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Motexafin gadolinium induces mitochondrially-mediated caspase-dependent apoptosis

J Chen1, J Ramos, M Sirisawad

  • 1Pharmacyclics Inc., 995 Arques Ave., Sunnyvale, CA 94085, USA.

Apoptosis : an International Journal on Programmed Cell Death
|September 10, 2005
PubMed

Insights

Motexafin gadolinium (MGd) triggers apoptosis in lymphoma cells by generating reactive oxygen species (ROS) and activating the mitochondrial pathway. This process is caspase-dependent, challenging previous definitions of caspase-independent apoptosis.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Death Pathways

Background:

  • Motexafin gadolinium (MGd) is a redox mediator that localizes to tumors and generates reactive oxygen species (ROS).
  • MGd enhances the efficacy of radiation and chemotherapy in preclinical models.
  • Understanding the precise cell death mechanisms induced by MGd is crucial for its clinical application.

Purpose of the Study:

  • To elucidate the specific apoptotic pathway triggered by Motexafin gadolinium (MGd) in the HF-1 lymphoma cell line.
  • To investigate the role of caspases in MGd-induced apoptosis.
  • To re-evaluate the definition of caspase-independent apoptosis based on inhibitor sensitivity.

Main Methods:

  • Assessed mitochondrial apoptotic pathway markers: mitochondrial membrane potential, cytochrome c release, caspase activation (caspase-9, caspase-8, caspase-3), PARP cleavage, and annexin V binding.
  • Utilized specific caspase inhibitors: z-VAD-fmk (pan-caspase inhibitor) and Q-VD-OPh (potent pan-caspase inhibitor).
  • Compared MGd-induced apoptosis sensitivity to known mitochondrial pathway inducers (dexamethasone, doxorubicin, etoposide) using caspase inhibitors.

Main Results:

  • MGd induced apoptosis via the mitochondrial pathway, evidenced by loss of mitochondrial membrane potential, cytochrome c release, caspase-9 activation preceding caspase-8, PARP cleavage, and annexin V binding.
  • MGd-induced apoptosis was significantly inhibited by the potent caspase inhibitor Q-VD-OPh, confirming caspase dependence.
  • Minimal inhibition was observed with z-VAD-fmk, highlighting differential caspase inhibitor efficacy and suggesting limitations in defining apoptosis solely by z-VAD-fmk resistance.

Conclusions:

  • Motexafin gadolinium (MGd) triggers apoptosis through the mitochondrial pathway in HF-1 lymphoma cells.
  • MGd-induced apoptosis is caspase-dependent, contrary to potential interpretations based on z-VAD-fmk insensitivity.
  • The study suggests that the definition of 'caspase-independent apoptosis' requires refinement, as it cannot be solely based on resistance to z-VAD-fmk.

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