Novel therapy for therapy-resistant mantle cell lymphoma: multipronged approach with targeting of hedgehog signaling

Targeting cancer hallmark vulnerabilities in hematologic malignancies by interfering with Hedgehog/GLI signaling

Understanding the genetic alterations, disrupted signaling pathways, and hijacked mechanisms in oncogene-transformed hematologic cells is critical for the development of effective and durable treatment strategies against liquid tumors. In this review, we focus on the specific involvement of the Hedgehog (HH)/GLI pathway in the manifestation and initiation of various cancer features in hematologic malignancies, including multiple myeloma, T- and B-cell lymphomas, and lymphoid and myeloid leukemias. By reviewing canonical and noncanonical, Smoothened-independent HH/GLI signaling and summarizing preclinical in vitro and in vivo studies in hematologic malignancies, we elucidate common molecular mechanisms by which HH/GLI signaling controls key oncogenic processes and cancer hallmarks such as cell proliferation, cancer stem cell fate, genomic instability, microenvironment remodeling, and cell survival. We also summarize current clinical trials with HH inhibitors and discuss successes and challenges, as well as opportunities for future combined therapeutic approaches. By providing a bird's eye view of the role of HH/GLI signaling in liquid tumors, we suggest that a comprehensive understanding of the general oncogenic effects of HH/GLI signaling on the formation of cancer hallmarks is essential to identify critical vulnerabilities within tumor cells and their supporting remodeled microenvironment, paving the way for the development of novel and efficient personalized combination therapies for hematologic malignancies.

A novel approach to eliminate therapy-resistant mantle cell lymphoma: synergistic effects of Vorinostat with Palbociclib

Mantle cell lymphoma (MCL) represents an aggressive B-cell lymphoma with frequent relapse and poor survival. Recently, dysregulated histone-deacetylases (HDACs) and cell cycle CDK-Rb pathway have been shown to be commonly associated with MCL pathogenesis, and are considered promising targets for relapsed-lymphoma therapy. Therefore, we investigated the single agents and combination efficacy of HDACs inhibitor Vorinostat, CDK4/6 dual-inhibitor Palbociclib on MCL cell growth/survival and underlying molecular mechanism(s) using MCL cell lines including therapy-resistant MCL cell lines. Our results showed that both inhibitors as single agents or combined, significantly suppressed the cell growth and induced apoptosis in therapy-resistant and parental MCL lines. In addition, the combination of Vorinostat and Palbociclib significantly inhibited the activation of the key molecules of the CDK4/6-Rb pathway and HDAC activity and subsequently decreased the expression of Cyclin-D1 and Bcl-2. These studies demonstrated the potential for combining these two inhibitors as a novel therapeutic approach in refractory MCL therapy.

Inhibition of O-GlcNAcase Sensitizes Apoptosis and Reverses Bortezomib Resistance in Mantle Cell Lymphoma through Modification of Truncated Bid

Aberrant energy metabolism represents a hallmark of cancer and contributes to numerous aggressive behaviors of cancer cells, including cell death and survival. Despite the poor prognosis of mantle cell lymphoma (MCL), due to the inevitable development of drug resistance, metabolic reprograming of MCL cells remains an unexplored area. Posttranslational modification of proteins via O-GlcNAcylation is an ideal sensor for nutritional changes mediated by O-GlcNAc transferase (OGT) and is removed by O-GlcNAcase (OGA). Using various small-molecule inhibitors of OGT and OGA, we found for the first time that O-GlcNAcylation potentiates MCL response to bortezomib. CRISPR interference of MGEA5 (encoding OGA) validated the apoptosis sensitization by O-GlcNAcylation and OGA inhibition. To identify the potential clinical candidates, we tested MCL response to drug-like OGA inhibitor, ketoconazole, and verified that it exerts similar sensitizing effect on bortezomib-induced apoptosis. Investigations into the underlying molecular mechanisms reveal that bortezomib and ketoconazole act in concert to cause the accumulation of truncated Bid (tBid). Not only does ketoconazole potentiate tBid induction, but also increases tBid stability through O-GlcNAcylation that interferes with tBid ubiquitination and proteasomal degradation. Remarkably, ketoconazole strongly enhances bortezomib-induced apoptosis in de novo bortezomib-resistant MCL cells and in patient-derived primary cells with minimal cytotoxic effect on normal peripheral blood mononuclear cells and hepatocytes, suggesting its potential utility as a safe and effective adjuvant for MCL. Together, our findings provide novel evidence that combination of bortezomib and ketoconazole or other OGA inhibitors may present a promising strategy for the treatment of drug-resistant MCL. Mol Cancer Ther; 17(2); 484-96. ©2017 AACR.

Murine Models of Splenic Marginal Zone Lymphoma: A Role for Cav1?

Dozens of murine models of indolent and aggressive B-cell lymphomas have been generated to date. These include those manifesting chronic lymphocytic leukemia (CLL), diffuse large B-cell lymphoma (DLBCL), as well as xenografts of mantle cell lymphoma (MCL). These models have led to an improved understanding of disease etiology, B-cell biology, immunomodulation, and the importance of the tumor microenvironment. Despite these efforts in CLL, DLBCL, and MCL, considerably little progress toward a model of splenic marginal zone lymphoma (SMZL) has been accomplished. Herein, we describe the similarities and differences between CLL, MCL, and SMZL and highlight effective murine models that mimic disease in the two former, in hopes of informing a potential model of the latter. At the time of writing this review, the precise molecular events of SMZL remain to be determined and a treatment regimen remains to be identified. Therefore, based on the efforts put forth in the B-cell lymphoma field throughout the past three decades, the established role of caveolin-1 in B- and T-cell biology as an oncogene or tumor suppressor, and the recurrent deletion or loss of heterozygosity (LOH) of 7q in many cancers, we make recommendations for a murine model of SMZL.

Modulation of p73 isoforms expression induces anti-proliferative and pro-apoptotic activity in mantle cell lymphoma independent of p53 status

Mantle cell lymphoma (MCL) is characterized by a clinically aggressive course with frequent relapse and poor survival. The p53 pathway is frequently dysregulated and p53 status predicts clinical outcome. In this report, we investigated whether modulation of p73 isoforms by diclofenac inhibits cell growth, induces apoptosis and/or cell cycle arrest in MCL relative to p53 status. Wild-type p53 [Granta-519 and JVM-2], mutant p53 [Jeko-1 and Mino-1] expressing cells, therapy resistant cell lines, and primary human cells isolated from MCL patients were used. Overexpression of pro-apoptotic TAp73 enhanced MCL cell apoptosis. Diclofenac induced a concentration- and duration-dependent increase in TAp73, cell cycle arrest, cell death, and inhibited MCL cell growth independent of p53 status. Diclofenac treatment was associated with increased activity of caspases 3, 7, and 8 and induction of p53 transcriptional target genes. These studies demonstrate the potential for diclofenac as novel therapeutic agent in MCL independent of p53 status.

Hedgehog signaling in cancer stem cells: a focus on hematological cancers

The stem cell paradigm was first demonstrated in hematopoietic stem cells. Whilst classically it was cytokines and chemokines which were believed to control stem cell fate, more recently it has become apparent that the stem cell niche and highly conserved embryonic pathways play a key role in governing stem cell behavior. One of these pathways, the hedgehog signaling pathway, found in all organisms, is vitally important in embryogenesis, performing the function of patterning through early stages of development, and in adulthood, through the control of somatic stem cell numbers. In addition to these roles in health however, it has been found to be deregulated in a number of solid and hematological malignancies, components of the hedgehog pathway being associated with a poor prognosis. Further, these components represent viable therapeutic targets, with inhibition from a drug development perspective being readily achieved, making the hedgehog pathway an attractive potential therapeutic target. However, although the concept of cancer stem cells is well established, how these cells arise and the factors which influence their behavior are not yet fully understood. The role of the hedgehog signaling pathway and its potential as a therapeutic target in hematological malignancies is the focus of this review.

The tumour microenvironment in B cell lymphomas

B cell lymphomas are cancers that arise from cells that depend on numerous highly orchestrated interactions with immune and stromal cells in the course of normal development. Despite the recent focus on dissecting the genetic aberrations within cancer cells, it has been increasingly recognized that tumour cells retain a range of dependence on interactions with the non-malignant cells and stromal elements that constitute the tumour microenvironment. A fundamental understanding of these interactions gives insight into the pathogenesis of most B cell lymphomas and, moreover, identifies novel therapeutic opportunities for targeting oncogenic pathways, both now and in the future.

New insight into hedgehog signaling in hematological malignancies

The hedgehog (Hh) signaling pathway is well established as being evolutionarily conserved across vertebrates, and is involved in organogenesis, hematopoiesis, embryogenesis and homeostasis of adult tissues. At a microscopic level, the Hh signaling pathway controls the proliferation, apoptosis, cell-cycle and differentiation programs of stem and progenitor cells. Increasing evidence suggests that aberrant activation of the Hh signaling pathway is related to neoplasm, including solid tumors and hematologic malignancies. Currently the Hh signaling pathway has become one of the most studied potential therapeutic targets in hematological malignancies. In this review, we focus on findings related to Hh signaling in the initiation, maintenance, progression and chemoresistance of hematological malignancies, looking forward to better targeted treatment strategies.

Nonclassical hedgehog-GLI signaling and its clinical implications

Hedgehog (Hh) signaling regulates embryonic patterning and organ morphogenesis. It is also involved in regeneration and repair of tissues. Aberrant Hh pathway activation is a feature of many human malignancies. Classical Hh signaling is activated by Hh ligands that can signal in an autocrine or paracrine manner generating a tumor-stromal crosstalk. In contrast to canonical Hh signaling that culminates in the activation of GLI transcription factors, "noncanonical" Hh signaling does not involve GLI transcriptional activity. Several Hh pathway inhibitors have progressed to clinical trials, where the outcomes have not been very encouraging in many solid tumors. Here we discuss the likely role of "nonclassical" Hh-GLI signaling that is activated by growth factors and cytokines from the tumor and/or its microenvironment; these uncouple Hh signaling from the vital regulatory protein Smoothened, and result in the activation of GLI. While efforts are being made to target tumor-intrinsic Hh targets, it is imperative to acknowledge the role of the complex molecular networks and crosstalk between different components of the tumor microenvironment that can result in the emergence of resistance to conventional Hh therapy. These considerations have an important bearing on appreciating the need to mitigate the effects of tumor microenvironment to combat resistance to Hh inhibitors.

Novel treatment for mantle cell lymphoma including therapy-resistant tumor by NF-κB and mTOR dual-targeting approach

Mantle cell lymphoma (MCL) is one of the most aggressive B-cell non-Hodgkin lymphomas with a median survival of approximately five years. Currently, there is no curative therapy available for refractory MCL because of relapse from therapy-resistant tumor cells. The NF-κB and mTOR pathways are constitutively active in refractory MCL leading to increased proliferation and survival. Targeting these pathways is an ideal strategy to improve therapy for refractory MCL. Therefore, we investigated the in vitro and in vivo antilymphoma activity and associated molecular mechanism of action of a novel compound, 13-197, a quinoxaline analog that specifically perturbs IκB kinase (IKK) β, a key regulator of the NF-κB pathway. 13-197 decreased the proliferation and induced apoptosis in MCL cells including therapy-resistant cells compared with control cells. Furthermore, we observed downregulation of IκBα phosphorylation and inhibition of NF-κB nuclear translocation by 13-197 in MCL cells. In addition, NF-κB-regulated genes such as cyclin D1, Bcl-XL, and Mcl-1 were downregulated in 13-197-treated cells. In addition, 13-197 inhibited the phosphorylation of S6K and 4E-BP1, the downstream molecules of mTOR pathway that are also activated in refractory MCL. Further, 13-197 reduced the tumor burden in vivo in the kidney, liver, and lungs of therapy-resistant MCL-bearing nonobese diabetic severe-combined immunodeficient (NOD/SCID) mice compared with vehicle-treated mice; indeed, 13-197 significantly increased the survival of MCL-transplanted mice. Together, results suggest that 13-197 as a single agent disrupts the NF-κB and mTOR pathways leading to suppression of proliferation and increased apoptosis in malignant MCL cells including reduction in tumor burden in mice.