Bioactivity and Cytotoxic Effect of Cyanobacterial Toxin Against Hepatocellular Carcinoma

Cyanobacteria from exotic niches represent a rich resource of a wide array of unique bioactive compounds that are largely under explored, and proving to be potent source of anticancer drugs. A filamentous non-heterocystous isolate was identified by light microscopy and molecular methods using 23S rDNA as a marker was found to belong to Plectonema genus of Cyanobacteria. Organic extract of different cyanobacterial isolates was screened for their cytotoxicity against hepatocellular carcinoma cell line (HepG2). Extracts of (Cyanothece sp.) and (Plectonema terebrans) were found to have the most cytotoxic effect as they caused cell growth inhibition with IC50 value of 13.3% and 8.3% respectively. The cell viability, cell cycle analysis and caspase3 activity were measured. The cell viability of (Cyanothece sp.) and (Plectonema terebrans) showed high reduced (66.7% 57.4% respectively) compared with untreated cells (6.6%). Cell cycle analysis results showed significant arrest in G0/G1 and G2/M phases in the cells treated with Cyanothece sp recorded (52.8%, 0.33%) respectively, low percentage in 2n phase recorded (46.4%), while cells treated with Plectonema terebrans showed (G0/G1 recorded 63.3% and G2/M recorded 0.3 and 2n recorded 35.6%) compared to control which showed relative accumulation of cells in G0/G1 and G2/M recorded (7.38% and 0.13%) respectively and aggressive accumulation of cells in 2n phase recorded (91.8%). Also, Caspase-3 activity increased in the cells treated with Cyanothece sp with highest activity at concentration 13.3% recorded 0.397 ± SD 0.02 and Plectonema terebrans with highest activity at concentration 4% recorded 0.402 ± SD 0.002 and with significant (p<0.05) compared to untreated cells (0.157 ± SD 0.05 nM/mL). These results indicated that two extracts of Cyanobacteria have a promising agent against hepatocellular carcinoma. and saccharides. More than 50% of the marine cyanobacteria are potentially exploitable for extracting bioactive substances which are effective in killing cancer cells by inducing apoptotic death. Their role as anti-viral, anti-tumor, antimicrobial, anti-HIV and a food additive have also been well established [7]. Several compounds with anticancer activities have been discovered from cyanobacteria and some of these have succeeded to enter the clinical trial. Humisto and his colleague have been reported that cyanobacteria harbor specific anti-leukemic compounds since several studied strains induced apoptosis against AML cells but keeping non-malignant cells like hepatocytes unaffected [8]. Also, a recent study postulated that Samoamide A, a pure compound isolated from American samoan marine cyanobacterium was shown to have in vitro cytotoxic activity against several human cancer cell lines in both traditional cell culture and zone inhibition bioassays and it was shown that although there was no particular selectivity between the cell lines tested for samoamide A, the most potent activity was observed against H460 human non-small-cell lung cancer cells (IC50=1.1 μM) [2]. Citation: Ahmed WA, El-Semary NA, Abd El-Hameed OM, El Tawill G, Ibrahim DM (2017) Bioactivity and Cytotoxic Effect of Cyanobacterial Toxin Against Hepatocellular Carcinoma. J Cancer Sci Ther 9: 505-511. doi: 10.4172/1948-5956.1000468 J Cancer Sci Ther, an open access journal ISSN: 1948-5956 Volume 9(6) 505-511 (2017) 506 Cyanobacteria isolated from Egypt with its hot dry weather and different water bodies are proving to be a very rich source of bioactive compounds including antimicrobials [9,10]. as well as the recently discovered anticancer activity [11]. In that regard, several studies showed that the bioactive compounds derived from cyanobacteria had anticancer effect, e.g., [12,13]. Some compounds with anticancer activity from cyanobacteria were even identified including synthadotin [14], cryptophycin [15] and curacin [16]. Recently, the cyanobacteria isolated from extreme environments are proving to be potent source of anticancer drugs especially against new cancer types and the resisting existing ones [17]. Therefore, there is a need for extensive exploration of cyanobacterial isolates because of their unique bioactive metabolites [17]. In line with that, aqueous extracts from several filamentous cyanobacteria from Egypt proved to be very effective against diffrent cancer cell lines [18]. Interestingly, [6] Zanchett and Oliveira-Filho suggested the possible applications of toxins produced by cyanobacteria as anticancer agents such as the hepatotoxin microcystins that cause hepatic cellular damage and induce reactive oxygen species [6]. Clinical traditional therapies such as surgery, chemotherapy, radiotherapy have several side effects and that lead to searching for new more safe cancer treatment modality. And hence the need for searching new more safe cancer treatment modality as biological therapy; varying anticancer agents are needed to overcome increasing challenges in cancer treatments. Different search methods are used to reveal anticancer compounds from natural products that represent one of the most effective treatment modality with low side effects and low cost. The aim of this study is to evaluate the cytotoxic effect and anti-tumor activity of different cyanobacterial isolates against hepatocellular carcinoma. Materials and Methods Cyanobacterial strain identification and extract preparation One unidentified cyanobacterium alongside other cyanobacterial strains was used in initial screening for their organic extract. The identified Isolates were Leptolygya badia, Oscillatoria limentica, Phormidium uncinatum, Cyanothece sp., Phormidium pristleyi, Synechocystis salina and Cyanobacterium notatum. The unidentified isolate was isolated and kept at Helwan culture collection and all selected isolates were tested for the anticancer activity of their extracts. The isolate was identified as non-heterocystous unbranched cyanobacterium belonging to section III of cyanobacteria. In order to identify this strain, the DNA was extracted using Promega DNA extraction kit. The large 23S subunit rDNA was used as a taxonomic marker [10]. The purified genomic DNA was used as a template for amplification of partial 23S rDNA using the primer pair p23SrV_f1: GGA CAG AAA GAC CCT ATG AA and p23SrV_r1: TCA GCC TGT TAT CCC TAG AG by Sherwood and Presting in 2007. The partial 23S rDNA sequence was deposited in the GenBank database under the accession number KM392421. Cyanbacterial extracts were obtained in a combined solvent system (hexane: methanol: water; 1: 1: 1; v: v: v) by sonicating about 0.5 gm fresh weight cyanobacterial biomass for nearly two minutes in this solvent system and incubating the mixture in the fridge. The mixture was then centrifuged and the supernatant was used in the cytotoxicity tests.