Chemoprotective Horizons: Bioactive Molecules as Therapeutic Shields Against Cytotoxicity

Abstract: Cancer cells, compared to normal cells, are under increased oxidative stress with higher level of ROS. When exposed to environmental or intracellular stresses like ROS, NFE-related factor 2 (Nrf2) is the key to antioxidant response by transcriptionally activate various detoxification and antioxidant enzymes. We have previously shown that wogonin (5,7-Dihydroxy-8-methoxy-2-phenyl-4H-1-benzopyran-4-one), a flavonoid isolated from the root of Scutellaria baicalensis Georgi, could reverse drug resistance in MCF-7/ DOX cells through blocking the translocation of Nrf2 into nucleus, however, the effects of wogonin on Nrf2 signaling pathway have not previously been reported. In our study, we observed that wogonin reduced Nrf2 nuclear translocation, and therefore elevated the level of intracellular ROS to accomplish the purpose of killing malignant cells. In order to confirm the roles of Nrf2, it was activated by tBHQ and knocked down by the Nrf2 siRNA, and the results demonstrated that the activation of Nrf2 was involved in the wogonin-induced accumulation of ROS and cell death. Furthermore, the suppression of Nrf2 by wogonin can potentiate cytotoxic effects of chemotherapeutic agents in HepG2 cells. On one hand, down-regulation of Nrf2 lead to reduction of cytoprotective effect through inducing phage II enzymes which sensitize cells to chemotherapeutic agents. On the other hand, inhibition of multidrug resistance-associated protein (MRPs) by wogonin to enhance the effective drug level in cancer cells is another way to potentiates chemotherapeutic effects. At last, we found that the down-regulation of Nrf2 is associated with over-expression of p53. Using p53 siRNA to knock down the endogenous p53 expression, the level of both c-Myc and Nrf2 in nucleus increased when exposed to wogonin. The present study indicated that wogonin can be used in chemotherapy not only because its own antitumor ability, but also due to the enhanced cytotoxic effects of chemotherapeutic agents. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C99. Citation Format: Chen Qian, Rong Hu. Wogonin enhanced reactive oxygen species-induced apoptosis and potentiated cytotoxic effects of chemotherapeutic agents by Nrf2 suppression in HepG2 cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C99.

Cancer cells, compared with normal cells, are under increased oxidative stress with higher level of reactive oxygen species (ROS). When exposed to environmental stresses such as ROS, NFE-related factor 2 (Nrf2) is the key to antioxidant response by transcriptionally activating various detoxification and antioxidant enzymes. Previously, we have shown that wogonin, a flavonoid isolated from the root of Scutellaria baicalensis Georgi, could reverse drug resistance in MCF-7/DOX cells by blocking the translocation of Nrf2 into nucleus. However, the exact mechanism underlying the effect remains unclear. In this study, we observed that wogonin reduced the Nrf2 nuclear translocation, and therefore elevated the level of intracellular ROS to accomplish the purpose of killing malignant cells. Furthermore, the suppression of Nrf2 by wogonin can potentiate cytotoxic effects of chemotherapeutic agents in HepG2 cells. On one hand, down-regulation of Nrf2 lead to reduction of cytoprotective effect by inducing phage II enzymes which sensitize cells to chemotherapeutic agents. On the other hand, inhibition of multidrug resistance-associated proteins (MRPs) by wogonin enhances the effective drug level in cancer cells and potentiates their chemotherapeutic effects. Finally, we found that the decrease of Nrf2 may be related to overexpression of p53. Using p53 siRNA to knock down the endogenous p53 expression, the levels of both c-myc and Nrf2 in nucleus increased when exposed to wogonin. The present study indicates that wogonin can be used in chemotherapy not only because of its own antitumor ability, but also due to the enhanced cytotoxic effects of chemotherapeutic agents.

Axl is a member of the TAM (Tyro3, Axl and Mer) family of receptor tyrosine kinases that regulate multiple cellular responses including cell survival, proliferation, and migration. Axl expression is predictive of poor patient overall survival in a variety of human cancers including triple negative breast (TNBC), pancreatic ductal adenocarcinoma (PDA) and non-small cell lung cancer (NSCLC). Axl expression is induced by the epithelial-to-mesenchymal transition (EMT) gene program in cancer cells and Axl signaling is required to maintain EMT-associated features including invasiveness, metastasis, stem cell-like traits and resistance to targeted inhibitors and other chemotherapeutic agents. BGB324/R428 is an oral, selective small molecule inhibitor of Axl that recently was evaluated in early clinical safety studies in healthy volunteers. Treatment with BGB324 up to and including 1.5 gms daily (per os) was established as being safe and well tolerated. The endpoints of the study included pharmacokinetics and safety. Bioavailability was increased in the presence of food and systemic exposure increased dose proportionately. At the highest dose the apparent elimination half-life approached four days presenting a range of dosing options. We evaluated the effects of BGB324 in preclinical models of TNBC, PDA and NSCLC, including 2D/3D cell culture and mouse xenograft models, in combination with targeted and chemotherapeutic agents. BGB324 treatment of mesenchymal carcinoma cells blocked invasiveness and enhanced chemotherapeutic efficacy. BGB324 abrogated the tumor initiation capacity of TNBC cells, an activity associated with cancer stem cells. BGB324 treatment blocked the emergence of EMT-associated acquired resistance to erlotinib in human NSCLC xenografts. Furthermore, combination treatment of BGB324 with chemotherapy inhibited the growth of human NSCLC xenografts and significantly prolonged survival in orthotopic and genetically engineered mouse models of PDA. Collectively, these data suggest that the first-in-class selective Axl inhibitor BGB324 can overcome EMT-related acquired therapeutic resistance and enhance the efficacy of multiple anti-cancer strategies. Together with the results of results of the early clinical safety studies, this provides a rationale for further clinical studies. Citation Format: Katarzyna Wnuk-Lipinska, Crina Tiron, Gro Gausdal, Tone Sandal, Robin Frink, Stefan Hinz, Monica Hellesøy, Lavina Ahmed, Hallvard Haugen, Xiao Liang, Magnus Blø, David Micklem, Murray Yule, John Minna, Longen Zhou, Rolf Brekken, James Lorens. BGB324, a selective small molecule Axl kinase inhibitor to overcome EMT-associated drug resistance in carcinomas: Therapeutic rationale and early clinical studies. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1747. doi:10.1158/1538-7445.AM2014-1747

Programmed cell death (apoptosis), is a normal physiological process which involves a distinct, well-characterized signaling cascade. However, dysregulation of the apoptotic machinery is commonly observed in many pathophysiological conditions. In particular, human cancer is commonly associated with a reduced capacity of cells to undergo apoptosis in response to cell stress, leading to an abnormal accumulation of damaged cells. Human ovarian cancer is the most lethal gynecological malignancy, a statistic that is due, in part, to the phenomenon a chemoresistance, by which tumour cells evade the cytotoxic effects of chemotherapeutic agents used to eradicate the disease. Cisplatin (CDDP) and paclitaxel are first-line chemotherapeutics for human ovarian cancer, but resistance to these agents is common, and significantly attenuates positive clinical outcomes. Recent evidence suggests that aberrant regulation of the apoptotic cascade may be a causative factor for chemoresistance. To that end, gene products implicated in the regulation of apoptosis, including the P13K/Akt and Inhibitor of Apoptosis Protein family are frequently over-expressed and/or dysregulated in chemoresistant cells. Activation of the TP53 tumor suppressor gene product, p53, is critical for DNA-damage-induced apoptosis in many cell types, and mutation of this gene is the most frequently observed abnormality in all of human cancer. p53 mutations are commonly, but not always, associated with poor prognosis and chemoresistance. Since the aberrant regulation of p53 may have critical implications for the clinical management of human ovarian cancer, it is of paramount importance to understand the molecular and cellular mechanisms by which p53 is regulated in these cells, and if and how dysregulated p53 activation may play a role in the etiology of chemoresistance. Cultured human ovarian cancer cells were used to establish the in vitro regulation of p53 and to assess the requirement for p53-dependent apoptosis for CDDP-induced apoptosis. We observed that CDDP induced apoptosis in chemosensitive ovarian cancer cells, but not in their chemoresistant variants. In addition, we demonstrated that over-expression of X-Linked Inhibitor of Apoptosis Protein (XIAP) induces chemoresistance in ovarian cancer cells, while down-regulation of XIAP sensitizes chemoresistant ovarian cancer cells to CDDP-induced apoptosis. Attenuation of Akt signalling using a dominant-negative Akt attenuated XIAP-mediated chemoresistance, suggesting a functional link between XIAP and Akt with respect to the regulation of chemosensitivity. Akt activation, a frequently observed event in human ovarian cancer, inhibited CDDP-induced apoptosis in chemosensitive cells, while dominant-negative Akt up-regulated p53 and sensitized chemoresistant cells to CDDP in a p53-dependent manner, suggesting a functional link between Akt activation and p53-mediated apoptosis. Akt-mediated chemoresistance was also associated with ablated CDDP-induced down-regulation of the anti-apoptotic protein XIAP. We further demonstrated that CDDP induced the up-regulation of the p53-responsive gene product PUMA, and induced apoptosis in a PUMA-dependent manner, although PUMA expression was not sufficient to confer a chemosensitive phenotype. CDDP also induced phosphorylation of p53 on numerous N-terminal residues in chemosensitive, but not chemoresistant cells. Activation of Akt inhibits the CDDP-induced phosphorylation of p53, while inhibition of Akt function induces p53 phosphorylation. Phosphorylation of Ser15 and Ser20, but not Ser37, was required for p53-dependent apoptosis but not for p53-dependent up-regulation of PUMA. Moreover, we showed that basal p53 levels are maintained, in part, by the constitutive activation of the soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP) pathway, and inhibition of this pathway depletes basal cGMP levels, up-regulates p53 content, stability, and phosphorylation, and induces apoptosis in a partially p53-dependent manner. These results suggest that: (a) p53 is a critical determinant of cell fate in human ovarian cancer cells, and is regulated by diverse signaling cascades including the Akt and sGC/cGMP pathways, (b) CDDP-induced apoptosis proceeds via a p53-dependent mechanism involving PUMA and p53 phosphorylation, (c) Akt confers resistance to ovarian cancer cells, in part, by suppressing the CDDP-induced activation and phosphorylation of p53. Akt also contributes to chemoresistance by attenuating the CDDP-induced down-regulation of XIAP. The current study significantly extends our understanding of how the p53 pathway is regulated, and how dysregulation of p53 activation may have profound effects upon the sensitivity of ovarian cancer cells to stress-induced apoptosis. This, in turn, may have important effects upon our understanding of the pathophysiology of chemoresistance in human ovarian cancer; a phenomenon that significantly attenuates successful treatment outcomes for this disease.

The present study was undertaken to explore the effect of the administration of high doses of sodium selenite on apoptosis in polymorphonuclear leukocytes in patients with non-Hodgkin's lymphoma. Thirty patients with newly diagnosed non-Hodgkin's lymphoma were randomly divided into two groups. Group I was treated with chemotherapy and group II received 0.2 mg/kg/d sodium selenite in addition to chemotherapy. Flow cytometry was used for the monitoring of apoptosis on peripheral blood neutrophils at the time of diagnosis and after treatment in both groups of patients. Sodium selenite administration resulted in a significant reduction in neutrophils apoptosis (82+/-10% vs 32+/-18%, p<0.05) and this was associated with significant reduction in infection rate following chemotherapy (67% vs 20%, p<0.05). Also, significant improvement in cardiac ejection fraction was observed (62+/-4% vs 69+/-5% p<0.05). It is concluded that sodium selenite administration at the dosage chosen acts as a cytoprotective agent, alleviating side effects and immunosuppressive effects of cytotoxic chemotherapeutic agents.

Melatonin has antitumor activity via several mechanisms including its antiproliferative and proapoptotic effects in addition to its potent antioxidant actions. Therefore, melatonin may be useful in the treatment of tumors in association with chemotherapy drugs. This study was performed to study the role of melatonin receptors on the cytotoxicity and apoptosis induced by the chemotherapeutic agents cisplatin and 5-fluorouracil in two tumor cell lines, such as human colorectal cancer HT-29 cells and cervical cancer HeLa cells. We found that both melatonin and the two chemotherapeutic agents tested induced a decrease in HT-29 and HeLa cell viability. Furthermore, melatonin significantly increased the cytotoxic effect of chemotherapeutic agents, particularly, in 5-fluorouracil-challenged cells. Stimulation of cells with either of the two chemotherapeutic agents in the presence of melatonin further increased caspase-3 activation. Concomitant treatments with melatonin and chemotherapeutic agents augmented the population of apoptotic cells compared to the treatments with chemotherapeutics alone. Blockade of MT1 and/or MT2 receptors with luzindole or 4-P-PDOT was unable to reverse the enhancing effects of melatonin on both cytotoxicity, caspase-3 activation and the amount of apoptotic cells evoked by the chemotherapeutic agents, whereas when MT3 receptors were blocked with prazosin, the synergistic effect of melatonin with chemotherapy on cytotoxicity and apoptosis was reversed. Our findings provided evidence that in vitro melatonin strongly enhances chemotherapeutic-induced cytotoxicity and apoptosis in two tumor cell lines, namely HT-29 and HeLa cells and, this potentiating effect of melatonin is mediated by MT3 receptor stimulation.

Optimizing chemotherapy for transitional cell carcinoma by application of bcl-2 and bcl-xL antisense oligodeoxynucleotides

Anticancer chemotherapeutic agents are effective in inhibiting growth of cancer cells in vitro and in vivo, however, toxicity to normal cells is a major problem. In this study, we assessed the effect of a novel IH636 grape seed proanthocyanidin extract (GSPE) to ameliorate chemotherapy-induced toxic effects in cultured Chang epithelial cells, established from nonmalignant human tissue. These cells were treated in vitro with idarubicin (Ida) (30 nM) or 4-hydroxyperoxycyclophosphamide (4HC) (1 microg/ml) with or without GSPE (25 microg/ml). The cells were grown in vitro and the growth rate of the cells was determined using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; thiazolyl blue] assay. Our results showed that GSPE decreased the growth inhibitory and cytotoxic effects of Ida as well as 4HC on Chang epithelial cells in vitro. Because these chemotherapeutic agents are known to induce apoptosis in the target cells, we analyzed the Chang epithelial cells for apoptotic cell population by flow cytometry. There was a significant decrease in the number of cells undergoing apoptosis following treatment with GSPE. We also found increased expression of the anti-apoptotic protein Bcl-2 in GSPE-treated cells using western blot techniques. Thus, these results indicate that GSPE can be a potential candidate to ameliorate the toxic effects associated with chemotherapeutic agents and one of the mechanisms of action of GSPE includes upregulation of Bcl-2 expression.

DNA demethylation increases sensitivity of neuroblastoma cells to chemotherapeutic drugs

Enhanced permeation retention (EPR) was a significant milestone discovery by Maeda et al. paving the path for the emerging field of nanomedicine to become a powerful tool in the fight against cancer. Sildenafil is a potent inhibitor of phosphodiesterase 5 (PDE-5) used for the treatment of erectile dysfunction (ED) through the relaxation of smooth muscles and the modulation of vascular endothelial permeability. Overexpression of PDE-5 has been reported in lung, colon, metastatic breast cancers, and bladder squamous carcinoma. Moreover, sildenafil has been reported to increase the sensitivity of tumor cells of different origins to the cytotoxic effect of chemotherapeutic agents with augmented apoptosis mediated through inducing the downregulation of Bcl-xL and FAP-1 expression, enhancing reactive oxygen species (ROS) generation, phosphorylating BAD and Bcl-2, upregulating caspase-3,8,9 activities, and blocking cells at G0/G1 cell cycle phase. Sildenafil has also demonstrated inhibitory effects on the efflux activity of ATP-binding cassette (ABC) transporters such as ABCC4, ABCC5, ABCB1, and ABCG2, ultimately reversing multidrug resistance. Accordingly, there has been a growing interest in using sildenafil as monotherapy or chemoadjuvant in EPR augmentation and management of different types of cancer. In this review, we critically examine the basic molecular mechanism of sildenafil related to cancer biology and discuss the overall potential of sildenafil in enhancing EPR-based anticancer drug delivery, pointing to the outcomes of the most important related preclinical and clinical studies.

Clusterin is a heterodimeric disulfide-linked glycoprotein (449 amino acids) isolated in the rat prostate after castration. It is widely distributed in different tissues and highly conserved in species. There are two isoforms (1 and 2) with antagonistic actions regarding apoptosis. Clusterin is implicated in a number of biological processes, including lipid transport, membrane recycling, cell adhesion, programmed cell death, and complement cascade, representing a truly multifunctional protein. Isoform 2 is overexpressed under cellular stress conditions and protects cells from apoptosis by impeding Bax actions on the mitochondrial membrane and exerts other protumor activities, like phosphatidylinositol 3-kinase/protein kinase B pathway activation, modulation of extracellular signal-regulated kinase 1/2 signaling and matrix metallopeptidase-9 expression, increased angiogenesis, modulation of the nuclear factor kappa B pathway, among others. Its overexpression should be considered as a nonspecific cellular response to a wide variety of tissue insults like cytotoxic chemotherapy, radiation, excess of free oxygen radicals, androgen or estrogen deprivation, etc. A review of the recent literature strongly suggests potential roles for custirsen in particular, and proapoptosis treatments in general, as novel modalities in cancer management. Inhibition of clusterin is known to increase the cytotoxic effects of chemotherapeutic agents, and custirsen, a second-generation antisense oligonucleotide that blocks clusterin, is being tested in a Phase III clinical trial after successful results were achieved in Phase II studies. A major issue in cancer evolution that remains unanswered is whether clusterin represents a driving force of tumorigenesis or a late phenomenon after chemotherapy. This review presents preclinical data that encourages trials in various types of cancer other than advanced castration-resistance prostate cancer and discusses briefly the appropriate timing for clusterin inhibition in the clinical context.

9693 Background: Cyclooxygenase (COX)-2 inhibitors have been shown to exert antitumor activity against human lung cancer cell lines in vitro, and suppressive effect on lung tumors implanted into recipient mice, but concurrent use of COX-2 inhibitors and antineoplastic agents has not been proven clinically to be superior to chemotherapeutic agent alone. Sequential use of COX-2 inhibitors with chemotherapeutic agent might be a possible treatment option. We initiate in vitro study on the growth-inhibitory effect of inductive, concurrent and sequential celecoxib with cisplatin against A549 cell line to determine the most effective dose and schedule for maximal synergistic cytotoxic effects. We anticipate further appropriate treatment strategies to enhance the cytotoxic effect of chemotherapeutic agents using COX-2 inhibitors in the treatment of lung cancer. Methods: A549 cells were incubated with various concentration and combination of celecoxib and cisplatin for 4 days: celecoxib 24 hours prior to cisplatin as induction, celecoxib simultaneous with cisplatin as concurrent, and celecoxib 24 hours subsequent to cisplatin as sequential treatment. Time of exposure to cisplatin for all combination was 72 hours. Cell viability was determined using MTT assay. Results: The IC50 of cisplatin and celecoxib alone to A549 cell line was 16.64μM/l and 90.42μM/l, respectively. IC50 of cisplatin with celecoxib at 1.55μM/l for induction and concurrent treatment was 23.31μM/l, and 16.52μM/l, respectively, which was not superior to cisplatin alone while that of sequential treatment was 9.98μM/l, which showed synergistic cytotoxic effect against A549 cell line. Conclusions: Sequential celecoxib subsequent to cisplatin exerted the most potent in vitro synergistic cytotoxic effect against lung cancer cells. These may provide a rationale for future clinical trial to evaluate the effect of incorporating COX-2 inhibitors into the cisplatin-based regimen for the treatment of lung cancer. No significant financial relationships to disclose.

HSPC1 is a critical protein in cancer development and progression, including colorectal cancer (CRC). However, clinical trial data reporting the effectiveness of HSPC1 inhibitors on several cancer types has not been as successful as predicted. Furthermore, some N-terminal inhibitors appear to be much more successful than others despite similar underlying mechanisms. This study involved the application of three N-terminal HSPC1 inhibitors, 17-DMAG, NVP-AUY922 and NVP-HSP990 on CRC cells. The effects on client protein levels over time were examined. HSPC1 inhibitors were also applied in combination with chemotherapeutic agents commonly used in CRC treatment (5-fluorouracil, oxaliplatin and irinotecan). As HSPA1A and HSPB1 have anti-apoptotic activity, gene-silencing techniques were employed to investigate the significance of these proteins in HSPC1 inhibitor and chemotherapeutic agent resistance. When comparing the action of the three HSPC1 inhibitors, there are distinct differences in the time course of important client protein degradation events. The differences between HSPC1 inhibitors were also reflected in combination treatment—17-DMAG was more effective compared with NVP-AUY922 in potentiating the cytotoxic effects of 5-fluorouracil, oxaliplatin and irinotecan. This study concludes that there are distinct differences between N-terminal HSPC1 inhibitors, despite their common mode of action. Although treatment with each of the inhibitors results in significant induction of the anti-apoptotic proteins HSPA1A and HSPB1, sensitivity to HSPC1 inhibitors is not improved by gene silencing of HSPA1A or HSPB1. HSPC1 inhibitors potentiate the cytotoxic effects of chemotherapeutic agents in CRC, and this approach is readily available to enter clinical trials. From a translational point of view, there may be great variability in sensitivity to the inhibitors between individual patients.

Osteosarcomas are the most common malignant bone tumors. Although the multi-agent chemotherapy has improved the long-term survival rate of osteosarcoma patients, some patients show a poor response to chemotherapy, leading to recurrence and poor prognosis. Therefore, the enhancement of chemosensitivity is required to cure patients with osteosarcomas. We recently developed a telomerase-specific replication-competent oncolytic adenovirus, Telomelysin (OBP-301), and confirmed the antitumor effect of OBP-301 in human osteosarcoma cells. A phase I clinical trial in US has also shown the safety of OBP-301 in cancer patients. In this study, we investigated whether OBP-301 enhances the antitumor effect of chemotherapeutic agents, doxorubicin and cisplatin, that are used for the treatment of osteosarcomas, and the molecular mechanism of chemotherapy- and OBP-301-mediated cell death pathway, autophagy and apoptosis, in human osteosarcoma cell lines. We used four human osteosarcoma cell lines, HOS, MNNG/HOS, 143B and SaOS2. OBP-301 is an attenuated adenovirus, in which the human telomerase reverse transcriptase (hTERT) promoter element drives expression of E1A and E1B genes, and causes tumor-selective lysis in a variety of human malignant tumor cells with high telomerase activity. OBP-301 infection enhanced the cytotoxic effect of chemotherapeutic agents and the calculation of combination index revealed the synergistic effects in all human osteosarcoma cell lines. To analyze the molecular mechanism in the synergistic effect induced by combination therapy, western blot analysis for apoptosis (PARP) and autophagy (LC3, p62) was performed. Combination of OBP-301 increased both apoptosis (the cleavage of PARP) and autophagy (conversion of LC3-I to LC3-II and p62 downregulation) in the chemotherapeutic agents-treated human osteosarcoma cells. In contrast, the replication of OBP-301 was not suppressed by chemotherapeutic agents. Moreover, combination therapy of chemotherapeutic agents with OBP-301 significantly suppressed tumor growth in a subcutaneous xenograft tumor model compared to monotherapy with chemotherapeutic agents or OBP-301. These results suggest that combination therapy of chemotherapeutic agents with OBP-301 provides a novel therapeutic strategy for human osteosarcomas. Citation Format: Shuhei Osaki, Tsuyoshi Sasaki, Hiroshi Tazawa, Joe Hasei, Yasuaki Yamakawa, Yuuri Hashimoto, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Enhanced chemosensitivity of osteosarcoma cells by telomerase-specific oncolytic adenovirus in combination therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 584. doi:10.1158/1538-7445.AM2013-584

74 Novel class I PI3K inhibitor CH5132799: disruption of the activated PI3K signaling in PIK3CA mutants confers potent antitumor efficacy