Raptinal bypasses BAX, BAK, and BOK for mitochondrial outer membrane permeabilization and intrinsic apoptosis

Abstract

Most antineoplastic chemotherapies eliminate cancer cells through activation of the mitochondria-controlled intrinsic apoptotic pathway. Therein, BAX, BAK, and/or BOK function as the essential pore-forming executioners of mitochondrial outer membrane permeabilization (MOMP). The activation threshold of BAX and BAK also correlates inversely with the required strength of an apoptotic stimulus to induce MOMP and thereby effectively determines a cell’s readiness to undergo apoptosis. Consequently, the ‘gatekeepers’ BAX and BAK emerged as therapeutic targets, but functional or genetic loss renders BAX/BAK-targeting strategies prone to fail. Here, we show that the small molecule Raptinal overcomes this limitation by triggering cytochrome c release in a BAX/BAK/BOK-independent manner. Raptinal exerts a dual cytotoxic effect on cancer cells by rapid activation of the intrinsic apoptotic pathway and simultaneous shutdown of mitochondrial function. Together with its efficacy to eliminate cancer cells in vivo, Raptinal could be useful in difficult-to-treat cancer entities harboring defects in the intrinsic apoptosis pathway.

Gamma Radiation-Attenuated Toxoplasma gondii Provokes Apoptosis in Ehrlich Ascites Carcinoma-Bearing Mice Generating Long-Lasting Immunity

“…In addition, caspase 9 stimulates the effector caspases 3 and 7, both apoptosis performers. 48,49 In many cancers, however, proteins that control the permeability of the outer mitochondrial membrane to release cytochrome c are defective via mutations. 50 Ehrlich ascites carcinoma-vaccinated group revealed high significant increase in the level of apoptotic molecule (Bax, Bak, cytochrome-c, and caspase 3) compared to EAC-bearing mice ( Figure 6).…”

The extracellular lactate-to-pyruvate ratio modulates the sensitivity to oxidative stress-induced apoptosis via the cytosolic NADH/NAD+ redox state

“…Under oxidative stress, JNK-mediated phosphorylation of 14-3-3, a cytoplasmic anchor of Bax, and downstream Bcl2-family proteins including Bax itself, leads to liberation and mitochondrial translocation of Bax to initiate MOMP [30,32,44]. In HCT116 cells, Raptinal is capable of inducing cytochrome c release even in the absence of the essential components (Bak/Bax/Box) required for canonical pore formation [45], suggesting a yet unidentified mechanism for Raptinal induced cytochrome c release in these cells. Consistently, our data indicate that this unidentified mechanism is rather insensitive to changes in the cytosolic [NADH]/[NAD + ] ratio or JNK inhibition (Fig.…”

Hypertonicity counteracts MCL‐1 and renders BCL‐XL a synthetic lethal target in head and neck cancer

“…Cell viability was measured using MTT-based assays and has also been described in earlier studies [56,57]. Cells were seeded in 96-well plates (2 9 10 4 cells/well) and challenged with the indicated concentrations of the indicated substances in duplicates (technical replicates).…”

“…Fluorescence-based assessment of caspase activity has also been described in our previous studies [56,57]. Activity of caspase-3 and caspase-7 was measured using the caspase-3/-7 activity kit (AAT Bioquest, Sunnyvale, CA, USA) according to the manufacturer's instructions.…”

“…Cell death was assessed by annexin-V and 7-AAD staining and has already been described in our earlier studies [56,57]. In brief, cells were challenged with the indicated concentrations of WEHI-539 in the presence and absence of NaCl for 8 h. Afterward, cells were stained with 7-AAD and annexin-V (4°C for 15 min in the dark) following the standard procedures and analyzed immediately using a FACSCanto flow cytometer (BD Biosciences, Heidelberg, Germany) [58].…”