Noninvasive measurement of microvascular and interstitial oxygen profiles in a human tumor in SCID mice

Simultaneous measurements of intravascular and interstitial oxygen partial pressure (PO2) in any tissue have not previously been reported, despite the importance of oxygen in health and in disease. This is due to the limitations of current techniques, both invasive and noninvasive. We have optically measured microscopic profiles of PO2 with high spatial resolution in subcutaneous tissue and transplanted tumors in mice by combining an oxygen-dependent phosphorescence quenching method and a transparent tissue preparation. The strengths of our approach include the ability to follow PO2 in the same location for several weeks and to relate these measurements to local blood flow and vascular architecture. Our results show that (i) PO2 values in blood vessels in well-vascularized regions of a human colon adenocarcinoma xenograft are comparable to those in surrounding arterioles and venules, (ii) carbogen (95% O2/5% CO2) breathing increases microvascular PO2 in tumors, and (iii) in unanesthetized and anesthetized mice PO2 drops to hypoxic values at < 200 microns from isolated vessels but drops by < 5 mmHg (1 mmHg = 133 Pa) in highly vascularized tumor regions. Our method should permit noninvasive evaluations of oxygen-modifying agents and offer further mechanistic information about tumor pathophysiology in tissue preparations where the surface of the tissue can be observed.

Evaluation of photodynamic therapy-induced heating of hamster melanoma and its effect on local tumour eradication

To investigate the contribution of hyperthermia on local tumour eradication by photodynamic therapy (PDT) we quantified PDT induced tumour heating and evaluated its biological effect in vivo. Syrian Golden hamsters bearing an amelanotic melanoma implanted into the dorsal skin received intravenous injections of Photofrin (5 mg kg-1). Twenty-four hours later tumours were illuminated by red light (630 nm; total energy: 100 J cm-2) at 100 and 200 mW cm-2 and tumour surface and tumour centre temperature were measured. The tumoricidally threshold temperature of 43 degrees C was exceeded at 200 mW cm-2 only, revealing a calculated equivalent treatment time at 43 degrees C of about 10 min. Melanomas treated by PDT at both light intensities disappeared within 48 h and did not reappear locally within the observation period of 32 days. Tumours treated by hyperthermia (water bath) at the maximum temperatures measured during illumination at 200 mW cm-2 (45.5 degrees C for 500 s) or animals receiving laser light at 200 mW cm-2 alone showed a significant growth delay compared to controls (p < 0.05), whereas illumination at 100 mW cm-2 alone or hyperthermia corresponding to the maximum temperature obtained at 100 mW cm-2 (39.5 degrees C for 1000 s) did not alter tumour growth. These data indicate that tumour temperature increased during PDT and exceeded the hyperthermic threshold temperature of 43 degrees C at 200 mW cm-2. In our tumour model hyperthermia was not necessary for a complete tumour eradication by PDT. Although a combination of PDT and hyperthermia might act in an additive or synergistic manner, an unrecognized overlap of both effects might complicate the interpretation of studies on the mechanisms of PDT.

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

The effect of photodynamic therapy (PDT) on interstitial fluid pressure (IFP), tumour volume and water content was measured in melanomas grown in hamsters. Unlike control tumours, treated tumours exhibited a 40-60% increase in volume at 1, 3 and 6 h post PDT. IFP also increased at 1 and 3 h after PDT, but decreased to 50% of control value after 24 h, presumably as a result of PDT-induced microcirculatory impairment.

Fluorescence photobleaching with spatial Fourier analysis: measurement of diffusion in light-scattering media

A new method for the measurement of diffusion in thick samples is introduced, based upon the spatial Fourier analysis of Tsay and Jacobson (Biophys. J. 60: 360-368, 1991) for the video image analysis of fluorescence recovery after photobleaching (FRAP). In this approach, the diffusion coefficient is calculated from the decay of Fourier transform coefficients in successive fluorescence images. Previously, the application of FRAP in thick samples has been confounded by the optical effects of out-of-focus light and scattering and absorption by the sample. The theory of image formation is invoked to show that the decay rate is the same for both the observed fluorescence intensity and the true concentration distribution in the tissue. The method was tested in a series of macromolecular diffusion measurements in aqueous solution, in agarose gel, and in simulated tissue consisting of tumor cells (45% v/v) and blood cells (5% v/v) in an agarose gel. For a range of fluorescently labeled proteins (MW = 14 to 600 kD) and dextrans (MW = 4.4 to 147.8 kD), the diffusion coefficients in aqueous solution were comparable to previously published values. A comparison of the spatial Fourier analysis with a conventional direct photometric method revealed that even for the weakly scattering agarose sample, the conventional method gives a result that is inaccurate and dependent on sample thickness whereas the diffusion coefficient calculated by the spatial Fourier method agreed with published values and was independent of sample thickness. The diffusion coefficient of albumin in the simulated tissue samples, as determined by the spatial Fourier analysis, varied slightly with sample thickness. In contrast, when the same video images were analyzed by direct photometric analysis, the calculated diffusion coefficients were grossly inaccurate and highly dependent on sample thickness. No simple correction could be devised to ensure the accuracy of the direct photometric method of analysis.These in vitro experiments demonstrate the advantage of our new analysis for obtaining an accurate measure of the local diffusion coefficient in microscopic samples that are thick (thickness greater than the microscope depth of focus) and scatter light.

Dorsal skinfold chamber technique for intravital microscopy in nude mice

For many years, observation chambers, implanted in various animal species and in man, have been used for intravital microscopy of the microcirculation in granulation tissue, preformed tissue, or of the microvascularization of tissue implants. We describe herein a skinfold chamber model for the intravital microscopic investigation of striated skin muscle in immunoincompetent, nude mice over a minimum period of 2 weeks. Using fluorescent markers for contrast enhancement of plasma (fluorescein isothiocyanate-dextran) and leukocytes (acridine orange), the presented model allows the quantitative analysis of 1) the microhemodynamic parameters microvessel diameter and red blood cell velocity in arterioles (16 to 50 mu diameter), capillaries (4 to 9 mu diameter), and post-capillary venules (19 to 60 mu diameter), 2) leukocyte/endothelium interaction in these vessel segments, 3) functional capillary density and intercapillary distance, and 4) endothelial cell integrity. These parameters can be assessed in the microcirculation of the striated muscle tissue under normal or pathological conditions, as well as in the microcirculation of transplanted xenogeneic (human) neoplastic and non-neoplastic tissue grafts.

Tumour localisation kinetics of photofrin and three synthetic porphyrinoids in an amelanotic melanoma of the hamster

In this study the localisation of porphyrinoid photosensitizers in tumours was investigated. To determine if tumour selectivity results from a preferential uptake or prolonged retention of photosensitizers, intravital fluorescence microscopy and chemical extraction were used. Amelanotic melanoma (A-Mel-3) were implanted in a skin fold chamber in Syrian Golden hamsters. Distribution of the porphyrin mixture Photofrin and three porphycenes, pure porphyrinoid model compounds, was studied quantitatively by intravital fluorescence microscopy. Extraction of tissue and blood samples was performed to verify and supplement intravital microscopic results. Photofrin accumulated in melanomas reaching a maximum tumour:skin tissue ratio of 1.7:1. Localisation of the different porphycenes was found to be highly tumour selective (3.2:1), anti-tumour selective (0.2:1), and non-selective (1:1) with increasing polarity of the porphycenes. The two non-tumour selective porphycenes had distinctly accelerated serum and tissue kinetics; serum halflife times being as short as 1 min. The specific localisation of the slowly distributed, tumour selective photosensitizers, occurred exclusively during the distribution from serum and uptake into tissues. For the most selective porphycene, the tumour selection process had a halflife of 260 +/- 150 min and led to a strongly fluorescent tumour edge edema. Accumulation of porphyrines by the amelanotic melanoma (A-Mel-3) can be attributed to an enhanced uptake rate for lipophilic molecules in this subcutaneously growing neoplasm. The slow distribution of the two tumour specific photosensitizers and the strong fluorescence of these hydrophobic molecules in the tumour compartment with a high water content indicate a carrier role of serum proteins in the selection process. Enhanced permeability of the tumour vasculature to macromolecules appears to be the most probable reason for the tumour selectivity of these two sensitisers.

[Importance of increased interstitial fluid pressure in therapy of malignant tumors of the head-neck area]

Animal experiments showed that elevated interstitial fluid pressure (IFP) is associated with poor blood supply and inadequate supply of drugs to solid tumours. IFP is approximately 0 mmHg in most normal tissues. Up to now there have been only few studies showing elevated interstitial pressure in human tumours in situ: Mammary carcinomas, cervical carcinomas and colorectal cancers have an elevated IFP. We measured IFP in squamous cell carcinomas of the head and neck region in humans using the "wick-in-needle" technique. In all lesions (n = 25), the IFP was elevated (4-39 mmHg). The IFP increased with tumour size. The highest IFP was 39 mmHg in a 26 ml tumour. These results show that squamous cell carcinomas of the head and neck region in humans have an elevated interstitial fluid pressure. The elevation of IFP associated with inadequate delivery of drugs to the interstitium of malign tumours may reduce the response to therapy.

Microvascular permeability of albumin, vascular surface area, and vascular volume measured in human adenocarcinoma LS174T using dorsal chamber in SCID mice

A novel method was developed to measure the effective permeability of microvessels in three-dimensional tumors. Two unique features characterized our approach: (i) Texas Red (with peak excitation and peak emission wavelengths of 596 and 615 nm, respectively) was used for macromolecular labeling, to minimize the absorption of fluorescence light by hemoglobin in blood. Thus the tumor tissue could be treated approximately as a uniform medium with respect to light absorption. (ii) The light absorption and scattering in tumor tissues were accounted for in relating the fluorescence intensity to the amount of Texas Red-labeled macromolecules extravasated. The vascular permeability of Texas Red-labeled bovine serum albumin in human tumor xenograft LS174T implanted in dorsal skin-fold chamber in severe combined immunodeficient mice was measured using this method. The average permeability-surface area product per unit volume (PS/V, x 10(-4) sec-1) and the average effective permeability (P, x 10(-7) cm/sec) were found to be 1.26 +/- 0.72 and 6.06 +/- 4.30, respectively; the fractional volume of tumor vessels (Vves/V, %) was found to be 9.2 +/- 2.9, and the total surface area of vessels per unit volume (S/V, cm2/cm3) was found to be 239 +/- 82. The errors in the estimation of these parameters are discussed. The method described here is general and can be adapted to study the microvascular permeability of superficial tumors in various organs in patients or animals.

Angiogenesis, microvascular architecture, microhemodynamics, and interstitial fluid pressure during early growth of human adenocarcinoma LS174T in SCID mice

To date, most quantitative information on tumor angiogenesis, microcirculation, and transport has been derived from rodent tumors grown in transparent chamber preparations. In this paper we present a chamber technique adapted to immunodeficient mice for the study of human tumor xenografts. Microcirculatory parameters in severe combined immunodeficient mice bearing a dorsal skin fold chamber preparation were quantified using intravital microscopy and image analysis. The take rate of the human colon adenocarcinoma LS174T in the chamber preparation was 100%, and the tumor area doubling time was 6.5 days. Three days following implantation of 2 x 10(5) tumor cells onto the striated skin muscle, capillary sprouts were noted in the tumor cell mass. Microvasculature in the tumors was established after 10 days. Capillary density, vessel diameter, red blood cell velocity, and blood flow rates in individual microvessels measured on days 10, 14, 18, and 22 showed no statistical difference in the striated muscle (capillaries) and subcutaneous tissue (arterioles and venules) of the skin of tumor-free animals (N = 6), whereas these parameters increased slightly, but not significantly, in the LS174T tumors (N = 7). Mean interstitial fluid pressure (+/- SD) in these small tumors was 4.6 +/- 1.7 mmHg (N = 4) on day 10 and 5.1 +/- 0.9 mmHg (N = 4) on day 22 and significantly elevated compared to that in the subcutaneous and skin tissue (-0.9 +/- 0.8 mmHg) (N = 4) (P < 0.001). To our knowledge, this is the first model enabling intravital microscopic studies of human tumor xenografts in a transparent chamber preparation in severe combined immunodeficient mice. Studies on angiogenesis, microcirculation, and transport using such a preparation should provide new insights into microcirculation-mediated mechanisms for cancer treatment.

Interstitial hypertension in head and neck tumors in patients: correlation with tumor size

Elevated interstitial fluid pressure (IFP) is associated with poor blood supply and inadequate delivery of drugs to solid tumors. IFP was measured in squamous cell carcinomas of the head and neck region in humans using the wick-in-needle technique. In all lesions (n = 19), the IFP was elevated (4-33 mm Hg). Furthermore, the IFP increased with tumor size. The highest IFP was 33 mm Hg in a 24-ml tumor. In one tumor, the IFP was found to be negative (-2.6 mm Hg), which is comparable to that in human skin or subcutaneous tissue. The histopathology of this tumor was benign. If this pressure difference between malignant and benign lesions can be confirmed in a large number of tumors, then the IFP could be used to aid tumor detection during needle biopsy. The value of IFP as a predictor of response to radiotherapy, photodynamic therapy, hyperthermia, and chemotherapy should be assessed prospectively.

Interstitial fluid pressure in solid tumors following hyperthermia: possible correlation with therapeutic response

Elevated interstitial fluid pressure (IFP) of tumors may be a physiological barrier to the delivery of certain therapeutic agents. The objective of this study was to find out if IFP could be lowered using localized hyperthermia and if the reduction in IFP could predict the tumor response to treatment. Amelanotic melanoma (A-Mel-3) implanted into the dorsal skin of Syrian golden hamsters was exposed to hyperthermic treatment after 7 days of tumor growth at tumor volumes of about 100-150 mm3. Hyperthermia was induced by immersing the tumor in a water bath at 43 degrees C for 30 or 60 min. Forty-eight h later the IFP of control and treated tumors was determined by using the wick-in-needle technique. The mean IFP in control tumors was 12.6 mmHg. Hyperthermic treatment for 30 min induced a significant decrease to 2.8 mmHg (P less than 0.001 versus controls), whereas a 60-min immersion of the tumors induced a further decrease to 0.8 mmHg (P less than 0.05 versus 43 degrees C for 30 min). Separate experiments on tumor growth in corresponding groups of animals revealed a significant growth delay of 2.7 days after hyperthermia for 30 min. Enhanced growth delay and partial tumor response in 66% of the tumors were found following 60 min of hyperthermia at 43 degrees C. The thermal dose-dependent decrease in IFP presumably results from the dose-dependent damage to the tumor vasculature. In addition, the association of an enhanced biological effect with a more pronounced reduction of interstitial fluid pressure suggests that the IFP might serve as a quantitative parameter to predict the response of tumors to hyperthermic therapy.