Fate of Recirculating B16 Melanoma Metastatic Variant Cells in Parabiotic Syngeneic Recipients: Brief Communication 2

Abstract

The fate of recirculating [¹²⁵I]-5-iodo-2′-deoxyuridine [¹²⁵I]UdR-labeled melanoma cells and their potential for developing into metastases were studied in syngeneic C57BL/6 parabiotic mice. After circulatory anastomosis between the parabionts was confirmed, 1 mouse of each pair was inoculated iv with labeled tumor cells from either line B16-F1 (unselected variant, with low metastatic potential) or line B16-F10 (selected for growth in lungs, with high metastatic potential). The quantitative distribution of tumor emboli was then determined in both iv-inoculated and noninoculated parablonts. The number of gross tumor colonies in both partners was also determined 14 days after injection. The kinetic distribution of (¹²⁵I]UdR-labeled B16-F1 and B16-F10 cells in the iv-inoculated parabiont was similar to that observed previously in nonparabiotic mice. B16-F10 cells were arrested, survived, and formed significantly more pulmonary tumor colonies than did B16-F1 cells. However, the arrest and survival pattern of tumor cells that traversed the anastomosed capillaries and circulated in the non inoculated parabionts was different. Viable B16-F1 tumor cells reached the circulation of the noninoculated parablonts, and few cells were arrested, survived, and formed gross lung tumor colonies. Conversely, more B16-F10 cells reached the circulation of the noninoculated parabiont; yet in most pairs these cells failed to be arrested in lungs and to develop into tumor colonies. The results suggested that the in vivo selection of tumor cell lines with enhanced ability to implant, survive, and grow in the lungs may be associated with the initial (immediate) arrest of tumor emboli in the capillary bed of organs.