Effects of the ortho-quinone and catechol of the antitumor drug VP-16-213 on the biological activity of single-stranded and double-stranded phi X174 DNA.
We have studied the effects of the recently reported two new metabolites of the antitumor agent VP-16-213, the ortho-dihydroxy derivative or catechol and the ortho-quinone, on the biological activity of single-stranded and double-stranded phi X174 DNA, the binding of the metabolites to calf thymus DNA and the conversion of the catechol into the ortho-quinone. Evidence was obtained for the oxidation of the catechol into the ortho-quinone and for the fact that the ortho-quinone is the metabolite of VP-16-213 responsible for its binding to rat liver microsomal proteins. The catechol and ortho-quinone of VP-16-213 were found to bind 7-9 times more strongly to calf thymus DNA than VP-16-213 itself. In contrast to the parent compound VP-16-213, the catechol as well as the ortho-quinone inactivated both single-stranded (ss) and double-stranded (RF) biologically active phi X174 DNA. The mean T37-values for inactivation of ss and RF phi X174 DNA by 2.2 x 10(-4)M catechol at 37 degrees and pH 7.4 were 96 and 640 min, respectively. Reduction of the ortho-quinone by NADPH cytochrome P-450 reductase resulted in formation of the catechol. The system ortho-quinone/NADPH cytochrome P-450 reductase inactivated ss phi X174 DNA with a mean T37-value of 454 min, and this inactivation was inhibited by DMSO. The mean T37-value for inactivation of ss phi X174 DNA by 1.8 x 10(-4) M ortho-quinone at 37 degrees and pH 4.0 was 24 min. The chemical stability of the ortho-quinone and the extent of inactivation of ss phi X174 DNA by the ortho-quinone were both pH-dependent: at higher pH the ortho-quinone was less stable and gave less inactivation of DNA. The aqueous decomposition product(s) of the ortho-quinone formed at pH 7.4 inactivated ss phi X174 DNA with a mean T37-value of 175 min. The rate of inactivation of RF phi X174 DNA by the ortho-quinone at pH 4.0 was twice as low as the rate of inactivation of ss phi X174 DNA: T37 = 49 min. When using excision repair deficient E. coli mutants (uvrA- or uvrC-), a higher inactivation of RF phi X174 DNA was found: T37 = 29 min for uvrA- E. coli, indicating that a part of the DNA damage introduced by the incubation with ortho-quinone is removed by excision repair.(ABSTRACT TRUNCATED AT 400 WORDS)
van Maanen
J M
JM
Department of Oncology, Free University Hospital, Amsterdam, The Netherlands.
Lafleur
M V
MV
Mans
D R
DR
van den Akker
E
E
de Ruiter
C
C
Kootstra
P R
PR
Pappie
D
D
de Vries
J
J
Retèl
J
J
Pinedo
H M
HM
D000818:Animals; D010584:Bacteriophage phi X 174 / Q000187:drug effects; D002396:Catechols / Q000494:pharmacology*; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000187:drug effects; D004279:DNA, Viral / Q000187:drug effects* / Q000378:metabolism; D005047:Etoposide / Q000378:metabolism* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D010084:Oxidation-Reduction; D011485:Protein Binding; D011809:Quinones / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D002396:Catechols; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D011809:Quinones; D005047:Etoposide; C034221:catechol