DNA-targeted 1,2,4-benzotriazine 1,4-dioxides: potent analogues of the hypoxia-selective cytotoxin tirapazamine.
Tirapazamine (TPZ, 1,2,4-benzotriazin-3-amine 1,4-dioxide) is a bioreductive hypoxia-selective cytotoxin, currently in phase II/III clinical trials in combination with radiotherapy and with cisplatin-based chemotherapy. We have prepared a series of 1,2,4-benzotriazine 1,4-dioxide (BTO) analogues of TPZ where a DNA-targeting chromophore is attached at the 3-position via a flexible linker. DNA binding affinity was modified through variation of the chromophore or the pK(a) of the linker chain. The association constants (K(DNA)) for calf thymus DNA ranged from 1 x 10(2) to 5.6 x 10(5) M(-1) (ionic strength of 0.01 M). DNA binding affinity was dependent on the presence of a positive charge, either in the linker chain or in the chromophore, and (for a series of 4-acridine carboxamide chromophore analogues) correlated strongly with linker chain pK(a). The efficacy of these BTOs in killing aerobic and hypoxic mouse SCCVII tumor cells in vitro was determined by clonogenic survival. Cytotoxicity was measured as the concentration required to reduce plating efficiency to 10% of controls (C(10)), and the hypoxic cytotoxicity ratio (HCR) for each BTO was calculated as C(10)(aerobic)/C(10)(hypoxic). BTOs bearing a positive charge showed increased hypoxic cytotoxicity (1.5-56-fold) compared to TPZ and mostly modest HCRs (8-51), but some excellent (>167 and 400) values. There was a strong correlation between K(DNA) and hypoxic cytotoxicity but no correlation between K(DNA) and HCR. Cytotoxicity in HT-29 human colon carcinoma cells, determined using IC(50) assays, showed similar relationships with a correlation between K(DNA) and hypoxic cytotoxicity but no correlation between K(DNA) and HCR. In this cell line, a higher proportion of compounds (7 of 11) had HCRs greater than or equal to that of TPZ. The data confirm that DNA targeting is a useful concept for increasing potency while maintaining hypoxic selectivity and provide a direction for the further development of DNA-targeted analogues of TPZ.
Hay
Michael P
MP
Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
Pruijn
Frederik B
FB
Gamage
Swarna A
SA
Liyanage
H D Sarath
HD
Kovacs
Mary S
MS
Patterson
Adam V
AV
Wilson
William R
WR
Brown
J Martin
JM
Denny
William A
WA
D000818:Animals; D000970:Antineoplastic Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D045744:Cell Line, Tumor; D004247:DNA / Q000737:chemistry*; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D020128:Inhibitory Concentration 50; D051379:Mice; D013329:Structure-Activity Relationship; D000077704:Tirapazamine; D014227:Triazines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
D000970:Antineoplastic Agents; D014227:Triazines; D000077704:Tirapazamine; D004247:DNA