The hybrid spheroid clonogenic assay for the intrinsic radio- and chemo-sensitivities of human tumors.

The Hybrid Spheroid assay is based on packaging tumor cells into agglomerates of non-proliferating, but metabolically active, HeLa cells. These agglomerates provide an in vivo-like environment for entrapped test cells. Clonogenicity is determined by varying the number of test cells per hybrid spheroid so that some, but not all, spheroids give rise to macrocolonies. From the fraction of noncolony forming spheroids and the Poisson distribution, the average number of clonogens per spheroid can be calculated. The clonogenicity and radiation survival curves of cells derived from human tumors (of the maxilla, tongue, larynx, mouth floor, lung, breast, ovary, and colon) were so determined. Plating efficiency was increased in these normally poorly plating tumor cells, thus enabling survival measurements which are not practical using conventional methods. The Hybrid Spheroid assay has also been applied to determine the chemosensitivity of colon cancer cells.