Bioactive sesquiterpene lactones identified by multivariate correlation between metabolite profiles of asteraceae and their antiprotozoal activity

Advances in analytical techniques have excelled the discovery of bioactive compounds by combining metabolic profiling, in vitro pharmacological assays, and computer-aided techniques. As part of the ongoing research of our group to find new active natural products against protozoan neglected diseases (PND) [1 – 3], we are applying those approaches to discover antiprotozoal hits. Here we report on the isolation and identification of five bioactive sesquiterpene lactones (STLs), found among several other potential antiprotozoan compounds by correlating the LC-MS metabolite profiles of Asteraceae plant extracts and their in vitro biological activity using partial least squares regression (PLS). Extracts (n = 140) of Brazilian Asteraceae were analyzed by UHPLC/ESI-qQTOF MS/MS, in positive ionization mode. The extracts were tested in vitro against T. b. rhodesiense, L. donovani, and P. falciparum. Chromatographic data were pre-processed and the MS-metabolic profile data were mean-normalized. Correlative models for the dependent Y-variables (activities in % of growth inhibition) and sets of independent X-variables (metabolite data: m/z and rt) were generated with PLS1 using The Unscrambler v. 9.2. The PLS models described from 60% to 90% of the total variance in the Y data by up to five significant PCs. The presence of peaks assigned to variables positively correlated with activity was checked by re-inspecting the extract chromatograms and their mass spectra. The STLs 1 – 5 (Fig. 1) were isolated, identified, and tested against the mentioned parasites and for cytotoxicity. Even though the STLs show only moderate selectivity (Table 1), those and further compounds yet to be identified in the most active extracts may have an interesting potential to be evaluated further against PND [2]. Additionally, the results confirm the usefulness of our approach previously reported [3] as a rapid tool to access bioactive compounds in complex mixtures.

Fig. 1: Molecular structures of the STLs 1 (budlein A [2. 3])-5.

Tab. 1: Summary of the 50% Inhibitory concentrations for compounds 1 – 5.

Compound	T. brucei rhodesiense	L. donovani	P. falciparum	Cytotoxicity (L6)
1 [2,3]	0.072	5.140	1.240	0.384
2	0.663	1.455	1.448	1.482
3	1.432	0.869	1.110	1.245
4	2.065	2.617	1.704	7.591
5	1.609	2.741	2.189	5.163
IC50 values in µM

Keywords: Sesquiterpene lactones, antiprotozoan, Asteraceae, PLS, plant metabolic profile

References:

[1] Schmidt TJ et al. 2012, Curr Med Chem, 19, 2128 – 75 and 2176 – 228.

[2] Schmidt TJ et al.2014, Antimicrob Agents Chemother, 58, 325 – 352.

[3] Nogueira, MS et al. 2013, Planta Med, 79, 1107 – 1108.