Dual inhibition of class IA phosphatidylinositol 3-kinase and mammalian target of rapamycin as a new therapeutic option for T-cell acute lymphoblastic leukemia

Rigosertib is more potent than wortmannin and rapamycin against adult T-cell leukemia-lymphoma

Human T lymphotropic virus type 1 (HTLV-1) infection can cause adult T-cell lymphoblastic leukemia (ATLL), an incurable, chemotherapy-resistant malignancy. In a quest for new therapeutic targets, our study sought to determine the levels of AKT, mTOR, and PI3K in ATLL MT-2 cells, HTLV-1 infected NIH/3T3 cells (Inf-3T3), and HTLV-1 infected patients (Carrier, HAM/TSP, and ATLL). Furthermore, the effects of rigosertib, wortmannin, and rapamycin on the PI3K/Akt/mTOR pathway to inhibit the proliferation of ATLL cells were examined. The results showed that mRNA expression of Akt/PI3K/mTOR was down-regulated in carrier, HAM/TSP, and ATLL patients, as well as MT-2, and Inf-3T3 cells, compared to the healthy individuals and untreated MT-2 and Inf-3T3 as controls. However, western blotting revealed an increase in the phosphorylated and activated forms of AKT and mTOR. Treating the cells with rapamycin, wortmannin, and rigosertib decreased the phosphorylated forms of Akt and mTOR and restored their mRNA expression levels. Using these inhibitors also significantly boosted the expression of the pro-apoptotic genes, Bax/Bcl-2 ratio as well as the expression of the tumor suppressor gene p53 in the MT-2 and Inf-3T3cells. Rigosertib was more potent than wortmannin and rapamycin in inducing sub-G1 and G2-M cell cycle arrest, as well as late apoptosis in the Inf-3T3 and MT-2 cells. It also synergized the cytotoxic effects of vincristine. These findings demonstrate that HTLV-1 downregulation of the mRNA level may occur as a negative feedback response to increased PI3K-Akt-mTOR phosphorylation by HTLV-1. Therefore, using rigosertib alone or in combination with common chemotherapy drugs may be beneficial in ATLL patients.

The pathogenesis and development of targeted drugs in acute T lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) is mainly classified into acute T- and B-lymphoblastic leukaemia according to the source of its lymphocytes, thymus and bone. Among them, the incidence of adult T-cell accounts for about 25% of adult acute lymphoblastic leukaemia, but the degree of malignancy is high and the treatment rate and prognosis are poor. At this stage, there are few targeted drugs and the commonly used broad-spectrum chemotherapeutic drugs have poor efficacy and many adverse drug reactions. Understanding and investigating the pathogenesis of T-acute lymphoblastic leukaemia is very important for further developing new targeting drugs and improving existing drugs. Dysregulated signalling pathways are the main aetiological factors of T-acute lymphoblastic leukaemia. They play crucial roles in promoting tumour initiation, progression, drug design and therapy responses. This is primarily because signalling pathways are indispensable for many cellular biological processes, including tumour growth, migration, invasion, metastasis and others. As a result, small molecule inhibitors targeting the major kinase components of the signalling pathway have received a lot of attention and have been developed and evaluated in preclinical models and clinical trials. Already marketed drugs are also being repurposed in combination therapies to further improve efficacy and overcome tumour cell resistance. In this review, we have aimed to examine the latest and most classical signalling pathways in the aetiology of T-acute lymphoblastic leukaemia and shed light on potential targets for novel therapeutic agents to act on.

Ailanthone Inhibits Cell Proliferation in Tongue Squamous Cell Carcinoma via PI3K/AKT Pathway

Tongue squamous cell carcinoma (TSCC) is the most widespread and invasive subtype of oral cancer with high recurrence rates. Ailanthone (AIL) is an active ingredient in the plant extracts of Ailanthus altissima (Mill.) Swingle. Here, we showed that AIL inhibited the proliferation of human TSCC, the cell viability of Cal-27 and Tca8113 was significantly decreased after AIL treatment for 24 h. Hoechst 33258 staining demonstrated apoptotic characteristics (such as chromatin aggregation) after AIL treatment. The ratio of early- and late-apoptotic cells in AIL-treated Cal-27 and TCA8113 cells increased remarkably when compared with the control group. Bcl-2/Bax ratio and the levels of PARP1, caspase-9, and caspase-3 decreased after AIL treatment, accompanied by significant increase of cleaved PARP1, cleaved caspase-9, and caspase-3 in Cal-27 and TCA8113 cells. Meanwhile, AIL led to Cal-27 cell cycle arrest at G2/M phase. Western blot implied decreased levels of CDK1 and cyclin B1 after AIL treatment. The level of phospho-PI3K p55 subunit and p-Akt were significantly downregulated by AIL in both Cal-27 and TCA8113 cells. These findings implied the potential applications of AIL in the treatment of human TSCC.

Modern treatment approaches to adult acute T-lymphoblastic and myeloid/T-lymphoblastic leukemia: from current standards to precision medicine

PURPOSE OF REVIEW

To review the most recent advancements in the management of adult T-cell acute lymphoblastic leukemia (T-ALL), we summarize insights into molecular diagnostics, immunotherapy, targeted therapy and new techniques of drug sensitivity profiling that may support further therapeutic progress in T-ALL subsets.

RECENT FINDINGS

With current induction/consolidation chemotherapy and/or risk-oriented allogeneic stem cell transplantation programs up to 95% adult T-ALL patients achieve a remission and >50% (up to 80% in adolescents and young adults) are cured. The group of patients who fail upfront therapy, between 25% and 40%, is enriched in high-risk characteristics (unfavorable genetics, persistent minimal residual disease) and represents the ideal setting for the study of molecular mechanisms of disease resistance, and consequently explore novel ways of restoration of drug sensitivity and assess patient/subset-specific patterns of drug vulnerability to targeting agents, immunotherapy and cell therapy.

SUMMARY

The emerging evidence supports the contention that precision medicine may soon allow valuable therapeutic chances to adult patients with high-risk T-ALL. The ongoing challenge is to identify the best way to integrate all these new data into the therapeutic path of newly diagnosed patients, with a view to optimize the individual treatment plan and increase the cure rate.

Redox Control in Acute Lymphoblastic Leukemia: From Physiology to Pathology and Therapeutic Opportunities

Acute lymphoblastic leukemia (ALL) is a hematological malignancy originating from B- or T-lymphoid progenitor cells. Recent studies have shown that redox dysregulation caused by overproduction of reactive oxygen species (ROS) has an important role in the development and progression of leukemia. The application of pro-oxidant therapy, which targets redox dysregulation, has achieved satisfactory results in alleviating the conditions of and improving the survival rate for patients with ALL. However, drug resistance and side effects are two major challenges that must be addressed in pro-oxidant therapy. Oxidative stress can activate a variety of antioxidant mechanisms to help leukemia cells escape the damage caused by pro-oxidant drugs and develop drug resistance. Hematopoietic stem cells (HSCs) are extremely sensitive to oxidative stress due to their low levels of differentiation, and the use of pro-oxidant drugs inevitably causes damage to HSCs and may even cause severe bone marrow suppression. In this article, we reviewed research progress regarding the generation and regulation of ROS in normal HSCs and ALL cells as well as the impact of ROS on the biological behavior and fate of cells. An in-depth understanding of the regulatory mechanisms of redox homeostasis in normal and malignant HSCs is conducive to the formulation of rational targeted treatment plans to effectively reduce oxidative damage to normal HSCs while eradicating ALL cells.

T-cell Acute Lymphoblastic Leukemia: A Roadmap to Targeted Therapies

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy characterized by aberrant proliferation of immature thymocytes. Despite an overall survival of 80% in the pediatric setting, 20% of patients with T-ALL ultimately die from relapsed or refractory disease. Therefore, there is an urgent need for novel therapies. Molecular genetic analyses and sequencing studies have led to the identification of recurrent T-ALL genetic drivers. This review summarizes the main genetic drivers and targetable lesions of T-ALL and gives a comprehensive overview of the novel treatments for patients with T-ALL that are currently under clinical investigation or that are emerging from preclinical research.

SIGNIFICANCE

T-ALL is driven by oncogenic transcription factors that act along with secondary acquired mutations. These lesions, together with active signaling pathways, may be targeted by therapeutic agents. Bridging research and clinical practice can accelerate the testing of novel treatments in clinical trials, offering an opportunity for patients with poor outcome.

Dual Kinase Targeting in Leukemia

Pharmacological cancer therapy is often based on the concurrent inhibition of different survival pathways to improve treatment outcomes and to reduce the risk of relapses. While this strategy is traditionally pursued only through the co-administration of several drugs, the recent development of multi-targeting drugs (i.e., compounds intrinsically able to simultaneously target several macromolecules involved in cancer onset) has had a dramatic impact on cancer treatment. This review focuses on the most recent developments in dual-kinase inhibitors used in acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), and lymphoid tumors, giving details on preclinical studies as well as ongoing clinical trials. A brief overview of dual-targeting inhibitors (kinase/histone deacetylase (HDAC) and kinase/tubulin polymerization inhibitors) applied to leukemia is also given. Finally, the very recently developed Proteolysis Targeting Chimeras (PROTAC)-based kinase inhibitors are presented.

Development of a bioavailable boron-containing PI-103 Bioisostere, PI-103BE

PI-103 (7) is a potent dual phosphatidylinositol 3-kinase (PI3K)/mTOR inhibitor, but its rapid in vivo metabolism hinders its further clinical development. To improve the bioavailability of PI-103, we designed and synthesized a PI-103 bioisostere, PI-103BE (9) in which the phenolic hydroxyl group of PI-103 was replaced by a boronate, a structural modification known to enhance bioavailability of molecules containing phenolic hydroxyl moieties. In cell culture, PI-103BE is partially converted to its corresponding boronic acid (10) and to a lesser extent the active ingredient, PI-103. This mixture contributes to the in vitro activity of 9 that shows reduced potency compared to the parent compound. When administered to mice by oral gavage, 9 displays a significantly improved pharmacokinetic profile compared to PI-103, which shows no oral bioavailability at the same dose. Drug exposure of 9 as measured by the area under curve (AUC) value is 88.2 ng/mL*h for 7 and 8879.9 ng/mL*h for 10. When given by intraperitoneal injection (IP), the prodrug afforded an AUC of 32.3 ng/mL*h for 7 and 400.9 ng/mL*h for 10, compared to 9.7 ng/mL*h from PI-103 injection. In plasma from both pharmacokinetic studies, 9 is fully converted to 10 and 7, with the boronic acid metabolite (10) displaying antiproliferative activities comparable to 9, but weaker than 7. The boronic bioisostere of PI-103 thus offers an improved bioavailability that could be translated to in vivo efficacy of PI-103.

Autophagy in endothelial cells regulates their haematopoiesis-supporting ability

Background

Endothelial cells (ECs) function as an instructive platform to support haematopoietic stem cell (HSC) homeostasis. Our recent studies found that impaired bone marrow (BM) ECs are responsible for the defective haematopoiesis in patients with poor graft function (PGF), which is characterised by pancytopenia post-allotransplant. Although activated autophagy was reported to benefit ECs, whether EC autophagy plays a critical role in supporting HSCs and its effect on PGF patients post-allotransplant remain unclear.

Methods

To evaluate whether the autophagy status of ECs modulates their ability to support haematopoiesis, human umbilical vein endothelial cells (HUVECs) and primary BM ECs derived from healthy donors were subjected to knockdown or overexpression of Beclin-1 (an autophagy-related protein). Moreover, BM ECs derived from PGF patients were studied.

Findings

Beclin-1 knockdown significantly reduced the haematopoiesis-supporting ability of ECs by suppressing autophagy, which could be restored by activating autophagy via Beclin-1 upregulation. Moreover, autophagy positively regulated haematopoiesis-related genes in HUVECs. Subsequently, a prospective case-control study demonstrated that defective autophagy reduced Beclin-1 expression and the colony-forming unit (CFU) plating efficiency in BM ECs from PGF patients compared to matched patients with good graft function. Rapamycin, an autophagy activator, quantitatively and functionally improved BM ECs from PGF patients in vitro and enhanced their ability to support HSCs by activating the Beclin-1 pathway.

Interpretation

Our results suggest that the autophagy status of ECs modulates their ability to support haematopoiesis by regulating the Beclin-1 pathway. Defective autophagy in BM ECs may be involved in the pathogenesis of PGF post-allotransplant. Rapamycin provides a promising therapeutic approach for PGF patients.

Funding

Please see funding sources.

Targeting Wnt/β-catenin and PI3K/Akt/mTOR pathways in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological disorder that results from the clonal transformation of T-cell precursors. Phosphatidylinositol 3-kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) and canonical Wnt/β-catenin signaling pathways play a crucial role in T-cell development and in self-renewal of healthy and leukemic stem cells. Notably, β-catenin is a transcriptional regulator of several genes involved in cancer cell proliferation and survival. In this way, aberrations of components belonging to the aforementioned networks contribute to T-ALL pathogenesis. For this reason, inhibition of both pathways could represent an innovative strategy in this hematological malignancy. Here, we show that combined targeting of Wnt/β-catenin pathway through ICG-001, a CBP/β-catenin transcription inhibitor, and of the PI3K/Akt/mTOR axis through ZSTK-474, a PI3K inhibitor, downregulated proliferation, survival, and clonogenic activity of T-ALL cells. ICG-001 and ZSTK-474 displayed cytotoxic effects, and, when combined together, induced a significant increase in apoptotic cells. This induction of apoptosis was associated with the downregulation of Wnt/β-catenin and PI3K/Akt/mTOR pathways. All these findings were confirmed under hypoxic conditions that mimic the bone marrow niche where leukemic stem cells are believed to reside. Taken together, our findings highlight potentially promising treatment consisting of cotargeting Wnt/β-catenin and PI3K/Akt/mTOR pathways in T-ALL settings.

From tea to treatment; epigallocatechin gallate and its potential involvement in minimizing the metabolic changes in cancer

As the most abundant bioactive polyphenol in green tea, epigallocatechin gallate (EGCG) is a promising natural product that should be used in the discovery and development of potential drug leads. Due to its association with chemoprevention, EGCG may find a role in the development of therapeutics for prostate cancer. Natural products have long been used as a scaffold for drug design, as their already noted bioactivity can help accelerate the development of novel treatments. Green tea and the EGCG contained within have become associated with chemoprevention, and both in vitro and in vivo studies have correlated EGCG to inhibiting cell growth and increasing the metabolic stress of cancer cells, possibly giving merit to its long utilized therapeutic use in traditional therapies. There is accumulating evidence to suggest EGCG's role as an inhibitor of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin signaling cascade, acting upon major axis points within cancer survival pathways. The purpose of this review is to examine the research conducted on tea along with EGCG in the areas of the treatment of and/or prevention of cancer. This review discusses Camellia sinensis as well as the bioactive phytochemical compounds contained within. Clinical uses of tea are explored, and possible pathways for activity are discussed before examining the evidence for EGCG's potential for acting on these processes. EGCG is identified as being a possible lead phytochemical for future drug design investigations.

New advances in targeting aberrant signaling pathways in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disorder characterized by malignant transformation of immature progenitors primed towards T-cell development. Over the past 15 years, advances in the molecular characterization of T-ALL have uncovered oncogenic key drivers and crucial signaling pathways of this disease, opening new chances for the development of novel therapeutic strategies. Currently, T-ALL patients are still treated with aggressive therapies, consisting of high dose multiagent chemotherapy. To minimize and overcome the unfavorable effects of these regimens, it is critical to identify innovative targets and test selective inhibitors of such targets. Major efforts are being made to develop small molecules against deregulated signaling pathways, which sustain T-ALL cell growth, survival, metabolism, and drug-resistance. This review will focus on recent improvements in the understanding of the signaling pathways involved in the pathogenesis of T-ALL and on the challenging opportunities for T-ALL targeted therapies.

IGF1R/IRS1 targeting has cytotoxic activity and inhibits PI3K/AKT/mTOR and MAPK signaling in acute lymphoblastic leukemia cells

The IGF1R/IRS1 signaling is activated in acute lymphoblastic leukemia (ALL) and can be targeted by the pharmacological inhibitors NT157 (IGF1R-IRS1/2 inhibitor) and OSI-906 (IGF1R/IR inhibitor). Here we investigate the cellular and molecular effects of NT157 and OSI-906 in ALL cells. NT157 and OSI-906 treatment reduced viability, proliferation and cell cycle progression in ALL cell lines. Similarly, in primary samples of patients with ALL, both OSI-906 and NT157 reduced viability, but only NT157 induced apoptosis. NT157 and OSI-906 did not show cytotoxicity in primary samples from healthy donor. NT157 and OSI-906 significantly decreased Jurkat cell migration, but did not modulate Namalwa migration. Consistent with the more potent effect of NT157 on cells, NT157 significantly modulated expression of 25 genes related to the MAPK signaling pathway in Jurkat cells, including oncogenes and tumor suppressor genes. Both compounds inhibited mTOR and p70S6K activity, but only NT157 inhibited AKT and 4-EBP1 activation. In summary, in ALL cells, NT157 has cytotoxic activity, whereas OSI-906 is cytostatic. NT157 has a stronger effect on ALL cells, and thus the direct inhibition of IRS1 may be a potential therapeutic target in ALL.

Targeting steroid resistance in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is characterized by a variable response to steroids during induction and/or consolidation therapy. Notably, recent work suggested that these differences in glucocorticoid sensitivity might, at least in part, be mediated by hyperactivation of specific oncogenic pathways such as RAS/MEK/ERK, PI3K/AKT and IL7R/JAK/STAT. In this review, we elaborate on putative associations between aberrant signaling, therapy resistance, incidence of relapse and clinical outcome in human T-ALL. Furthermore, we emphasize that this potential association with clinical parameters might also be mediated by the tumor microenvironment as a result of increased sensitivity of leukemic T-cells towards cytokine induced signaling pathway activation. With this in mind, we provide an overview of small molecule inhibitors that might have clinical potential for the treatment of human T-ALL in the near future as a result of their ability to overcome steroid resistance thereby potentially increasing survival rates in this aggressive hematological neoplasm.

Autophagy regulation and its role in normal and malignant hematopoiesis

Autophagy, the molecular machinery of self-eating, plays a dual role of a tumor promoter and tumor suppressor. This mechanism affects different clinical responses in cancer cells. Autophagy is targeted for treating patients resistant to chemotherapy or radiation. Limited reports investigate the significance of autophagy in cancer therapy, the regulation of hematopoietic and leukemic stem cells and leukemia formation. In the current review, the role of autophagy is discussed in various stages of hematopoiesis including quiescence, self-renewal, and differentiation.

Mitochondria as emerging targets for therapies against T cell acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) comprises a heterogeneous group of hematologic malignancies, arising from diverse genetic alterations in the early lymphocyte development. T-cell subtype of ALL (T-ALL) accounts for about 15% and 25% of ALL in children and adults, respectively. Being less frequent among ALL subtypes, T-ALL represents a high-risk factor for poor prognosis due to its aggressiveness and resistance to common antileukemic drugs. Mitochondria were widely explored recently as a target for anticancer treatment because they are involved in a metabolic reprogramming of a cancer cell and play key roles in reactive oxygen species generation, Ca²⁺ signaling, and cell death induction. Accordingly, a new class of anticancer compounds named mitocans has been developed, which target mitochondria at distinct crucial points to promote their dysfunction and subsequent cell death. The present review analyses the role of mitochondria in malignant reprogramming and emerging therapeutic strategies targeting mitochondria as an "Achilles' heel" in T-ALL, with an emphasis on BH3 mimetics, sequestering pro-survival BCL proteins and voltage-dependent anion channel (VDAC)1-directed drugs, which promote the suppression of aerobic glycolysis, VDAC1 closure, mitochondrial Ca²⁺ overload, stoppage of the oxidative phosphorylation, oxidative stress, and release of proapoptotic factors.

Memantine potentiates cytarabine-induced cell death of acute leukemia correlating with inhibition of Kv1.3 potassium channels, AKT and ERK1/2 signaling

Background

Treatment of acute leukemia is challenging and long-lasting remissions are difficult to induce. Innovative therapy approaches aim to complement standard chemotherapy to improve drug efficacy and decrease toxicity. Promising new therapeutic targets in cancer therapy include voltage-gated K_v1.3 potassium channels, but their role in acute leukemia is unclear. We reported that K_v1.3 channels of lymphocytes are blocked by memantine, which is known as an antagonist of neuronal N-methyl-D-aspartate type glutamate receptors and clinically applied in therapy of advanced Alzheimer disease. Here we evaluated whether pharmacological targeting of K_v1.3 channels by memantine promotes cell death of acute leukemia cells induced by chemotherapeutic cytarabine.

Methods

We analyzed acute lymphoid (Jurkat, CEM) and myeloid (HL-60, Molm-13, OCI-AML-3) leukemia cell lines and patients’ acute leukemic blasts after treatment with either drug alone or the combination of cytarabine and memantine. Patch-clamp analysis was performed to evaluate inhibition of K_v1.3 channels and membrane depolarization by memantine. Cell death was determined with propidium iodide, Annexin V and SYTOX staining and cytochrome C release assay. Molecular effects of memantine co-treatment on activation of Caspases, AKT, ERK1/2, and JNK signaling were analysed by Western blot. K_v1.3 channel expression in Jurkat cells was downregulated by shRNA.

Results

Our study demonstrates that memantine inhibits K_v1.3 channels of acute leukemia cells and in combination with cytarabine potentiates cell death of acute lymphoid and myeloid leukemia cell lines as well as primary leukemic blasts from acute leukemia patients. At molecular level, memantine co-application fosters concurrent inhibition of AKT, S6 and ERK1/2 and reinforces nuclear down-regulation of MYC, a common target of AKT and ERK1/2 signaling. In addition, it augments mitochondrial dysfunction resulting in enhanced cytochrome C release and activation of Caspase-9 and Caspase-3 leading to amplified apoptosis.

Conclusions

Our study underlines inhibition of K_v1.3 channels as a therapeutic strategy in acute leukemia and proposes co-treatment with memantine, a licensed and safe drug, as a potential approach to promote cytarabine-based cell death of various subtypes of acute leukemia.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0317-z) contains supplementary material, which is available to authorized users.

Therapeutic Targeting of mTOR in T-Cell Acute Lymphoblastic Leukemia: An Update

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive blood malignancy that arises from the clonal expansion of transformed T-cell precursors. Although T-ALL prognosis has significantly improved due to the development of intensive chemotherapeutic protocols, primary drug-resistant and relapsed patients still display a dismal outcome. In addition, lifelong irreversible late effects from conventional therapy are a growing problem for leukemia survivors. Therefore, novel targeted therapies are required to improve the prognosis of high-risk patients. The mechanistic target of rapamycin (mTOR) is the kinase subunit of two structurally and functionally distinct multiprotein complexes, which are referred to as mTOR complex 1 (mTORC1) and mTORC2. These two complexes regulate a variety of physiological cellular processes including protein, lipid, and nucleotide synthesis, as well as autophagy in response to external cues. However, mTOR activity is frequently deregulated in cancer, where it plays a key oncogenetic role driving tumor cell proliferation, survival, metabolic transformation, and metastatic potential. Promising preclinical studies using mTOR inhibitors have demonstrated efficacy in many human cancer types, including T-ALL. Here, we highlight our current knowledge of mTOR signaling and inhibitors in T-ALL, with an emphasis on emerging evidence of the superior efficacy of combinations consisting of mTOR inhibitors and either traditional or targeted therapeutics.

Comprehensive analysis of T cell leukemia signals reveals heterogeneity in the PI3 kinase-Akt pathway and limitations of PI3 kinase inhibitors as monotherapy

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic cancer. Poly-chemotherapy with cytotoxic and genotoxic drugs causes substantial toxicity and more specific therapies targeting the underlying molecular lesions are highly desired. Perturbed Ras signaling is prevalent in T-ALL and occurs via oncogenic RAS mutations or through overexpression of the Ras activator RasGRP1 in ~65% of T-ALL patients. Effective small molecule inhibitors for either target do not currently exist. Genetic and biochemical evidence link phosphoinositide 3-kinase (PI3K) signals to T-ALL, PI3Ks are activated by Ras-dependent and Ras-independent mechanisms, and potent PI3K inhibitors exist. Here we performed comprehensive analyses of PI3K-Akt signaling in T-ALL with a focus on class I PI3K. We developed a multiplex, multiparameter flow cytometry platform with pan- and isoform-specific PI3K inhibitors. We find that pan-PI3K and PI3K γ-specific inhibitors effectively block basal and cytokine-induced PI3K-Akt signals. Despite such inhibition, GDC0941 (pan-PI3K) or AS-605240 (PI3Kγ-specific) as single agents did not efficiently induce death in T-ALL cell lines. Combination of GDC0941 with AS-605240, maximally targeting all p110 isoforms, exhibited potent synergistic activity for clonal T-ALL lines in vitro, which motivated us to perform preclinical trials in mice. In contrast to clonal T-ALL lines, we used a T-ALL cancer model that recapitulates the multi-step pathogenesis and inter- and intra-tumoral genetic heterogeneity, a hallmark of advanced human cancers. We found that the combination of GDC0941 with AS-605240 fails in such trials. Our results reveal that PI3K inhibitors are a promising avenue for molecular therapy in T-ALL, but predict the requirement for methods that can resolve biochemical signals in heterogeneous cell populations so that combination therapy can be designed in a rational manner.

Drug discovery targeting the mTOR pathway

Mechanistic target of rapamycin (mTOR) is the kinase subunit of two structurally and functionally distinct large multiprotein complexes, referred to as mTOR complex 1 (mTORC1) and mTORC2. mTORC1 and mTORC2 play key physiological roles as they control anabolic and catabolic processes in response to external cues in a variety of tissues and organs. However, mTORC1 and mTORC2 activities are deregulated in widespread human diseases, including cancer. Cancer cells take advantage of mTOR oncogenic signaling to drive their proliferation, survival, metabolic transformation, and metastatic potential. Therefore, mTOR lends itself very well as a therapeutic target for innovative cancer treatment. mTOR was initially identified as the target of the antibiotic rapamycin that displayed remarkable antitumor activity in vitro Promising preclinical studies using rapamycin and its derivatives (rapalogs) demonstrated efficacy in many human cancer types, hence supporting the launch of numerous clinical trials aimed to evaluate the real effectiveness of mTOR-targeted therapies. However, rapamycin and rapalogs have shown very limited activity in most clinical contexts, also when combined with other drugs. Thus, novel classes of mTOR inhibitors with a stronger antineoplastic potency have been developed. Nevertheless, emerging clinical data suggest that also these novel mTOR-targeting drugs may have a weak antitumor activity. Here, we summarize the current status of available mTOR inhibitors and highlight the most relevant results from both preclinical and clinical studies that have provided valuable insights into both their efficacy and failure.

Notch in Leukemia

Notch is commonly activated in lymphoid malignancies through ligand-independent and ligand-dependent mechanisms. In T-cell acute lymphoblastic leukemia/lymphoma (T-ALL), ligand-independent activation predominates. Negative Regulatory Region (NRR) mutations trigger supraphysiological Notch1 activation by exposing the S2 site to proteolytic cleavage in the absence of ligand. Subsequently, cleavage at the S3 site generates the activated form of Notch, intracellular Notch (ICN). In contrast to T-ALL, in mature lymphoid neoplasms such as chronic lymphocytic leukemia (CLL), the S2 cleavage site is exposed through ligand-receptor interactions. Thus, agents that disrupt ligand-receptor interactions might be useful for treating these malignancies. Notch activation can be enhanced by mutations that delete the C-terminal proline (P), glutamic acid (E), serine (S), and threonine (T) (PEST) domain. These mutations do not activate the Notch pathway per se, but rather impair degradation of ICN. In this chapter, we review the mechanisms of Notch activation and the importance of Notch for the genesis and maintenance of lymphoid malignancies. Unfortunately, targeting the Notch pathway with pan-Notch inhibitors in clinical trials has proven challenging. These clinical trials have encountered dose-limiting on-target toxicities and primary resistance. Strategies to overcome these challenges have emerged from the identification and improved understanding of direct oncogenic Notch target genes. Other strategies have arisen from new insights into the "nuclear context" that selectively directs Notch functions in lymphoid cancers. This nuclear context is created by factors that co-bind ICN at cell-type specific transcriptional regulatory elements. Disrupting the functions of these proteins or inhibiting downstream oncogenic pathways might combat cancer without the intolerable side effects of pan-Notch inhibition.

Aberrant Signaling Pathways in T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease caused by the malignant transformation of immature progenitors primed towards T-cell development. Clinically, T-ALL patients present with diffuse infiltration of the bone marrow by immature T-cell blasts high blood cell counts, mediastinal involvement, and diffusion to the central nervous system. In the past decade, the genomic landscape of T-ALL has been the target of intense research. The identification of specific genomic alterations has contributed to identify strong oncogenic drivers and signaling pathways regulating leukemia growth. Notwithstanding, T-ALL patients are still treated with high-dose multiagent chemotherapy, potentially exposing these patients to considerable acute and long-term side effects. This review summarizes recent advances in our understanding of the signaling pathways relevant for the pathogenesis of T-ALL and the opportunities offered for targeted therapy.

Targeting signaling and apoptotic pathways involved in chemotherapeutic drug-resistance of hematopoietic cells

A critical problem in leukemia as well as other cancer therapies is the development of chemotherapeutic drug-resistance. We have developed models of hematopoietic drug resistance that are based on expression of dominant-negative TP53 [TP53 (DN)] or constitutively-active MEK1 [MEK1(CA)] oncogenes in the presence of chemotherapeutic drugs. In human cancer, functional TP53 activity is often lost in human cancers. Also, activation of the Raf/MEK/ERK pathway frequently occurs due to mutations/amplification of upstream components of this and other interacting pathways. FL5.12 is an interleukin-3 (IL−3) dependent hematopoietic cell line that is sensitive to doxorubicin (a.k.a Adriamycin). FL/Doxo is a derivative cell line that was isolated by culturing the parental FL5.12 cells in doxorubicin for prolonged periods of time. FL/Doxo + TP53 (DN) and FL/Doxo + MEK1 (CA) are FL/Doxo derivate cell lines that were infected with retrovirus encoding TP53 (DN) or MEK1 (CA) and are more resistant to doxorubicin than FL/Doxo cells. This panel of cell lines displayed differences in the sensitivity to inhibitors that suppress mTORC1, BCL2/BCLXL, MEK1 or MDM2 activities, as well as, the proteasomal inhibitor MG132. The expression of key genes involved in cell growth and drug-resistance (e.g., MDM2, MDR1, BAX) also varied in these cells. Thus, we can begin to understand some of the key genes that are involved in the resistance of hematopoietic cells to chemotherapeutic drugs and targeted therapeutics.

Everolimus suppresses invasion and migration of renal cell carcinoma by inhibiting FAK activity and reversing epithelial to mesenchymal transition in vitro and in vivo

Renal cell carcinoma (RCC) is the most common type of kidney cancer in adults and the major cause of mortality in urological cancer. Most patients with RCC are asymptomatic until the disease is advanced and unresectable. In this situation, systemic therapy with immunotherapy or molecularly targeted therapy agents play an important role in therapeutic strategy. Everolimus (EVE), an m-TOR inhibitor, has the potential to inhibit tumor progression at multiple levels and is indicated for the treatment of advanced RCC in patients whose disease has metastasis. In this study, we provide molecular evidence associated with the antimetastatic effect of everolimus by demonstrating the suppression of lung metastasis of 786-O cells in mouse model. This effect was associated with reduced protein expressions of p-FAK (Tyr 925), p-Src (Tyr416), Vimentin, and RhoA and also with increased the E-cadherin protein expression. In summary, these findings provide new insights into the molecular mechanisms involved in the antimetastatic effect of everolimus and are thus valuable in the treatment of metastatic RCC.

Acute lymphoblastic leukemia: a comprehensive review and 2017 update

Acute lymphoblastic leukemia (ALL) is the second most common acute leukemia in adults, with an incidence of over 6500 cases per year in the United States alone. The hallmark of ALL is chromosomal abnormalities and genetic alterations involved in differentiation and proliferation of lymphoid precursor cells. In adults, 75% of cases develop from precursors of the B-cell lineage, with the remainder of cases consisting of malignant T-cell precursors. Traditionally, risk stratification has been based on clinical factors such age, white blood cell count and response to chemotherapy; however, the identification of recurrent genetic alterations has helped refine individual prognosis and guide management. Despite advances in management, the backbone of therapy remains multi-agent chemotherapy with vincristine, corticosteroids and an anthracycline with allogeneic stem cell transplantation for eligible candidates. Elderly patients are often unable to tolerate such regimens and carry a particularly poor prognosis. Here, we review the major recent advances in the treatment of ALL.

From the outside, from within: Biological and therapeutic relevance of signal transduction in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological cancer that arises from clonal expansion of transformed T-cell precursors. In this review we summarize the current knowledge on the external stimuli and cell-intrinsic lesions that drive aberrant activation of pivotal, pro-tumoral intracellular signaling pathways in T-cell precursors, driving transformation, leukemia expansion, spread or resistance to therapy. In addition to their pathophysiological relevance, receptors and kinases involved in signal transduction are often attractive candidates for targeted drug development. As such, we discuss also the potential of T-ALL signaling players as targets for therapeutic intervention.

Signaling pathways as therapeutic targets in biliary tract cancer

INTRODUCTION

The incidence of biliary tract cancer (BTC) is increasing, and the disease is frequently diagnosed during advanced stages, leading to poor overall survival. Limited treatment options are currently available and novel therapeutic approaches are needed. A number of completed clinical trials have evaluated the role of chemotherapy for BTC, demonstrating a marginal benefit. Thus, there is increased interest in applying targeted therapies for this disease. Areas covered: This review article summarizes the role of chemotherapeutic regimens for the treatment of BTC, and highlights key signal transduction pathways of interest for targeted inhibition. Of particular interest are the MEK or MAP2K (mitogen-activated protein kinase kinase), phosphatidylinositol-3 kinase (PI3K) and signal transducer and activator of transcription-3 (STAT3) pathways. We discuss the available data on several promising inhibitors of these pathways, both in the pre-clinical and clinical settings. Expert opinion: Future treatment strategies should address targeting of MEK, PI3K and STAT3 for BTC, with a focus on combined therapeutic approaches.

Dual targeting of eIF4E by blocking MNK and mTOR pathways in leukemia

Dysregulation of mRNA translation leads to aberrant activation of cellular pathways that promote expansion and survival of leukemic clones. A key element of the initiation translation complex is eIF4E (eukaryotic translation initiation factor 4E). The mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) pathways play important roles in the regulation of eIF4E expression and downstream functional outcomes. Mitogen-activated protein kinase interacting protein kinases (Mnks) control translation by phosphorylation of eIF4E, whereas the mTOR kinase phosphorylates/de-activates the eIF4E inhibitor, 4E-BP1, to release translational repression. Both pathways are often abnormally activated in leukemia cells and promote cell survival events by controlling expression of oncogenic proteins. Targeting these pathways may provide approaches to avoid aberrant proliferation and neoplastic transformation.

Upregulation of Nicotinic Acetylcholine Receptor alph4+beta2 through a Ligand-Independent PI3Kbeta Mechanism That Is Enhanced by TNFalpha and the Jak2/p38Mapk Pathways

High affinity nicotine-binding sites in the mammalian brain are neuronal nicotinic acetylcholine receptors (nAChR) assembled from at least alpha4 and beta2 subunits into pentameric ion channels. When exposed to ligands such as nicotine, these receptors respond by undergoing upregulation, a correlate of nicotine addiction. Upregulation can be measured using HEK293 (293) cells that stably express alpha4 and beta2 subunits using quantification of [³H]epibatidine ([³H]Eb) binding to measure mature receptors. Treatment of these cells with choline also produces upregulation through a hemicholinium3 (HC3)-sensitive (choline kinase) and an HC3-insensitive pathway which are both independent of the mechanism used by nicotine for upregulation. In both cases, upregulation is significantly enhanced by the pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) which signals through its receptor Tnfr1 to activate p38Mapk. Here we report that the inhibition of class1 phosphoinositide 3-kinases isoform PI3Kbeta using the selective antagonist PI828 is alone sufficient to produce upregulation and enhance both nicotine and choline HC3-sensitive mediated upregulation. Further, these processes are impacted upon by an AG-490 sensitive Jak2-associated pathway. Both PI3Kbeta (negative) and Jak2 (positive) modulation of upregulation converge through p38Mapk and both overlap with TNFalpha enhancement of this process. Upregulation through the PI3Kbeta pathway did not require Akt. Collectively these findings support upregulation of endogenous alpha4beta2 as a balance among cellular signaling networks that are highly responsive to multiple environmental, inflammatory and metabolic agents. The findings also suggest how illness and metabolic stress could alter the expression of this important nicotinic receptor and novel avenues to intercede in modifying its expression.

Novel biological insights in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive type of blood cancer that accounts for about 15% of pediatric and 25% of adult acute lymphoblastic leukemia (ALL) cases. It is considered as a paradigm for the multistep nature of cancer initiation and progression. Genetic and epigenetic reprogramming events, which transform T-cell precursors into malignant T-ALL lymphoblasts, have been extensively characterized over the past decade. Despite our comprehensive understanding of the genomic landscape of human T-ALL, leukemia patients are still treated by high-dose multiagent chemotherapy, potentially followed by hematopoietic stem cell transplantation. Even with such aggressive treatment regimens, which are often associated with considerable acute and long-term side effects, about 15% of pediatric and 40% of adult T-ALL patients still relapse, owing to acquired therapy resistance, and present with very dismal survival perspectives. Unfortunately, the molecular mechanisms by which residual T-ALL tumor cells survive chemotherapy and act as a reservoir for leukemic progression and hematologic relapse remain poorly understood. Nevertheless, it is expected that enhanced molecular understanding of T-ALL disease biology will ultimately facilitate a targeted therapy driven approach that can reduce chemotherapy-associated toxicities and improve survival of refractory T-ALL patients through personalized salvage therapy. In this review, we summarize recent biological insights into the molecular pathogenesis of T-ALL and speculate how the genetic landscape of T-ALL could trigger the development of novel therapeutic strategies for the treatment of human T-ALL.

Outlook on PI3K/AKT/mTOR inhibition in acute leukemia

Technological advances allowing high throughput analyses across numerous cancer tissues have allowed much progress in understanding complex cellular signaling. In the future, the genetic landscape in cancer may have more clinical relevance than diagnosis based on tumor origin. This progress has emphasized PI3K/AKT/mTOR, among others, as a central signaling center of cancer development due to its governing control in cellular growth, survival, and metabolism. The discovery of high frequencies of mutations in the PI3K/AKT/mTOR pathway in different cancer entities has sparked interest to inhibit elements of this pathway. In acute leukemia pharmacological interruption has yet to achieve desirable efficacy as targetable downstream mutations in PI3K/AKT/mTOR are absent. Nevertheless, mutations in membrane-associated genes upstream of PI3K/AKT/mTOR are frequent in acute leukemia and are associated with aberrant activation of PI3K/AKT/mTOR thus providing a good rationale for further exploration. This review attempts to summarize key findings leading to aberrant activation and to reflect on both promises and challenges of targeting PI3K/AKT/mTOR in acute leukemia. Our emphasis lies on the insights gained through high-throughput data acquisition that open up new avenues for identifying specific subgroups of acute leukemia as ideal candidates for PI3K/AKT/mTOR targeted therapy.

Co-targeting of Akt and Myc inhibits viability of lymphoma cells from Lck-Dlx5 mice

Constitutive activation of AKT is a frequent occurrence in the development of human T-cell acute lymphocytic leukemia/lymphomas (T-ALLs), due largely to inactivation of PTEN. Up regulation of MYC is also commonly observed in human T-ALLs. We previously demonstrated that expression of a constitutively active form of Lck-Akt2 alone is sufficient to initiate T-cell lymphoma in mice, and that tumor formation typically requires up regulation of Myc or Dlx5 caused by specific chromosomal rearrangements. Furthermore, Lck-Dlx5 mice develop T-ALLs that consistently acquire overexpression of Myc and activation of Akt, the latter due to loss of Pten expression. Proliferation of T-ALL cells from Lck-Dlx5 mice was found to be highly sensitive to the Akt pathway inhibitors BEZ235 and RAD001, as well as to JQ1, an inhibitor of bromodomain proteins, one of which (BRD4) regulates Myc transcription. Additionally, low concentrations of BEZ235 were found to cooperate with JQ1 to enhance cell cycle arrest. Higher concentrations of BEZ235 (≥0.5 µM) promoted cell death, although the addition of JQ1 did not result in a further increase in apoptosis. In contrast, the specific Myc inhibitor 10058-F4 caused apoptosis, and when combined with BEZ235 (≥0.5 µM), an enhanced effect on apoptosis was consistently observed. In addition, BEZ235 and RAD001 potentiated vincristine-induced apoptosis when the cells were treated with both drugs simultaneously, whereas pretreatment with BEZ235 antagonized the cell-killing effect of vincristine. Collectively, these experimental findings provide rationale for the design of novel combination therapies for T-ALL that includes targeting of AKT and MYC.

Outlook on PI3K/AKT/mTOR inhibition in acute leukemia

Technological advances allowing high throughput analyses across numerous cancer tissues have allowed much progress in understanding complex cellular signaling. In the future, the genetic landscape in cancer may have more clinical relevance than diagnosis based on tumor origin. This progress has emphasized PI3K/AKT/mTOR, among others, as a central signaling center of cancer development due to its governing control in cellular growth, survival, and metabolism. The discovery of high frequencies of mutations in the PI3K/AKT/mTOR pathway in different cancer entities has sparked interest to inhibit elements of this pathway. In acute leukemia pharmacological interruption has yet to achieve desirable efficacy as targetable downstream mutations in PI3K/AKT/mTOR are absent. Nevertheless, mutations in membrane-associated genes upstream of PI3K/AKT/mTOR are frequent in acute leukemia and are associated with aberrant activation of PI3K/AKT/mTOR thus providing a good rationale for further exploration. This review attempts to summarize key findings leading to aberrant activation and to reflect on both promises and challenges of targeting PI3K/AKT/mTOR in acute leukemia. Our emphasis lies on the insights gained through high-throughput data acquisition that open up new avenues for identifying specific subgroups of acute leukemia as ideal candidates for PI3K/AKT/mTOR targeted therapy.

Targeting signaling pathways in T-cell acute lymphoblastic leukemia initiating cells

Leukemia initiating cells (LICs) represent a reservoir that is believed to drive relapse and resistance to chemotherapy in blood malignant disorders. T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive neoplastic disorder of immature hematopoietic precursors committed to the T-cell lineage. T-ALL comprises about 15% of pediatric and 25% of adult ALL cases and is prone to early relapse. Although the prognosis of T-ALL has improved especially in children due to the use of new intensified treatment protocols, the outcome of relapsed T-ALL cases is still poor. Putative LICs have been identified also in T-ALL. LICs are mostly quiescent and for this reason highly resistant to chemotherapy. Therefore, they evade treatment and give rise to disease relapse. At present great interest surrounds the development of targeted therapies against signaling networks aberrantly activated in LICs and important for their survival and drug-resistance. Both the Notch1 pathway and the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) network are involved in T-ALL LIC survival and drug-resistance and could be targeted by small molecules. Thus, Notch1 and PI3K/Akt/mTOR inhibitors are currently being developed for clinical use either as single agents or in combination with conventional chemotherapy for T-ALL patient treatment. In this review, we summarize the existing knowledge of the relevance of Notch1 and PI3K/Akt/mTOR signaling in T-ALL LICs and we examine the rationale for targeting these key signal transduction networks by means of selective pharmacological inhibitors.

Therapeutic potential of targeting mTOR in T-cell acute lymphoblastic leukemia (review)

T-cell acute lymphoblastic leukemia (T-ALL) is a heterogeneous neoplastic disorder of immature hematopoietic precursors committed to the T-cell lineage. T-ALL comprises about 15% of pediatric and 25% of adult ALL cases. Even if the prognosis of T-ALL has improved especially in the childhood due to the use of new intensified treatment protocols, the outcome of relapsed patients who are resistant to conventional chemotherapeutic drugs or who relapse is still poor. For this reason, there is a need for novel and less toxic targeted therapies against signaling pathways aberrantly activated in T-ALL, such as the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR). Small molecules designed to target key components of this signaling axis have proven their efficacy both in vitro and in vivo in pre-clinical settings of T-ALL. In particular, different classes of mTOR inhibitors have been disclosed by pharmaceutical companies, and they are currently being tested in clinical trials for treating T-ALL patients. One of the most promising approaches for the treatment of T-ALL seems to be the combination of mTOR inhibitors with traditional chemotherapeutic agents. This could lead to a lower drug dosage that may circumvent the systemic side effects of chemotherapeutics. In this review, we focus on the different classes of mTOR inhibitors that will possibly have an impact on the therapeutic arsenal we have at our disposal against T-ALL.

Rapamycin inhibits pre-B acute lymphoblastic leukemia cells by downregulating DNA and RNA polymerases

Rapamycin has been shown to inhibit the growth of leukemic cells via an unknown mechanism. In our current study, we show that rapamycin activates autophagy in pediatric t(1;19) pre-B acute lymphoblastic leukemia (pre-B ALL) cells and thereby inhibits proliferation and induces growth arrest in these cells. Rapamycin was found to downregulate an extensive array of positive cell cycle regulators, reduce the total DNA and RNA levels, and specifically downregulate the gene transcription of DNA pol δ1 and RNA pol II. Furthermore, we show that both rapamycin and starvation caused a downregulation of the DNA pol δ1 and RNA pol II proteins which was reversed by the autophagy inhibitor 3-MA. Consistent with the results of our autophagic flux analysis, confocal microscopy indicated that both rapamycin and starvation cause the colocalization of DNA pol δ1 and RNA pol II with GFP-LC3 at autophagosomes. This colocalization was blocked by the autophagy inhibitor bafilomycin A1 which inhibits the fusion between autophagosomes and lysosomes. These data suggest that rapamycin inhibits the growth of pediatric t(1;19) pre-B ALL cells through both transcriptional inhibition and autophagic degradation of DNA pol δ1 and RNA pol II.

Targeting the PI3K/mTOR Pathway in Pediatric Hematologic Malignancies

A complex interplay of intracellular signaling networks orchestrates normal cell growth and survival, including translation, transcription, proliferation, and cell cycle progression. Dysregulation of such signals occurs commonly in many malignancies, thereby giving the cancer cell a survival advantage, but also providing possible targets for therapeutic intervention. Activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway contributes to the proliferative advantage of malignant cells and may confer resistance to chemotherapy in various hematologic malignancies. The initial mTOR inhibitor, sirolimus (also known as rapamycin), was first discovered in 1975 in the soil of Easter Island. Sirolimus was originally developed as an anti-fungal agent given its macrolide properties, but was approved by the Food and Drug Administration (FDA) in 1999 as an immunosuppressive agent for renal transplantation patients once its T cell suppression characteristics were recognized. Shortly thereafter, recognition of sirolimus's ability to inhibit cellular proliferation and cell cycle progression brought sirolimus to the forefront as a possible inhibitor of mTOR. In the subsequent decade, the functional roles of the mTOR protein have been more fully elucidated, and this protein is now known to be a key regulator in a highly complex signaling pathway that controls cell growth, proliferation, metabolism, and apoptosis. This article discusses the dysregulation of PI3K/mTOR signaling in hematologic malignancies, including acute and chronic leukemias, lymphomas, and lymphoproliferative disorders. The current repertoire of PI3K/mTOR pathway inhibitors in development and clinical trials to date are described with emphasis upon pediatric hematologic malignancies (Figure 1). Investigation of small molecule inhibitors of this complex signaling network is an active area of oncology drug development.

What a tangled web we weave: emerging resistance mechanisms to inhibition of the phosphoinositide 3-kinase pathway

The phosphoinositide 3-kinase (PI3K) pathway is one of the most frequently mutated pathways in cancer, and is actively being pursued as a therapeutic target. Despite the importance of the PI3K pathway in cancer, durable responses to PI3K pathway-targeted therapies are uncommon with monotherapy. Several in vitro and xenograft models have elucidated compensatory signaling and genomic changes which may limit the therapeutic effectiveness of PI3K inhibitors in the clinic. Future clinical trials with prospective evaluation of tumor signaling and genomic changes are likely to identify novel resistance mechanisms as well as subsets of patients who may derive maximal benefit from PI3K pathway inhibitors.

SIGNIFICANCE

There are multiple ongoing clinical trials targeting the PI3K pathway members in several malignancies. This review summarizes the known mechanisms of resistance to targeting the PI3K pathway. Understanding of resistance mechanisms will help to inform more rational clinical trial design to optimize the clinical impact of targeting the PI3K pathway in cancer.

Clinical development of phosphatidylinositol 3-kinase inhibitors for non-Hodgkin lymphoma

Phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway is extensively explored in cancers. It functions as an important regulator of cell growth, survival and metabolism. Activation of this pathway also predicts poor prognosis in numerous human malignancies. Drugs targeting this signaling pathway have been developed and have shown preliminary clinical activity. Accumulating evidence has highlighted the important role of PI3K in non-Hodgkin lymphoma (NHL), especially in the disease initiation and progression. Therapeutic functions of PI3K inhibitors in NHL have been demonstrated both in vivo and in vitro. This review will summarize recent advances in the activation of PI3K signaling in different types of NHL and the applications of PI3K inhibitors in NHL treatment.

Activity of the pan-class I phosphoinositide 3-kinase inhibitor NVP-BKM120 in T-cell acute lymphoblastic leukemia

Constitutively active phosphoinositide 3-kinase (PI3K) signaling is a common feature of T-cell acute lymphoblastic leukemia (T-ALL), where it upregulates cell proliferation, survival and drug resistance. These observations lend compelling weight to the application of PI3K inhibitors in the therapy of T-ALL. Here, we have analyzed the therapeutic potential of the pan-PI3K inhibitor NVP-BKM120 (BKM120), an orally bioavailable 2,6-dimorpholino pyrimidine derivative, which has entered clinical trials for solid tumors, on both T-ALL cell lines and patient samples. BKM120 treatment resulted in G2/M phase cell cycle arrest and apoptosis, being cytotoxic to a panel of T-ALL cell lines and patient T lymphoblasts, and promoting a dose- and time-dependent dephosphorylation of Akt and S6RP. BKM120 maintained its pro-apoptotic activity against Jurkat cells even when cocultured with MS-5 stromal cells, which mimic the bone marrow microenvironment. Remarkably, BKM120 synergized with chemotherapeutic agents currently used for treating T-ALL patients. Moreover, in vivo administration of BKM120 to a subcutaneous xenotransplant model of human T-ALL significantly delayed tumor growth, thus prolonging survival time. Taken together, our findings indicate that BKM120, either alone or in combination with chemotherapeutic drugs, may be an efficient treatment for T-ALLs that have aberrant upregulation of the PI3K signaling pathway.

RasGRP Ras guanine nucleotide exchange factors in cancer

RasGRP proteins are activators of Ras and other related small GTPases by the virtue of functioning as guanine nucleotide exchange factors (GEFs). In vertebrates, four RasGRP family members have been described. RasGRP-1 through -4 share many structural domains but there are also subtle differences between each of the different family members. Whereas SOS RasGEFs are ubiquitously expressed, RasGRP proteins are expressed in distinct patterns, such as in different cells of the hematopoietic system and in the brain. Most studies have concentrated on the role of RasGRP proteins in the development and function of immune cell types because of the predominant RasGRP expression profiles in these cells and the immune phenotypes of mice deficient for Rasgrp genes. However, more recent studies demonstrate that RasGRPs also play an important role in tumorigenesis. Examples are skin- and hematological-cancers but also solid malignancies such as melanoma or prostate cancer. These novel studies bring up many new and unanswered questions related to the molecular mechanism of RasGRP-driven oncogenesis, such as new receptor systems that RasGRP appears to respond to as well as regulatory mechanism for RasGRP expression that appear to be perturbed in these cancers. Here we will review some of the known aspects of RasGRP biology in lymphocytes and will discuss the exciting new notion that RasGRP Ras exchange factors play a role in oncogenesis downstream of various growth factor receptors.

Targeting the PI3-kinase/Akt/mTOR signaling pathway

This article presents an overview of the PI3K/Akt/mTOR signaling pathway. As a central regulator of cell growth, protein translation, survival, and metabolism, activation of this signaling pathway contributes to the pathogenesis of many tumor types. Biochemical and genetic aberrations of this pathway observed in various cancer types are explored. Last, pathway inhibitors both in development and already approved by the Food and Drug Administration are discussed.

Harnessing the PI3K/Akt/mTOR pathway in T-cell acute lymphoblastic leukemia: eliminating activity by targeting at different levels

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignant hematological disorder arising in the thymus from T-cell progenitors. T-ALL mainly affects children and young adults, and remains fatal in 20% of adolescents and 50% of adults, despite progress in polychemotherapy protocols. Therefore, innovative targeted therapies are desperately needed for patients with a dismal prognosis. Aberrant activation of PI3K/Akt/mTOR signaling is a common event in T-ALL patients and portends a poor prognosis. Preclinical studies have highlighted that modulators of PI3K/Akt/mTOR signaling could have a therapeutic relevance in T-ALL. However, the best strategy for inhibiting this highly complex signal transduction pathway is still unclear, as the pharmaceutical companies have disclosed an impressive array of small molecules targeting this signaling network at different levels. Here, we demonstrate that a dual PI3K/PDK1 inhibitor, NVP-BAG956, displayed the most powerful cytotoxic effects against T-ALL cell lines and primary patients samples, when compared with a pan class I PI3K inhibitor (GDC-0941), an allosteric Akt inhibitor (MK-2206), an mTORC1 allosteric inhibitor (RAD-001), or an ATP-competitive mTORC1/mTORC2 inhibitor (KU-63794). Moreover, we also document that combinations of some of the aforementioned drugs strongly synergized against T-ALL cells at concentrations well below their respective IC₅₀. This observation indicates that vertical inhibition at different levels of the PI3K/Akt/mTOR network could be considered as a future innovative strategy for treating T-ALL patients.

Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascade inhibitors: how mutations can result in therapy resistance and how to overcome resistance

The Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascades are often activated by genetic alterations in upstream signaling molecules such as receptor tyrosine kinases (RTK). Targeting these pathways is often complex and can result in pathway activation depending on the presence of upstream mutations (e.g., Raf inhibitors induce Raf activation in cells with wild type (WT) RAF in the presence of mutant, activated RAS) and rapamycin can induce Akt activation. Targeting with inhibitors directed at two constituents of the same pathway or two different signaling pathways may be a more effective approach. This review will first evaluate potential uses of Raf, MEK, PI3K, Akt and mTOR inhibitors that have been investigated in pre-clinical and clinical investigations and then discuss how cancers can become insensitive to various inhibitors and potential strategies to overcome this resistance.

The evolution of the TOR pathway and its role in cancer

The target of rapamycin (TOR) pathway is highly conserved among eukaryotes and has evolved to couple nutrient sensing to cellular growth. TOR is found in two distinct signaling complexes in cells, TOR complex 1 (TORC1) and TOR complex 2 (TORC2). These complexes are differentially regulated and act as effectors for the generation of signals that drive diverse cellular processes such as growth, proliferation, protein synthesis, rearrangement of the cytoskeleton, autophagy, metabolism and survival. Mammalian TOR (mTOR) is very important for development in embryos, while in adult organisms it is linked to aging and lifespan effects. In humans, the mTOR pathway is implicated in the tumorigenesis of multiple cancer types and its deregulation is associated with familial cancer syndromes. Because of its high biological relevance, different therapeutic strategies have been developed to target this signaling cascade, resulting in the emergence of unique pharmacological inhibitors that are either already approved for use in clinical oncology or currently under preclinical or clinical development. Multimodal treatment strategies that simultaneously target multiple nodes of the pathway and/or negative feedback regulatory loops may ultimately provide the best therapeutic advantage in targeting this pathway for the treatment of malignancies.