Investigating the Role of a T-type Calcium Channel Antagonist (TTA-A2) as a Potential Adjuvant of Paclitaxel in Chemotherapy

Background: Chemoresistance is a prevalent issue in cancer treatment. Paclitaxel (PTX), a microtubule-binding anticancer drug, often exhibits chemoresistance due to P-glycoprotein (Pgp), a drug efflux pump. It has also been observed that overexpressed T-type calcium (Ca2+) channels (TTCCs) maintain Ca2+ homeostasis in cancer cells, contributing to chemoresistance.

Aim: This study aims to investigate the adjuvant role of TTA-A2, a TTCC blocker, in enhancing the anticancer effects of PTX on the A549 lung adenocarcinoma cell line.

Methods: Morphology assay, Ca2+ imaging, clonogenic assay, apoptosis assay, and real-time PCR were performed. Samples were treated with 10 nM PTX and TTA-A2 at 50 nM and 100 nM, including a combination of 10 nM PTX and 100 nM TTA-A2.

Results and Conclusion: Immunocytochemistry and real-time PCR confirmed Cav3.1 and Cav3.2 (TTCC isoforms) expression, with higher Cav3.2 levels. The morphology assay showed no differences among treatment groups. The adjuvant effects of TTA-A2 were seen in Ca2+ imaging, clonogenic, and apoptosis assays. In the Ca2+ imaging assay, a significant reduction in the 340/380 ratio was seen in combination treatment with spheroids. The clonogenic assay showed the minimum number of colonies in the combination treatment. Similarly, the apoptosis assay showed the highest number of PI-stained (dead) cells in the combination treatment in both monolayer and spheroids. Furthermore, no significant changes in the Pgp mRNA expression were observed in real-time PCR in any treatment group, indicating that PTX and TTA-A2 treatment does not significantly alter Pgp expression. Since cancer cells show resistance to PTX through Pgp activity and TTA-A2 is not a substrate of Pgp, a combination of a reduced PTX concentration and TTA-A2 treatment may prove to be a more effective cancer treatment. Overall, our results indicated an adjuvant role of TTA-A2 in combination with PTX, which can help in overcoming chemoresistance and provide better cancer treatment.