The search for bioactive compounds in tropical plants to target hormone imbalance associated diseases

Benign prostatic hyperplasia (BPH) and/or prostate cancer (PC) will affect at least 50% of the
males once they have reached their fifties. However, despite the range of medical therapies
available, effective treatment against BPH and PC still currently remains inadequate for some.
The annoying symptoms of BPH are mainly attributed to an enlarged prostate. Therefore, the
current treatment strategy is to halt the androgen-dependent growth of the prostate and reduce
its size. Several drugs have been employed with variable success to control prostatic growth.
However, patients tend to self-medicate over a long period. As a result, this leads to another
problem, unpleasant long-term side effects.
The treatment of PC in its early stages often warrants disease free survival for about 70-80% of
the patients. Despite early aggressive therapy, 20% of the cases, unfortunately, experience
disease progression to a state where the cancer no longer responses to therapy. At the
moment, well-established medical options for this condition are limited and thus PC is one of the
leading causes of cancer-associated deaths in western countries.
Evidence has supported the undoubted role of the androgen-signalling pathway in BPH, the pre
cancerous prostatic hyperplasia and dysplasia that may progress to PC. The reduction of
androgen-dependent prostatic growth has been the rational endocrine therapy for both BPH and
PC. However, since the etiology of both diseases is multi-faceted, it is necessary to consider
other contributing factors to develop more effective medication.
Medicinal plants are considered to be multi-component drugs (they contain numerous
phytochemicals) and are thought to display a wide range of beneficial effects. They have been
used therapeutically for centuries. Because of their historical place in medicine, they may have
a better safety profile than synthetic drugs.
The objective of this thesis is to identify tropical medicinal plants, which could be used to target
or support treatments for BPH and PC. Twenty herbal plants, with no known to date indications
for both diseases, were selected. They were fractionated by using different ethanol (EtOH)
concentrations. The initial screen (Chapter 4) aimed to identify plant extracts with the ability to
inhibit the proliferation of LNCaP cells, an androgen dependent human prostate cancer cell line.
All extracts were tested at a concentration of 30 μg/mL.
Four extracts, Api, (70% EtOH Alpinia oxyphylla extract), Aquil (70% EtOH Aquilaria sinensis
extract), Astra (aqueous Astragalus membranaceus extract) and P9605 (96% EtOH Piper
cubeba extract) were selected for further investigations.
Recent research has demonstrated that androgens are not solely responsible for BPH and PC,
estrogens, defective apoptosis and inflammation are, for example, also involved. An
experimental test system using several methodological approaches was designed to test the
above-mentioned extracts. The potential cytotoxicity of the extracts was investigated first to
ensure that they did not attenuate LNCaP growth by inducing unspecific cell death. The extracts
were also tested on HepG2 cells, a human hepatocarcinoma cell line, to identity any potential
induction of liver-toxicity. Anti-androgenic and anti-estrogenic effects were determined by
observing if the extracts 1) blocked the production of certain androgens and estrogens, 2) the
steroid hormone receptor activation process, and 3) the actions of these sex hormones. The
ability to induce apoptosis and the anti-inflammatory properties of the extracts were also tested.
The methods employed were validated and synthetic controls were used whenever possible
and compared with literature.
Api reduced the cellular viability of LNCaP and HepG2 cells at 20-30 μg/mL. It was not further
investigated because the apparent reduced LNCap cell growth was most probably attributed to
due to its cytotoxicity. The other extracts were non-cytotoxic on both cell lines at 30 μg/mL.
Astra inhibited androgen-dependent growth of LNCaP cells, however it did not show significant
anti-androgenic, anti-estrogenic and anti-inflammatory properties. Unfortunately, it is beyond
the scope of this project to discover its anti-proliferative mode of action.
The results of Aquil and P9605 derived from the test system were more promising. P9605
inhibited 5a-reductase type II and aromatase, which were involved in synthesising
dihydrotestosterone (DHT) and estradiol respectively. It also antagonised the effects of DHT by
several mechanisms. Furthermore, it inhibited the cyclo-oxygenases (COX) and 5-lipooxygenase
which are involved in generating inflammatory mediators. Aquil possessed similar
properties as P9605, except that it had no effects on the COXs.
In conclusion, we have identified some possible mechanisms of 2 tropical plants, Aquilaria
sinensis and Piper cubeba, which could potentially be used to prevent/alleviate BPH and/or PC.
This is the first time that these plants have shown to possess anti-androgenic and antiestrogenic
properties.