New anthra[2,3-b]furancarboxamides: A role of positioning of the carboxamide moiety in antitumor properties

Highlights

• A series of new anthra[2,3-b]furan-2-carboxamides was synthesized and evaluated.

• Individual compounds were potent against wild type and drug resistant tumor cells.

• Anthra[2,3-b]furan-2-carboxamides inhibit topoisomerase 1-mediated DNA unwinding and induce apoptosis.

• Position of the carboxamide moiety is important for antitumor properties.

Abstract

Derivatives of the anthraquinone (anthracene-9,10-dione) such as doxorubicin, mitoxantrone and others have proved great clinical efficacy for decades. Currently the search in this exceptionally productive chemical class is aimed at optimization of antitumor properties including circumvention of drug resistance. Previously we have reported that heteroarene-fused anthraquinones fused to a 5-membered heterocyclic ring are advantageous in killing drug resistant tumor cells. Herein we present the synthesis and antitumor properties of a series of new anthra[2,3-b]furan-2-carboxamides. Vast majority of new derivatives were similarly cytotoxic to wild type tumor cell lines and their isogenic sublines with P-glycoprotein overexpression and/or p53 inactivation. Comparison of structurally close derivatives varying in their position relative to the furan moiety, that is, furan-3-carboxamide 1 vs furan-2-carboxamides 5 and 6, revealed fundamental differences in the cytotoxicity profiles, formation of drug-DNA complexes, efficacy of topoisomerase 1 inhibition and mechanisms of tumor cell death. Together with previous SAR data on the role of individual substituents, these results provide evidence that regioisomerization of anthra[2,3-b]furancarboxamides generates the practically perspective derivatives whose properties may vary significantly.

Introduction

Since the discovery in 1970s the anthraquinone (anthracene-9,10-dione) containing antitumor drugs keep proving their exceptional clinical value. These drugs are used in a variety of chemotherapeutic regimens including solid and hematological malignancies, with clinical drugs doxorubicin (Dox, Fig. 1A), mitoxantrone, idarubicin and valrubicin as the most significant achievements [[1], [2], [3]]. Molecular determinants of tumor cell death/survival in the presence of anthraquinones are the ATP binding cassette transporters (multidrug resistance (MDR) mediated by the MDR1/P-glycoprotein (Pgp) as a prototypic mechanism) and the drug-DNA interaction sensed largely (but not exclusively) by p53 pathways. Although eventually more mechanisms have been implicated, such as mitochondrial metabolism and modulation of protein kinases [[4], [5], [6], [7]], Pgp-mediated MDR and DNA binding are considered the key factors for screening of new anthraquinone based chemotypes.

Researchers worldwide as well as our group have developed a series of derivatives in which different side chain moieties were conjugated to the anthraquinone scaffold [[8], [9], [10], [11], [12], [13]]. Two major prerequisites for the new compound were considered taking into account Dox as a reference drug: 1) the retained submicromolar cytotoxicity; 2) potency against MDR sublines and cells with a non-functional p53, the mechanisms that limit Dox efficacy.

In particular, heteroarene-fused anthraquinones represent a promising class for antitumor drug development due to circumvention of drug resistance phenotypes, multiple targeting of tumor survival mechanisms, and favorable pharmacological profile [8]. To dissect the role of side chains with cationic groups, a series of anthraquinone congeners fused with pyrrole, thiophene and furan has been developed. Of special interest are anthra[2,3-b]furan-5,10-diones capable of inducing tumor cell death via targeting topoisomerases 1 and 2 (Top 1, 2), G-quadruplexes in nucleic acids, Sirtuin 1, tumor-associated NADH oxidase, and protein kinases [[14], [15], [16], [17]]. Furthermore, anthra[2,3-b]furan-3-carboxamides represent an attractive scaffold for further optimization since its derivatives demonstrated an in vivo therapeutic efficacy against Р388 leukemia, its variant Р388/ADR, and B16/F10 melanoma models [16,18,19]. The analysis of structure-activity relationship (SAR) revealed that 4,11-hydroxy groups, a carbonyl spacer of the amide moiety, as well as a cyclic diamine, constitute the crucial structural elements mechanistically associated with anticancer activity (Fig. 1B) [19]. In addition, (S)-3-aminopyrrolidine at the side chain (compounds 1 and 2) has been proved the preferred substituent in the series demonstrating a superior anticancer activity and a lower general toxicity than (R)-isomer [16,18,19].

In further analysis of structural modifications of anthraquinones, we addressed the role of the positioning of an individual moiety in the side chain(s). We synthesized a series of anthra[2,3-b]furan-5,10-diones bearing the carboxamide fragment at the position 2 of the furan ring. Comparison with the previously reported anthra[2,3-b]furan-3-carboxamide 1 revealed that spatial positioning of the carboxamide moiety relative to the anthrafuran core may significantly change intracellular localization, interaction with targets, and cytotoxicity profiles.