Cross talk of cancer signaling pathways by cyclic hexapeptides and anthraquinones from Rubia cordifolia

Authors: BALACHANDRAN, PREMALATHA - University Of Mississippi; IBRAHIM, MOHAMED - University Of Mississippi; ZHANG, JIN - University Of Mississippi; Wang, Mei; PASCO, DAVID - University Of Mississippi; MUHAMMAD, ILIAS - University Of Mississippi

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2021
Publication Date: 1/31/2021
Citation: Balachandran, P., Ibrahim, M.A., Zhang, J., Wang, M., Pasco, D.S., Muhammad, I. 2021. Cross talk of cancer signaling pathways by cyclic hexapeptides and anthraquinones from Rubia cordifolia. Molecules. 26/735. https://doi.org/10.3390/molecules26030735.
DOI: https://doi.org/10.3390/molecules26030735

Interpretive Summary: Rubia cordifolia Linn. (Fam. Rubiaceae), commonly called Indian Madder or Manjistha is a perennial climber herb. The genus Rubia consists of about 70 species world-wide. Commercially, they were used as natural dyes for hair and food products while in the folk medicine, they have been used as early as 2000 B.C. for the treatment of wounds, ulcers, skin disorders, rheumatism, inflammation. The plants in this family are known to produce anthraquinones and their glycosides in significant amounts, iridoids, oleananes, triterpenoids, and bicyclic hexapeptides. Due to the potential anticancer activity of R. cordifolia extract, and the significance of targeting cancer related signaling pathways towards anti-cancer drug discovery, this current study was conducted to evaluate the influence of Rubia extract and its isolated anthraquinones and cyclic hexapeptides and mixture thereof on cancer signaling pathways. The results showed that the potent anticancer potency of R. cordifolia has been mainly contributed by the presence of cyclic hexapeptide, whose activity is mediated through the inhibition of several cancer signaling pathways. It further confirms that the anthraquinones play a minor role in anticancer potential of R. cordifolia when compared to cyclic hexapeptides as they exhibit less inhibition toward these cancer signaling pathways. The cross talk between cancer signaling pathways plays several complex roles in cancer and identifying targets modulating these pathways serve as a current focus on cancer treatment approaches.

Technical Abstract: The anticancer activities of Rubia cordifolia and its constituents have been reported earlier, but their influence on cross-talk of complex cancer-related signaling metabolic pathways (i.e., 18 transcription factors; TF) has not yet been fully investigated. In this study, the roots of R. cordifolia were subjected to TF- based bioactivity-guided fractionation, which yielded three anthraquinones, alizarin (1), purpurin (2) and emodin (3), two lignans; eudesmin (4) and compound 5, and two cyclic hexapeptides; deoxybouvardin RA-V (6), and mixture of 6 and 9 (RA-XXI). The structures of the isolated compounds were determined by using full NMR spectroscopy and HRESIMS. Compounds 1-3, 6 and 6+9, together with reference anthraquinones, chrysophanol (11), danthron (12), quinizarin (13), aloe-emodin (14) and a-lapachone (15) were tested against a panel of luciferase reporter genes that assesses the activity of a wide-range of cancer-related signaling pathways. Among the compounds, the cyclic hexapeptide 6 was found to be very active against several signaling pathways, notably wnt, myc and notch with IC50 values of 50, 75 and 93 ng/mL, respectively. Compound 6 was tested for stability in simulated intestinal and gastric fluids since the stability in biological fluid is a key shortcoming of cyclic hexapeptides. The anticancer activity of 6 was found to remain unchanged before and after treatment of simulated gastric/intestinal fluids, indicating that RA-V was stable, thereby, could be bioavailable when orally used in therapeutics and possibly a drug candidate for cancer treatment. The mechanism for the preferential inhibition of these pathways and the possible cross-talk effect with other previously reported signaling pathways has been discussed.