Antimicrobial, anticancer, and antioxidant compounds from Premna resinosa growing in Saudi Arabia

Premna resinosa (Hochst.) Schauer (Lamiaceae) is used in many places to treat bronchitis, respiratory illness and convulsions of the rib cage.

This study evaluates the anticancer, antimicrobial and antioxidant activities of P. resinosa, and isolates some responsible constituents.

The methanol extract of P. resinosa aerial parts and its fractions (n-hexane, dichloromethane, ethyl acetate and n-butanol) were tested. Antimicrobial activity was tested using microdilution method against three Gram-positive and four Gram-negative bacteria. The tested concentrations ranged from 4000 to 7.8 μg/mL and MIC values were determined after 24 h incubation. Anticancer activity was evaluated against three human cancer cell lines (Daoy, HepG2 and SK-MEL28) using MTT assay. Antioxidant activity was investigated by DPPH scavenging method and β-carotene-linoleic acid assay.

The greatest antimicrobial activity was exhibited by n-hexane fraction (MIC 10 μg/mL) against Staphylococcus aureus, Enterococcus faecalis, and Shigella flexneri. The n-hexane fraction induced the greatest cytotoxic activity against Daoy, HepG2, and SK-MEL28 cell lines with IC₅₀ values of 9.0, 8.5 and 13.2, respectively. Moreover, the dichloromethane and ethyl acetate fractions showed the highest antioxidant potential. A bioassay-guided fractionation led to the isolation and characterization of seven compounds for the first time, namely, quercetin (1), 3-methoxy quercetin (2), kaempferol (3), 3-methoxy kaempferol (4), myricetin 3,7,3'-trimethyl ether (5), lupeol (6), and stigmasterol (7).

Our results indicate that P. resinosa is a source for antimicrobial and cytotoxic compounds. However, further work is required to isolate other active principles and to determine the mechanism of action.