PAD combination therapy (PS-341/bortezomib, doxorubicin and dexamethasone) for previously untreated patients with multiple myeloma

Summary Bortezomib (formerly PS-341) has significant activity in patients with relapsed multiple myeloma (MM), its efficacy is increased with the addition of dexamethasone and it demonstrates synergy with doxorubicin, thus providing the rationale for combination therapy with bortezomib, doxorubicin and dexamethasone (PAD). Patients with untreated MM received four 21-d cycles of PAD, comprising bortezomib 1·3 mg/m2 on days 1, 4, 8 and 11, along with dexamethasone 40 mg on days 1–4, 8–11 and 15–18 during cycle 1 and days 1–4 during cycles 2–4. During days 1–4, patients also received 0, 4·5 or 9 mg/m2 of doxorubicin at dose levels 1, 2, and 3 respectively. Following peripheral blood stem cell (PBSC) collection, patients received high-dose melphalan (MEL200) with PBSC transplantation (PBSCT). After PAD induction alone, 20 of 21 patients (95%) achieved at least a partial response (PR), including complete response (CR) in five patients (24%). Twenty of 21 had PBSC mobilized, and 18 of 20 received MEL200/PBSCT. In an intention-to-treat analysis, response rates were: CR 43%, near CR 14%, very good PR 24%, PR 14% and stable disease 5%. PAD was effective, did not prejudice subsequent PBSC collection, and should be further evaluated in prospective randomized trials.

Bortezomib induces apoptosis in primitive chronic myeloid leukemia cells including LTC-IC and NOD/SCID repopulating cells

Chronic myeloid leukemia (CML) is treated effectively with tyrosine kinase inhibitors (TKIs); however, 2 key problems remain-the insensitivity of CML stem and progenitor cells to TKIs and the emergence of TKI-resistant BCR-ABL mutations. BCR-ABL activity is associated with increased proteasome activity and proteasome inhibitors (PIs) are cytotoxic against CML cell lines. We demonstrate that bortezomib is antiproliferative and induces apoptosis in chronic phase (CP) CD34(+) CML cells at clinically achievable concentrations. We also show that bortezomib targets primitive CML cells, with effects on CD34(+)38(-), long-term culture-initiating (LTC-IC) and nonobese diabetic/severe combined immunodeficient (NOD/SCID) repopulating cells. Bortezomib is not selective for CML cells and induces apoptosis in normal CD34(+)38(-) cells. The effects against CML cells are seen when bortezomib is used alone and in combination with dasatinib. Bortezomib causes proteasome but not BCR-ABL inhibition and is also effective in inhibiting proteasome activity and inducing apoptosis in cell lines expressing BCR-ABL mutations, including T315I. By targeting both TKI-insensitive stem and progenitor cells and TKI-resistant BCR-ABL mutations, we believe that bortezomib offers a potential therapeutic option in CML. Because of known toxicities, including myelosuppression, the likely initial clinical application of bortezomib in CML would be in resistant and advanced disease. (Blood. 2010;115:2241-2250)

A Phase I Trial of Bortezomib in Combination with Epirubicin, Carboplatin and Capecitabine (VECarboX) in Advanced Gastric and Gastro-oesophageal Junction Adenocarcinoma

PURPOSE:
The protease inhibitor bortezomib attenuates the action of NF-κB and has shown preclinical activity alone and in combination with chemotherapy.

DESIGN:
A Phase I dose-escalation study was performed administering bortezomib (0.7, 1.0, 1.3 and 1.6 mg m(-2) on days 1 and 8 from cycle 2 onwards) in combination with Epirubicin 50 mg m(-2) intravenously on day 1, Carboplatin AUC 5 day 1 and Capecitabine 625 mg m(-2) BD days 1-21 every 21 days (VECarboX regimen), in patients with advanced oesophagogastric adenocarcinoma. The primary objective was to define the maximum tolerated dose (MTD) of Bortezomib when combined with ECarboX.

RESULTS:
18 patients received bortezomib 0.7 (n = 6), 1.0 (n = 3), 1.3 (n = 6) and 1.6 mg m(-2) (n = 3) and a protocol amendment reducing the capecitabine dose to 500 mg m(-2) BD was enacted due to myelotoxicity. Common treatment-related non-haematological adverse events of any grade were fatigue (83.3 %), anorexia (55.6 %), constipation (55.6 %) and nausea (55.6 %). Common Grade 3/4 haematological toxicities were neutropenia (77.8 %) and thrombocytopenia (44.4 %). Objective responses were achieved in 6 patients (33.3 %) and a further 5 patients (27.8 %) had stable disease for >8 weeks.

CONCLUSIONS:
The addition of Bortezomib to ECarboX is well tolerated and response rates are comparable with standard chemotherapy.

Proteasome inhibitors: a therapeutic strategy for haematological malignancy

The proteasome is a multicatalytic enzyme complex responsible for the regulated degradation of intracellular proteins. In recent years, inhibition of proteasome function has emerged as a novel anti-cancer therapy. Proteasome inhibition is now established as an effective treatment for relapsed and refractory multiple myeloma and offers great promise for the treatment of other haematological malignancies, when used in combination with conventional therapeutic agents. Bortezomib is the first proteasome inhibitor to be used clinically and a second generation of proteasome inhibitors with differential pharmacological properties are currently in early clinical trials. This review summarises the development of proteasome inhibitors as therapeutic agents and describes how novel assays for measuring proteasome activity and inhibition may help to further delineate the mechanisms of action of different proteasome inhibitors. This will allow for the optimized use of proteasome inhibitors in combination therapies and provide the opportunity to design more potent and therapeutically efficacious proteasome inhibitors.

Proteasome inhibitors in cancer therapy

The ubiquitin proteasome pathway plays a critical role in regulating many processes in the cell which are important for tumour cell growth and survival. Inhibition of proteasome function has emerged as a powerful strategy for anti-cancer therapy. Clinical validation of the proteasome as a therapeutic target was achieved with bortezomib and has prompted the development of a second generation of proteasome inhibitors with improved pharmacological properties. This review summarises the main mechanisms of action of proteasome inhibitors in cancer, the development of proteasome inhibitors as therapeutic agents and the properties and progress of next generation proteasome inhibitors in the clinic.

Targeting the ubiquitin proteasome system in haematological malignancies

The ubiquitin proteasome system (UPS) plays a central role in cellular protein homeostasis through the targeted destruction of damaged/misfolded proteins and regulatory proteins that control critical cellular functions. The UPS comprises a sequential series of enzymatic activities to covalently attach ubiquitin to proteins to target them for degradation through the proteasome. Aberrancies within this system have been associated with transformation and tumourigenesis and thus, the UPS represents an attractive target for the development of anti-cancer therapies. The use of the first-in-class proteasome inhibitor, bortezomib, in the treatment of Plasma Cell Myeloma and Mantle Cell Lymphoma has validated the UPS as a therapeutic target. Following on its success, efforts are focused on the development of second-generation proteasome inhibitors and small molecule inhibitors of other components of the UPS. This review will provide an overview of the UPS and discuss current and novel therapies targeting the UPS.

Synergistic effects of proteasome inhibitor carfilzomib in combination with tyrosine kinase inhibitors in imatinib-sensitive and -resistant chronic myeloid leukemia models

The tyrosine kinase inhibitor (TKI) imatinib has transformed the treatment and outlook of chronic myeloid leukemia (CML); however, the development of drug resistance and the persistence of TKI-resistant stem cells remain obstacles to eradicating the disease. Inhibition of proteasome activity with bortezomib has been shown to effectively induce apoptosis in TKI-resistant cells. In this study, we show that exposure to the next generation proteasome inhibitor carfilzomib is associated with a decrease in ERK signaling and increased expression of Abelson interactor proteins 1 and 2 (ABI-1/2). We also investigate the effect of carfilzomib in models of imatinib-sensitive and -resistant CML and demonstrate a potent reduction in proliferation and induction of apoptosis in a variety of models of imatinib-resistant CML, including primitive CML stem cells. Carfilzomib acts synergistically with the TKIs imatinib and nilotinib, even in imatinib-resistant cell lines. In addition, we found that the presence of immunoproteasome subunits is associated with an increased sensitivity to carfilzomib. The present findings provide a rational basis to examine the potential of carfilzomib in combination with TKIs as a potential therapy for CML, particularly in imatinib-resistant disease.