Quantitative lung colony assay for tumor immunity in mice

Adjuvant chemotherapy in a new metastasizing caecum tumor model

A metastasizing tumour model in which a non-immunogenic tumor (Lewis lung carcinoma) is implanted in the caecum of syngeneic mice, is described. The most interesting property of this model is the formation of spontaneous hepatic and transperitoneal metastases. Resection of the caecum tumor 14 days after implantation leaves micrometastases in liver, peritoneum and lungs. This gives the opportunity for the study of adjuvant therapy. Adjuvant chemotherapy with cyclophosphamide cured a significant percentage of animals with micrometastases in liver and peritoneum. Cyclophosphamide therapy had no effect on micrometastases in liver and peritoneum when the primary tumor was left in place. This finding underlines the importance of aggressive treatment of the primary tumor before adjuvant chemotherapy can be effective in colorectal cancer.

Sarcomas routinely produced from putatively nontumorigenic Balb/3T3 and C3H/10T1/2 cells by subcutaneous inoculation attached to plastic platelets

The Balb/3T3 and C3H/10T1/2 lines, noted for their marked postconfluence inhibition of proliferation and anchorage dependence, and frequently studied as non-tumorigenic lines that are compared with tumorigenic sublines transformed with various agents, produced tumors within two to four months at low-cell dosage (3 X 10(4) cells) when implanted subcutaneously attached to 1 X 5 X 10 mm polycarbonate platelets. Platelets alone did not produce tumors. The cultured Balb/3T3 tumor cells showed loss of both postconfluence inhibition of proliferation and anchorage dependence. Tumors arising from attached Balb/3T3 cells in (BALB/c X C57B1/6)F1 hybrids were shown to be transplantable to BALB/c but not to C57B1/6 mice, proving that the tumors were derived from Balb/3T3 and not from host cells. The tumors exhibited unique transplantation rejection antigens that did not cross-react with each other. Scanning electronmicroscopy of Balb/3T3 cells and derived tumor cells on Teflon substrates (on which only the tumor cells and not the parent Balb/3T3 cells could grow) revealed that the two cell types were remarkably similar in appearance, except that the tumor cells were larger and showed many more microvilli that tended to concentrate over the nucleus. We conclude that Balb/3T3 cells and C3H/10T1/2 cells are preneoplastic and give rise to spontaneously transformed clones when implanted in vivo attached to a solid substrate.

Development of an in vitro colony formation assay for the evaluation of in vivo chemotherapy of a rat brain tumor

An in vitro colony formation assay for the evaluation of in vivo brain tumor therapy has been developed. When plated, disaggregated cells derived from solid tumors proliferated to form relatively homogeneous colonies after a latency period of 2 to 6 days. Increasing concentrations of fetal calf serum enhanced colony-forming efficiency (CFE) with a plateau between 7 and 16%. Supplementation with either irradiated feeder cells (10(3) to 10(5) cells per dish), or medium conditioned by 1 to 3 days of in vitro incubation with the same cell line, doubled the CFE. The density of tumor cells (untreated or previously treated with chemotherapeutic agents) did not affect the CFE when a minimum of 10(4) total cells (tumor plus feeder) were plated. Therefore, in this system the optimal experimental conditions for evaluating chemotherapy and radiotherapy require incubation of disaggregated tumor cells for 12 days in medium containing 10% of fetal calf serum and enough feeder cells to provide a minimum of 10(4) cells per dish. The CFE for untreated tumors was 18 +/- 10% (+/-S.D.), demonstrating that there is significant biological variation. The assay appeared sensitive, with reproducible results, when applied to individual chemically treated tumors. An estimate of the percentage of clonogenic cells affected by in vivo chemotherapy may be obtained by comparing the CFE of cells from treated and untreated tumors. This assay can measure up to a 5 log(10) cell kill, and it should prove to be valuable in developing more effective regimens for the treatment of solid tumors in animals and man.

Enhancement by drugs of metastatic lung nodule formation after intravenous tumour cell injection

In studies on a model of induced pulmonary metastasis in mice a tumour host system was analysed which was not affected by immunogenicity of the tumour for the host; neither intensive immunosuppression nor immunization caused a significant change in the quantity of pulmonary metastatic nodules. In contrast the application of cytostatic drugs and of Corynebacterium parvum could modify the pulmonary resistance to the formation of tumour nodules by a factor greater than 100 in either direction. This finding confirms the observation of others that major modification of the resistance to metastatic tumour formation can occur independently of classical immunological mechanisms. Special attention is drawn to the fact that cyclophosphamide enhances the formation of metastatic nodules in this model by factors of 100 to more than 1,000 whereas other cytostatic drugs including the cyclophosphamide congeners iphosphamide and trophosphamide are active only factors between 2 and 12. The possible practical significance of these findings is discussed.

Malignant hemangioendotheliomas produced by subcutaneous inoculation of Balb/3T3 cells attached to glass beads

The Balb/3T3 mouse embryo cell line has been frequently used in cancer research as representative of nontumorigenic cells with the characteristic in vitro properties of postconfluence inhibition of cell division, low saturation density, and anchorage dependence. On the reasoning that anchorage dependence might also apply in vivo, each of nine mice were subcutaneously inoculated with an average of 15,400 Balb/3T3 cells attached to two glass beads 3 millimeters in diameter. After 8 weeks, all the mice had developed large bloody tumors that microscopically proved to be hemangioendotheliomas. Ther inoculation of Balb/3T3 cells alone or beads alone produced no tumors. Transplants of each tumor into normal mice grew to kill the animal within 6 weeks. Tumor cells from collagenase-disaggregated tumor tissue had a plating efficiency of 21.2 percent compared to that of normal adult subcutaneous fibroblasts of less than 0.1 percent. The tumor cells in vitro closely resembled Balb/3T3 cells in appearance and were tumorigenic at a dose of 10-4 cells. A second, repeat experiment produced the same type of tumors grossly and microscopically in 17 of 25 mice between 99 and 211 days after inoculation of the Balb/3T3 cells attached to glass beads. These findings require a reassessment of the postulate that low saturation density, postconfluence of cell division, and anchorage dependence are characteristic in vitro properties only of nonneoplastic cells.