Influences of the host and local conditions on the in vivo clonogenic expression of subcutaneously inoculated R-1,M tumour cells

In order to study possible variations in the expression of the clonogenic capacity of cultured R-1,M tumour cells due to different conditions of the growth substrate, assays were performed by employing the in vitro plating, technique described by Puck & Marcus (1956) and the in vivo TD50 assay developed by Hewitt & Wilson (1959). Assays were performed with cell suspensions containing R-1,M cells alone or admixed with either heavily irradiated R-1,M cells designated as F(R-1,M) cells or normal, syngeneic MER-1 cells that have a phagocytic capacity. In vitro assays demonstrated a maximal capacity for colony formation of 80 to 100% of the R-1,M cells plated. TD50 assays performed with the syngeneic WAG/Rij rat and the allogeneic BALB/c.nu mouse revealed that R-1,M cells can express their clonogenic capacity in both strains equally well, with a TD50 of 6,000 cells. From results of assays performed with admixed cells, it was concluded that, in the BALB/c.nu mouse, MER-1 cells are capable of reducing the TD50 by a factor of 600, while admixture with both MER-1 and F(R-1,M) cells in the WAG/Rij rat resulted in a reduction by a factor of only 3-4. The intrinsic radiosensitivity of R-1,M cells grown in single cultures, and mixed cultures with MER-1 cells, was studied by the in vitro assay after in vitro irradiation. For R-1,M cells DQ and D0 values of 2.5 and 1.3 Gy, respectively, were obtained. However, in vivo assays for survival of in vitro irradiated R-1,M cells in single culture provided data which cannot be correlated in a simple manner with data obtained by the in vitro assay.