The mechanism of protriptyline-induced Ca2+movement and non-Ca2+-triggered cell death in PC3 human prostate cancer cells

Repurposing antidepressants for anticancer drug discovery

Drug repurposing is an attractive strategy for identifying new indications for existing drugs. Three approved antidepressants have advanced into clinical trials for cancer therapy. In particular, further medicinal chemistry efforts with tranylcypromine (TCP) have led to the discovery of several TCP-based histone lysine specific demethylase 1 (LSD1) inhibitors that display therapeutic promise for treating cancer in the clinic. Thus repurposing antidepressants could be a promising strategy for cancer treatment. In this review, we illustrate the anticancer mechanisms of action of antidepressants and also discuss the challenges and future directions of repurposing antidepressants for anticancer drug discovery, to provide an overview of approved antidepressant cancer therapies.

Targeting Ion Channels for Cancer Treatment: Current Progress and Future Challenges

Ion channels are key regulators of cancer cell pathophysiology. They contribute to a variety of processes such as maintenance of cellular osmolarity and membrane potential, motility (via interactions with the cytoskeleton), invasion, signal transduction, transcriptional activity and cell cycle progression, leading to tumour progression and metastasis. Ion channels thus represent promising targets for cancer therapy. Ion channels are attractive targets because many of them are expressed at the plasma membrane and a broad range of existing inhibitors are already in clinical use for other indications. However, many of the ion channels identified in cancer cells are also active in healthy normal cells, so there is a risk that certain blockers may have off-target effects on normal physiological function. This review describes recent research advances into ion channel inhibitors as anticancer therapeutics. A growing body of evidence suggests that a range of existing and novel Na⁺, K⁺, Ca²⁺ and Cl^- channel inhibitors may be effective for suppressing cancer cell proliferation, migration and invasion, as well as enhancing apoptosis, leading to suppression of tumour growth and metastasis, either alone or in combination with standard-of-care therapies. The majority of evidence to date is based on preclinical in vitro and in vivo studies, although there are several examples of ion channel-targeting strategies now reaching early phase clinical trials. Given the strong links between ion channel function and regulation of tumour growth, metastasis and chemotherapy resistance, it is likely that further work in this area will facilitate the development of new therapeutic approaches which will reach the clinic in the future.

Ca2+ Signaling and Cell Death Induced by Protriptyline in HepG2 Human Hepatoma Cells

The effect of protriptyline on Ca²⁺ physiology in human hepatoma is unclear. This study explored the effect of protriptyline on [Ca²⁺ ]_i and cytotoxicity in HepG2 human hepatoma cells. Protriptyline (50-150 μM) evoked [Ca²⁺ ]_i rises. The Ca²⁺ entry was inhibited by removal of Ca²⁺ . Protriptyline-induced Ca²⁺ entry was confirmed by Mn²⁺ -induced quench of fura-2 fluorescence. Except nifedipine, econazole, SKF96365, GF109203X, and phorbol 12-myristate 13 acetate did not inhibit Ca²⁺ entry. Treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) inhibited 40% of protriptyline-induced response. Treatment with protriptyline abolished BHQ-induced response. Inhibition of phospholipase C (PLC) suppressed protriptyline-evoked response by 70%. At 20-40 μM, protriptyline killed cells which was not reversed by the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in HepG2 cells, protriptyline induced [Ca²⁺ ]_i rises that involved Ca²⁺ entry through nifedipine-sensitive Ca²⁺ channels and PLC-dependent Ca²⁺ release from endoplasmic reticulum. Protriptyline induced Ca²⁺ -independent cell death.