Soursop is a tropical fruit from the plant Annona muricata. It is also sometimes called graviola or pawpaw. It is apparently becoming popular as a dietary supplement. Extracts have been shown to be able to kill some types of cancer cells in vitro (in “test tube studies”). There doesn’t appear to be any clinical study in humans, but that hasn’t stopped supplement manufacturers from claiming soursop to be an all-natural miracle cancer cure.
The bioactive constituents of soursop have been identified as members of the acetogenin class of compounds. In particular, soursop contains a chemical called annonacin that has been found to posses in vitro anticancer activity; for example, it can cause cell growth arrest and apoptosis in the MCF-7 breast cancer cell line.
However, annonacin is also a neurotoxin.
This is a common problem encountered by medicinal chemists. When optimizing chemical compounds for one particular desirable pharmacological effect, one can also get an unwanted “off-target” effect that is associated with it. These off-target activities can be the source of a pharmaceutical drug’s side effects. It is often hard to get rid of these off-target activities entirely, so the idea is to find compounds that maximize the ratio between desirable and undesirable effects.
For annonacin, investigators are looking into the fact that it is a mitochondrial complex I inhibitor, which can lead to destruction of neurons and gives rise to the potential to cause neurodegenerative disease. There are also a number of published studies that show an association between heavy consumption of soupsop and Parkinson’s disease, or more broadly, atypical parkinsonism.
The research that makes a connection between soursop and anticancer effects is preliminary and hasn’t been established in humans. The research that makes a connection between soursop and neurodegeneration spans in vitro studies, animal studies, and epidemiological studies. For a health supplement, that certainly doesn’t sound like a good bet to me.