Naphthoquinones are known to exhibit a broad range of biological activities against microbes, cancer and parasitic diseases and have been widely used in Indian traditional medicine. Plumbagin is a plant-derived naphthoquinone metabolite (5-hydroxy-2-methyl-1,4-naphthoquinone) reported to inhibit trypanothione reductase, the principal enzyme and a validated drug target involved in detoxification of oxidative stress in Leishmania. Here, we report the mechanistic aspects of cell death induced by plumbagin including physiological effects in the promastigote form and ultrastructural alterations in both promastigote and amastigote forms of Leishmania donovani which till now remained largely unknown. Our observations show that oxidative stress induced by plumbagin resulted in depolarization of the mitochondrial membrane, depletion in ATP levels, elevation of cytosolic calcium, increase in caspase 3/7-like protease activity and lipid peroxidation in promastigotes. Apoptosis-like cell death induction post plumbagin treatment was confirmed by biochemical assays like Annexin V/FITC staining, TUNEL as well as morphological and ultrastructural studies. These findings collectively highlight the mode of action and importance of oxidative stress inducing agents in effectively killing both forms of the Leishmania parasite and opens up the possibility of exploring plumbagin and its derivatives as promising candidates in the chemotherapy of Leishmaniasis.
Aim:
Chemoresistance is a prevalent issue in cancer treatment. Paclitaxel (PTX) is a microtubule-binding anticancer drug used in various cancer treatments. However, cancer cells often show chemoresistance against PTX with the help of P-glycoprotein (Pgp) - a drug efflux pump. It has also been observed that overexpressed T-type calcium channels (TTCCs) maintain calcium homeostasis in cancer cells, and calcium has a role in chemoresistance. Therefore, the aim of this study was to test the adjuvant role of TTA-A2, a TTCC blocker, in enhancing the anticancer effect of PTX on the A549 lung adenocarcinoma cell line.
Methods:
Morphology assay, calcium imaging assay, clonogenic assay, apoptosis assay, and real-time polymerase chain reaction (real-time PCR) were performed to find the adjuvant role of TTA-A2. Samples were treated with PTX at 10 nM concentration and TTA-A2 at 50 and 100 nM concentrations. PTX and TTA-A2 were used in the combination treatment at 10 and 100 nM concentrations, respectively.
Results:
Immunocytochemistry confirmed the expression of TTCC in A549 cells. Morphology assay showed altered morphology of A549 cells. The adjuvant role of TTA-A2 was observed in the calcium imaging assay in spheroids, in the clonogenic assay in monolayers, and in the apoptosis assay in both cultures. With real-time PCR, it was observed that, even though cells express the mRNA of Pgp, it is non-significant upon treatment with PTX and TTA-A2.
Conclusion:
TTA-A2 can be used as an adjuvant to reduce chemoresistance in cancer cells as well as to enhance the anticancer effect of the standard anticancer drug PTX. Being a potent TTCC inhibitor, TTA-A2 may also enhance the anticancer effects of other anticancer drugs.
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