Summary EMT6 multicellular spheroids were introduced into the peritoneal cavities of mice and allowed to become vascularised, resulting in solid spherical tumours. The necrotic cores of the initially avascular spheroids were replaced by vascularised tumour tissue but the outer zones of the spheroids failed to become vascularised. The presence of both vascular and avascular components in each spheroid allowed the role of the vasculature in the antitumour action of flavone acetic acid (FAA) to be determined. Eighteen hours after treatment with FAA 0.8 mmol kg-', the vascularised core became necrotic and haemorrhagic, while the outer avascular zone remained viable. Tumour Materials and methodsHistological studies EMT6 multicellular tumour spheroids were grown in spinner flask culture in a-MEM + 10% fetal calf serum, and between 15 and 25 spheroids, varying in size from 0.5 to 1.2 mm in diameter, were injected into the peritoneal cavities of anaesthetised Balb/C mice through a 161 gauge needle, as described previously (Zwi et al., 1989). Seven days later the mice in the treatment group (n = 7) were injected with FAA 0.8 mmol kg-' (kindly supplied by Dr K.D. Paull, National Cancer Institute) in 5% w/v sodium bicarbonate by the intravenous (i.v.) or intraperitoneal (i.p.) route, and were killed after a further 18 h. Untreated spheroid-bearing mice (n = 2) were killed after the same interval. The peritoneal cavities of the mice were opened, the free spheroids were collected, and those spheroids which had become attached to host structures were excised with a cuff of adjacent tissue. The spheroids were fixed in either 4% neutral formaldehyde or 2.5% phosphate buffered glutaraldehyde (pH 7.4). The formalin-fixed tissue was embedded in paraffin, and 5 gm sections were stained with haematoxylin and eosin (H&E). The glutaraldehyde-fixed spheroids were embedded in epoxy resin and 2 gim sections stained with toluidine blue. Multiple sections were examined from each spheroid.
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