Although many advances have been achieved to treat aggressive tumours, cancer remains a leading cause of death and a public health problem worldwide. Among the main approaches for the discovery of new bioactive agents, the prospect of microbial secondary metabolites represents an effective source for the development of drug leads. In this study, we investigated the actinobacterial diversity associated with an endemic Antarctic species, Deschampsia antarctica, by integrated culture-dependent and culture-independent methods and acknowledged this niche as a reservoir of bioactive strains for the production of antitumour compounds. The 16S rRNA-based analysis showed the predominance of the Actinomycetales order, a well-known group of bioactive metabolite producers belonging to the Actinobacteria phylum. Cultivation techniques were applied, and 72 psychrotolerant Actinobacteria strains belonging to the genera Actinoplanes, Arthrobacter, Kribbella, Mycobacterium, Nocardia, Pilimelia, Pseudarthrobacter, Rhodococcus, Streptacidiphilus, Streptomyces and Tsukamurella were identified. The secondary metabolites were screened, and 17 isolates were identified as promising antitumour compound producers. However, the bio-guided assay showed a pronounced antiproliferative activity for the crude extracts of Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653. The TGI and LC₅₀ values revealed the potential of these natural products to control the proliferation of breast (MCF-7), glioblastoma (U251), lung/non-small (NCI-H460) and kidney (786-0) human cancer cell lines. Cinerubin B and actinomycin V were the predominant compounds identified in Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653, respectively. Our results suggest that the rhizosphere of D. antarctica represents a prominent reservoir of bioactive actinobacteria strains and reveals it as an important environment for potential antitumour agents.

This work used the broth microdilution method to investigate the antimicrobial activity of the essential oil obtained from the leaves ofPlectranthus neochilus(PN-EO) against a representative panel of oral pathogens. We assessed the antimicrobial activity of this oil in terms of the minimum inhibitory concentration (MIC). PN-EO displayed moderate activity againstEnterococcus faecalis(MIC = 250 μg/mL) andStreptococcus salivarus(MIC = 250 μg/mL), significant activity againstStreptococcus sobrinus(MIC = 62.5 μg/mL),Streptococcus sanguinis(MIC = 62.5 μg/mL),Streptococcus mitis(MIC = 31.25 μg/mL), andLactobacillus casei(MIC = 31.25 μg/mL), and interesting activity againstStreptococcus mutans(MIC = 3.9 μg/mL). GC-FID and GC-MS helped to identify thirty-one compounds in PN-EO;α-pinene (1, 14.1%),β-pinene (2, 7.1%),trans-caryophyllene (3, 29.8%), and caryophyllene oxide (4, 12.8%) were the major chemical constituents of this essential oil. When tested alone, compounds1,2,3, and4were inactive (MIC > 4000 μg/mL) against all the microorganisms. These results suggested that the essential oil extracted from the leaves ofPlectranthus neochilusdisplays promising activity against most of the evaluated cariogenic bacteria, especiallyS. mutans.

Uncaria tomentosa (Rubiaceae) has a recognized therapeutic potential against various diseases associated with oxidative stress. The aim of this research was to evaluate the antioxidant potential of an aqueous leaf extract (ALE) from U. tomentosa, and its major alkaloids mitraphylline and isomitraphylline. The antioxidant activity of ALE was investigated in vitro using standard assays (DPPH, ABTS and FRAP), while the in vivo activity and mode of action were studied using Caenorhabditis elegans as a model organism. The purified alkaloids did not exhibit antioxidant effects in vivo. ALE reduced the accumulation of reactive oxygen species (ROS) in wild-type worms, and was able to rescue the worms from a lethal dose of the pro-oxidant juglone. The ALE treatment led to a decreased expression of the oxidative stress response related genes sod-3, gst-4, and hsp-16.2. The treatment of mutant worms lacking the DAF-16 transcription factor with ALE resulted in a significant reduction of ROS levels. Contrarily, the extract had a pro-oxidant effect in the worms lacking the SKN-1 transcription factor. Our results suggest that the antioxidant activity of ALE in C. elegans is independent of its alkaloid content, and that SKN-1 is required for ALE-mediated stress resistance.