A new glioma model in rat: the C6 spheroid implantation technique permeability and vascular characterization

Abstract

The C6 spheroid implantation glioma model is a simple, easily reproduced model for primary gliomas in which C6 astrocytoma cells are grown in vitro as spheroids and subsequently implanted into the brains of Sprague Dawley rat hosts. This report describes the growth, histology, vessel architecture and vascular permeability of the resulting tumors. The appearance of the tumor was investigated by light and electron microscopy, and by using the alkaline phosphatase technique. The leakage of tracer was measured from vessels in the tumor and peritumoral area at various times during tumor development. The spheroid implant produces a fully vascularized, rapidly growing tumor with many of the characteristics of glioblastoma multiforme, from an avascular focus of neoplastic cells. The major advantage of this model is that the tumors grow in a spheroidal fashion and the tumor-brain interface can be easily located. Many of the important events in the process of vascularization take place at the tumor-brain interface. Two distinctive vascular events appear to occur simultaneously: proliferation of blood vessels and their growth into the tumor mass so that they develop into typical, permeable tumor vessels, and migration of tumor cells along normal vessels into the surrounding brain. Tumor vessels were permeable to the tracer Evans Blue (EB) from the earliest days of ingrowth. Leakage of the EB increased as the tumors increased in size, but eventually leakage plateaued as tumors developed necrotic centers. It is well known that the structural and permeability characteristics of vessels associated with the tumor affect tumor growth. This model will be useful for a number of proposed studies including assessment of various clinical therapies on tumor growth and development, and more specifically, quantitative analysis of the vascularization process in tumors.