The in vitro sponge-gel-supported three-dimensional histoculture chemosensitivity assay (Hoffman assay) allows the in vivo-like culture of human tumors. In this study, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide (MTT) end point was applied to the Hoffman assay in an attempt to increase in vitro-in vivo correlation. The chemosensitivities of 16 human tumor lines were determined in vitro by the histoculture assay, and retrospectively correlated to their in vivo chemosensitivity as xenografts in nude mice. The in vitro test was considered to be positive if tumor-cell MTT reduction activity was lowered by more than 50%. The cutoff drug concentrations to determine sensitivity in vitro were determined for mitomycin C, doxorubicin, 5-fluorouracil and cisplatin. Using these cutoff drug concentrations in vitro we found, as a function of time of exposure, a strong correlation between serum drug concentrations found in nude mice given maximum tolerated doses and drug concentrations found in the histoculture media in vitro, thereby establishing a relationship between the amounts of drugs to which tumors were exposed in vivo and in vitro. The overall correlation rate of the efficacy results of the drug-response assay to in vivo chemosensitivities was 89.8%, with 90.0% true-positive and 89.7% true-negative rates, 81.7% sensitivity and 94.6% specificity, thereby indicating potential clinical use for tumor histoculture with the MTT end point.

The results of in vitro chemosensitivity testing using the MTT assay of tumor cells from 140 patients were analyzed with reference to the clinical antitumor effects of the chemotherapy. One hundred and twenty-four (88.6%) of 140 specimens were successfully tested by the method of Mosmann (J Immunol Methods 65:55-63, 1983) with some modifications. When the results of the assay were compared with the clinical effects of chemotherapy in 22 patients with remaining measurable tumor lesions, the overall prediction rate was 86.4% (19/22). Among 31 patients with stage III-V gastric and colorectal carcinomas without remaining measurable tumor lesions, the survival rate of nine patients treated with drugs shown to be effective in the assay was significantly (P less than 0.05) better than that of 22 patients treated with drugs shown to be ineffective.

Twenty-three fresh tumor specimens obtained at surgery and 5 serially transferable human tumor xenografts were implanted subcutaneously into nude mice and mice with severe combined immunodeficiency (SCID) to compare the take rates of the fresh surgical specimens and the growth rates of the transferable strains. The overall take rates were 65% for the SCID mice and 60% for the nude mice, without any significant difference, although colon carcinoma seemed to have higher acceptance in the SCID mice with a take rate of 6/8. All the serially transferable strains were successfully accepted in the SCID mice, their growth rates being essentially identical to those in the nude mice. These results indicate that the SCID mouse can be used as a human tumor xenograft-mouse system as well as the nude mouse.

COL-2-JCK, a human colon cancer xenograft line able to be transplanted into nude mice, was implanted in the subserosal layer of the cecum, either as cancer tissue or as a single cell suspension. When cancer tissue was used for the cecal implantation, 100% extensive local tumor growth and a high incidence of metastases to the regional lymph nodes, peritoneum, liver, and lung was observed. In contrast, when the cell suspension of this line was injected into the cecal wall, no metastases were observed, with significantly reduced local tumor growth. The use of cancer tissue maintaining the original cancer tissue structure is therefore considered imperative for allowing full expression of the biological characteristics of cancer cells. This nude mouse model using the cecal implantation of cancer tissue should thus prompt further study on the biology of human colon cancer.

The synergistic antitumor activity of mitomycin C (MMC) and cisplatin (DDP) against the gastric cancer cell lines MKN-28 and MKN-45 was assessed in vitro using the MTT assay. The synergism of the two agents was evaluated in terms of the interaction index (I.I.). The sequence of MMC followed by DDP showed higher antitumor activity than the reverse sequence against MKN-28 and MKN-45, and the intracellular concentration of platinum was significantly increased in MKN-45 by preincubation with MMC, suggesting that MMC modulates cellular permeability to DDP or the ability of DDP to intercalate DNA. Since these two antitumor agents show different types of toxicity clinically, i.e., myelotoxicity by MMC and nephrotoxicity by DDP, this combination chemotherapy could be advantageous by providing synergistic antitumor activity without increased toxicity.