Structural Determinants of Imidazoacridinones Facilitating Antitumor Activity Are Crucial for Substrate Recognition by ABCG2

Abstract

Symadex is the lead acridine compound of a novel class of imidazoacridinones (IAs) currently undergoing phase II clinical trials for the treatment of various cancers. Recently, we have shown that Symadex is extruded by ABCG2-overexpressing lung cancer A549/K1.5 cells, thereby resulting in a marked resistance to certain IAs. To identify the IA residues essential for substrate recognition by ABCG2, we here explored the ability of ABCG2 to extrude and confer resistance to a series of 23 IAs differing at defined residue(s) surrounding their common 10-azaanthracene structure. Taking advantage of the inherent fluorescent properties of IAs, ABCG2-dependent efflux and drug resistance were determined in A549/K1.5 cells using flow cytometry in the presence or absence of fumitremorgin C, a specific ABCG2 transport inhibitor. We find that a hydroxyl group at one of the R1, R2, or R3 positions in the proximal IA ring was essential for ABCG2-mediated efflux and consequent IA resistance. Moreover, elongation of the common distal aliphatic side chain attenuated ABCG2-dependent efflux, thereby resulting in the retention of parental cell sensitivity. Hence, the current study offers novel molecular insight into the structural determinants that facilitate ABCG2-mediated drug efflux and consequent drug resistance using a unique platform of fluorescent IAs. Moreover, these results establish that the IA determinants mediating cytotoxicity are precisely those that facilitate ABCG2-dependent drug efflux and IA resistance. The possible clinical implications for the future design of novel acridines that overcome ABCG2-dependent multidrug resistance are discussed.

Hyaluronic acid-serum albumin conjugate-based nanoparticles for targeted cancer therapy

“…Certain acridinone derivatives are new potent cytotoxic agents which have shown promise against leukemia, melanoma, breast cancer and others [28, 29]. IAs apparently function via several mechanisms such as arresting the cell in the G 2 phase of the cell cycle, inducing cell death, inhibiting cleavable complexes of topoisomerase II with DNA, intercalating into DNA and binding to the minor groove [29–31].…”

“…One of the dominant mechanisms of MDR is mediated by efflux pumps of the ATP-Binding Cassette (ABC) superfamily which exert enhanced extrusion of various hydrophobic and amphiphilic cytotoxic drugs [28, 32–34]. One of the strategies to overcome MDR is by using novel NP systems [33].…”

InactivatingPSMB5Mutations and P-Glycoprotein (Multidrug Resistance-Associated Protein/ATP-Binding Cassette B1) Mediate Resistance to Proteasome Inhibitors: Ex Vivo Efficacy of (Immuno)Proteasome Inhibitors in Mononuclear Blood Cells from Patients with Rheumatoid Arthritis

“…Hence, identifying the structural elements within peptide epoxyketone-based chemical structures that render them Pgp substrates may be an important strategy for evading Pgp-mediated drug efflux and overcoming drug resistance. In fact, we have shown that small chemical modifications can generate analogs of a class of topoisomerase drug inhibitors, i.e., imidazoacridinones, which were no longer substrates for the drug efflux transporter BCRP (Bram et al, 2009). Indeed, Zhou et al (2009) showed that modifications in the N-cap of the peptide epoxyketone backbone, in particular introducing (5-Me)-3-isoxazole or 2-(S)-tetrahydrofuran, retained chymotrypsinlike proteasome activity while Pgp substrate activity was abolished.…”

Overcoming Multidrug Resistance via Photodestruction of ABCG2-Rich Extracellular Vesicles Sequestering Photosensitive Chemotherapeutics

“…Recently we have shown that a class of cytotoxic drugs known as IAs including C-1371, C-1492, C-1309 and C-1336 are bona fide transport substrates of ABCG2 [12]. We therefore hypothesized that IAs may be actively sequestered and concentrated within ABCG2-rich EVs.…”

“…IAs bearing a hydroxyl group at one of the R1, R2, R3 positions in the proximal IA ring, including C-1371, C-1492 and C-1309 were recognized as ABCG2 transport substrates and were actively extruded from ABCG2-overexpressing MDR cells [12]. In contrast, IAs lacking a hydroxyl group such as C-1266 and C-1375 were not recognized by the MDR efflux pump ABCG2.…”