Pathogenesis of mantle-cell lymphoma: all oncogenic roads lead to dysregulation of cell cycle and DNA damage response pathways

Targeting the DNA damage response through TBL1X in mantle cell lymphoma

ABSTRACT

Mantle cell lymphoma (MCL) is an incurable B-cell lymphoma characterized by significant genomic instability. Patients with MCL who progress on targeted therapies have a short survival; thus, novel therapeutic strategies are urgently needed. Overexpression of transducin β-like protein 1 X-linked (TBL1X) has been documented in several types of cancer and associated with poor prognosis. TBL1X is a critical regulator of multiple oncogenic networks; however, its function in MCL has not been explored. Our data show that, unlike normal B cells, MCL cells express abundant levels of TBL1X and that genetic knockdown of TBL1X and treatment with tegavivint (Iterion), a first-in-class small molecule targeting TBL1X, promote MCL cell death in vitro and in vivo. Moreover, TBL1X controls the stability of key MCL oncogenic drivers, cyclin D1 and RAD51; and targeting TBL1X results in significant DNA damage, cell cycle arrest, and ultimately cell death. Combining tegavivint with poly(adenosine 5'-diphosphate-ribose) polymerase-1/2 inhibitor talazoparib results in synergistic MCL cell death in vitro, and in vivo this combination significantly prolongs the survival of a patient-derived MCL xenograft. Together, our results define the role of TBL1X in maintaining genomic stability in MCL and establish targeting TBL1X as a novel therapeutic strategy for patients with this incurable disease.

Characterization and molecular targeting of CFIm25 (NUDT21/CPSF5) mRNA using miRNAs

Changes in protein levels of the mammalian cleavage factor, CFIm25, play a role in regulating pathological processes including neural dysfunction, fibrosis, and tumorigenesis. However, despite these effects, little is known about how CFIm25 (NUDT21) expression is regulated at the RNA level. A potential regulator of NUDT21 mRNA are small non-coding microRNAs (miRNAs). In general, miRNAs bind to the 3'untranslated regions (3'UTRs) and can target the bound mRNA for degradation or inhibit translation thus affecting the levels of protein in cells. Interestingly, a mechanism known as alternative polyadenylation (APA) enables mRNAs to escape miRNA regulation by generating mRNAs with 3'UTRs of different sizes. As many miRNA target sites are located within the 3'UTR, shortening the 3'UTR allows mRNAs to evade miRNAs targeting this region. The differences in the lengths and the sequence composition of the 3'UTRs may also impact the mRNA's translatability and subcellular localization. APA has been reported to regulate over 70% of protein coding genes, thus increasing the transcript repertoire. Several proteins, including mammalian cleavage factor, CFIm25 (NUDT21), have been shown to regulate APA. In this study we wanted to determine whether CFIm25 (NUDT21), itself a regulator of APA, undergoes APA to evade miRNA regulation. We used the blood cancer mantle cell lymphoma (MCL) cells as a model and showed that in these cells, NUDT21 is relatively stable with a long half-life. In addition, the NUDT21 pre-mRNA undergoes alternative APA within the same terminal exon. The three different sized NUDT21 mRNAs have different 3'UTR lengths and they each use a different canonical polyadenylation signal, AAUAAA, for 3'end cleavage and polyadenylation. Use of miRNA mimics and inhibitors showed that miR-23a, miR-222, and miR-323a play a significant role in regulating NUDT21 expression. Hence, these results suggest that NUDT21 mRNA is stable and the different 3'UTRs generated through APA of NUDT21 play an important role in evading miRNA regulation and offers insights into how levels of CFIm25 (NUDT21) may be fine-tuned as needed under different physiological and pathological conditions.

PI3K inhibitor idelalisib enhances the anti-tumor effects of CDK4/6 inhibitor palbociclib via PLK1 in B-cell lymphoma

Relapsed or refractory diffuse large B cell lymphoma (DLBCL) and mantle cell lymphoma (MCL) patients still faced with poor survival, representing an unmet clinical need. In-depth research into the disease's pathogenesis and the development of targeted treatment strategies are urgently needed. Here, we conducted a comprehensive bioinformatic analysis of gene mutation and expression using data from our center and public databases. Cell cycle-related genes especially for CDKN2A/B-CDK4/6/CCND1 machinery altered frequently in DLBCL and MCL. Clinically, high CDK4 and CDK6 expression were correlated with poor prognosis of DLBCL and MCL patients. Furthermore, we also validated the pharmacological efficacy of CDK4/6 inhibitor palbociclib and its synergy effect with PI3K inhibitor idelalisib utilizing in vitro cell lines and in vivo cell-derived xenograft (CDX) and patient-derived xenograft (PDX) mouse models. Our results provided sufficient pre-clinical evidence to support the potential combination of palbociclib and idelalisib for DLBCL and MCL patients.

B-cell non-Hodgkin lymphomas

B-cell lymphomas occur with an incidence of 20 new cases per 100 000 people per year in high-income countries. They can affect any organ and are characterised by heterogeneous clinical presentations and courses, varying from asymptomatic, to indolent, to very aggressive cases. Since the topic of B-cell non-Hodgkin lymphomas was last reviewed in The Lancet in 2017, a deeper understanding of the biological background of this heterogeneous group of malignancies, the availability of new diagnostic methods, and the development and implementation of new targeted and immunotherapeutic approaches have improved our ability to treat patients. This Seminar provides an overview of the pathobiology, classification, and prognostication of B-cell non-Hodgkin lymphomas and summarises the current knowledge and standard of care regarding biology and clinical management of the most common subtypes of mature B-cell non-Hodgkin lymphomas. It also highlights new findings in deciphering the molecular background of disease development and the implementation of new therapeutic approaches, particularly those targeting the immune system.

SENP3 Promotes Mantle Cell Lymphoma Development through Regulating Wnt10a Expression

OBJECTIVE

SUMO-specific protease 3 (SENP3), a member of the SUMO-specific protease family, reverses the SUMOylation of SUMO-2/3 conjugates. Dysregulation of SENP3 has been proven to be involved in the development of various tumors. However, its role in mantle cell lymphoma (MCL), a highly aggressive lymphoma, remains unclear. This study was aimed to elucidate the effect of SENP3 in MCL.

METHODS

The expression of SENP3 in MCL cells and tissue samples was detected by RT-qPCR, Western blotting or immunohistochemistry. MCL cells with stable SENP3 knockdown were constructed using short hairpin RNAs. Cell proliferation was assessed by CCK-8 assay, and cell apoptosis was determined by flow cytometry. mRNA sequencing (mRNA-seq) was used to investigate the underlying mechanism of SENP3 knockdown on MCL development. A xenograft nude mouse model was established to evaluate the effect of SENP3 on MCL growth in vivo.

RESULTS

SENP3 was upregulated in MCL patient samples and cells. Knockdown of SENP3 in MCL cells inhibited cell proliferation and promoted cell apoptosis. Meanwhile, the canonical Wnt signaling pathway and the expression of Wnt10a were suppressed after SENP3 knockdown. Furthermore, the growth of MCL cells in vivo was significantly inhibited after SENP3 knockdown in a xenograft nude mouse model.

CONCLUSION

SENP3 participants in the development of MCL and may serve as a therapeutic target for MCL.

PRMT5 supports multiple oncogenic pathways in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an incurable B-cell malignancy with an overall poor prognosis, particularly for patients that progress on targeted therapies. Novel, more durable treatment options are needed for patients with MCL. Protein arginine methyltransferase 5 (PRMT5) is overexpressed in MCL and plays an important oncogenic role in this disease via epigenetic and posttranslational modification of cell cycle regulators, DNA repair genes, components of prosurvival pathways, and RNA splicing regulators. The mechanism of targeting PRMT5 in MCL remains incompletely characterized. Here, we report on the antitumor activity of PRMT5 inhibition in MCL using integrated transcriptomics of in vitro and in vivo models of MCL. Treatment with a selective small-molecule inhibitor of PRMT5, PRT-382, led to growth arrest and cell death and provided a therapeutic benefit in xenografts derived from patients with MCL. Transcriptional reprograming upon PRMT5 inhibition led to restored regulatory activity of the cell cycle (p-RB/E2F), apoptotic cell death (p53-dependent/p53-independent), and activation of negative regulators of B-cell receptor-PI3K/AKT signaling (PHLDA3, PTPROt, and PIK3IP1). We propose pharmacologic inhibition of PRMT5 for patients with relapsed/refractory MCL and identify MTAP/CDKN2A deletion and wild-type TP53 as biomarkers that predict a favorable response. Selective targeting of PRMT5 has significant activity in preclinical models of MCL and warrants further investigation in clinical trials.

Targeting the p53 signaling pathway in cancers: Molecular mechanisms and clinical studies

Tumor suppressor p53 can transcriptionally activate downstream genes in response to stress, and then regulate the cell cycle, DNA repair, metabolism, angiogenesis, apoptosis, and other biological responses. p53 has seven functional domains and 12 splice isoforms, and different domains and subtypes play different roles. The activation and inactivation of p53 are finely regulated and are associated with phosphorylation/acetylation modification and ubiquitination modification, respectively. Abnormal activation of p53 is closely related to the occurrence and development of cancer. While targeted therapy of the p53 signaling pathway is still in its early stages and only a few drugs or treatments have entered clinical trials, the development of new drugs and ongoing clinical trials are expected to lead to the widespread use of p53 signaling-targeted therapy in cancer treatment in the future. TRIAP1 is a novel p53 downstream inhibitor of apoptosis. TRIAP1 is the homolog of yeast mitochondrial intermembrane protein MDM35, which can play a tumor-promoting role by blocking the mitochondria-dependent apoptosis pathway. This work provides a systematic overview of recent basic research and clinical progress in the p53 signaling pathway and proposes that TRIAP1 is an important therapeutic target downstream of p53 signaling.

p53 directly downregulates the expression of CDC20 to exert anti-tumor activity in mantle cell lymphoma

BACKGROUND

Cell cycle dysregulation characterized by cyclin D1 overexpression is common in mantle cell lymphoma (MCL), while mitotic disorder was less studied. Cell division cycle 20 homologue (CDC20), an essential mitotic regulator, was highly expressed in various tumors. Another common abnormality in MCL is p53 inactivation. Little was known about the role of CDC20 in MCL tumorigenesis and the regulatory relationship between p53 and CDC20 in MCL.

METHODS

CDC20 expression was detected in MCL patients and MCL cell lines harboring mutant p53 (Jeko and Mino cells) and wild-type p53 (Z138 and JVM2 cells). Z138 and JVM2 cells were treated with CDC20 inhibitor apcin, p53 agonist nutlin-3a, or in combination, and then cell proliferation, cell apoptosis, cell cycle, cell migration and invasion were determined by CCK-8, flow cytometry and Transwell assays. The regulatory mechanism between p53 and CDC20 was revealed by dual-luciferase reporter gene assay and CUT&Tag technology. The anti-tumor effect, safety and tolerability of nutlin-3a and apcin were investigated in vivo in the Z138-driven xenograft tumor model.

RESULTS

CDC20 was overexpressed in MCL patients and cell lines compared with their respective controls. The typical immunohistochemical marker of MCL patients, cyclin D1, was positively correlated with CDC20 expression. CDC20 high expression indicated unfavorable clinicopathological features and poor prognosis in MCL patients. In Z138 and JVM2 cells, either apcin or nutlin-3a treatment could inhibit cell proliferation, migration and invasion, and induce cell apoptosis and cell cycle arrest. GEO analysis, RT-qPCR and WB results showed that p53 expression was negatively correlated with CDC20 expression in MCL patients, Z138 and JVM2 cells, while this relationship was not observed in p53-mutant cells. Dual-luciferase reporter gene assay and CUT&Tag assay revealed mechanistically that CDC20 was transcriptionally repressed by p53 through directly binding p53 to CDC20 promoter from - 492 to + 101 bp. Moreover, combined treatment of nutlin-3a and apcin showed better anti-tumor effect than single treatment in Z138 and JVM2 cells. Administration of nutlin-3a/apcin alone or in combination confirmed their efficacy and safety in tumor-bearing mice.

CONCLUSIONS

Our study validates the essential role of p53 and CDC20 in MCL tumorigenesis, and provides a new insight for MCL therapeutics through dual-targeting p53 and CDC20.

The Serum- and Glucocorticoid-Inducible Kinase 1 (SGK1) as a Novel Therapeutic Target in Mantle Cell Lymphoma

INTRODUCTION

Mantle cell lymphoma (MCL) is an aggressive and incurable B-cell-derived malignant disease. MCL is treated using general chemotherapy; however, disease progression and relapse are common; thus, the development of novel therapeutic targets for treatment of MCL is urgently required. Serum- and glucocorticoid-inducible kinase 1 (SGK1) is involved in various cellular activities, and its dysregulation contributes to the pathogenesis of multiple types of cancer. However, little is known regarding its functional roles and associated molecular mechanisms in MCL.

METHODS

SGK1 inhibition mediated by either shRNA or treatment with SGK1 inhibitor (GSK650394) was conducted in MCL cell lines. Western blotting analysis was performed to figure out the expression of related proteins. MCL-cell-derived xenograft models were constructed to evaluate the anti-tumor effects of SGK1 inhibition or/and Bruton's tyrosine kinase (BTK) inhibition in vivo.

RESULTS

In this study, it was shown that inhibition of SGK1 significantly reduced cell proliferation, invasion and migration, increased apoptosis and blocked cell cycle progression in MCL cells. Furthermore, SGK1 inhibition significantly reduced the activation of ERK, AKT/mTOR, JAK2/STAT3 and the NF-κB signaling pathways. Using MCL-cell-derived xenograft mice models, SGK1 inhibition decreased tumor cell proliferation and tumor growth. Importantly, SGK1 overexpression significantly promoted xenograft tumor growth. Moreover, simultaneous inhibition of SGK1 and Bruton tyrosine kinase (BTK) resulted in synergistic anti-tumor effects on MCL both in vitro and in vivo.

CONCLUSION

SGK1 may be a novel candidate therapeutic target and simultaneous inhibition of SGK1 and BTK may be a promising therapeutic strategy for MCL patients. Further pre-clinical and even clinical studies of SGK1 inhibitor or combination with BTK inhibitor are essential.

Symptomatic leptomeningeal carcinomatosis: a rare presentation of chronic lymphocytic leukaemia relapse

Central nervous system (CNS) involvement in patients with chronic lymphocytic leukaemia (CLL) is very rare and, when present, it is frequently asymptomatic. Rather, CNS involvement is more common in other haematological malignancies such as mantle cell lymphoma or diffuse large B cell lymphoma. The paucity of literature on CNS involvement in CLL underscores the importance of increasing awareness about its presentation, diagnosis and optimal management. We describe a case of symptomatic leptomeningeal leukaemic involvement as an atypical presentation of CLL relapse. A favourable clinical response was observed following systemic monotherapy with venetoclax.

HSP90 Inhibitor Ganetespib Enhances the Sensitivity of Mantle Cell Lymphoma to Bruton’s Tyrosine Kinase Inhibitor Ibrutinib

Mantle cell lymphoma (MCL) is a highly aggressive and heterogeneous B-cell lymphoma. Though Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib has shown great efficacy as a single agent for MCL treatment, the real-world use of ibrutinib is still subject to limitations. Our previous study has shown the treatment with HSP90 inhibitor ganetespib can attack major targets of MCL, luckily complementary to ibrutinib’s targets. In this study, transient ganetespib treatment sensitizes MCL cells to ibrutinib as manifested by the significant decrease of IC50 values, percentages of EdU (5-Ethynyl-2′-deoxyuridine) positive cells, and levels of p-AKT and NF-κB after combinational treatment. Additionally, pretreatment with ganetespib enhanced cell cycle arrest induced by ibrutinib at G0/G1 phase and significantly decreased levels of cell cycle promoting proteins CDK2, 4, and 6. Pretreatment with ganetespib also enhanced cell apoptosis induced by ibrutinib through the upregulation of cleaved-caspase 9 and downregulation of BCL-2 in MCL cells at the molecular level. The sequential administration of ganetespib and ibrutinib had similar effects on increasing DNA damage as the transient treatment with ganetespib as demonstrated by the improved percentage of γH2AX and 53BP1 foci. Furthermore, ganetespib significantly increased inhibition of tumor growth mediated by ibrutinib in vivo, confirmed by the changes of the expression levels of Ki-67 and BCL-2 through immunohistochemistry assays. This study indicates that HSP90 inhibitor ganetespib maybe ideal for the combinational use with BTK inhibitor ibrutinib to target major pathogenesis-associated signaling pathways for MCL treatment which may help identify new possibilities for clinical trials.

SOX11 Inhibitors Are Cytotoxic in Mantle Cell Lymphoma

PURPOSE

Mantle cell lymphoma (MCL) is a fatal subtype of non-Hodgkin lymphoma. SOX11 transcription factor is overexpressed in the majority of nodal MCL. We have previously reported that B cell-specific overexpression of SOX11 promotes MCL pathogenesis via critically increasing BCR signaling in vivo. SOX11 is an attractive target for MCL therapy; however, no small-molecule inhibitor of SOX11 has been identified to date. Although transcription factors are generally considered undruggable, the ability of SOX11 to bind to the minor groove of DNA led us to hypothesize that there may exist cavities at the protein-DNA interface that are amenable to targeting by small molecules.

EXPERIMENTAL DESIGN

Using a combination of in silico predictions and experimental validations, we report here the discovery of three structurally related compounds (SOX11i) that bind SOX11, perturb its interaction with DNA, and effect SOX11-specific anti-MCL cytotoxicity.

RESULTS

We find mechanistic validation of on-target activity of these SOX11i in the inhibition of BCR signaling and the transcriptional modulation of SOX11 target genes, specifically, in SOX11-expressing MCL cells. One of the three SOX11i exhibits relatively superior in vitro activity and displays cytotoxic synergy with ibrutinib in SOX11-expressing MCL cells. Importantly, this SOX11i induces cytotoxicity specifically in SOX11-positive ibrutinib-resistant MCL patient samples and inhibits Bruton tyrosine kinase phosphorylation in a xenograft mouse model derived from one of these subjects.

CONCLUSIONS

Taken together, our results provide a foundation for therapeutically targeting SOX11 in MCL by a novel class of small molecules.

Synchronous primary malignancy of colon cancer and mantle cell lymphoma: A case report

Multiple primary malignancies in a single patient are relatively rare; however, the frequency of this has increased significantly in recent decades. Here, we retrospectively reported an unusual case of a 70-year-old man who was admitted to the hospital with mantle cell lymphoma (MCL) and colon cancer and aimed to explore measures to reduce missed diagnosis. Based on the data, the investigation of the related literatures, colonoscopy examination, and abdominal computed tomography (CT) scan were conducted for the detection of colon cancer. Following this, a precise diagnosis of MCL was confirmed by immunohistochemistry and bone marrow biopsy, which were performed to analyze the clinical characteristics and essentials for the diagnosis and differential of the disease. The results of colonoscopy showed that the patient had colon cancer, while the abdominal CT scan demonstrated colon cancer accompanied by multiple lymphadenopathy throughout the entire body. Besides, the results of immunohistochemistry confirmed that the patient suffered from MCL. The bone marrow biopsy revealed the active hematopoietic tissue hyperplasia but no tumor issue involvement in the bone marrow. In conclusion, our study combined the analysis and summary of the diagnosis and treatment of the colon cancer with MCL to provide clinical guidance for the rare multiple primary malignancy.

Mantle cell lymphoma - advances in molecular biology, prognostication and treatment approaches

Mantle cell lymphoma (MCL) is clinically characterised by its heterogenous behaviour with courses ranging from indolent cases that do not require therapy for years to highly aggressive MCL with a very limited prognosis. A better understanding of the complex biology of MCL has already led to the approval of several innovative agents, expanding the landscape of MCL therapies and improving therapeutic options especially for refractory/relapsed (R/R) disease. Nevertheless, to further optimise MCL treatment, early identification of individual risk profile and risk-adapted, patient-tailored choice of therapeutic strategy needs to be prospectively incorporated into clinical patient management. The present review highlights recent advances in deciphering the molecular background of MCL, the definition of prognostically relevant factors and the identification of potential druggable targets and summarises current treatment recommendations for primary and R/R MCL including novel targeted therapies.

Preclinical discovery and development of abemaciclib used to treat breast cancer

Introduction: Cyclin-dependent kinase (CDK) 4/6 inhibitors have altered the standard-of-care treatment for patients with ER-positive, HER2-negative metastatic breast cancer. One such inhibitor, abemaciclib, a reversible ATP-competitive CDK4/6 inhibitor developed by Eli Lilly and Company, was approved by the FDA for ER-positive, HER2-negative metastatic breast cancer.Areas covered: Preclinical studies revealed abemaciclib's distinct structure, efficacy as monotherapy, and ability to penetrate the Central Nervous System. In this review, the authors have examined the literature regarding the development of CDK 4/6 inhibitors before providing a focused review on the preclinical discovery and development of abemaciclib. The authors then conclude their manuscript by providing their expert opinion and future perspectives.Expert opinion: Understanding the genesis and evolution from concept to approval and beyond will allow one to analyze the impact of abemaciclib. With its unique characteristics, abemaciclib has provided a meaningful addition to the therapeutic arsenal for metastatic breast cancer. There is, however, a need for predictive biomarkers to identify patients who may not benefit from or may develop resistance to CDK4/6 inhibition.

Targeting DNA Repair, Cell Cycle, and Tumor Microenvironment in B Cell Lymphoma

The DNA double-strand break (DSB) is the most cytotoxic lesion and compromises genome stability. In an attempt to efficiently repair DSBs, cells activate ATM kinase, which orchestrates the DNA damage response (DDR) by activating cell cycle checkpoints and initiating DSB repair pathways. In physiological B cell development, however, programmed DSBs are generated as intermediates for effective immune responses and the maintenance of genomic integrity. Disturbances of these pathways are at the heart of B cell lymphomagenesis. Here, we review the role of DNA repair and cell cycle control on B cell development and lymphomagenesis. In addition, we highlight the intricate relationship between the DDR and the tumor microenvironment (TME). Lastly, we provide a clinical perspective by highlighting treatment possibilities of defective DDR signaling and the TME in mantle cell lymphoma, which serves as a blueprint for B cell lymphomas.

Metabolic reprogramming toward oxidative phosphorylation identifies a therapeutic target for mantle cell lymphoma

Metabolic reprogramming is linked to cancer cell growth and proliferation, metastasis, and therapeutic resistance in a multitude of cancers. Targeting dysregulated metabolic pathways to overcome resistance, an urgent clinical need in all relapsed/refractory cancers, remains difficult. Through genomic analyses of clinical specimens, we show that metabolic reprogramming toward oxidative phosphorylation (OXPHOS) and glutaminolysis is associated with therapeutic resistance to the Bruton's tyrosine kinase inhibitor ibrutinib in mantle cell lymphoma (MCL), a B cell lymphoma subtype with poor clinical outcomes. Inhibition of OXPHOS with a clinically applicable small molecule, IACS-010759, which targets complex I of the mitochondrial electron transport chain, results in marked growth inhibition in vitro and in vivo in ibrutinib-resistant patient-derived cancer models. This work suggests that targeting metabolic pathways to subvert therapeutic resistance is a clinically viable approach to treat highly refractory malignancies.

Ampelopsin-sodium induces apoptosis in human lung adenocarcinoma cell lines by promoting tubulin polymerization in vitro

Previous studies have demonstrated that ampelopsin (AMP), a type of flavonoid isolated from the stems and leaves of Ampelopsis grossedentata, exhibits anti-cancer activity in various types of cancer. Conversion of AMP into its sodium salt (AMP-Na) conferred enhanced solubility and stability to it. The present study aimed to evaluate the anti-cancer activity of AMP-Na in human lung adenocarcinoma cell lines and to investigate its mechanisms of action. Cell proliferation and viability were assessed by MTT and colony formation assays, and cell migration was determined using a scratch wound healing assay. The cell cycle distribution, apoptosis rate and tubulin immunofluorescence intensity were analyzed using flow cytometry, the cell ultra-microstructure was examined using transmission electron microscopy and the accumulation of tubulin was determined using laser confocal microscopy. The results demonstrated that AMP-Na significantly inhibited the proliferation, clonogenicity and migration of human lung adenocarcinoma cells. Furthermore, AMP-Na induced SPC-A-1 cell apoptosis, and promoted tubulin polymerization. The results suggested that the underlying mechanisms of AMP-Na may involve targeting of microtubules and tubulin polymerization to subsequently disrupt mitosis and induce cell cycle arrest at the S-phase.

CDK 4/6 Inhibitors as Single Agent in Advanced Solid Tumors

Cyclin-dependent kinases (CDK) 4/6 inhibitors, namely abemaciclib, palbociclib, and ribociclib, interfere with cell cycle progression, induce cell senescence and might promote cancer cell disruption by a cytotoxic T cells-mediated effect. Phase III randomized clinical trials have proven that CDK4/6 inhibitors (CDK4/6i) in combination with several endocrine agents improve treatment efficacy over endocrine agents alone for hormone receptor positive (HR+) HER2 negative (HER2-) metastatic breast cancer (MBC). Based on such results, these combinations have been approved for clinical use. Preclinical studies in cell cultures and mouse models proved that CDK4/6i are active against a broad spectrum of solid tumors other than breast cancer, including liposarcoma, rhabdomyosarcoma, non-small cell lung cancer, glioblastoma multiforme, esophageal cancer, and melanoma. The role of CDK4/6i in monotherapy in several solid tumors is currently under evaluation in phase I, II, and III trials. Nowadays, abemaciclib is the only of the three inhibitors that has received approval as single agent therapy for pretreated HR+ HER2- MBC. Here we review biological, preclinical and clinical data on the role of CDK4/6 inhibitors as single agents in advanced solid tumors.

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.

Cyclin D1-CDK4 activity drives sensitivity to bortezomib in mantle cell lymphoma by blocking autophagy-mediated proteolysis of NOXA

BACKGROUND

Mantle cell lymphoma (MCL) is an aggressive B-non-Hodgkin lymphoma with generally poor outcome. MCL is characterized by an aberrantly high cyclin D1-driven CDK4 activity. New molecular targeted therapies such as inhibitors of the ubiquitin-proteasome system (UPS) have shown promising results in preclinical studies and MCL patients. Our previous research revealed stabilization of the short-lived pro-apoptotic NOXA as a critical determinant for sensitivity to these inhibitors. It is currently unclear how cyclin D1 overexpression and aberrant CDK4 activity affect NOXA stabilization and treatment efficacy of UPS inhibitors in MCL.

METHODS

The effect of cyclin D1-driven CDK4 activity on response of MCL cell lines and primary cells to proteasome inhibitor treatment was investigated using survival assays (Flow cytometry, AnnexinV/PI) and Western blot analysis of NOXA protein. Half-life of NOXA protein was determined by cycloheximide treatment and subsequent Western blot analysis. The role of autophagy was analyzed by LC3-II protein expression and autophagolysosome detection. Furthermore, silencing of autophagy-related genes was performed using siRNA and MCL cells were treated with autophagy inhibitors in combination with proteasome and CDK4 inhibition.

RESULTS

In this study, we show that proteasome inhibitor-mediated cell death in MCL depends on cyclin D1-driven CDK4 activity. Inhibition of cyclin D1/CDK4 activity significantly reduced proteasome inhibitor-mediated stabilization of NOXA protein, mainly driven by an autophagy-mediated proteolysis. Bortezomib-induced cell death was significantly potentiated by compounds that interfere with autophagosomal function. Combined treatment with bortezomib and autophagy inhibitors enhanced NOXA stability leading to super-induction of NOXA protein. In addition to established autophagy modulators, we identified the fatty acid synthase inhibitor orlistat to be an efficient autophagy inhibitor when used in combination with bortezomib. Accordingly, this combination synergistically induced apoptosis both in MCL cell lines and in patient samples.

CONCLUSION

Our data demonstrate that CDK4 activity in MCL is critical for NOXA stabilization upon treatment with UPS inhibitors allowing preferential induction of cell death in cyclin D transformed cells. Under UPS blocked conditions, autophagy appears as the critical regulator of NOXA induction. Therefore, inhibitors of autophagy are promising candidates to increase the activity of proteasome inhibitors in MCL.

SOX11 augments BCR signaling to drive MCL-like tumor development

Mantle cell lymphoma (MCL) is characterized by increased B-cell receptor (BCR) signaling, and BTK inhibition is an effective therapeutic intervention in MCL patients. The mechanisms leading to increased BCR signaling in MCL are poorly understood, as mutations in upstream regulators of BCR signaling such as CD79A, commonly observed in other lymphomas, are rare in MCL. The transcription factor SOX11 is overexpressed in the majority (78% to 93%) of MCL patients and is considered an MCL-specific oncogene. So far, attempts to understand SOX11 function in vivo have been hampered by the lack of appropriate animal models, because germline deletion of SOX11 is embryonically lethal. We have developed a transgenic mouse model (Eμ-SOX11-EGFP) in the C57BL/6 background expressing murine SOX11 and EGFP under the control of a B-cell-specific IgH-Eμ enhancer. The overexpression of SOX11 exclusively in B cells exhibits oligoclonal B-cell hyperplasia in the spleen, bone marrow, and peripheral blood, with an immunophenotype (CD5⁺CD19⁺CD23^-) identical to human MCL. Furthermore, phosphocytometric time-of-flight analysis of the splenocytes from these mice shows hyperactivation of pBTK and other molecules in the BCR signaling pathway, and serial bone marrow transplant from transgenic donors produces lethality with decreasing latency. We report here that overexpression of SOX11 in B cells promotes BCR signaling and a disease phenotype that mimics human MCL.

Molecular evidence of Zn chelation of the procaspase activating compound B-PAC-1 in B cell lymphoma

The resistance of apoptosis in cancer cells is pivotal for their survival and is typically ruled by mutations or dysregulation of core apoptotic cascade. Mantle cell lymphoma (MCL) is a non-Hodgkin's B-cell malignancy expressing higher anti-apoptotic proteins providing survival advantage. B-PAC-1, a procaspase activating compound, induces apoptosis by sequestering Zn bound to procaspase-3, but the amino acids holding Zn in Caspase-3 is not known. Here we show that reintroduction of WT caspase-3 or 7 in Caspase3-7 double knock-out (DKO) mouse embryonic fibroblasts (MEF) promoted B-PAC-1 to induce apoptosis (27-43%), but not in DKO MEFs or MEFs expressing respective Casp3-7 catalytic mutants (12-13%). Using caspase-6 and -9 exosite analysis, we identified and mutated predicted Zn-ligands in caspase-3 (H108A, C148S and E272A) and overexpressed into DKO MEFs. Mutants carrying E272A abrogated Zn-reversal of apoptosis induced by B-PAC-1 via higher XIAP and smac expressions but not in H108A or C148S mutants. Co-immunoprecipitation analysis revealed stronger XIAP-caspase-3 interaction suggesting a novel mechanism of impulsive apoptosis resistance by disrupting predicted Zn-ligands in caspase-3. B-PAC-1 sponsored apoptosis in MCL cell lines (30-73%) via caspase-3 and PARP cleavages accompanied by loss of Mcl-1 and IAPs including XIAP while Zn substantially abrogated B-PAC-1-driven apoptosis (18-36%). In contrary, Zn is dispensable to inhibit staurosporin, bendamustine, ABT199 or MK206-induced apoptosis. Consistent to cell lines, B-PAC-1 stimulated cell death in primary B-lymphoma cells via caspase-3 cleavage with decline in both Mcl-1 and XIAP. This study underscores the first genetic evidence that B-PAC-1 driven apoptosis is mediated via Zn chelation.

Unraveling the DNA Methylome in Mantle Cell Lymphoma: New Insights into the Cellular Origin

Our understanding of the DNA methylome and its impact on cancer evolution and disease progression is rapidly evolving. In this issue of Cancer Cell, Queirós et al. provide a detailed characterization of the DNA methylome in mantle cell lymphoma and reveal novel molecular subtypes, potentially with different cellular origins.

Natriuretic peptide receptor A inhibition suppresses gastric cancer development through reactive oxygen species-mediated G2/M cell cycle arrest and cell death

Natriuretic peptide receptor A (NPRA), the major receptor for atrial natriuretic peptide (ANP), has been implicated in tumorigenesis; however, the role of ANP-NPRA signaling in the development of gastric cancer remains unclear. Immunohistochemical analyses indicated that NPRA expression was positively associated with gastric tumor size and cancer stage. NPRA inhibition by shRNA induced G2/M cell cycle arrest, cell death, and autophagy in gastric cancer cells, due to accumulation of reactive oxygen species (ROS). Either genetic or pharmacologic inhibition of autophagy led to caspase-dependent cell death. Therefore, autophagy induced by NPRA silencing may represent a cytoprotective mechanism. ROS accumulation activated c-Jun N-terminal kinase (JNK) and AMP-activated protein kinase (AMPK). ROS-mediated activation of JNK inhibited cell proliferation by disturbing cell cycle and decreased cell viability. In addition, AMPK activation promoted autophagy in NPRA-downregulated cancer cells. Overall, our results indicate that the inhibition of NPRA suppresses gastric cancer development and targeting NPRA may represent a promising strategy for the treatment of gastric cancer.

Small Molecule Inhibition of the Ubiquitin-specific Protease USP2 Accelerates cyclin D1 Degradation and Leads to Cell Cycle Arrest in Colorectal Cancer and Mantle Cell Lymphoma Models

Deubiquitinases are important components of the protein degradation regulatory network. We report the discovery of ML364, a small molecule inhibitor of the deubiquitinase USP2 and its use to interrogate the biology of USP2 and its putative substrate cyclin D1. ML364 has an IC₅₀ of 1.1 μm in a biochemical assay using an internally quenched fluorescent di-ubiquitin substrate. Direct binding of ML364 to USP2 was demonstrated using microscale thermophoresis. ML364 induced an increase in cellular cyclin D1 degradation and caused cell cycle arrest as shown in Western blottings and flow cytometry assays utilizing both Mino and HCT116 cancer cell lines. ML364, and not the inactive analog 2, was antiproliferative in cancer cell lines. Consistent with the role of cyclin D1 in DNA damage response, ML364 also caused a decrease in homologous recombination-mediated DNA repair. These effects by a small molecule inhibitor support a key role for USP2 as a regulator of cell cycle, DNA repair, and tumor cell growth.

[Anti-tumor effects of 13-cis-retinoic acid combined with interferon α-2b in animal model of mantle cell lymphoma]

目的

评估13-顺式维甲酸（13cRA）和IFN-α-2b单用，以及二者联合应用对套细胞淋巴瘤（MCL）动物模型的抗肿瘤效应，并探讨其作用机制。

方法

构建MCL细胞株Jeko-1细胞重症联合免疫缺陷小鼠模型，将荷瘤小鼠随机分成阴性对照组（溶剂），高（200 mg/kg）、中（100 mg/kg）、低（50 mg/kg）13cRA剂量组，IFN-α-2b组，不同剂量13cRA联合IFN-α-2b组，阳性对照组（硼替佐米＋利妥昔单抗＋环磷酰胺），同时进行干预治疗。定期观察荷瘤小鼠肿瘤体积变化，计算相对肿瘤增殖率、抑瘤率。采用免疫组化法检测Ki-67的表达。采用缺口末端标记法检测肿瘤组织细胞凋亡情况。采用Western blot法检测Cyclin D1、caspase-9及视网膜神经胶质瘤蛋白（Rb）等的表达水平。

结果

①中、高剂量13cRA组及中、高剂量13cRA联合IFN-α-2b组的相对肿瘤增殖率分别为30%、37%、32％和33%。②低、中、高剂量13cRA组或其联合IFN-α-2b组的抑瘤率均较阴性对照组明显增高（P<0.05），不同剂量13cRA组间、单用IFN-α-2b组抑瘤率与阴性对照组比较差异均无统计学意义（P值均>0.05）。中剂量13cRA组或其联合IFN-α-2b组抑瘤率最高，分别为59.2%、62.6%，与阳性对照组（69.4%）差异无统计学意义（P>0.05）。③Ki-67在各组的表达差异无统计学意义（P=0.342）。④不同剂量13cRA组及其联合IFN-α-2b组凋亡细胞数均较阴性对照组明显增加（P<0.05），与阳性对照组差异无统计学意义（P=0.170）；阴性对照组凋亡细胞数与IFN-α-2b组差异无统计学意义（P=0.098）。⑤不同剂量13cRA联合IFN-α-2b组与阴性对照组比较，cycling D1及procaspase-9降低，cleaved caspase-9升高，与阳性对照组表达相当；不同剂量13cRA组与阴性对照组比较，则未见明显差异。

结论

在MCL动物模型中IFN-α-2b单用并未显示出疗效；13cRA单用及其与IFN-α-2b联合应用均显示出抑制肿瘤生长效应，其作用机制可能为通过下调Cyclin D1的表达而抑制细胞增殖或者激活caspase-9诱导凋亡。

Characterization of a mantle cell lymphoma cell line resistant to the Chk1 inhibitor PF-00477736

Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma characterized by the chromosomal translocation t(11;14) that leads to constitutive expression of cyclin D1, a master regulator of the G1-S phase. Chk1 inhibitors have been recently shown to be strongly effective as single agents in MCL. To investigate molecular mechanisms at the basis of Chk1 inhibitor activity, a MCL cell line resistant to the Chk1 inhibitor PF-00477736 (JEKO-1 R) was obtained and characterized. The JEKO-1 R cell line was cross resistant to another Chk1 inhibitor (AZD-7762) and to the Wee1 inhibitor MK-1775. It displayed a shorter doubling time than parental cell line, likely due to a faster S phase. Cyclin D1 expression levels were decreased in resistant cell line and its re-overexpression partially re-established PF-00477736 sensitivity. Gene expression profiling showed an enrichment in gene sets involved in pro-survival pathways in JEKO-1 R. Dasatinib treatment partly restored PF-00477736 sensitivity in resistant cells suggesting that the pharmacological interference of pro-survival pathways can overcome the resistance to Chk1 inhibitors. These data further corroborate the involvement of the t(11;14) in cellular sensitivity to Chk1 inhibitors, fostering the clinical testing of Chk1 inhibitors as single agents in MCL.

Targeting CDK4/6 in patients with cancer

The cyclin D-cyclin dependent kinase (CDK) 4/6-inhibitor of CDK4 (INK4)-retinoblastoma (Rb) pathway controls cell cycle progression by regulating the G1-S checkpoint. Dysregulation of the cyclin D-CDK4/6-INK4-Rb pathway results in increased proliferation, and is frequently observed in many types of cancer. Pathway activation can occur through a variety of mechanisms, including gene amplification or rearrangement, loss of negative regulators, epigenetic alterations, and point mutations in key pathway components. Due to the importance of CDK4/6 activity in cancer cells, CDK4/6 inhibitors have emerged as promising candidates for cancer treatment. Moreover, combination of a CDK4/6 inhibitor with other targeted therapies may help overcome acquired or de novo treatment resistance. Ongoing studies include combinations of CDK4/6 inhibitors with endocrine therapy and phosphatidylinositol 3-kinase (PI3K) pathway inhibitors for hormone receptor-positive (HR+) breast cancers, and with selective RAF and MEK inhibitors for tumors with alterations in the mitogen activated protein kinase (MAPK) pathway such as melanoma. In particular, the combination of CDK4/6 inhibitors with endocrine therapy, such as palbociclib's recent first-line approval in combination with letrozole, is expected to transform the treatment of HR+ breast cancer. Currently, three selective CDK4/6 inhibitors have been approved or are in late-stage development: palbociclib (PD-0332991), ribociclib (LEE011), and abemaciclib (LY2835219). Here we describe the current preclinical and clinical data for these novel agents and discuss combination strategies with other agents for the treatment of cancer.

Mantle Cell Lymphoma: First-line Therapy in Patients Not Eligible for Stem Cell Transplantation

OPINION STATEMENT

Mantle cell lymphoma is a distinct subtype of non-Hodgkin's lymphoma, which has historically been associated with a poor prognosis. It is now recognized as a heterogeneous disease with variable biologic and clinical behavior. Treatment paradigms have evolved along two lines. Younger, fit mantle cell lymphoma (MCL) patients are generally treated with intensive strategies and older less fit patients with non-intensive strategies. Most of the published literature has focused on intensive strategies, which appear to result in more durable remissions, but with an unclear impact on overall survival. The literature is more sparse for the roughly 50% of patients who are not candidates for intensive strategies, and no "standard" approach has been established for this patient population. However, clues are emerging. Randomized clinical trials have (a) established that bendamustine-rituximab (BR) is more efficacious and less toxic than rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP); (b) established that bortezomib should replace vincristine if using an R-CHOP backbone; and (c) established that maintenance rituximab (MR) is beneficial after an R-CHOP induction. In our opinion, it is reasonable to extrapolate the data supporting MR after R-CHOP and apply MR after a BR induction. In our practice, we recommend BR followed by MR for 2 years to MCL patients not eligible for intensive therapy. An ongoing US intergroup trial is testing the addition of bortezomib to the BR backbone and the addition of lenalidomide to MR. This trial may establish a standard of care in the older MCL population. In addition, exciting options for relapsed MCL have emerged in the last few years, with the introduction of the Bruton tyrosine kinase (BTK) inhibitor ibrutinib and the development of the lenalidomide-rituximab combination. In this article, we will discuss the current available options for these older MCL patients and the evidence supporting those options.

Palbociclib: A breakthrough in breast carcinoma in women

Breast cancer (BC) is the most common cancer and leading cause of death in women worldwide. Cellular proliferation, growth, and division are tightly controlled by the cell-cycle regulatory machinery. An important pathway is cyclin-dependent kinases (CDKs) which regulate cell cycle and thus control transcriptional processes. In human cancer, multiple CDK family members are commonly deregulated. The cyclin D-CDK4/6-retinoblastoma (RB) protein-INK4 axis is particularly affected in many solid tumors which leads to cancer cell proliferation. This has led to long-standing interest in targeting CDK4/6 as an anticancer strategy. Different investigational agents that have been tested which inhibit multiple cell cycle and transcriptional CDKs but have carried excessive toxicity thus failed to stand the rational of human use. Amongst several selective and potent inhibitors of CDK4/6, palbociclib is the first to be accessed suitable for human use having explicit selectivity toward CDK4/6. Its mechanism is to arrest cells in G1 phase by blocking RB phosphorylation at CDK4/6-specfic sites without affecting the growth of cells which are RB-deficient. Studies conducted in patients of BC having cells with advanced RB-expression demonstrated acceptable side effects but dose-limiting toxicities primarily neutropenia and thrombocytopenia, with prolonged stable disease in patients.

High-dose cytarabine does not overcome the adverse prognostic value of CDKN2A and TP53 deletions in mantle cell lymphoma

CDKN2A and TP53 deletions remain of bad prognostic value in younger MCL patients treated according to the current standard of care. CDKN2A and TP53 deletions have independent deleterious effects and should be considered for treatment decisions in addition to MIPI and Ki-67 index.

Updated survival analysis of two sequential prospective trials of R-MACLO-IVAM followed by maintenance for newly diagnosed mantle cell lymphoma

A phase II trial of R-MACLO-IVAM followed by thalidomide maintenance for mantle cell lymphoma (MCL) demonstrated promising progression-free survival (PFS) and overall survival (OS) rates. Thalidomide maintenance was associated with significant toxicity and was subsequently modified to rituximab maintenance. Herein, we present updated results and follow-up. Two sequential phase II trials included chemotherapy-naïve patients with MCL up to 75 years old. Four cycles of R-MACLO-IVAM chemotherapy were delivered as previously described. Patients who achieved complete responses (CR) were eligible for thalidomide or rituximab maintenance therapy. Among 36 patients enrolled, the MCL International Prognostic Index (MIPI) was low in 53%, intermediate in 36% and high in 11%. Thirty-five patients completed at least 2 cycles of chemotherapy; 34 (94%) achieved a CR. After a median follow-up of 74.4 months, the 5-year PFS was 51% (95% CI 33-68%) and the 5-year OS was 85% (95% CI 73-97%). Two deaths occurred during the chemotherapy phase due to disease progression and neutropenic sepsis, respectively. One patient developed secondary acute myeloid leukemia after 7 years. R-MACLO-IVAM chemotherapy is effective for patients with newly diagnosed MCL.

Primary lymphomas in the gastrointestinal tract

Primary gastrointestinal (GI) lymphomas are uncommon diseases that can involve the whole GI tract. The etiologies of the disease remain unclear, and potential risk factors include celiac disease, Helicobacter pylori infection, use of immunosuppressive agents, human immunodeficiency virus (HIV) or Epstein-Barr virus (EBV) infection and inflammatory bowel disease, etc. Diffuse large B-cell lymphoma (DLBCL) and mucosa-associated lymphoid tissue (MALT) lymphoma are the most common subtypes of GI lymphomas. B-cell lymphomas of the GI tract are more common in Western countries, while in Asia-Pacific region T-cell lymphomas are more frequently reported. In this review, lymphomas in the esophagus, stomach and intestine are described, including their epidemiology, histology, clinical manifestations, endoscopic findings, radiological features and treatment.

Computerized image analysis of the Ki-67 proliferation index in mantle cell lymphoma

AIMS

Manual counting of the fraction of Ki-67-positive cells (the Ki-67 index) in 1000 tumour cells is considered the 'gold standard' to predict prognosis in mantle cell lymphoma (MCL). This time-consuming method is replaced by the faster, but less accurate, semiquantitative estimation in routine practice. The aim of this study was to investigate the use of computerized image analysis software for scoring of Ki-67 in MCL.

METHODS AND RESULTS

We developed an automated method for determining the Ki-67 index by computerized image analysis and tested it using a cohort of 62 MCL patients. The data were compared to Ki-67 scores obtained by semiquantitative estimation and image-based manual counting. When using the Ki-67 index as a continuous parameter, both image-based manual counting and computerized image analysis were related inversely to survival (P = 0.020 and P = 0.025, respectively). Ki-67 index obtained by semiquantitative estimation was not associated significantly with survival (P = 0.093). The results were validated in a second patient cohort with similar results.

CONCLUSION

Computerized image analysis of the Ki-67 index in MCL is an attractive alternative to semiquantitative estimation and can be introduced easily in a routine diagnostic setting for risk stratification in MCL.

PARP1 expression in mantle cell lymphoma: the utility of PARP1 immunohistochemistry and its relationship with markers of DNA damage

Mantle cell lymphoma (MCL) is an aggressive disease with poor overall survival, attributable in part to frequent defects of the DNA repair genes. In such malignancies, additional inhibition of the ubiquitous DNA damage repair protein, poly-ADP ribose polymerase-1 (PARP1) has shown enhanced cytotoxicity (so-called synthetic lethality). We studied PARP1 expression in a series of clinical cases of MCL, with the secondary aim to ascertain the relationship between PARP1 expression and DNA repair gene expression (namely ATM and p53) by immunohistochemical methods. We also examined the relationship between PARP1 expression and the well-established prognostic biomarker Ki-67, in addition to correlating PARP1 expression with the overall survival. From amongst our series of 79 unselected cases of MCL, we detected PARP1 expression in all but two cases with variable intensity. We also noted correlations between PARP1 expression and ATM and p53 expression. As described in previous studies, we identified a significant survival difference on the basis of Ki-67 and p53 expression. When digital H-score analysis of PARP1 expression was performed, there was a distinct survival advantage noted in patients with lower levels of expression. When our biomarker data were assessed by Cox regression, furthermore, the dominant effects of p53 and PARP1 expression were highlighted. Our data support the need for further research into the potential utility of PARP1 as a biomarker in MCL and for the potential direction of future PARP1 inhibitor-targeted therapy studies.

Functional characterization of breast cancer using pathway profiles

BACKGROUND

The molecular characteristics of human diseases are often represented by a list of genes termed "signature genes". A significant challenge facing this approach is that of reproducibility: signatures developed on a set of patients may fail to perform well on different sets of patients. As diseases are resulted from perturbed cellular functions, irrespective of the particular genes that contribute to the function, it may be more appropriate to characterize diseases based on these perturbed cellular functions.

METHODS

We proposed a profile-based approach to characterize a disease using a binary vector whose elements indicate whether a given function is perturbed based on the enrichment analysis of expression data between normal and tumor tissues. Using breast cancer and its four primary clinically relevant subtypes as examples, this approach is evaluated based on the reproducibility, accuracy and resolution of the resulting pathway profiles.

RESULTS

Pathway profiles for breast cancer and its subtypes are constructed based on data obtained from microarray and RNA-Seq data sets provided by The Cancer Genome Atlas (TCGA), and an additional microarray data set provided by The European Genome-phenome Archive (EGA). An average reproducibility of 68% is achieved between different data sets (TCGA microarray vs. EGA microarray data) and 67% average reproducibility is achieved between different technologies (TCGA microarray vs. TCGA RNA-Seq data). Among the enriched pathways, 74% of them are known to be associated with breast cancer or other cancers. About 40% of the identified pathways are enriched in all four subtypes, with 4, 2, 4, and 7 pathways enriched only in luminal A, luminal B, triple-negative, and HER2+ subtypes, respectively. Comparison of profiles between subtypes, as well as other diseases, shows that luminal A and luminal B subtypes are more similar to the HER2+ subtype than to the triple-negative subtype, and subtypes of breast cancer are more likely to be closer to each other than to other diseases.

CONCLUSIONS

Our results demonstrate that pathway profiles can successfully characterize both common and distinct functional characteristics of four subtypes of breast cancer and other related diseases, with acceptable reproducibility, high accuracy and reasonable resolution.

Preclinical characterization of the CDK4/6 inhibitor LY2835219: in-vivo cell cycle-dependent/independent anti-tumor activities alone/in combination with gemcitabine

The G1 restriction point is critical for regulating the cell cycle and is controlled by the Rb pathway (CDK4/6-cyclin D1-Rb-p16/ink4a). This pathway is important because of its inactivation in a majority of human tumors. Transition through the restriction point requires phosphorylation of retinoblastoma protein (Rb) by CDK4/6, which are highly validated cancer drug targets. We present the identification and characterization of a potent CDK4/6 inhibitor, LY2835219. LY2835219 inhibits CDK4 and CDK6 with low nanomolar potency, inhibits Rb phosphorylation resulting in a G1 arrest and inhibition of proliferation, and its activity is specific for Rb-proficient cells. In vivo target inhibition studies show LY2835219 is a potent inhibitor of Rb phosphorylation, induces a complete cell cycle arrest and suppresses expression of several Rb-E2F-regulated proteins 24 hours after a single dose. Oral administration of LY2835219 inhibits tumor growth in human tumor xenografts representing different histologies in tumor-bearing mice. LY2835219 is effective and well tolerated when administered up to 56 days in immunodeficient mice without significant loss of body weight or tumor outgrowth. In calu-6 xenografts, LY2835219 in combination with gemcitabine enhanced in vivo antitumor activity without a G1 cell cycle arrest, but was associated with a reduction of ribonucleotide reductase expression. These results suggest LY2835219 may be used alone or in combination with standard-of-care cytotoxic therapy. In summary, we have identified a potent, orally active small-molecule inhibitor of CDK4/6 that is active in xenograft tumors. LY2835219 is currently in clinical development.

Discrepant NOXA (PMAIP1) transcript and NOXA protein levels: a potential Achilles' heel in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm with transient response to conventional chemotherapy. We here investigated the role of the Bcl-2 homology domain 3-only protein NOXA for life–death decision in MCL. Surprisingly, NOXA (PMAIP1) mRNA and NOXA protein levels were extremely discrepant in MCL cells: NOXA mRNA was found to be highly expressed whereas NOXA protein levels were low. Chronic active B-cell receptor signaling and to a minor degree cyclin D1 overexpression contributed to high NOXA mRNA expression levels in MCL cells. The phoshatidyl-inositol-3 kinase/AKT/mammalian target of rapamycin pathway was identified as the major downstream signaling pathway involved in the maintenance of NOXA gene expression. Interestingly, MCL cells adapt to this constitutive pro-apoptotic signal by extensive ubiquitination and rapid proteasomal degradation of NOXA protein (T_½∼15–30 min). In addition to the proteasome inhibitor Bortezomib, we identified the neddylation inhibitor MLN4924 and the fatty acid synthase inhibitor Orlistat as potent inducers of NOXA protein expression leading to apoptosis in MCL. All inhibitors targeted NOXA protein turnover. In contrast to Bortezomib, MLN4924 and Orlistat interfered with the ubiquitination process of NOXA protein thereby offering new strategies to kill Bortezomib-resistant MCL cells. Our data, therefore, highlight a critical role of NOXA in the balance between life and death in MCL. The discrepancy between NOXA transcript and protein levels is essential for sensitivity of MCL to ubiquitin-proteasome system inhibitors and could therefore provide a druggable Achilles' heel of MCL cells.

TORC1 and class I HDAC inhibitors synergize to suppress mature B cell neoplasms

Enhanced proliferative signaling and loss of cell cycle regulation are essential for cancer progression. Increased mitogenic signaling through activation of the mTOR pathway, coupled with deregulation of the Cyclin D/retinoblastoma (Rb) pathway is a common feature of lymphoid malignancies, including plasmacytoma (PCT), multiple myeloma (MM), Burkitt's lymphoma (BL), and mantle cell lymphoma (MCL). Here we evaluate the synergy of pharmacologically affecting both of these critical pathways using the mTOR inhibitor sirolimus and the histone deacetylase inhibitor entinostat. A dose-matrix screening approach found this combination to be highly active and synergistic in a panel of genetically diverse human MM cell lines. Synergy and activity was observed in mouse PCT and human BL and MCL cell lines tested in vitro, as well as in freshly isolated primary MM patient samples tested ex vivo. This combination had minimal effects on healthy donor cells and retained activity when tested in a co-culture system simulating the protective interaction of cancer cells with the tumor microenvironment. Combining sirolimus with entinostat enhanced cell cycle arrest and apoptosis. At the molecular level, entinostat increased the expression of cell cycle negative regulators including CDKN1A (p21) and CDKN2A (p16), while the combination decreased critical growth and survival effectors including Cyclin D, BCL-XL, BIRC5, and activated MAPK.

Role of T cell death in maintaining immune tolerance during persistent viral hepatitis

Virus-specific T cells play an important role in the resolution of hepatic infection. However, during chronic hepatitis infection these cells lack their effector functions and fail to control the virus. Hepatitis B virus and hepatitis C virus have developed several mechanisms to generate immune tolerance. One of these strategies is the depletion of virus-specific T cells by apoptosis. The immunotolerogenic liver has unique property to retain and activate naïve T cell to avoid the over reactivation of immune response against antigens which is exploited by hepatotropic viruses to persist. The deletion of the virus-specific T cells occurs by intrinsic (passive) apoptotic mechanism. The pro-apoptotic molecule Bcl-2 interacting mediator (Bim) has attracted increasing attention as a pivotal involvement in apoptosis, as a regulator of tissue homeostasis and an enhancer for the viral persistence. Here, we reviewed our current knowledge on the evidence showing critical role of Bim in viral-specific T cell death by apoptotic pathways and helps in the immune tolerance.

P110α-mediated constitutive PI3K signaling limits the efficacy of p110δ-selective inhibition in mantle cell lymphoma, particularly with multiple relapse

Phosphoinositide-3 kinase (PI3K) pathway activation contributes to mantle cell lymphoma (MCL) pathogenesis, but early-phase studies of the PI3K p110δ inhibitor GS-1101 have reported inferior responses in MCL compared with other non-Hodgkin lymphomas. Because the relative importance of the class IA PI3K isoforms p110α, p110β, and p110δ in MCL is not clear, we studied expression of these isoforms and assessed their contribution to PI3K signaling in this disease. We found that although p110δ was highly expressed in MCL, p110α showed wide variation and expression increased significantly with relapse. Loss of phosphatase and tensin homolog expression was found in 16% (22/138) of cases, whereas PIK3CA and PIK3R1 mutations were absent. Although p110δ inhibition was sufficient to block B-cell receptor-mediated PI3K activation, combined p110α and p110δ inhibition was necessary to abolish constitutive PI3K activation. In addition, GDC-0941, a predominantly p110α/δ inhibitor, was significantly more active compared with GS-1101 against MCL cell lines and primary samples. We found that a high PIK3CA/PIK3CD ratio identified a subset of primary MCLs resistant to GS-1101 and this ratio increased significantly with relapse. These findings support the use of dual p110α/p110δ inhibitors in MCL and suggest a role for p110α in disease progression.

Genomic profiling of mantle cell lymphoma

Genomic profiling of mantle cell lymphoma (MCL) cells has enabled a better understanding of the complex mechanisms underlying the pathogenesis of disease. Besides the t(11;14)(q13;q32) leading to cyclin D1 overexpression, MCL exhibits a characteristic pattern of DNA copy number aberrations that differs from those detected in other B-cell lymphomas. These genomic changes disrupt selected oncogenes and suppressor genes that are required for lymphoma development and progression, many of which are components of cell cycle, DNA damage response and repair, apoptosis, and cell-signaling pathways. Additionally, some of them may represent effective therapeutic targets. A number of genomic and molecular abnormalities have been correlated with the clinical outcome of patients with MCL and are considered prognostic factors. However, only a few genomic markers have been shown to predict the response to current or novel targeted therapies. One representative example is the high-level amplification of the BCL2 gene, which predicts a good response to pro-apoptotic BH3 mimetic drugs. In summary, genomic analyses have contributed to the substantial advances made in the comprehension of the pathogenesis of MCL, providing a solid basis for the identification of optimal therapeutic targets and for the design of new molecular therapies aiming to cure this fatal disease.

Gastrointestinal B-cell lymphomas: From understanding B-cell physiology to classification and molecular pathology

The gut is the most common extranodal site where lymphomas arise. Although all histological lymphoma types may develop in the gut, small and large B-cell lymphomas predominate. The sometimes unexpected finding of a lymphoid lesion in an endoscopic biopsy of the gut may challenge both the clinician (who is not always familiar with lymphoma pathogenesis) and the pathologist (who will often be hampered in his/her diagnostic skill by the limited amount of available tissue). Moreover, the past 2 decades have spawned an avalanche of new data that encompasses both the function of the reactive B-cell as well as the pathogenic pathways that lead to its neoplastic counterpart, the B-cell lymphoma. Therefore, this review aims to offer clinicians an overview of B-cell lymphomas in the gut, and their pertinent molecular features that have led to new insights regarding lymphomagenesis. It addresses the question as how to incorporate all presently available information on normal and neoplastic B-cell differentiation, and how this knowledge can be applied in daily clinical practice (e.g., diagnostic tools, prognostic biomarkers or therapeutic targets) to optimalise the managment of this heterogeneous group of neoplasms.