A soft-agar procedure measuring growth of human colonic carcinomas

Cell suspensions from 5 human colonic carcinomas were fractionated by velocity sedimentation and plated in soft agar. Cluster formation was restricted to the purest fraction of epithelial cells, as had been determined by immuno- and histochemical criteria. Plating efficiencies for the 5 specimens were 1.0-4.5%. The effects of varying the incubation period and inoculum size upon growth were studied using unseparated cell suspensions from 6 specimens. Clusters were apparent after 3 weeks in culture, and maximum cluster formation was typically seen by 5 weeks. Cluster formation appeared concentration-dependent, and individual specimens varied with respect to the inoculum most conducive to growth. The maximum plating efficiencies for unseparated cells were unseparated cells were 0.4-1.7%.