Increased amplification of abl oncogene in K562 cells after passage in nude mice

Human chronic myelogenous leukemic cells K562, carrying the Ph+ chromosome and an amplified abl oncogene, were injected subcutaneously in nude mice and gave rise to myeloid solid tumors after 4-5 weeks. DNA from the cells of the solid tumors was analyzed by Southern blotting using v-abl and actin probes. Increased amplification of human abl oncogene, but not of the actin gene was found. This suggests a clonal selection of a cell population with more copies of the abl oncogene. This in vivo selection appears to increase the tumorigenicity of K562 cells since, in a second transplantation in nude mice, we observed a shorter period of latency before tumor appearance (3 weeks) when compared to the initial transplantation.