Production of anti-cancer triterpene (betulinic acid) from callus cultures of different Ocimum species and its elicitation

Betulinic acid (BA), a pentacyclic triterpenoid, is gaining unmatched attention owing to its unique anti-cancer activity with selective melanoma growth inhibition without damaging normal cells. It is also well-known for its multifaceted pharmacokinetics, entailing antibacterial, antimalarial, anti-HIV and antioxidant merits. Considering the escalating demand with diminishing bioresource of this molecule, the present study was undertaken that revealed the untapped potentials of Ocimum calli, contrasting to that in the in vitro derived leaves, as effective production alternative of BA in three out of four tested species (i.e. Ocimum basilicum, Ocimum kilimandscharicum, Ocimum sanctum excluding Ocimum grattisimum). Callus inductions were obtained in all the four species with different 2,4-dichlorophenoxyacetic acid (2,4-D)/alpha-naphthaleneacetic acid (NAA) concentrations with kinetin. Notably, 2,4-D favoured maximum callus growth in all whereas NAA proved beneficial for the highest metabolite yield in the calli of each BA-producing species. The O. basilicum calli demonstrated the maximum growth (growth index (GI) 678.7 +/- 24.47) and BA yield (2.59 +/- 0.55 % dry weight [DW]), whereas those in O. kilimandscharicum (GI 533.33 +/- 15.87; BA 1.87 +/- 0.6 % DW) and O. sanctum (GI 448 +/- 16.07; BA 0.39 +/- 0.12 % DW) followed a descending order. The O. gratissimum calli revealed minimum growth (GI 159 +/- 13.25) with no BA accumulation. Elicitation with methyl jasmonate at 200-mu M concentration after 48-h exposure doubled the BA yield (5.10 +/- 0.18 % DW) in NAA-grown O. basilicum calli compared to that in the untreated counterpart (2.61 +/- 0.19 % DW), which further enthused its future application.