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Synthesis and Biological Evaluation of Novel Heterocyclic Imines Linked Coumarin-Thiazole Hybrids as Anticancer Agents.

BACKGROUND
Human Galectin-1, protein of lectin family showing affinity towards β-galactosides has emerged as critical regulator of tumor progression and metastasis, by modulating diverse biological events including homotypic cell aggregation, migration, apoptosis, angiogenesis and immune escape. Therefore, galectin-1 inhibitors might represent novel therapeutic agents for cancer.


METHODS
A new series of heterocyclic imines linked coumarin-thiazole hybrids (6a-6r) has been synthesized and evaluated for their cytotoxic potential against a panel of six human cancer cell lines namely, lung (A549), prostate (DU-145), breast (MCF-7 & MDA-MB-231), colon (HCT-15 & HT-29) using MTT assay. Characteristic apoptotic assays like DAPI staining, cell cycle, annexin V and Mitochondrial membrane potential studies are performed for most active compound. Further Gal-1 inhibition was confirmed by ELISA and fluorescence spectroscopy.


RESULTS
Among all, the compound 6g {3-(2-(2-(pyridin-2-ylmethylene) hydrazineyl) thiazol-4-yl)-2H-chromen-2-one} exhibited promising growth inhibition against HCT-15 colorectal cancer cells with an IC50 value of 1.28 ± 0.14 µM. The characteristic apoptotic morphological features like chromatin condensation, membrane blebbing and apoptotic body formation were clearly observed with compound 6g on HCT-15 cells using DAPI staining studies. Further, annexin V-FITC/PI assay confirmed effective early apoptosis induction by treatment with compound 6g. Loss of mitochondrial membrane potential and enhancing ROS generation were confirmed with JC-1 and DCFDA staining method respectively by treatment with compound 6g, suggest a possible mechanism for inducing apoptosis. Moreover, flow cytometric analysis revealed that compound 6g blocks G0/G1 phase of the cell cycle in a dose dependent manner. The compound 6g effectively reduces the levels of Gal-1 protein in a dose dependent manner. The binding constant (Ka) of 6g with Gal-1 was calculated from the intercept value which was observed as 1.9 x 107 M-1 by Fluorescence spectroscopy. Molecular docking studies showed strong interactions of compound 6g with Gal-1 protein.


CONCLUSION
Our studies demonstrate the anticancer potential and Gal-1 inhibition of heterocyclic imines linked coumarin-thiazole hybrids.