/m 20–56 mmHg, cervix 2–26 mmHg, MMTV-PyMT: i/m: 13–45 mmHg, spontaneous 2–20 mmHg and transplanted 2–22 mmHg. Additionally, there was significant variation between individual tumours growing in the same mouse, and there was no correlation between donor and recipient tumour IFP values. Metastatic dissemination to the lungs or lymph nodes demonstrated no correlation with tumour IFP. Tumour hypoxia, proliferation, and lymphatic or blood vessel density also showed no relationship with tumour IFP. Speckle variance analysis of ultrasound images showed no differences in vascular perfusion between ME180 tumours grown i/m versus orthotopically despite differences in IFP.

Conclusion

Our studies across a range of different tumour models showed substantial heterogeneity in tumour IFP, suggesting differences in the vascular development and interstitial fluid dynamics in the individual tumours. The results demonstrate a strong stochastic aspect to tumour IFP development, notably the variation apparent between different tumours within the same animal and the lack of correlation between donor and recipient tumours.

Drug Resistance and the Solid Tumor Microenvironment

Resistance of human tumors to anticancer drugs is most often ascribed to gene mutations, gene amplification, or epigenetic changes that influence the uptake, metabolism, or export of drugs from single cells. Another important yet little-appreciated cause of anticancer drug resistance is the limited ability of drugs to penetrate tumor tissue and to reach all of the tumor cells in a potentially lethal concentration. To reach all viable cells in the tumor, anticancer drugs must be delivered efficiently through the tumor vasculature, cross the vessel wall, and traverse the tumor tissue. In addition, heterogeneity within the tumor microenvironment leads to marked gradients in the rate of cell proliferation and to regions of hypoxia and acidity, all of which can influence the sensitivity of the tumor cells to drug treatment. In this review, we describe how the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and discuss potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumor microenvironment.

Immuno-PET of undifferentiated thyroid carcinoma with radioiodine-labelled antibody cMAb U36: application to antibody tumour uptake studies

PURPOSE

We tested the suitability of the chimeric monoclonal anti-human CD44 splice version 6 antibody (cMAb U36) for targeting and visualising human anaplastic thyroid carcinoma with PET. We also performed experiments aimed at elucidating the relation between tumour interstitial fluid pressure (TIFP) and the tumour uptake of antibodies.

METHODS

The affinity and specificity of the cMAb U36 for KAT-4 cells were evaluated in vitro, as was the Na+/I- symporter (NIS) expression. Biodistribution studies were performed on KAT-4 carcinoma-bearing mice injected with 124I-cMAb U36 or free iodine. Biodistribution studies were also performed in animals treated with the specific TGF-beta1 and -beta3 inhibitor Fc:TbetaRII, which lowers TIFP. Treated and non-treated animals were scanned by microPET.

RESULTS

Cultured human undifferentiated/anaplastic thyroid carcinoma KAT-4 cells expressed low levels of NIS and uptake of free iodine was insignificant. The cMAb U36 expressed an affinity (KD) of 11+/-2 nM. Tumour radioactivity uptake reached maximum values 48 h after injection of 124I-cMAb U36 (approximately 22%IA/g). KAT-4 carcinomas were readily identified in all 124I-immuno-PET images. Radioactivity tumour uptake in Fc:TbetaRII-treated animals was significantly lower at 24 and 48 h after injection, and five times higher thyroid uptake was also noted.

CONCLUSION

We successfully used 124I-cMAb U36 to visualise CD44v6-expressing human anaplastic thyroid carcinoma. Given the lack of NIS expression in KAT-4, tumour visualisation is not due to free iodine uptake. Lowering the TIFP in KAT-4 carcinomas did not increase the uptake of mAbs into tumour tissue.

Inhibition of carcinoma cell-derived VEGF reduces inflammatory characteristics in xenograft carcinoma

The stroma of carcinomas shares several characteristics with inflamed tissues including a distorted vasculature, active angiogenesis and macrophage infiltration. In addition, the tumor interstitial fluid pressure (P(IF)) of the stroma is pathologically elevated. We show here that bevacizumab [rhuMab vascular endothelial growth factor (VEGF), Avastin], a monoclonal antibody to VEGF, at a dose of 5 mg/kg modulated inflammation in KAT-4 xenograft human anaplastic thyroid carcinoma tissue. At this dose, bevacizumab reduced the density of macrophages, MHC class II antigen expression by macrophages and IL-1beta mRNA expression. Furthermore, bevacizumab lowered tumor extracellular fluid volume, plasma protein leakage from tumor vessels, the number of CD31-positive structures and tumor P(IF). The tumor plasma volume and the number of alpha-smooth muscle actin-positive vessels, however, remained unchanged. Our data suggest that carcinoma cell-derived VEGF either directly or indirectly participates in maintaining an inflammatory microenvironment in experimental KAT-4 carcinoma. Furthermore, our data indicate that the reduction of inflammation resulting in reduced vascular permeability and decrease in the tumor extracellular fluid volume by bevacizumab contributes to reduced tumor P(IF).

Lowering of tumor interstitial fluid pressure reduces tumor cell proliferation in a xenograft tumor model

High tumor interstitial fluid pressure (TIFP) is a characteristic of most solid tumors. TIFP may hamper adequate uptake of macromolecular therapeutics in tumor tissue. In addition, TIFP generates mechanical forces affecting the tumor cortex, which might influence the growth parameters of tumor cells. This seems likely as, in other tissues (namely, blood vessels or the skin), mechanical stretch is known to trigger proliferation. Therefore, we hypothesize that TIFP-induced stretch modulates proliferation-associated parameters. Solid epithelial tumors (A431 and A549) were grown in Naval Medical Research Institute nude mice, generating a TIFP of about 10 mm Hg (A431) or 5 mm Hg (A549). Tumor drainage of the central cystic area led to a rapid decline of TIFP, together with visible relaxation of the tumor cortex. It was found by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analysis that TIFP lowering yields a decreased phosphorylation of proliferation-associated p44/42 mitogen-activated protein kinase and tumor relaxation. In confirmation, immunohistochemical staining showed a decrease of tumor-associated proliferation marker Ki-67 after TIFP lowering. These data suggest that the mechanical stretch induced by TIFP is a positive modulator of tumor proliferation.

Biology of platelet-derived growth factor and its involvement in disease

Platelet-derived growth factor (PDGF) is mainly believed to be an important mitogen for connective tissue, especially for fibroblasts that serve in wound healing. However, PDGF also has important roles during embryonal development, and its overexpression has been linked to different types of fibrotic disorders and malignancies. Platelet-derived growth factor is synthesized by many different cell types, and its expression is broad. Its synthesis is in response to external stimuli, such as exposure to low oxygen tension, thrombin, or stimulation by other cytokines and growth factors. In addition, PDGF may function in autocrine stimulation of tumor cells, regulation of interstitial fluid pressure, and angiogenesis. Recently, several drugs were developed that are potent inhibitors of the tyrosine kinase activity of PDGF receptors. Thus, it is important to understand the physiology of PDGF and its receptors and the role of PDGF in different diseases. This review summarizes the physiologic activity of PDGF, the expression of PDGF during embryonal development, and the roles of PDGF expression in nonmalignant disease and in different tumors.

Effects of the vascular disrupting agent ZD6126 on interstitial fluid pressure and cell survival in tumors

Interstitial fluid pressure (IFP) is elevated in tumors due to abnormal vasculature, lack of lymphatic drainage, and alterations in the tumor interstitium. ZD6126 is a tubulin-binding agent that selectively disrupts tumor vasculature resulting in tumor necrosis. This study examined the effect of ZD6126 on tumor IFP and the response of tumors with different IFP levels to ZD6126. Pretreatment IFP was measured using the wick-in-needle method in tumors (murine KHT-C and human CaSki) growing i.m. in the hind legs of mice. Mice were treated i.p. with a single dose of ZD6126 (100 or 200 mg/kg) and posttreatment IFP measurements were made. Blood flow imaging was conducted using Doppler optical coherence tomography, whereas oxygen partial pressure was measured using a fiber optic probe. Clonogenic assays were done to determine tumor cell survival. In KHT-C tumors, IFP dropped significantly at 1 hour posttreatment, returned to pretreatment values at 3 hours, and then declined to approximately 25% of the pretreatment values by 72 hours. In CaSki tumors, the IFP decreased progressively, beginning at 1 hour, to approximately 30% of pretreatment values by 72 hours. Clonogenic cell survival data indicated that ZD6126 was less effective in tumors with high IFP values (>25 mm Hg). Vascular disrupting agents, such as ZD6126, can affect IFP levels and initial IFP levels may predict tumor response to these agents. The higher cell survival in high IFP tumors may reflect greater microregional blood flow limitations in these tumors and reduced access of the drug to the target endothelial cells.

Resistance of tumor interstitial pressure to the penetration of intraperitoneally delivered antibodies into metastatic ovarian tumors

PURPOSE

Despite evidence that regional chemotherapy improves the treatment of metastatic peritoneal ovarian carcinoma, monoclonal antibodies have not shown significant success in i.p. delivery. The present study was designed to address the hypothesis that convective penetration of macromolecular antineoplastic agents depends on a positive pressure difference between the i.p. therapeutic solution and the tumor.

EXPERIMENTAL DESIGN

Nude rats with human ovarian xenografts implanted in the abdominal wall were used in experiments to facilitate in vivo measurement of tumor pressure and the treatment of the tumor with i.p. solutions at high pressures. Penetration of (125)I-labeled trastuzumab was measured with quantitative autoradiography.

RESULTS

Tumor pressure profiles showed peak pressures of 32 mm Hg with mean pressures (+/- SD, mm Hg) in 12 SKOV3 tumors of 9.7 +/- 8.3 and in 15 OVCAR3 tumors of 12.5 +/- 7.0. I.p. therapeutic dwells at 6 to 8 mm Hg (maximum feasible pressure) showed significantly less penetration of trastuzumab than in adjacent normal muscle. To establish a driving force for convection into the tumor, various maneuvers were attempted to reduce tumor pressure, including treatment with taxanes or prostaglandin E(1), elimination of tumor circulation, and removal of the tumor capsule. Tumor decapsulation decreased the pressure to zero but did not enhance the penetration of antibody. Binding to specific trastuzumab receptors on each tumor was shown to be not a significant barrier to antibody penetration.

CONCLUSIONS

The results only partially support our hypothesis and imply that the microenvironment of the tumor is in itself a major barrier to delivery of charged macromolecules.

Improving delivery of antineoplastic agents with anti-vascular endothelial growth factor therapy

It is believed that impairments in delivery of antineoplastic agents to solid tumors result from abnormalities of the tumor microenvironment. Vascular endothelial growth factor (VEGF), the prototypical angiogenic molecule, is one of the main factors responsible for the development and maintenance of the aberrant tumor vascular network, which is characterized by chaotic, leaky blood vessels with high interstitial fluid pressure and inefficient blood flow. The authors proposed that anti-VEGF therapy would reduce the elevated interstitial fluid pressure in tumors, thereby improving blood flow and potentially improving delivery of cytotoxic agents to tumor cells. For the current report, the authors reviewed characteristics of the abnormal tumor vasculature created under the influence of VEGF, the resulting tumor microenvironment, how the tumor microenvironment may impede delivery of antineoplastic agents, and how the combination of anti-VEGF and cytotoxic therapy may maximize the efficacy of antineoplastic treatment regimens.

Inhibition of TGF-beta modulates macrophages and vessel maturation in parallel to a lowering of interstitial fluid pressure in experimental carcinoma

A pathologically elevated interstitial fluid pressure (IFP) is a characteristic of both clinical and experimental carcinoma. The soluble TGF-beta receptor type II-murine Fc:IgG2A chimeric protein (Fc:TbetaRII) lowers IFP in the KAT-4 experimental model for anaplastic thyroid carcinoma. Analyses of messenger RNA (mRNA) expressions by Affymetrix microarrays and RNase protection assays, as well as of protein expressions identified tumor macrophages as targets for Fc:TbetaRII. Treatment with Fc:TbetaRII reduced albumin extravasation, increased coverage of alpha-smooth muscle actin-positive cells and reduced expression of NG2, a marker of activated pericytes, in KAT-4 carcinoma blood vessels. Specific inhibition of interleukin-1 (IL-1), a major cytokine produced by activated macrophages, lowered carcinoma IFP to a similar degree as Fc:TbetaRII but had no significant effect on the parameters of blood vessel maturation. Neither Fc:TbetaRII nor inhibition of IL-1 changed blood vessel density. Finally, pretreatment of KAT-4 carcinomas with Fc:TbetaRII increased the antitumor efficacy of doxorubicin. Our data emphasize a potential role of tumor macrophages in carcinoma physiology and identify these cells as potential stromal targets for treatment aimed to improve efficacy of chemotherapy.

Paclitaxel Decreases the Interstitial Fluid Pressure and Improves Oxygenation in Breast Cancers in Patients Treated With Neoadjuvant Chemotherapy: Clinical Implications

Purpose

It has been hypothesized that tumors with high interstitial fluid pressure (IFP) and/or hypoxia respond poorly to chemotherapy (CT) because of poor drug delivery. Preclinical studies have shown that paclitaxel reduces the IFP and improves the oxygenation (pO2) of tumors. Our aim is to evaluate the IFP and pO2 before and after neoadjuvant CT using sequential paclitaxel and doxorubicin in patients with breast cancer tumors of ≥ 3 cm.

Patients and Methods

Patients were randomly assigned, according to an institutional review board–approved phase II protocol, to receive neoadjuvant sequential CT consisting of either four cycles of dose-dense doxorubicin at 60 mg/m2 every 2 weeks followed by nine cycles of weekly paclitaxel at 80 mg/m2 (group 1) or vice versa, with paclitaxel administered before doxorubicin (group 2). Patients were re-evaluated clinically and radiologically. The IFP (wick-in-needle technique) and pO2 (Eppendorf) were measured in tumors at baseline and after completing the administration of the first and second drug.

Results

IFP and pO2 were measured in 54 patients at baseline and after the first CT. Twenty-nine and 25 patients were randomly assigned to groups 1 and 2, respectively. Paclitaxel, when administered first, decreased the mean IFP by 36% (P = .02) and improved the tumor pO2 by almost 100% (P = .003). In contrast, doxorubicin did not have a significant effect on either parameter. This difference was independent of the tumor size or response measured by ultrasound.

Conclusion

Paclitaxel significantly decreased the IFP and increased the pO2, whereas doxorubicin did not cause any significant changes. Tumor physiology could potentially be used to optimize the sequence of neoadjuvant CT in breast cancer.

Thalidomide Radiosensitizes Tumors through Early Changes in the Tumor Microenvironment

Purpose: The aim of this work was to study changes in the tumor microenvironment early after an antiangiogenic treatment using thalidomide (a promising angiogenesis inhibitor in a variety of cancers), with special focus on a possible “normalization” of the tumor vasculature that could be exploited to improve radiotherapy.

Experimental Design: Tumor oxygenation, perfusion, permeability, interstitial fluid pressure (IFP), and radiation sensitivity were studied in an FSAII tumor model. Mice were treated by daily i.p. injection of thalidomide at a dose of 200 mg/kg. Measurements of the partial pressure of oxygen (pO2) were carried out using electron paramagnetic resonance oximetry. Three complementary techniques were used to assess the blood flow inside the tumor: dynamic contrast-enhanced magnetic resonance imaging, Patent Blue staining, and laser Doppler imaging. IFP was measured by a “wick-in-needle” technique.

Results: Our results show that thalidomide induces tumor reoxygenation within 2 days. This reoxygenation is correlated with a reduction in IFP and an increase in perfusion. These changes can be attributed to extensive vascular remodeling that we observed using CD31 labeling.

Conclusions: In summary, the microenvironmental changes induced by thalidomide were sufficient to radiosensitize tumors. The fact that thalidomide radiosensitization was not observed in vitro, and that in vivo radiosensitization occurred in a narrow time window, lead us to believe that initial vascular normalization by thalidomide accounts for tumor radiosensitization.

High interstitial fluid pressure - an obstacle in cancer therapy

Many solid tumours show an increased interstitial fluid pressure (IFP), which forms a barrier to transcapillary transport. This barrier is an obstacle in tumour treatment, as it results in inefficient uptake of therapeutic agents. There are a number of factors that contribute to increased IFP in the tumour, such as vessel abnormalities, fibrosis and contraction of the interstitial matrix. Lowering the tumour IFP with specific signal-transduction antagonists might be a useful approach to improving anticancer drug efficacy.

Increasing tumor uptake of anticancer drugs with imatinib

Solid malignancies often exhibit high interstitial fluid pressure (IFP), which causes poor uptake of anticancer drugs. While there are several mechanisms that regulate IFP in tumors, activation of platelet-derived growth factor receptor, which is expressed in various cell types within the tumor microenvironment, has been observed to play an important role in elevating IFP. In preclinical studies, treatment with imatinib, which inhibits both alpha- and beta-platelet-derived growth factor receptors, as well as KIT, ABL, ARG, and BCR-ABL tyrosine kinases, has been shown to decrease tumor IFP and concomitantly augment uptake of chemotherapeutic drugs, thereby enhancing the efficacy of chemotherapy. This review discusses preclinical studies showing the ability of imatinib to lower IFP and increase drug uptake within solid tumors, as well as the scientific rationale for clinical use of imatinib as combination therapy for chemotherapy.

Continuous measurements of plasma protein extravasation with microdialysis after various inflammatory challenges in rat and mouse skin

This study describes the use of microdialysis technique for continuous measurement of plasma protein extravasation (PPE) in rat and mouse skin with drug application either intravenously or via the microdialysis fiber. Hollow plasmapheresis fibers (3-cm length, 0.4-mm diameter, cutoff 3,000 kDa) were placed subcutaneously on the back of anesthetized mice and rats. Intravenous injection of dextran (Macrodex, 60 mg/ml) increased PPE by 355% from baseline within 30 min in rats with ligated kidneys (n = 6; P < 0.05) but not in animals with intact kidneys. Phalloidin (500 microg/kg iv 40 min before dextran, n = 6; P < 0.05) did not change the response to dextran in either group. Animals receiving PGE1, compound 48/80 (mice), paclitaxel, docetaxel, and cremophor EL via the microdialysis fiber were also provided with a control fiber receiving vehicle. Both rats and mice had constant PPE in the control fiber, and there was no change in PPE in the NaCl-treated groups (rats, n = 4; mice, n = 6). Application via the fiber of PGE1 (20 microg/ml), compound 48/80 (mice; 4 mg/ml), and docetaxel (0.5 mg/ml) increased PPE compared with baseline within 60 min by 139% (n = 6; P < 0.05), 273% (n = 6; P < 0.05), and 325% (n = 5; P < 0.05), respectively. Phalloidin alone did not increase PPE (n = 5; P < 0.05). Pretreatment with phalloidin did not inhibit the increase after PGE1 or compound 48/80 but inhibited that after docetaxel (n = 6). Paclitaxel (0.6 mg/ml, n = 5) or vehicle (Cremophor) (n = 5) gave no increase in PPE. The results demonstrate that microdialysis can be used to continuously measure changes in PPE after inflammatory challenges in skin of rats and mice.

Lowering of tumor interstitial fluid pressure specifically augments efficacy of chemotherapy

Chemotherapy of solid tumors is presently largely ineffective at dosage levels that are compatible with survival of the patient. Here, it is argued that a condition of raised interstitial fluid pressure (IFP) that can be observed in many tumors is a major factor in preventing optimal access of systemically administered chemotherapeutic agents. Using prostaglandin E1-methyl ester (PGE1), which is known transiently to reduce IFP, it was shown that 5-fluorouracil (5-FU) caused significant growth inhibition on two experimental tumors in rats but only after administration of PGE1. Furthermore, timing experiments showed that only in the period in which IFP is reduced did 5-FU have an antitumor effect. These experiments uniquely demonstrate a clear and, according to the starting hypothesis, logical, synergistic effect of PGE1 and 5-FU that offers hope for better treatment of many tumors in which raised IFP is likely to be inhibiting optimal results with water-soluble cancer chemotherapeutic agents.

Hyaluronan content in experimental carcinoma is not correlated to interstitial fluid pressure

Mechanism(s) for generation of the high tumor interstitial fluid pressure (TIFP) that is characteristic of carcinoma is not known. We investigated the role of hyaluronan, the major water-binding polysaccharide of the extracellular matrix, for the generation of a high TIFP. A human anaplastic thyroid carcinoma (KAT-4) xenografted to athymic mice and a syngeneic rat colon carcinoma (PROb) were used. Neither KAT-4 nor PROb cells produced hyaluronan (HA) in culture, however, both cell lines produced factors that stimulated HA-synthesis by cultured fibroblasts. Modulating hyaluronan levels by transfection of PROb carcinoma cells with hyaluronan synthase-2 revealed no correlation between hyaluronan content and TIFP. Furthermore, lowering of TIFP by treating KAT-4 tumors with a specific inhibitor of TGF-beta 1 and -beta 3 did not change the concentration of hyaluronan in the tumors. In summary, our results suggest that a modulation of hyaluronan content is not a major pathogenetic mechanism for the generation of the characteristically high TIFP in malignant carcinomas.

New and active role of the interstitium in control of interstitial fluid pressure: potential therapeutic consequences

Here we present recent data indicating that the present view of the interstitium as a passive fluid reservoir has to be revised. The connective tissue cells and extracellular matrix have a role in the control of P(if) and a fundamental role in the rapid development of edema in burns and in the initial swelling in inflammation by generating a lowering of interstitial fluid pressure. In this process, the beta1-integrin system seems to provide a common pathway by which the cells can lower as well as raise P(if). Inflammatory swelling can be reversed by endo- and exogenous substances, thereby suggesting that the connective tissue can serve as a novel target for pharmacological intervention. Furthermore, the new knowledge in interstitial physiology on means to reduce interstitial fluid pressure may be of importance for drug delivery into solid tumors, where a high P(if) limits the uptake of therapeutic agents.

Interference with TGF-beta1 and -beta3 in tumor stroma lowers tumor interstitial fluid pressure independently of growth in experimental carcinoma

A high tumor interstitial fluid pressure (TIFP) is a pathologic characteristic distinguishing the stroma of carcinomas from normal interstitial loose connective tissues. The role of TGF-beta1 and -beta3 in generating a high TIFP was investigated in xenografted experimental anaplastic thyroid carcinoma (ATC) derived from the human ATC cell line KAT-4. A single intravenous injection of a soluble recombinant TGF-beta receptor type II-murine Fc:IgG(2A) chimeric protein that specifically inhibits TGF-beta1 and -beta3, significantly lowered TIFP in a time and concentration dependent manner but did not change total tissue water content in the tumors. Tumor growth rate was higher in tumors treated with the TGF-beta1 and -beta3 inhibitor compared to control tumors during the first 10 days after administration of the inhibitor. The apoptotic index of carcinoma cells, and expression of the cell cycle inhibitor p27(Kip1), were, however, increased in TGF-beta1 and -beta3 inhibitor-treated tumors. Prolonged treatment periods and administration of a second dose of the inhibitor decreased tumor growth rate. The TGF-beta1 and -beta3 inhibitor did not affect proliferation or expression of phosphorylated Smad2 protein in KAT-4 cells cultured in vitro. Our results indicate that members of the TGF-beta family are potential targets for novel anti-cancer treatment directed to the stroma. First by controlling TIFP and by that potentially the uptake of anticancer drugs into tumors and second by their suggested role in maintaining a supportive tumor stroma.

PGE1 induced transcapillary transport of 51Cr-EDTA in rat skin measured by microdialysis

Interstitial fluid pressure (P(if)) is a key determinant in increasing the transcapillary driving pressure, pulling fluid from the microcirculation into the interstitial space at the onset of acute inflammatory reactions and the oedema formation associated with these. Prostaglandin E1 (PGE1) induces lowering of P(if) in rat skin which increases transcapillary transport of 51Cr-EDTA into the center of a tumor as measured by microdialysis. The aim of this study was twofold: First, to evaluate and develop the microdialysis technique thoroughly with regard to its suitability for investigating transcapillary water transport in rat skin using 51Cr-EDTA as a tracer. Secondly, to evaluate the effect of PGE1 on transcapillary transport of 51Cr-EDTA. This study demonstrates that PGE1 increases transcapillary transport of 51Cr-EDTA into skin interstitium. There were no significant differences between the experimental probe and the control probe when calculations from the entire experiment (90 min) were compared. On the other hand, significant differences were observed by examining the experiment in smaller time intervals. PGE1 increased transcapillary transport of 51Cr-EDTA during the first 15 min when administered through the microdialysis probe. This observation suggests that increased blood flow and/or permeability-surface area product are responsible for raising the transcapillary transport of 51Cr-EDTA, i.e. the transport is diffusion limited. Administration of PGE1 through the probe rather than around the probe resulted in less scatter between experiments than when PGE1 was injected subcutaneously around the probe.

Use of microdialysis to study platinum anticancer agent pharmacokinetics in preclinical models

Microdialysis sampling of blood and extracellular fluid (ECF) of living tissue offers unique advantages for studying anticancer drug distribution, metabolism, and mechanisms of tumor drug resistance. We applied microdialysis sampling in a rat model to describe the pharmacokinetics of cisplatin and carboplatin simultaneously in blood and several peripheral tissues, including tumor tissue. After i.v. bolus drug administration, samples were collected every 10 min for 4-6 h using microdialysis probes implanted into the jugular vein, kidney, and either liver or subcutaneously growing breast tumor tissue in anesthetized Fisher 344 rats. Analyte concentrations are expressed as absolute extracellular concentrations obtained by correction of the data for in vivo recovery. For cisplatin, peak renal concentrations (mean, 36.7 and 80.1 micrograms/mL) always exceeded peak plasma (8.4 and 13.2 micrograms/mL) and hepatic (6.3 and 10.4 micrograms/mL) concentrations following 5 and 10 mg/kg doses, respectively. For carboplatin, doses of 20 and 30 mg/kg also resulted in high peak renal concentrations, which were similar at both dose levels (mean, 87.9 and 89.3 micrograms/mL). However, at 30 mg/kg peak hepatic carboplatin concentrations were increased significantly, resulting in a disproportionate 3.5-fold increase in mean AUC at the higher dose level. Tumor cisplatin and carboplatin AUCs were similar to that in the circulation, but variable, ranging from 52 to 109% of the corresponding plasma AUCs. Microdialysis was determined to be a reliable methodology for examining the in vivo disposition of platinum anticancer agents in multiple tissue types. Our results revealed expected large renal exposures following i.v. administration, and variable tumor exposure with dose. Significant increases in hepatic carboplatin exposure with increasing dose suggest a possible mechanism for high-dose carboplatin-induced hepatic toxicity.

The influence of combretastatin A-4 and vinblastine on interstitial fluid pressure in BT4An rat gliomas

The influence of combretastatin A-4 disodium phosphate (CA-4, 50mg/kg intraperitoneally (i.p.)) and vinblastine (2mg/kg i.p.) on interstitial fluid pressure (IFP) was assessed in BT4An rat gliomas implanted subcutaneously in the neck. Furthermore the growth inhibitory effect of vinblastine and the distribution of fluorescence-conjugated vinblastine (BODIPY-vinblastine) were investigated. Tumors at different volumes were compared. Whereas CA-4 had no major influence on IFP, independent of tumor size, vinblastine increased the IFP in neoplasms above 8 cm(3) (P=0.03). Vinblastine yielded a significant tumor response only in tumors below 2.1 cm(3) (P=0.03). The distribution of BODIPY-vinblastine was heterogeneous and comparable despite tumor volume differences. We conclude that the influence of vinblastine on IFP is more pronounced than that of CA-4 in BT4An neck tumors, and that vinblastine may reduce subsequent drug delivery to solid tumors by increasing the IFP.

Collagen type I expression in experimental anaplastic thyroid carcinoma: regulation and relevance for tumorigenicity

Fibrosis in solid malignancies plays a significant role in tumor pathophysiology. Potential mechanisms for collagen type I deposition in anaplastic thyroid carcinoma (ATC) were investigated using 6 characterized ATC cell lines. Three of these cell lines, which produced collagen type I, had, as a group, a poor tumorigenicity when inoculated in athymic mice. This group of cells generated tumors in 4 of 24 injected animals (17%). Pro-alpha 1(I) collagen mRNA-expressing carcinoma and stromal cells were interdispersed in the tumors generated by these ATC cells. By contrast, the 3 noncollagen-producing ATC cell lines were all tumorigenic with a tumor take of 60% in the whole group. In the latter tumors, pro-alpha 1(I) collagen mRNA-expressing cells were confined to the stromal compartment, well delineated from carcinoma cell islets. To study the influence of ATC cells on collagen type I synthesis by fibroblasts, we used AG 1518 diploid human fibroblasts cultured on poly-(2-hydroxyethyl methacrylate) (poly[HEMA])-coated plates. This culture condition allows the study of the effect of collagen mRNA translation in the regulation of collagen type I synthesis. Conditioned media from the 6 ATC cell lines did not influence collagen synthesis. The ATC cell line KAT-4 stimulated fibroblast synthesis of collagen type I when the two cell types were cocultured on poly[HEMA]-coated substrates. Specific inhibitors of PDGF and TGF-beta reduced the KAT 4 carcinoma cell-induced stimulation of collagen type I synthesis. Our data suggest that collagen type I production by carcinoma cells correlates negatively with tumorigenicity and that the formation of a well-defined stroma is of importance for tumor growth. Furthermore, our data suggest that tumor cells are able to stimulate collagen mRNA translation in stromal fibroblasts in direct cell-cell contact by, at least in part, transferring PDGF or TGF-beta.

Uptake of IgG in osteosarcoma correlates inversely with interstitial fluid pressure, but not with interstitial constituents

The uptake of therapeutic macromolecules in solid tumours is assumed to be hindered by the heterogeneous vascular network, the high interstitial fluid pressure, and the extracellular matrix. To study the impact of these factors, we measured the uptake of fluorochrome-labelled IgG using confocal laser scanning microscopy, interstitial fluid pressure by the 'wick-in-needle' technique, vascular structure by stereological analysis, and the content of the extracellular matrix constituents collagen, sulfated glycosaminoglycans and hyaluronan by colourimetric assays. The impact of the microenvironment on these factors was studied using osteosarcomas implanted either subcutaneously or orthotopically around the femur in athymic mice. The uptake of IgG was found to correlate inversely with the interstitial fluid pressure and the tumour volume in orthotopic, but not subcutaneous tumours. No correlation was found between IgG uptake and the level of any of the extracellular matrix constituents. The content of both collagen and glycosaminoglycans depended on the site of tumour growth. The orthotopic tumours had a higher vascular density than the subcutaneous tumours, as the vascular surface and length were 2-3-fold higher. The data indicate that the interstitial fluid pressure is a dominant factor in controlling the uptake of macromolecules in solid tumours; and the site of tumour growth is important for the uptake of macromolecules in small tumours, extracellular matrix content and vascularization.