Heat sensitization of G₁ and S phase cells by procaine HCl. II: toxicity and probability of dividing following treatment

Abstract

Extended studies of the procaine sensitization of synchronous populations of CHO cells heated in monolayers were performed to help explain the mechanism for this sensitization. Cells were treated with 43·0, 45·5 and 43·0°C + procaine, clonal survival of cells was determined, and time-lapse cinematography was used to monitor the time-dependent morphological changes and division delay of the various populations for up to 72 h following treatment. Procaine sensitized Gi and S phase populations to killing by 43·0°C with thermal enhancement ratios of 7 4 ±0·5 and 7·9±11 (mean±SE), respectively. The division delays (39·2±3·5 h) of G₁ cells exposed to 45·5 or 43·0°C ± procaine were longer than those (21·9 ± 2·3 h) of S phase cells treated to comparable surviving fractions (SF). In these experiments the SF of the Gi populations was 0·50 ± 0·17 versus 0 33 ± 008 for the S phase populations. G₁ populations heated with 43·0°C alone (SF, 0·34 ± 0·05) had division delays of 19·4 ± 2·4 h. Colony formation correlated well with both G₁ and S phase cells that had regular divisions subsequent to treatments; the heat-induced death of G₁ and S phase cells correlated with interphase lysis and irregular divisions (including bipolar divisions yielding micro-nucleated progeny). Deaths due to both categories of lesions are increased by treatment with procaine; however, death due to interphase lysis is enhanced more by procaine. In summary, procaine HCl sensitized G₁ and S phase cells comparably to killing by 43·0°C.

Key Words:

• hyperthermic cytotoxicity
• division delay
• procaine
• CHO cells