Arsenic trioxide and paclitaxel induce apoptosis by different mechanisms

Area of Science:

• Oncology
• Molecular Biology
• Cell Biology

Background:

• Arsenic trioxide (ATO) and paclitaxel (TAXOL) are established cancer therapeutics inducing G2/M arrest.
• ATO has been shown to induce apoptosis in myeloma cells with mutant p53 via intrinsic and extrinsic pathways.
• The role of Bcl-2 in mediating the apoptotic effects of these drugs in myeloma remains to be fully elucidated.

Purpose of the Study:

• To compare the mechanisms of apoptosis induced by ATO and paclitaxel in myeloma cells with mutant p53 and varying Bcl-2 expression.
• To investigate the differential involvement of Bcl-2 in ATO- and paclitaxel-induced cell death.

Main Methods:

• Myeloma cell lines expressing mutant p53 and differential Bcl-2 levels were treated with ATO and paclitaxel.
• Apoptosis was assessed by evaluating caspase activation, mitochondrial membrane potential, cytochrome c and AIF release, and chromatin condensation.
• The influence of Bcl-2 on these apoptotic events was specifically examined.

Main Results:

• ATO rapidly induced apoptosis through Apo2/TRAIL, caspase 8 activation, BID cleavage, mitochondrial membrane depolarization, and AIF release, independent of Bcl-2.
• ATO-induced apoptosis was characterized by early perinuclear condensed chromatin formation colocalized with AIF.
• Paclitaxel-induced apoptosis, including mitochondrial depolarization, cytochrome c release, and caspase 9 activation, was inhibited by Bcl-2.
• Paclitaxel-induced apoptosis involved random chromatin condensation and nuclear fragmentation without early AIF involvement.

Conclusions:

• ATO induces apoptosis via a Bcl-2-independent pathway involving the extrinsic pathway and AIF.
• Paclitaxel's apoptotic effects are sensitive to Bcl-2 inhibition, primarily engaging the intrinsic pathway.
• These findings highlight distinct mechanisms of action for ATO and paclitaxel in myeloma, offering potential for targeted therapeutic strategies.