Halting pro-survival autophagy by TGFß inhibition in bone marrow fibroblasts overcomes bortezomib resistance in multiple myeloma patients.

Bortezomib (bort) has improved overall survival in patients with multiple myeloma (MM), but the majority of them develop drug resistance. In this study, we demonstrate that bone marrow (BM) fibroblasts (cancer-associated fibroblasts; CAFs) from bort-resistant patients are insensitive to bort and protect the RPMI8226 and patients' plasma cells against bort-induced apoptosis. Bort triggers CAFs to produce high levels of interleukin (IL)-6, IL-8, insulin-like growth factor (IGF)-1 and transforming growth factor (TGF) ß. Proteomic studies on CAFs demonstrate that bort resistance parallels activation of oxidative stress and pro-survival autophagy. Indeed, bort induces reactive oxygen species in bort-resistant CAFs and activates autophagy by increasing light chain 3 protein (LC3)-II and inhibiting p62 and phospho-mammalian target of rapamycin. The small-interfering RNA knockdown of Atg7, and treatment with 3-methyladenine, restores bort sensitivity in bort-resistant CAFs and produces cytotoxicity in plasma cells co-cultured with CAFs. In the syngeneic 5T33 MM model, bort-treatment induces the expansion of LC3-II(+) CAFs. TGFß mediates bort-induced autophagy, and its blockade by LY2109761, a selective TßRI/II inhibitor, reduces the expression of p-Smad2/3 and LC3-II and induces apoptosis in bort-resistant CAFs. A combination of bort and LY2109761 synergistically induces apoptosis of RPMI8226 co-cultured with bort-resistant CAFs. These data define a key role for CAFs in bort resistance of plasma cells and provide the basis for a novel targeted therapeutic approach.

A phase 2 study of three low-dose intensity subcutaneous bortezomib regimens in elderly frail patients with untreated multiple myeloma.

This phase 2 trial evaluated three low-dose intensity subcutaneous bortezomib-based treatments in patients ⩾75 years with newly diagnosed multiple myeloma (MM). Patients received subcutaneous bortezomib plus oral prednisone (VP, N=51) or VP plus cyclophosphamide (VCP, N=51) or VP plus melphalan (VMP, N=50), followed by bortezomib maintenance, and half of the patients were frail. Response rate was 64% with VP, 67% with VCP and 86% with VMP, and very good partial response rate or better was 26%, 28.5% and 49%, respectively. Median progression-free survival was 14.0, 15.2 and 17.1 months, and 2-year OS was 60%, 70% and 76% in VP, VCP, VMP, respectively. At least one drug-related grade ⩾3 non-hematologic adverse event (AE) occurred in 22% of VP, 37% of VCP and 33% of VMP patients; the discontinuation rate for AEs was 12%, 14% and 20%, and the 6-month rate of toxicity-related deaths was 4%, 4% and 8%, respectively. The most common grade ⩾3 AEs included infections (8-20%), and constitutional (10-14%) and cardiovascular events (4-12%); peripheral neuropathy was limited (4-6%). Bortezomib maintenance was effective and feasible. VP, VCP and VMP regimens demonstrated no substantial difference. Yet, toxicity was higher with VMP, suggesting that a two-drug combination followed by maintenance should be preferred in frail patients.

Efficacy and tolerability of bendamustine, bortezomib and dexamethasone in patients with relapsed-refractory multiple myeloma: a phase II study.

Bendamustine demonstrated synergistic efficacy with bortezomib against multiple myeloma (MM) cells in vitro and seems an effective treatment for relapsed-refractory MM (rrMM). This phase II study evaluated bendamustine plus bortezomib and dexamethasone (BVD) administered over six 28-day cycles and then every 56 days for six further cycles in patients with rrMM treated with 4 prior therapies and not refractory to bortezomib. The primary study end point was the overall response rate after four cycles. In total, 75 patients were enrolled, of median age 68 years. All patients had received targeted agents, 83% had 1-2 prior therapies and 33% were refractory to the last treatment. The response ratepartial response (PR) was 71.5% (16% complete response, 18.5% very good PR, 37% partial remission). At 12 months of follow-up, median time-to-progression (TTP) was 16.5 months and 1-year overall survival was 78%. According to Cox regression analysis, only prior therapy with bortezomib plus lenalidomide significantly reduced TTP (9 vs 17 months; hazard ratio=4.5; P=0.005). The main severe side effects were thrombocytopenia (30.5%), neutropenia (18.5%), infections (12%), neuropathy (8%) and gastrointestinal and cardiovascular events (both 6.5%). The BVD regimen is feasible, effective and well-tolerated in difficult-to-treat patients with rrMM.