Induction of prolonged early G1 arrest by CDK4/CDK6 inhibition reprograms lymphoma cells for durable PI3Kδ inhibition through PIK3IP1

PIK3IP1: structure, aberration, function, and regulation in diseases

Phosphoinositide 3-kinase (PI3K) pathway, controlling diverse functions in cells, is one of the most frequently dysregulated pathways in cancer. Several negative regulators have been reported to intricately constrain the overactivation of PI3K pathway. Phosphatidylinoinosidine-3-kinase interacting protein 1 (PIK3IP1), as a unique transmembrane protein, is a newly discovered negative regulator of PI3K pathway. PIK3IP1 negatively regulates PI3K activity by directly binding to the p110 catalytic subunit of PI3K. It has been reported that PIK3IP1 is frequently low expressed in tumors and autoimmune diseases. In tumor cells and impaired cardiomyocyte, PIK3IP1 inhibits cell proliferation and survival. Consistently, the expression of PIK3IP1 is related with the condition of cancer. In addition, PIK3IP1 inhibits the inflammatory response and immune function via maintaining the quiescent state of immune cells. Thus, low expression of PIK3IP1 represents the severe condition of autoimmune diseases. PIK3IP1 is regulated by transcription factors, epigenetic factors or micro-RNAs to facilitate its normal function in different cellular contexts. This review integrates the total findings on PIK3IP1 in different disease, and summaries the structure, biological functions and regulatory mechanisms of PIK3IP1.

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.

Exploiting the fibroblast growth factor receptor-1 vulnerability to therapeutically restrict the MYC-EZH2-CDKN1C axis-driven proliferation in Mantle cell lymphoma

Mantle cell lymphoma (MCL) is a lethal hematological malignancy with a median survival of 4 years. Its lethality is mainly attributed to a limited understanding of clinical tumor progression and resistance to current therapeutic regimes. Intrinsic, prolonged drug treatment and tumor-microenvironment (TME) facilitated factors impart pro-tumorigenic and drug-insensitivity properties to MCL cells. Hence, elucidating neoteric pharmacotherapeutic molecular targets involved in MCL progression utilizing a global "unified" analysis for improved disease prevention is an earnest need. Using integrated transcriptomic analyses in MCL patients, we identified a Fibroblast Growth Factor Receptor-1 (FGFR1), and analyses of MCL patient samples showed that high FGFR1 expression was associated with shorter overall survival in MCL patient cohorts. Functional studies using pharmacological intervention and loss of function identify a novel MYC-EZH2-CDKN1C axis-driven proliferation in MCL. Further, pharmacological targeting with erdafitinib, a selective small molecule targeting FGFRs, induced cell-cycle arrest and cell death in-vitro, inhibited tumor progression, and improved overall survival in-vivo. We performed extensive pre-clinical assessments in multiple in-vivo model systems to confirm the therapeutic potential of erdafitinib in MCL and demonstrated FGFR1 as a viable therapeutic target in MCL.

NOTCH1 mutation in chronic lymphocytic leukaemia is associated with an enhanced cell cycle G1 /S transition and specific cyclin overexpression: Preclinical ground for targeted inhibition

Studies prior to next-generation sequencing (NGS) showed that the frequent indolent course of chronic lymphocytic leukaemia (CLL) is related to most cells remaining quiescent in the G₀ -G₁ cell cycle phase, due to the expression of dysregulated cyclin genes. Of note, the activating nature of the NOTCH1 mutation in T lymphoblastic leukaemia also drives the dysregulation of cell cycle genes. Our goal was to comprehensively revisit the cell cycle in NOTCH1-mutated CLL (NOTCH1^MUT ) to test for potential therapeutic targets. Among 378 NGS-annotated CLL cases, NOTCH1^MUT cells displayed a unique transcriptome profile of G₀ -G₁ cell cycle components, with an overexpression of early-phase effectors, reaching a 38-, 27- and ninefold change increase for the complex elements CCND3, CDK4 and CDK6, respectively. This NOTCH1^MUT cells' profile was related to more cells traversing through the cell cycle. In-vitro targeted inhibition of NOTCH1 gamma-secretase and CDK4/6 reversed the distribution of cells through the cycle phases and enhanced the killing of NOTCH1^MUT CLL cells, suggesting new therapeutic approaches.

A FOXO1-dependent transcription network is a targetable vulnerability of mantle cell lymphomas

Targeting lineage-defined transcriptional dependencies has emerged as an effective therapeutic strategy in cancer treatment. Through screening for molecular vulnerabilities of mantle cell lymphoma (MCL), we identified a set of transcription factors (TFs) including FOXO1, EBF1, PAX5, and IRF4 that are essential for MCL propagation. Integrated chromatin immunoprecipitation and sequencing (ChIP-Seq) with transcriptional network reconstruction analysis revealed FOXO1 as a master regulator that acts upstream in the regulatory TF hierarchy. FOXO1 is both necessary and sufficient to drive MCL lineage commitment through supporting the lineage-specific transcription programs. We further show that FOXO1, but not its close paralog FOXO3, can reprogram myeloid leukemia cells and induce B-lineage gene expression. Finally, we demonstrate that cpd10, a small molecule identified from an enriched FOXO1 inhibitor library, induces a robust cytotoxic response in MCL cells in vitro and suppresses MCL progression in vivo. Our findings establish FOXO1 inhibition as a therapeutic strategy targeting lineage-driven transcriptional addiction in MCL.

Treatment Landscape of Relapsed/Refractory Mantle Cell Lymphoma: An Updated Review

Mantle cell lymphoma (MCL) accounts for nearly 2-6% of all non-Hodgkin lymphoma (NHL) cases, with a steady incidence increase over the past few decades. Although many patients achieve an adequate response to the upfront treatment, the short duration of remission with rapid relapse is challenging during MCL management. In this regard, there is no consensus on the best treatment options for relapsed/refractory (R/R) disease, and the international guidelines demonstrate wide variations in the recommended approaches. The last decade has witnessed the introduction of new agents in the treatment landscape of R/R MCL. Since the introduction of Bruton's tyrosine kinase (BTK) inhibitors, the treatment algorithm and response of R/R MCL patients have dramatically changed. Nevertheless, BTK resistance is common, necessitating further investigations to develop novel agents with a more durable response. Novel agents targeting the B-cell receptor (BCR) signaling have exhibited clinical activity and a well-tolerable safety profile. However, as the responses to these novel agents are still modest in most clinical trials, combination strategies were investigated in pre-clinical and early clinical settings to determine whether the combination of novel agents would exhibit a better durable response than single agents. In this report, we provide an updated literature review that covers recent clinical data about the safety and efficacy of novel therapies for the management of R/R MCL.

A sumoylation program is essential for maintaining the mitotic fidelity in proliferating mantle cell lymphoma cells

BACKGROUND

Mantle cell lymphoma (MCL) is a rare, highly heterogeneous type of B-cell non-Hodgkin's lymphoma. The sumoylation pathway is known to be upregulated in many cancers including lymphoid malignancies. However, little is known about its oncogenic role in MCL.

METHODS

Levels of sumoylation enzymes and sumoylated proteins were quantified in MCL cell lines and primary MCL patient samples by scRNA sequencing and immunoblotting. The sumoylation enzyme SAE2 was genetically and pharmacologically targeted with shRNA and TAK-981 (subasumstat). The effects of SAE2 inhibition on MCL proliferation and cell cycle were evaluated using confocal microscopy, live-cell microscopy, and flow cytometry. Immunoprecipitation and orbitrap mass spectrometry were used to identify proteins targeted by sumoylation in MCL cells.

RESULTS

MCL cells have significant upregulation of the sumoylation pathway at the level of the enzymes SAE1 and SAE2 which correlated with poor prognosis and induction of mitosis associated genes. Selective inhibition of SAE2 with TAK-981 results in significant MCL cell death in vitro and in vivo with mitotic dysregulation being an important mechanism of action. We uncovered a sumoylation program in mitotic MCL cells comprised of multiple pathways which could be directly targeted with TAK-981. Centromeric localization of topoisomerase 2A, a gene highly upregulated in SAE1 and SAE2 overexpressing MCL cells, was lost with TAK-981 treatment likely contributing to the mitotic dysregulation seen in MCL cells.

CONCLUSIONS

This study not only validates SAE2 as a therapeutic target in MCL but also opens the door to further mechanistic work to uncover how to best use desumoylation therapy to treat MCL and other lymphoid malignancies.

LncRNA CDKN2B‑AS1 sponges miR‑28‑5p to regulate proliferation and inhibit apoptosis in colorectal cancer

Long noncoding RNA (lncRNA) CDKN2B‑antisense RNA 1 (AS1) functions as a tumor oncogene in numerous cancers. However, the roles and mechanism of CDKN2B‑AS1 in colorectal cancer (CRC) have not been explored. The present study aimed to investigate whether and how CDKN2B‑AS1 contributes to CRC progression. The data revealed that CDKN2B‑AS1 expression was upregulated in CRC tissues. Loss‑of‑function assays demonstrated that CDKN2B‑AS1 in CRC modulated cell proliferation and apoptosis, which was mediated by cyclin D1, cyclin‑dependent kinase (CDK) 4, p‑Rb, caspase‑9 and caspase‑3. Bioinformatics analysis and luciferase reporter assays indicated direct binding of microRNA (miR)‑28‑5p to CDKN2B‑AS1. Moreover, the results herein revealed that the expression of miR‑28‑5p was negatively correlated with that of CDKN2B‑AS1 in CRC tissue. Moreover, CDKN2B‑AS1 acted as a miR‑28‑5p competing endogenous RNA (ceRNA) to target and regulate the expression of URGCP. These findings indicated that CDKN2B‑AS1 plays roles in CRC progression, providing a potential therapeutic target or novel diagnostic biomarker for CRC.

Genome instability and lymphoma

Lymphoma is one of the most common malignant tumor of the hematologic system. The genome instability is not only an important molecular basis for the development of lymphoma, but also has important value in the diagnosis and prognosis of lymphoma. There are 2 types of genome instability: Microsatellite instability (MSI/MIN) at gene level and chromosomal instability at chromosome level. Through the study on genes associated with lymphoma, the unstable genes associated with lymphoma could be found, meanwhile the mechanism of its occurrence and development of lymphoma could be explored, and the important basis of molecular biology could also be provided in the field of current hot lymphoma precision medical research.

Cyclin-Dependent Kinase Inhibitors in Hematological Malignancies-Current Understanding, (Pre-)Clinical Application and Promising Approaches

Simple Summary

Cyclin-dependent kinases are involved in the regulation of cancer-initiating processes like cell cycle progression, transcription, and DNA repair. In hematological neoplasms, these enzymes are often overexpressed, resulting in increased cell proliferation and cancer progression. Early (pre-)clinical data using cyclin-dependent kinase inhibitors are promising but identifying the right drug for each subgroup and patient is challenging. Certain chromosomal abnormalities and signaling molecule activities are considered as potential biomarkers. We therefore summarized relevant studies investigating cyclin-dependent kinase inhibitors in hematological malignancies and further discuss molecular mechanisms of resistance and other open questions.

Abstract

Genetically altered stem or progenitor cells feature gross chromosomal abnormalities, inducing modified ability of self-renewal and abnormal hematopoiesis. Cyclin-dependent kinases (CDK) regulate cell cycle progression, transcription, DNA repair and are aberrantly expressed in hematopoietic malignancies. Incorporation of CDK inhibitors (CDKIs) into the existing therapeutic regimens therefore constitutes a promising strategy. However, the complex molecular heterogeneity and different clinical presentation is challenging for selecting the right target and defining the ideal combination to mediate long-term disease control. Preclinical and early clinical data suggest that specific CDKIs have activity in selected patients, dependent on the existing rearrangements and mutations, potentially acting as biomarkers. Indeed, CDK6, expressed in hematopoietic cells, is a direct target of MLL fusion proteins often observed in acute leukemia and thus contributes to leukemogenesis. The high frequency of aberrancies in the retinoblastoma pathway additionally warrants application of CDKIs in hematopoietic neoplasms. In this review, we describe the preclinical and clinical advances recently made in the use of CDKIs. These include the FDA-approved CDK4/6 inhibitors, traditional and novel pan-CDKIs, as well as dual kinase inhibitors. We additionally provide an overview on molecular mechanisms of response vs. resistance and discuss open questions.

Copanlisib synergizes with conventional and targeted agents including venetoclax in B- and T-cell lymphoma models

Copanlisib is a pan-class I phosphoinositide 3-kinase (PI3K) inhibitor with preferred activity toward PI3Kα and PI3Kδ. Despite the clear overall clinical benefit, the number of patients achieving complete remissions with the single agent is relatively low, a problem shared by the vast majority of targeted agents. Here, we searched for novel copanlisib-based combinations. Copanlisib was tested as a single agent, in combination with an additional 17 drugs in 26 cell lines derived from mantle cell lymphoma (MCL), marginal zone lymphoma (MZL), and T-cell lymphomas. In vivo experiments, transcriptome analyses, and immunoblotting experiments were also performed. Copanlisib as a single agent showed in vitro dose-dependent antitumor activity in the vast majority of the models. Combination screening identified several compounds that synergized with copanlisib. The strongest combination was with the B-cell lymphoma 2 (BCL2) inhibitor venetoclax. The benefit of the combination over single agents was also validated in an MZL xenograft model and in MCL primary cells, and was due to increased induction of apoptosis, an effect likely sustained by the reduction of the antiapoptotic proteins myeloid cell leukemia 1 (MCL1) and BCL-XL, observed in MCL and MZL cell lines, respectively. These data supported the rationale for the design of the Swiss Group for Clinical Cancer Research (SAKK) 66/18 phase 1 study currently exploring the combination of copanlisib and venetoclax in relapsed/refractory lymphomas.

Inhibitors of Chemoresistance Pathways in Combination with Ara-C to Overcome Multidrug Resistance in AML. A Mini Review

Acute myeloid leukemia (AML), the most common type of leukemia in older adults, is a heterogeneous disease that originates from the clonal expansion of undifferentiated hematopoietic progenitor cells. These cells present a remarkable variety of genes and proteins with altered expression and function. Despite significant advances in understanding the molecular panorama of AML and the development of therapies that target mutations, survival has not improved significantly, and the therapy standard is still based on highly toxic chemotherapy, which includes cytarabine (Ara-C) and allogeneic hematopoietic cell transplantation. Approximately 60% of AML patients respond favorably to these treatments and go into complete remission; however, most eventually relapse, develop refractory disease or chemoresistance, and do not survive for more than five years. Therefore, drug resistance that initially occurs in leukemic cells (primary resistance) or that develops during or after treatment (acquired resistance) has become the main obstacle to AML treatment. In this work, the main molecules responsible for generating chemoresistance to Ara-C in AML are discussed, as well as some of the newer strategies to overcome it, such as the inclusion of molecules that can induce synergistic cytotoxicity with Ara-C (MNKI-8e, emodin, metformin and niclosamide), subtoxic concentrations of chemotherapy (PD0332991), and potently antineoplastic treatments that do not damage nonmalignant cells (heteronemin or hydroxyurea + azidothymidine).

Long intergenic noncoding RNA 00665 promotes proliferation and inhibits apoptosis in colorectal cancer by regulating miR-126-5p

Long intergenic noncoding RNAs (lincRNAs) regulate a series of biological processes, and their anomalous expression plays critical roles in the progression of multiple malignancies, including colorectal cancer (CRC). Although many studies have reported the oncogenic function of LINC00665 in multiple cancers, few studies have explored its role in CRC. The aim of this study was to assess the effect of LINC00665 on the malignant behaviors of CRC and explore the underlying regulatory mechanism of LINC00665. LINC00665 was significantly upregulated in CRC. A loss-of-function assay revealed that LINC00665 downregulation inhibited the proliferation and promoted the apoptosis of CRC cells, which was mediated by cyclin D1, CDK4, caspase-9 and caspase-3. Through mechanistic exploration, we found that miR-126-5p directly bound to LINC00665. Moreover, LINC00665 and miR-126-5p both regulated PAK2 and FZD3 expression. Mechanistically, miR-126-5p was predicted and further verified as a target of both PAK2 and FZD3. These findings demonstrate that LINC00665 might play an important pro-proliferative and antiapoptotic role in CRC and might be a potential biomarker and a new therapeutic target for CRC.

Impact of treatment schedule on the efficacy of cytostatic and immunostimulatory agents

Radiation therapy (RT) and cyclin-dependent kinase 4/6 (CDK4/6) inhibitors mediate poorly overlapping cytostatic and immunostimulatory effects, suggesting that combinatorial regimens may enable supra-additive tumor control. Our preclinical findings demonstrate that administration schedule stands out as a major determinant of efficacy when RT and CDK4/6 inhibitors are combined for breast cancer therapy.

Radiotherapy Delivered before CDK4/6 Inhibitors Mediates Superior Therapeutic Effects in ER+ Breast Cancer

PURPOSE

Recent preclinical data suggest that cyclin-dependent kinase 4/6 (CDK4/6) inhibition may be harnessed to sensitize estrogen receptor-positive (ER⁺) breast cancer to radiotherapy. However, these findings were obtained in human ER⁺ breast cancer cell lines exposed to subclinical doses of CDK4/6 inhibitors with limited attention to treatment schedule. We investigated the activity of radiotherapy combined with the prototypic CDK4/6 inhibitor palbociclib placing emphasis on therapeutic schedule.

EXPERIMENTAL DESIGN

We combined radiotherapy and palbociclib in various doses and therapeutic schedules in human and mouse models of ER⁺ and ER-negative (ER^-) breast cancer, including an immunocompetent mouse model that recapitulates key features of human luminal B breast cancer in women. We assessed proliferation, cell death, cell-cycle control, and clonogenic survival in vitro, as well as tumor growth, overall survival, and metastatic dissemination in vivo.

RESULTS

Radiotherapy and palbociclib employed as standalone agents had partial cytostatic effects in vitro, correlating with suboptimal tumor control in vivo. However, while palbociclib delivered before focal radiotherapy provided minimal benefits as compared with either treatment alone, delivering focal radiotherapy before palbociclib mediated superior therapeutic effects, even in the absence of p53. Such superiority manifested in vitro with enhanced cytostasis and loss of clonogenic potential, as well as in vivo with improved local and systemic tumor control.

CONCLUSIONS

Our preclinical findings demonstrate that radiotherapy delivered before CDK4/6 inhibitors mediates superior antineoplastic effects compared with alternative treatment schedules, calling into question the design of clinical trials administering CDK4/6 inhibitors before radiotherapy in women with ER⁺ breast cancer.

PIK3IP1 Promotes Extrafollicular Class Switching in T-Dependent Immune Responses

PI3K plays multiple roles throughout the life of a B cell. As such, its signaling is tightly regulated. The importance of this is illustrated by the fact that both loss- and gain-of-function mutations in PI3K can cause immunodeficiency in humans. PIK3IP1, also known as TrIP, is a transmembrane protein that has been shown to inhibit PI3K in T cells. Results from the ImmGen Consortium indicate that PIK3IP1 expression fluctuates throughout B cell development in a manner inversely correlated with PI3K activity; however, its role in B cells is poorly understood. In this study, we define the consequences of B cell-specific deletion of PIK3IP1. B cell development, basal Ig levels, and T-independent responses were unaffected by loss of PIK3IP1. However, there was a significant delay in the production of IgG during T-dependent responses, and secondary responses were impaired. This is likely due to a role for PIK3IP1 in the extrafollicular response because germinal center formation and affinity maturation were normal, and PIK3IP1 is not appreciably expressed in germinal center B cells. Consistent with a role early in the response, PIK3IP1 was downregulated at late time points after B cell activation, in a manner dependent on PI3K. Increased activation of the PI3K pathway was observed in PIK3IP1-deficient B cells in response to engagement of both the BCR and CD40 or strong cross-linking of CD40 alone. Taken together, these observations suggest that PIK3IP1 promotes extrafollicular responses by limiting PI3K signaling during initial interactions between B and T cells.

Cell Cycle Dysregulation in Mantle Cell Lymphoma: Genomics and Therapy

Cell cycle dysregulation caused by aberrant cyclin D1 and CDK4 expression is a major determinant for proliferation of cancer cells in mantle cell lymphoma (MCL). Inhibition of CDK4/6 induces G1 arrest of MCL cells in patients, appearing to deepen and prolong the clinical response to partner agents. This article reviews aberrations of cell cycle genes in MCL cells and clinical trials of CDK4/6 inhibitors for MCL. Integrative longitudinal functional genomics is discussed as a strategy to discover genomic drivers for resistance in cancer cells and cancer-immune interactions that potentially contribute to the clinical response to palbociclib combination therapy in MCL.

Long intergenic noncoding RNA 00908 promotes proliferation and inhibits apoptosis of colorectal cancer cells by regulating KLF5 expression

Long intergenic noncoding RNAs (lincRNAs) play a vital role in the occurrence and progression of cancer. The mechanism of lincRNAs in colorectal cancer (CRC) has not been fully elucidated. In this context, an integrated comparative long noncoding RNA (lncRNA) microarray technology was used to determine the expression profile of lncRNAs in CRC. The roles of LINC00908 are unclear. We found that LINC00908 was significantly upregulated in CRC. Inhibition of LINC00908 resulted in reduced cell proliferation and G1 cell cycle arrest, which was mediated by cyclin D1, cyclin-dependent kinase 4, and phosphorylated retinoblastoma. Moreover, inhibition of LINC00908-induced apoptosis through the intrinsic apoptosis signaling pathway, as shown by the activation of caspase-9 and caspase-3. Mechanistically, miR-143-3p directly bound to LINC00908. miR-143-3p expression was negatively correlated with LINC00908 expression in CRC tissue. Functional experiments revealed opposing roles for miR-143-3p and LINC00908, suggesting that LINC00908 negatively regulates miR-143-3p. Mechanistically, miR-143-3p directly targets LINC00908. The KLF5 inhibitor ML264 affected proliferation and apoptosis, indicating that LINC00908 may act as a competing endogenous RNA to facilitate the expression of the miR-143-3p target gene KLF5. Thus, LINC00908 has an important proliferative and antiapoptotic role in CRC by regulating the cell cycle and intrinsic apoptosis. LINC00908 could be a potential biomarker and a new therapeutic target for CRC.

Emerging therapies in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a rare, B cell non-Hodgkin's lymphoma with highly heterogeneous clinical presentation and aggressiveness. First-line treatment consists of intensive chemotherapy with autologous stem cell transplant for the fit, transplant eligible patients, or less intensive chemotherapy for the less fit (and transplant-ineligible) patients. Patients eventually relapse with a progressive clinical course. Numerous therapeutic approaches have emerged over the last few years which have significantly changed the treatment landscape of MCL. These therapies consist of targeted approaches such as BTK and BCL2 inhibitors that provide durable therapeutic responses. However, the optimum combination and sequencing of these therapies is unclear and is currently investigated in several ongoing studies. Furthermore, cellular therapies such as chimeric antigen receptor (CAR) T cells and bispecific T cell engager (BiTe) antibodies have shown impressive results and will likely shape treatment approaches in relapsed MCL, especially after failure with BTK inhibitors. Herein, we provide a comprehensive review of past and ongoing studies that will likely significantly impact our approach to MCL treatment in both the frontline (for transplant eligible and ineligible patients) as well as in the relapsed setting. We present the most up to date results from these studies as well as perspectives on future studies in MCL.

Management of Drug Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a rare but aggressive B-cell hemopathy characterized by the translocation t(11;14)(q13;q32) that leads to the overexpression of the cell cycle regulatory protein cyclin D1. This translocation is the initial event of the lymphomagenesis, but tumor cells can acquire additional alterations allowing the progression of the disease with a more aggressive phenotype and a tight dependency on microenvironment signaling. To date, the chemotherapeutic-based standard care is largely inefficient and despite the recent advent of different targeted therapies including proteasome inhibitors, immunomodulatory drugs, tyrosine kinase inhibitors, relapses are frequent and are generally related to a dismal prognosis. As a result, MCL remains an incurable disease. In this review, we will present the molecular mechanisms of drug resistance learned from both preclinical and clinical experiences in MCL, detailing the main tumor intrinsic processes and signaling pathways associated to therapeutic drug escape. We will also discuss the possibility to counteract the acquisition of drug refractoriness through the design of more efficient strategies, with an emphasis on the most recent combination approaches.

MicroRNA-Mediated Suppression of the TGF-β Pathway Confers Transmissible and Reversible CDK4/6 Inhibitor Resistance

CDK4/6 inhibition is now part of the standard armamentarium for patients with estrogen receptorpositive (ER⁺) breast cancer, so that defining mechanisms of resistance is a pressing issue. Here, we identify increased CDK6 expression as a key determinant of acquired resistance after palbociclib treatment in ER⁺ breast cancer cells. CDK6 expression is critical for cellular survival during palbociclib exposure. The increased CDK6 expression observed in resistant cells is dependent on TGF-b pathway suppression via miR-432-5p expression. Exosomal miR-432-5p expression mediates the transfer of the resistance phenotype between neighboring cell populations. Levels of miR-432-5p are higher in primary breast cancers demonstrating CDK4/6 resistance compared to those that are sensitive. These data are Furthermore confirmed in pre-treatment and post-progression biopsies from a parotid cancer patient who had responded to ribociclib, demonstrating the clinical relevance of this mechanism. Finally, the CDK4/6 inhibitor resistance phenotype is reversible in vitro and in vivo by a prolonged drug holiday.

Cornell et al. demonstrate a mechanism of acquired CDK4/6 inhibitor resistance that is independent of inherent genetic mutations, is conferred through extracellular signaling, and is reversible in vitro and in vivo. Resistance was mediated by exosomal miRNA, causing increased expression of CDK6 to overcome G1 arrest and promote cell survival.

Epigenetic therapies in acute myeloid leukemia: the role of hypomethylating agents, histone deacetylase inhibitors and the combination of hypomethylating agents with histone deacetylase inhibitors

Epigenetic regulation includes changes of DNA methylation and modifications of histone proteins and is essential for normal physiologic functions, especially for controlling gene expression. Epigenetic dysregulation plays a key role in disease pathogenesis and progression of some malignancies, including acute myeloid leukemia (AML). Epigenetic therapies, including hypomethylating agents (HMAs) and histone deacetylase (HDAC) inhibitors, were developed to reprogram the epigenetic abnormalities in AML. However, the molecular mechanisms and therapeutic effects of the two agents alone or their combination remain unknown. An overview of these epigenetic therapies is given here. A literature search was conducted through PubMed database, looking for important biological or clinical studies related to the epigenetic regimens in the treatment of AML until October 15th, 2019. Various types of articles, including original research and reviews, were assessed, identified, and eventually summarized as a collection of data pertaining the mechanisms and clinical effects of HMAs and HDAC inhibitors in AML patients. We provided here an overview of the current understanding of the mechanisms and clinical therapeutic effects involved in the treatment with HMAs and HDAC inhibitors alone, the combination of epigenetic therapies with intensive chemotherapy, and the combination of both types of epigenetic therapies. Relevant clinical trials were also discussed. Generally speaking, the large number of studies and their varied outcomes demonstrate that effects of epigenetic therapies are heterogeneous, and that HMAs combination regimens probably contribute to significant response rates. However, more research is needed to explore therapeutic effects of HDAC inhibitors and various combinations of HMAs and HDAC inhibitors.

Targeting CDK4/6 in mantle cell lymphoma

Targeting the cell cycle represents a rational approach to mantle cell lymphoma (MCL) therapy, as aberrant expression of cyclin D1 and dysregulation of CDK4 underlie cell cycle progression and proliferation of MCL cells. Although cell cycle cancer therapy was historically ineffective due to a lack of selective and effective drugs, this landscape changed with the advent of selective and potent small-molecule oral CDK4/6 inhibitors. Here, we review the anti-tumor activities and clinical data of selective CDK4/6 inhibitors in MCL. We summarize the known mechanism of action of palbociclib, the most specific CDK4/6 inhibitor to date, and the strategy to leverage this specificity to reprogram MCL for a deeper and more durable clinical response to partner drugs. We also discuss integrative longitudinal functional genomics as a strategy to discover tumor-intrinsic genomic biomarkers and tumor-immune interactions that potentially contribute to the clinical response to palbociclib in combination therapy for MCL. Understanding the genomic basis for targeting CDK4/6 and the mechanisms of action and resistance in MCL may advance personalized therapy for MCL and shed light on drug resistance in other cancers.

Inhibition of angiotensin II-induced cerebrovascular smooth muscle cell proliferation by LRRC8A downregulation through suppressing PI3K/AKT activation

Cerebrovascular smooth muscle cell proliferation is the major contributor to cerebrovascular remodeling and stroke. Chloride channels have been suggested to play an important role in the regulation of smooth muscle cell proliferation. This study aims to investigate the effect of leucine-rich repeat-containing 8A (LRRC8A), an essential component of volume-sensitive chloride channels, on cerebrovascular smooth muscle cell proliferation. The data showed that LRRC8A expression was increased in mouse brain artery during angiotensin II (AngII)-induced cerebrovascular remodeling. Similarly, AngII also increased the expression of LRRC8A in human brain vascular smooth muscle cells (HBVSMCs). Knockdown of LRRC8A by siRNA significantly inhibited AngII-induced the proliferation, migration, and invasion in HBVSMCs. The inhibition of HBVSMCs proliferation by LRRC8A downregulation appeared to be involved in suppression of cell-cycle transition. AngII-induced the decrease in p21 and p27 expression and the increase in CDK4 and cyclin D1 expression were attenuated by LRRC8A downregulation. Moreover, inhibition of LRRC8A suppressed AngII-induced PI3K/AKT activation and reactive oxygen species generation, but had no effect on JNK, ERK, and p38 phosphorylation. In addition, activation of PI3K/AKT-signaling pathways with specific agonists significantly abolished the effect of LRRC8A deficiency on HBVSMC proliferation. This present study demonstrates that knockdown of LRRC8A ameliorates AngII-induced cerebrovascular smooth muscle cell proliferation via inhibiting PI3K/AKT pathway, suggesting that LRRC8A may be a novel molecular target in the treatment of vascular remodeling and stroke.

Dual blockade of the PI3K/Akt/mTOR pathway inhibits posttransplant Epstein-Barr virus B cell lymphomas and promotes allograft survival

Posttransplant lymphoproliferative disorder (PTLD) is a serious complication of organ transplantation that often manifests as Epstein-Barr virus (EBV)-associated B cell lymphomas. Current treatments for PTLD have limited efficacy and can be associated with graft rejection or systemic toxicities. The mTOR inhibitor, rapamycin, suppresses tumor growth of EBV+ B cell lymphoma cells in vitro and in vivo; however, the efficacy is limited and clinical benefits of mTOR inhibitors for PTLD are variable. Here, we show constitutive activation of multiple nodes within the PI3K/Akt/mTOR pathway in EBV+ PTLD-derived cell lines. Inhibition of either PI3K or Akt, with specific inhibitors CAL-101 and MK-2206, respectively, diminished growth of EBV+ B cell lines from PTLD patients in a dose-dependent manner. Importantly, rapamycin combined with CAL-101 or MK-2206 had a synergistic effect in suppressing cell growth as determined by IC₅₀ isobolographic analysis and Loewe indices. Moreover, these combinations were significantly more effective than rapamycin alone in inhibiting tumor xenograft growth in NOD-SCID mice. Finally, both CAL-101 and MK-2206 also prolonged survival of heterotopic cardiac allografts in C57BL/6 mice. Thus, combination therapy with rapamycin and a PI3K inhibitor, or an Akt inhibitor, can be an efficacious treatment for EBV-associated PTLD, while simultaneously promoting allograft survival.

Dynamic analysis of proteomic alterations in response to N-linked glycosylation inhibition in a drug-resistant ovarian carcinoma cell line

Glycosylation inhibition can improve the efficacy of antitumor drugs and enhance the apoptosis of cancer cells, thus holding great potential for cancer treatment. Inhibition of N-glycosylation induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), and eventually triggers ER stress-related apoptosis. Unfortunately, the detailed timeline of these cell responses and protein expression alterations related to N-glycosylation inhibition is not explicit yet, and the pathways involved in different stages of N-glycosylation inhibition still need to be characterized. In this study, the dynamic proteome alterations related to N-glycosylation inhibition were investigated by further analyzing our previously published quantitative proteomics data from tunicamycin (TM)-treated ovarian carcinoma (OVCAR-3) cells. The results revealed that N-glycosylation inhibition not only directly affects the expression of glycosylated proteins but also alters an extended scale of proteins. Functional annotation of these altered proteins demonstrated that proteins related to ER stress start changing within 6 h, followed by UPR within 24 h, and eventually ER stress-related apoptosis is triggered after 48 h, indicating the conversion of cellular response from positive to negative. The dynamic proteome data presented here provide important information for better understanding of the significance of N-glycosylation to cell survival and TM-related cancer treatment.

Epigenetic Modifications in Acute Myeloid Leukemia: Prognosis, Treatment, and Heterogeneity

Leukemia, specifically acute myeloid leukemia (AML), is a common malignancy that can be differentiated into multiple subtypes based on leukemogenic history and etiology. Although genetic aberrations, particularly cytogenetic abnormalities and mutations in known oncogenes, play an integral role in AML development, epigenetic processes have been shown as a significant and sometimes independent dynamic in AML pathophysiology. Here, we summarize how tumors evolve and describe AML through an epigenetic lens, including discussions on recent discoveries that include prognostics from epialleles, changes in RNA function for hematopoietic stem cells and the epitranscriptome, and novel epigenetic treatment options. We further describe the limitations of treatment in the context of the high degree of heterogeneity that characterizes acute myeloid leukemia.

Lorlatinib Treatment Elicits Multiple On- and Off-Target Mechanisms of Resistance in ALK-Driven Cancer

: Targeted therapy changed the standard of care in ALK-dependent tumors. However, resistance remains a major challenge. Lorlatinib is a third-generation ALK inhibitor that inhibits most ALK mutants resistant to current ALK inhibitors. In this study, we utilize lorlatinib-resistant anaplastic large cell lymphoma (ALCL), non-small cell lung cancer (NSCLC), and neuroblastoma cell lines in vitro and in vivo to investigate the acquisition of resistance and its underlying mechanisms. ALCL cells acquired compound ALK mutations G1202R/G1269A and C1156F/L1198F in vitro at high drug concentrations. ALCL xenografts selected in vivo showed recurrent N1178H (5/10 mice) and G1269A (4/10 mice) mutations. Interestingly, intracellular localization of NPM/ALKN^1178H skewed toward the cytoplasm in human cells, possibly mimicking overexpression. RNA sequencing of resistant cells showed significant alteration of PI3K/AKT and RAS/MAPK pathways. Functional validation by small-molecule inhibitors confirmed the involvement of these pathways in resistance to lorlatinib. NSCLC cells exposed in vitro to lorlatinib acquired hyperactivation of EGFR, which was blocked by erlotinib to restore sensitivity to lorlatinib. In neuroblastoma, whole-exome sequencing and proteomic profiling of lorlatinib-resistant cells revealed a truncating NF1 mutation and hyperactivation of EGFR and ErbB4. These data provide an extensive characterization of resistance mechanisms that may arise in different ALK-positive cancers following lorlatinib treatment. SIGNIFICANCE: High-throughput genomic, transcriptomic, and proteomic profiling reveals various mechanisms by which multiple tumor types acquire resistance to the third-generation ALK inhibitor lorlatinib.

Knockdown of long non-coding RNA linc00511 suppresses proliferation and promotes apoptosis of bladder cancer cells via suppressing Wnt/β-catenin signaling pathway

More and more studies have shown that long non-coding RNAs (lncRNAs) play critical roles in various biological processes of bladder cancer, including proliferation, apoptosis, migration and cell cycle arrest. LncRNA long intergenic noncoding RNA 00511 (linc00511) is one of the lncRNAs highly expressed in bladder cancer tissues and cells. However, little is known about the roles and mechanisms of linc00511 in bladder cancer. Here, we demonstrated that linc00511 was highly expressed in bladder cancer tissues and cells. Linc00511 knockdown could cause the cell proliferation suppression and cell cycle arrest, which were mediated by p18, p21, CDK4, cyclin D1 and phosphorylation Rb. Suppressed linc00511 could induce the apoptosis in T24 and BIU87 cells via activating the caspase pathway. Down-regulation of linc00511 could also suppress the migration and invasion of T24 and BIU87 cells. In addition, we found that the expression of linc00511 was negatively correlated with that of miR-15a-3p in the clinical bladder cancer samples. Further mechanistic studies showed that linc00511 knockdown induced proliferation inhibition, and apoptosis increase might be regulated through suppressing the activities of Wnt/β-catenin signaling pathway. Thus, we revealed that knockdown of linc00511 suppressed the proliferation and promoted apoptosis of bladder cancer cells through suppressing the activities of Wnt/β-catenin signaling pathway. Moreover, we suggested that linc00511 could be a potential therapeutic target and novel biomarker in bladder cancer.

[Role of PD 0332991 on the Proliferation and Apoptosis of Vascular Endothelial Cells]

BACKGROUND

Angiogenesis is an important process in the development of tumor. PD 0332991, a cell cycle inhibitor, can specifically inhibit CD4/6 phosphorylation and cell cycle progression. In xeongraft mice models, PD 0332991 treated mice had significantly decreased angiogenesis and vascular density compared with the control group, but the mechanism remains unknown. The purpose of this study is to investigate the role and molecular mechanism of PD 0332991 on vascular endothelial cells.

METHODS

EA.hy926 cells, a kind of vascular endothelial cell, were used as the research model. The effects of PD 0332991 on the activity and proliferation of EA.hy926 cells were detected by the MTT, EdU assays. Wound-healing assays and transwell assays were used to determine the effects of PD 0332991 on the mobility of EA.hy926. The influence of PD 0332991 on cell cycle and apoptosis of endothelial cells was tested by flow cytometry, and the Western blot was applied to observe the expression of cell cycle related proteins in EA.hy926 cells treated by PD 0332991.

RESULTS

PD 0332991 significantly inhibited the proliferation and mobility of EA.hy926 cells, caused cell cycle arrest and apoptosis. At the same time, PD 0332991 inhibited the expression of CDK4/6 and phosphorylation of Rb, and thus inhibited the cell cycle progression of EA.hy926 cells.

CONCLUSIONS

PD 0332991 can inhibit the proliferation and activity of endothelial cells and induces apoptosis.

The B cell receptor signaling pathway in mantle cell lymphoma

Signal transduction through the constitutively activated B cell receptor (BCR) plays a key role in the pathogenesis of B-cell tumors by promoting survival and proliferation of malignant B cells. The BCR signaling pathway is known to be deregulated in Mantle Cell Lymphoma (MCL) due to mutations or epigenetic events that impact regulatory proteins. One such protein is Bruton's tyrosine kinase (BTK), an integral component of the BCR signaling pathway. The success of ibrutinib, a BTK inhibitor, and other drugs that target components of the BCR pathway is evidence that regulation of the BCR signaling pathway is an effective method of MCL treatment. The complexity of the pathway indicates that it contains other potential therapeutic targets for the treatment of MCL. This is supported by recent and ongoing clinical trials of inhibitors of molecules such as PI3K, BCL-2, and BTK that show promising initial results. Additionally, agents that target different points of the pathway may have synergistic effects when used in combination. This review provides a description of the BCR signaling pathway on the molecular level followed by an explanation of its relationship to MCL. The role of the BCR signaling pathway in the pathogenesis of MCL is explained through an overview of the drugs that target BCR signaling in MCL treatment.

Cyclin E overexpression confers resistance to the CDK4/6 specific inhibitor palbociclib in gastric cancer cells

Palbociclib is a specific inhibitor of CDK4/6 and has been shown to provide a survival benefit in hormone receptor-positive advanced breast cancer. TCGA database reported that about half of gastric cancers exhibit abnormalities in cell-cycle-related molecules, suggesting that gastric cancer is a good candidate for palbociclib treatment; however, the antitumor effects and predictive markers of palbociclib in gastric cancer remain incompletely described. Herein, the effect and predictive markers of palbociclib on gastric cancer cells were investigated. Our results reveal that palbociclib showed anti-proliferative effects by inducing G1 phase cell-cycle arrest and cellular senescence in some gastric cancer cells. Basal protein expression level of cyclin E showed an inverse correlation of cancer cell sensitivity to palbociclib. In addition, palbociclib enhanced the antitumor effect of 5-FU in vitro and in vivo by modulating thymidine synthase expression. These results suggest that cyclin E protein expression determines the anti-proliferative effect of palbociclib, and palbociclib acts synergistically with 5-FU in gastric cancer. These findings provide a rationale for future clinical trials of palbociclib and 5-FU combination-based chemotherapy in gastric cancer.

Gene mutations and actionable genetic lesions in mantle cell lymphoma

Mutations and epigenetic alterations are key events in transforming normal cells to cancer cells. Mantle cell lymphoma (MCL), a non-Hodgkin's lymphoma of the B-cell, is an aggressive malignancy with poor prognosis especially for those patients who are resistant to the frontline drugs. There is a great need to describe the molecular basis and mechanism of drug resistance in MCL to develop new strategies for treatment. We reviewed frequent somatic mutations and mutations involving the B-cell pathways in MCL and discussed clinical trials that attempted to disrupt these gene pathways and/or epigenetic events. Recurrent gene mutations were discussed in the light of prognostic and therapeutic opportunity and also the challenges of targeting these lesions. Mutations in the ATM, CCND1, TP53, MLL2, TRAF2 and NOTCH1 were most frequently encountered in mantle cell lymphoma. Translational models should be built that would assess mutations longitudinally to identify important compensatory, pro-survival and anti-apoptic pathways and actionable genetic targets.

Cdc37 facilitates cell survival of colorectal carcinoma via activating the CDK4 signaling pathway

Cell division cycle 37 (Cdc37) is an important partner for heat shock protein 90 (HSP90), assisting in molecular chaperone activities, particularly with regard to the regulation of protein kinases. Given its influence on cell growth pathways, Cdc37 has been discussed as a potential intermediate in carcinogenesis. However, to date, the potential functional roles and molecular mechanisms by which Cdc37 regulates cell survival in colorectal carcinoma (CRC) remain unclear. Here, we investigated the expression of Cdc37 and its clinical significance in CRC, and systematically explored the role and the underlying mechanism of Cdc37 in CRC cell survival both in vitro and in vivo. Our results showed that Cdc37 was remarkably up-regulated in CRC, which facilitated cell survival mainly by promoting cell proliferation, G1-S transition, and inhibiting cell apoptosis. Our data further indicated that Cdc37 increased the stability of cyclin-dependent kinase 4 (CDK4) to activate the retinoblastoma 1 (RB1) signaling pathway, followed by increased expression of Bcl-2 and Bcl-xL, which ultimately promoted cell survival in CRC. Moreover, knockdown of CDK4 reversed the Cdc37-mediated effect in promoting the progression of CRC. Our findings showed that Cdc37 played a critical role in promoting CRC cell survival by increasing CDK4 stability to activate the RB1 signaling pathway. Thereby, Cdc37 might serve as a potential therapeutic target in CRC patients.

Mantle cell lymphoma in the era of precision medicine-diagnosis, biomarkers and therapeutic agents

Despite advances in the development of clinical agents for treating Mantle Cell Lymphoma (MCL), treatment of MCL remains a challenge due to complexity and frequent relapse associated with MCL. The incorporation of conventional and novel diagnostic approaches such as genomic sequencing have helped improve understanding of the pathogenesis of MCL, and have led to development of specific agents targeting signaling pathways that have recently been shown to be involved in MCL. In this review, we first provide a general overview of MCL and then discuss about the role of biomarkers in the pathogenesis, diagnosis, prognosis, and treatment for MCL. We attempt to discuss major biomarkers for MCL and highlight published and ongoing clinical trials in an effort to evaluate the dominant signaling pathways as drugable targets for treating MCL so as to determine the potential combination of drugs for both untreated and relapse/refractory cases. Our analysis indicates that incorporation of biomarkers is crucial for patient stratification and improve diagnosis and predictability of disease outcome thus help us in designing future precision therapies. The evidence indicates that a combination of conventional chemotherapeutic agents and novel drugs designed to target specific dysregulated signaling pathways can provide the effective therapeutic options for both untreated and relapse/refractory MCL.

HnRNP-L promotes prostate cancer progression by enhancing cell cycling and inhibiting apoptosis

Expression of the RNA-binding protein HnRNP-L was previously shown to associate with tumorigenesis in liver and lung cancer. In this study, we examined the role of HnRNP-L in prostate cancer (Pca). We found that HnRNP-L is overexpressed in prostate tissue samples from 160 PC patients compared with tissue samples from 32 donors with cancers other than Pca. Moreover, HnRNP-L positively correlated with aggressive tumor characteristics. HnRNP-L knockdown inhibited cell proliferation and promoted cell apoptosis of Pca cell lines in vitro, and suppressed tumor growth when the cells were subcutaneously implanted in an athymic mouse model. Conversely, overexpression of HnRNP-L promoted cell proliferation and tumor growth while prohibiting cell apoptosis. HnRNP-L promoted cell proliferation and tumor growth in Pca in part by interacting with endogenous p53 mRNA, which was closely associated with cyclin p21. In addition, HnRNP-L affected cell apoptosis by directly binding the classical apoptosis protein BCL-2. These observations suggest HnRNP-L is an important regulatory factor that exerts pro-proliferation and anti-apoptosis effects in Pca through actions affecting the cell cycle and intrinsic apoptotic signaling. Thus HnRNP-L could potentially serve as a valuable molecular biomarker or therapeutic target in the treatment of Pca.

FH535 Inhibits Proliferation and Motility of Colon Cancer Cells by Targeting Wnt/β-catenin Signaling Pathway

Aberrant Wnt/β-catenin pathway activation is frequently observed in human colorectal cancer (CRC) and has become a promising target for CRC treatment. Our study aimed to evaluate the effect of FH535, a small molecule inhibitor of Wnt/β-catenin pathway, on two colon cancer cell lines, HT29 and SW480. We found FH535 significantly inhibited colon cancer cell proliferation in vitro and induced cell cycle arrest. Moreover, FH535 inhibited colon cancer xenograft growth in vivo. Wound-healing assay and Transwell assay revealed that FH535 notably suppressed migration and invasion of SW480 cells. FH535 also repressed expression of cancer stem cell markers, CD24, CD44 and CD133 in HT29 cells. Real time-quantitative PCR and Western blotting revealed that targeting Wnt/β-catenin pathway using FH535 effectively downregulated target genes including cyclin D1 and survivin at mRNA and protein level, which contributed to the FH535-induced inhibitory effect on colon cancer cell proliferation. As mechanisms for suppressing cancer cell motility, FH535 downregulated expression of matrix metalloproteinase-7 and -9, Snail and vimentin. RNA sequencing revealed that FH535 prominently altered multiple biological pathways associated with DNA replication, cell cycle and metabolism. Our study highlights the anti-cancer effect of FH535 on colon cancer and presents its potential in colon cancer treatment.

Cell-Cycle Therapeutics Come of Age

The ability to sustain unscheduled proliferation is a hallmark of cancer. The normal process of cell division occurs via the cell cycle, a series of highly regulated steps that are orchestrated at the molecular level by specific cyclins that act in association with cyclin-dependent kinases (CDKs). Cyclin D and CDK4/6 play a key role in cell-cycle progression by phosphorylating and inactivating the retinoblastoma protein, a tumor suppressor that restrains G1- to S-phase progression. The first-generation CDK inhibitors demonstrated broad activity upon several CDKs, which likely explains their considerable toxicities and limited efficacy. Palbociclib, ribociclib, and abemaciclib represent a new class of highly specific ATP-competitive CDK4/6 inhibitors that induce reversible G1-phase cell-cycle arrest in retinoblastoma-positive tumor models. Both palbociclib and ribociclib have been approved in combination with hormone-based therapy for the treatment of naïve hormone receptor-positive advanced breast cancer on the basis of an improvement in progression-free survival. In general, CDK4/6 inhibitors are cytostatic as monotherapy but demonstrate favorable tolerability, which has prompted interest in combination approaches. Combinations with phosphatidylinositol 3-kinase and mammalian target of rapamycin inhibitors in breast cancer, and inhibitors of the RAS/RAF/mitogen-activated protein kinase pathway in RAS-mutant cancers are particularly promising approaches that are currently being evaluated. Although the subject of intense preclinical study, predictive biomarkers for response and resistance to these drugs remain largely undefined. CDK4/6 inhibitors have emerged as the most promising of the cell-cycle therapeutics and intense efforts are now underway to expand the reach of this paradigm.

Suppression of B-cell development genes is key to glucocorticoid efficacy in treatment of acute lymphoblastic leukemia

Glucocorticoids (GCs), including dexamethasone (dex), are a central component of combination chemotherapy for childhood B-cell precursor acute lymphoblastic leukemia (B-ALL). GCs work by activating the GC receptor (GR), a ligand-induced transcription factor, which in turn regulates genes that induce leukemic cell death. Which GR-regulated genes are required for GC cytotoxicity, which pathways affect their regulation, and how resistance arises are not well understood. Here, we systematically integrate the transcriptional response of B-ALL to GCs with a next-generation short hairpin RNA screen to identify GC-regulated "effector" genes that contribute to cell death, as well as genes that affect the sensitivity of B-ALL cells to dex. This analysis reveals a pervasive role for GCs in suppression of B-cell development genes that is linked to therapeutic response. Inhibition of phosphatidylinositol 3-kinase δ (PI3Kδ), a linchpin in the pre-B-cell receptor and interleukin 7 receptor signaling pathways critical to B-cell development (with CAL-101 [idelalisib]), interrupts a double-negative feedback loop, enhancing GC-regulated transcription to synergistically kill even highly resistant B-ALL with diverse genetic backgrounds. This work not only identifies numerous opportunities for enhanced lymphoid-specific combination chemotherapies that have the potential to overcome treatment resistance, but is also a valuable resource for understanding GC biology and the mechanistic details of GR-regulated transcription.

Knockdown of linc-POU3F3 suppresses the proliferation, apoptosis, and migration resistance of colorectal cancer

Long intergenic noncoding RNAs (lincRNAs) play important roles in regulating the biological functions and underlying molecular mechanisms of colorectal cancer (CRC). Here, we investigated the association of linc-POU3F3 and prognosis in CRC. We demonstrated that linc-POU3F3 was overexpressed in CRC tissues and positively correlated with tumor grade and N stage. Inhibition of linc-POU3F3 resulted in inhibition of cell proliferation and G1 cell cycle arrest, which was mediated by cyclin D1, CDK4, p18, Rb, and phosphorylated Rb. Inhibition of linc-POU3F3 induced apoptosis, and suppressed migration and invasion in LOVO and SW480 cell lines. This inhibition also increased the expressions of epithelial markers and decreased the expressions of mesenchymal markers, thus inhibiting the cancer epithelial-mesenchymal transition. The decreased migration and invasion following linc-POU3F3 knockdown were mediated by an increased BMP signal. Furthermore, autophagy was enhanced by linc-POU3F3 knockdown, suggesting the involvement of autophagy in the induced apoptosis. Collectively, linc-POU3F3 might be crucial in pro-proliferation, anti-apoptosis, and metastasis in LOVO and SW480 cells by regulating the cell cycle, intrinsic apoptosis, BMP signaling and autophagy. Thus, linc-POU3F3 is a potential therapeutic target and novel molecular biomarker for CRC.

Rational targeted therapies to overcome microenvironment-dependent expansion of mantle cell lymphoma

Mantle cell lymphoma (MCL) accumulates in lymphoid organs, but disseminates early on in extranodal tissues. Although proliferation remains located in lymphoid organs only, suggesting a major role of the tumor ecosystem, few studies have assessed MCL microenvironment. We therefore cocultured primary circulating MCL cells from 21 patients several weeks ex vivo with stromal or lymphoid-like (CD40L) cells to determine which interactions could support their proliferation. We showed that coculture with lymphoid-like cells, but not stromal cells, induced cell-cycle progression, which was amplified by MCL-specific cytokines (insulin-like growth factor-1, B-cell activating factor, interleukin-6, interleukin-10). Of interest, we showed that our model recapitulated the MCL in situ molecular signatures (ie, proliferation, NF-κB, and survival signatures). We further demonstrated that proliferating MCL harbored an imbalance in Bcl-2 family expression, leading to a consequent loss of mitochondrial priming. Of interest, this loss of priming was overcome by the type II anti-CD20 antibody obinutuzumab, which counteracted Bcl-x_L induction through NF-κB inhibition. Finally, we showed that the mitochondrial priming directly correlated with the sensitivity toward venetoclax and alkylating drugs. By identifying the microenvironment as the major support for proliferation and drug resistance in MCL, our results highlight a selective approach to target the lymphoma niche.

Idelalisib Impacts Cell Growth through Inhibiting Translation-Regulatory Mechanisms in Mantle Cell Lymphoma

PURPOSE

PI3K is a critical node in the B-cell receptor pathway, which is responsible for survival and proliferation of B-cell malignancies. Idelalisib, a PI3Kδ-isoform-specific inhibitor, has been approved to treat B-cell malignancies. Although biological activity of the drug has been evaluated, molecular mechanisms and signaling pathway disruption leading to the biological effects of idelalisib are not yet well defined. Prior laboratory reports have identified transcription and translation as the primary events for attenuation of PI3Kα isoform. We hypothesized that PI3Kδ-isoform inhibition by idelalisib should also affect gene transcription and protein translation.

EXPERIMENTAL DESIGN

Using three mantle cell lymphoma cell lines and primary cells from patients, biological consequences such as apoptosis/cell-cycle analysis, as well as RNA/protein synthesis were evaluated. Proteomics analyses (RPPA and immunoblot assays) defined molecular events downstream of PI3K/AKT cassette.

RESULTS

Idelalisib treatment resulted in inhibition of protein synthesis, which correlated with reduction in cell size and cell growth. A moderate loss of viability without any change in cell-cycle profile was observed. Idelalisib treatment inhibited AKT activation, an immediate downstream PI3K effector, and also reduced phosphorylation levels of downstream AKT/mTOR pathway proteins such as PRAS40. In addition, idelalisib treatment impeded activation of the MAPK pathway, and MEK, ERK and p90RSK phosphorylation levels were reduced. Reduction in AKT, PDK1, and MEK phosphorylation correlated with protein synthesis inhibition.

CONCLUSIONS

Collectively, these results clarify the molecular mechanisms of actions and may provide biomarkers and targets for combination with idelalisib in B-cell malignancies. Clin Cancer Res; 23(1); 181-92. ©2016 AACR.

Knockdown of linc-UFC1 suppresses proliferation and induces apoptosis of colorectal cancer

Long intergenic noncoding RNAs (lincRNAs) have important roles in biological functions, molecular mechanisms and prognostic values in colorectal cancer (CRC). In this context, the roles of linc-UFC1 remain to be elucidated. In this study, linc-UFC1 was overexpressed in CRC patient tissues and positively correlated with tumor grade, N stage and M stage. Inhibition of linc-UFC1 resulted in cell proliferation inhibition and G1 cell cycle arrest, which was mediated by cyclin D1, CDK4, Rb and phosphorylated Rb. In addition, inhibition of linc-UFC1 induced cell apoptosis through the intrinsic apoptosis signaling pathway, as evidenced by the activation of caspase-9 and caspase-3. An investigation of the signaling pathway revealed that the effects on proliferation and apoptosis following linc-UFC1 knockdown were mediated by suppression of β-catenin and activation of phosphorylated P38. Furthermore, the P38 inhibitor SB203580 could attenuate the apoptotic effect achieved by linc-UFC1 knockdown, confirming the involvement of P38 signaling in the induced apoptosis. Taken together, linc-UFC1 might have a critical role in pro-proliferation and anti-apoptosis in CRC by regulating the cell cycle, intrinsic apoptosis, and β-catenin and P38 signaling. Thus, linc-UFC1 could be a potential therapeutic target and novel molecular biomarker for CRC.

Targeting CDK4 and CDK6: From Discovery to Therapy

Biochemical and genetic characterization of D-type cyclins, their cyclin D-dependent kinases (CDK4 and CDK6), and the polypeptide CDK4/6 inhibitor p16(INK4)over two decades ago revealed how mammalian cells regulate entry into the DNA synthetic (S) phase of the cell-division cycle in a retinoblastoma protein-dependent manner. These investigations provided proof-of-principle that CDK4/6 inhibitors, particularly when combined with coinhibition of allied mitogen-dependent signal transduction pathways, might prove valuable in cancer therapy. FDA approval of the CDK4/6 inhibitor palbociclib used with the aromatase inhibitor letrozole for breast cancer treatment highlights long-sought success. The newest findings herald clinical trials targeting other cancers.

SIGNIFICANCE

Rapidly emerging data with selective inhibitors of CDK4/6 have validated these cell-cycle kinases as anticancer drug targets, corroborating longstanding preclinical predictions. This review addresses the discovery of these CDKs and their regulators, as well as translation of CDK4/6 biology to positive clinical outcomes and development of rational combinatorial therapies.

Treating cancer with selective CDK4/6 inhibitors

Uncontrolled cellular proliferation, mediated by dysregulation of the cell-cycle machinery and activation of cyclin-dependent kinases (CDKs) to promote cell-cycle progression, lies at the heart of cancer as a pathological process. Clinical implementation of first-generation, nonselective CDK inhibitors, designed to inhibit this proliferation, was originally hampered by the high risk of toxicity and lack of efficacy noted with these agents. The emergence of a new generation of selective CDK4/6 inhibitors, including ribociclib, abemaciclib and palbociclib, has enabled tumour types in which CDK4/6 has a pivotal role in the G1-to-S-phase cell-cycle transition to be targeted with improved effectiveness, and fewer adverse effects. Results of pivotal phase III trials investigating palbociclib in patients with advanced-stage oestrogen receptor (ER)-positive breast cancer have demonstrated a substantial improvement in progression-free survival, with a well-tolerated toxicity profile. Mechanisms of acquired resistance to CDK4/6 inhibitors are beginning to emerge that, although unwelcome, might enable rational post-CDK4/6 inhibitor therapeutic strategies to be identified. Extending the use of CDK4/6 inhibitors beyond ER-positive breast cancer is challenging, and will likely require biomarkers that are predictive of a response, and the use of combination therapies in order to optimize CDK4/6 targeting.

Low dose of lenalidmide and PI3K/mTOR inhibitor trigger synergistic cytoxicity in activated B cell-like subtype of diffuse large B cell lymphoma

Background

Activated B cell-like subtype of diffuse large B cell lymphoma (ABC-DLBCL) presents aggressive clinical courses and poor prognosis. Targeting key pathways may raise the possibility of improving clinical outcomes.

Methods

The synergetic effects were assessed by CCK-8 assay and measured by isobologram analysis. The NVP-Bez235 and lenalidomide cytotoxicity were measured by flow cytometry, Western Blot and si-RNA transfection. The combined treatment inducing tumor regression in vivo was performed in nude mice of OCI-Ly10 xenograft mouse model.

Results

Low dose of two agents represented significant inhibition of proliferation with CI value < 1. NVP-Bez235 combined with lenalidomide remarkably increased apoptosis through intrinsic pathway by upregulating Bim, Bax and downregulating Bcl-xL. Akt, especially NF-κB, played an important role in the synergetic effects. Cotreatment also induced the cell cycle to be arrested in G0/G1 phase, and decreased S phase by increasing p21 expression, downregulating cyclinA and diminishing CDK2 phosphorylation in Su-DHL2 and OCI-Ly3 but not in OCI-Ly10. Mice treated with NVP-Bez235/lenalidomide represented obvious tumor growth regression and prolonged overall survival.

Conclusions

Our findings demonstrated the synergistic effect of low dose of NVP-Bez235 and lenalidomide in ABC-DLBCL, the underlying mechanism may be multifunctional, involving apoptosis, Akt and NF-κB inactivation and cell cycle arrest. Cotreatment was also effective in vivo. These data pave the way for potential treatment of ABC-DLBCL with combination of NVP-Bez235 and lenalidomide.