Related Experiment Video
Updated: Mar 6, 2026
A 3D Organotypic Melanoma Spheroid Skin Model
Published on: May 18, 2018
Proteasome inhibitors against amelanotic melanoma
Justyna Sidor-Kaczmarek1, Mirosława Cichorek2, Jan Henryk Spodnik3
1Department of Anatomy and Neurobiology, Medical University of Gdansk, Gdansk, Poland. j.sidor@gumed.edu.pl.
Abstract:
The incidence of malignant melanoma, the most aggressive skin cancer, is increasing constantly. Despite new targeted therapies, the prognosis for patients with metastatic disease remains poor. Thus, there is a need for new combinational treatments, and antineoplastic agents potentially valuable in this approach are inhibitors of the ubiquitin-proteasome system (UPS). In this work, we analyze the cytotoxicity mechanisms of proteasome inhibitors (MG-132, epoxomicin, and lactacystin) in a specific form of melanoma which does not synthesize melanin-the amelanotic melanoma (Ab cells). We found that the most cytotoxic of the compounds tested was epoxomicin. Caspase-9 activation as well as cytochrome C and AIF release from mitochondria indicated that exposure to epoxomicin induced the mitochondrial pathway of apoptosis. Epoxomicin treatment also resulted in accumulation of Bcl-2 family members-proapoptotic Noxa and antiapoptotic Mcl-1, which were postulated as the targets for bortezomib in melanoma. Inhibition of caspases by BAF revealed that cell death was partially caspase-independent. We observed no cell cycle arrest preceding the apoptosis of Ab cells, even though cdk inhibitors p21Cip1/Waf1 and p27Kip1 were up-regulated. The cell cycle was blocked only after inactivation of caspases by the pan-caspase inhibitor BAF. In summary, this is the first study exploring molecular mechanisms of cell death induced by epoxomicin in melanoma. We found that Ab cells died on the mitochondrial pathway of apoptosis and also partially by the caspase-independent way of death. Apoptosis induction was fast and efficient and was not preceded by cell cycle arrest.
Insights
Epoxomicin effectively induces apoptosis in amelanotic melanoma cells via the mitochondrial pathway, offering a potential new treatment. This proteasome inhibitor triggers cell death rapidly, even independently of caspases, without prior cell cycle arrest.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Malignant melanoma incidence is rising, with poor prognosis for metastatic cases.
- Targeted therapies show limitations, necessitating novel combinational treatments.
- Ubiquitin-proteasome system (UPS) inhibitors are potential antineoplastic agents.
Purpose of the Study:
- To investigate the cytotoxicity mechanisms of proteasome inhibitors (MG-132, epoxomicin, lactacystin) in amelanotic melanoma (Ab cells).
- To elucidate the specific pathways of cell death induced by epoxomicin in this melanoma subtype.
Main Methods:
- Cytotoxicity assays using MG-132, epoxomicin, and lactacystin on Ab cells.
- Analysis of caspase-9 activation, cytochrome C, and AIF release.
- Assessment of Bcl-2 family member accumulation (Noxa, Mcl-1).
- Inhibition of caspases using BAF to determine cell death pathways.
- Cell cycle analysis and evaluation of cdk inhibitors (p21, p27) expression.
Main Results:
- Epoxomicin demonstrated the highest cytotoxicity among tested proteasome inhibitors.
- Epoxomicin induced apoptosis via the mitochondrial pathway, evidenced by caspase-9 activation and mitochondrial release of cytochrome C and AIF.
- Accumulation of Noxa and Mcl-1 was observed following epoxomicin treatment.
- Cell death was partially caspase-independent, as indicated by BAF inhibition experiments.
- No cell cycle arrest preceded apoptosis, despite upregulation of p21 and p27.
Conclusions:
- Epoxomicin is a potent inducer of rapid apoptosis in amelanotic melanoma cells.
- The primary mechanism involves the mitochondrial pathway, with a significant caspase-independent component.
- These findings highlight epoxomicin's potential as a novel therapeutic agent for amelanotic melanoma, warranting further investigation.
Related Concept Videos
02:57Targeted Cancer Therapies
There are several types of targeted therapies against...
02:50Combination Therapies and Personalized Medicine
The combination of the drug acetazolamide and sulforaphane is a good example of combination therapy to treat cancer. The cells in the interior of a large tumor often die due to the hypoxic and...
01:27Tumor Immunotherapy
02:18The Proteasome
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...