Inhibition of Breast Cancer Cell Migration by Cyclotides Isolated from Pombalia calceolaria

Abstract

Two new bracelet cyclotides from roots of Pombalia calceolaria with potential anticancer activity have been characterized in this work. The cyclotides Poca A and B (1 and 2) and the previously known CyO4 (3) were de novo sequenced by MALDI-TOF/TOF mass spectrometry (MS). The MS2 spectra were examined and the amino acid sequences were determined. The purified peptides were tested for their cytotoxicity and effects on cell migration of MDA-MB-231, a triple-negative breast cancer cell line. The isolated cyclotides reduced the number of cancer cells by more than 80% at 20 μM, and the concentration-related cytotoxic responses were observed with IC50 values of 1.8, 2.7, and 9.8 μM for Poca A (1), Poca B (2), and CyO4 (3), respectively. Additionally, the inhibition of cell migration (wound-healing assay) exhibited that CyO4 (3) presents an interesting activity profile, in being able to inhibit cell migration (50%) at a subtoxic concentration (2 μM). The distribution of these cyclotides in the roots was analyzed by MALDI imaging, demonstrating that all three compounds are present in the phloem and cortical parenchyma regions.

Natural and grafted cyclotides in cancer therapy: An insight

“…Poca A and Poca B, the two bracelet types of cyclotides, recently extracted from the root tissues of plant Pombalia calceolaria were found to be highly effective against breast cancer cell lines MDA and MB‐231 . The cyclotides, Poca A and Poca B, could inhibit the growth of breast cancer cells up to 80% with IC 50 values of 1.8 and 2.7 μM, respectively .…”

“…Poca A and Poca B, the two bracelet types of cyclotides, recently extracted from the root tissues of plant Pombalia calceolaria were found to be highly effective against breast cancer cell lines MDA and MB‐231 . The cyclotides, Poca A and Poca B, could inhibit the growth of breast cancer cells up to 80% with IC 50 values of 1.8 and 2.7 μM, respectively . Three diffusa cyclotides DC1, DC2, and DC3, derived from a Chinese medicinal herb Hedyotis diffusa were proved to be effective against prostate cancer cells (PC3, DU145, and LNCap) by inducing apoptosis and inhibiting growth and cell migration with IC 50 < 10 μM .…”

Discovery and mechanistic studies of cytotoxic cyclotides from the medicinal herb Hybanthus enneaspermus

“…Two Möbius cyclotides (varv A and varv F), and a bracelet cyclotide (cycloviolacin O2, cyO2), have been identified as having strong cytotoxic activity against 10 different human tumor cell lines (43). Other cyclotides with anti-tumor effects include vitri A (44), vibi (E, G and H) (12), psyle (A, C and E) (42), viphi (A, D-G) (45), mram 8, viba (15 and 17), varv (A and E) (44,45), vitri F (46), mela (1-7), mech (2 and 3) (47), vila (A and B) (48), Poca (A and B), cyO4 (49), kalata B1 and B2 (50). Previous studies indicate cyclotides exert their cytotoxic activity by disrupting the lipid bilayer of cell membranes (51,52).…”

The Potential of the Cyclotide Scaffold for Drug Development

“…Several cyclotides have shown selective cytotoxicity against several cancer cell lines, including primary cancer cell lines, when compared to normal cells [100,101,102]. More recently, several cyclotides isolated from Viola ignobilis ( Violaceae family), Hedyotis diffusa ( Rubiaceae family), and Pombalia calceolaria have shown cytotoxicity against HeLa [103], several prostate cancer cell lines [104,105], and breast cancer, respectively [106]. Unfortunately, the therapeutic index (i.e., the ratio between the dose required for therapeutic effects versus toxic effects on normal cells) of cytotoxic cyclotides is not optimal yet, requiring optimization before that can be developed into effective anti-cancer therapeutic agents.…”