Inflated endoplasmic reticulum and autophagy induction promoted death in aggressive cancer cells grown in adherent and in-vitro CTC conditions.

Abstract Cancer metastasis is the leading cause of death in cancer patients and is a major challenging aspect of cancer biology. Various adaptive molecular signaling pathways play a crucial role in cancer metastasis and later in the formation of secondary tumors. Aggressive cancer cells like Triple Negative breast cancer (TNBCs) are more inclined to undergo metastasis hence having a high recurrence rate and potential for secondary tumor formation. Such aggressive cancer cells have fewer treatment options available with poor prognoses. Metastatic cells in circulation known as circulating tumor cells (CTCs) could be an appealing alternative target for cancer therapy with potentially better outcomes. Cell cycle regulation and stress response of CTCs in blood has a crucial role in their survival and progression and thus may be considered therapeutically active hotspots. The cyclin D/cyclin-dependent kinase (CDK) pathway regulates cell cycle checkpoints, a process that is frequently dysregulated in cancer cells. Selective CDK inhibitors can limit the phosphorylation of cell cycle regulatory proteins by inducing cell cycle phase arrest, and thus may be an effective therapeutic strategy for aggressive cancer cells in their dividing phase at the primary or secondary site. However, during the floating condition, cancer cells halt their division process and proceed through the various steps of metastasis. Our study showed that a novel CDK inhibitor 4ab besides showing anti-proliferative activity in aggressive cancer cells also induces cell death by activating endoplasmic reticulum stress and strong autophagy induction in both adherent and floating conditions which resulted in cytoplasmic vacuolation (paraptosis) and ultimately resulted in cell death. Further our results showed that 4ab efficiently induced apoptosis in aggressive cancer cells by initiating the ER-mitochondrial membrane potential loss-JNK pathway. Further, our in vivo data showed a promising inhibitory effect of 4ab on aggressive 4T1 cells in tumor formation and metastasis. The above data gave us encouraging results to consider 4ab as a potential inhibitor for anti-metastatic therapeutic intervention.