Background: The use of medicinal plants for general wellbeing and disease treatment is a common practice among tribal communities of Kokrajhar districts of Assam. However, little works have been done to study the pharmacological aspect of the plants.

Objectives: The present study intends to study the antioxidant and antiproliferative properties of selected medicinal plants used by the tribal communities of Kokrajhar district of Assam since ancient times.

Methods: Five traditionally important medicinal plants namely, Cassia fistula, Citrus grandis, Lindernia crustacea, Sacciolepis myosuroides, and Zingiber zerumbet were investigated for antioxidant, antiproliferative (cytotoxic) and apoptosis-inducing potential in the malignant cancer cell line. Phytochemical content such as phenolic and flavonoid content were estimated following standard protocol. The methanolic extract of plants were investigated following phosphomolybdate method (TAC), FRAP, DPPH, ABTS, and TBARS assays. Antiproliferative activities of the plants were carried out by MTT assay in DL and PBMC cells. The apoptotic study was carried out following the acridine orange and ethidium bromide staining method and fluorescent microscopic imaging. Based on the significant (P≤0.05) high apoptotic inducing potential of the plant and to further dissect the molecular mode of action including downstream biological action, major phytochemicals derived from L. crustacea were investigated for its prospective binding affinity with antiapoptotic cancer target proteins.

Results: Antioxidant studies by FRAP, DPPH, ABTS, and TBARS assay revealed that all the five plants contain considerable free radical scavenging activity. C. fistula showed the strongest free radical scavenging activity while the fruit peel extract of C. grandis showed poor activity. The overall antioxidant activities of plants such as TAC, FRAP, DPPH, ABTS, and TBARS may be arranged in decreasing activity as C. fistula > Z. zerumbet > L. crustacea > S. myosuroides > C. grandis. MTT based cell proliferation study showed that all the plants extract significantly (P≤0.05) inhibited cell viability with negligible cytotoxicity (~5-12%) in normal cells. Moreover, L. crustacea showed promising antiproliferative and apoptosis-inducing ability against Dalton's lymphoma. It is worth mentioning that the major bioactive compounds of the most potent plant extract, L. crustacea interacted with anti-apoptotic proteins (cancer target) with higher affinity and the results are compared with reference inhibitors.

Conclusion: It is worth noting that these plants have the potential to consider for further scientific studies in different cell lines and animal models. Furthermore, isolation and characterization of bioactive compound(s), may promise the discovery of new and valuable drugs candidate to tackle various human diseases.

Keywords: Antioxidant; Kokrajhar; antiproliferative; apoptosis; docking; ethnomedicine.