Cytotoxic and apoptotic evaluations of marine bacteria isolated from brine-seawater interface of the Red Sea

Abstract

Background: High salinity and temperature combined with presence of heavy metals and low oxygen renders deep-sea anoxic brines of the Red Sea as one of the most extreme environments on Earth. The ability to adapt and survive in these extreme environments makes inhabiting bacteria interesting candidates for the search of novel bioactive molecules.

Methods: Total 20 i.e. lipophilic (chloroform) and hydrophilic (70% ethanol) extracts of marine bacteria isolated from brine-seawater interface of the Red Sea were tested for cytotoxic and apoptotic activity against three human cancer cell lines, i.e. HeLa (cervical carcinoma), MCF-7 (Breast Adenocarcinoma) and DU145 (Prostate carcinoma).

Results: Among these, twelve extracts were found to be very active after 24 hours of treatment, which were further evaluated for their cytotoxic and apoptotic effects at 48 hr. The extracts from the isolates P1-37B and P3-37A (Halomonas) and P1-17B (Sulfitobacter) have been found to be the most potent against tested cancer cell lines.

Conclusion: Overall, bacterial isolates from the Red Sea displayed promising results and can be explored further to find novel drug-like molecules. The cell line specific activity of the extracts may be attributed to the presence of different polarity compounds or the cancer type i.e. biological differences in cell lines and different mechanisms of action of programmed cell death prevalent in different cancer cell lines.

Figure 1

Percent growth inhibition of MCF-7 cells after treatment with 1 mg/mL marine bacterial extracts for 24 hr. Data were normalized to DMSO treatment controls, and error bars represent the standard deviation for triplicate experiments. Values marked as asterisk (*p<0.05 and **p<0.01) are significantly different from untreated control (Un). +ve represents positive control (H₂O₂).

Figure 2

Percent growth inhibition of HeLa cells after treatment with 1 mg/mL marine bacterial extracts for 24 hr. Data were normalized to DMSO treatment controls, and error bars represent the standard deviation for triplicate experiments. Values marked as asterisk (*p<0.05 and **p<0.01) are significantly different from untreated control (Un). +ve represents positive control (H₂O₂).

Figure 3

Percent growth inhibition of DU145 cells after treatment with 1 mg/mL marine bacterial extracts for 24 hr. Data were normalized to DMSO treatment controls, and error bars represent the standard deviation for triplicate experiments. Values marked as asterisk (*p<0.05 and **p<0.01) are significantly different from untreated control (Un). +ve represents positive control (H₂O₂).

Figure 4

Percent apoptosis in HeLa, DU145 and MCF-7 cells after treatment with 1 mg/mL marine bacterial extracts. The treatment of extracts was done for 48 hr in duplicates. Data were normalized to untreated controls.