Avninder S. Bhambra

Phytoestrogens as natural prodrugs in cancer prevention: towards a mechanistic model

It has been widely acknowledged that regular consumption of fresh fruits and vegetables is linked with a relatively low incidence of cancers (e.g. breast, cervix, and colon). Notably, dietary polyphenolic compounds that show some structural similarity to human estrogen, e.g. isoflavones, coumestans, lignans, flavones, have been proposed to play a role in cancer prevention. However, at present there is no satisfactory explanation for the cancer preventative properties of this group of compounds. Whereas polyphenolic compounds have been shown to inhibit proliferation of tumour cells in vitro, the results of in vivo tests have mostly been disappointing in this respect. It seems that mammalian phase II detoxification mechanisms make that dietary polyphenols are rapidly and effectively removed from the body, i.e. their concentration in the blood plasma hardly ever reaches levels high enough to have a possible effect on tumour growth. The polymethoxyflavones nobiletin and tangeretin, common constituents of Citrus peel, are better absorbed than polyhydroxy flavonoids, and maintain their biological activity for a longer period of time. The compounds are known to be substrates for the estrogen-converting cytochrome P450 enzymes CYP1A1 and CYP1B1, which are typically over-expressed in a range of tumour tissues. The enzymes catalyse regioselective hydroxylation and dealkylation of the polymethoxyflavones, resulting in reaction products that appear to inhibit cell proliferation via interference with the MAPK/ERK cell signalling pathway.

Specialized Plant Metabolism Characteristics and Impact on Target Molecule Biotechnological Production.

Plant secondary metabolism evolved in the context of highly organized and differentiated cells and tissues, featuring massive chemical complexity operating under tight environmental, developmental and genetic control. Biotechnological demand for natural products has been continuously increasing because of their significant value and new applications, mainly as pharmaceuticals. Aseptic production systems of plant secondary metabolites have improved considerably, constituting an attractive tool for increased, stable and large-scale supply of valuable molecules. Surprisingly, to date, only a few examples including taxol, shikonin, berberine and artemisinin have emerged as success cases of commercial production using this strategy. The present review focuses on the main characteristics of plant specialized metabolism and their implications for current strategies used to produce secondary compounds in axenic cultivation systems. The search for consonance between plant secondary metabolism unique features and various in vitro culture systems, including cell, tissue, organ, and engineered cultures, as well as heterologous expression in microbial platforms, is discussed. Data to date strongly suggest that attaining full potential of these biotechnology production strategies requires being able to take advantage of plant specialized metabolism singularities for improved target molecule yields and for bypassing inherent difficulties in its rational manipulation.

The synthesis of chalcones as anticancer prodrugs and their bioactivation in CYP1 expressing breast cancer cells

BACKGROUND Although the expression levels of many P450s differ between tumour and corresponding normal tissue, CYP1B1 is one of the few CYP subfamilies which is significantly and consistently overexpressed in tumours. CYP1B1 has been shown to be active within tumours and is capable of metabolising a structurally diverse range of anticancer drugs. Because of this, and its role in the activation of procarcinogens, CYP1B1 is seen as an important target for anticancer drug development. OBJECTIVE To synthesise a series of chalcone derivatives based on the chemopreventative agent DMU-135 and investigate their antiproliferative activities in human breast cancer cell lines which express CYP1B1 and CYP1A1. METHOD A series of chalcones were synthesised in yields of 43-94% using the Claisen-Schmidt condensation reaction. These were screened using a MTT assay against a panel of breast cancer cell lines which have been characterised for CYP1 expression. RESULT A number of derivatives showed promising antiproliferative activities in human breast cancer cell lines which express CYP1B1 and CYP1A1, while showing significantly lower toxicity towards a non-tumour breast cell line with no CYP expression. Experiments using the CYP1 inhibitors acacetin and α-naphthoflavone provided supporting evidence for the involvement of CYP1 enzymes in the bioactivation of these compounds. CONCLUSION Chalcones show promise as anticancer agents with evidence suggesting that CYP1 activation of these compounds may be involved.

Investigation of Linum flavum (L.) Hairy Root Cultures for the Production of Anticancer Aryltetralin Lignans.

Linum flavum hairy root lines were established from hypocotyl pieces using Agrobacterium rhizogenes strains LBA 9402 and ATCC 15834. Both strains were effective for transformation but induction of hairy root phenotype was more stable with strain ATCC 15834. Whereas similar accumulation patterns were observed in podophyllotoxin-related compounds (6-methoxy-podophyllotoxin, podophyllotoxin and deoxypodophyllotoxin), significant quantitative variations were noted between root lines. The influence of culture medium and various treatments (hormone, elicitation and precursor feeding) were evaluated. The highest accumulation was obtained in Gamborg B5 medium. Treatment with methyl jasmonate, and feeding using ferulic acid increased the accumulation of aryltetralin lignans. These results point to the use of hairy root culture lines of Linum flavum as potential sources for these valuable metabolites as an alternative, or as a complement to Podophyllum collected from wild stands.