6. Miscellaneous specialized metabolites
Cancer suppression through the use of natural plant specialized
metabolites, such as flavonoids, phenolic acids, carotenoids have been
shown more effective and beneficial (Russo
et al., 2005). The main mode of action of flavonoids and its
derivatives is to inhibit cell proliferation and angiogenesis
(development of abnormal blood cells), cause cell cycle arrest, induce
cell apoptosis, and reverse multidrug resistance. Some derivatives such
as quercetin targets the cell cycle at G1/S and G2/M checkpoints by
inducing the p21 CDK inhibitor while decreasing pRb phosphorylation,
thereby blocking an important transcription factor of DNA synthesis
proteins which is E2F1.
In vitro studies of Fagonia indica revealed its potential
to produce important specialized metabolites such as phenolic compounds
(gallic acid, caffeic acid, catechin, epigenin, myricetin) with
anticancer activity by the use of plant growth regulator thidiazuron
(TDZ) in callus culture of stem and leaf of this species. TZD acts as an
elicitor in the callus culture of this plant
(Khan et al., 2016). There is also
improved production of anticancer compound naphthodianthrones fromHypericum perforatum L. when elicitor salicylic acid is
incorporated in the shoot and callus cultures of this plant
(Gadzovska et al., 2013). Secondary
compounds, β-glucan, and galactomannan, polysaccharides extracted from
lichens, are also active against several cancer cell lines
(Shrestha and Clair, 2013; Watanabe
et al., 1986). Another class of secondary
metabolites, rosmarinic acid (RA) and salvianolic acid B (Sal. B)
obtained by in vitro techniques such as callus cultures of stems
and leaves of Salvia miltiorrhiza (Danshen) is yet another
anticancer compound known to produce cytotoxicity against leukemia cell
lines. Here, callus stem extracts proved to show more cytotoxicity
towards leukemia cell lines than callus leaf extracts. Thus, callus
culture techniques from Danshen for producing RA and Sal. B can be
promising for anticancer therapy (Wu et
al., 2016).