Abstract:
Cancer remains a challenge in Africa despite the recent therapeutic advances. Due to the
side effects associated with the use of clinical drugs, Lamiaceae plants such as Ocimum
gratissimum and Rosmarinus officinalis have been used as anti-proliferatives against
various cancer cell lines, and their leaves used as traditional medicine in conditions such
as diabetes, cancer, diarrhea and typhoid. Even then, limited studies exist on the nature and
variability of polyphenols in these plants and their efficacy as anti-proliferatives on
prostate, colorectal and cervical cancer cell lines. The aim of this study was to isolate,
characterize and determine the antioxidant and anti-proliferative properties of phenolic
compounds of crude leaf extracts of O. gratissimum and R. officinalis. Specific objectives
were; to determine the total phenolic content (TPC) and antioxidant(AO) activity of crude
organic extracts, to evaluate the in vitro antiproliferative activity of crude organic extracts
against human prostate (DU145), cervical (HeLa229) and colorectal (CT26) cancer cell
lines, to isolate and characterize phenolic compounds in bioactive crude organic extracts,
to evaluate in vitro antiproliferative activity of phenolic crude isolates against DU145,
HeLa229 & CT26, and to evaluate the in vitro cytotoxic activity of phenolic crude
compounds. Experimental design was used in the study. The plant leaf samples were
obtained from their cultivated areas in Wakiso district, Uganda by judgemental sampling.
Crude organic extracts were obtained by maceration method using n-hexane,
dichloromethane, ethylacetate and methanol and their total phenolic content and
antioxidant activity determined by Folin Ciocalteu and 2,2-diphenyl-1-picryl-hydrazyl-
hydrate (DPPH) methods respectively. In vitro antiproliferative activity of seven different
concentrations (1000 to 1.37 μg/ml) of crude organic extracts against cancer cell lines was
evaluated by MTT assay. The Methanol extract showed the highest antiproliferative
bioactivity. The extract was fractionated using n-hexane, dichloromethane, ethylacetate
and methanol, in their order of increasing polarity. The fractions were further isolated into
polyphenols using Solid phase extraction (SPE) and characterized by Liquid
chromatography mass spectrometry (LC-MS/MS). The isolates antiproliferative activity
against cancer cell lines and cytotoxicity activity on normal vero cells was evaluated by
MTT method. Doxorubicin was used as the positive control drug in all bioassays. Crude
methanol extracts yielded the highest Total phenolic content (R. officinalis: 476.80± 0.40
μg/ml; O. gratissimum: 401.00±6.47 μg/ml) and % inhibition of DPPH (R. officinalis:
69.76 ± 0.09%; O. gratissimum: 61.26 ± 0.09%), with significant differences between the
two plants extracts (p˂0.05). FTIR spectra confirmed presence of phenolic groups,
alcohols, aromatics, nitro groups as well as carbonyl groups which is the reason for the
various medicinal properties of these plants. Gallic acid, Rutin, Catechin & Quercetin
compounds were found to be common in both plants’ extracts. Procyanidin,
Carboxystrictosinedine, Isoferullic acid, Psychotrin, hydroxyplorentin, cephalin,
Isoquercetin, Diadzin and hyperin were reported for the first time in O. gratissimum while
8 compounds were reported for the first time in R. officinalis which include Procyanidin,
hydroxyplorentin, cephalin, Isoquercetin, Latifoliamide, Diadzin, hyperin and emetine.
Also, methanol crude extracts had the highest antiproliferative activity on all cancer cell
lines, and whose minimum inhibitory concentration (μg/ml) that killed 50% of cells (IC 50 )
was DU145-147.378, CT26-301.992 and HeLa229-432.4745 for R. officinalis and DU145-
104.839, CT26-586.683 and HeLa229-359.914 for O. gratissimum. The results obtained
show that all the extracts under investigation were not toxic to normal vero cells, compared
to the positive control which was doxorubicin drug (6.36 ± 0.45 μg/ml) which is potentially
very toxic. Therefore, results show selective action and potential use of these plants to
generate lead compounds for use in developing drugs against prostate, colorectal and
cervical cancers. Further antiproliferative activity studies in pure compounds of O.
gratissimum & R. officinalis as well as vivo models are recommended.