A model for testing chemotherapeutic agents in vitro is described. It is based on an organoid culture method which allows human carcinomas to grow in vitro and to maintain many typical in vivo properties, including 3-dimensional architecture, growth of multiple cell types, expression of morphological differentiation and formation of histotypical structures. The preservation of drug sensitivity and resistance under the conditions of our organoid culture assay (OCA) was demonstrated by investigating 3 strains of a human hypopharynx carcinoma which differed by different sensitivity to cisplatin in in vivo conditions. These differences were retained in vitro and the modified neutral-red (NR) assay was especially suitable for revealing drug-induced cytotoxic damage in OCA. On the basis of our findings, the following approach is proposed for the in vitro testing of cytostatic drugs before they are administered to patients. (1) Removal of carcinomas from patients; (2) dense cell suspensions of these carcinomas to be dropped on membrane filters at the air-medium interface, resulting in growth of solid nodules of organized carcinoma tissues; (3) addition of cytostatic drugs to the growth medium for 2 or 3 days; (4) detachment and bisection of the culture nodules; (5) determination of viable cells by NR uptake and total cell mass by the sulforhodamin B (SRB) assay; (6) determination of quotient NR:SRB absorbance, related as percentage to control value: this indicates the fraction of viable cells and gives a measure of the cytotoxic injury caused by the applied cytotoxic drug. Thus, the OCA seems to be suitable for defining the patterns of drug sensitivity and resistance of individual human carcinomas in vitro within a few days.

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