Marinopyrrole Derivatives with Sulfide Spacers as Selective Disruptors of Mcl-1 Binding to Pro-Apoptotic Protein Bim

Abstract

A series of novel marinopyrroles with sulfide and sulphone spacers were designed and synthesized. Their activity to disrupt the binding of the pro-apoptotic protein, Bim, to the pro-survival proteins, Mcl-1 and Bcl-xL, was evaluated using ELISA assays. Fluorescence-quenching (FQ) assays confirmed the direct binding of marinopyrroles to Mcl-1. Benzyl- and benzyl methoxy-containing sulfide derivatives 4 and 5 were highly potent dual Mcl-1/Bim and Bcl-xL/Bim disruptors (IC50 values of 600 and 700 nM), whereas carboxylate-containing sulfide derivative 9 exhibited 16.4-fold more selectivity for disrupting Mcl-1/Bim over Bcl-xL/Bim binding. In addition, a nonsymmetrical marinopyrrole 12 is as equally potent as the parent marinopyrrole A (1) for disrupting both Mcl-1/Bim and Bcl-xL/Bim binding. Some of the derivatives were also active in intact human breast cancer cells where they reduced the levels of Mcl-1, induced programd cell death (apoptosis) and inhibited cell proliferation.

A twist of nature – the significance of atropisomers in biological systems

“…Various manipulations to 28 and some of its synthetic precursors have allowed access to multiple analogues for SAR studies. 64,65,69,70 The first, and thus far only, synthesis of marinopyrrole B (29) was reported in 2013 by Cheng et al (not shown), whereby the bipyrrole core in this case was instead generated through alkylation of a trihalogenated pyrrole, which underwent further manipulations to complete a Paal-Knorr construction of the second pyrrole ring, a precursor which allowed for the generation of rac-29. 71 Scheme 5: Convergent total synthesis of racemic marinopyrrole A (28).…”

Design, synthesis and evaluation of marinopyrrole derivatives as selective inhibitors of Mcl-1 binding to pro-apoptotic Bim and dual Mcl-1/Bcl-xL inhibitors

“…Marinopyrrole derivatives, 29 , 30 , 34 – 36 , 38 , 39 , 41 , 43–46 were inactive at decreasing Mcl-1 levels and at inducing caspase 3 cleavage at concentrations as high as 10 μM (data not shown). As we have reported previously, none of the sulfides or sulphone derivatives are active at the 3 μM concentration; however, at higher concentrations (40 μM) some of the sulfide and sulphone derivatives are cell-active [40]. …”

“…Marinopyrrole 23 [35], the bistrifluoromethyl derivative of 1, exhibited similar potency to that of 1 against Mcl-1/Bim complex and was slightly more potent against Bcl-xL/Bim complex. Nonsymmetrical marinopyrroles with either chlorine [39] or fluorine [40] substitution in ring B (47 to 52) showed that chlorine in either 3′ or 4′ position improves potency against both Mcl-1 and Bcl-xL. Chlorine in position 5′ improves potency against Mcl-1 but not Bcl-xL.…”

“…Previously several Mcl-1 small molecules inhibitors and stapled peptides have been discovered through structure-based design, high-throughput and fragment-based screening approaches [21–31]. Most compounds are not highly selective for Mcl-1 or have not been developed sufficiently for potent cellular and in vivo activity.…”

Elucidating the Mode of Action of Marine Natural Products through an Immunoaffinity Fluorescent (IAF) Approach

“…26 More recently, a series of target-guided screening and SAR programs have identified ligation of Mcl-1, indicating that indeed marinopyrrole A binds to Mcl-1. 27 However, the targeting of Mcl-1 was not observed by others through use of additional models including the screening of cell lines with altered Mcl-1 expression. 28 It should be emphasized that marinopyrrole is a potent electrophile that readily adds nucleophilic residues in proteins by displacement of chlorine.…”