Two previously synthesized and two structurally novel thiazoline iron chelators are described. N4-Benzyl-N1,N8-bis[[2-(2-hydroxyphenyl)thiazolin-4-yl]carbonyl] homospermidine (5) proved to be the most potent antiproliferative and cytocidal compound in the series with in vitro IC50 values of 3 and 1 microM on L1210 and P388 murine cell lines. The N4-acetyl analogue 7 was considerably less active than 5 with IC50 and cell viability values that were similar to those of the structurally simple thiazolines 2 and 3. The antiproliferative activity of 3 and 7 could be substantially reduced or ablated by delivery to cell suspensions as a 1:1 molar mixture with FeCl3, while the activity of 5 was unaffected by Fe(III) chelation. As expected, 3 induced a G1/S cell cycle block at the 100 microM block consistent with interference with DNA synthesis while 10 microM 5 did not affect L1210 cell cycle distribution. Tritiated thymidine incorporation studies confirmed that 5 was incapable of interfering with DNA synthesis at concentrations below 40 microM. Alkaline elution studies indicate that 5 does not cause DNA strand breaks in vitro at concentrations of 10 microM. The N4-benzyl group of 5 appears to impart in vitro potency as the N4-acetyl analogue 7 lacks comparable in vitro antiproliferative and cytocidal activity.

Two uncouplers of oxidative phosphorylation, 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP), were tested for their ability to modify the survival of cultured Chinese hamster ovary (CHO) and Chinese hamster V79 cells treated with hyperthermia. The uncouplers were used under conditions that inhibit oxidative ATP synthesis, as judged from measurements of cellular ATP levels. Incubation of CHO cells in glucose-free Hanks' balanced salt solution (HBSS) containing 1 mM DNP for 1 h at 37 degrees C followed by reincubation at 37 degrees C in complete growth medium for 3 or 16 h, showed no substantial changes in the 45 degrees C heat survival curve as compared to heated cells not exposed to DNP. Thus, DNP treatment of CHO cells did not induce thermotolerance. Carbonyl cyanide m-chlorophenylhydrazone (CCCP), tested under similar experimental conditions, did alter cellular heat resistance. The major change in the 45 degrees C survival curve of CHO cells pretreated with CCCP was an increase in the width of the shoulder: the Dq value increased from 14 min to 24 min, for the control and CCCP-treated cells respectively. The D0 value did not change appreciably. In contrast, heat-induced thermotolerance (10 min, 45 degrees C + 16 h, 37 degrees C) was characterized primarily by an increase in the D0 parameter from 4 min (unheated cells) to 17 min. Similar results were observed with CCCP-treated V79 cells. The data demonstrate that heat resistance induced by 1.2 microM CCCP was manifest as an increased cellular capacity to accumulate and/or repair hyperthermia damage, rather than an induction of thermotolerance, and that this effect probably was not related to the action of CCCP as an uncoupler of oxidative phosphorylation.