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PS-341 (bortezomib, Velcade™) is a promising novel agent for treatment of advanced multiple myeloma (MM); however, 65%of patients with relapsed refractory disease in a phase II study do not respond to PS-341. We have previously shown that lysophosphatidic acid acyltransferase (LPAAT)-ßinhibitor CT-32615 triggers caspase-dependent apoptosis, and can overcome resistance to conventional therapeutics (i.e., dexamethasone, doxorubicin, melphalan) in MM cells. In this study, we therefore determined whether CT-32615 could also overcome resistance to PS-341. We first characterized molecular mechanisms of resistance to PS-341 in DHL-4 cells. DHL-4 cells express low levels of caspase-3 and caspase-8; furthermore, no cleavage in caspase-8, caspase-9, caspase-3, poly ADP-ribose polymerase (PARP), or DNA fragmentation factor 45 was triggered by PS-341 treatment. We have previously shown that PS-341 treatment triggers phosphorylation of c-Jun NH2-terminal kinase (JNK), which subsequently induces caspase-dependent apoptosis; conversely, JNK inhibition blocks PS-341-induced apoptosis. We here show that phosphorylation of SEK-1, JNK, and c-Jun are not induced by PS-341 treatment, suggesting that PS-341 does not trigger a stress response in DHL-4 cells. Importantly, CT-32615 inhibits growth of DHL-4 cells in a time- and dose-dependent fashion: a transient G2/M cell cycle arrest induced by CT-32615 is mediated via downregulation of cdc25c and cdc2. CT-32615 triggered swelling and lysis of DHL-4 cells, without caspase/PARP cleavage or TUNEL-positivity, suggesting a necrotic response. Our studies therefore demonstrate that LPAAT-ßinhibitor CT-32615 triggers necrosis, even in PS-341-resistant DHL-4 cells, providing the framework for its evaluation to overcome clinical PS-341 resistance and improve patient outcome.Oncogene (2005) 24, 3121-3129. doi:10.1038/sj.onc.1208522 Published online 21 February 2005 [ABSTRACT FROM AUTHOR]

We present the case of a woman with relapsed multiple myeloma (MM) who received combination lenalidomide and bortezomib therapy for 90 cycles followed by continuous lenalidomide monotherapy and has completed over 100 cycles of treatment to date. The patient was diagnosed with advanced-stage, symptomatic MM in 2001. Following a partial response (PR) to dexamethasone in combination with pamidronate and thalidomide, the patient underwent protocol-directed non-myeloablative allogeneic bone marrow transplantation from her matched sibling donor the following year. In 2004, the patient relapsed and was enrolled in a phase I, dose-escalation trial of lenalidomide plus bortezomib for relapsed and refractory MM. After eight cycles of study treatment, the patient achieved a minimal response. The patient received a total of 90 cycles of treatment with lenalidomide 5 mg given for 14 d every 21 d, and 1 mg/m2 of bortezomib initially given on days 1, 4, 8, and 11 for the first 20 cycles, and then weekly thereafter on days 1 and 8. Bortezomib was discontinued after 90 cycles, and the patient continued to receive lenalidomide monotherapy. As of cycle 100, the patient achieved a PR. Currently, she is clinically stable with response sustained for over 7 yrs. Therapy has been well tolerated with no significant long-term toxicity; no dose reductions of lenalidomide and bortezomib were required. The excellent tolerability of this steroid-free approach and the durable response seen underscore the potential benefits of participating in early-phase clinical trials evaluating novel therapies and new drug combinations. This case further supports that combination treatment with lenalidomide and bortezomib is an effective therapy in the management of patients with relapsed and refractory MM. [ABSTRACT FROM AUTHOR]

The proteasome inhibitor bortezomib has shown impressive clinical activity alone and in combination with conventional and other novel agents for the treatment of multiple myeloma (MM). Although bortezomib is known to be a selective proteasome inhibitor, the downstream mechanisms of cytotoxicity and drug resistance are poorly understood. However, resistance to bortezomib as a single agent develops in the majority of patients, and activity in other malignancies has been less impressive. To elucidate mechanisms of bortezomib resistance, we compared differential gene expression profiles of bortezomib-resistant SUDHL-4 and bortezomib-sensitive SUDHL-6 diffuse large B-cell lymphoma lines in response to bortezomib. At concentrations that effectively inhibited proteasome activity, bortezomib induced apoptosis in SUDHL-6 cells, but not in SUDHL-4 cells. We showed that overexpression of activating transcription factor 3 (ATF3), ATF4, ATF5, c-Jun, JunD and caspase-3 is associated with sensitivity to bortezomib-induced apoptosis, whereas overexpression of heat shock protein (HSP)27, HSP70, HSP90 and T-cell factor 4 is associated with bortezomib resistance. [ABSTRACT FROM AUTHOR]