Photodynamic therapy-induced alterations in interstitial fluid pressure, volume and water content of an amelanotic melanoma in the hamster

Modulating tumor physical microenvironment for fueling CAR-T cell therapy

Chimeric antigen receptor (CAR) T cell therapy has achieved unprecedented clinical success against hematologic malignancies. However, the transition of CAR-T cell therapies for solid tumors is limited by heterogenous antigen expression, immunosuppressive microenvironment (TME), immune adaptation of tumor cells and impeded CAR-T-cell infiltration/transportation. Recent studies increasingly reveal that tumor physical microenvironment could affect various aspects of tumor biology and impose profound impacts on the antitumor efficacy of CAR-T therapy. In this review, we discuss the critical roles of four physical cues in solid tumors for regulating the immune responses of CAR-T cells, which include solid stress, interstitial fluid pressure, stiffness and microarchitecture. We highlight new strategies exploiting these features to enhance the therapeutic potency of CAR-T cells in solid tumors by correlating with the state-of-the-art technologies in this field. A perspective on the future directions for developing new CAR-T therapies for solid tumor treatment is also provided.

Flow-induced Shear Stress Confers Resistance to Carboplatin in an Adherent Three-Dimensional Model for Ovarian Cancer: A Role for EGFR-Targeted Photoimmunotherapy Informed by Physical Stress

A key reason for the persistently grim statistics associated with metastatic ovarian cancer is resistance to conventional agents, including platinum-based chemotherapies. A major source of treatment failure is the high degree of genetic and molecular heterogeneity, which results from significant underlying genomic instability, as well as stromal and physical cues in the microenvironment. Ovarian cancer commonly disseminates via transcoelomic routes to distant sites, which is associated with the frequent production of malignant ascites, as well as the poorest prognosis. In addition to providing a cell and protein-rich environment for cancer growth and progression, ascitic fluid also confers physical stress on tumors. An understudied area in ovarian cancer research is the impact of fluid shear stress on treatment failure. Here, we investigate the effect of fluid shear stress on response to platinum-based chemotherapy and the modulation of molecular pathways associated with aggressive disease in a perfusion model for adherent 3D ovarian cancer nodules. Resistance to carboplatin is observed under flow with a concomitant increase in the expression and activation of the epidermal growth factor receptor (EGFR) as well as downstream signaling members mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) and extracellular signal-regulated kinase (ERK). The uptake of platinum by the 3D ovarian cancer nodules was significantly higher in flow cultures compared to static cultures. A downregulation of phospho-focal adhesion kinase (p-FAK), vinculin, and phospho-paxillin was observed following carboplatin treatment in both flow and static cultures. Interestingly, low-dose anti-EGFR photoimmunotherapy (PIT), a targeted photochemical modality, was found to be equally effective in ovarian tumors grown under flow and static conditions. These findings highlight the need to further develop PIT-based combinations that target the EGFR, and sensitize ovarian cancers to chemotherapy in the context of flow-induced shear stress.

Photodynamic Therapy and the Biophysics of the Tumor Microenvironment

Targeting the tumor microenvironment (TME) provides opportunities to modulate tumor physiology, enhance the delivery of therapeutic agents, impact immune response and overcome resistance. Photodynamic therapy (PDT) is a photochemistry-based, nonthermal modality that produces reactive molecular species at the site of light activation and is in the clinic for nononcologic and oncologic applications. The unique mechanisms and exquisite spatiotemporal control inherent to PDT enable selective modulation or destruction of the TME and cancer cells. Mechanical stress plays an important role in tumor growth and survival, with increasing implications for therapy design and drug delivery, but remains understudied in the context of PDT and PDT-based combinations. This review describes pharmacoengineering and bioengineering approaches in PDT to target cellular and noncellular components of the TME, as well as molecular targets on tumor and tumor-associated cells. Particular emphasis is placed on the role of mechanical stress in the context of targeted PDT regimens, and combinations, for primary and metastatic tumors.

Millimeter-Wave Substrate Integrated Waveguide Probe for Skin Cancer Detection

This article presents an efficient and low-cost near-field probe, designed for early-stage skin cancer detection. Thanks to a tapered section, the device can achieve a sharp concentration of electric field at its tip. Moreover, the adoption of substrate integrated waveguide (SIW) technology ensures an easy and cheap fabrication process. The probe is realized on a high dielectric constant substrate (Rogers RO3210) that provides a good impedance matching with the skin, thus allowing to use the device in direct contact with it. This feature is essential to ensure that the proposed system can be adopted as a practical and effective tool for a fast scanning of many suspected skin regions. The probe is designed to operate at around 40 GHz in order to achieve the penetration depth required to detect small cancer lumps in the skin, while preventing the fields from interacting with the underlying biological tissues. Furthermore, the concept of detection depth is defined with the goal of introducing a metric that is more suitable than the penetration depth to express the notion of the maximum distance from the skin surface at which a tumor can be detected. Thanks to a differential imaging algorithm, the probe is capable of working on every different skin types and body region. The proposed device has a lateral sensitivity and detection depth of 0.2 and 0.55 mm respectively. The probe was designed and tested through simulations in CST Microwave Studio, as well as fabricated and validated through measurements on an artificial human skin phantom.

Pharmacokinetics and Tissue Transport of Intraperitoneal Chemotherapy

The presence of a peritoneal barrier results in a pharmacokinetic advantage associated with intraperitoneal (IP) delivery of anticancer drugs. The anticancer efficacy of IP chemotherapy depends, however, on its ability to penetrate the tumor stroma. Tumor tissue transport is governed by diffusion and convection and is affected by numerous physical, biological, and pharmaceutical variables. From preclinical and clinical studies, it appears that tissue penetration after IP chemotherapy delivery is very limited. Several approaches are studied in order to improve tissue penetration of small molecular and macromolecular anticancer drugs after IP instillation.

Tumour tissue transport after intraperitoneal anticancer drug delivery

Intraperitoneal (IP) drug delivery, either as an intraoperative chemoperfusion or as an adjuvant, repeated instillation, is an established treatment modality in patients with peritoneal carcinomatosis. The efficacy of IP drugs depends on its ability to penetrate the tumour stroma in order to reach their (sub)cellular target. It is known, that drug penetration after IP delivery is limited to a few millimetres. Here, we review the basic tissue transport mechanisms after IP delivery and discuss the biophysical barriers and obstacles that limit penetration distance. In addition, we review the physical and pharmaceutical interventions that have been studied in order to improve delivery of small molecular and macromolecular drugs after IP instillation. These interventions could inform the design of future clinical trials aiming at an improved efficacy of IP-based drug delivery in carcinomatosis patients.

Millimeter-wave emissivity as a metric for the non-contact diagnosis of human skin conditions

A half‐space electromagnetic model of human skin over the band 30–300 GHz was constructed and used to model radiometric emissivity. The model showed that the radiometric emissivity rose from 0.4 to 0.8 over this band, with emission being localized to a layer approximately one millimeter deep in the skin. Simulations of skin with differing water contents associated with psoriasis, eczema, malignancy, and thermal burn wounds indicated radiometry could be used as a non‐contact technique to detect and monitor these conditions. The skin emissivity of a sample of 30 healthy volunteers, measured using a 95 GHz radiometer, was found to range from 0.2 to 0.7, and the experimental measurement uncertainty was ±0.002. Men on average were found to have an emissivity 0.046 higher than those of women, a measurement consistent with men having thicker skin than women. The regions of outer wrist and dorsal forearm, where skin is thicker, had emissivities 0.06–0.08 higher than the inner wrist and volar forearms where skin is generally thinner. Recommendations are made to develop a more sophisticated model of the skin and to collect larger data sets to obtain a deeper understanding of the signatures of human skin in the millimeter wave band. Bioelectromagnetics. 38:559–569, 2017. © 2017 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc.

Overview of Methods for Overcoming Hindrance to Drug Delivery to Tumors, with Special Attention to Tumor Interstitial Fluid

Every drug used to treat cancer (chemotherapeutics, immunological, monoclonal antibodies, nanoparticles, radionuclides) must reach the targeted cells through the tumor environment at adequate concentrations, in order to exert their cell-killing effects. For any of these agents to reach the goal cells, they must overcome a number of impediments created by the tumor microenvironment (TME), beginning with tumor interstitial fluid pressure (TIFP), and a multifactorial increase in composition of the extracellular matrix (ECM). A primary modifier of TME is hypoxia, which increases the production of growth factors, such as vascular endothelial growth factor and platelet-derived growth factor. These growth factors released by both tumor cells and bone marrow recruited myeloid cells form abnormal vasculature characterized by vessels that are tortuous and more permeable. Increased leakiness combined with increased inflammatory byproducts accumulates fluid within the tumor mass (tumor interstitial fluid), ultimately creating an increased pressure (TIFP). Fibroblasts are also up-regulated by the TME, and deposit fibers that further augment the density of the ECM, thus, further worsening the TIFP. Increased TIFP with the ECM are the major obstacles to adequate drug delivery. By decreasing TIFP and ECM density, we can expect an associated rise in drug concentration within the tumor itself. In this overview, we will describe all the methods (drugs, nutraceuticals, and physical methods of treatment) able to lower TIFP and to modify ECM used for increasing drug concentration within the tumor tissue.

Low-Dose Vascular Photodynamic Therapy Decreases Tumor Interstitial Fluid Pressure, which Promotes Liposomal Doxorubicin Distribution in a Murine Sarcoma Metastasis Model

INTRODUCTION

Solid tumors are known to have an abnormal vasculature that limits the distribution of chemotherapy. We have recently shown that tumor vessel modulation by low-dose photodynamic therapy (L-PDT) could improve the uptake of macromolecular chemotherapeutic agents such as liposomal doxorubicin (Liporubicin) administered subsequently. However, how this occurs is unknown. Convection, the main mechanism for drug transport between the intravascular and extravascular spaces, is mostly related to interstitial fluid pressure (IFP) and tumor blood flow (TBF). Here, we determined the changes of tumor and surrounding lung IFP and TBF before, during, and after vascular L-PDT. We also evaluated the effect of these changes on the distribution of Liporubicin administered intravenously (IV) in a lung sarcoma metastasis model.

MATERIALS AND METHODS

A syngeneic methylcholanthrene-induced sarcoma cell line was implanted subpleurally in the lung of Fischer rats. Tumor/surrounding lung IFP and TBF changes induced by L-PDT were determined using the wick-in-needle technique and laser Doppler flowmetry, respectively. The spatial distribution of Liporubicin in tumor and lung tissues following IV drug administration was then assessed in L-PDT-pretreated animals and controls (no L-PDT) by epifluorescence microscopy.

RESULTS

L-PDT significantly decreased tumor but not lung IFP compared to controls (no L-PDT) without affecting TBF. These conditions were associated with a significant improvement in Liporubicin distribution in tumor tissues compared to controls (P < .05).

DISCUSSION

L-PDT specifically enhanced convection in blood vessels of tumor but not of normal lung tissue, which was associated with a significant improvement of Liporubicin distribution in tumors compared to controls.

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.

Phenomenological model of interstitial fluid pressure in a solid tumor

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

Disparity between prostate tumor interior versus peripheral vasculature in response to verteporfin-mediated vascular-targeting therapy

Photodynamic therapy (PDT) is a light-based cancer treatment modality. Here we employed both in vivo and ex vivo fluorescence imaging to visualize vascular response and tumor cell survival after verteporfin-mediated PDT designed to target tumor vasculature. EGFP-MatLyLu prostate tumor cells, transduced with EGFP using lentivirus vectors, were implanted in athymic nude mice. Immediately after PDT with different doses of verteporfin, tumor-bearing animals were injected with a fluorochrome-labeled albumin. The extravasation of fluorescent albumin along with tumor EGFP fluorescence was monitored noninvasively with a whole-body fluorescence imaging system. Ex vivo fluorescence microscopy was performed on frozen sections of tumor tissues taken at different times after treatment. Both in vivo and ex vivo imaging demonstrated that vascular-targeting PDT with verteporfin significantly increased the extravasation of fluorochrome-labeled albumin in the tumor tissue, especially in the tumor periphery. Although PDT induced substantial vascular shutdown in interior blood vessels, some peripheral tumor vessels were able to maintain perfusion function up to 24 hr after treatment. As a result, viable tumor cells were typically detected in the tumor periphery in spite of extensive tumor cell death. Our results demonstrate that vascular-targeting PDT with verteporfin causes a dose- and time-dependent increase in vascular permeability and decrease in blood perfusion. However, compared to the interior blood vessels, peripheral tumor blood vessels were found less sensitive to PDT-induced vascular shutdown, which was associated with subsequent tumor recurrence in the tumor periphery.

Multimode near-field microwave monitoring of free water content of skin and imaging of tissue

We have used the near-field scanning microwave microscopy (NSMM) technique in the 1-10 GHz range to monitor the free water content of skin. The water content is interpreted from the measured dielectric properties of the epidermis. The finger skin was first hydrated by soaking in water at 37 degrees C for 30 min followed by monitoring of water content as the free water evaporated under ambient conditions. The same technique has also been employed to image a 1 cm x 1 cm sample of chicken skin. It has been shown that variations exist in the resonant frequencies and quality factors of tissue under varying physical parameters. The samples analysed were as-received and thermally dehydrated or damaged chicken tissue samples. We contrast between the dielectric properties with the optical images. We also discuss possible application of our imaging technique in clinical monitoring of the wound healing process.

A simple method for measuring interstitial fluid pressure in cancer tissues

A novel procedure using a polyurethane transducer-tipped catheter (Millar) is described that allows reliable measurement of interstitial fluid pressure (IFP) in cancer tissues. Before and after each use, the transducer is calibrated at 37 degrees C by a water column. After calibration, the transducer is passed through the lumen of a surgical needle. The sensor is kept in the lumen of the needle during penetration into the tumor. The sensor tip is then introduced into the center core of the tumor as the needle sleeve is withdrawn from the tumor surface. Our new technique is simple and provides IFPs equal to those provided by the well-established, wick-in-needle technique. Using our new technique, we compared IFP in skin melanoma grafts in NG2 knockout and wild-type mice. Knocking out NG2 proteoglycan on vasculogenic and angiogenic pericytes reduced interstitial fluid pressure in melanoma from +4.9 cm H2O to -0.4 cm H2O (P=0.0054 Mann-Whitney U test).

Free water content and monitoring of healing processes of skin burns studied by microwave dielectric spectroscopyin vivo

We have investigated the dielectric properties of human skin in vivo at frequencies up to 10 GHz using a time-domain reflectometry method with open-ended coaxial probes. Since gamma-dispersion results from the reorientation of free water molecules, the free water content of skin is quantitatively determined by dielectric measurements. The free water content of finger skin increased by about 10% after soaking in 37 degrees C water for 30 min, and it systematically decreased again through the drying process, as expected. Thus this analytical method has been applied to the study of skin burns. The free water content of burned human cheek skin due to hydrofluoric acid was significantly lower than that of normal skin, and the burned skin recovered through the healing process. In the case of a human hand skin burn due to heat, although the free water content was almost the same as that of normal skin at the beginning, it decreased during the healing process for the first 10 days, then began to increase. Although the number of test subjects was one for each experiment, it was shown that free water content is a good indicator for evaluating skin health and can be well monitored by dielectric spectroscopy.

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.

Revascularization of transplanted adipose tissue: a study in the dorsal skinfold chamber of hamsters

Adipose tissue seems to be an ideal material for use as a permanent soft-tissue substitute in reconstructive surgery. However, knowledge of the behavior of the graft--in particular, its revascularization--is scarce. Therefore, the aim of the current study was to establish a novel model that allows for long-term in vivo quantitative analysis of revascularization of adipose tissue after transplantation. Hamsters (n = 8) were fitted with transparent titanium dorsal skinfold chambers. Immediately after en bloc harvest of adipose tissue from the left inguinal area, the graft was placed gently into the chamber. At days 1, 3, 12, and 21, red blood cell-perfused vessels were assessed in surrounding host tissue, in the border of the graft, and in its center (n = 6 areas each) using intravital fluorescent microscopy. The model allowed for permanent observations of adipose tissue and quantitative analysis of functional vessel density (FVD). At the border zone of the graft, an FVD of 2 +/- 1 cm per cm(2) was measured at day 1. In this region FVD increased constantly and finally reached values (184 +/- 10 cm per cm(2); day 21) that were comparable with those of the surrounding host tissue. Revascularization in the center of the graft started at day 3 after transplantation (14 +/- 3 cm per cm(2)). Here, FVD increased constantly, but lower values compared with the grafts' border zone were measured (139 +/- 10 cm per cm(2); day 21). FVD data obtained from transplanted adipose tissue may contribute to understanding fundamental mechanisms of graft failure.

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.

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.

Pharmacokinetics and pharmacodynamics of tetra(m-hydroxyphenyl)chlorin in the hamster cheek pouch tumor model: comparison with clinical measurements

The pharmacokinetics (PK) of the photosensitizer tetra(m-hydroxyphenyl)chlorin (mTHPC) was measured by optical fiber-based light-induced fluorescence spectroscopy (LIFS) in the normal and tumoral cheek pouch mucosa of 29 Golden Syrian hamsters with chemically induced squamous cell carcinoma. Similar measurements were carried out on the normal oral cavity mucosa of five patients up to 30 days after injection. The drug doses were between 0.15 and 0.3 mg per kg of body weight (mg/kg), and the mTHPC fluorescence in the tissue was excited at 420 nm. The PK in both human and hamster exhibited similar behavior although the PK in the hamster mucosa was slightly delayed in comparison with that of its human counterpart. The mTHPC fluorescence signal of the hamster mucosa was smaller than that of the human mucosa by a factor of about 3 for the same injected drug dose. A linear correlation was found between the fluorescence signal and the mTHPC dose in the range from 0.075 to 0.5 mg/kg at times between 8 and 96 h after injection. No significant selectivity in mTHPC fluorescence between the tumoral and normal mucosa of the hamsters was found at any of the applied conditions. The sensitivity of the normal and tumoral hamster cheek pouch mucosa to mTHPC photodynamic therapy as a function of the light dose was determined by light irradiation at 650 nm and 150 mW/cm2, 4 days after the injection of a drug dose of 0.15 mg/kg. These results were compared with irradiations of the normal oral and normal and tumoral bronchial mucosa of 37 patients under the same conditions. The reaction to PDT of both types of human mucosae was considerably stronger than that of the hamster cheek pouch mucosa. The sensitivity to PDT became comparable between hamster and human mucosa when the drug dose for the hamster was increased to 0.5 mg/kg. A significant therapeutic selectivity between the normal and neoplastic hamster cheek pouch was observed. Less selectivity was found following irradiations of normal mucosa and early carcinomas in the human bronchi. The pharmacodynamic behavior of mTHPC was determined by test irradiations of the normal mucosa of hamsters and patients between 6 h and 8 days after injection of 0.5 and 0.15 mg/kg in the hamsters and the patients, respectively. The normal hamster cheek pouch showed a maximum response to irradiation 6 h after injection and then decreased continuously to no observable reaction at 8 days after injection. The reaction of the normal human oral mucosa, however, showed an increasing sensitivity to the applied light between 6 h and 4 days after mTHPC injection and then decreased again at 8 days. The hamster model with the chemically induced early squamous cell cancer in the cheek pouch thus showed some similarity to the early squamous cell cancer of the human oral mucosa considering the PK. However, a quantitative difference in fluorescence signal for identical mTHPC doses as well as a significant difference in pharmacodynamic behavior were also observed. The suitability of this animal model for the optimization of PDT parameters in the clinic is therefore limited. Hence great care must be taken in screening new dyes for PDT of early squamous cell cancer of the upper aerodigestive tract based upon observables in the hamster cheek pouch model.

Tumoricidal effects of onconase on various tumors

BACKGROUND AND OBJECTIVES

The effects of Onconase (Onc) on the tumor growth in vitro and in vivo were examined. Because elevated tumor interstitial fluid pressure (TIFP) is one of the major causes of inadequate drug delivery into solid tumors, we tested if Onc could lower TIFP in solid tumors.

METHODS

We used several assays including a clonogenic assay and a growth delay assay for the determination of anti-tumoricidal effects of Onc. We also measured Onc-induced changes in several tumor physiological parameters.

RESULTS

Onc demonstrated cytotoxic effects in all eight exponentially growing cell lines in vitro. It effectively inhibited the growth of all four transplanted tumors in vivo, and significantly reduced TIFP in all four tumors. Onc also induced increases in tumor blood flow (TBF) as well as increases in median tumor oxygen partial pressure (pO(2)) in solid tumors.

CONCLUSIONS

Onc showed anti-tumoral effects on various tumor cells in vitro as well as in vivo. We also gained some insight regarding the potential physiological benefit of Onc as a new therapeutic agent in cancer treatment. Due to increases in both TBF and tumor pO(2), Onc could be a potential candidate as a novel radiation enhancer; therefore, the study of the radiation response in vivo is warranted.

Current concepts in gastrointestinal photodynamic therapy

OBJECTIVE

To review current concepts of photodynamic therapy (PDT) applied to the treatment of tumors of the gastrointestinal tract.

SUMMARY BACKGROUND DATA

PDT initially involves the uptake or production of a photosensitive compound by tumor cells. Subsequent activation of the photoreactive compound by a specific wavelength of light results in cell death, either directly or as a result of vascular compromise and/or apoptosis.

METHODS

The authors selectively review current concepts relating to photosensitization, photoactivation, time of PDT application, tissue selectivity, sites of photodynamic action, PDT effects on normal tissue, limitations of PDT, toxicity of photosensitizers, application of principles of PDT to tumor detection, and current applications of PDT to tumors of the gastrointestinal tract.

RESULTS

PDT is clearly effective for small cancers, but it is not yet clear in which cases such treatment is more effective than other currently acceptable approaches. The major side effect of PDT is cutaneous photosensitization. The major limitation of PDT is depth of tumor kill. As data from current and future clinical trials become available, a clearer perspective of where PDT fits in the treatment of cancers will be gained. Many issues regarding pharmacokinetic data of photosensitizers, newer technology involved in light sources, optimal treatment regimens that take advantage of the pharmacophysiology of photoablation, and light dosimetry still require solution. One can foresee application of differing sensitizers and light sources depending on the specific clinical situation. As technologic advances occur, interstitial PDT may have significant application.

CONCLUSIONS

PDT has a potentially important role either as a primary or adjuvant mode of treatment of tumors of the gastrointestinal tract.

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.

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.

The biology of photodynamic therapy

The subcellular, cellular and tissue/tumour interactions with non-toxic photosensitizing chemicals plus non-thermal visible light (photodynamic therapy (PDT) are reviewed. The extent to which endothelium/vasculature is the primary target is discussed, and the biochemical opportunities for manipulating outcome highlighted. The nature of tumour destruction by PDT lends itself to imaging outcome by MRI and PET.

Proton relaxation times and interstitial fluid pressure in human melanoma xenografts

The interstitial fluid pressure (IFP) and the proton spin-lattice and spin-spin relaxation times (T1 and T2) of some experimental tumours have been shown to be related to tumour water content. These observations have led to the hypothesis that magnetic resonance imaging (MRI) might be a clinically useful non-invasive method for assessment of tumour IFP. The purpose of the work reported here was to examine the general validity of this hypothesis. R-18 human melanoma xenografts grown intradermally in Balb/c nu/nu mice were used as the tumour model system. Median T1 and T2 were determined by spin-echo MRI using a 1.5-T clinical whole-body tomograph. IFP was measured using the wick-in-needle technique. No correlation was found between tumour IFP and fractional tumour water content. Moreover, there was no correlation between median T1 or T2 and IFP, suggesting that proton T1 and T2 values determined by MRI cannot be used clinically to assess tumour IFP and thereby to predict the uptake of macromolecular therapeutic agents.

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.

Interstitial fluid pressure, perfusion rate and oxygen tension in human melanoma xenografts

Interstitial fluid pressure (IFP) has been reported to be inversely correlated to rate of perfusion and oxygen tension (pO2) in experimental tumours (Lee et al., 1992; Roh et al., 1991 a). Studies of patients with squamous cell carcinoma of the uterine cervix have provided clinical data consistent with the experimental data (Roh et al., 1991b; Milosevic et al., 1995). These observations have led to the hypothesis that IFP might be a useful indicator of tumour oxygenation status. The purpose of the work reported here was to examine in detail the general validity of this hypothesis. R-18 human melanoma xenografts grown intradermally in Balb/c nu/nu mice were used as tumour model system. IFP and perfusion rate or IFP and pO2 were measured in the same individual tumours in two independent series of experiments. The wick-in-needle method was used to record IFP. Perfusion rate was studied by using the 86Rb uptake method. The KIMOC-6650 Eppendorf histograph was used to measure pO2. IFP, perfusion rate and pO2 differed considerably between individual tumours. However, there was no relationship between IFP and perfusion rate or IFP and pO2, suggesting that the oxygenation status of tumours cannot be derived from measurements of IFP. Consequently, IFP is probably not a useful predictor of radiation resistance caused by hypoxia.

Wavelength dependency of photodynamic effects after sensitization with 5-aminolevulinic acid in vitro and in vivo

A promising new therapeutic modality for skin cancer, administration of the heme precursor 5-aminolevulinic acid followed by light irradiation, is known as photodynamic therapy. Photofrin, the only clinically approved sensitizer, has an absorption maximum at 630 nm, the wavelength used in most experimental and clinical trials with 5-aminolevulinic acid. We investigated photodynamic efficacy of irradiation with coherent light at wavelengths ranging from 622 to 649 nm in vitro and in vivo as well as the content and distribution of intracellular porphyrin after administration of 5-aminolevulinic acid. HaCaT immortalized human keratinocytes were sensitized with 30 micrograms/ml 5-aminolevulinic acid for 24 h in vitro. By cell viability determined with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, the best cell-killing effects were observed after irradiation at 635 nm. Using an amelanotic melanoma (A-Mel-3) grown subcutaneously in Syrian Golden hamsters, we confirmed these results in vivo: tumor growth was markedly delayed in animals treated with 100 mg/kg 5-aminolevulinic acid intravenously and irradiated with coherent light at 635 nm as compared to animals irradiated at 630 nm. This photodynamic effect is probably mediated by large amounts of the photosensitizing porphyrin, protoporphyrin IX, localized in cell membranes as visualized by confocal laser scan microscopy and as determined by high pressure liquid chromatography in vitro. The results suggest that irradiation at 635 nm with a coherent light source is more effective than irradiation at 630 nm for photodynamic therapy with 5-aminolevulinic acid.