Maroh Suzuki

In vivo Analysis of Tumor Vascularization in the Rat

By using transparent chambers in rats, we have directly observed tumor‐induced neovascularization in the early stage and the formation of intricate networks in Yoshida rat ascites hepatoma AH109A and Sato lung carcinoma at high magnification. We counted branching point numbers per unit area in the microvascular network with and without tumors in order to clarify the sites from which new vascular sprouts originate. Branching point number per unit area in normal tissue was 13.6 ± 7.4/0.1 mm2 in the field near a terminal arteriole, and 12.9 ± 7.3/0.1 mm2 in the field distant from a terminal arteriole. There was no significant difference between these two fields in the normal vascular network. On the other hand, in the tumor vascular network, the branching point number in the field near a terminal arteriole was 50.4 ± 12.6/0.1 mm2, and 30.1 ± 11.5/0.1 mm2 in the field distant from a terminal arteriole. The difference is highly significant (P<0.001). The frequency with which new capillaries originated from veins and venules was very low. We concluded from these results that the position from which tumor vessels originated was usually the terminal portion of a terminal arteriole.

Functional characterization of the microcirculation in tumors

SummaryThis review describes some aspects of tumor vessels and the influence of vasoactive agents on tumor blood flow, particularly the characteristic microcirculation of tumors with regard to its selective increase in blood flow. Elevation of blood pressure by infusion of angiotensin II produced a severalfold increase in tumor blood flow. The increase was selective and specific to the tumor vessels as long as the mean arterial blood pressure was kept under 150 mm Hg. Pressure elevation by angiotensin II also selectively increased tumor oxygen tension and influx of lymph flow from the primary transplanted lesion to the lymph node metastatic lesion. Newly devised techniques for analyzing microhemodynamics of tumor vessels showed that the velocity of tumor blood flow, the vascular area in tumor tissue, and the hydrostatic pressure difference between the tumor vessel and extravascular tissue were markedly enhanced. Thus, the extravasation of material into tumor tissues can be increased by the enhancement of blood flow. This demonstration allowed the development of a new approach to cancer chemotherapy, in which the delivery to tumor tissue of systemically administered anticancer drugs can be selectively enhanced.

Increased Intratumor Concentration of Fluorescein‐isothiocyanate‐labeled Neocarzino‐statin in Rats under Angiotensin‐induced Hypertension

On the basis of the observation that the tumor tissue blood flow selectively increases under angiotensin (AT)‐induced hypertension, the change of the drug concentration in the tumor and normal tissues was examined in male Donryu rats. The intratumor concentration of fluorescein isothiocyanate‐labeled neocarzinostatin was about 2‐fold higher in the AT‐induced hypertension group than in the control up to 20 min after the drug injection. In the normal organs or the uninvolved organs of the tumor‐bearing rats, however, no clear increase was seen in the experimental group compared with the control, as anticipated from the observation of the tissue blood flow. The present study supports the hypothesis that the enhanced anticancer effect in chemotherapy under AT‐induced hypertension formerly reported is due to the tumor‐selective enhancement of the drug delivery.

Bone marrow scintigraphy in the early diagnosis of experimental metastatic bone carcinoma

Paralleled experimental studies of radioisotopic bone marrow imaging, bone scanning, and skeletal radiologic survey were undertaken upon the intramedullary‐implanted and hematogenously metastatic VX‐2 rabbit bone carcinoma in order to see their temporal relationship in delineating such lesions. Both bone and bone marrow scans turned positive far earlier than the x‐rays. Moreover, lesion‐depicting marrow scans were obtainable before the bone scans became positive. Radiocolloidal marrow scanning appears to be one of the techniques of choice in the early diagnosis of metastatic skeletal malignancies.

Some aspects of size-dependent differential drug response in primary and metastatic tumors

SummaryThe response of cancer to various anticancer drugs is tumor-size dependent in many aspects. In general, problems stem partly from the fact that the entire tumor cell populations do not respond equally to a certain treatment. As a result of recent progress in cancer biology, it has become evident that cellular heterogeneity of the tumor underlies the difficulties of treating primary and metastatic tumors with chemotherapy. Moreover, as tumors grow, marked diversity develops on the tissue level as well. An uneven distribution with an increase of areas of lower growth fraction and of poorer drug delivery is more distinct in larger tumors. Heterogeneous distribution and low levels of tumor blood flow are considered to be causally related to the heterogeneous nature of tumor tissue. Considering the lack of evidence of a lymphatic system within the tumor, increased interstitial fluid pressure may be a natural result that further impedes blood flow in the tumor. The fact that the temporary and selective increase in tumor tissue blood flow by angiotensin-induced hypertension produces a remarkable chemotherapeutic effect should vividly indicate that delivery of the drug to the tumor is really the ‘bottleneck’ of cancer chemotherapy. Tumor-size-related change in the transvascular and extravascular transport of molecules and its relevance to chemotherapy are also discussed in this article.

Changes in drug delivery (by blood-brain barrier dysfunction) on arachnoid leukemia: implication for CNS leukemic dissemination.

The infiltrates of intracerebrally inoculated DBLA-6 leukemia cells of the rat were used as an experimental model of meningeal leukemia in acute leukemia. Systemic administration of an antileukemic agent (daunomycin) started at the early stage of the leukemic involvement in the arachnoid, when the blood-brain barrier (blood-cerebrospinal fluid barrier) was not yet broken in the pial microcirculation. In those animals in which the antileukemic agent alone was administered, leukemic infiltration was decreased in the dura while it was clearly observed in the subarachnoid space. In those animals in which the blood-brain barrier was damaged by acute angiotensin-induced hypertension, the chemotherapeutic effect on leukemic infiltration was markedly enhanced in the arachnoid and other parts of the brain. The blood-brain barrier dysfunction was analysed using the technique of fluorescein cine-angiography. The results indicated that the chemotherapeutic effect of the agent given systemically was impeded by the barrier, particularly in early arachnoidal infiltration of leukemic cells. Also, this in vivo experiment showed the importance of drug delivery to tumor cells growing outside blood vessels in cancer chemotherapy.

Angioarchitecture of pulmonary malignancies in humans.

Selective bronchial arteriography in 46 patients with lung cancer was performed to scrutinize the vasculature of pulmonary malignancies in vivo. This, together with further studies on 17 surgical materials by magnified and microscopic methods, has revealed many interesting characteristics of vasculature of pulmonary neoplasms. A gross classification of these vascular patterns of “vascular” and “avascular” was attempted from the results of clinical angiography. The existence of those two vascular patterns was able to be confirmed by pathologic angiographies on resected specimens. Bronchial arteriography in vivo revealed either marked or moderate development of blood vessels in 28 out of 46 patients, and this study also showed a relatively well‐developed vasculature in adenocarcinoma rather than in epidermoid. Microscopic examination was done on the same materials in which angiographies were achieved, and demonstrated that tumor vessels proved sinusoidal blood canals consisting of a thin‐layered endothelial wall. Electron microscopically, endothelial cells of tumor vessels had fenestrations, diaphragms, and pores elsewhere which are observed in the fenestrated type capillary in inflammation. These characteristics of the intraneoplastic vasculatures may suggest a manifestation of necessity for a good amount of blood flow for rapid growth of malignancies and rapid exchange of metabolic properties through the vessel wall.

Sodium erythorbate is not carcinogenic in F344 rats

Carcinogenicity of sodium erythorbate, a widely used antioxidant food additive, was evaluated using a total of 306 eight-week-old male and female F344/DuCrj rats. Test rats were given 1.25 or 2.5% aqueous solution as drinking water for 104 weeks. Controls were given tap water. All the rats were fed commercial pellets. None of the tumors observed was attributable to sodium erythorbate in drinking water. Neither concentration of sodium erythorbate changed the pattern of spontaneous tumor development in both sexes, except for a slight reduction in aggregate tumor incidence in the 2.5% Group females. Additionally, 2.5% solution suppressed body weight gains in both males and females. These results and prior data by others together suggest that weak mutagens may be noncarcinogenic under certain conditions.

Comparison of the Effects of Intravenously Bolus‐administered Endothelin‐1 and Infused Angiotensin II on the Subcutaneous Tumor Blood Flow in Anesthetized Rats

To evaluate the effects of endothelin‐1 (ET‐1) on tumor blood flow, the authors measured the mean arterial blood pressure (MABP) of enflurane‐anesthetized male Donryu rats and the tissue blood flow of subcutaneously implanted tumor (Yoshida rat ascites hepatoma LY‐80) by using a hydrogen clearance method. The tumor blood flow was evaluated in terms of the ratio to the maximum blood flow, which was defined as the largest flow in the same position during successive measurements. After bolus intravenous administration of ET‐1 (1.0 nmol/kg), MABP reached approximately 140 mmHg (at 5 30 min), diminishing gradually to the baseline level over 2 h. The tumor blood flow increased from 36.7 ± 20.6 to 59.5 ± 30.2% (n = 32, P <0.001, at 2 min), returning to the baseline level at 10 min. On the other hand, at 2 min after the beginning of continuous intravenous infusion of [Asp1, Ile5]‐angiotensin II (AII; the dose was determined by a blood pressure control system for keeping MABP at approximately 150 mmHg, consequently 0.26 μg/kg/min on the average), the tumor blood flow increased from 42.3 ±21.6 to 76.4±22.6% (n = 32, P < 0.001), which was significantly larger than the flow after ET‐1. The results indicate that hypertension induced by systemic ET‐1 injection is less effective than hypertension induced by continuous systemic AII infusion in increasing tumor blood flow; AII is probably a suitable agent as a safe and effective enhancer of tumor blood flow. Moreover, ET‐1 appears to constrict arterial vessels in the microcirculation time‐dependently, while AII constricts probably only normal peripheral arterioles.

Effects of intravenous infusion of dopamine on tumor blood flow in rat subcutis.

To determine the effects of intravenous administration of dopamine hydrochloride (DA) on tumor blood flow (TBF), we measured the blood flow of normal subcutaneous tissue and subcutaneous tumor (LY‐80, a variant of Yoshida sarcoma) in enflurane‐anesthetized male Donryu rats using a hydrogen clearance method. Measurements were made before and during intravenous infusion of DA at a rate of 5μg/kg/min, while recording the mean arterial blood pressure of the rats. Under mild hypertension induced by DA, the blood flow of normal subcutis decreased and TBF increased significantly. SCH‐23390, an antagonist of the DA1 receptor, inhibited the enhancement of TBF by DA; while domperidone, an antagonist of the DA2 receptor, did not modify the effects of DA. In experimental chemotherapy against the tumor using adriamycin (ADM) 5 mg/kg i.v., only the combination of DA and ADM significantly inhibited the tumor growth. Moreover, DA reduced the weight loss caused by ADM. These results indicate that DA could have a role in increasing TBF and possibly enhance drug delivery to tumors. Moreover, it appears that the DA1 receptor contributes, at least in part, to the enhanced blood flow in rat subcutaneous tumor following DA administration.