Structure-activity relationships of wollamide cyclic hexapeptides with activity against drug-resistant and intracellular Mycobacterium tuberculosis [Experimental Therapeutics]

Wollamides are cyclic hexapeptides, recently isolated from an Australian soil Streptomyces, that exhibit promising in vitro anti-mycobacterial activity against Mycobacterium bovis Bacille Calmette Guérin, without displaying cytotoxicity against a panel of mammalian cells. Here, we report the synthesis and anti-mycobacterial activity of x36 new synthetic wollamides, collated with all known synthetic and natural wollamides, to reveal structure characteristics responsible for in vitro growth inhibitory activity against Mycobacterium tuberculosis (Mtb) (H37Rv, H37Ra, CDC1551, HN878, HN353). The most potent anti-mycobacterial wollamides were those where residue VI d-Orn (wollamide B) was replaced by d-Arg (wollamide B1) or d-Lys (wollamide B2), with all activity being lost when residue VI was substituted by Gly, l-Arg or l-Lys (wollamide B3). Substitution of other amino acid residues mainly reduced or ablated anti-mycobacterial activity. Significantly, whereas wollamide B2 was the most potent in restricting Mtb in vitro, wollamide B1 restricted Mtb intracellular burden in infected macrophages. Wollamide B1 synergised with pretomanid (PA-824) in inhibiting Mtb in vitro growth, but did not antagonise prominent first- and second-line tuberculosis antibiotics. Furthermore, Wollamide B1 exerted bactericidal activity against non-replicating Mtb, and impaired growth of multi-drug (MDR) and extensively-drug (XDR) resistant clinical isolates. In vivo pharmacokinetic profiles for wollamide B1 in rats and mice encourage further optimization of the wollamide pharmacophore for in vivo bioavailability. Collectively, these observations highlight the potential of the wollamide anti-mycobacterial pharmacophore.

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