Proteasome inhibitors exhibit antitumor activity against malignancies of different histology. Yet, the mechanisms underlying this effect are poorly understood. Recent evidence indicates that ...antiapoptotic factors may also accumulate as a consequence of exposure to these drugs, possibly reducing their cytotoxicity. These include the Bcl-2 family member Mcl-1, whose down-regulation has been proposed to initiate apoptosis in response to genotoxic stimuli. In this study, we found that proteasome inhibitors release cyotochrome c and second mitochondria-derived activator of caspase (SMAC)/Diablo and trigger the subsequent apoptotic cascade in spite of concomitant Mcl-1 increase. However, our data indicate that subtraction of Mcl-1 during apoptosis, although not required for early release of proapoptotic factors, is probably relevant in speeding up cell demise, since RNA interference-mediated Mcl-1 silencing is lethal in lymphoma cells. Consistent with this, the cytotoxic effects of proteasome inhibitors are enhanced when Mcl-1 increase is impeded. Thus, this study identifies Mcl-1 accumulation as an unwanted molecular consequence of exposure to proteasome inhibitors, which slows down their proapoptotic effects. Pharmacologic or genetic approaches targeting Mcl-1, including therapeutic RNAi, may increase the effectiveness of these compounds. (Blood. 2005;105:3255-3262)
Proteasome inhibitors possess potent antitumor activity against a broad spectrum of human malignancies. However, the effects of these compounds on the immune system still have to be clearly ...determined. In the present study, we have investigated the effects of proteasome inhibitors on dendritic cells (DC), antigen‐presenting cells playing a key role in the initiation of immune responses. Exposure to the proteasome inhibitors bortezomib, MG132 or epoxomicin was found to promote apoptosis of human monocyte‐derived DC and to reduce the yield of viable DC when given to monocytes early during differentiation to DC. DC apoptosis via proteasome inhibition was accompanied by mitochondria disruption and subsequent activation of the caspase cascade. Up‐regulation and intracellular redistribution of Bcl‐2‐associated X protein (Bax), a pro‐apoptotic Bcl‐2 family protein, were observed in DC treated with these compounds and represent a suitable mechanism leading to activation of the intrinsic apoptotic pathway. Finally, active protein synthesis was found to represent an upstream prerequisite for DC apoptosis induced by proteasome inhibitors, since the translation inhibitor cycloheximide blocked all of the steps of the observed apoptotic response. In conclusion, induction of apoptosis in DC may represent a novel mechanism by which proteasome inhibitors affect the immune response at the antigen‐presenting cell level.
Patients who relapse after an autologous hematopoietic stem cell transplantation (SCT) have a very poor prognosis. We have retrospectively analyzed diffuse large B cell lymphoma patients who ...underwent an allo-SCT after an auto-SCT relapse reported in the Gruppo Italiano Trapianto di Midollo Osseo (GITMO) database. From 1995 to 2008, 3449 autologous transplants were reported in the GITMO database. Eight hundred eighty-four patients relapsed or progressed after transplant; 165 patients, 19% of the relapsed patients, were treated with allo-transplant. The stem cell donor was related to the patient in 108 cases. A reduced intensity conditioning regimen was used in 116. After allo-SCT, 72 patients (43%) obtained a complete response and 9 obtained a partial response with an overall response rate of 49%; 84 patients (51%) experienced rapid progression of disease. Ninety-one patients died, 45 due to disease and 46 due to treatment-related mortality. Acute graft-versus-host disease was recorded in 57 patients and a chronic GvHD in 38 patients. With a median follow-up of 24 months (2–144) after allo, overall survival (OS) was 39%, and after a median of 21 months (2–138) after allo, progression-free survival (PFS) was 32%. Multivariate analysis indicated that the only factors affecting OS were status at allo-SCT, and those affecting PFS were status at allo-SCT and stem cell donor. This retrospective analysis shows that about one-fifth of patients with diffuse large B cell lymphoma who experience relapse after autologous transplantation may be treated with allogeneic transplantation. Moreover, the only parameter affecting either OS or PFS was the response status at the time of allo-SCT.
Bcl-2 overexpression is frequently detected in lymphoid malignancies, being associated with poor prognosis and reduced response to therapy. Here, we evaluated whether Bcl-2 overexpression affects the ...cytotoxic activity of proteasome inhibitors taken alone or in association with conventional anticancer drugs or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL).
Jurkat cells engineered to overexpress Bcl-2 were treated with proteasome inhibitors (MG132, epoxomicin, and bortezomib), anticancer drugs (etoposide and doxorubicin), TRAIL, or combinations of these compounds. Cell death and loss of mitochondrial transmembrane potential were detected by flow cytometry. Cytosolic relocalization of cytochrome c and SMAC/Diablo, caspase cleavage, and Bcl-2 and Mcl-1 levels were determined by immunoblotting. Nuclear factor-kappaB inhibition was done by retroviral transduction with a dominant-negative mutant of IkappaBalpha.
Bcl-2 overexpression results in significant inhibition of apoptosis in response to proteasome inhibitors, antiblastics, and TRAIL. Addition of TRAIL to proteasome inhibitors results in a synergistic cytotoxic effect in Bcl-2-overexpressing cells, whereas this result is not reproduced by the combination of proteasome inhibitors with antiblastic drugs. Importantly, proteasome inhibitors plus TRAIL induce mitochondrial dysfunction irrespective of up-regulated Bcl-2. Bcl-2 cleavage to a fragment with putative proapoptotic activity and elimination of antiapoptotic Mcl-1 may both play a role in proteasome inhibitors-TRAIL cooperation. Conversely, nuclear factor-kappaB inhibition by proteasome inhibitors is per se insufficient to explain the observed synergy.
Combined proteasome inhibitors and TRAIL overcome the apoptotic threshold raised by Bcl-2 and may prove useful in the treatment of chemoresistant malignancies with up-regulated Bcl-2.
The benefits of allografting noted in some malignant diseases might be safely extended to metastatic breast cancer by a combination of cytoreduction with high-dose chemotherapy (HDT) and autologous ...stem-cell transplant (ASCT) with graft-versus-tumour effect mediated by transplanted donor immune cells with nonmyeloablative allografting (reduced intensity conditioning transplantation, RICT). 17 patients with heavily pretreated disease were given tandem transplants. 13 patients sustained donor engraftment. Three had partial remission after HDT and ASCT and complete remission after RICT; they achieved full chimerism and all developed graft-versus-host disease (GVHD) before regression of cancer. Another patient did not respond to HDT and ASCT but had partial remission after RICT, giving an overall response rate of 24%. Five patients had grade II or higher acute GVHD and five had extensive chronic GVHD. No non-relapse-related deaths occurred during the first 100 days. Five patients (29%) were alive 90–2160 days (median 1320) after RICT. This two-step approach is feasible in patients with metastatic breast cancer.
The purpose of the present study was to evaluate the feasibility and the efficacy of employing a high-dose chemotherapy (HDT) regimen with tandem peripheral blood progenitor cells (PBPC) supported ...transplantation in the initial treatment of aggressive non-Hodgkin's lymphoma (NHL). HDT was preceded by a standard course of conventional dose chemotherapy in 17 out of the 25 patients treated, while in 8 cases it was delivered after only one or two cycles. HDT was a three-step procedure which included high-dose (6-7 g/m2) cyclophosphamide (CY) supported by haematopoietic growth factors, the first myeloablative course with mitoxantrone (NOV) 60, 75 or 90 mg/m2 plus melphalan (L-PAM) 140-180 mg/m2 with haematopoietic rescue, and the second myeloablative course with etoposide (VP) and carboplatin (CARBO) given at 1.5 g/m2 each with haematopoietic rescue. PBPC were collected after CY administration. Twenty-two patients (88%) completed the HDT, haematological reconstitution was rapid and complete at each step and there were no toxic deaths. The activity of the treatment was high with a CR rate over 90% in the entire patient population. The 2-year overall survival (OS) and failure-free survival (FFS) rates of patients in both Age-Adjusted International Prognostic Index (A-AIPI) groups 2 and 3 are 79% and the disease-free survival (DFS) rate for the CRs is 85%. In A-AIPI group 1 the 2-year OS and FFS rates are both 91%.
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