Venoms of cobras (Naja spp.) contain high abundances of
cytotoxins, which contribute to tissue
necrosis in cobra envenomation. The tissue-necrotizing activity of cobra
cytotoxins, nevertheless, indicates anticancer potentials. This study set to explore the anticancer properties of the
venoms and
cytotoxins from Naja sumatrana (equatorial spitting cobra) and Naja kaouthia (monocled cobra), two highly venomous species in Southeast Asia. The cytotoxicity, selectivity, and cell death mechanisms of their
venoms and
cytotoxins (NS-CTX from N. sumatrana: NS-CTX; N. kaouthia: NK-CTX) were elucidated in human lung (A549), prostate (PC-3), and breast (MCF-7)
cancer cell lines.
Cytotoxins were purified through a sequential fractionation approach using
cation-exchange chromatography, followed by C18 reverse-phase high-performance liquid chromatography (HPLC) to homogeneity validated with
sodium dodecyl sulfate-
polyacrylamide gel electrophoresis, and identified by liquid chromatography-tandem mass spectrometry (LCMS/MS). The
cobra venoms and their respective
cytotoxins exhibited concentration-dependent growth inhibitory effects in all cell lines tested, with the
cytotoxins being more potent compared to the corresponding whole
venoms. NS-CTX and NK-CTX are, respectively, P-type and S-type
isoforms of
cytotoxin, based on the amino acid sequences as per LCMS/MS analysis. Both
cytotoxins exhibited differential cytotoxic effects in the cell lines tested, with NS-CTX (P-type
cytotoxin) being significantly more potent in inhibiting the growth of the
cancer cells. Both
cytotoxins demonstrated promising selectivity only for the A549
lung cancer cell line (selectivity index = 2.17 and 2.26, respectively) but not in prostate (PC-3) and breast (MCF-7)
cancer cell lines (selectivity index < 1). Flow cytometry revealed that the A549
lung cancer cells treated with NS-CTX and NK-CTX underwent
necrosis predominantly. Meanwhile, the
cytotoxins induced mainly
caspase-independent late apoptosis in the prostate (PC-3) and breast (MCF-7)
cancer cells lines but lacked selectivity. The findings revealed the limitations and challenges that could be faced during the development of new
cancer therapy from cobra
cytotoxins, notwithstanding their potent anticancer effects. Further studies should aim to overcome these impediments to unleash the anticancer potentials of the
cytotoxins.