Synthesis of Marine α-Methoxylated Fatty Acid Analogs that Effectively Inhibit the Topoisomerase IB from Leishmania donovani with a Mechanism Different from that of Camptothecin

Abstract

Sponges biosynthesize α-methoxylated fatty acids with unusual biophysical and biological properties and in some cases they display enhanced anticancer activities. However, the antiprotozoal properties of the α-methoxylated fatty acids have been less studied. In this work, we describe the total synthesis of (5Z,9Z)-(±)-2-methoxy-5,9-eicosadienoic acid (1) and its acetylenic analog (±)-2-methoxy-5,9-eicosadiynoic acid (2), and report that they inhibit (EC50 values between 31 and 22 µM) the Leishmania donovani DNA topoisomerase IB enzyme (LdTopIB). The inhibition of LdTopIB (EC50 = 53 µM) by the acid (±)-2-methoxy-6-icosynoic acid (12) was studied as well. The potency of LdTopIB inhibition followed the trend 2 > 1 > 12, indicating that the effectiveness of inhibition depends on the degree of unsaturation. All of the studied α-methoxylated fatty acids failed to inhibit the human topoisomerase IB enzyme (hTopIB) at 100 µM. However, the α-methoxylated fatty acids were capable of inhibiting an active but truncated LdTopIB with which camptothecin (CPT) cannot interact suggesting that the methoxylated fatty acids inhibit LdTopIB with a mechanism different from that of CPT. The diunsaturated fatty acids displayed low cytotoxicity towards Leishmania infantum promastigotes (EC50 values between 260 and 240 µM), but 12 displayed a better cytotoxicity towards Leishmania donovani promastigotes (EC50 = 100 µM) and a better therapeutic index.

Novel Very Long‐Chain α‐Methoxylated Δ5,9 Fatty Acids from the Sponge Asteropus niger Are Effective Inhibitors of Topoisomerases IB

“…2). Nevertheless, the displayed inhibition of 1a – 1b towards L TopIB is also the best we have observed so far for any tested 2-methoxylated FA towards a leishmania topoisomerase IB [13, 28]. Interesting is the fact that by changing the alkyl chain length of a 2-OMe-Δ5,9 FA it is possible to fine-tune the preference of these acids towards one TopIB enzyme over the other.…”

“…Previous work from our laboratory has shown that short chain FA are better inhibitors of L TopIB than of h TopIB [28]. This is not surprising since both enzymes bear significant differences [14].…”

“…Since the Δ5,9 FA have only been tested against h TopI, with one exception [28], we decided to test them against another important topoisomerase IB, namely L TopIB, an important therapeutic target against L. infantum , the causative agent of visceral leishmaniasis in the Mediterranean Basin [14]. Previous work from our laboratory has shown that short chain FA are better inhibitors of L TopIB than of h TopIB [28].…”

“…This is not surprising since both enzymes bear significant differences [14]. For example, the synthetic fatty acid (±)-2-OMe-5,9–20:2, which is also a natural FA to be found in the sponge E. goffrilleri [3], preferentially inhibits L TopIB (EC 50 = 31 μM) over h TopIB (EC 50 > 100 μM) [28]. However, in the case of 1a – 1b this trend was reversed.…”

“…It is known that due to the amphipathic character of FA they can incorporate into lipid membranes creating instability of the lipid bilayer and rendering the lipid membrane more permeable [29]. The (±)-2-OMe-5,9–20:2 acid was not tested in previous studies against cancer cell lines, but it was found that the latter was 2/3-fold more efficient towards L. infantum promastigotes [28]. Therefore, until more analogs are tested, we can only speculate at this time that the very-long chain 2-OMe-Δ5,9 FA (e.g., C 27:2 ) are more efficient anticancer compounds than antileishmanial agents.…”