Proteasome inhibition in cancer: development of PS-341
1Millennium Pharmaceuticals, Inc., 75 Sydney Street, Cambridge, MA 02139, USA.
Abstract:
The 26S proteasome regulates protein turnover in eukaryotic cells. This is relevant in human cancer because the cell cycle, tumor growth, and survival are governed by a large repertoire of intracellular proteins that are regulated by the ubiquitin-mediated proteasome degradative pathway. In the development of new antitumor agents whose mechanisms are distinct from currently available therapies, we have discovered a potent, selective inhibitor of the proteasome: PS-341, a dipeptide boronic acid. Compared with normal cells, cancer cells--and specifically myeloma--treated with PS-341 are differentially sensitive to proteasome inhibition and apoptosis. A unique feature of PS-341 involves the inhibition of nuclear factor (NF)-kappaB activation through stabilization of the inhibitor protein IkappaB. Myeloma cells depend on NF-kappaB-mediated transcription of cytokine growth factor interleukin-6, angiogenesis through vascular endothelial growth factor, and the cell adhesion molecule VCAM-1 for adherence of the plasma cells to the stromal tissue in bone marrow. At low nanomolar concentrations, PS-341 is highly effective in abrogating the transcription of these genes, which are under the direct regulation of NF-kappaB. Moreover, PS-341 appears to synergize with dexamethasone in myeloma cell culture, which may prove to be of additional benefit clinically. The safety profile in phase I trials of PS-341 in patients with cancer appears encouraging. Because proteasome inhibition with PS-341 results in potent antitumor activity in vitro, PS-341 may offer a promising new approach to treating otherwise fatal malignancy.
Insights
PS-341, a novel proteasome inhibitor, effectively targets cancer cells, particularly myeloma, by blocking key survival pathways. This drug shows promise as a new antitumor agent with encouraging early trial results.
Area of Science:
- Molecular Biology
- Oncology
- Pharmacology
Background:
- The 26S proteasome is crucial for protein turnover in eukaryotic cells, impacting cell cycle, tumor growth, and survival.
- Dysregulation of the ubiquitin-proteasome pathway is implicated in human cancers.
- Novel therapeutic strategies targeting protein degradation are needed.
Purpose of the Study:
- To discover and characterize a potent, selective proteasome inhibitor for cancer therapy.
- To evaluate the efficacy and mechanism of action of PS-341 in cancer cells, especially myeloma.
- To assess the potential of PS-341 in combination with existing therapies.
Main Methods:
- Discovery and characterization of PS-341, a dipeptide boronic acid proteasome inhibitor.
- Differential sensitivity assays comparing cancer cells (myeloma) and normal cells to PS-341.
- Investigation of PS-341's effect on nuclear factor-kappaB (NF-kappaB) activation and downstream gene transcription.
- In vitro studies assessing synergy with dexamethasone and safety in Phase I trials.
Main Results:
- PS-341 demonstrated potent and selective inhibition of the proteasome.
- Cancer cells, particularly myeloma, showed differential sensitivity to PS-341, leading to apoptosis.
- PS-341 effectively inhibited NF-kappaB activation by stabilizing IkappaB, abrogating transcription of key genes like IL-6 and VEGF.
- PS-341 showed synergy with dexamethasone in myeloma cell cultures.
- Phase I trials indicated an encouraging safety profile.
Conclusions:
- PS-341 is a promising novel proteasome inhibitor with potent antitumor activity.
- Its mechanism, involving NF-kappaB inhibition, offers a distinct approach to cancer therapy.
- PS-341 holds potential for treating malignancies like myeloma, possibly in combination with other agents.
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