Description
Mitoxantrone (MTX) is an antitumor agent that
causes cardiotoxicity in 18 % patients. The metabolic
profile of MTX was assessed after incubation of 100 lM
MTX with hepatic S9 fraction isolated from rats. The
presence of MTX and its metabolites was also assessed
in vivo through the analysis of liver and heart extracts of
MTX-treated rats. The cytotoxic effects of MTX and MTX
metabolites were evaluated in the H9c2 cells after 24-h
incubation with MTX alone and MTX ? metabolites. The
influence of CYP450- and CYP2E1-mediated metabolism
for the cytotoxicity of MTX was assessed after 96-h
incubation with MTX (100 nM and 1 lM) in the presence/
absence of CYP450 or CYP2E1 inhibitors. After 4-h
incubation in supplemented S9 fraction, the MTX content
was 35 % lower and 5 metabolites were identified: an
acetoxy ester derivative (never described before), two
glutathione conjugates, a monocarboxylic acid derivative,
and the naphtoquinoxaline, the later commonly related to
MTX pharmacological effects. The presence of MTX and
naphtoquinoxaline metabolite was evidenced in vivo in
liver and heart of MTX-treated rats. The cytotoxicity
caused by MTX ? metabolites was higher than that
observed in the H9c2 cells incubated with non-metabolized
MTX group. The co-incubation of MTX with CYP450 and
CYP2E1 inhibitors partially prevented the cytotoxicity
observed in the MTX groups incubated with H9c2 cells,
highlighting that the metabolism of MTX is relevant for its
undesirable effects. The naphtoquinoxaline metabolite is
described in heart and liver in vivo, highlighting that this
metabolite accumulates in these tissues. It was demonstrated
that MTX P450-mediated metabolism contributed
to MTX toxicity. This work was supported by the Fundac¸a˜o para a Cieˆncia e
Tecnologia (FCT)—project [EXPL/DTP-FTO/0290/2012]—QREN
initiative with EU/FEDER financing through COMPETE—Operational
Programme for Competitiveness Factors. LGR and VMC thank
FCT for their Ph.D. grant (SFRH/BD/63473/2009) and Post-doc grant
(SFRH/BPD/63746/2009), respectively. The authors are also grateful
to Fundac¸a˜o para a Cieˆncia e a Tecnologia (FCT) for Grant No. PEst-
C/EQB/LA0006/2011
; Costa, Vera Marisa 
