Comparison of fluorescence intensity of Hoechst 33342-stained EMT6 tumour cells and tumour-infiltrating host cells

Morpho-Functional Study of Vascular Fluorochrome Delivery to Lung and Liver Metastases of Lewis Lung Carcinoma (3Ll)

The growth of 3LL liver and lung metastases related to Its vascular organization was studied by morphological and functional methods, using the Hoechst 33342 fluorescent DNA staining technique. Experimental liver and lung metastases were produced in syngeneic C57BL/6 mice by injection of 3LL tumor cells into a lateral tail vein or into the spleen, respectively. The resulting neoplasms were composed of large cells arranged in sheets with a thin irregularly distributed stroma. Scattered blood vessels with an open or closed lumen were observed within the tumor. Functional study of H33342 diffusion showed a single and reticular fluorescent pattern in liver metastases. In contrast, in lung metastases the fluorochrome diffusion revealed two different fluorescent patterns related to the location of the metastasis. Thus, parenchymal and subpleural metastasis presented a fluorescent pattern similar to that observed in the liver whereas metastases located around blood vessels and conducting airways never displayed fluorescence. In summary, our results suggest that the target metastatic organ and/or intra-organ location modulates the characteristics of metabolic exchange of the tumor cells In relation to the vascular organization of the metastatic focus.

Evaluation of wedged arterial injection as a new technique for delivery of experimental therapeutic substances into the porcine pancreas

OBJECTIVES

To prospectively evaluate the technical feasibility and efficacy of wedged arterial injection (WAI) as a potential route for experimental selective therapy to the pancreas of healthy pigs.

MATERIALS AND METHODS

Selective angiographies were completed in ten pigs under general anaesthesia. By superselective angiography, the catheter was inserted and wedged into the major pancreatic artery, blocking the blood flow. In order to evaluate the efficacy of the WAI method, a DNA-specific fluorescent dye (Hoechst 33258) was used.

RESULTS

Histological study revealed a uniform distribution of the fluorescent dye within the nuclei of the endocrine and exocrine pancreatic cells. Pancreatic and liver enzymes as well as histopathology of the pancreas were normal.

CONCLUSION

WAI is a highly effective minimally invasive methodology to target the porcine pancreas. The findings suggest that WAI may contribute to developing preclinical assays of pancreas gene or cell-transfer therapies in swine model.

[125I/127I]iodoHoechst 33342: synthesis, DNA binding, and biodistribution

An iodinated analog of the DNA-minor-groove-binding agent Hoechst 33342 has been synthesized and evaluated for DNA binding and tumor targeting. The bis-benzimidazole ring system of the title compound was constructed from the piperazinyl terminus via a Pinner-type cyclization followed by oxidative cyclization of the diamine Schiff base. To synthesize radioiodoHoechst 33342, (trimethylstannyl)Hoechst 33342 was prepared by the same strategy and subjected to mild radioiododestannylation in the presence of lactoperoxidase. After purification by HPLC, the radiochemical was separated in carrier-free form with > 85% radiochemical yield and > 99% chemical and radiochemical purity. Fluorescence spectrometric analysis of the binding of iodoHoechst 33342 to calf thymus DNA gave an equilibrium association constant (Ka) of 2.57 x 10(7) M-1 comparable to the Ka value of Hoechst 33342. Fluorescence microscopy of viable V79 cells demonstrated that the iodinated dye stained the nuclei with avidity similar to that of the noniodinated dye. The biodistribution of [125I]-iodoHoechst 33342 in LS174T tumor-bearing athymic mice 4 h postadministration showed a tumor uptake of 3-4% injected dose per gram (ID/g), tumor/blood ratio of 6-8, and tumor/ nontumor ratios above unity for most organs. A low thyroid uptake (approximately 2% ID/g) indicated that the radiochemical did not deiodinate and was stable in vivo.

Differential uptake of systemic fluorochrome Hoechst 33342 in lung and liver metastasis of B16 melanoma

The growth and vascularization patterns of B16 melanoma colonies in the liver and lungs were measured and compared by histological techniques and dye diffusion patterns after injection of the fluorochrome Hoechst 33342. In the liver, the fluorescent pattern of dye diffusion revealed that uninodular tumours measuring up to 146 microns in diameter were not functionally vascularized. However, when the nodules fused to give rise to multinodular tumours measuring between 256 and 366 microns in diameter, a reticular dye diffusion pattern revealed functional tumour vascularization. In the lungs, subpleural, parenchymal and peritubular (i.e. surrounding blood vessels and airways) tumours were observed. The two former classes were vascularized down to thicknesses and diameters of 49 and 24 microns respectively. In contrast, dye diffusion was never seen in peritubular tumour cuffs up to 609 microns in thickness. The results indicate differences in vascularization patterns in B16 tumours in the liver and lungs, and differences between tumours growing in different sites within the lungs. If these results are applicable to metastases in these two organs, they indicate potential diffusion-mediated resistance to chemotherapy, and potential hypoxia-mediated resistance to radiotherapy of both metastases and micrometastases.

Analysis of distribution of tumor- and preneoplasia-infiltrating lymphocytes using simultaneous Hoechst 33342 labeling and immunophenotyping

Hoechst 33342 in vivo staining was combined with immunofluorescent staining of cell surface antigens to quantify the distribution, relative to blood supply, of lymphocytes in a preneoplastic mammary lesion, the murine C4 hyperplastic alveolar nodule (HAN), and the C4 adenocarcinoma which develops from C4 HAN. The vascular supply to lymphocytes expressing Thy 1.2, L3T4, Ly2, and ASGM1 cell surface antigens was evaluated in both tissues. The distribution of ASGM1+ cells, which include natural killer cells, differed between the two tissues, being significantly increased in the 20% brightest Hoechst-stained lymphocyte fraction in HAN but not in C4 tumor. Distribution of T lymphocytes did not differ between the two tissues. The combination of in vivo Hoechst 33342 with in vitro immunofluorescence provides a simple method to evaluate the distribution with regard to blood supply of lymphocyte subsets in solid tumors and preneoplastic lesions.

Effect of vascular marker Hoechst 33342 on tumour perfusion and cardiovascular function in the mouse

The fluorescent stain Hoechst 33342 (H33342) has been employed extensively as an in vivo marker of functional tumour vasculature. We have found that H33342 causes a transient, dose-dependent decrease in tumour red blood cell (RBC) flow in SCCVII tumours as measured using laser Doppler flowmetry. After intravenous bolus injection of 15 mg kg-1 to anaesthetised mice, blood flow in subcutaneous back tumours declined to 19 +/- 11% of pretreatment values, returning to normal in less than 7 min. The effect was less pronounced in mice bearing foot tumours in which flow decreased to 52 +/- 14% of pretreatment values in unanaesthetised mice and to 50 +/- 15% in anaesthetised animals. RBC flow in foot tumours remained significantly depressed for only 2-3 min. A dose of 5 mg kg-1 was not significantly vasoactive in back tumours. H33342 also caused a transient 20 +/- 6 mmHg decline in mouse arterial blood pressure. Blood pH and haematocrit, and tumour cell oxygen consumption were unchanged by H33342. H33342-induced flow changes did not affect results obtained using an in vivo double staining protocol provided that the interval between stain injections was greater than 5 min. Due to its transient effects on tumour perfusion, the stain caused radiobiological tumour hypoxia if injected immediately prior to X-irradiation. Injection 20 min before irradiation had no influence on tumour radiation response. We conclude that the transient nature of H33342-induced perturbations in mouse cardiovascular physiology and tumour blood flow must always be considered but do not preclude the use of the stain as a vascular marker to detect spontaneous tumour blood flow fluctuations or acute hypoxia.

Intermittent blood flow in the KHT sarcoma--flow cytometry studies using Hoechst 33342

The administration of the fluorescent DNA stain, Hoechst 33342, to mice bearing the KHT sarcoma, combined with flow cytometry, can be used to select cells according to their proximity to functional vasculature. Different protocols of administration of Hoechst 33342 were used in order to differentiate between the presence of temporary and chronically hypoxic cells. The results show a large difference in radiosensitivity between cells close to, and distant from, functional vasculature. However, this pattern of radiosensitivity is observed only when the staining period with Hoechst 33342 is short and coincides with the period of irradiation. When the radiation treatment is temporally divorced from the staining period then the radiosensitivity and staining intensity are not related. This result can be interpreted as indicating that hypoxic cells exist within this tumour as a result of fluctuations in tumour blood flow.

Lymphocytic infiltration and cytotoxicity under hypoxic conditions in the EMT6 mouse mammary tumor

Infiltration of lymphocytes, neutrophils and macrophages was evaluated in hypoxic and well-oxygenated areas of the EMT6 mouse mammary adenocarcinoma, by in vivo staining with the fluorescent dye Hoechst 33342 followed by cell sorting on the basis of fluorescence intensity. Tumors were grouped by days post-injection (days 11-14, 15-17 and 20-27). As lymphocytes are the only host cell population in this tumor model to possess lytic activity against EMT6 tumor cells, the ability of sensitized T lymphocytes to lyse syngeneic EMT6 cells was examined under conditions of varying oxygen concentrations. Infiltrating lymphocytes were detected to the same extent in cell fractions from both areas in all tumors. In contrast, neutrophils were found in significantly higher percentages in the hypoxic population than in the well-oxygenated cell fraction of all but the largest tumors. Macrophages were present in significantly higher percentages in the well-oxygenated fraction than in the hypoxic fraction of day-11 to -14 tumors. Extreme radiobiological hypoxia (0% O2) resulted in a significant decrease in T-cell-mediated lysis of EMT6 tumor cells, compared to lysis in room air (20% O2), but lysis was not impaired under conditions of mild radiobiological hypoxia (1% O2). Our study indicates that host-cell infiltration into areas of differing oxygenation may be quantitated via in situ Hoechst staining followed by cell sorting; in the EMT6 tumor, lymphocytes appear to infiltrate hypoxic areas to the same extent as well-oxygenated areas, and T-lymphocyte killing of syngeneic tumor cells is significantly reduced, although still present, under these hypoxic conditions.

Radiation sensitivity of tumour cells stained in vitro or in vivo with the bisbenzimide fluorochrome Hoechst 33342

The DNA-binding bisbenzimide fluorochrome Hoechst 33342 is being used routinely in radiobiological studies to assess cell kinetic parameters and tumour blood flow. However, there are reports in the literature which indicate that exposure to this compound can affect the radiation sensitivity of tumour cell populations. In this investigation, it was found that staining murine tumour cells in vitro with H33342 at concentrations greater than 0.1 microM before irradiation resulted in radioprotection. The protection factor calculated for fibrosarcoma cells stained with 10 microM H33342 was 1.7. Varying the time between radiation treatment and exposure to the fluorochrome demonstrated that the effect rapidly changed to radiosensitization when staining was performed subsequent to irradiation. Cells in transplanted KHT tumours were stained in vivo by intravenous administration of H33342 to determine whether the radiation sensitivity of these populations might also be modified. Flow cytometric analysis of suspensions prepared from tumours stained in this manner revealed that recovered cells exhibited a greater than 100-fold range in fluorescence intensities. These suspensions were irradiated in vitro and the cells were then fractionated according to fluorochrome content using cell sorting. Little evidence for a radioprotective effect was observed when these subpopulations were assessed for survival, even when tumour-bearing mice were given doses of H33342 which approached the LD50. Further analysis demonstrated that insufficient amounts of the fluorochrome were taken up by cells during in vivo staining to attain levels required for radioprotection. However, our results indicate that the amount of H33342 accumulated by cells may affect the radiation sensitivity of populations exposed to high concentrations of this fluorochrome, such as those required to achieve stoichiometric binding to DNA.

Misonidazole binding in SCCVII tumors in relation to the tumor blood supply

Misonidazole (MISO) binding was examined in murine squamous cell carcinomas as a function of distance from the tumor blood supply. C3H mice bearing subcutaneous SCCVII tumors were injected intraperitoneally with 3H-MISO followed at various times later by intravenous injection or infusion of the fluorescent perfusion probe, Hoechst 33342. Tumors were then excised, and single cell suspensions prepared for fluorescence activated cell sorting. Cells sorted on the basis of Hoechst 33342 fluorescence were examined for 3H-MISO content by liquid scintillation counting or autoradiography. MISO content in the 10% of cells most distant from the blood supply was as much as 8 times greater than the amount in the 10% of cells closest to the blood supply. The largest differentials in MISO content between dimly and brightly staining regions were obtained if (a) tumors greater than about 300 mg were used, (b) at least 3 hr were allowed for MISO metabolism and binding prior to analysis, and (c) cell sorting was performed on the basis of concentration of Hoechst (correcting for cell size) rather than on the basis of total fluorescence intensity per cell. As tumors enlarged, MISO content increased even in the cells closest to the blood supply suggesting a decrease in net tumor oxygenation perhaps caused by intermittent hypoxia.

Characterization of radiation resistant hypoxic cell subpopulations in KHT sarcomas. (II). Cell sorting

Hypoxic cells in KHT sarcomas were characterized using fluorescence activated cell sorting based on the diffusion properties of the fluorochrome Hoechst 33342. Tumour-bearing female C3H/HeJ mice were injected i.v. with 10 micrograms g-1 Hoechst 33342 and the cells derived from the tumours sorted on the basis of their staining intensities. For each sorted fraction the DNA histogram was evaluated using FCM analysis. The results indicated that the bright and dim cells were not equally distributed about the cell cycle. For example, a greater proportion of S phase cells were in the bright subpopulations whereas the dim subpopulations contained an increased proportion of cells in G1. When the tumours were irradiated with a single dose of radiation prior to cell sorting, the dim cells survived preferentially. Dose response curves for the 20% most dim and 20% most bright cells, sorted on the basis of fluorescence intensity, then were determined. The survival curves of the dim and bright cells were found to have slopes similar to those of KHT cells irradiated in situ in dead animals or in vitro under fully oxic conditions, respectively. In addition, when KHT sarcoma-bearing mice were given a 2.5 mmol kg-1 dose of misonidazole (MISO) prior to irradiation and cell sorting, the dim subpopulation was sensitized whereas the bright subpopulation was not. These findings suggest that (i) compared to well-oxygenated areas, hypoxic regions of KHT tumours contain a smaller percentage of cells actively proliferating and (ii) Hoechst 33342 sorting may allow the detailed in situ evaluation of agents acting directly against hypoxic cells in solid tumours.

Tumor infiltrating lymphocytes of spontaneous versus transplanted mouse mammary tumors

Tumor infiltrating lymphocytes (TIL) were isolated by centrifugal elutriation from C4 mouse mammary tumors and characterized with regard to phenotype and natural killer (NK) activity. Tumors that had arisen spontaneously in preneoplastic hyperplastic alveolar nodules and tumors that had been passaged one to two times in either naive or presensitized mice were studied. Mice were sensitized by limited s.c. tumor growth and subsequent surgical removal of the tumor. The total numbers of T or B cells in the infiltrates were similar in spontaneous tumors and in passaged tumors from either naive or sensitized mice. The ratio of L3T4-positive to lyt-2-positive cells was reduced, however, from 1.10 +/- 0.2 in spontaneous tumors to 0.53 +/- 0.28 or 0.48 +/- 0.04 in passaged tumors from untreated or sensitized mice. The site of tumor implantation, whether intramammary fat pad or s.c., did not affect the profiles of the infiltrates. The TIL from both spontaneous and passaged tumors demonstrated enhanced NK activity relative to peripheral lymphoid cells. The TIL of passaged tumors sensitized mice, however, had lower NK activity than those from naive mice.