Bioactive diterpenoid metabolism and cytotoxic activities of genetically transformed Euphorbia lathyris roots

Nicholas H. Oberlies,Dianella G. Howarth,Vincent P. Sica,Nicole Diette,Vincent A. Ricigliano,Sonja L. Knowles

doi:10.1016/j.phytochem.2020.112504

Abstract

Plants in the genus Euphorbia produce a wide variety of pharmacologically active diterpenoids with anticancer, multidrug resistance reversal, and antiviral properties. Some are the primary industrial source of ingenol mebutate, which is approved for treatment of the precancerous skin condition actinic keratosis. Similar to other high value phytochemicals, Euphorbia diterpenoids accumulate at low concentrations in planta and chemical synthesis produces similarly low yields. We established genetically transformed root cultures of Euphorbia lathryis as a strategy to gain greater access to diterpenoids from this genus. Transformed roots produced via stem explant infection with Agrobacterium rhizogenes strain 15834 recapitulated the metabolite profiles of field-grown plant roots and aerial tissues. Several putative diterpenoids were present in transformed roots, including ingenol and closely related structures, indicating that root cultures are a promising approach to Euphorbia-specific diterpenoid production. Treatment with methyl jasmonate led to a significant, albeit transient increase in mRNA levels of early diterpenoid biosynthetic enzymes (farnesyl pyrophosphate synthase, geranylgeranyl pyrophosphate synthase, and casbene synthase), suggesting that elicitation could prove useful in future pathway characterization and metabolic engineering efforts. We also show the potential of transformed E. lathyris root cultures for natural product drug discovery applications by measuring their cytotoxic activities using a panel of human carcinoma cell lines derived from prostate, cervix, breast, and lung.

Highlights

Diterpenoids from plants in the genus Euphorbia are in the focus of natural product drug discovery due to their broad range of pharmacological activities
As a metabolic qualification of the transformed root cultures, chemical profiles of roots stably transformed with A. rhizogenes harboring Ri plasmid pRi15834 were compared to wild-type plant roots and aerial tissues from soil-grown E. lathyris plants
We found that transformed roots derived from A. rhizogenes-mediated transformation of E. lathryis possess the biosynthetic capacity for ingenol and related diterpenoid structures

Summary

Introduction

Diterpenoids from plants in the genus Euphorbia (family: Euphorbiaceae) are in the focus of natural product drug discovery due to their broad range of pharmacological activities. Multiple plant species within the genus Euphorbia contain the diterpenoid ingenol, which is generally present in conjugated forms and substituted by various carboxylic acids (Béres et al, 2018). Some naturally occurring ingenol conjugates possess anticancer and anti-HIV properties (Abreu et al, 2014; Vasas et al, 2012), whereas semi-synthetic derivatives show potential for increased efficacy (Silva et al, 2019). A naturally occurring ester derivative containing angelic acid, has gained significant attention due to its approval by the Food and Drug Administration in 2012 and the European Medicines Agency in 2013 for treatment of the precancerous skin condition, actinic keratosis (Braun et al, 2018; Martin and Swanson, 2013; Ogbourne and Parsons, 2014; Ortega Del Olmo and Salido-Vallejo, 2018). One strategy for improving access to ingenol and other pharmaceutically relevant Euphorbia diterpenoids is to apply biotechnological approaches (Atanasov et al, 2015)

Results

Discussion

Conclusion