Enhancing hyperthermic cytotoxicity in L929 cells by energy source restriction and insulin exposure

When L929 cells are maintained in medium containing only glutamine, heat shock protein (HSP) induction by heat shock is suppressed and sensitivity to killing by hyperthermia progressively increases for at least 3 days. Maintenance in medium containing only glucose has similar, but much less pronounced, effects on HSP synthesis and sensitivity to hyperthermic cytotoxicity. Pyruvate reverses the suppression of HSP induction by glucose or glutamine deprivation and increases resistance to killing significantly, but it does not revert the survival curves to those obtained if both glucose and glutamine are available. Insulin further suppresses HSP inducibility in the systems containing glucose or glutamine alone, and greatly increases hyperthermic cytotoxicity. These effects on cytotoxicity appear to be due to nontransport mediated actions of the hormone and do not correlate exactly with effects on HSP induction. Although insulin completely blocks the pyruvate dependent enhancement of HSP inducibility, pyruvate affords protection to killing similar to that seen in the absence of insulin. Thus, the energy source requirements for HSP induction are established in detail and suggest that perturbed energy source utilization may be exploited to enhance hyperthermic cytotoxicity. This system, in which insulin has profound effects in the absence of glucose, may also be useful for studying the nontransport mediated actions of the hormone.