We hypothesized these agents could yield augmented anti-tumor activity. Methods Mantle cell lymphoma lines (Granta-519, Jeko-1, Rec-1) were treated with escalating concentrations of bortezomib and fenretinide singly and in combination. arrest, with an increase of 1 1.3 fold over control. In combination G2 phase arrest predominated, with a 1.4 fold-increase compared to control, and reduced expression of Cyclin D1 to 24%, Cyclin B to 52% and 64%, Cyclin D3 to 25% and 43%, IB to 23% and 46%, and IB kinase to 34% and 44%. Conclusions Bortezomib and fenretinide exhibit synergistic cytotoxicity against MCL cell lines. This activity is mediated by IB kinase modulation, decreased cyclin expression, cell cycle dysregulation, and apoptotic cell death. gene with the immunoglobulin heavy chain gene locus, resulting in overexpression of cyclin ATN-161 trifluoroacetate salt D1 [4]. While some patients have a clinically indolent disease, MCL is generally aggressive with most patients demonstrating Stage III or IV disease at diagnosis [2]. Historically, MCL has been associated with a poorer prognosis than many other aggressive lymphomas [2]. Over the last 3 decades, there has been a dramatic improvement in the management of patients with MCL C with the advent of advances in transplantation, targeted novel therapies C and driven by an improved understanding of the molecular biology of MCL. Typically, front-line management of MCL takes a risk-adapted strategy, reserving intensive high-dose therapy followed by autologous stem cell transplantation for younger, fitter patients [2, 5]. The standard approach for elderly patients (defined as greater than 65 years old), is immunochemotherapy with bendamustine and rituximab, or rituximab and Cyclophosphamide, Hydroxydaunorubicin (Doxorubicin), Oncovin (Vincristine), Prednisone (CHOP), followed by maintenance rituximab [2]. Other options include rituximab in combination with bendamustine, chlorambucil, or Cyclophosphamide, Vincristine, Prednisone (CVP) [5]. Despite the efficacy of these regimens, MCL remains an incurable disease. Novel, improved treatments that maximize therapeutic benefits and minimize toxicities are needed. Proteasome inhibitors (PI) were developed and studied in a wide variety of solid tumors and hematologic malignancies before clinical efficacy was demonstrated in multiple myeloma and mantle cell lymphoma [5]. The proteasome is an important cellular component responsible for degradation of proteins involved with apoptosis and cell cycle regulation [6]. The initial Phase II studies of single-agent bortezomib in MCL documented response rates between 38 and 55 percent, and a median time to progression of 6.2 months [7, 8]. The results from the phase II PINNACLE study were later updated to report an overall response rate of 33%, and a median time to progression of 6.2 months C indicating that bortezomib-induced responses are generally not durable. [9]. Bortezomib – similar to other PIs – inhibits the 20S proteasome, resulting in accumulation of BH3-only proteins, which act to induce apoptosis in cancer cells [10]. Proposed mechanisms by which PIs cause cytotoxicity include production of reactive oxygen species (ROS), upregulation of NOXA, and reduction of autocrine signaling by IL6 and IL10, among others [11-13]. Bortezomib and other proteasome inhibitors, paradoxically, also induce a calpain-mediated degradation of IB, resulting in increased nuclear factor-B (NF-B) activation and diminishing apoptosis [14]. Clinically, bortezomib is active at plasma concentrations up to 0.5 mol/L at typical doses [15-17]. Retinoids are analogues of Vitamin A and represent both synthetic and natural compounds which, have been examined extensively in the treatment of human malignancies. The Retinoic acid ATN-161 trifluoroacetate salt receptor (RAR) and Retinoid X receptor (RXR) are two classes of receptors that the retinoid compounds are thought to act through C though retinoids also function in the absence of an identified receptor [18, 19]. Following dimerization, they act as.CTEP, CLL Topics; the Mary Wright Memorial Fund; the David and Patricia Giuliani Family Foundation; and philanthropic gifts from Frank and Betty Vandermeer and Don and Debbie Hunkins. Footnotes Competing interests: The authors declare that they have no competing interests. Authors’ contributions: AC participated in the design of the study and wrote the manuscript. in Jeko-1 and Rec-1. Bortezomib induced G2 phase arrest with a 1.7 fold-increase over control, and fenretinide resulted in G1 phase arrest, with an increase of 1 1.3 ATN-161 trifluoroacetate salt fold over control. In combination G2 phase arrest predominated, with a 1.4 fold-increase compared to control, and reduced expression of Cyclin D1 to 24%, Cyclin B to 52% and 64%, Cyclin D3 to 25% and 43%, IB to 23% and 46%, and IB kinase to 34% and 44%. Conclusions Bortezomib and fenretinide exhibit synergistic cytotoxicity against MCL cell lines. This activity is mediated by IB kinase modulation, decreased cyclin expression, cell cycle dysregulation, and apoptotic cell death. gene with the immunoglobulin heavy chain gene locus, resulting in overexpression of cyclin D1 [4]. While some patients have a clinically indolent disease, MCL is generally aggressive with most patients demonstrating Stage III or IV disease at diagnosis [2]. Historically, MCL has been associated with a poorer prognosis than many other aggressive lymphomas [2]. Over the last 3 decades, there has been a dramatic improvement in the management of patients with MCL C with the advent of advances in transplantation, targeted novel therapies C and driven by an improved understanding of the molecular biology of MCL. Typically, front-line management of MCL takes a risk-adapted strategy, reserving intensive high-dose therapy followed by autologous stem cell transplantation for younger, fitter patients [2, 5]. The standard approach for elderly patients (defined as greater than 65 years old), is immunochemotherapy with bendamustine and rituximab, or rituximab and Cyclophosphamide, Hydroxydaunorubicin (Doxorubicin), Oncovin (Vincristine), Prednisone (CHOP), followed by maintenance rituximab [2]. Other options include rituximab in combination with bendamustine, chlorambucil, or Cyclophosphamide, Vincristine, Prednisone (CVP) [5]. Despite the efficacy of these regimens, MCL remains an incurable disease. Novel, improved treatments that maximize therapeutic benefits and minimize toxicities are needed. Proteasome inhibitors (PI) were developed and studied in a wide variety of solid tumors and hematologic malignancies before clinical efficacy was demonstrated in multiple myeloma and mantle ATN-161 trifluoroacetate salt cell lymphoma ATN-161 trifluoroacetate salt [5]. The proteasome is an Rabbit Polyclonal to BAGE3 important cellular component responsible for degradation of proteins involved with apoptosis and cell cycle regulation [6]. The initial Phase II studies of single-agent bortezomib in MCL documented response rates between 38 and 55 percent, and a median time to progression of 6.2 months [7, 8]. The results from the phase II PINNACLE study were later updated to report an overall response rate of 33%, and a median time to progression of 6.2 months C indicating that bortezomib-induced responses are generally not durable. [9]. Bortezomib – similar to other PIs – inhibits the 20S proteasome, resulting in accumulation of BH3-only proteins, which act to induce apoptosis in cancer cells [10]. Proposed mechanisms by which PIs cause cytotoxicity include production of reactive oxygen species (ROS), upregulation of NOXA, and reduction of autocrine signaling by IL6 and IL10, among others [11-13]. Bortezomib and other proteasome inhibitors, paradoxically, also induce a calpain-mediated degradation of IB, resulting in increased nuclear factor-B (NF-B) activation and diminishing apoptosis [14]. Clinically, bortezomib is active at plasma concentrations up to 0.5 mol/L at typical doses [15-17]. Retinoids are analogues of Vitamin A and represent both synthetic and natural compounds which, have been examined extensively in the treatment of human malignancies. The Retinoic acid receptor (RAR) and Retinoid X receptor (RXR) are two classes of receptors that the retinoid compounds are thought to act through C though retinoids also function in the absence of an identified receptor [18, 19]. Following dimerization, they act as ligand-dependent transcription factors, acting on various target genes. One such retinoid compound, N-(4-hydroxyphenyl) retinamide, also known as fenretinide, has been shown to be both anti-proliferative and pro-apoptotic in multiple pre-clinical studies employing both solid tumor and hematologic malignancy cell lines[20-25]. Although relatively weaker in binding to the RAR and RXR receptors compared with other compounds in this class, fenretinide also modulates apoptosis through down regulation of IB kinase (IKK) and NF-B gene products[26], modulation of Bcl-2 [27, 28], and caspase activation [29]. Fenretinide has also been studied in Phase I and II human clinical trialsin multiple solid tumors [30-38]. In these early-phase studies, plasma concentrations at peak and steady state were documented at 13 mol/L and 0.9-10 mol/L, respectively [33, 39]. We hypothesized that fenretinide could potentiate the anti-tumor activity of clinically attainable bortezomib concentrations in MCL lines based on a common mechanism of anti-tumor activity C induction of apoptosis C and a shared pathway involving regulation of IB. We demonstrated that the combination of bortezomib and fenretinide revealed synergistic cytotoxic activity in all tested.