Target of rapamycin signaling in leukemia and lymphoma

Novel pharmacological and dietary approaches to target mTOR in B-cell acute lymphoblastic leukemia

High-risk subtypes of B-cell acute lymphoblastic leukemia (B-ALL) are frequently associated with aberrant activation of tyrosine kinases (TKs). These include Ph+ B-ALL driven by BCR-ABL, and Ph-like B-ALL that carries other chromosomal rearrangements and/or gene mutations that activate TK signaling. Currently, the tyrosine kinase inhibitor (TKI) dasatinib is added to chemotherapy as standard of care in Ph+ B-ALL, and TKIs are being tested in clinical trials for Ph-like B-ALL. However, growth factors and nutrients in the leukemia microenvironment can support cell cycle and survival even in cells treated with TKIs targeting the driving oncogene. These stimuli converge on the kinase mTOR, whose elevated activity is associated with poor prognosis. In preclinical models of Ph+ and Ph-like B-ALL, mTOR inhibitors strongly enhance the anti-leukemic efficacy of TKIs. Despite this strong conceptual basis for targeting mTOR in B-ALL, the first two generations of mTOR inhibitors tested clinically (rapalogs and mTOR kinase inhibitors) have not demonstrated a clear therapeutic window. The aim of this review is to introduce new therapeutic strategies to the management of Ph-like B-ALL. We discuss novel approaches to targeting mTOR in B-ALL with potential to overcome the limitations of previous mTOR inhibitor classes. One approach is to apply third-generation bi-steric inhibitors that are selective for mTOR complex-1 (mTORC1) and show preclinical efficacy with intermittent dosing. A distinct, non-pharmacological approach is to use nutrient restriction to target signaling and metabolic dependencies in malignant B-ALL cells. These two new approaches could potentiate TKI efficacy in Ph-like leukemia and improve survival.

Construction of a DLBCL Prognostic Signature Based on Tumor Microenvironment

BACKGROUNDS

Diffuse large B-cell lymphoma (DLBCL) is a common curable non-Hodgkin's lymphoma. Patients with this disease can be cured after the R-CHOP immunochemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone). Nonetheless, most cured patients will relapse again and have dismal prognosis. In this study, we aim to identify a potential biomarker by analyzing gene expression data, and to predict patient's survival rate by constructing a risk model.

METHODS

Firstly, mRNA chip data (GSE87371) and clinical data of DLBCL patients were obtained from Gene Expression Omnibus (GEO). Samples were scored with estimate package. The obtained stromal score (P < 0.05) and ESTIMATE score (P < 0.05) were significantly correlated with the prognosis. Differentially expressed genes (DEGs) screened through the above two scoring methods were intersected and 279 DEGs were obtained. Next, five feature genes (CD163, CLEC4A, COL15A1, GABRB2, IFIT3) were identified by univariate Cox, LASSO and multivariate Cox regression analyses to establish a risk evaluation model. Thereafter, the 5-gene risk model was validated on a validation set. ROC and survival analyses were performed to assess the performance of the model.

RESULTS

Further analysis showed that the risk model was capable of independently determining the prognosis of patients, and a nomogram was sequentially established.

CONCLUSIONS

Authors screened DEGs related to ESTIMATE and stromal scores from GEO database, and established a 5-gene prognostic signature through Cox regression analysis and LASSO analysis. The risk model and nomogram will help individuals accurately predict the prognosis of DLBCL patients.

New biomarkers and therapeutic strategies in acute lymphoblastic leukemias: Recent advances

Acute lymphoblastic leukemia (ALL) represents a heterogeneous group of hematologic malignancies, and it is normally characterized by an aberrant proliferation of immature lymphoid cells. Moreover, dysregulation of multiple signaling pathways that normally regulate cellular transcription, growth, translation, and proliferation is frequently encountered in this malignancy. ALL is the most frequent tumor in childhood, and adult ALL patients still correlate with poor survival. This review focuses on modern therapies in ALL that move beyond standard chemotherapy, with a particular emphasis on immunotherapeutic approaches as new treatment strategies. Bi-specific T-cell Engagers (BiTE) antibodies, the chimeric antigen receptor (CAR)-T cells, or CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats [CRISPR]-associated nuclease 9) represent other new innovative approaches for this disease. Target and tailored therapy could make the difference in previously untreatable cases, i.e., precision and personalized medicine. Clinical trials will help to select the most efficient novel therapies in ALL management and to integrate them with existing treatments to achieve durable cures.

Baicalein induces apoptosis and autophagy of breast cancer cells via inhibiting PI3K/AKT pathway in vivo and vitro

Purpose

Baicalein, a widely used Chinese herbal medicine, has shown anticancer effects on many types of human cancer cell lines. However, little is known about the underlying mechanism in human breast cancer cells. In this study, we examined the apoptotic and autophagic pathways activated following baicalein treatment in human breast cancer cells in vitro and in vivo.

Materials and methods

In in vitro study, we used MTT and clone formation assay to confirm the inhibitory role of baicalein on proliferation of MCF-7 and MDA-MB-231 breast cancer cells. Apoptosis was detected employing Hoechst 33258 staining, JC-1 staining, and flow cytometry. Autophagy was monitored by acridine orange staining and transmission electron microscopy observation. Quantitative real-time PCR and Western blot analysis were employed to study the effects of baicalein on PI3K/AKT signaling components of MCF-7 and MDA-MB-231 breast cancer cells. In in vivo study, the effect of baicalein was tested with a breast cancer cells transplantation tumor model.

Results

Our study showed that baicalein has the potential to suppress cell proliferation, induce apoptosis and autophagy of breast cancer cells in vitro and in vivo. Furthermore, baicalein significantly downregulated the expression of p-AKT, p-mTOR, NF-κB, and p-IκB while enhancing the expression of IκB in MCF-7 and MDA-MB-231 cells. It also decreased the p-AKT/AKT and p-mTOR/mTOR ratios.

Conclusion

Our study demonstrated that baicalein induces apoptosis and autophagy of breast cancer cells via inhibiting the PI3K/AKT signaling pathway in vivo and vitro. Our study revealed that baicalein may be a potential therapeutic agent for breast cancer.

A Blood Pact: the Significance and Implications of eIF4E on Lymphocytic Leukemia

Elevated levels of eukaryotic initiation factor 4E (eIF4E) are implicated in neoplasia, with cumulative evidence pointing to its role in the etiopathogenesis of hematological diseases. As a node of convergence for several oncogenic signaling pathways, eIF4E has attracted a great deal of interest from biologists and clinicians whose efforts have been targeting this translation factor and its biological circuits in the battle against leukemia. The role of eIF4E in myeloid leukemia has been ascertained and drugs targeting its functions have found their place in clinical trials. Little is known, however, about the pertinence of eIF4E to the biology of lymphocytic leukemia and a paucity of literature is available in this regard that prospectively evaluates the topic to guide practice in hematological cancer. A comprehensive analysis on the significance of eIF4E translation factor in the clinical picture of leukemia arises, therefore, as a compelling need. This review presents aspects of eIF4E involvement in the realm of the lymphoblastic leukemia status; translational control of immunological function via eIF4E and the state-of-the-art in drugs will also be outlined.

An oral quinoline derivative, MPT0B392, causes leukemic cells mitotic arrest and overcomes drug resistant cancer cells

Despite great advances in the treatment of acute leukemia, a renaissance of current chemotherapy needs to be improved. The present study elucidates the underlying mechanism of a new synthetic quinoline derivative, MPT0B392 (B392) against acute leukemia and its potential anticancer effect in drug resistant cells. B392 caused mitotic arrest and ultimately led to apoptosis. It was further demonstrated to be a novel microtubule-depolymerizing agent. The effects of oral administration of B392 showed relative potent anti-leukemia activity in an in vivo xenograft model. Further investigation revealed that B392 triggered induction of the mitotic arrest, followed by mitochondrial membrane potential loss and caspases cleavage by activation of c-Jun N-terminal kinase (JNK). In addition, B392 enhanced the cytotoxicity of sirolimus in sirolimus-resistant acute leukemic cells through inhibition of Akt/mTOR pathway and Mcl-1 protein expression, and also was active in the p-glycoprotein (p-gp)-overexpressing National Cancer Institute/Adriamycin-Resistant cells with little susceptibility to p-gp. Taken together, B392 has potential as an oral mitotic drug and adjunct treatment for drug resistant cancer cells.

mTOR inhibition enhances efficacy of dasatinib in ABL-rearranged Ph-like B-ALL

High-risk subtypes of B-cell acute lymphoblastic leukemia (B-ALL) include Philadelphia chromosome-positive (Ph+) B-ALL driven by the BCR-ABL1 oncogene and a more recently identified subtype known as BCR-ABL-like or Ph-like B-ALL. A hallmark of both Ph+ and Ph-like B-ALL is constitutive activation of tyrosine kinase signaling that is potentially targetable with tyrosine kinase inhibitors (TKIs). B-ALL cells also receive extracellular signals from the microenvironment that can maintain proliferation and survival following treatment with TKIs. Therefore, there is strong rationale for combining TKIs with other therapies targeting signal transduction pathways. Here we show that combinations of the ABL-directed TKI dasatinib with mTOR kinase inhibitors (TOR-KIs) are more effective than TKI alone against patient-derived Ph-like B-ALL cells harboring rearrangements of ABL1 or ABL2. We also report the establishment of a new human Ph-like B-ALL cell line that is stromal cell-independent in vitro and can be used for xenograft experiments in vivo. These findings provide rationale for clinical testing of TKI plus TOR-KIs in children and adults with Ph-like B-ALL and a new experimental tool to test promising therapeutic strategies in this poor prognosis subtype of B-ALL.

TAK-228 (formerly MLN0128), an investigational dual TORC1/2 inhibitor plus paclitaxel, with/without trastuzumab, in patients with advanced solid malignancies

PURPOSE

This phase I trial evaluated the safety, pharmacokinetic profile, and antitumor activity of investigational oral TORC1/2 inhibitor TAK-228 plus paclitaxel, with/without trastuzumab, in patients with advanced solid malignancies.

METHODS

Sixty-seven patients received TAK-228 6-40 mg via three dosing schedules; once daily for 3 days (QDx3d QW) or 5 days per week (QDx5d QW), and once weekly (QW) plus paclitaxel 80 mg/m² (dose-escalation phase, n = 47) and with/without trastuzumab 2 mg/kg (expansion phase, n = 20). Doses were escalated using a modified 3 + 3 design, based upon dose-limiting toxicities in cycle 1.

RESULTS

TAK-228 pharmacokinetics exhibited dose-dependent increase in exposure when dosed with paclitaxel and no apparent differences when administered with or 24 h after paclitaxel. Dose-limiting toxicities were dehydration, diarrhea, stomatitis, fatigue, rash, thrombocytopenia, neutropenia, leukopenia, and nausea. The maximum tolerated dose of TAK-228 was determined as 10-mg QDx3d QW; the expansion phase proceeded with 8-mg QDx3d QW. Overall, the most common grade ≥3 drug-related toxicities were neutropenia (21%), diarrhea (12%), and hyperglycemia (12%). Of 54 response-evaluable patients, eight achieved partial response and six had stable disease lasting ≥6 months.

CONCLUSION

TAK-228 demonstrated a safety profile consistent with other TORC inhibitors and promising preliminary antitumor activity in a range of tumor types; no meaningful difference was noted in the pharmacokinetics of TAK-228 when administered with or 24 h after paclitaxel. These findings support further investigation of TAK-228 in combination with other agents including paclitaxel, with/without trastuzumab, in patients with advanced solid tumors. CLINICALTRIALS.

GOV IDENTIFIER

NCT01351350.

Control of B lymphocyte development and functions by the mTOR signaling pathways

Mechanistic target of rapamycin (mTOR) is a serine/threonine kinase originally discovered as the molecular target of the immunosuppressant rapamycin. mTOR forms two compositionally and functionally distinct complexes, mTORC1 and mTORC2, which are crucial for coordinating nutrient, energy, oxygen, and growth factor availability with cellular growth, proliferation, and survival. Recent studies have identified critical, non-redundant roles for mTORC1 and mTORC2 in controlling B cell development, differentiation, and functions, and have highlighted emerging roles of the Folliculin-Fnip protein complex in regulating mTOR and B cell development. In this review, we summarize the basic mechanisms of mTOR signaling; describe what is known about the roles of mTORC1, mTORC2, and the Folliculin/Fnip1 pathway in B cell development and functions; and briefly outline current clinical approaches for targeting mTOR in B cell neoplasms. We conclude by highlighting a few salient questions and future perspectives regarding mTOR in B lineage cells.

miR-340 Inhibits Proliferation and Induces Apoptosis in Gastric Cancer Cell Line SGC-7901, Possibly via the AKT Pathway

BACKGROUND Gastric cancer is among the most common types of cancer, with high morbidity and mortality. MicroRNAs (miRNAs) play vital roles in the tumorigenesis and biology of gastric cancer. This study aimed to reveal the role of miR-340 in gastric cancer cell proliferation and apoptosis and to elucidate the potential mechanisms. MATERIAL AND METHODS Human gastric cancer cells SGC-7901 were used in this study for cell transfection with miR-340 mimic or inhibitor. After transfection, cell viability, proliferation, and apoptosis were examined by MTT, BrdU, and flow cytometry assays, respectively. The protein level changes of p27, p21, Caspase 3 (CASP3), B cell lymphoma 2 (BCL2), BCL2-associated X protein (BAX), and v-AKT murine thymoma viral oncogene (AKT) were detected by Western blot. RESULTS Overexpression of miR-340 significantly reduced cell viability and proliferation (P<0.01), and induced cell apoptosis (P<0.01) of SGC-7901. miR-340 elevated the protein level of cell cycle inhibitor p27, but did not affect the level of p21. Apoptosis-related factors pro-CASP3, cleaved-CASP3, and BAX were promoted, and BCL2 was inhibited by miR-340. miR-340 also suppressed the phosphorylation of AKT. Opposite effects were detected when SGC-7901 cells were transfected with miR-340 inhibitor. CONCLUSIONS These results indicate that miR-340 can inhibit proliferation and induce apoptosis of SGC-7901 cells, suggesting its roles in protecting against gastric cancer. The roles of miR-340 in gastric cancer cells may be associated with its regulation of the AKT pathway. Thus, miR-340 may be a potential therapeutic strategy for gastric cancer treatment.

Phase Ib trial of the PI3K/mTOR inhibitor voxtalisib (SAR245409) in combination with chemoimmunotherapy in patients with relapsed or refractory B-cell malignancies

This phase Ib, dose-escalation study investigated the maximum tolerated dose (MTD), recommended phase II dose (RP2D), safety, pharmacokinetics (PK) and preliminary efficacy of the pan-class I phosphoinositide 3-kinase (PI3K) and mechanistic target of rapamycin (mTOR) inhibitor voxtalisib [30 or 50 mg twice daily (BID)], in combination with rituximab (voxtalisib+rituximab) or rituximab plus bendamustine (voxtalisib+rituximab+bendamustine), in relapsed or refractory indolent B-cell non-Hodgkin lymphoma (NHL), mantle cell lymphoma and chronic lymphocytic leukaemia (CLL). MTD and RP2D of voxtalisib were determined using a 3 + 3 dose-escalation design. Adverse events (AEs), plasma PK and disease response were recorded. Thirty-seven patients were enrolled. The RP2D of voxtalisib in combination with rituximab or rituximab+bendamustine was 50 mg BID. Four patients experienced a total of five dose-limiting toxicities. The most frequent AEs were nausea (45·9%), fatigue (37·8%) headache (32·4%) and pyrexia (32·4%). The most frequent grade ≥3 AEs were neutropenia (27·0%), thrombocytopenia (24·3%), anaemia (16·2%) and febrile neutropenia (10·8%). Voxtalisib PK parameters were not affected by co-administration with rituximab or rituximab+bendamustine. Of 35 efficacy-evaluable patients, four (11·4%) achieved complete response and 13 (37·1%) achieved partial response. Voxtalisib, in combination with rituximab or rituximab+bendamustine, demonstrated an acceptable safety profile and encouraging anti-tumour activity in relapsed or refractory B-cell malignancies.

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.

mTOR kinase inhibitors synergize with histone deacetylase inhibitors to kill B-cell acute lymphoblastic leukemia cells

High activity of the mechanistic target of rapamycin (mTOR) is associated with poor prognosis in pre-B-cell acute lymphoblastic leukemia (B-ALL), suggesting that inhibiting mTOR might be clinically useful. However, emerging data indicate that mTOR inhibitors are most effective when combined with other target agents. One strategy is to combine with histone deacetylase (HDAC) inhibitors, since B-ALL is often characterized by epigenetic changes that silence the expression of pro-apoptotic factors. Here we tested combinations of mTOR and pan-HDAC inhibitors on B-ALL cells, including both Philadelphia chromosome-positive (Ph+) and non-Ph cell lines. We found that mTOR kinase inhibitors (TOR-KIs) synergize with HDAC inhibitors to cause apoptosis in B-ALL cells and the effect is greater when compared to rapamycin plus HDAC inhibitors. The combination of TOR-KIs with the clinically approved HDAC inhibitor vorinostat increased apoptosis in primary pediatric B-ALL cells in vitro. Mechanistically, TOR-KI and HDAC inhibitor combinations increased expression of pro-death genes, including targets of the Forkhead Box O (FOXO) transcription factors, and increased sensitivity to apoptotic triggers at the mitochondria. These findings suggest that targeting epigenetic factors can unmask the cytotoxic potential of TOR-KIs towards B-ALL cells.

Targeting of hyperactivated mTOR signaling in high-risk acute lymphoblastic leukemia in a pre-clinical model

Despite increasingly successful treatment of pediatric ALL, up to 20% of patients encounter relapse. By current biomarkers, the majority of relapse patients is initially not identified indicating the need for prognostic and therapeutic targets reflecting leukemia biology. We previously described that rapid engraftment of patient ALL cells transplanted onto NOD/SCID mice (short time to leukemia, TTL^short) is indicative of early patient relapse. Gene expression profiling identified genes coding for molecules involved in mTOR signaling to be associated with TTL^short/early relapse leukemia.

Here, we now functionally address mTOR signaling activity in primograft ALL samples and evaluate mTOR pathway inhibition as novel treatment strategy for high-risk ALL ex vivo and in vivo. By analysis of S6-phosphorylation downstream of mTOR, increased mTOR activation was found in TTL^short/high-risk ALL, which was effectively abrogated by mTOR inhibitors resulting in decreased leukemia proliferation and growth. In a preclinical setting treating individual patient-derived ALL in vivo, mTOR inhibition alone, and even more pronounced together with conventional remission induction therapy, significantly delayed post-treatment leukemia reoccurrence in TTL^short/high-risk ALL.

Thus, the TTL^short phenotype is functionally characterized by hyperactivated mTOR signaling and can effectively be targeted ex vivo and in vivo providing a novel therapeutic strategy for high-risk ALL.

Emerging immunotherapy and strategies directly targeting B cells for the treatment of diffuse large B-cell lymphoma

During the last decade, significant prolonged survival in diffusive large B-cell lymphoma (DLBCL) has been observed. The efficacy of initial treatment improved mostly due to addition of a chimeric anti-CD20 monoclonal antibody (rituximab) to standard chemotherapeutic regimens. Moreover, accurate understanding of DLBCL pathogenesis and remarkable progress in gene expression profiling have led to the development of a variety of tumor-specific regimens. Novel agents target directly the pathways involved in signal transduction, lead to apoptosis and cancer cells differentiation. In this article, we mainly focus on new treatment options, such as monoclonal antibodies, tyrosine kinase inhibitors and immunomodulatory drugs, currently investigated in aggressive B-cell lymphoma with particular attention to DLBCL type.

Molecular effects of the phosphatidylinositol-3-kinase inhibitor NVP-BKM120 on T and B-cell acute lymphoblastic leukaemia

BACKGROUND

Constitutive activation of the PI3K pathway in T cell acute lymphoblastic leukaemia (T-ALL) has been reported and in a mouse model, PI3K activation, together with MYC, cooperates in Burkitt lymphoma (BL) pathogenesis. We investigated the effects of NVP-BKM120, a potent pan-class I PI3K inhibitor, in lymphoblastic leukaemia cell lines.

METHODS

Effects of NVP-BKM120 on cell viability, clonogenicity, apoptosis, cell cycle, cell signalling and autophagy were assessed in vitro on T-ALL (Jurkat and MOLT-4) and BL (Daudi and NAMALWA) cell lines.

RESULTS

NVP-BKM120 treatment decreased cell viability and clonogenic growth in all tested cells. Moreover, the drug arrested cell cycling in association with a decrease in Cyclin B1 protein levels, and increased apoptosis. Immunoblotting analysis of cells treated with the drug revealed decreased phosphorylation, in a dose-dependent manner, of AKT, mTOR, P70S6K and 4EBP1, with stable total protein levels. Additionally, we observed a dose-dependent decrease in BAD phosphorylation, in association with augmented BAX:BCL2 ratio. Quantification of autophagy showed a dose-dependent increase in acidic vesicular organelles in all cells tested.

CONCLUSION

In summary, our present study establishes that NVP-BKM120 presents an effective antitumour activity against T-ALL and BL cell lines.

Short-Term PTEN Inhibition Improves In Vitro Activation of Primordial Follicles, Preserves Follicular Viability, and Restores AMH Levels in Cryopreserved Ovarian Tissue From Cancer Patients

Introduction

In vitro activation and growth of primordial dormant follicles to produce fertilizable oocytes would provide a useful instrument for fertility preservation. The employment of Phosphatase and TENsin homolog (PTEN) inhibitors, in combination with Protein kinase B (Akt) stimulating molecules, has been previously employed to increase follicular activation through the stimulation of the PTEN-Akt pathway.

Methods

We aim to establish improved in vitro activation also for cancer patients whose ovarian tissue has already been cryopreserved. Fresh and previously cryopreserved human ovarian cortex were exposed to short-term, low-concentration and ovary-specific treatment with only a PTEN inhibitor.

Results

Our in vitro activation protocol enhances the activation mechanisms of primordial follicles in both fresh and cryopreserved samples, and enlarges growing populations without inducing apoptosis in either follicles or the surrounding stroma. Treatment augments estradiol secretion and restores the expression levels of the previously diminished Anti-Müllerian hormone by means of cryopreservation procedures. Genomic modulation of the relative expression of PTEN pathway genes was found in treated samples.

Conclusion

The in vitro activation protocol offers new alternatives for patients with cryopreserved tissue as it increases the pool of viable activated follicles available for in vitro growth procedures. The combination of ovarian tissue cryopreservation and in vitro activation of primordial follicles, the main ovarian reserve component, will be a major advancement in fertility preservation.

The Potential of Vitamin D-Regulated Intracellular Signaling Pathways as Targets for Myeloid Leukemia Therapy

The current standard regimens for the treatment of acute myeloid leukemia (AML) are curative in less than half of patients; therefore, there is a great need for innovative new approaches to this problem. One approach is to target new treatments to the pathways that are instrumental to cell growth and survival with drugs that are less harmful to normal cells than to neoplastic cells. In this review, we focus on the MAPK family of signaling pathways and those that are known to, or potentially can, interact with MAPKs, such as PI3K/AKT/FOXO and JAK/STAT. We exemplify the recent studies in this field with specific relevance to vitamin D and its derivatives, since they have featured prominently in recent scientific literature as having anti-cancer properties. Since microRNAs also are known to be regulated by activated vitamin D, this is also briefly discussed here, as are the implications of the emerging acquisition of transcriptosome data and potentiation of the biological effects of vitamin D by other compounds. While there are ongoing clinical trials of various compounds that affect signaling pathways, more studies are needed to establish the clinical utility of vitamin D in the treatment of cancer.

Regulation of the cell cycle and PI3K/Akt/mTOR signaling pathway by tanshinone I in human breast cancer cell lines

Breast cancer is the second leading cause of cancer‑related mortality in females worldwide. Therefore, identifying alternative strategies to combat the disease mortality is important. The aim of the present study was to investigate the effect of tanshinone I (Tan I) on the tumorigenicity of estrogen‑responsive MCF‑7 and estrogen‑independent MDA‑MB‑453 human breast cancer cells. The cytotoxicity of Tan I was evaluated using a Cell Counting Kit‑8 assay, the apoptosis and cell cycle distribution were detected using flow cytometry and the cell morphology was observed using a fluorescence microscope. In addition, the cell cycle regulatory proteins and apoptosis‑associated proteins involved in the phosphatidylinositide 3‑kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway were detected using western blot analysis using specific protein antibodies. The MCF‑7 and MDA‑MB‑453 cells were equally sensitive to Tan I regardless of their responsiveness to estrogen. Tan I exerted similar antiproliferative activities and induction of apoptosis, resulting in S phase arrest accompanied by decreases in cyclin B and increases in cyclin E and cyclin A proteins, which may have been associated with the upregulation of cyclin‑dependent kinase inhibitors p21Cip1 and p27Kip1. In addition, Tan I was found to downregulate anti‑apoptotic and upregulate associated apoptotic components of the PI3K/Akt/mTOR signaling pathway. Notably, treatment with the PI3K inhibitor, LY294002, decreased the levels of phosphorylated (p)‑PI3K, p‑Akt and p‑mTOR. These results clearly indicated that the mechanism of action of Tan I involved, at least partially, an effect on the PI3K/Akt/mTOR signaling pathway, providing new information for anticancer drug design and development.

Positron emission tomographic monitoring of dual phosphatidylinositol-3-kinase and mTOR inhibition in anaplastic large cell lymphoma

Background

Dual phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibition offers an attractive therapeutic strategy in anaplastic large cell lymphoma depending on oncogenic nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) signaling. We tested the efficacy of a novel dual PI3K/mTOR inhibitor, NVP-BGT226 (BGT226), in two anaplastic large cell lymphoma cell lines in vitro and in vivo and performed an early response evaluation with positron emission tomography (PET) imaging using the standard tracer, 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) and the thymidine analog, 3′-deoxy-3′-[¹⁸F] fluorothymidine (FLT).

Methods

The biological effects of BGT226 were determined in vitro in the NPM-ALK positive cell lines SU-DHL-1 and Karpas299 by 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay, propidium iodide staining, and biochemical analysis of PI3K and mTOR downstream signaling. FDG-PET and FLT-PET were performed in immunodeficient mice bearing either SU-DHL-1 or Karpas299 xenografts at baseline and 7 days after initiation of treatment with BGT226. Lymphomas were removed for immunohistochemical analysis of proliferation and apoptosis to correlate PET findings with in vivo treatment effects.

Results

SU-DHL-1 cells showed sensitivity to BGT226 in vitro, with cell cycle arrest in G0/G1 phase and an IC₅₀ in the low nanomolar range, in contrast with Karpas299 cells, which were mainly resistant to BGT226. In vivo, both FDG-PET and FLT-PET discriminated sensitive from resistant lymphoma, as indicated by a significant reduction of tumor-to-background ratios on day 7 in treated SU-DHL-1 lymphoma-bearing animals compared with the control group, but not in animals with Karpas299 xenografts. Imaging results correlated with a marked decrease in the proliferation marker Ki67, and a slight increase in the apoptotic marker, cleaved caspase 3, as revealed by immunostaining of explanted lymphoma tissue.

Conclusion

Dual PI3K/mTOR inhibition using BGT226 is effective in ALK-positive anaplastic large cell lymphoma and can be monitored with both FDG-PET and FLT-PET early on in the course of therapy.

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.

Everolimus prolonged survival in transgenic mice with EGFR-driven lung tumors

Everolimus is an orally administered mTOR inhibitor. The effect, and mechanism of action, of everolimus on lung cancers with an epidermal growth factor receptor (EGFR) mutation remain unclear. Four gefitinib-sensitive and -resistant cell lines were used in the present work. Growth inhibition was determined using the MTT assay. Transgenic mice carrying the EGFR L858R mutation were treated with everolimus (10 mg/kg/day), or vehicle alone, from 5 to 20 weeks of age, and were then sacrificed. To evaluate the efficacy of everolimus in prolonging survival, everolimus (10 mg/kg/day) or vehicle was administered from 5 weeks of age. The four cell lines were similarly sensitive to everolimus. Expression of phosphorylated (p) mTOR and pS6 were suppressed upon treatment with everolimus in vitro, whereas the pAKT level increased. The numbers of lung tumors with a long axis exceeding 1mm in the everolimus-treated and control groups were 1.9 ± 0.9 and 9.4 ± 3.2 (t-test, p<0.001), respectively. pS6 was suppressed during eve r olimus treatment. Although apoptosis and autophagy were not induced in everolimus-treated EGFR transgenic mice, angiogenesis was suppressed. The median survival time in the everolimus-treated group (58.0 weeks) was significantly longer than that in the control group (31.2 weeks) (logrank test, p<0.001). These findings suggest that everolimus had an indirect effect on tumor formation by inhibiting angiogenesis and might be effective to treat lung tumors induced by an activating EGFR gene mutation.

Molecular therapeutic approaches for pediatric acute myeloid leukemia

Approximately two-thirds of children with acute myeloid leukemia (AML) are cured with intensive multi-agent chemotherapy. However, refractory and relapsed AML remains a significant source of childhood cancer mortality, highlighting the need for new therapies. Further therapy intensification with traditional cytotoxic chemotherapy in pediatric AML is not feasible given the risks of both short-term and long-term organ dysfunction. Substantial emphasis has been placed upon the development of molecularly targeted therapeutic approaches for adults and children with high-risk subtypes of AML with the goal of improving remission induction and minimizing relapse. Several promising agents are currently in clinical testing or late preclinical development for AML, including monoclonal antibodies against leukemia cell surface proteins, kinase inhibitors, proteasome inhibitors, epigenetic agents, and chimeric antigen receptor engineered T cell immunotherapies. Many of these therapies have been specifically tested in children with relapsed/refractory AML in Phase 1 and 2 trials with a smaller number of new agents under Phase 3 evaluation for children with de novo AML. Although successful identification and implementation of new drugs for children with AML remain a formidable challenge, enthusiasm for novel molecular therapeutic approaches is great given the potential for significant clinical benefit for children who do not have other curative options.

Resistance to mTOR kinase inhibitors in lymphoma cells lacking 4EBP1

Inhibitors of the mechanistic target of rapamycin (mTOR) hold promise for treatment of hematological malignancies. Analogs of the allosteric mTOR inhibitor rapamycin are approved for mantle cell lymphoma but have limited efficacy in other blood cancers. ATP-competitive "active-site" mTOR inhibitors produce more complete mTOR inhibition and are more effective than rapamycin in preclinical models of leukemia, lymphoma and multiple myeloma. In parallel to clinical trials of active-site mTOR inhibitors, it will be important to identify resistance mechanisms that might limit drug efficacy in certain patients. From a panel of diffuse large B-cell lymphoma cell lines, we found that the VAL cell line is particularly resistant to apoptosis in the presence of active-site mTOR inhibitors. Mechanistic investigation showed that VAL does not express eukaryotic initiation factor 4E-binding protein-1 (4EBP1), a key negative regulator of translation controlled by mTOR. Although VAL cells express the related protein 4EBP2, mTOR inhibitor treatment fails to displace eukaryotic initiation factor 4G from the mRNA cap-binding complex. Knockdown of eukaryotic initiation factor 4E, or re-expression of 4EBP1, sensitizes cells to apoptosis when treated with active-site mTOR inhibitors. These findings provide a naturally occurring example of 4EBP deficiency driving lymphoma cell resistance to active-site mTOR inhibitors.

Pediatric relapsed or refractory leukemia: new pharmacotherapeutic developments and future directions

Over the past 50 years, numerous advances in treatment have produced dramatic increases in the cure rates of pediatric leukemias. Despite this progress, the majority of children with relapsed leukemia are not expected to survive. With current chemotherapy regimens, approximately 15 % of children with acute lymphoblastic leukemia and 45 % of children with acute myeloid leukemia will have refractory disease or experience a relapse. Advances in the treatment of pediatric relapsed leukemia have not mirrored the successes of upfront therapy, and newer treatments are desperately needed in order to improve survival in these challenging patients. Recent improvements in our knowledge of cancer biology have revealed an extensive number of targets that have the potential to be exploited for anticancer therapy. These advances have led to the development of a number of new treatments that are now being explored in children with relapsed or refractory leukemia. Novel agents seek to exploit the same molecular aberrations that contribute to leukemia development and resistance to therapy. Newer classes of drugs, including monoclonal antibodies, tyrosine kinase inhibitors and epigenetic modifiers are transforming the treatment of patients who are not cured with conventional therapies. As the side effects of many new agents are distinct from those seen with conventional chemotherapy, these treatments are often explored in combination with each other or combined with conventional treatment regimens. This review discusses the biological rationale for the most promising new agents and the results of recent studies conducted in pediatric patients with relapsed leukemia.

Characteristic mTOR activity in Hodgkin-lymphomas offers a potential therapeutic target in high risk disease--a combined tissue microarray, in vitro and in vivo study

Background

Targeting signaling pathways is an attractive approach in many malignancies. The PI3K/Akt/mTOR pathway is activated in a number of human neoplasms, accompanied by lower overall and/or disease free survival. mTOR kinase inhibitors have been introduced in the therapy of renal cell carcinoma and mantle cell lymphoma, and several trials are currently underway. However, the pathological characterization of mTOR activity in lymphomas is still incomplete.

Methods

mTOR activity and the elements of mTOR complexes were investigated by immunohistochemistry on tissue microarrays representing different human non-Hodgkin-lymphomas (81 cases) and Hodgkin-lymphomas (87 cases). The expression of phospho-mTOR, phospho-4EBP1, phospho-p70S6K, phospho-S6, Rictor, Raptor and Bcl-2, Bcl-xL, Survivin and NF-kappaB-p50 were evaluated, and mTOR activity was statistically analyzed along with 5-year survival data. The in vitro and in vivo effect of the mTOR inhibitor rapamycin was also examined in human Hodgkin-lymphoma cell lines.

Results

The majority (>50%) of mantle cell lymphoma, Burkitt lymphoma, diffuse large B-cell lymphoma, anaplastic large-cell lymphoma and Hodgkin-lymphoma cases showed higher mTOR activity compared to normal lymphoid tissues. Hodgkin-lymphoma was characterized by high mTOR activity in 93% of the cases, and Bcl-xL and NF-kappaB expression correlated with this mTOR activity. High mTOR activity was observed in the case of both favorable and unfavorable clinical response. Low mTOR activity was accompanied by complete remission and at least 5-year disease free survival in Hodgkin-lymphoma patients. However, statistical analysis did not identify correlation beetween mTOR activity and different clinical data of HL patients, such as survival. We also found that Rictor (mTORC2) was not overexpressed in Hodgkin-lymphoma biopsies and cell lines. Rapamycin inhibited proliferation and induced apoptosis in Hodgkin-lymphoma cells both in vitro and in vivo, moreover, it increased the apoptotic effect of chemotherapeutic agents.

Conclusions

Targeting mTOR activity may be a potential therapeutic tool in lymphomas. The presence of mTOR activity probably indicates that the inclusion of mTOR inhibition in the therapy of Hodgkin-lymphomas may be feasible and beneficial, especially when standard protocols are ineffective, and it may also allow dose reduction in order to decrease late treatment toxicity. Most likely, the combination of mTOR inhibitors with other agents will offer the highest efficiency for achieving the best clinical response.

ERG transcriptional networks in primary acute leukemia cells implicate a role for ERG in deregulated kinase signaling

High expression of the E26 transforming sequence related gene (ERG) is associated with poor prognosis in a subgroup of leukemia patients with acute myeloid (AML) and acute T-lymphoblastic leukemia (T-ALL). In a previous study we proposed that ERG overexpression may deregulate several signaling cascades in acute leukemia. Herein, we further expand those studies by identifying a consensus of biological targets in primary blasts of newly diagnosed acute leukemia patients. Our findings of chromatin immunoprecipitation-on-chip of primary samples revealed 48 significantly enriched single genes including DAAM1 and NUMB. Significantly enriched signaling pathways included WNT/β-catenin, p53, and PI3K/AKT with ERG overexpression inducing dephosphorylation of AKT(Ser473) relative to non ERG expressing K562 cells. Cell based ERG overexpression studies also revealed drug resistance to multi-kinase inhibitor, BAY 43-9006 (Sorafenib) and to the tyrosine kinase inhibitor TKI258. Thus in primary leukemic cells, ERG may contribute to the dysregulation of kinase signaling, which results in resistance to kinase inhibitors.

MicroRNA-21 regulates the sensitivity of diffuse large B-cell lymphoma cells to the CHOP chemotherapy regimen

Numerous studies have demonstrated that microRNA-21 (miR-21), as an oncogene, is involved in the occurrence of many types of tumor and the sensitivity of tumor cells to chemotherapeutic drugs. In the present study, we investigated whether miR-21 is involved in regulating the sensitivity of the diffuse large B-cell lymphoma (DLBCL) cell line CRL2631 to the cyclophosphamide, vincristine, Adriamycin, and prednisone (CHOP) chemotherapeutic regimen. Knockdown of miR-21 with antisense oligonucleotides significantly increased the cytotoxic effects of the CHOP regimen in CRL2631 cells. A luciferase reporter assay showed that PTEN is a target gene of miR-21 in CRL2631 cells, and subsequent experiments demonstrated that miR-21 impacts the PI3K/AKT signaling pathway through the regulation of PTEN, thereby affecting cellular sensitivity to the CHOP chemotherapeutic regimen. Furthermore, knockdown of NF-κB decreased miR-21 expression and sensitized CRL2631 cells to CHOP treatment. These results provide evidence that it may be possible to overcome microRNA-based DLBCL drug resistance.

Cellular entry of human papillomavirus type 16 involves activation of the phosphatidylinositol 3-kinase/Akt/mTOR pathway and inhibition of autophagy

The mammalian target of rapamycin (mTOR) downstream of phosphatidylinositol 3-kinase (PI3K) in the growth factor receptor (GFR) pathway is a crucial metabolic sensor that integrates growth factor signals in cells. We recently showed that human papillomavirus (HPV) type 16 exposure activates signaling from GFRs in human keratinocytes. Thus, we predicted that the virus would induce the PI3K/mTOR pathway upon interaction with host cells. We detected activation of Akt and mTOR several minutes following exposure of human keratinocytes to HPV type 16 (HPV16) pseudovirions. Activated mTOR induced phosphorylation of the mTOR complex 1 substrates 4E-BP1 and S6K, which led to induction of the functional protein translational machinery. Blockade of epidermal GFR (EGFR) signaling revealed that each of these events is at least partially dependent upon EGFR activation. Importantly, activation of PI3K/Akt/mTOR signaling inhibited autophagy in the early stages of virus-host cell interaction. Biochemical and genetic approaches revealed critical roles for mTOR activation and autophagy suppression in HPV16 early infection events. In summary, the HPV-host cell interaction stimulates the PI3K/Akt/mTOR pathway and inhibits autophagy, and in combination these events benefit virus infection.

Efficacy of the investigational mTOR kinase inhibitor MLN0128/INK128 in models of B-cell acute lymphoblastic leukemia

The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase whose activity contributes to leukemia proliferation and survival. Compounds targeting the mTOR active site inhibit rapamycin-resistant functions and have enhanced anticancer activity in mouse models. MLN0128 (formerly known as INK128) is a novel, orally active mTOR kinase inhibitor currently in clinical development. Here, we evaluated MLN0128 in preclinical models of B-cell acute lymphoblastic leukemia (B-ALL). MLN0128 suppressed proliferation of B-ALL cell lines in vitro and reduced colony formation by primary human leukemia cells from adult and pediatric B-ALL patients. MLN0128 also boosted the efficacy of dasatinib (DA) in Philadelphia Chromosome-positive (Ph+) specimens. In a syngeneic mouse model of lymphoid BCR-ABL+ disease, daily oral dosing of MLN0128 rapidly cleared leukemic outgrowth. In primary xenografts of Ph+ B-ALL specimens, MLN0128 significantly enhanced the efficacy of DA. In non-Ph B-ALL xenografts, single agent MLN0128 had a cytostatic effect that was most pronounced in mice with low disease burden. In all in vivo models, MLN0128 was well tolerated and did not suppress endogenous bone marrow proliferation. These findings support the rationale for clinical testing of MLN0128 in both adult and pediatric B-ALL and provide insight towards optimizing therapeutic efficacy of mTOR kinase inhibitors.

Down-regulation of the PI3K/Akt signaling pathway and induction of apoptosis in CA46 Burkitt lymphoma cells by baicalin

Background

Baicalin, a flavone present in Scutellaria baicalensis Georgi, inhibits the growth of human leukemia and myeloma cells through induction of apoptosis.

Methods

The present study was undertaken to ascertain whether cultured Burkitt lymphoma cells undergo apoptosis when treated with baicalin. Growth rates were measured using MTT and colony formation assays, and induction of apoptosis was quantified using Annexin V and DNA fragmentation assays. Mechanisms underlying observed growth suppression were examined using Western blotting.

Results

Treatment of CA46 Burkitt lymphoma cells with baicalin for 48 h markedly decreased the rate of cell proliferation; an IC₅₀ value of 10 μM was obtained. Colony formation was almost fully suppressed at 10 μM baicalin. CA46 cells underwent apoptosis in response to baicalin treatment as evidenced by an increase in the percentage of cells stainable with Annexin V, by increased DNA fragmentation, and by activation of the intrinsic (mitochondrial) pathway for cell death as characterized by increased expression of the cleaved forms of caspase-9, caspase-3, and poly (ADP-ribose) polymerase. Additionally, baicalin was found to down-regulate anti-apoptotic and up-regulate apoptotic components of the phosphatidylinositide-3-kinase (PI3K)/serine/threonine kinase (Akt) signaling pathway.

Conclusions

The concentrations at which baicalin altered expression of components of the PI3K/Akt pathway in CA46 cells were comparable to those that suppressed growth and induced apoptosis, supporting the hypothesis that the observed growth-inhibitory and apoptosis-inducing actions of baicalin in these cells are mediated by down-regulation of this pathway.

The in vivo evaluation of active-site TOR inhibitors in models of BCR-ABL+ leukemia

Preclinical evaluation of candidate anticancer compounds requires appropriate animal models. Most commonly, solid tumor xenograft systems are employed in which immunocompromised mice are implanted with human cancer cell lines. Genetically engineered mouse models of solid tumors are also frequently employed. Both of these approaches can also be applied to studies of hematological malignancies. In this chapter, we describe three types of mouse models of leukemia driven by the human BCR-ABL oncogene. We also discuss the application of these models to preclinical testing of active-site TOR inhibitors, a novel class of compounds that selectively target the ATP-binding pocket of the target of rapamycin (TOR) kinase.

Phosphoinositide 3-kinase/AKT/mTORC1/2 signaling determines sensitivity of Burkitt's lymphoma cells to BH3 mimetics

Burkitt's lymphoma (BL), driven by translocation and overexpression of the c-MYC gene, is an aggressive, highly proliferative lymphoma, and novel therapeutic strategies are required to overcome drug resistance following conventional treatments. The importance of the prosurvival BCL-2 family member BCL-X(L) in BL cell survival suggests that antagonistic BH3-mimetic compounds may have therapeutic potential. Here, we show that treatment of BL cell lines with ABT-737 induces caspase-3/7 activation and apoptosis with varying potency. Using selective inhibitors, we identify phosphoinositide 3-kinase (PI3K) as a proproliferative/survival pathway in BL cells and investigate the potential of combined pharmacologic inhibition of both the BCL-2 family and PI3K signaling pathway. PI3K/AKT inhibition and ABT-737 treatment induced synergistic caspase activation, augmented BL cell apoptosis, and rendered chemoresistant cells sensitive. Targeting mTORC1/2 with PP242 was also effective, either as a monotherapy or, more generally, in combination with ABT-737. The combined use of a dual specificity PI3K/mTOR inhibitor (PI 103) with ABT-737 proved highly efficacious. PI 103 treatment of BL cells was associated with an increase in BIM/MCL-1 expression ratios and loss of c-MYC expression. Furthermore, blocking c-MYC function using the inhibitor 10058-F4 also induced apoptosis synergistically with ABT-737, suggesting that maintenance of expression of BCL-2 family members and/or c-MYC by the PI3K/AKT/mTOR pathway could contribute to BL cell survival and resistance to ABT-737. The combined use of BH3 mimetics and selective mTORC1/2 inhibitors may therefore be a useful novel therapeutic approach for the treatment of B-cell malignancy, including chemoresistant lymphomas.

Emerging roles for mammalian target of rapamycin inhibitors in the treatment of solid tumors and hematological malignancies

PURPOSE OF REVIEW

The mammalian target of rapamycin (mTOR) is a key regulator of cell growth and survival in mammalian cells. mTOR pathways are frequently dysregulated in various malignancies, providing targets for new anticancer drugs and therapeutic strategies. Here, we summarize the clinical experience of trials using the first generation of mTOR inhibitors, the rapalogs, and highlight the development of the next generation of catalytic inhibitors of the pathway.

RECENT FINDINGS

mTOR inhibitors have shown major clinical activity in the treatment of renal cell carcinoma and two rapalogs have been approved for treatment of this malignancy. Recently, clinically significant trials with these agents were conducted in mantle cell lymphoma, pancreatic neuroendocrine tumors and astrocytomas. There are also promising results emerging in sarcomas, breast cancer and lung carcinoma. Multiple agents targeting mTOR, belonging to the new class of catalytic inhibitors with activity against both mTORC1 and mTORC2, are currently in various stages of preclinical and clinical development.

SUMMARY

The rapalogs are the first mTOR inhibitors to show promising, yet modest, antitumor effects. To fully exploit the potential of targeting this pathway, it will be important to better understand the mechanisms of action and precise targets of the various inhibitors. Moreover, definition of biomarkers of susceptibility and identification of predictors and/or correlates to drug resistance will substantially advance this area.

New therapeutic targets and drugs in non-Hodgkin's lymphoma

PURPOSE OF REVIEW

Although enormous progress has been made in treating non-Hodgkin's lymphoma (NHL), and some patients can be cured with combination immunochemotherapy, patients with relapsed and refractory lymphoma often succumb to their disease. Advances in our understanding of lymphoma biology and molecular pathogenesis are yielding new therapeutic targets.

RECENT FINDINGS

This article reviews NHL biology and describes how our understanding of molecular pathogenesis is leading to the discovery of many therapeutic targets, including the cell signaling and cell cycle regulatory proteins, pro-apoptotic family members, the B-cell antigen receptor (BCR), and histone deacetylase. Recent preclinical and clinical data with inhibitors of phosphatidylinositol 3-kinase, AKT, mammalian target of rapamycin, histone deacetylase, bcl-2, and the Bruton's tyrosine kinase, a pivotal enzyme in the BCR pathway, are discussed.

SUMMARY

Understanding these novel targets in the context of NHL biology will bring new therapies and allow us to develop new therapeutic platforms for the treatment of relapsed and refractory NHL, and will hopefully improve the clinical outcome for these patients.

Redeployment-based drug screening identifies the anti-helminthic niclosamide as anti-myeloma therapy that also reduces free light chain production

Despite recent therapeutic advancements, multiple myeloma (MM) remains incurable and new therapies are needed, especially for the treatment of elderly and relapsed/refractory patients. We have screened a panel of 100 off-patent licensed oral drugs for anti-myeloma activity and identified niclosamide, an anti-helminthic. Niclosamide, at clinically achievable non-toxic concentrations, killed MM cell lines and primary MM cells as efficiently as or better than standard chemotherapy and existing anti-myeloma drugs individually or in combinations, with little impact on normal donor cells. Cell death was associated with markers of both apoptosis and autophagy. Importantly, niclosamide rapidly reduced free light chain (FLC) production by MM cell lines and primary MM. FLCs are a major cause of renal impairment in MM patients and light chain amyloid and FLC reduction is associated with reversal of tissue damage. Our data indicate that niclosamides anti-MM activity was mediated through the mitochondria with rapid loss of mitochondrial membrane potential, uncoupling of oxidative phosphorylation and production of mitochondrial superoxide. Niclosamide also modulated the nuclear factor-κB and STAT3 pathways in MM cells. In conclusion, our data indicate that MM cells can be selectively targeted using niclosamide while also reducing FLC secretion. Importantly, niclosamide is widely used at these concentrations with minimal toxicity.

The Role of mTOR Inhibitors for the Treatment of B-Cell Lymphomas

Despite the fact that the majority of lymphomas initially respond to treatment, many patients relapse and die from disease that is refractory to current regimens. The need for new treatment strategies in lymphomas has led to the investigation and evaluation of novel agents that target cellular pathways. The mammalian target of rapamycin (mTOR) is a representative pathway that may be implicated in lymphomagenesis. Rapamycin and especially its derivatives (temsirolimus, everolimus, and deforolimus) represent the first described mTOR inhibitors. These agents have shown promising results in the treatment of lymphoid malignancies. On the other hand, new ATP-competitive mTOR inhibitors that provoke a broader inhibition of mTOR activity are in early stages of clinical development. The purpose of this paper is to summarize the existing knowledge about mTOR inhibitors and their use in the treatment of B-cell lymphomas. Relevant issues regarding mTOR biology in general as well as in B-cell lymphoid neoplasms are also discussed in short.