Dual phosphoinositide 3-kinase/mammalian target of rapamycin blockade is an effective radiosensitizing strategy for the treatment of non-small cell lung cancer harboring K-RAS mutations

Dual inhibition of the PI3K/mTOR pathway increases tumor radiosensitivity by normalizing tumor vasculature

The aberrant vascular architecture of solid tumors results in hypoxia that limits the efficacy of radiotherapy. Vascular normalization using antiangiogenic agents has been proposed as a means to improve radiation therapy by enhancing tumor oxygenation, but only short-lived effects for this strategy have been reported so far. Here, we show that NVP-BEZ235, a dual inhibitor of phosphoinositide-3-kinase (PI3K) and mTOR, can improve tumor oxygenation and vascular structure over a prolonged period that achieves the aim of effective vascular normalization. Because PI3K inhibition can radiosensitize tumor cells themselves, our experimental design explicitly distinguished effects on the blood vasculature versus tumor cells. Drug administration coincident with radiation enhanced the delay in tumor growth without changing tumor oxygenation, establishing that radiosensitization is a component of the response. However, the enhanced growth delay was substantially greater after induction of vascular normalization, meaning that this treatment enhanced the tumoral radioresponse. Importantly, changes in vascular morphology persisted throughout the entire course of the experiment. Our findings indicated that targeting the PI3K/mTOR pathway can modulate the tumor microenvironment to induce a prolonged normalization of blood vessels. The substantial therapeutic gain observed after combination of NVP-BEZ235 with irradiation has conceptual implications for cancer therapy and could be of broad translational importance.

Inhibition of DNA-dependent protein kinase induces accelerated senescence in irradiated human cancer cells

DNA-dependent protein kinase (DNA-PK) plays a pivotal role in the repair of DNA double-strand breaks (DSB) and is centrally involved in regulating cellular radiosensitivity. Here, we identify DNA-PK as a key therapeutic target for augmenting accelerated senescence in irradiated human cancer cells. We find that BEZ235, a novel inhibitor of DNA-PK and phosphoinositide 3-kinase (PI3K)/mTOR, abrogates radiation-induced DSB repair resulting in cellular radiosensitization and growth delay of irradiated tumor xenografts. Importantly, radiation enhancement by BEZ235 coincides with a prominent p53-dependent accelerated senescence phenotype characterized by positive β-galactosidase staining, G(2)-M cell-cycle arrest, enlarged and flattened cellular morphology, and increased p21 expression and senescence-associated cytokine secretion. Because this senescence response to BEZ235 is accompanied by unrepaired DNA DSBs, we examined whether selective targeting of DNA-PK also induces accelerated senescence in irradiated cells. Significantly, we show that specific pharmacologic inhibition of DNA-PK, but not PI3K or mTORC1, delays DSB repair leading to accelerated senescence after radiation. We additionally show that PRKDC knockdown using siRNA promotes a striking accelerated senescence phenotype in irradiated cells comparable with that of BEZ235. Thus, in the context of radiation treatment, our data indicate that inhibition of DNA-PK is sufficient for the induction of accelerated senescence. These results validate DNA-PK as an important therapeutic target in irradiated cancer cells and establish accelerated senescence as a novel mechanism of radiosensitization induced by DNA-PK blockade.

The dual PI3K/mTOR inhibitor NVP-BEZ235 induces tumor regression in a genetically engineered mouse model of PIK3CA wild-type colorectal cancer

Purpose

To examine the in vitro and in vivo efficacy of the dual PI3K/mTOR inhibitor NVP-BEZ235 in treatment of PIK3CA wild-type colorectal cancer (CRC).

Experimental Design

PIK3CA mutant and wild-type human CRC cell lines were treated in vitro with NVP-BEZ235, and the resulting effects on proliferation, apoptosis, and signaling were assessed. Colonic tumors from a genetically engineered mouse (GEM) model for sporadic wild-type PIK3CA CRC were treated in vivo with NVP-BEZ235. The resulting effects on macroscopic tumor growth/regression, proliferation, apoptosis, angiogenesis, and signaling were examined.

Results

In vitro treatment of CRC cell lines with NVP-BEZ235 resulted in transient PI3K blockade, sustained decreases in mTORC1/mTORC2 signaling, and a corresponding decrease in cell viability (median IC₅₀ = 9.0–14.3 nM). Similar effects were seen in paired isogenic CRC cell lines that differed only in the presence or absence of an activating PIK3CA mutant allele. In vivo treatment of colonic tumor-bearing mice with NVP-BEZ235 resulted in transient PI3K inhibition and sustained blockade of mTORC1/mTORC2 signaling. Longitudinal tumor surveillance by optical colonoscopy demonstrated a 97% increase in tumor size in control mice (p = 0.01) vs. a 43% decrease (p = 0.008) in treated mice. Ex vivo analysis of the NVP-BEZ235-treated tumors demonstrated a 56% decrease in proliferation (p = 0.003), no effects on apoptosis, and a 75% reduction in angiogenesis (p = 0.013).

Conclusions

These studies provide the preclinical rationale for studies examining the efficacy of the dual PI3K/mTOR inhibitor NVP-BEZ235 in treatment of PIK3CA wild-type CRC.

Augmentation of NVP-BEZ235's anticancer activity against human lung cancer cells by blockage of autophagy

Autophagy is a cellular lysosomal degradation pathway essential for regulation of cell survival and death to maintain homeostasis. This process is negatively regulated by mammalian target of rapamycin (mTOR) signaling and often counteracts efficacy of certain cancer therapeutic agents. NVP-BEZ235 (BEZ235) is a novel, orally bioavailable dual PI3K/mTOR inhibitor that has exhibited promising activity against non-small cell lung cancer (NSCLC) in preclinical models. The current study focuses on evaluating the role of BEZ235 in regulating autophagy. BEZ235 was effective in inhibiting the growth of NSCLC cells including induction of apoptosis. It also potently induced the expression of type-II LC3, indicating induction of autophagy. When BEZ235 was used in combination with the lysosomal or autophagic inhibitor chloroquine (CQ), enhanced inhibitory effects on monolayer growth and colony formation of NSCLC cells was observed. In addition, enhanced induction of apoptosis was also detected in cells exposed to the combination of BEZ235 and CQ. Moreover, the combination of BEZ235 and CQ was more effective than each single agent alone in inhibiting the growth of NSCLC xenografts in nude mice. Thus, induction of autophagy by BEZ235 appears to be a survival mechanism that may counteract its anticancer effects. Based on these, we suggest a strategy to enhance BEZ235's anticancer efficacy by blockade of autophagy.

Selective targeting of the mTORC1/2 protein kinase complexes leads to antileukemic effects in vitro and in vivo

The BCR/ABL tyrosine kinase promotes leukemogenesis through activation of several targets that include the phosphoinositide 3-kinase (PI3K). Tyrosine kinase inhibitors (TKIs), which target BCR/ABL, induce striking clinical responses. However, therapy with TKIs is associated with limitations such as drug intolerance, inability to universally eradicate the disease and emergence of BCR/ABL drug-resistant mutants. To overcome these limitations, we tested whether inhibition of the PI3K/target of rapamycin (mTOR) signaling pathway has antileukemic effect in primary hematopoietic stem cells and BA/F3 cells expressing the BCR/ABL oncoprotein. We determined that dual inhibition of PI3K/mTOR causes growth arrest and apoptosis leading to profound antileukemic effects both in vitro and in vivo. We also established that pharmacologic inhibition of the mTORC1/mTORC2 complexes is sufficient to cause these antileukemic effects. Our results support the development of inhibitors of the mTORC1/2 complexes for the therapy of leukemias that either express BCR/ABL or display deregulation of the PI3K/mTOR signaling pathway.

The combination of RAD001 and NVP-BEZ235 exerts synergistic anticancer activity against non-small cell lung cancer in vitro and in vivo

The phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling axis has emerged as a novel target for cancer therapy. Agents that inhibit PI3K, mTOR or both are currently under development. The mTOR allosteric inhibitor, RAD001, and the PI3K/mTOR dual kinase inhibitor, BEZ235, are examples of these agents. We were interested in developing strategies to enhance mTOR-targeted caner therapy. In this study, we found that BEZ235 alone effectively inhibited the growth of rapamycin-resistant cancer cells. Interestingly, the combination of sub-optimal concentrations of RAD001 and BEZ235 exerted synergistic inhibition of the growth of human lung cancer cells along with induction of apoptosis and G1 arrest. Furthermore, the combination was also more effective than either agent alone in inhibiting the growth of lung cancer xenografts in mice. The combination showed enhanced effects on inhibiting mTOR signaling and reducing the expression of c-Myc and cyclin D1. Taken together, our results suggest that the combination of RAD001 and BEZ235 is a novel strategy for cancer therapy.

Effectiveness of combined treatment using X-rays and a phosphoinositide 3-kinase inhibitor, ZSTK474, on proliferation of HeLa cells in vitro and in vivo

ZSTK474 is a novel orally applicable phosphoinositide 3-kinase-specific inhibitor that strongly inhibits cancer cell proliferation. To further explore the antitumor effect of ZSTK474 for future clinical usage, we studied its combined effects with radiation. The proliferation of HeLa cells was inhibited by treatment with X-rays alone or ZSTK474 alone. Combination treatment using X-rays then ZSTK474 given orally for 8 days, starting 24 h post-irradiation, significantly enhanced cell growth inhibition. The combined effect was also observed for clonogenic survival with continuous ZSTK474 treatment. Western blot analysis showed enhanced phosphorylation of Akt and GSK-3β by X-irradiation, whereas phosphorylation was inhibited by ZSTK474 treatment alone. Treatment with ZSTK474 after X-irradiation also inhibited phosphorylation, and remarkably inhibited xenograft tumor growth. Combined treatment with X-rays and ZSTK474 has greater therapeutic potential than radiation or drug therapy alone, both in vitro and in vivo.

A cell-based screen identifies ATR inhibitors with synthetic lethal properties for cancer-associated mutations

Oncogene activation has been shown to generate replication-born DNA damage, also known as replicative stress. The primary responder to replicative stress is not Ataxia-Telangiectasia Mutated (ATM) but rather the kinase ATM and Rad3-related (ATR). One limitation for the study of ATR is the lack of potent inhibitors. We here describe a cell-based screening strategy that has allowed us to identify compounds with ATR inhibitory activity in the nanomolar range. Pharmacological inhibition of ATR generates replicative stress, leading to chromosomal breakage in the presence of conditions that stall replication forks. Moreover, ATR inhibition is particularly toxic for p53-deficient cells, this toxicity being exacerbated by replicative stress-generating conditions such as the overexpression of cyclin E. Notably, one of the compounds we identified is NVP-BEZ235, a dual phosphatidylinositol-3-OH kinase (PI3K) and mTOR inhibitor that is being tested for cancer chemotherapy but that we now show is also very potent against ATM, ATR and the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs).

[PI3K/Akt/mTOR signaling pathway and non-small cell lung cancer]

Lung cancer is one of the leading causes of cancer-related deaths worldwide and non-small cell lung cancer (NSCLC) accounts for about 75%-85% of all lung cancers. NSCLC often presents at stages too late for surgical intervention and traditional treatments including chemotherapy and radiotherapy are inadequate. The 5-year survival rate of NSCLC is only 5%-10%. PI3K/Akt/mTOR signaling pathway is an important intracellular signal transduction pathway. It plays an important role in cell apoptosis and survival by affecting the activity of downstream effector molecules, and it is closely associated with the development and progression of NSCLC. This article reviewed recent progress on the composition, anti-apoptosis and proproliferation of PI3K/Akt/mTOR signaling pathway, and discussed its potential targets to NSCLC therapy.

Vertical targeting of the phosphatidylinositol-3 kinase pathway as a strategy for treating melanoma

PURPOSE

Melanoma is relatively resistant to chemotherapy; improved targeting of molecules critical for cell proliferation and survival are needed. Phosphatidylinositol-3 kinase (PI3K) is an important target in melanoma; however, activity of PI3K inhibitors (PI3KI) is limited. Our purpose was to assess mTOR as a cotarget for PI3K.

METHODS

Using a method of quantitative immunofluorescence to measure mTOR expression in a large melanoma cohort, we studied associations with PI3K subunits, p85 and p110α. We assessed addition of the mTOR inhibitor rapamycin to 2 PI3KIs, NVP-BKM120 and LY294002. We studied in vitro activity of a novel dual PI3K/mTOR inhibitor NVP-BEZ235 and activity of the combination of NVP-BEZ235 and the MAP/ERK kinase (MEK) inhibitor AZD6244.

RESULTS

Strong coexpression of mTOR and p110α was observed (ρ = 0.658; P < 0.0001). Less coexpression was seen with p85 (ρ = 0.239; P < 0.0001). Strong synergism was shown between rapamycin and both PI3KIs. Activity of both PI3KIs was similarly enhanced with all rapamycin concentrations used. The dual PI3K/mTOR inhibitor effectively inhibited viability in 23 melanoma cell lines (IC(50) values in the nanomolar range), regardless of B-Raf mutation status, with resultant reduction in clonogenicity and downregulation of pAkt and pP70S6K. Synergism was seen when combining NVP-BEZ235 and AZD6244, with resultant increases in poly(ADP-ribose) polymerase and caspase-2 cleavage.

CONCLUSIONS

mTOR and p110α are coexpressed in melanoma. Rapamycin concentrations as low as 1 nmol/L enhance activity of PI3KIs. The dual PI3K/mTOR inhibitor NVP-BEZ235 is highly active in melanoma cells in vitro, suggesting that concurrent PI3K and mTOR targeting in melanoma warrants further investigation, both alone and in combination with MEK inhibitors.

Dependence on the MUC1-C oncoprotein in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) cells are often associated with constitutive activation of the phosphoinositide 3-kinase (PI3K) → Akt → mTOR pathway. The mucin 1 (MUC1) heterodimeric glycoprotein is aberrantly overexpressed in NSCLC cells and induces gene signatures that are associated with poor survival of NSCLC patients. The present results show that the MUC1 C-terminal subunit (MUC1-C) cytoplasmic domain associates with PI3K p85 in NSCLC cells. We show that inhibition of MUC1-C with cell-penetrating peptides blocks this interaction with PI3K p85 and suppresses constitutive phosphorylation of Akt and its downstream effector, mTOR. In concert with these results, treatment of NSCLC cells with the MUC1-C peptide inhibitor GO-203 was associated with downregulation of PI3K → Akt signaling and inhibition of growth. GO-203 treatment was also associated with increases in reactive oxygen species (ROS) and induction of necrosis by a ROS-dependent mechanism. Moreover, GO-203 treatment of H1975 (EGFR L858R/T790M) and A549 (K-Ras G12S) xenografts growing in nude mice resulted in tumor regressions. These findings indicate that NSCLC cells are dependent on MUC1-C both for activation of the PI3K → Akt pathway and for survival.

Mammalian target of rapamycin: biological function and target for novel anticancer agents

PURPOSE

The biological function of the mammalian target of rapamycin (mTOR) and mechanisms of action of mTOR inhibitors currently available for clinical use are described.

SUMMARY

mTOR is a target for anticancer agents due to its role in cancer development, progression, and resistance to other antineoplastic agents. Currently, two mTOR inhibitors, temsirolimus and everolimus, are approved for the treatment of patients with advanced renal cell carcinoma (RCC). Clinical trials comparing single-agent temsirolimus with interferon alfa-2a demonstrated an improvement in overall survival and progression-free survival (PFS) in patients with metastatic RCC. Clinical studies comparing everolimus with placebo indicated improved PFS in advanced RCC patients whose disease had progressed on or after vascular endothelial growth factor (VEGF) inhibitor therapy. Due to its role in the phosphatidylinositol 3-kinase (PI3K) signaling pathway, mTOR is a rational target for inhibition in combination with other agents, including traditional chemotherapy and agents that are affected by or target the PI3K pathway. Data from these studies review the use of mTOR inhibitors in non-Hodgkin's lymphoma and endometrial, breast, and neuroendocrine tumors. Common toxicities of mTOR inhibitors include mucositis, stomatitis, rash, asthenia, fatigue, and myelosuppression. Additional toxicities requiring monitoring include hyperglycemia, hyperlipidemia, and pneumonitis.

CONCLUSION

The mTOR signaling pathway is upregulated in a variety of solid and hematologic tumors. Two inhibitors of this pathway, temsirolimus and everolimus, have been approved for use in metastatic RCC. Although relatively safe, these drugs are associated with some unique adverse effects, such as hyperlipidemia, hyperglycemia, and pneumonitis, that require monitoring and may require clinical intervention.

Dual targeting of phosphoinositide 3-kinase and mammalian target of rapamycin using NVP-BEZ235 as a novel therapeutic approach in human ovarian carcinoma

PURPOSE

This study evaluates the effect of dual PI3K and mTOR inhibition using NVP-BEZ235 in preclinical models of ovarian cancer as a potential novel therapeutic strategy.

EXPERIMENTAL DESIGN

Inhibition of PI3K/Akt/mTOR signaling by NVP-BEZ235 was demonstrated by immunoblotting. The effect on cell proliferation was assessed in 18 ovarian cancer cell lines, including four pairs of syngeneic cisplatin-sensitive and cisplatin-resistant cell lines. The in vivo effects of NVP-BEZ235 on established tumor growth were evaluated using an immunocompetent, transgenic murine ovarian cancer model (LSL-K-ras(G12D/+)Pten(loxP/loxP)).

RESULTS

NVP-BEZ235 decreased cell proliferation in all ovarian cancer cell lines assayed and sensitized cisplatin-resistant cells to the cytotoxic effects of cisplatin. Cell lines with PI3K-activating mutations or Pten deletions were significantly more sensitive to the effect of NVP-BEZ235 than cell lines without these mutations (P < 0.05). A statistically significant correlation was found between relative levels of p4E-BP1 and the IC(50) for NVP-BEZ235. In LSL-K-ras(G12D/+)Pten(loxP/loxP) mice with established intraperitoneal tumor disease, oral administration of NVP-BEZ235 decreased pAkt, p4E-BP1 and Ki67 in tumor tissue, and resulted in significantly longer survival compared to control animals (P < 0.05). NVP-BEZ235 also induced cell cycle arrest, caspase 3 activity, and reduced cell migration.

CONCLUSIONS

Targeting PI3K and mTOR simultaneously using NVP-BEZ235 effectively inhibits ovarian cancer cell growth even in the presence of platinum resistance and prolongs survival of mice with intra-abdominal ovarian tumor disease. We propose that dual PI3K and mTOR inhibition using NVP-BEZ235 may be an effective novel therapeutic approach in patients with ovarian cancer.

Antitumor efficacy of PKI-587, a highly potent dual PI3K/mTOR kinase inhibitor

PURPOSE

The aim of this study was to show preclinical efficacy and clinical development potential of PKI-587, a dual phosphoinositide 3-kinase (PI3K)/mTOR inhibitor.

EXPERIMENTAL DESIGN

In vitro class 1 PI3K enzyme and human tumor cell growth inhibition assays and in vivo five tumor xenograft models were used to show efficacy.

RESULTS

In vitro, PKI-587 potently inhibited class I PI3Ks (IC(50) vs. PI3K-α = 0.4 nmol/L), PI3K-α mutants, and mTOR. PKI-587 inhibited growth of 50 diverse human tumor cell lines at IC(50) values of less than 100 nmol/L. PKI-587 suppressed phosphorylation of PI3K/mTOR effectors (e.g., Akt), and induced apoptosis in human tumor cell lines with elevated PI3K/mTOR signaling. MDA-MB-361 [breast; HER2(+), PIK3CA mutant (E545K)] was particularly sensitive to this effect, with cleaved PARP, an apoptosis marker, induced by 30 nmol/L PKI-587 at 4 hours. In vivo, PKI-587 inhibited tumor growth in breast (MDA-MB-361, BT474), colon (HCT116), lung (H1975), and glioma (U87MG) xenograft models. In MDA-MB-361 tumors, PKI-587 (25 mg/kg, single dose i.v.) suppressed Akt phosphorylation [at threonine(T)308 and serine(S)473] for up to 36 hours, with cleaved PARP (cPARP) evident up to 18 hours. PKI-587 at 25 mg/kg (once weekly) shrank large (∼1,000 mm(3)) MDA-MB-361 tumors and suppressed tumor regrowth. Tumor regression correlated with suppression of phosphorylated Akt in the MDA-MB-361 model. PKI-587 also caused regression in other tumor models, and efficacy was enhanced when given in combination with PD0325901 (MEK 1/2 inhibitor), irinotecan (topoisomerase I inhibitor), or HKI-272 (neratinib, HER2 inhibitor).

CONCLUSION

Significant antitumor efficacy and a favorable pharmacokinetic/safety profile justified phase 1 clinical evaluation of PKI-587.

Global downstream pathway analysis reveals a dependence of oncogenic NF-E2-related factor 2 mutation on the mTOR growth signaling pathway

In multicellular organisms, adaptive responses to oxidative stress are regulated by NF-E2-related factor 2 (NRF2), a master transcription factor of antioxidant genes and phase II detoxifying enzymes. Aberrant activation of NRF2 by either loss-of-function mutations in the Keap1 gene or gain-of-function mutations in the Nrf2 gene occurs in a wide range of human cancers, but details of the biological consequences of NRF2 activation in the cancer cells remain unclear. Here, we report that mutant NRF2 induces epithelial cell proliferation, anchorage-independent growth, and tumorigenicity and metastasis in vivo. Genome-wide gene expression profiling revealed that mutant NRF2 affects diverse molecular pathways including the mammalian target of rapamycin (mTOR) pathway. Mutant NRF2 upregulates RagD, a small G-protein activator of the mTOR pathway, which was also overexpressed in primary lung cancer. Consistently, Nrf2-mutated lung cancer cells were sensitive to mTOR pathway inhibitors (rapamycin and NVP-BEZ235) in both in vitro and an in vivo xenograft model. The gene expression signature associated with mutant NRF2 was a marker of poor prognosis in patients with carcinoma of the head and neck region and lung. These results show that oncogenic Nrf2 mutation induces dependence on the mTOR pathway during carcinogenesis. Our findings offer a rationale to target NRF2 as an anticancer strategy, and they suggest NRF2 activation as a novel biomarker for personalized molecular therapies or prognostic assessment.

Inhibitors of phosphatidylinositol-3-kinase in cancer therapy

The phosphatidylinositol-3-kinase (PI3K) signaling pathway is implicated in multiple aspects of tumorigenesis and tumor maintenance, and recent years have seen significant efforts towards developing agents to inhibit the pathway. However, the development of such agents raises issues such as what specific member or members in the PI3K family should be inhibited to achieve maximal therapeutic benefit, and can specific inhibitors be developed with the necessary pharmacologic properties to allow them to proceed to clinical trials? The number of PI3K inhibitors has gone from a handful of archetypal inhibitors which largely determined how the pathway was initially defined through their inhibition of PI3K, but also due to their off target properties, to a much larger number of inhibitors of not only PI3K but also other members of the PI3K family. The question remains to be answered whether greater therapeutic efficacy will be obtained through the use of inhibitors with increased specificity, or through inhibitors that target a spectrum of targets within the pathway. This review will cover the development of agents targeting the pathway, and will discuss current issues surrounding the development of such agents.