In a previous study, it was reported that secondary untreated
melanoma tumors implanted several weeks after and at distance from primary chloroethylnitrosourea (
CENU)-treated
tumors underwent differentiation and growth inhibition. To see whether the primary treated
tumor released soluble factors that mediated the secondary
tumor response, serum transfer experiments were performed in vivo. Administration of serum from
CENU-treated
tumor-bearing donors arrested
tumor proliferation, decreased vessel formation and induced
tumor metabolite alterations encompassing
glutathione decrease and
polyunsaturated fatty acid and
phosphoethanolamine increase. These changes mimicked secondary
tumor phenotype. To reproduce the model in vitro, cell culture supernatant transfer experiments were performed.
CENU-treated cell cultures showed
polyploidy and
reactive oxygen species (ROS) production. Cell cultures challenged by a
conditioned medium of
CENU-treated cells underwent growth inhibition, cytoskeleton disorders, cytokinesis retardation, metabolite alterations,
glutathione decrease and
phosphoethanolamine increase, without ROS elicitation. Proteomics of
CENU-treated cell
conditioned media revealed altered
protein secretion activity by
CENU-treated cells. Among de novo secreted
proteins, the most expressed were
phosphatidylethanolamine-binding protein (PEBP), cardiovascular
heat shock protein (cHsp), Rho-associated coiled-coil forming
kinase 2 (ROCK) and actin fragments. These
proteins testified of cytoskeleton disorders, growth inhibition and metabolite alterations. This article demonstrates the release by
CENU-treated
tumors of growth inhibitory differentiation-inducing soluble factors. These factors mediate remote bystander effects and attest persistent
biological activity of
residual tumors after
chemotherapy.