Tissue-isolated human tumor xenografts in athymic nude mice

Delivery of molecular and cellular medicine to solid tumors

To reach cancer cells in a tumor, a blood-borne therapeutic molecule or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium, and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically, and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of physiological barriers in solid tumors, and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Malignant cells facilitate lung metastasis by bringing their own soil

Metastatic cancer cells (seeds) preferentially grow in the secondary sites with a permissive microenvironment (soil). We show that the metastatic cells can bring their own soil--stromal components including activated fibroblasts--from the primary site to the lungs. By analyzing the efferent blood from tumors, we found that viability of circulating metastatic cancer cells is higher if they are incorporated in heterotypic tumor-stroma cell fragments. Moreover, we show that these cotraveling stromal cells provide an early growth advantage to the accompanying metastatic cancer cells in the lungs. Consistent with this hypothesis, we demonstrate that partial depletion of the carcinoma-associated fibroblasts, which spontaneously spread to the lung tissue along with metastatic cancer cells, significantly decreases the number of metastases and extends survival after primary tumor resection. Finally, we show that the brain metastases from lung carcinoma and other carcinomas in patients contain carcinoma-associated fibroblasts, in contrast to primary brain tumors or normal brain tissue. Demonstration of the direct involvement of primary tumor stroma in metastasis has important conceptual and clinical implications for the colonization step in tumor progression.

Tumour Angiogenesis, Vascular Biology and Enhanced Drug Delivery

It is now common knowledge that for a solid tumour to become life-threatening clinically, an adequate blood supply to the neoplasm has to be established. Although neovascularisation via angiogenesis leads to a subsequent rapid growth of the tumour mass, it provides the most reliable route by which neoplastic cells may be reached by cytotoxics. In addition, for a majority of tumours, the lesion's vasculature is more permeable and tortuous than that of the surrounding healthy host tissue. Such deviation potentiates selective delivery of drugs to be achieved. This review examines, from various viewpoints, the area of tumour angiogenesis and vascularisation, currently one of the most fertile and active fields of cancer research.

Interstitial transport and transvascular fluid exchange during infusion into brain and tumor tissue

A model of convection-enhanced delivery in brain and neoplastic tissue is presented that includes transvascular fluid exchange in addition to interstitial fluid transport. Measured values for the relevant material parameters are compiled from published literature. The transient distributions of interstitial fluid pressure and fluid velocity resulting from infusion into brain tissue and into a tissue-isolated tumor are derived, in addition to the steady-state distribution of interstitial fluid pressure and fluid velocity resulting from infusion into a tumor with a necrotic core. The analytic solutions suggest that (1) the distributions of both pressure and fluid velocity are very sensitive to the ratio of vascular conductivity and hydraulic conductivity; (2) in brain tissue, the convective fluid velocity is significant (within three orders of magnitude of the peak value, for example) for a large number of infusion catheter diameters away from the infusion site, whereas in neoplastic tissue the convective velocity is significant for a small number of infusion catheter diameters away from the infusion site; (3) the presence of a necrotic core substantially increases the convective fluid velocity in its vicinity; and (4) infusion proximal to a tumor is greatly impeded by the outward flow at the tumor's periphery. These and related findings are discussed in terms of their relevance to the treatment of tumors.

In-vitro and in-vivo assays for angiogenesis-modulating drug discovery and development

In the past 35 years, significant findings have been made in relation to angiogenesis, and how this usually normal physiological function is converted into an abnormal state in cancer. To search for agents that can inhibit angiogenesis, and thereby prevent a tumour from proliferation and spread that is ultimately fatal to the patient, various in-vitro assays have been developed. In addition, older assays have been refined usually into high throughput screening formats, mainly by the biopharmaceutical industry in their attempts to develop novel therapeutic molecules and maintain a pipeline of lead candidates. The central aim is to extract more accurate data that would facilitate the birth of innovative mechanisms to defeat aberrant angiogenesis in-vivo. At the same time, better in-vivo models have been established, with the goal to mimic as close as possible the natural progression of various types of neoplasms in response to a good angiogenic response. More clinically relevant models are needed as anti-angiogenesis drug discovery and drug development companies fast track their lead molecules from preclinical investigations to phase I clinical trials.

Mosaic tumor vessels: cellular basis and ultrastructure of focal regions lacking endothelial cell markers

Endothelial cells of blood vessels in tumors may be thin, fragile, and defective in barrier function. We found previously that the endothelium of vessels in human colon carcinoma xenografts in mice is a mosaic structure. Approximately 85% of tumor vessels have uniform CD31 and/or CD105 immunoreactivity, but the remainder have focal regions that lack these common endothelial markers. The present study assessed the ultrastructure of the vessel lining and the integrity of the basement membrane in these regions. Using immunolabeling and confocal microscopy, we identified blood vessels that lacked CD31 and CD105 immunoreactivity and then analyzed the ultrastructure of these vessels by transmission electron microscopy. Eleven percent of vessels in orthotopic tumors and 24% of vessels in ectopic tumors had defects in CD31 and CD105 staining measuring on average 10.8 microm (range, 1-41.2 microm). Ultrastructural studies identified endothelial cells at 92% of CD31- and CD105-negative sites in orthotopic tumors and 70% of the sites in ectopic tumors. Thus, most regions of tumor vessels that lack CD31 and CD105 immunoreactivity represent attenuated endothelial cells with abnormal expression of endothelial cell markers, but some are gaps between endothelial cells. More than 80% of the defects lacked immunoreactivity for multiple basement membrane proteins.

Transport of molecules, particles, and cells in solid tumors

Extraordinary advances in molecular biology and biotechnology have led to the development of a vast number of therapeutic anti-cancer agents. To reach cancer cells in a tumor, a blood-borne therapeutic molecule, particle, or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium, which it then must migrate through. Unfortunately, tumors often develop in ways that hinder these steps. The goal of research in this area is to analyze each of these steps experimentally and theoretically and integrate the resulting information into a unified theoretical framework. This paradigm of analysis and synthesis has fostered a better understanding of physiological barriers in solid tumors and aided in the development of novel strategies to exploit and/or overcome these barriers for improved cancer detection and treatment.

Vascular morphogenesis and remodeling in a human tumor xenograft: blood vessel formation and growth after ovariectomy and tumor implantation

To determine mechanisms of blood vessel formation and growth in solid tumors, we used a model in which LS174T human colon adenocarcinomas are grown in the isolated ovarian pedicle of nude mice. Reconstruction of 3500 histological serial sections demonstrated that a new vascular network composed of venous-venous loops of varying sizes grows inside the tumor from the wall of the adjacent main vein. Loops elongate and remodel to establish complex loop systems. The mechanisms of loop formation and remodeling correspond to intussusceptive microvascular growth (IMG). In the tissue surrounding the tumor segmentation, another mechanism of IMG is prevalent in venous vessels. Comparison to vascular morphogenesis in the ovariectomized pedicle not only confirms the existence of corresponding mechanisms in both systems, but also reveals numerous sprouts that are superimposed onto loop systems and pathological deviations of loop formation, remodeling, and segmentation in the tumor. These pathological mechanisms interfere with vessel patency that likely cause heterogenous perfusion and hypoxia thus perpetuating angiogenesis. Blood vessel formation based on IMG was also detected in a large thrombus that completely occluded a part of an ovarian artery branch.

Vascular morphogenesis and remodeling in a model of tissue repair: blood vessel formation and growth in the ovarian pedicle after ovariectomy

To investigate mechanisms of vascular morphogenesis in tissue repair, we performed ovariectomy with resection of the corresponding branches of the ovarian vessels in nude mice. This induces a vascular network remodeling response in the healing ovarian pedicle. Reconstruction of 2000 histological serial sections demonstrated that a new vascular network composed of venous-venous loops forms in the wall of the dilated ovarian vein. Preexisting veins of all sizes, including a branch of the main artery, are subjected to segmentation. Loop formation and segmentation are based on intussusceptive microvascular growth. Loop formation is followed by elongation. Loop remodeling occurs also by intussusception and results in the formation of compound loop systems. All loop systems observed were completely patent. Blind-ending sprouts were extremely rare. Anastomoses between the preexisting vessels subjected to segmentation and the loop systems were established to include the newly formed vessels into the preexisting vascular network. The formation of an increasing number of patent loop systems likely decreases hypoxia and subsequently arrests angiogenesis with transformation of the granulation tissue into a scar. Loop formation also occurred inside a large thrombus that occluded a part of the lumen of the main vein.

Delivery of molecular medicine to solid tumors: lessons from in vivo imaging of gene expression and function

Extraordinary advances in molecular medicine and biotechnology have led to the development of a vast number of anti-cancer therapeutic agents. To reach cancer cells in a tumor, a blood-borne therapeutic molecule, particle or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of microcirculatory barriers in solid tumors and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Tissue-engineered cells producing complex recombinant proteins inhibit ovarian cancer in vivo

Techniques of tissue engineering and cell and molecular biology were used to create a biodegradable scaffold for transfected cells to produce complex proteins. Mullerian Inhibiting Substance (MIS) causes regression of Mullerian ducts in the mammalian embryo. MIS also causes regression in vitro of ovarian tumor cell lines and primary cells from ovarian carcinomas, which derive from Mullerian structures. In a strategy to circumvent the complicated purification protocols for MIS, Chinese hamster ovary cells transfected with the human MIS gene were seeded onto biodegradable polymers of polyglycolic acid fibers and secretion of MIS confirmed. The polymer-cell graft was implanted into the right ovarian pedicle of severe combined immunodeficient mice. Serum MIS in the mice rose to supraphysiologic levels over time. One week after implantation of the polymer-cell graft, IGROV-1 human tumors were implanted under the renal capsule of the left kidney. Growth of the IGROV-1 tumors was significantly inhibited in the animals with a polymer-cell graft of MIS-producing cells, compared with controls. This novel MIS delivery system could have broader applications for other inhibitory agents not amenable to efficient purification and provides in vivo evidence for a role of MIS in the treatment of ovarian cancer.

Delivery of molecular and cellular medicine to solid tumors

To reach cancer cells in a tumor, a blood-borne therapeutic molecule or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium, and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically, and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of physiological barriers in solid tumors, and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Mosaic blood vessels in tumors: frequency of cancer cells in contact with flowing blood

The presence of "mosaic" vessels in which both endothelial cells and tumor cells form the luminal surface has profound implications for metastasis, drug delivery, and antivascular therapy. Yet little is known of the frequency, and thus importance, of mosaic vessels in tumors. Using CD31 and CD105 to identify endothelial cells and endogenous green fluorescent protein labeling of tumor cells, we show that approximately 15% of perfused vessels of a colon carcinoma xenografted at two different sites in mice were mosaic vessels having focal regions where no CD31/CD105 immunoreactivity was detected and tumor cells appeared to contact the vessel lumen. These regions occupied approximately 25% of the perimeter of the mosaic vessels, or approximately 4% of the total vascular surface area in these colon carcinomas. In addition, we found similar numbers of mosaic vessels in human colon carcinoma biopsies. Our results are consistent with the observation that approximately 10(6) cells are shed daily per g of tumor. More importantly, our data offer a possible explanation for the antivascular effects of cytotoxic agents and suggest potential strategies for targeting the tumor vasculature.

Changes in vascularization of human breast cancer xenografts responding to antiestrogen therapy

To elucidate the previously suggested vascular effect(s) of antiestrogen therapy, we studied the effect of estrogen withdrawal and tamoxifen on 1) vascular resistance, 2) glucose and oxygen consumption, and 3) vascular density in a perfused breast cancer line (ZR75-1). Furthermore, we examined ZR75-1 tumors by functional CT-scanning (fCT) to determine changes in parameters related to tumor capillary transfer constants and vascular volume fraction in response to antiestrogenic manipulations. The vascular resistance decreased significantly from 42.7 to 20.8 mmHg x min x g x ml(-1) (P< .03) on day 9 after estrogen withdrawal, but not after 9 days of tamoxifen treatment. The estrogen-depleted tumors were significantly smaller than controls on day 9. There was no difference in nutrient consumption or vascular density in any of the experimental groups compared to controls. fCT showed an increase (P < .03) in vascular volume fraction during tumor growth, and this parameter was significantly lower after estrogen withdrawal when compared to controls (P < .05). Vascular resistance correlated with tumor size (R = 0.7, P < .0001), indicating that vascular resistance increases during tumor growth. The changes in vascular parameters after estrogen withdrawal indicate a vascular remodeling effect. This inhibition of vascular development by hormone deprivation may have important implications for future planning of multimodal treatment regimens.

Pharmacokinetics of anticancer drugs, plasmid DNA, and their delivery systems in tissue-isolated perfused tumors

To achieve an optimal chemotherapy or gene therapy against tumors or to realize rational design of delivery systems for cancer therapy, pharmacokinetic information in tumor should be obtained. A tissue-isolated tumor preparation is a useful experimental system to investigate the intratumoral disposition of drugs, carriers, and their complexes. The disposition of drugs in the solid tumor was analyzed in this system after intraarterial infusion (systemic route) or by intratumoral injection (topical route). Here the results of low-molecular weight drugs, their macromolecular prodrugs, lipid carriers like fat emulsions and liposomes, and plasmid DNA and its complexes, are addressed. Pharmacokinetic analyses in the tumor clearly indicate that the intratumoral fate of drugs and delivery systems are determined by (i) the anatomical and physiological properties of the tissue and (ii) the physicochemical characteristics of drugs and delivery systems such as molecular weight, size, lipophilicity, and electrical charge. These approaches are useful for designing and developing optimized drug delivery systems.

Cells shed from tumours show reduced clonogenicity, resistance to apoptosis, and in vivo tumorigenicity

The goal of this study was to compare growth characteristics of cells shed from a tumour with the native tumour cells. The human colon adenocarcinoma LS174T and its highly metastatic subline LS LiM 6 were grown as tissue-isolated tumours in nude mice and perfused to collect shed cells. The tumours were then excised and prepared into single-cell suspensions. Clonogenicity in 0.3-0.9% agarose, apoptotic fraction, and in vivo tumorigenicity were determined for each population. In both tumour lines, shed cells were less clonogenic, more apoptotic and less tumorigenic than cells isolated directly from their native tissue. These findings suggest that shed cells have a low metastatic potential compared to native tumour cells, most likely because they represent an apoptotic population.

Enhancement of fluid filtration across tumor vessels: implication for delivery of macromolecules

Cancer therapies using genes and other macromolecules might realize their full clinical potential if they could be delivered to tumor tissue in optimal quantities. Unfortunately, the compromised circulation within tumors poses a formidable resistance to adequate and uniform penetration of these agents. Previously, we have proposed elevated interstitial fluid pressure (IFP) as a major physiological barrier to delivery of macromolecules. Here we postulate that modulation of tumor microvascular pressure (MVP) and associated changes in IFP would enhance macromolecular delivery into a solid tumor. To test our hypothesis, we altered tumor MVP by either periodic injection or continuous infusion of angiotensin II (AII) and measured the resulting changes in IFP and uptake of macromolecules. We used the nicotinyl hydrazine derivative of human polyclonal IgG (HYNIC-IgG) as a nonspecific macromolecule and CC49 antibody as a specific macromolecule. We found that both chronic and periodic modulation of tumor MVP enhances transvascular fluid filtration, leading to a 40% increase in total uptake of the specific antibody within 4 hr of its administration. Conversely, neither continuous nor periodic infusion of AII induced any increase in uptake of nonspecific antibodies. Strategies to improve delivery of macromolecules and limitations of this approach are identified.

Enhanced tumor targeting by an intratumoral injection of colloidal chromic 32P in two human tumors (AsPC-1 pancreas and Ls174T colon) in nude mice

BACKGROUND AND OBJECTIVES

To find the mechanisms of the ongoing clinical trials in intralesional colloidal chromic 32P (32P-CP) brachytherapy, the cellular uptake of 32P-CP, changes in tumor interstitial fluid pressure (TIFP), and tumor blood flow (TBF) using two (AsPC-1, Ls174T) human tumors were measured.

METHODS

After exposure to 32p-CP using exponential and plateau-phase cells, cells were trypsinized at various time intervals, then measured for the levels of radioactivity using a y-counter. Also measured were TIFP using the WIN technique and TBF with laser Doppler flowmetry.

RESULTS

The plateau growth-phase of both tumors showed the maximal uptake of 32P-CP at approximately 100 min. TBF decreased within 10 min after an intratumoral (i.t.) injection of 32P-CP, and reached 75% of control value by 1 h.

CONCLUSIONS

If 32P-CP was introduced i.t., it maintained highly efficient tumor targeting, mainly due to two physiological mechanisms: the high adherence of 32P-CP to the infused regions and the reduction in TBF by this therapeutic colloid.

Transvascular drug delivery in solid tumors

The microvessel wall is a barrier for the delivery of various therapeutic agents to tumor cells. Tumor microvessels are, in general, more permeable to macromolecules than normal vessels. The hyperpermeability is presumably due to the existence of large pore structures in the vessel wall, induced by various cytokines. The cutoff pore size is tumor dependent, as determined by transport studies of nanoparticles. The vascular permeability is heterogeneous in tumors and dependent on physicochemical properties of molecules as well as the ultrastructure of the vessel wall. The ultrastructure is dynamic and can be modulated by the tumor microenvironment. The microenvironment itself can be altered by the transvascular transport because the transport may facilitate angiogenesis, reduce blood flow, and induce interstitial hypertension in tumors. Future studies of transport need to address mechanisms of the barrier formation and emphasize development of novel strategies for circumventing or exploiting the vascular barrier.

Delivery of molecular and cellular medicine to solid tumors

To reach cancer cells in a tumor, a blood-borne therapeutic molecule or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium, and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically, and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of physiological barriers in solid tumors, and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Confocal laser scanning microscopy of tumor/vessel relationship in xenografts in nude and scid mice

Using confocal laser scanning microscopy we studied sections of the T24B, a human bladder carcinoma, grown in C.B.-17 scid/scid or NMRI nu/nu mice in order to examine the relationship between tumor tissue and tumor vessels. Tumor cells were labelled with FITC-anti-cytokeratin and blood vessel endothelia with Cy3-labelled BS-I lectin. In contrast to our expectation, no major leaks in the endothelial lining of blood vessels were observed. We are looking for a suitable marker for mouse lymphatics in order to investigate their possible role.

Quantitation and gompertzian analysis of tumor growth

Human tumor xenografts in immune-deficient animals are used to establish tumor growth curves and for studying the effect of experimental therapy on tumor growth. In this review we describe a method for making serial measurements of tumor size in the nude mouse model as well as methods used to transform the experimental data into useful growth curves. A transformed Gompertz function is used as the basis for calculating relevant parameters pertaining to tumor growth and response to therapy. The calculations are facilitated by use of a computer program which performs the necessary calculations and presents the growth data in graphic form.

Delivery of molecular and cellular medicine to solid tumors

To reach cancer cells in a tumor, a blood-borne therapeutic molecule or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium, and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically, and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of physiological barriers in solid tumors, and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Pharmacokinetic analysis of drug disposition after intratumoral injection in a tissue-isolated tumor perfusion system

PURPOSE

The purpose of this study was to establish an experimental system for evaluation of the intratumoral behavior of drugs after intratumoral injection using perfused tissue-isolated tumor preparations of Walker 256 carcinoma (3.46-9.73g, n = 16).

METHODS

We quantified the recovery of Phenol Red (model drug) in the tumor, leakage from the tumor surface and the venous outflow after intratumoral injection using perfused tissue-isolated tumors, and analyzed venous appearance curves based on a pharmacokinetic model in which the tumor tissue was assumed to be divided into two compartments, i.e., well- and poorly-perfused regions.

RESULTS

In small tumors (Type 1, 5.42 +/- 0.39 g), the drug appeared immediately in the venous outflow, and the amount remaining in the tumor tissue at 2 hr after injection was small. In contrast the venous appearance rate reached a significantly lower peak a few minutes after injection, and a large amount of injected drug remained in some large tumors (Type 2.8.17 +/- 0.51 g). Pharmacokinetic analysis revealed that there was a correlation between tumor weight and the rate constants of transfer from the poorly-perfused region to the well-perfused region, and between the rate constants of transfer from the well-perfused region to the venous outflow and dosing ratios into the well-perfused region.

CONCLUSIONS

An experimental system and analytical method were established for the evaluation of the intratumoral behavior of drugs after intratumoral injection using a tissue-isolated tumor perfusion system. This experimental system will be useful in analyzing the antitumor drug disposition after intratumoral injection.

1995 Whitaker Lecture: delivery of molecules, particles, and cells to solid tumors

To reach cancer cells in a tumor, a blood-borne therapeutic agent must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium, and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically, and then to integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of physiological barriers in solid tumors, and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.