INHIBITION OF MALIGNANT-CELL PROLIFERATION BY CULTURE MEDIA CONDITIONED BY CARDIAC OR SKELETAL-MUSCLE

The present work is an attempt to explain the high resistance of muscl es to cancer development. We used primary cultures of rat skeletal and cardiac muscle, and examined the effect of the supernatant of these c ultures (conditioned medium; CM) on proliferation of cancer cells. The results demonstrated that CM inhibited the proliferation of several t ypes of malignant cells by more than 50%, without a significant inhibi tion on normal cells. Cell cycle analysis revealed that CM increased t he number of cells in S and G2 phases, suggesting a cytostatic effect of CM. For defining the biological properties of the factor(s) which a re present in the CM, skeletal muscle cultures were grown in chemicall y defined medium (serum free medium). The concentrated sample was appl ied to a Sephadex G-50 column and three fractions were obtained. Only one fraction showed inhibitory activity. Four protein bands were obser ved in this fraction, as revealed by SDS-PAGE. We suggest that some, o r all of these proteins are responsible for inhibition of tumor cell r eplication. (C) 1997 Academic Press Limited.