Utility of mTOR inhibition in hematologic malignancies

Regulation of B-Cell Receptor Signaling and Its Therapeutic Relevance in Aggressive B-Cell Lymphomas

The proliferation and survival signals emanating from the B-cell receptor (BCR) constitute a crucial aspect of mature lymphocyte's life. Dysregulated BCR signaling is considered a potent contributor to tumor survival in different subtypes of B-cell non-Hodgkin lymphomas (B-NHLs). In the last decade, the emergence of BCR-associated kinases as rational therapeutic targets has led to the development and approval of several small molecule inhibitors targeting either Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), or phosphatidylinositol 3 kinase (PI3K), offering alternative treatment options to standard chemoimmunotherapy, and making some of these drugs valuable assets in the anti-lymphoma armamentarium. Despite their initial effectiveness, these precision medicine strategies are limited by primary resistance in aggressive B-cell lymphoma such as diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL), especially in the case of first generation BTK inhibitors. In these patients, BCR-targeting drugs often fail to produce durable responses, and nearly all cases eventually progress with a dismal outcome, due to secondary resistance. This review will discuss our current understanding of the role of antigen-dependent and antigen-independent BCR signaling in DLBCL and MCL and will cover both approved inhibitors and investigational molecules being evaluated in early preclinical studies. We will discuss how the mechanisms of action of these molecules, and their off/on-target effects can influence their effectiveness and lead to toxicity, and how our actual knowledge supports the development of more specific inhibitors and new, rationally based, combination therapies, for the management of MCL and DLBCL patients.

American College of Rheumatology Guidance for the Management of Rheumatic Disease in Adult Patients During the COVID-19 Pandemic: Version 3

OBJECTIVE

To provide guidance to rheumatology providers on the management of adult rheumatic disease in the context of the coronavirus disease 2019 (COVID-19) pandemic.

METHODS

A task force, including 10 rheumatologists and 4 infectious disease specialists from North America, was convened. Clinical questions were collated, and an evidence report was rapidly generated and disseminated. Questions and drafted statements were reviewed and assessed using a modified Delphi process. This included asynchronous anonymous voting by email and webinars with the entire panel. Task force members voted on agreement with draft statements using a 1-9-point numerical scoring system, and consensus was determined to be low, moderate, or high based on the dispersion of votes. For approval, median votes were required to meet predefined levels of agreement (median values of 7-9, 4-6, and 1-3 defined as agreement, uncertainty, or disagreement, respectively) with either moderate or high levels of consensus.

RESULTS

Draft guidance statements approved by the task force have been combined to form final guidance.

CONCLUSION

These guidance statements are provided to promote optimal care during the current pandemic. However, given the low level of available evidence and the rapidly evolving literature, this guidance is presented as a "living document," and future updates are anticipated.

American College of Rheumatology Guidance for the Management of Rheumatic Disease in Adult Patients During the COVID-19 Pandemic: Version 2

OBJECTIVE

To provide guidance to rheumatology providers on the management of adult rheumatic disease in the context of the coronavirus disease 2019 (COVID-19) pandemic.

METHODS

A task force, including 10 rheumatologists and 4 infectious disease specialists from North America, was convened. Clinical questions were collated, and an evidence report was rapidly generated and disseminated. Questions and drafted statements were reviewed and assessed using a modified Delphi process. This included asynchronous anonymous voting by e-mail and webinars with the entire panel. Task force members voted on agreement with draft statements using a 1-9-point numerical scoring system, and consensus was determined to be low, moderate, or high based on the dispersion of votes. For approval, median votes were required to meet predefined levels of agreement (median values of 7-9, 4-6, and 1-3 defined as agreement, uncertainty, or disagreement, respectively) with either moderate or high levels of consensus.

RESULTS

To date, the task force has approved 80 guidance statements: 36 with moderate and 44 with high consensus. These were combined, resulting in 27 final guidance statements.

CONCLUSION

These guidance statements are provided to promote optimal care during the current pandemic. However, given the low level of available evidence and the rapidly evolving literature, this guidance is presented as a "living document," and future updates are anticipated.

Autophagy Modulators: Mechanistic Aspects and Drug Delivery Systems

Autophagy modulation is considered to be a promising programmed cell death mechanism to prevent and cure a great number of disorders and diseases. The crucial step in designing an effective therapeutic approach is to understand the correct and accurate causes of diseases and to understand whether autophagy plays a cytoprotective or cytotoxic/cytostatic role in the progression and prevention of disease. This knowledge will help scientists find approaches to manipulate tumor and pathologic cells in order to enhance cellular sensitivity to therapeutics and treat them. Although some conventional therapeutics suffer from poor solubility, bioavailability and controlled release mechanisms, it appears that novel nanoplatforms overcome these obstacles and have led to the design of a theranostic-controlled drug release system with high solubility and active targeting and stimuli-responsive potentials. In this review, we discuss autophagy modulators-related signaling pathways and some of the drug delivery strategies that have been applied to the field of therapeutic application of autophagy modulators. Moreover, we describe how therapeutics will target various steps of the autophagic machinery. Furthermore, nano drug delivery platforms for autophagy targeting and co-delivery of autophagy modulators with chemotherapeutics/siRNA, are also discussed.

Targeting Cancer at the Intersection of Signaling and Epigenetics

While mutations resulting in the chronic activation of signaling pathways drive human cancer, the epigenetic state of a cell ultimately dictates the biological response to any given oncogenic signal. Moreover, large-scale genomic sequencing efforts have now identified a plethora of mutations in chromatin regulatory genes in human tumors, which can amplify, modify, or complement traditional oncogenic events. Nevertheless, the co-occurrence of oncogenic and epigenetic defects appears to create novel therapeutic vulnerabilities, which can be targeted by specific drug combinations. Here we discuss general mechanisms by which oncogenic and epigenetic alterations cooperate in human cancer and synthesize the field's early efforts in developing promising therapeutic combinations. Collectively, these studies reveal common themes underlying potential chemical synthetic lethal interactions and support both the expansion and refinement of this type of therapeutic approach.

Targeting Autophagy to Overcome Human Diseases

Autophagy is an evolutionarily conserved cellular process, through which damaged organelles and superfluous proteins are degraded, for maintaining the correct cellular balance during stress insult. It involves formation of double-membrane vesicles, named autophagosomes, that capture cytosolic cargo and deliver it to lysosomes, where the breakdown products are recycled back to cytoplasm. On the basis of degraded cell components, some selective types of autophagy can be identified (mitophagy, ribophagy, reticulophagy, lysophagy, pexophagy, lipophagy, and glycophagy). Dysregulation of autophagy can induce various disease manifestations, such as inflammation, aging, metabolic diseases, neurodegenerative disorders and cancer. The understanding of the molecular mechanism that regulates the different phases of the autophagic process and the role in the development of diseases are only in an early stage. There are still questions that must be answered concerning the functions of the autophagy-related proteins. In this review, we describe the principal cellular and molecular autophagic functions, selective types of autophagy and the main in vitro methods to detect the role of autophagy in the cellular physiology. We also summarize the importance of the autophagic behavior in some diseases to provide a novel insight for target therapies.

Identification of differential PI3K pathway target dependencies in T-cell acute lymphoblastic leukemia through a large cancer cell panel screen

Selective phosphoinositide 3-kinase (PI3K)/AKT/mTOR inhibitors are currently under evaluation in clinical studies. To identify tumor types that are sensitive to PI3K pathway inhibitors we screened compounds targeting PI3Kα/δ (AZD8835), PI3Kβ/δ (AZD8186), AKT (AZD5363) and mTORC1/2 (AZD2014) against a cancer cell line panel (971 cell lines). There was an enrichment of hematological malignancies that were sensitive to AKT and mTOR inhibition, with the greatest degree of sensitivity observed in T-cell acute lymphoblastic leukemia (T-ALL). We found that all NOTCH mutant T-ALL cell lines were sensitive to AKT and mTORC1/2 inhibitors, with only partial sensitivity to agents that target the PI3K α, β or δ isoforms. Induction of apoptosis only occurred following AKTi treatment in cell lines with PTEN protein loss and high levels of active AKT. In summary, we have demonstrated that T-ALL cell lines show differential sensitivity to inhibition at different nodes in the PI3K/AKT/mTOR pathway and inhibiting AKT or mTOR may have a therapeutic benefit in this disease setting.

mTOR activity in AIDS-related diffuse large B-cell lymphoma

BACKGROUND

Patients infected with HIV have a significantly increased risk of developing non-Hodgkin lymphomas despite the widespread use of HAART. To investigate mTOR pathway activity in acquired immunodeficiency syndrome (AIDS) related diffuse large B-cell lymphoma AR-DLBCL, we used immunohistochemistry to examine the presence of the phosphorylated 70 ribosomal S6 protein-kinase (p70S6K), an extensively studied effector of mTOR Complex 1 (mTORC1) and the phosphorylated phosphatase and tensin homolog (pPTEN), a negative regulator of mTORC1 pathway.

MATERIALS AND METHODS

We evaluated tissue samples from 126 patients with AR-DLBCL. Among them, 98 samples were from tissue microarrays (TMAs) supplied by the Aids and Cancer Specimen Resource (ACSR), the remaining 28 samples were from cases diagnosed and treated at the University of California, San Diego (UCSD). The presence of p70S6K was evaluated with two antibodies directed against the combined epitopes Ser235/236 and Ser240/244, respectively; and additional monoclonal anti-bodies were used to identify pPTEN and phosphorylated proline-rich Akt substrate of 40kDa (pPRAS40). The degree of intensity and percentage of cells positive for p70S6K and pPTEN were assessed in all the samples. In addition, a subgroup of 28 patients from UCSD was studied to assess the presence of pPRAS40, an insulin-regulated activator of the mTORC1. The expression of each of these markers was correlated with clinical and histopathologic features.

RESULTS

The majority of the patients evaluated were males (88%); only two cases (1.6%) were older than 65 years of age. We found high levels of both p70S6K-paired epitopes studied, 48% positivity against Ser235/236 (44% in ACSR and 64% in UCSD group), and 86% positivity against Ser240/244 (82% in ACSR and 100% in UCSD group). We observed more positive cells and stronger intensity with epitope Ser240/244 in comparison to Ser235/236 (p<0.0001). The degree of intensity and percentage of cells positive for pPTEN was positively correlated with p70S6K levels (p = 0.016 for 235/236 and p = 0.007 for 240/244). High levels of pPRAS40 were observed in the majority of the cases evaluated (64.3%), but no correlation was found with either pPTEN (p = 0.9) or p70S6K (p = 0.9) levels.

CONCLUSION

AR-DLBCL frequently contain p70S6K, a main downstream effector of the mTOR pathway. The presence of p70S6K is positively correlated with pPTEN, an inactive form of PTEN, which makes mTORC1 activated. The presence of p70S6K was independent of HIV viral load or CD4 (+) counts. These results suggest that the mTOR pathway is active in the majority of AR-DLBCL, and p70S6K, particularly the Ser240/244 epitope immunohistochemistry is an excellent surrogate biomarker, which could be used to identify cases expected to be responsive to mTOR inhibitors.

TAK-228 (formerly MLN0128), an investigational oral dual TORC1/2 inhibitor: A phase I dose escalation study in patients with relapsed or refractory multiple myeloma, non-Hodgkin lymphoma, or Waldenström's macroglobulinemia

The PI3K/AKT/mTOR signaling pathways are frequently dysregulated in multiple human cancers, including multiple myeloma (MM), non-Hodgkin lymphoma (NHL), and Waldenström's macroglobulinemia (WM). This was the first clinical study to evaluate the safety, tolerability, maximal-tolerated dose (MTD), dose-limiting toxicity (DLT), pharmacokinetics, and preliminary clinical activity of TAK-228, an oral TORC1/2 inhibitor, in patients with MM, NHL, or WM. Thirty-nine patients received TAK-228 once daily (QD) at 2, 4, 6, or 7 mg, or QD for 3 days on and 4 days off each week (QDx3d QW) at 9 or 12 mg, in 28-day cycles. The overall median age was 61.0 years (range 46-85); 31 patients had MM, four NHL, and four WM. Cycle 1 DLTs occurred in five QD patients (stomatitis, urticaria, blood creatinine elevation, fatigue, and nausea and vomiting) and four QDx3d QW patients (erythematous rash, fatigue, asthenia, mucosal inflammation, and thrombocytopenia). The MTDs were determined to be 4 mg QD and 9 mg QDx3d QW. Thirty-six patients (92%) reported at least one drug-related toxicity; the most common grade ≥3 drug-related toxicities were thrombocytopenia (15%), fatigue (10%), and neutropenia (5%). TAK-228 exhibited a dose-dependent increase in plasma exposure and no appreciable accumulation with repeat dosing; mean plasma elimination half-life was 6-8 hr. Of the 33 response-evaluable patients, one MM patient had a minimal response, one WM patient achieved partial response, one WM patient had a minor response, and 18 patients (14 MM, two NHL, and two WM) had stable disease. These findings encourage further studies including combination strategies.

Targeting mTOR/p70S6K/glycolysis signaling pathway restores glucocorticoid sensitivity to 4E-BP1 null Burkitt Lymphoma

Background

Increasing evidence indicates that rapamycin could be used as a potential glucocorticoid (GC) sensitizer in lymphoblastic malignancies via genetic prevention of 4E-BP1 phosphorylation. Interestingly, we found that combined rapamycin with dexamethasone can effectively reverse GC resistance in 4E-BP1 null lymphoma cells. In this study, we investigated the potential link between mTOR/p70S6K signaling pathway, glycolysis, autophagy and GC resistance.

Methods

Antitumor effects of the combination of rapamycin and dexamethasone were evaluated on cell viability by MTT assay and in vivo studies, on cell cycle and apoptosis by flow cytometry, on autophagy by western blot, MDC staining and transmission electron microscopy and on cell signaling by western blot. Moreover, to test whether inhibiting glycolysis is the core mechanism in rapamycin restoring GC sensitivity, we took glycolysis inhibitor 2-deoxyglucose to replace rapamycin and then evaluated the antitumor effects in vitro.

Results

Raji cells are resistant to rapamycin (IC₅₀ > 1000 nM) or dexamethasone (IC₅₀ > 100 μM) treatment alone. The combination of rapamycin and dexamethasone synergistically inhibited the viability of Raji cells in vitro and in vivo by inducing caspase-dependent and -independent cell death and G₀/G₁ cell cycle arrest. These effects were achieved by the inhibition of mTOR/p70S6K signaling pathway, which led to the inhibition of glycolysis and the induction of autophagy. Pretreatment with pan-caspase inhibitor z-VAD-fmk or autophagy inhibitor 3-MA failed to protect the cells from combined treatment-induced death. Glycolysis inhibitor combined with dexamethasone produced a similar antitumor effects in vitro.

Conclusions

Inhibition of mTOR/p70S6K/glycolysis signaling pathway is the key point of therapy in reversing GC resistant in Burkitt lymphoma patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1535-z) contains supplementary material, which is available to authorized users.

The NO-modified HIV protease inhibitor as a valuable drug for hematological malignancies: Role of p70S6K

Covalent attachment of NO to the first approved HIV protease inhibitor Saquinavir (Saq-NO) expands the therapeutic potential of the original drug. Apart from retained antiviral activity, the modified drug exerts strong antitumor effects and lower toxicity. In the present study, we have evaluated the sensitivity of different hematological malignancies to Saq-NO. Saq-NO efficiently diminished the viability of Jurkat, Raji, HL-60 and K562 cells. While Jurkat and Raji cells (established from pediatric patients) displayed abrogated proliferative potential, HL-60 and K652 cells (originated from adults) exposed to Saq-NO treatment underwent caspase dependent apoptosis. In addition, similar sensitivity to Saq-NO was observed in mononuclear blood cells obtained from pediatric patients with acute lymphoblastic leukemia (ALL) and adult patients with acute myeloid leukemia (AML). Western blot analysis indicated p70S6 kinase as a possible intracellular target of Saq-NO action. Moreover, the addition of a NO moiety to Lopinavir resulted in improved antitumor potential as compared to the parental compound, suggesting that NO-derived HIV protease inhibitors are a potential new source of anticancer drugs with unique mode of action.

Rapamycin can restore the negative regulatory function of transforming growth factor beta 1 in high grade lymphomas

TGF-β1 (transforming growth factor beta 1) is a negative regulator of lymphocytes, inhibiting proliferation and switching on the apoptotic program in normal lymphoid cells. Lymphoma cells often lose their sensitivity to proapoptotic/anti-proliferative regulators such as TGF-β1. Rapamycin can influence both mTOR (mammalian target of rapamycin) and TGF-β signaling, and through these pathways it is able to enhance TGF-β induced anti-proliferative and apoptotic responses. In the present work we investigated the effect of rapamycin and TGF-β1 combination on cell growth and on TGF-β and mTOR signalling events in lymphoma cells. Rapamycin, an inhibitor of mTORC1 (mTOR complex 1) did not elicit apoptosis in lymphoma cells; however, the combination of rapamycin with exogenous TGF-β1 induced apoptosis and restored TGF-β1 dependent apoptotic machinery in several lymphoma cell lines with reduced TGF-β sensitivity in vitro. In parallel, the phosphorylation of p70 ribosomal S6 kinase (p70S6K) and ribosomal S6 protein, targets of mTORC1, was completely eliminated. Knockdown of Smad signalling by Smad4 siRNA had no influence on apoptosis induced by the rapamycin+TGF-β1, suggesting that this effect is independent of Smad signalling. However, apoptosis induction was dependent on early protein phosphatase 2A (PP2A) activity, and in part on caspases. Rapamycin+TGF-β1 induced apoptosis was not completely eliminated by a caspase inhibitor. These results suggest that high mTOR activity contributes to TGF-β resistance and lowering mTORC1 kinase activity may provide a tool in high grade B-cell lymphoma therapy by restoring the sensitivity to normally available regulators such as TGF-β1.

Discovery and development of the Polo-like kinase inhibitor volasertib in cancer therapy

Owing to their integral involvement in cell cycle regulation, the Polo-like kinase (Plk) family, particularly Plk1, has emerged as an attractive therapeutic target in oncology. In recent years, several Plk1 inhibitors have been developed, with some agents showing encouraging results in early-phase clinical trials. This review focuses on volasertib (BI 6727; an investigational agent), a potent and selective Plk inhibitor. Volasertib has shown promising activity in various cancer cell lines and xenograft models of human cancer. Trials performed to date suggest that volasertib has clinical efficacy in a range of malignancies, with the most promising results seen in patients with acute myeloid leukemia (AML). Encouragingly, recent phase II data have demonstrated that volasertib combined with low-dose cytarabine (LDAC) was associated with higher response rates and improved event-free survival than LDAC alone in patients with previously untreated AML. Based on these observations, and its presumably manageable safety profile, volasertib is currently in phase III development as a potential treatment for patients with AML who are ineligible for intensive remission induction therapy. Given that many patients with AML are of an older age and frail, this constitutes an area of major unmet need. In this review, we discuss the biologic rationale for Plk1 inhibitors in cancer, the clinical development of volasertib to date in solid tumors and AML, and the future identification of biomarkers that might predict response to volasertib and help determine the role of this agent in the clinic.

Targeting the phosphoinositide 3-kinase pathway in hematologic malignancies

The phosphoinositide 3-kinase pathway represents an important anticancer target because it has been implicated in cancer cell growth, survival, and motility. Recent studies show that PI3K may also play a role in the development of resistance to currently available therapies. In a broad range of cancers, various components of the phosphoinositide 3-kinase signaling axis are genetically modified, and the pathway can be activated through many different mechanisms. The frequency of genetic alterations in the phosphoinositide 3-kinase pathway, coupled with the impact in oncogenesis and disease progression, make this signaling axis an attractive target in anticancer therapy. A better understanding of the critical function of the phosphoinositide 3-kinase pathway in leukemias and lymphomas has led to the clinical evaluation of novel rationally designed inhibitors in this setting. Three main categories of phosphoinositide 3-kinase inhibitors have been developed so far: agents that target phosphoinositide 3-kinase and mammalian target of rapamycin (dual inhibitors), pan-phosphoinositide 3-kinase inhibitors that target all class I isoforms, and isoform-specific inhibitors that selectively target the α, -β, -γ, or -δ isoforms. Emerging data highlight the promise of phosphoinositide 3-kinase inhibitors in combination with other therapies for the treatment of patients with hematologic malignancies. Further evaluation of phosphoinositide 3-kinase inhibitors in first-line or subsequent regimens may improve clinical outcomes. This article reviews the role of phosphoinositide 3-kinase signaling in hematologic malignancies and the potential clinical utility of inhibitors that target this pathway.

Temsirolimus, the mTOR inhibitor, induces autophagy in adenoid cystic carcinoma: in vitro and in vivo

Temsirolimus acts as a mammalian target of rapamycin (mTOR)-dependent autophagic inhibitor. In order to clarify its effects and mechanisms on human salivary adenoid cystic carcinoma (ACC), we examined whether temsirolimus induced autophagy as the mTOR inhibitor in ACC, both in vitro and in vivo. In this study, MTT assay showed that the inhibition effect of temsirolimus assumed an obvious dose-response relationship on ACC-M cells, and the 50% inhibitory concentration (IC(50)) approached 20 μmol/l; numerous autophagosomes were observed by the transmission electron microscopy (TEM) in temsirolimus treatment groups; notably, expression of LC3 and Beclin1 was significantly up-regulated by temsirolimus. More importantly, the xenograft model provided further evidence of temsirolimus-induced autophagy in vivo by inhibiting mTOR activation as well as up-regulation the expression of Beclin1. These results suggest that temsirolimus could act as an mTOR inhibitor to induce autophagy in adenoid cystic carcinoma both in vitro and in vivo.

Autophagy as a pathogenic mechanism and drug target in lymphoproliferative disorders

Autophagy represents a key mechanism of cytoprotection that can be activated by a variety of extracellular and intracellular stresses and allows the cell to sequester cytoplasmic components and damaged organelles, delivering them to lysosomes for degradation and recycling. However, the autophagy process has also been associated with the death of the cell. It has been demonstrated to be constitutive in some instances and inducible in others, and the idea that it could represent a pathogenetic determinant as well as a possible prognostic tool and a therapeutic target in a plethora of human diseases has recently been considered. Among these, cancer represents a major one. In this review, we recapitulate the critical implications of autophagy in the pathogenesis, progression, and treatment of lymphoproliferative disorders. Leukemias and lymphomas, in fact, represent paradigmatic human diseases in which advances have recently been made in this respect.

Posttransplant lymphoproliferative disease after pediatric solid organ transplantation

Patients after solid organ transplantation (SOT) carry a substantially increased risk to develop malignant lymphomas. This is in part due to the immunosuppression required to maintain the function of the organ graft. Depending on the transplanted organ, up to 15% of pediatric transplant recipients acquire posttransplant lymphoproliferative disease (PTLD), and eventually 20% of those succumb to the disease. Early diagnosis of PTLD is often hampered by the unspecific symptoms and the difficult differential diagnosis, which includes atypical infections as well as graft rejection. Treatment of PTLD is limited by the high vulnerability towards antineoplastic chemotherapy in transplanted children. However, new treatment strategies and especially the introduction of the monoclonal anti-CD20 antibody rituximab have dramatically improved outcomes of PTLD. This review discusses risk factors for the development of PTLD in children, summarizes current approaches to therapy, and gives an outlook on developing new treatment modalities like targeted therapy with virus-specific T cells. Finally, monitoring strategies are evaluated.

Clinical efficacy and management of temsirolimus in patients with relapsed or refractory mantle cell lymphoma

Most patients with mantle cell lymphoma (MCL) relapse within a few years of treatment. Conventional agents provide little benefit, thus identification of new therapies is critical to improve patient outcomes. Temsirolimus, an inhibitor of mammalian target of rapamycin, is an effective, well-tolerated option authorized in Europe for treatment of patients with relapsed/refractory MCL. Intravenous temsirolimus has been extensively studied in MCL and has consistently demonstrated single-agent antitumor activity. In the pivotal phase III trial, treatment with temsirolimus 175 mg weekly for 3 weeks followed by 75 mg weekly (175/75 mg) resulted in significant improvements in progression-free survival (P = .0009) and objective response rate (P = .002) vs. investigator's choice of therapy. Hematologic toxicities (thrombocytopenia, neutropenia) were the principal grade 3/4 adverse events associated with temsirolimus 175/75 mg. Other toxicities included increases in serum cholesterol and triglycerides, hyperglycemia, fatigue, and dyspnea. Overall, the safety profile of temsirolimus is acceptable in this setting, and most toxicities are manageable with dose modification or medical intervention. Clinical studies of temsirolimus in relapsed or refractory MCL patients aim to clarify the optimal treatment schedule and to assess rational combinations with other therapeutic agents, such as rituximab or chemotherapy. Practical considerations are discussed for the clinical use of temsirolimus in patients with MCL.

Acute myeloid leukemia: potential for new therapeutic approaches targeting mRNA translation pathways

Despite advances in molecular research related to acute myeloid leukemia (AML) and a better understanding of the mechanisms of leukemogenesis and pathophysiology of the disease, the pharmacological agents used in the treatment of AML have remained essentially unchanged for the last three decades. Advances in the clinical management of AML patients have been achieved by defining better molecular prognostic markers, but there remains a need for new targeted drugs that disrupt non-overlapping pathways in leukemia cells. The mTOR cellular cascade is critical for cell metabolism, growth, proliferation and survival. Extensive preclinical work suggests that targeting mTOR may provide a powerful approach to block AML precursor cells, while other findings suggest enhanced antileukemic effects by combining mTOR inhibitors with traditional chemotherapy. Such combinations may increase antileukemic responses further, offering unique ways to overcome leukemic cell resistance and to eliminate primitive leukemic precursors.

Mammalian target of rapamycin inhibitors induce tumor cell apoptosis in vivo primarily by inhibiting VEGF expression and angiogenesis

We found that rapalog mTOR inhibitors induce G1 arrest in the PTEN-null HS Sultan B-cell lymphoma line in vitro, but that administration of rapalogs in a HS Sultan xenograft model resulted in significant apoptosis, and that this correlated with induction of hypoxia and inhibition of neoangiogenesis and VEGF expression. Mechanistically, rapalogs prevent cap-dependent translation, but studies have shown that cap-independent, internal ribosome entry site (IRES)-mediated translation of genes, such as c-myc and cyclin D, can provide a fail-safe mechanism that regulates tumor survival. Therefore, we tested if IRES-dependent expression of VEGF could likewise regulate sensitivity of tumor cells in vivo. To achieve this, we developed isogenic HS Sultan cell lines that ectopically express the VEGF ORF fused to the p27 IRES, an IRES sequence that is insensitive to AKT-mediated inhibition of IRES activity and effective in PTEN-null tumors. Mice challenged with p27-VEGF transfected tumor cells were more resistant to the antiangiogenic and apoptotic effects of the rapalog, temsirolimus, and active site mTOR inhibitor, pp242. Our results confirm the critical role of VEGF expression in tumors during treatment with mTOR inhibitors and underscore the importance of IRES activity as a resistance mechanism to such targeted therapy.

Targeting the PI3K/AKT/mTOR signaling axis in children with hematologic malignancies

The phosphatidylinositiol 3-kinase (PI3K), AKT, mammalian target of rapamycin (mTOR) signaling pathway (PI3K/AKT/mTOR) is frequently dysregulated in disorders of cell growth and survival, including a number of pediatric hematologic malignancies. The pathway can be abnormally activated in childhood acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), and chronic myelogenous leukemia (CML), as well as in some pediatric lymphomas and lymphoproliferative disorders. Most commonly, this abnormal activation occurs as a consequence of constitutive activation of AKT, providing a compelling rationale to target this pathway in many of these conditions. A variety of agents, beginning with the rapamycin analogue (rapalog) sirolimus, have been used successfully to target this pathway in a number of pediatric hematologic malignancies. Rapalogs demonstrate significant preclinical activity against ALL, which has led to a number of clinical trials. Moreover, rapalogs can synergize with a number of conventional cytotoxic agents and overcome pathways of chemotherapeutic resistance for drugs commonly used in ALL treatment, including methotrexate and corticosteroids. Based on preclinical data, rapalogs are also being studied in AML, CML, and non-Hodgkin's lymphoma. Recently, significant progress has been made using rapalogs to treat pre-malignant lymphoproliferative disorders, including the autoimmune lymphoproliferative syndrome (ALPS); complete remissions in children with otherwise therapy-resistant disease have been seen. Rapalogs only block one component of the pathway (mTORC1), and newer agents are under preclinical and clinical development that can target different and often multiple protein kinases in the PI3K/AKT/mTOR pathway. Most of these agents have been tolerated in early-phase clinical trials. A number of PI3K inhibitors are under investigation. Of note, most of these also target other protein kinases. Newer agents are under development that target both mTORC1 and mTORC2, mTORC1 and PI3K, and the triad of PI3K, mTORC1, and mTORC2. Preclinical data suggest these dual- and multi-kinase inhibitors are more potent than rapalogs against many of the aforementioned hematologic malignancies. Two classes of AKT inhibitors are under development, the alkyl-lysophospholipids (APLs) and small molecule AKT inhibitors. Both classes have agents currently in clinical trials. A number of drugs are in development that target other components of the pathway, including eukaryotic translation initiation factor (eIF) 4E (eIF4E) and phosphoinositide-dependent protein kinase 1 (PDK1). Finally, a number of other key signaling pathways interact with PI3K/AKT/mTOR, including Notch, MNK, Syk, MAPK, and aurora kinase. These alternative pathways are being targeted alone and in combination with PI3K/AKT/mTOR inhibitors with promising preclinical results in pediatric hematologic malignancies. This review provides a comprehensive overview of the abnormalities in the PI3K/AKT/mTOR signaling pathway in pediatric hematologic malignancies, the agents that are used to target this pathway, and the results of preclinical and clinical trials, using those agents in childhood hematologic cancers.

From drug discovery to biomarker-driven clinical trials in lymphoma

Over the past three decades, the pathological classification of lymphoma has substantially improved. The early Rappaport classification included a handful of subtypes that did not reflect the cell of origin and, not surprisingly, resulted in diagnostic inaccuracies. The WHO currently classifies lymphoma into 30 major distinctive types. While this classification improved the accuracy and consistency of the histological diagnosis of lymphoma, it had little impact on advancing drug development or improving the cure rate of this disease. One reason for this lack of improvement is that recent developments in cancer genomics show these histopathological subtypes to be heterogeneous. Basing treatment decisions on histopathological subtypes is inefficient as it groups different underlying molecular characteristics into one category. Such a strategy exposes many patients to potentially toxic drugs without providing benefits. The recent approval of two new cancer drugs with companion diagnostics to allow selection and treatment of patients with melanoma and non-small-cell lung cancer has raised hope that a similar approach may also expedite successful drug development in lymphoma. We review the current status of biomarker development in lymphoma, and discuss novel biomarker-directed clinical trial designs for lymphoma.

Managing post-transplant lymphoproliferative disorders in solid-organ transplant recipients: a review of immunosuppressant regimens

Post-transplant lymphoproliferative disorders (PTLD) are a heterogeneous group of potentially life-threatening complications that occur after solid organ and bone marrow transplantation. Risk factors for acquiring PTLD are type of organ transplanted, age, intensity of immunosuppression, viral infections such as Epstein-Barr virus (EBV) and time after transplantation. Due to a dearth of well designed prospective trials, treatment for PTLD is often empirical, with reduction in immunosuppression accepted as the first step. Rituximab, a monoclonal antibody directed against the CD20 antigen of immature B cells, is often used as monotherapy after reduction in immunosuppression, although this is associated with a high risk of relapse if patients have at least one of the following risk factors: age greater than 60 years, elevated lactate dehydrogenase levels and Eastern Cooperative Oncology Group Score between 2 and 4. For such patients, rituximab should be considered in combination with CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone), particularly if high-grade PTLD is present. Although widely prescribed, the use of ganciclovir for PTLD remains controversial as EBV-transformed cells lack the thymidine kinase necessary for ganciclovir activation. Newer antivirals that combine ganciclovir with activators of cellular thymidine kinase have shown promising results in preclinical studies. In the absence of controlled trials, surgery may be indicated for localized disease and radiotherapy for patients with impending spinal cord compression or disease localized to the central nervous system or orbit. Future interventions may include adoptive immunotherapy, intravenous immunoglobulin, mammalian target of rapamycin inhibitors, monoclonal antibodies to interleukin-6 and galectin-1, and even EBV vaccination. Although several trials are in progress, it is necessary to wait for the long-term outcome of these studies on risk of PTLD relapse.

Role of autophagy in immunity and autoimmunity, with a special focus on systemic lupus erythematosus

Autophagy is a lysosome-mediated catabolic process that allows cells to degrade unwanted cytoplasmic constituents and to recycle nutrients. Autophagy is also involved in innate and adaptive immune responses, playing a key role in interactions against microbes, in antigen processing for major histocompatibility complex (MHC) presentation, and in lymphocyte development, survival, and proliferation. Over recent years, perturbations in autophagy have been implicated in a number of diseases, including autoimmunity. Systemic lupus erythematosus (SLE) is a multifactorial disease characterized by autoimmune responses against self-antigens generated by dying cells. Genome-wide association studies have linked several single-nucleotide polymorphisms (SNPs) in the autophagy-related gene Atg5 to SLE susceptibility. Loss of Atg5-dependent effects, including clearance of dying cells and cell antigen presentation, might contribute to the autoimmunity and inflammation associated with SLE. Moreover, activation of the mammalian target of rapamycin (mTOR), a key player in the autophagy regulation, has recently been demonstrated in SLE, confirming an altered autophagy pathway in this disease. In the present review, we summarize the autophagy mechanisms, their molecular regulation, and their relevance in immunity and autoimmunity. The potential of targeting autophagy pathway in SLE, by developing innovative therapeutic approaches, has finally been discussed.