African plant substance can stop tumour growth

African medicinal plants contain chemicals that may be effective against multi-drug resistant cancers, a new study has found.
"The active substances present in African medicinal plants may be capable of killing off tumour cells that are resistant to more than one drug," said Professor Thomas Efferth from the Johannes Gutenberg University Mainz.
"They thus represent an excellent starting point for the development of new therapeutic treatments for cancers that do not respond to conventional chemotherapy regimens," he said.
Efferth and biochemist Dr Victor Keute of the University of Dschang in Cameroon have been studying the active substances in African plants such as the giant globe thistle, wild pepper, speargrass, and Ethiopian pepper.

"We are now looking for substances that can both break down tumour resistance and not produce side effects," said Efferth.
During the joint project with Mainz, the Cameroonian scientist Victor Kuete has examined more than 100 spices and plants from his homeland for their cytotoxic effects on cancer cells.

"We have already found an entire series of benzophenones and other phytochemicals that are able to elude resistance mechanisms and thus offer many new opportunities for continued research," said Efferth.
The researchers are focusing on three different resistance mechanisms. Transporter-mediated resistance prevents drugs taking effect because a substance called P-glycoprotein promotes their efflux from cancer cells.

In the case of tumour-suppressor-gene-mediated resistance, a mutation in protein p53 means that the cancer cells do not die but are resistant and become increasingly aggressive.
Lastly, in oncogene-mediated resistance, the epidermal growth factor receptor (EGFR) sends signals into the interior of cells causing tumors to grow faster.
The researchers in Mainz have cellular models of all three resistance mechanisms that will enable them to appropriately test the effectiveness of the substances obtained from plants.
In their latest of a total of eight publications produced to date, the research team reports that four naturally occurring benzophenones can prevent the proliferation of the tested cancer cell lines, including multi-drug resistant strains.

"The benzophenones investigated are potentially cytotoxic substances that need to be more extensively investigated with the aim of developing new cancer drugs that are effective against susceptible and resistant cancers," the researchers wrote in an article published in the journal Phytomedicine.