Abstract
Cancer is a serious health burden on global societies. The discovery and development of new anti-cancer therapies remains a challenging objective. Although it has been shown that lichen secondary metabolites may be potent sources for new anti-cancer agents, the Indonesian- grown folious lichens, Physcia millegrana, Parmelia dilatata and Parmeila aurulenta, have not yet been explored. In this study exhaustive preparative high-performance liquid chromatography was employed to isolate the lichen constituents with spectroscopic and spectrometric protocols identifying nine depsides 9–17, including the new methyl 4-formyl-2,3-dihydroxy-6-methylbenzoate 13. The cytotoxicity of the depsides towards cancer cells was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results indicated lowest toxicity of the depsides towards human A549 lung cancer cells. Importantly, the di-depsides (11, 12 and 17) showed greatest toxicity, indicating that these structures are biologically more active than the mono-depsides against the HepG2 liver cancer, A549 lung cancer and HL-60 leukemia cell lines.
Highlights
Lichens are unique organisms constituting a symbiosis between mycobiont and photobiont algae or cyanobacteria
The cells were grown in growth medium containing Dulbecco’s Modified Eagle Medium (DMEM), foetal bovine serum (FBS) (10% v/v) and penicillin/streptomycin (200 units/mL and 200 μg/mL, respectively)
The collection of lichen biomass is challenging due to its nature and the burden of ensuring that the samples were clean required extensive work. This is due to the small size of the folious lichens and the constraints on collecting samples—they were attached to the wood bark in which the folious was fully grown during wet season (January–June) leaving only the mid wet season as the best harvesting time
Summary
Lichens are unique organisms constituting a symbiosis between mycobiont and photobiont algae or cyanobacteria. ONtaobtaleblaenatinctaincacnercearctaicvteivleiclhicehnensecseocnodnadryarymemtaebtaobliotelistews iwthithsuscuccinciicn,icl,aclatacmta,md, edpespidseid, e, diddiedpespidsied,et,ritdriedpespidsiedaenadnda daedpespidsiodnoenme moloelceuclualrabrabcakcbkobnoen.e. A previous notable study on lichens of Indonesian origin reported the cytotoxicity of the methanol crude extract from Usnea misaminensis against the KB cell, lung cancer cell NCI-H187 and breast cancer cell MCF-7 with IC50 values of 28, 11, and 30 μg/mL, respectively[11]. An isocratic development (100% solvent B) was employed for 3 min before the solvent was developed back to 100% solvent A within 2 min (solvent A: 0.1% trifluoroacetic acid (TFA) in distilled water, solvent B: 0.1% TFA in acetonitrile) This chromatographic protocol produced compounds (2.5 mg), 9 (4.3 mg), (11.2 mg), (3.8 mg), 11 (4.5 mg), and 17 (25.1 mg) at retention times of 4.8, 10, 10.5, 20, 21 and 26 min, respectively
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