Proteasome inhibition as a novel mechanism of the proapoptotic activity of γ-secretase inhibitor I in cutaneous T-cell lymphoma.

BACKGROUND: We have previously discovered that Notch1 is expressed on malignant T cells in cutaneous T-cell lymphoma (CTCL), and is required for survival of CTCL cell lines. Notch can be inhibited by γ-secretase inhibitors (GSIs), which differ widely in their ability to induce apoptosis in CTCL. OBJECTIVES: To investigate whether GSI-I, in addition to inhibiting Notch, induces apoptosis in CTCL by proteasome inhibition, as GSI-I is very potent and has structural similarity to the proteasome inhibitor MG-132. METHODS: Cell lines derived from CTCL (MyLa, SeAx, JK, Mac1 and Mac2a) were treated with GSI-I and two other proteasome inhibitors (MG-132 and bortezomib). The effects on cell viability, apoptosis and proteasome activity were measured, as was the impact on the prosurvival, nuclear factor κB (NF-κB) pathway. RESULTS: In CTCL, GSI-I had proteasome-blocking activity with a potency comparable to the proteasome inhibitors MG-132 and bortezomib. Proteasome inhibition was the main mechanism responsible for GSI-I-induced cell death, as tiron, a compound known to reverse the effect of MG-132, restored proteasome activity and largely abrogated the cytotoxic effect of GSI-I. Although inactivation of NF-κB is an important mechanism of action for proteasome inhibitors, we demonstrated an apparent activation of NF-κB. Furthermore, we showed that while the tumour suppressor protein p53 was induced during proteasome inhibition, it was dispensable for CTCL apoptosis, as both SeAx cells, which harbour p53 mutations that attenuate the apoptotic capacity, and HuT-78 cells, which have a deleted p53 gene, demonstrated potent apoptotic response. CONCLUSIONS: GSI-I represents an interesting drug with a dual mechanism of action comprising inhibition of both Notch and the proteasome.

Low-dose total skin electron beam therapy as a debulking agent for cutaneous T-cell lymphoma: an open-label prospective phase II study.

BACKGROUND: Total skin electron beam therapy (TSEBT) is a powerful treatment for cutaneous T-cell lymphoma (CTCL). Based on the occurrence of relapses with low radiation doses, doses of 30-36Gy are commonly used but most patients still eventually relapse and repeat treatment courses are limited due to the cumulative toxicity. Complete response (CR) rates are about 60-90% for T2-4 stages with a 5-year relapse-free survival of 10-25% for stages IB-III. OBJECTIVES: To evaluate prospectively the efficacy of low-dose TSEBT (10Gy) in terms of complete cutaneous response rate, overall response rate and response duration in CTCL. METHODS: Ten patients with stage IB-IV mycosis fungoides (MF) were treated in an open-label manner with four fractions of TSEBT 1Gy weekly to a total skin dose of 10Gy. Treatment responses were assessed at 1 and 3months after treatment and subsequently at least every 6months for a total period of 2years or to disease relapse or progression. RESULTS: Patients achieved an overall response rate of 90%. The rate of CR or very good partial response (VGPR; <1% skin affected with patches/plaques) was 70%. The median response duration was 5·2months (range 83-469days) for CR and VGPR. Adverse effects were generally mild to moderate in severity. CONCLUSIONS: Low-dose TSEBT (10Gy) gave a satisfactory response rate and was well tolerated in patients with MF stage IB-IV. Future studies should determine if the combination of low-dose TSEBT with other agents could increase the rate of CR and response duration.

Notch signalling in primary cutaneous CD30+ lymphoproliferative disorders: a new therapeutic approach?

BACKGROUND: The oncogenic potential of deregulated Notch signalling has been described in several haematopoietic malignancies. We have previously reported an increased expression of Notch1 in primary cutaneous CD30+ lymphoproliferative disorders, lymphomatoid papulosis and primary cutaneous anaplastic large-cell lymphoma (pcALCL). OBJECTIVES: To investigate the functional importance of Notch signalling in cell lines derived from pcALCL. METHODS: Cell lines derived from pcALCL (Mac1, Mac2a and JK) were treated with different γ-secretase inhibitors (GSIs) (GSI I, IX, XX and XXI). The effects of GSIs on cell viability, apoptosis and cell cycle progression were measured as well as the impact of GSI I on the known prosurvival pathway Akt-mTOR-FOXO3a. RESULTS: Notch family members were expressed in all investigated pcALCL cell lines. GSI I had a marked proapoptotic effect, but GSI IX, XX and XXI were much less potent. The GSI I-triggered apoptosis was preceded by an accumulation of cells in the G2/M, cyclin B1-controlled phase of the cell cycle accompanied by an increase in the cyclin-dependent kinase inhibitor, p21(WAF/Cip) . GSI I induced the nuclear translocation of proapoptotic FOXO3a, probably via an Akt-independent pathway. CONCLUSIONS: Notch signalling may be a future therapeutic target for the treatment of advanced pcALCL.

Potential involvement of Notch1 signalling in the pathogenesis of primary cutaneous CD30-positive lymphoproliferative disorders.

BACKGROUND: The central role of Notch signalling in T-cell development and oncogenesis raises the question of the importance of this pathway in cutaneous T-cell lymphomas. OBJECTIVES: To investigate the pattern of expression of Notch and its ligands, Jagged and Delta, in skin samples of primary cutaneous CD30+ lymphoproliferative disorders. METHODS: Immunohistochemistry of formalin-fixed, paraffin-embedded skin samples from 12 patients with lymphomatoid papulosis (LyP) and 11 patients with primary cutaneous anaplastic large cell lymphoma (ALCL). Immunofluorescence studies of fresh skin samples obtained from three patients with LyP and two patients with primary cutaneous ALCL. RESULTS: We identified single Notch1-positive cells or small clusters of atypical cells in LyP. Similarly, strongly positive Jagged1 cells tended to be localized in clusters. Primary cutaneous ALCL had higher expression of Notch1 and Jagged1 compared with LyP. Cells expressing Notch1 and Jagged1 were colocalized and a subset of cells expressed both the receptor and the ligand. The expression of the ligand Delta1 was low to undetectable in both types of lymphoproliferations. A subpopulation of lymphoma cells was found to coexpress Notch1 and activated Akt kinase. CONCLUSIONS: These results imply a potential role for the Notch signalling pathway in the pathogenesis of primary cutaneous CD30+ lymphoproliferative disorders and provide a rationale for the exploration of the activity of Notch antagonists in the therapy of these diseases.