Advances in Cyclotide Research and Drug Discovery

Author(s): Samantha L. Gerlach

The prototypic cyclotide, kalata B1, was discovered during ethnobotanical observations of African indigenous healers using plant decoctions from Oldenlandia affinis (Rubiaceae) to hasten uterine contractions. During the past three decades, a substantial body of research has indicated that this family of exceptionally stable circular phytopeptides demonstrate a plethora of therapeutic properties which make them promising candidates for drug discovery. The current research builds on our established protocols for the extraction and identification of novel cyclotides using a combination of HPLC, LC-MS, and nanospray MS-MS sequencing. Purified cyclotides, such as cycloviolacin O2 (CyO2) from Viola odorata (Violaceae) were investigated, and nontoxic doses (< 0.5 μM) displayed selective inhibition against drug resistant breast cancer cells (MCF-7/ADR) and HIV-infected lymphocytes (HuT78, PM1) and monocytes (U1). Cyclotides actively disrupted membranes via pore formation and enhanced the uptake of FDA approved anti-cancer drugs (doxorubicin) and HAART medications (saquinavir, nelfinavir and enfuvirtide) during evaluations of cytotoxicity (MTT and CCK), membrane disruption (Sytox Green), p24 antigen levels (ELISA) and fluorescence uptake (microscopy and cytometry). Taken together, this research substantiates the assertion that a systematic investigation of the bioactivity of plant-derived cyclotides may yield innovative approaches to the treatment of some of the world’s most devastating diseases.

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