Flavin monooxygenases, FMO1 and FMO3, not cytochrome P450 isoenzymes, contribute to metabolism of anti-tumour triazoloacridinone, C-1305, in liver microsomes and HepG2 cells

Abstract

5-Dimethylaminopropylamino-8-hydroxytriazoloacridinone, C-1305, being the close structural analogue of the clinically tested imidazoacridinone anti-tumour agent, C-1311, expressed high activity against experimental tumours and is expected to have more advantageous pharmacological properties than C-1311. The aim of this study was to elucidate the role of selected liver enzymes in the metabolism of C-1305. We demonstrated that the studied triazoloacridinone was transformed with rat and human liver microsomes, HepG2 hepatoma cells and with human recombinant flavin-containing monooxygenases FMO1, FMO3 but not with CYPs. Furthermore, this compound was an effective inhibitor of CYP1A2 and CYP3A4. The product of FMO catalysed metabolism was shown to be identical to the main metabolite from liver microsomes and HepG2 cells. It was identified as an N-oxide derivative and, under hypoxia, it underwent retroreduction back to C-1305, what was extremely effective with participation of CYP3A4. In summary, this work revealed that the involvement of the P450 enzymatic system in microsomal and cellular metabolism of C-1305 was negligible, whereas this agent was an inhibitor of CYP1A2 and CYP3A4. In contrast, FMO1 and FMO3 were crucial for metabolism of C-1305 by liver microsomes and in HepG2 cells, which makes C-1305 an attractive potent anti-tumour agent.

Metabolic Transformation of Antitumor Acridinone C-1305 but Not C-1311 via Selective Cellular Expression of UGT1A10 Increases Cytotoxic Response: Implications for Clinical Use

“…We showed that cytochrome P450 enzymes were not involved in C-1305 or C-1311 activation, but both compounds were selective irreversible inhibitors of CYP1A2 and CYP3A4 but not of CYP2 family isoforms (Fedejko-Kap et al, 2011;Potega et al, 2011). The metabolites observed with rat and human microsomes, as well as with human hepatocellular liver carcinoma cell line (HepG2) cells, were shown to be flavin monooxygenase (FMO)-mediated Nv-oxide derivatives in the aminoalkyl side chain.…”

“…The metabolites observed with rat and human microsomes, as well as with human hepatocellular liver carcinoma cell line (HepG2) cells, were shown to be flavin monooxygenase (FMO)-mediated Nv-oxide derivatives in the aminoalkyl side chain. Identical metabolites were found with the human recombinant flavin-containing monooxygenases FMO1 and FMO3 (Fedejko-Kap et al, 2011;Potega et al, 2011).…”

Role of Human UDP-Glucuronosyltransferases in the Biotransformation of the Triazoloacridinone and Imidazoacridinone Antitumor Agents C-1305 and C-1311: Highly Selective Substrates for UGT1A10

“…In contrast, both compounds were shown to inhibit the activity of human recombinant and microsomal CYP1A2 and CYP3A4 (Fedejko-Kap et al, 2011;Potega et al, 2011), which suggested the formation of some reactive intermediates, followed by covalent binding to the active center of the enzyme. Furthermore, the 8-hydroxyl group of C-1311 participated in peroxidase-mediated metabolism, which produced reactive intermediates susceptible to substitution in the presence of cellular nucleophiles (Mazerska et al, 2003).…”

“…It has been shown previously that although cytochrome P450s are not involved in C-1305 or C-1311 activation, both compounds are selective irreversible inhibitors of CYP1A2 and CYP3A4 but not CYP2 isoforms (Fedejko-Kap et al, 2011;Potega et al, 2011). Each compound was also found to be metabolized by rat liver microsomes (RLM) and human liver microsomes (HLM) to N -oxide derivatives in the aminoalkyl side chain.…”

“…Identical metabolites were found to be products in reactions with the human recombinant flavin-containing monooxygenases FMO1 and FMO3. Therefore, N -oxide derivatives of C-1305 and C-1311 are believed to be the FMO-mediated products of RLM and HLM (Fedejko-Kap et al, 2011;Potega et al, 2011).…”