Lung Colonization Potential Research Articles

Selective therapy of metastasis. I. Quantitation of tumorigenic circulating and covert cancer cells disseminated from metastatic and nonmetastatic tumors.

To determine the potential efficacy of therapeutic agents and different drug delivery systems against metastases, it is necessary to develop methodologies that can assay the effects of treatment at each step of the metastatic process. This report presents quantitative studies on the total numbers and potential tumorigenicity of cancer cells in the circulation and also secondarily arrested in the lungs of mice following their spontaneous dissemination from methylcholanthrene-induced fibrosarcomas. MC1 fibrosarcomas rarely metastasize but MC2 fibrosarcomas frequently generate pulmonary metastases and it was found, using a combination of direct cancer cell isolation techniques and quantitative bioassays, that MC2 tumors released cancer cells into the bloodstream earlier and with greater frequency than MC1 fibrosarcomas. Also, although similar doses of radiolabeled MC1 and MC2 cells injected intravenously were cleared equally effectively following their arrest in the lung microvasculature, those MC2 cells that survived clearance processes had 10-fold greater lung colonization potential than MC1 cells. Therefore, these experimental systems can be used critically to evaluate the effects of therapeutic agents at individual stages of metastasis as an alternative to measuring their effects solely on solid tumors or the final incidence of metastases, which represents the net result of a number of sequential, complex interactions between cancer cells and the host.

Correlation between circulating cancer cells and incidence of metastases.

Quantitative aspects of the behaviour of B16 melanoma and Lewis lung carcinoma cells during the post-intravasation stages of metastasis were examined in relation to their spontaneous metastatic potential. Cancer cells were isolated from the blood of mice bearing i.m. tumours throughout tumour growth using a novel discontinuous gradient centrifugation technique. Four times more Lewis carcinoma cells than B16 melanoma cells were shed into the circulation, although the numbers of cells shed from either tumour were orders of magnitude more than the numbers of spontaneous pulmonary metastases which developed. Greater numbers of Lewis carcinoma cells were also shed as clumps and with leukocytes attached. However, although similar numbers of radiolabelled melanoma and Lewis carcinoma cells were arrested in the lungs after i.v. injection, fewer carcinoma cells were retained there and 12 times fewer Lewis carcinoma nodules developed in the lungs following injection of non-radiolabelled cells. It appears that the low lung colonization potential of the Lewis lung carcinoma is compensated for during spontaneous metastases by the numbers of cells shed from primary tumours as single cells and as clumps.

Variable susceptibility to NK activity of cloned cell lines derived from a primary rat rhabdomyosarcoma: relationship to metastatic potential.

In vitro cloned lines derived from a primary nickel-induced rat rhabdomyosarcoma exhibited diverse levels of susceptibility to spontaneous NK activity. The presence of NK target structures was revealed by competition assays on all cloned cell lines, and the NK susceptibility of the tumour lines varied according to their osmotic fragility. Tumour cell lines derived from metastatic lung nodules presented similar NK susceptibilities to cells originating from the primary tumour. However, cloned cell lines differed in their capacity to form lung colonies after i.v. injection, and in their potential for invading lungs after s.c. primary tumour development. No correlation was found between lung colonization potential and NK resistance. Studies of the correlation between metastatic potential and NK sensitivity revealed that (1) all the NK resistant tumour cells were highly metastatic; (2) NK susceptible tumour cells could be either highly or weakly metastatic. Therefore, highly metastatic tumour cells could be either resistant or susceptible to NK lysis. We conclude that the property of resistance to NK contributes to a high metastatic potential. However, other properties could counterbalance and finally prevail over NK susceptibility thus enabling NK susceptible cell lines to be also highly metastatic.

Differences in Cytotoxic Effects of Activated Murine Peritoneal Macrophages and J774 Monocytic Cells on Metastatic Variants of B16 Melanoma<xref ref-type="fn" rid="fn2">2</xref><xref ref-type="fn" rid="fn3">3</xref>

The cytotoxic effects of activated peritoneal macrophages and the J774 reticulum cell sarcoma cell line on B16 melanoma cells of differing metastatic potential were investigated in vitro. The melanoma target cells were sublines of low (B16-F1) or high (B16-F10) lung colonization potential as well as a subline of high (B16-B14b) brain colonization ability. Thioglycolate-elicited peritoneal macrophages from syngeneic C57BL/6 mice and J774 cells were activated in vitro with polyinosinic-polycytidylic acid (poly I:C) and used as effector cells. Macrophage-mediated cytolysis was determined by means of 24- to 72-hour radioactivity release assays with [125I]5-iodo-2'-deoxyuridine-labeled melanoma cells; the results indicated that the more metastatic sublines B16-F10 and B16-B14b were less susceptible to cytolysis by activated macrophages and J774 cells than was the poorly metastatic B16-F1 subline. The poly I:C-activated effector cells also released soluble cytotoxin(s), which resulted in melanoma cell lysis and growth inhibition. Cytotoxin-mediated melanoma cell cytolysis was determined by counting the number of viable mitomycin-treated target cells remaining after a 40-hour incubation period in the absence or presence of various concentrations of cell-released factors, and cytotoxin-mediated cytostasis was performed with the use of the same procedures without mitomycin pretreatment of targets. The factors released from both activated macrophages and J774 cells were more effective against the poorly metastatic B16-F1 cells than against the highly metastatic B16-F10 or B16-F14b cells. In addition, the activity of the factors from both activated effector cells was inhibited by fetal bovine serum. The J774 cells and the activated peritoneal macrophages demonstrated similar activities against B16 melanoma variants, indicating that the J774 cell line may be suitable as a model for the study of macrophage cytotoxicity. The results suggested that the potential of the highly metastatic melanoma cells to implant, survive, and grow at secondary sites may be due, in part, to their ability to circumvent host antitumor mechanisms.