Targeting the PI3K/Akt/mTOR signaling pathway in B-precursor acute lymphoblastic leukemia and its therapeutic potential

B-precursor acute lymphoblastic leukemia (B-pre ALL) is a malignant disorder characterized by the abnormal proliferation of B-cell progenitors. The prognosis of B-pre ALL has improved in pediatric patients, but the outcome is much less successful in adults. Constitutive activation of the phosphatidylinositol 3-kinase (PI3K), Akt and the mammalian target of rapamycin (mTOR) (PI3K/Akt/mTOR) network is a feature of B-pre ALL, where it strongly influences cell growth and survival. RAD001, a selective mTORC1 inhibitor, has been shown to be cytotoxic against many types of cancer including hematological malignancies. To investigate whether mTORC1 could represent a target in the therapy of B-pre ALL, we treated cell lines and adult patient primary cells with RAD001. We documented that RAD001 decreased cell viability, induced cell cycle arrest in G0/G1 phase and caused apoptosis in B-pre ALL cell lines. Autophagy was also induced, which was important for the RAD001 cytotoxic effect, as downregulation of Beclin-1 reduced drug cytotoxicity. RAD001 strongly synergized with the novel allosteric Akt inhibitor MK-2206 in both cell lines and patient samples. Similar results were obtained with the combination CCI-779 plus GSK 690693. These findings point out that mTORC1 inhibitors, either as a single agent or in combination with Akt inhibitors, could represent a potential therapeutic innovative strategy in B-pre ALL.

Effects of ectopic expression of NGAL on doxorubicin sensitivity

Neutrophil gelatinase-associated lipocalin (NGAL, a.k.a Lnc2) is a member of the lipocalin family which has diverse roles including stabilizing matrix metalloproteinase-9 from auto-degradation and as siderocalins which are important in the transport of iron. NGAL also has important biological functions involved in immunity and inflammation as well as responses to kidney damage. NGAL expression has also been associated with certain neoplasia and is important in the metastasis of breast cancer. Many advanced cancer patients have elevated levels of NGAL in their urine and it has been proposed that NGAL may be a prognostic indicator for certain cancers (e.g. breast, brain, and others). NGAL expression is detected in response to various chemotherapeutic drugs including doxorubicin and docetaxel. We were interested in the roles of NGAL expression in cancer and whether it is associated with chemotherapeutic drug resistance. In the present study, we investigated whether increased NGAL expression led to resistance to the chemotherapeutic drug doxorubicin in normal breast epithelial cells (MCF-10A), breast cancer cells (MCF-7), and colorectal cancer cells (HT-29). We infected the various cell lines with a retrovirus encoding NGAL which we constructed. Increased NGAL expression was readily detected in the NGAL-infected cells but not the empty vector-infected cells. However, increased NGAL expression did not alter the sensitivity of the cells to the chemotherapeutic drug doxorubicin. Thus, although NGAL expression is often detected after chemotherapeutic drug treatment, it by itself, does not lead to doxorubicin resistance.

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.

Cytoplasmic localization of DGKζ exerts a protective effect against p53-mediated cytotoxicity

The transcription factor p53 plays a crucial role in coordinating the cellular response to various stresses. Therefore, p53 protein levels and activity need to be kept under tight control. We report here that diacylglycerol kinase ζ (DGKζ) binds to p53 and modulates its function both in the cytoplasm and nucleus. DGKζ, one of the DGK family that metabolizes a lipid second messenger diacylglycerol, localizes primarily to the nucleus in various cell types. Recently, reports have described that excitotoxic stress induces DGKζ nucleocytoplasmic translocation in hippocampal neurons. In this study, we found that cytoplasmic DGKζ attenuates p53-mediated cytotoxicity against doxorubicin-induced DNA damage by facilitating cytoplasmic anchoring and degradation of p53 through a ubiquitin–proteasome system. Concomitantly, decreased levels of nuclear DGKζ engender down-regulation of p53 transcriptional activity. Consistent with these in vitro cellular experiments, DGKζ-deficient brain exhibits high levels of p53 protein after kainate-induced seizures and even under normal conditions. These findings provide novel insights into the regulation of p53 function and suggest that DGKζ serves as a sentinel to control p53 function both during normal homeostasis and in stress responses.

Ectopic NGAL expression can alter sensitivity of breast cancer cells to EGFR, Bcl-2, CaM-K inhibitors and the plant natural product berberine

Neutrophil gelatinase-associated lipocalin (NGAL, a.k.a Lnc2) is a member of the lipocalin family and has diverse roles. NGAL can stabilize matrix metalloproteinase-9 from autodegradation. NGAL is considered as a siderocalin that is important in the transport of iron. NGAL expression has also been associated with certain neoplasias and is implicated in the metastasis of breast cancer. In a previous study, we examined whether ectopic NGAL expression would alter the sensitivity of breast epithelial, breast and colorectal cancer cells to the effects of the chemotherapeutic drug doxorubicin. While abundant NGAL expression was detected in all the cells infected with a retrovirus encoding NGAL, this expression did not alter the sensitivity of these cells to doxorubicin as compared with empty vector-transduced cells. We were also interested in determining the effects of ectopic NGAL expression on the sensitivity to small-molecule inhibitors targeting key signaling molecules. Ectopic NGAL expression increased the sensitivity of MCF-7 breast cancer cells to EGFR, Bcl-2 and calmodulin kinase inhibitors as well as the natural plant product berberine. Furthermore, when suboptimal concentrations of certain inhibitors were combined with doxorubicin, a reduction in the doxorubicin IC 50 was frequently observed. An exception was observed when doxorubicin was combined with rapamycin, as doxorubicin suppressed the sensitivity of the NGAL-transduced MCF-7 cells to rapamycin when compared with the empty vector controls. In contrast, changes in the sensitivities of the NGAL-transduced HT-29 colorectal cancer cell line and the breast epithelial MCF-10A cell line were not detected compared with empty vector-transduced cells. Doxorubicin-resistant MCF-7/Dox (R) cells were examined in these experiments as a control drug-resistant line; it displayed increased sensitivity to EGFR and Bcl-2 inhibitors compared with empty vector transduced MCF-7 cells. These results indicate that NGAL expression can alter the sensitivity of certain cancer cells to small-molecule inhibitors, suggesting that patients whose tumors exhibit elevated NGAL expression or have become drug-resistant may display altered responses to certain small-molecule inhibitors.

Advances in targeting signal transduction pathways

Over the past few years, significant advances have occurred in both our understanding of the complexity of signal transduction pathways as well as the isolation of specific inhibitors which target key components in those pathways. Furthermore critical information is being accrued regarding how genetic mutations can affect the sensitivity of various types of patients to targeted therapy. Finally, genetic mechanisms responsible for the development of resistance after targeted therapy are being discovered which may allow the creation of alternative therapies to overcome resistance. This review will discuss some of the highlights over the past few years on the roles of key signaling pathways in various diseases, the targeting of signal transduction pathways and the genetic mechanisms governing sensitivity and resistance to targeted therapies.

Dual Inhibition of Phosphatidylinositol 3-Kinase and Mammalian Target of Rapamycin: a Therapeutic Strategy for Acute Leukemias

The phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) are two major signaling molecules in the PI3K/Akt/mTOR signal transduction cascade. This pathway is a key regulator of a wide range of physiological cell processes which include proliferation, differentiation, survival, metabolism, exocytosis, motility, and autophagy. However, aberrantly upregulated PI3K/Akt/mTOR signaling characterizes many types of cancers where it negatively influences response to therapeutic treatments. Therefore, targeting PI3K/Akt/mTOR signaling with small molecule inhibitors could improve cancer patient outcome. The PI3K/Akt/mTOR signaling network is activated in acute leukemias of both myelogenous and lymphoid lineage, where it correlates with poor prognosis and enhanced drug-resistance. The catalytic sites of PI3K and mTOR share a high degree of sequence homology. This feature has allowed the synthesis of ATP-competitive compounds that targeted the catalytic site of both PI3K and mTOR (e.g. PI-103, NVP-BEZ235). In preclinical settings, dual PI3K/mTOR inhibitors displayed a much stronger cytotoxicity against leukemic cells than either PI3K inhibitors or allosteric mTOR inhibitors, such as rapamycin and its derivatives (rapalogs). At variance with rapamycin/rapalogs, dual PI3K/mTOR inhibitors targeted both mTOR complex 1 and mTOR complex 2, and inhibited the rapamycin-resistant phosphorylation of eukaryotic initiation factor 4E-binding protein 1, resulting in a marked inhibition of oncogenetic protein translation in leukemic cells. Hence, they strongly reduced the proliferation rate and induced an important apoptotic response. Here, we reviewed the evidence documenting that dual PI3K/mTOR inhibitors represent a promising option for future targeted therapies of leukemic patients.

Two hits are better than one: targeting both phosphatidylinositol 3-kinase and mammalian target of rapamycin as a therapeutic strategy for acute leukemia treatment

Phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) are two key components of the PI3K/Akt/mTOR signaling pathway. This signal transduction cascade regulates a wide range of physiological cell processes, that include differentiation, proliferation, apoptosis, autophagy, metabolism, motility, and exocytosis. However, constitutively active PI3K/Akt/mTOR signaling characterizes many types of tumors where it negatively influences response to therapeutic treatments. Hence, targeting PI3K/Akt/mTOR signaling with small molecule inhibitors may improve cancer patient outcome. The PI3K/Akt/mTOR signaling cascade is overactive in acute leukemias, where it correlates with enhanced drug-resistance and poor prognosis. The catalytic sites of PI3K and mTOR share a high degree of sequence homology. This feature has allowed the synthesis of ATP-competitive compounds targeting the catalytic site of both kinases. In preclinical models, dual PI3K/mTOR inhibitors displayed a much stronger cytotoxicity against acute leukemia cells than either PI3K inhibitors or allosteric mTOR inhibitors, such as rapamycin. At variance with rapamycin, dual PI3K/mTOR inhibitors targeted both mTOR complex 1 and mTOR complex 2, and inhibited the rapamycin-resistant phosphorylation of eukaryotic initiation factor 4E-binding protein 1, resulting in a marked inhibition of oncogenic protein translation. Therefore, they strongly reduced cell proliferation and induced an important apoptotic response. Here, we reviewed the evidence documenting that dual PI3K/mTOR inhibitors may represent a promising option for future targeted therapies of acute leukemia patients.

Nuclear phospholipase C β1 signaling, epigenetics and treatments in MDS

Myelodysplastic syndromes (MDS), clonal hematopoietic stem-cell disorders mainly affecting older adult patients, show ineffective hematopoiesis in one or more of the lineages of the bone marrow. Most MDS are characterized by anemia, and a number of cases progresses to acute myeloid leukemia (AML). Indeed, the molecular mechanisms underlying the MDS evolution to AML are still unclear, even though the nuclear signaling elicited by PI-PLCβ1 has been demonstrated to play an important role in the control of the balance between cell cycle progression and apoptosis in MDS cells. Here we review both the role of epigenetic therapy on PI-PLCβ1 promoter and the changes in PI-PLCβ1 expression in MDS patients treated for anemia.

Mutations and deregulation of Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascades which alter therapy response

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). Certain components of these pathways, RAS, NF1, BRAF, MEK1, DUSP5, PP2A, PIK3CA, PIK3R1, PIK3R4, PIK3R5, IRS4, AKT, NFKB1, MTOR, PTEN, TSC1, and TSC2 may also be activated/inactivated by mutations or epigenetic silencing. Upstream mutations in one signaling pathway or even in downstream components of the same pathway can alter the sensitivity of the cells to certain small molecule inhibitors. These pathways have profound effects on proliferative, apoptotic and differentiation pathways. Dysregulation of components of these cascades can contribute to: resistance to other pathway inhibitors, chemotherapeutic drug resistance, premature aging as well as other diseases. This review will first describe these pathways and discuss how genetic mutations and epigenetic alterations can result in resistance to various inhibitors.

Nuclear PI-PLCβ1 and myelodysplastic syndromes: genetics and epigenetics

Among cellular second messengers inositides play key roles in signal transduction pathways. Indeed, nuclear phosphoinositide- specific phospholipase C (PI-PLC) β1 and Akt are involved in cell cycle progression and apoptosis. Nuclear lipid metabolism has raised interest in the last years, mainly because of its link with haematopoietic progenitor cells. Myelodysplastic syndromes (MDS) are stem-cell clonal diseases characterized by an impaired hempoiesis and a differentiation defect in one or more of the bone marrow lineages, often leading to progression to acute myeloid leukaemia (AML). The MDS evolution to AML is not completely understood but, at a molecular level, the nuclear inositide signalling pathways can play an important role in this process.

Targeting the cancer initiating cell: the ultimate target for cancer therapy

An area of therapeutic interest in cancer biology and treatment is targeting the cancer stem cell, more appropriately referred to as the cancer initiating cell (CIC). CICs comprise a subset of hierarchically organized, rare cancer cells with the ability to initiate cancer in xenografts in genetically modified murine models. CICs are thought to be responsible for tumor onset, self-renewal/maintenance, mutation accumulation and metastasis. CICs may lay dormant after various cancer therapies which eliminate the more rapidly proliferating bulk cancer (BC) mass. However, CICs may remerge after therapy is discontinued as they may represent cells which were either intrinsically resistant to the original therapeutic approach or they have acquired mutations which confer resistance to the primary therapy. In experimental mouse tumor transplant models, CICs have the ability to transfer the tumor to immunocompromised mice very efficiently while the BCs are not able to do so as effectively. Often CICs display increased expression of proteins involved in drug resistance and hence they are intrinsically resistant to many chemotherapeutic approaches. Furthermore, the CICs may be in a suspended state of proliferation and not sensitive to common chemotherapeutic and radiological approaches often employed to eliminate the rapidly proliferating BCs. Promising therapeutic approaches include the targeting of certain signal transduction pathways (e.g., RAC, WNT, PI3K, PML) with small molecule inhibitors or targeting specific cell-surface molecules (e.g., CD44), with effective cytotoxic antibodies. The existence of CICs could explain the high frequency of relapse and resistance to many currently used cancer therapies. New approaches should be developed to effectively target the CIC which could vastly improve cancer therapies and outcomes. This review will discuss recent concepts of targeting CICs in certain leukemia models.

Activity of the selective IκB kinase inhibitor BMS-345541 against T-cell acute lymphoblastic leukemia: involvement of FOXO3a

Several lines of evidence suggest that the IκB kinase (IKK)/nuclear factor-κB (NFκB) axis is required for viability of leukemic cells and is a predictor of relapse in T-cell acute lymphoblastic leukemia (T-ALL). Moreover, many anticancer agents induce NFκB nuclear translocation and activation of its target genes, which counteract cellular resistance to chemotherapeutic drugs. Therefore, the design and the study of IKK-specific drugs is crucial to inhibit tumor cell proliferation and to prevent cancer drug-resistance. Here, we report the anti-proliferative effects induced by BMS-345541 (a highly selective IKK inhibitor) in three Notch1-mutated T-ALL cell lines and in T-ALL primary cells from pediatric patients. BMS-345541 induced apoptosis and an accumulation of cells in the G 2/M phase of the cell cycle via inhibition of IKK/NFκB signaling. We also report that T-ALL cells treated with BMS-345541 displayed nuclear translocation of FOXO3a and restoration of its functions, including control of p21(Cip1) expression levels. We demonstrated that FOXO3a subcellular re-distribution is independent of AKT and ERK 1/2 signaling, speculating that in T-ALL the loss of FOXO3a tumor suppressor function could be due to deregulation of IKK, as has been previously demonstrated in other cancer types. It is well known that, differently from p53, FOXO3a mutations have not yet been found in human tumors, which makes therapeutics activating FOXO3a more appealing than others. For these features, BMS-345541 could be used alone or in combination with traditional therapies in the treatment of T-ALL.

Targeting the liver kinase B1/AMP-activated protein kinase pathway as a therapeutic strategy for hematological malignancies

INTRODUCTION

Despite considerable advances, several hematological malignancies remain incurable with standard treatments. Therefore, there is a need for novel targeted and less toxic therapies, particularly for patients who develop resistance to traditional chemotherapeutic drugs. The liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK) signaling pathway has recently emerged as a tumor suppressor axis. A critical point is that the LKB1/AMPK network remains functional in a wide range of cancers and could be stimulated by drugs, such as N,N-dimethylimidodicarbonimidic diamide (metformin) or 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR).

AREAS COVERED

The literature data show that drugs activating LKB1/AMPK signaling induced cell cycle arrest, caspase-dependent apoptosis or autophagy in hematopoietic tumors. Moreover, metformin effectively inhibited mammalian target of rapamycin complex 1 (mTORC1)-controlled oncogenetic protein translation, which does not occur with allosteric mTORC1 inhibitors, such as rapamycin and its derivatives. Metformin was also capable of targeting leukemic stem cells, the most relevant target for leukemia eradication.

EXPERT OPINION

Data emerging from preclinical settings suggest that the LKB1/AMPK pathway is critically involved in regulating proliferation and survival of malignant hematopoietic cells. Thus, it is proposed that drugs activating the LKB1/AMPK axis may offer a novel and less toxic treatment option for some types of hematological malignancies.

Cytotoxic activity of the novel Akt inhibitor, MK-2206, in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive neoplastic disorder arising from T-cell progenitors. T-ALL accounts for 15% of newly diagnosed ALL cases in children and 25% in adults. Although the prognosis of T-ALL has improved, due to the use of polychemotherapy schemes, the outcome of relapsed/chemoresistant T-ALL cases is still poor. A signaling pathway that is frequently upregulated in T-ALL, is the phosphatidylinositol 3-kinase/Akt/mTOR network. To explore whether Akt could represent a target for therapeutic intervention in T-ALL, we evaluated the effects of the novel allosteric Akt inhibitor, MK-2206, on a panel of human T-ALL cell lines and primary cells from T-ALL patients. MK-2206 decreased T-ALL cell line viability by blocking leukemic cells in the G(0)/G(1) phase of the cell cycle and inducing apoptosis. MK-2206 also induced autophagy, as demonstrated by an increase in the 14-kDa form of LC3A/B. Western blotting analysis documented a concentration-dependent dephosphorylation of Akt and its downstream targets, GSK-3α/β and FOXO3A, in response to MK-2206. MK-2206 was cytotoxic to primary T-ALL cells and induced apoptosis in a T-ALL patient cell subset (CD34(+)/CD4(-)/CD7(-)), which is enriched in leukemia-initiating cells. Taken together, our findings indicate that Akt inhibition may represent a potential therapeutic strategy in T-ALL.

Abstract 3750: The novel Akt inhibitor MK-2206, is cytotoxic in T-cell acute lymphoblastic leukemia: Therapeutic implications

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive neoplastic disorder arising within the thymus from the clonal proliferation of T-cell precursors. T-ALL accounts for 15% of ALL cases in children and 25% in adults. Although the prognosis of T-ALL has improved, due to the use of intensive polychemotherapy schemes, the outcome of relapsed and chemoresistant T-ALL is still poor, especially in adults, with a 35-40% survival at 5 years. Therefore, efforts are being made to develop targeted therapies against deregulated signaling cascades that sustain T-ALL cell proliferation, survival, and drug-resistance. A signaling pathway that is frequently upregulated in T-ALL, is the PI3K/Akt/mTOR network. To explore whether or not Akt could represent a potential target for therapeutic intervention in T-ALL, we evaluated the effects of the novel allosteric Akt inhibitor, MK-2206, on a panel of human T-ALL cell lines (MOLT-4, CEM, drug-resistant CEM) and primary cells from T-ALL patients, characterized by pathway upregulation. MK-2206 decreased T-ALL cell line viability as documented by MTT assays. IC50 for MK-2206 ranged from 1.0 to 4.8 μM at 48 hours. The drug was effective against drug-resistant CEM cells, overexpressing 170-kDa P-glycoprotein. MK-2206 blocked leukemic cells in the G1 phase of the cell cycle and induced caspase-dependent apoptotic cell death, as documented by Annexin V/propidium iodide staining and western blot analysis. In CEM cells, MK-2206 induced autophagy, as demonstrated by an increase in the 14-kDa form of LC3A/B. Western blotting documented a concentration-dependent dephosphorylation of Akt and its downstream targets, GSK-3β and FOXO3A, in response to MK-2206. mTORC1 downstream targets were also efficiently dephosphorylated by MK-2206, including p70S6K and 4E-BP1. MK-2206 decreased mTORC2 activity, as indicated by the downregulation of Ser 2481 p-mTOR levels, a readout for mTORC2 activity In MOLT-4 and CEM cells, MK-2206 strongly synergized (combination index: 0.1-0.33) with doxorubicin. Moreover, MK-2206 dephosphorylated Akt and induced apoptosis in a T-ALL patient cell subset (CD34+/CD4−/CD7−) which is enriched in leukemia initiating cells. Our findings indicate that Akt inhibition, either alone or in combination with chemotherapeutic drugs, represents a potential therapeutic target in T-ALL cells that require upregulation of the PI3K/Akt/mTOR signaling pathway for their proliferation and survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3750. doi:1538-7445.AM2012-3750

Abstract 3736: The mTOR inhibitor, RAD001, displays higher cytotoxicity in leukemias with hyperactivated PI3K/AKT/mTOR pathway

Acute myelogenous leukemia (AML) is a disease resulting from the clonal expansion and accumulation of hematopoietic stem cells arrested at various stages of development. B-cell Acute lymphoblastic leukemia (B-ALL) is a form of leukemia characterized by lymphoblast abnormal increase. B-ALL is the most common form of cancer in childhood with a peak of incidence at 2-5 years of age, and another peak in the elderly. The overall cure rate in children is about 80%, and about 38% to 60% of adults have long-term disease-free survival. Although the prognosis of AML and ALL has improved in the last decades, the outcome of relapsed and chemoresistant AML and ALL is still poor, especially in adults, with only a 35-40% survival at 5 years. Therefore, major efforts are being made to develop rationally targeted therapies against alterated signaling cascades that sustain AML and ALL cell proliferation, survival, and drug-resistance. A signaling pathway that is frequently upregulated in AML and ALL is the PI3K/Akt/mTOR network. To explore whether this pathway could represent a potential pharmacological target in AML and ALL, we evaluated the effects of the mTOR inhibitor, RAD001, on the HL60 AML cell line and on the SEM B-ALL cell line.RAD001decreased viability in AML and ALL cell lines, as demonstrated by MTT experiments. The values of IC50 at 24 and 48 hours in HL60 cell line was 8μM, while in SEM cell line, that displays an hyperactivation of the PI3K/Akt/mTOR pathway, the IC50 range was from 4,7 to 6,8 μM, thus showing an higher sensitivity of this cell line to this targeted therapy. As documented by Western Blotting, RAD001 showed a concentration-dependent induction of apoptosis with a relevant increment of PARP, Caspase 3, 8 and 9 cleavage in both cell lines. The ALL cell line SEM, with hyperactivated PI3K/Akt/mTOR pathway, displayed a much higher Caspase and PARP cleavage dependent apoptosis.PI3K/Akt/mTOR downstream targets were also partially dephosphorylated by RAD001, in particular GSK3β and 4E-BP1. RAD001 induced no significant changes in Akt dephosphorylation in HL60 and SEM cell lines, and this is in agreement with several reports showing no relevant changes in the phosphorylation of Akt. The cells always expressed unchanged total Akt. This indicates that PI3K/Akt/mTOR inhibition could be an attractive target to develop innovative therapeutic strategies directed towards AML and ALL leukemia cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3736. doi:1538-7445.AM2012-3736

Involvement of Akt-1 and mTOR in sensitivity of breast cancer to targeted therapy

Elucidating the response of breast cancer cells to chemotherapeutic and hormonal based drugs is clearly important as these are frequently used therapeutic approaches. A signaling pathway often involved in chemo- and hormonal-resistance is the Ras/PI3K/PTEN/Akt/mTOR cascades. In the studies presented in this report, we have examined the effects of constitutive activation of Akt on the sensitivity of MCF-7 breast cancer cells to chemotherapeutic- and hormonal-based drugs as well as mTOR inhibitors. MCF-7 cells which expressed a constitutively-activated Akt-1 gene [∆Akt-1(CA)] were more resistant to doxorubicin, etoposide and 4-OH-tamoxifen (4HT) than cells lacking ∆Akt-1(CA). Cells which expressed ∆Akt-1(CA) were hypersensitive to the mTOR inhibitor rapamycin. Furthermore, rapamycin lowered the IC50s for doxorubicin, etoposide and 4HT in the cells which expressed ∆Akt-1(CA), demonstrating a potential improved method for treating certain breast cancers which have deregulated PI3K/PTEN/Akt/mTOR signaling. Understanding how breast cancers respond to chemo- and hormonal-based therapies and the mechanisms by which they can become drug resistant may enhance our ability to treat breast cancer. These results also document the potential importance of knowledge of the mutations present in certain cancers which may permit more effective therapies.