The effects of l-phenylalanine (PHE) on cell growth and production of shikonin and its derivatives, acetylshikonin (ACS) and isobutyrylshikonin (IBS), in suspension cultures of Arnebia euchroma were examined. Supplementing media using PHE have been successfully utilized to enhance shikonin production in cell cultures of other species of Boraginaceae. l-Phenylalanine, the key compound in the phenylpropanoid pathway, is converted by phenylalanine ammonia lyase (PAL) to trans-cinnamic acid, which is the precursor of p-hydroxybenzoic acid (PHB). Coupling of PHB and geranyl pyrophosphate (derived from mevalonate pathway) by p-hydroxybenzoate-m-geranyltransferase leads later to biosynthesis of shikonins. The addition of 0.01 or 0.1 mM PHE to the culture medium stimulated cell proliferation, where the highest observed increase in fresh cell biomass (measured as a ratio of final weight to initial weight) was 12-fold, in contrast to an eightfold increase in control cultures. Whereas, growth media supplemented with 1 mM PHE markedly reduced the rate of cell growth (to only twofold). Precursor feeding had detrimental effects on both ACS and IBS production in all PHE-supplemented media. The highest total content (intracellular + extracellular) of the investigated red pigments (9.5 mg per flask) was detected in the control culture without PHE. ACS was the major component of the naphthoquinone fraction determined in cells and post-culture media. Shikonin itself was found only in the post-culture media from cultures supplemented with 0.01 or 0.1 mM PHE. Increases in PAL activity corresponded well with the accumulation of investigated naphthoquinones in control culture. However, peak PAL activity did not directly correlate with maximum production of shikonin derivatives. Cytotoxicity of extracts, prepared from the cells cultivated in the presence of PHE or in control cultures, was tested on three cancer cell lines: HL-60, HeLa, and MCF-7. The extracts prepared from the untreated control cultures proved to be the most potent against the examined cancer cell lines. The mean inhibitory concentration values were 0.3, 13, and 8 μg ml⁻¹ for the HL-60, HeLa, and MCF-7 cells, respectively.

The effects of medium exchange and methyl jasmonate addition on growth and production of shikonin and its derivatives acetylshikonin and isobutyrylshikonin in hairy root cultures of Lithospermum canescens were investigated. Responses varied depending on the transgenic line and stage of growth at which these lines were subjected to treatment. Shikonin itself was not detected, irrespective of the transgenic line and culture treatment used. A eightfold increase in acetylshikonin and isobutyrylshikonin accumulation was achieved when 32-day-old transgenic roots of Lc1D line were transferred from LS to M9 medium for the subsequent 3 weeks of culture. Methyl jasmonate exerted a detrimental effect on red naphthoquinones production. The extracts obtained from roots cultivated in M9 medium for 3 weeks were subjected to a cytotoxicity assay and displayed cytotoxic activity against human promyelocytic leukemia cells (HL-60) at the dose of 4 μg ml⁻¹.

Background: Recent years have brought the dynamic development in studies of naphthoquinones obtained from plants, in vitro cultures and semi- or total synthesis. This review presents the hairy root cultures approach for producing naphthoquinones and summarizes their most recent anti-cancer investigations. Objective: This review aimed to define biotechnological strategies impacted on naphthoquinones production in hairy root cultures. Up to now the major source of shikonin/alkannin derivatives, rhinacanthins and ramentaceone is isolation from plant material, also derived via biotechnological methods. Moreover, the most recent anti-cancer activity studies on naphthoquinones which could be produced in hairy root cultures were outlined. Methods: For databases survey two selection criteria were used: (i) naphthoquinone could be produced in hairy roots, and (ii) it exhibits anti-cancer properties. Results: Ninety two papers were included in the review, thirty described biotechnological approaches enhancing naphthoquinones production, among them twenty seven were dedicated to hairy root cultures. Forty papers outlined the anti-cancer activity of targeted naphthoquinones including the type of cancer and bioassays description. The synergistic effect of natural naphthoquinones and other anti-cancer therapies was reviewed and toxicity of natural naphthoquinones and plant extracts was discussed. The review highlights tendencies in hairy root investigations and indicates the possible future research directions for improving biotechnological production efficacy. Conclusion: This review demonstrates a great potential of hairy root cultures for naphthoquinones production, which could be furtherly developed for future medical purposes, especially as anti-cancer agents. This area of plant biotechnology will be surely still developed with traditional and new strategies.

The biosynthetic potential for six lignans accumulation in two lines of Taxus x media hairy roots was investigated. The cultures of KT and ATMA hairy root lines were supplemented with precursors: coniferyl alcohol (CA 1, 10 or 100 µM) and/or l-phenylalanine (100 µM PHEN) and/or methyl jasmonate (100 µM MeJa). Moreover the two-phase in vitro cultures supported with perfluorodecalin (PFD) as a gas carrier and in situ extrahent were used. The hairy root lines differed in lignan production profiles. In the control untreated cultures KT roots did not accumulate secoisolariciresinol and lariciresinol while ATMA roots did not accumulate matairesinol. In ATMA roots the treatment with CA (1 or 10 µM) resulted in the production of lariciresinol and secoisolariciresinol whereas solely lariciresinol was present after 100 µM CA application. Elicitation with 1 µM CA and MeJa yielded with hydroxymatairesinol aglyca and lariciresinol glucosides with their highest content 37.88 and 3.19 µg/g DW, respectively. The stimulatory effect of simultaneous treatment with 1 µM CA, PHEN and MeJa on lignan production was observed when the cultures were supplemented with PFD-aerated or degassed. In ATMA root cultures these applied conditions were the most favourable for matairesinol content which amounted to 199.86 and 160.25 µg/g DW in PFD-aerated and PFD-degassed supported cultures, respectively. In KT root cultures solely, hydroxymatairesinol and coniferin/CA content was enhanced with their highest yield 59.29 and 134.60 µg/g DW in PFD-aerated and PFD-degassed cultures, respectively.