Human
head and neck squamous cell carcinoma cells transfected with mutant TP53 (SAS/mp53) or with neo vector as a control (SAS/neo) were inoculated subcutaneously into both the hind legs of Balb/cA nude mice. Mice bearing the
tumors received
5-bromo-2'-deoxyuridine (
BrdU) continuously to label all proliferating (P) cells in the
tumors. The mice then received a hypoxic
cytotoxin,
tirapazamine (TPZ) or
TX-402, with or without a vascular targeting agent (VTA),
ZD6126. Another group of mice given
ZD6126 received a series of test doses of gamma-rays while alive or after
tumor clamping to obtain hypoxic fractions (HFs) in the
tumors. After each treatment, the
tumor cells were isolated and incubated with a cytokinesis blocker (
cytochalasin-B), and the micronucleus (MN) frequency in cells without
BrdU labeling [quiescent (Q) cells] was determined using immunofluorescence staining for
BrdU. The MN frequency in total (P+Q)
tumor cells was determined from the
tumors that were not pretreated with
BrdU. Both hypoxic
cytotoxins showed significantly greater toxicity toward SAS/mp53 and Q than SAS/neo and total
tumor cells, respectively. The sensitivity to
TX-402 was significantly higher than that to TPZ in both total and Q
tumor cells of both
tumors. The significant enhancive effect by
ZD6126 combined with each hypoxic
cytotoxin was similar irrespective of p53 status, and slightly greater for total than Q cells probably because of a more marked increase in the size of the HFs in total than Q cells on the use of
ZD6126 in both
tumors, resulting in a reduction of the difference in the sensitivity to the hypoxic
cytotoxin between total and Q cells. In the treatment of conventional
cancer therapy-resistant Q
tumor cells or p53-mutated
tumor cells, the use of hypoxic
cytotoxin was very promising either alone or when VTA was co-administered.
TX-402 might be more promising than TPZ, although further study of the toxicity to normal tissue is needed.