Ronald Richard Linnartz

A comprehensive survey of genomic alterations in gastric cancer reveals systematic patterns of molecular exclusivity and co-occurrence among distinct therapeutic targets

Objective Gastric cancer is a major gastrointestinal malignancy for which targeted therapies are emerging as treatment options. This study sought to identify the most prevalent molecular targets in gastric cancer and to elucidate systematic patterns of exclusivity and co-occurrence among these targets, through comprehensive genomic analysis of a large panel of gastric cancers. Design Using high-resolution single nucleotide polymorphism arrays, copy number alterations were profiled in a panel of 233 gastric cancers (193 primary tumours, 40 cell lines) and 98 primary matched gastric non-malignant samples. For selected alterations, their impact on gene expression and clinical outcome were evaluated. Results 22 recurrent focal alterations (13 amplifications and nine deletions) were identified. These included both known targets (FGFR2, ERBB2) and also novel genes in gastric cancer (KLF5, GATA6). Receptor tyrosine kinase (RTK)/RAS alterations were found to be frequent in gastric cancer. This study also demonstrates, for the first time, that these alterations occur in a mutually exclusive fashion, with KRAS gene amplifications highlighting a clinically relevant but previously underappreciated gastric cancer subgroup. FGFR2-amplified gastric cancers were also shown to be sensitive to dovitinib, an orally bioavailable FGFR/VEGFR targeting agent, potentially representing a subtype-specific therapy for FGFR2-amplified gastric cancers. Conclusion The study demonstrates the existence of five distinct gastric cancer patient subgroups, defined by the signature genomic alterations FGFR2 (9% of tumours), KRAS (9%), EGFR (8%), ERBB2 (7%) and MET (4%). Collectively, these subgroups suggest that at least 37% of gastric cancer patients may be potentially treatable by RTK/RAS directed therapies.

Targeting PI3K/mTOR Overcomes Resistance to HER2-Targeted Therapy Independent of Feedback Activation of AKT

Purpose: Altered PI3K/mTOR signaling is implicated in the pathogenesis of a number of breast cancers, including those resistant to hormonal and HER2-targeted therapies. Experimental Design: The activity of four classes of PI3K/mTOR inhibitory molecules, including a pan-PI3K inhibitor (NVP-BKM120), a p110α isoform–specific PI3K inhibitor (NVP-BYL719), an mTORC1-specific inhibitor (NVP-RAD001), and a dual PI3K/mTORC1/2 inhibitor (NVP-BEZ235), was evaluated both in vitro and in vivo against a panel of 48 human breast cell lines. Results: Each agent showed significant antiproliferative activity in vitro, particularly in luminal estrogen receptor–positive and/or HER2+ cell lines harboring PI3K mutations. In addition, monotherapy with each of the four inhibitors led to significant inhibition of in vivo growth in HER2+ breast cancer models. The PI3K/mTOR pathway inhibitors were also effective in overcoming both de novo and acquired trastuzumab resistance in vitro and in vivo. Furthermore, combined targeting of HER2 and PI3K/mTOR leads to increased apoptosis in vitro and induction of tumor regression in trastuzumab-resistant xenograft models. Finally, as previously shown, targeting mTORC1 alone with RAD001 leads to consistent feedback activation of AKT both in vitro and in vivo, whereas the dual mTOR1–2/PI3K inhibitor BEZ235 eliminates this feedback loop. However, despite these important signaling differences, both molecules are equally effective in inhibiting tumor cell proliferation both in vitro and in vivo. Conclusion: These preclinical data support the findings of the BOLERO 3 trial that shows that targeting of the PI3K/mTOR pathway in combination with trastuzumab is beneficial in trastuzumab-resistant breast cancer. Clin Cancer Res; 20(13); 3507–20. ©2014 AACR.

Dovitinib demonstrates antitumor and antimetastatic activities in xenograft models of hepatocellular carcinoma

BACKGROUND & AIMS Hepatocellular carcinoma (HCC) is the third leading cause of cancer death. Although sorafenib has been shown to improve survival of patients with advanced HCC, this improvement is modest and patients eventually have refractory disease. This study aims at investigating the antitumor, antiangiogenesis and antimetastatic activities of dovitinib in preclinical models of HCC. METHODS 21-0208 and SK-HEP1 cells as well as patient-derived HCC models were employed to study the antitumor effect of dovitinib. Changes of biomarkers relevant to FGFR/VEGFR/PDGFR pathways were determined by Western blotting. Microvessel density, apoptosis and cell proliferation were analyzed by immunohistochemistry. RESULTS Treatment of SK-HEP1 cells with dovitinib resulted in G2/M cell cycle arrest, inhibition of colony formation in soft agar and blockade of bFGF-induced cell migration. Dovitinib inhibited basal expression and FGF-induced phosphorylation of FGFR-1, FRS2-α and ERK1/2. In vivo, dovitinib potently inhibited tumor growth of six HCC lines. Inhibition of angiogenesis correlated with inactivation of FGFR/PDGFR-β/VEGFR-2 signaling pathways. Dovitinib also caused dephosphorylation of retinoblastoma, upregulation of p-histone H2A-X and p27, and downregulation of p-cdk-2 and cyclin B1, which resulted in a reduction in cellular proliferation and the induction of tumor cell apoptosis. In an orthotopic model, dovitinib potently inhibited primary tumor growth and lung metastasis and significantly prolonged mouse survival. CONCLUSIONS Dovitinib demonstrated significant antitumor and antimetastatic activities in HCC xenograft models. This study provides a compelling rationale for clinical investigation in patients with advanced HCC.

Population pharmacokinetics/toxicodynamics (PK/TD) relationship of SAM486A in phase I studies in patients with advanced cancers

SAM486A (previously termed CGP 48664), a potent inhibitor of S‐adenosylmethionine decarboxylase, is under clinical development for the treatment of advanced refractory malignancies. Hematological toxicity manifested by dose‐dependent neutropenia has been observed in phase I studies. Population methods were used to investigate pharmacokinetics (PK) as a prognostic factor for safety end point (hematological toxicity) in patients with advanced cancers. SAM486A plasma concentrations and neutrophil counts were collected from three ascending‐dose tolerability and PK studies (study 1: single 5‐day continuous intravenous (IV) infusion with doses ranging from 24–700 mg/m2/cycle; study 2:10‐minute to 3‐hour IV infusion once weekly with doses ranging from 16–325 mg/m2/week; study 3: 1‐hour IV infusion once daily for 5 days with doses ranging from 3.6–202.8 mg/m2/day). The PK of SAM486A were best estimated by a population linear three‐compartment model with NONMEM (version 5) using data from 79 patients in studies 1 through 3. The population pharmacokinetic parameters (SD) were CL = 6.2 (0.4) l/h/m2, Q2 = 15.4(1.5) l/h/m2, Q3, = 33.6 (5.3) l/h/m2, V1 = 9.5 (1.6) l/m2, V2 = 672 (52) l/m2, and V3 = 39.9 (8.3) l/m2, and the corresponding intersubject variability was 45.4%, 74.0%, 85.3%, 80.1%, 37.0%, and 103%, respectively, where CL is total body clearance, Q2 and Q3 are intercompartmental clearances, and V1, V2, and V3 are the volumes of distribution in central and peripheral compartments, respectively. The intrasubject variability was 24.0%. The cumulative AUC before the onset of neutrophil nadir count (AUC) and the duration of exposure over threshold SAM486A concentrations in the range of 0.05 to 0.1 μM based on Bayesian PK parameter estimates significantly correlated with absolute neutrophil count nadir (< 5 × 109/l). AUC showed the best correlation (R2 = 0.72) with absolute neutrophil count nadir by an inhibitory sigmoid Emax model and also correlated with percent decrease in neutrophil count from baseline to nadir by a simple Emax model (R2 = 0.53). Logistic regression analysis indicated that AUC and the duration of exposure over 0.05 to 0.1 μM, but not Cmax, were strong predictors of grade 4 neutropenia (< 0.5 × 109/l). Drug exposure parameters such as AUC derived from population analysis may be used clinically as a useful predictor of drug‐induced neutropenia.

Abstract 4756: In vivo efficacy of combined targeting of CDK4/6, ER and PI3K signaling in ER+ breast cancer

Approximately 60-70% of invasive breast cancers express estrogen receptor (ER) and/or progesterone receptor and are termed hormone receptor positive (ER+). Endocrine therapy remains the therapeutic backbone for the treatment of ER+ cancers and although anti-estrogen therapies are initially frequently effective, 50% of ER+ patients develop resistance to hormonal manipulation within their lifetime, ultimately leading to therapeutic failure. Two emerging mechanisms of endocrine resistance include activation of growth signaling pathways such as the phosphatidylinositol 3-kinase (PI3K) pathway and more recently, the decoupling of cell cycle control from ER-signaling, via deregulation of the cyclinD-cyclin dependent kinase (CDK-4/6:INK4:Rb) pathway. In this study we hypothesized that combining an anti-estrogen (letrozole or fulvestrant) with a CDK-4/6 inhibitor (LEE011) and PI3K inhibitors (buparlisib [BKM120; pan-PI3K inhibitor] or BYL719 [α-specific PI3K inhibitor] would elicit an improved tumor response over agents inhibiting either pathway alone. Four ER+ BC mouse models including, an ER+ patient primary human letrozole sensitive model (HBX34, PTEN/PIK3CA wild-type) and three ER+ cell lines; ZR75-1 (PTEN null), MCF7 (PIK3CA mutant) and KPL1 (PTEN/PIK3CA wild-type) were used for this study. Treatment was carried out daily at doses relevant to clinical exposures for a period of 4 weeks with fulvestrant combinations and 8 weeks with letrozole combinations followed by observation for tumor progression. Treatment doses were as follows: LEE011 (75 mg/kg), BKM120 (30mg/kg), BYL719 (35mg/kg), Letrozole (2.5mg), Fulvestrant (5mg/wk) either as single agents or in combinations (Hormone therapy (HT)+LEE011, HT+PI3Ki, HT+LEE011+PI3Ki). Significant tumor growth inhibition (TGI) was observed for single agent treatment with the CDK-4/6 inhibitor in each of the four ER+ xenograft models. The addition of letrozole (HBX34) or fulvestrant (MCF7, ZR751 and KPL1) with LEE011 increased the TGI observed with single agent. The triplet combination with each PI3K inhibitor increased the (TGI) even further, inducing tumor regressions in each of the four models. Response was independent of PI3K/PTEN mutation status. Complete tumor regressions were observed for a subset of mice within each of the triple combination arms. Tumor regressions were maintained for up to four weeks post-interruption of treatment. No significant toxicities were observed with any of the triplet combinations. These preclinical data highlight the potential efficacy and safety of targeting the ER, CDK-4/6 and PI3K signaling pathways in ER+ breast cancer. LEE011 in combination with an anti-estrogen is sufficient to inhibit tumor growth in vivo, while the addition of a PI3K inhibitor results in robust tumor regressions. The combination of LEE011 with an anti-estrogen and a PI3K inhibitor is a rational therapeutic approach that should be investigated in the clinic. Citation Format: Neil A. O9Brien, Emmanuelle Di Tomaso, Raul Ayala, Luo Tong, Shawnt Issakhanian, Ronald Linnartz, Richard S. Finn, Samit Hirawat, Dennis J. Slamon. In vivo efficacy of combined targeting of CDK4/6, ER and PI3K signaling in ER+ breast cancer. [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 4756. doi:10.1158/1538-7445.AM2014-4756

Abstract 3589: Dovitinib (TKI258), a multikinase inhibitor of FGFR, PDGFR, and VEGFR tyrosine kinases, induces growth inhibition in endometrial carcinoma cells

Background: Endometrial carcinoma is the most common gynecological malignancy in the western world. Activating mutations of the fibroblast growth factor receptor 2 (FGFR2) have been described in 12-16% of endometrial cancers. Moreover, vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF) and their receptors are involved in the neovascularization, invasiveness, and metastatic potential of endometrial cancer. Therefore, suppression of FGFR/VEGFR/PDGFR signaling by TKI258 may represent a novel approach for treatment of endometrial cancer. Experimental Design: The aims of this study were 1.) to assess the effect of TKI258 on tumor cell growth in two-dimensional (2D) and three-dimensional (3D) culture assays using a panel of 20 human endometrial cancer cell lines, 2.) to identify candidate molecular markers predicting sensitivity using baseline gene expression profiling and mutational analyses, and 3.) to determine the in vivo antineoplastic activity of TKI258 in endometrial cancer xenograft models. In addition, we screened 200 fresh frozen endometrial cancer specimens to comprehensively assess the distribution pattern of PI3K, PTEN, and FGFR mutations in endometrial cancer. Results: Concentration-dependent anti-proliferative effects of TKI285 using 2D assays were seen in all endometrial cancer cell lines tested, but varied significantly between individual cell lines (IC50 range: 0.42µM – 3.06 µM). The three most sensitive endometrial cancer cell lines demonstrated activating FGFR2 mutations (MFE296: N549K, IC50 0.42µM; AN3CA: N549K and K310R, IC50 0.50µM; MFE280: S252W, IC50 0.66µM). Assessment of TKI258 responses in 3D assays demonstrated similar results to those observed in 2D culture assays in that the 3 cell lines harboring FGFR2 mutations were the most sensitive to TKI258 achieving 100% growth inhibition at a concentration of 1µM. AN3CA and MFE296 endometrial cancer cells formed xenografts in nude mice and antitumor activity was studied in both models. Inhibition of p-FGFR, p-PDGFR, p-VEGFR-2, pAKT and p-ERK1/2 were observed. Comprehensive data on the pattern of PI3K, PTEN and FGFR mutations in endometrial cancer will be provided. Conclusion: TKI258 demonstrates significant antitumor activity in endometrial cancer cells with FGFR2 mutations. This study provides a strong rationale for the clinical evaluation of TKI258 in patients with endometrial cancer, specifically in those harboring FGFR2 mutations. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3589. doi:10.1158/1538-7445.AM2011-3589

Abstract 2437: MEK162 (ARRY 438162), a MEK1/2 inhibitor, has activity in melanoma cells independent of BRAF and NRAS mutation status.

Background. Activation of the Ras/Raf/MEK/MAP kinase pathway is implicated in uncontrolled cell proliferation and tumor growth. Mutated, oncogenic forms of Ras are found in colon, pancreatic, and lung cancers; BRAF mutations have been identified in more than 60% of malignant melanomas and from 40-60% of papillary thyroid cancers. MEK, a dual specific kinase, is a key player in this pathway; it is downstream of both Ras and Raf and activates ERK1/2 through phosphorylation of key tyrosine and threonine residues. MEK162 (ARRY 438162) is a novel small molecule ATP-uncompetitive inhibitor of the kinases MEK1 and MEK2. MEK162 showed promising data in an ongoing Phase 2 Clinical Trial in patients with BRAF and NRAS mutated advanced melanoma. This is the first targeted therapy to show activity in patients with NRAS mutated melanoma. Methods and Results. The melanoma cell line panel was the most sensitive after investigating the growth inhibitory effect of MEK162 on 328 cancer cell lines from diverse histologies including melanoma, head and neck, colon, pancreas, lung, ovarian, liver, kidney, breast and endometrial. When a cutoff of IC50 70% Inhibition at 1uM after 6 days of culture was used 83% out of 47 melanoma cell lines were sensitive to the treatment with the MEK inhibitor. Sensitivity to MEK162 was independent of BRAFV600E andNRASQ61mutation status in this cell line panel. Cell cycle arrest and apoptosis was assessed upon exposure to MEK162 using flow cytometry. MEK162 led to a G1 arrest and marked increase in apoptotic cells in the majority of the sensitive melanoma cell lines regardless of their origin and oncogenic driver mutations. Western blots were used to characterize the changes induced by exposure to MEK162 in the MAPK and PI3K/mTOR pathways. MEK1/2 inhibition resulted in a decrease in pERK in all the cell lines tested regardless of their mutational status and the in vitro sensitivity. We observed an increase in pMEK more prominently in NRASQ61L mutant and wild type for NRAS and BRAF mutations cell lines than in BRAFV600Emutant cell lines. We found pAKT and pS6 decreased in the NRAS and BRAF mutant cell lines after treatment, suggesting that the inhibition of the mTOR pathway by MEK162 may be crucial for the sensitivity to the drug. Conclusion. These data provide evidence for supporting the use of MEK162 in the treatment of patients with melanoma. Citation Format: Erika M. Von Euw, Hong-Mei Rong, Neil O9Brien, Dylan Conklin, Veerauo Konkankit, Ke-Wei Gong, Angela Zubel, Ronald Linnartz, Richard Finn, Bartosz Chmielowski, Dennis Slamon. MEK162 (ARRY 438162), a MEK1/2 inhibitor, has activity in melanoma cells independent of BRAF and NRAS mutation status. [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 2437. doi:10.1158/1538-7445.AM2013-2437

Abstract 3575: Dovitinib (TKI258), a dual inhibitor of FGFR and VEGFR, induces tumor growth suppression in xenograft models of human bladder cancer

Introduction: The aim of this study was to evaluate the efficacy of dovitinib (TKI258), a small molecule dual inhibitor of fibroblast growth factor receptor (FGFR) and vascular endothelial growth factor receptor (VEGFR) in mouse models of human bladder cancer. Molecular epidemiological studies have implicated FGFR and VEGFR pathways in the pathogenesis of high grade, muscle invasive bladder cancer. Somatic activating mutations in FGFR3 have been identified in 16%-20% of muscle-invasive bladder cancer and FGFR3 overexpression has also been documented in a high fraction of bladder cancers. High microvessel density, serum VEGF levels and urine FGF2 levels have also been associated with high grade bladder cancer and poor disease-free survival. Dual FGFR/VEGFR inhibitory activities of dovitinib make it an attractive molecule targeting advanced bladder cancer. Experimental Design: Dovitinib was evaluated in the RT112 human bladder carcinoma xenograft model. Dovitinib was administered orally at three dose levels (n = 10/group), once daily for 28 consecutive days (qd × 28). A rat RT112 xenograft study was also carried out to evaluate the PK/PD effect of single dose dovitinib administration. Results: Dovitinib at 15, 30, and 60 mg/kg resulted in tumor growth suppression, with mean changes of 60% T/C, 6% T/C (P Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3575. doi:10.1158/1538-7445.AM2011-3575

Abstract 4150: Anti-tumor activity of the PI3K/mTOR pathway inhibitors alpelisib (BYL719) and everolimus (RAD001) in xenograft models of acquired resistance to CDK-4/6 targeted therapy

The selective cyclin dependent kinases 4 and 6 (CDK-4/6) inhibitor, palbociclib, has recently been approved in combination with endocrine-based therapies for the treatment of advanced ER+/HER2- breast cancer (BC). Despite the improvements in progression-free and overall survivals, a significant number of patients on CDK-4/6 therapy will go on to develop progressive disease. As such, it is critical to identify the mechanisms by which tumor cells evade CDK-4/6 targeted therapy and to develop therapeutic strategies to overcome resistance. In this study, we evaluated the efficacy of a p110α-selective PI3K inhibitor, alpelisib (BYL719) and the mTORC1 specific inhibitor, everolimus (RAD001), in ER+/HER2- xenograft tumors conditioned in vitro and in vivo to acquire resistance to combined palbociclib + endocrine-based therapy. The EFM19 (ER+/HER2-, PIK3CA mt), MDA134 (ER+/HER2-, PIK3CA wt), and MDA361 (ER+/HER2+, PIK3CA mt) BC cell lines were conditioned to acquire palbociclib resistance through long-term culture in the presence of increasing concentrations of drug. Baseline total/phosphoprotein levels of over 280 cancer-associated analytes were measured in the parental and resistant cell lines by Reverse Phase Protein Array (RPPA). In vivo resistant models were developed from xenografts of the MCF7 and HCC1500 ER+ BC cell lines, treated until progression with palbociclib (75 mg/kg) + fulvestrant (5 mg/mse). EFM19-PR cells maintained palbociclib resistance in vivo and were included in the xenograft studies. Resistance to palbociclib was confirmed in vitro by a shift in growth inhibitory IC50 from an average of less 50nM to over 1 µM. Significantly reduced Rb and ER protein levels were detected in each of these palbociclib resistant cell lines by RPPA. Cross-resistance to an alternative CDK-4/6 inhibitor (ribociclib) was found in in vitro studies. In addition, switching treatment of the xenografts progressing on palbociclib + fulvestrant to ribociclib (75mg/kg) + fulvestrant did not impact tumor progression. However, when progressing tumors were switched to BYL719 (30mg/kg) + fulvestrant or RAD001 (10mg/kg) + fulvestrant, sustained tumor regression was observed for over 45 days of treatment in every model tested. The triplet combination of ribociclib + fulvestrant + BYL719 or RAD001 provided marginal additional benefit over the doublet combination of BYL719 or RAD001 + fulvestrant. RPPA analysis of xenograft tissue collected from these studies will help to identify additional molecular alterations involved in resistance to CDK-4/6 targeted therapy. These preclinical data indicate that acquired resistance to CDK-4/6 inhibition occurs through a loss of dependence on Rb-signaling. However, targeting an alternative pathway like PI3K/mTOR with molecules such as BYL719 or RAD001 may be a viable strategy for further clinical investigation. Citation Format: Neil A. O9Brien, Dylan Conklin, Tong Luo, Raul Ayala, Shawnt Issakhanian, Ondrej Kalous, Erika Von Euw, Sara A. Hurvitz, Emmanuelle DiTomaso, Faye Su, Ronald Linnartz, Stefan Scherer, Samit Hirawat, Dennis J. Slamon. Anti-tumor activity of the PI3K/mTOR pathway inhibitors alpelisib (BYL719) and everolimus (RAD001) in xenograft models of acquired resistance to CDK-4/6 targeted therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4150. doi:10.1158/1538-7445.AM2017-4150

Abstract 4698: Combination of ceritinib (LDK378) with PI3K inhibitors (buparlisib [BKM120] and alpelisib [BYL719]) demonstrates synergistic preclinical antitumor activity in ALK-rearranged non-small cell lung cancer (NSCLC)

Introduction: NSCLCs harboring rearrangements of the anaplastic lymphoma kinase (ALK) gene are highly sensitive to ALK inhibition. Ceritinib is a novel ALK inhibitor that demonstrates significant preclinical and clinical antitumor potency, including in tumors that have developed resistance to the approved ALK inhibitor crizotinib. Upregulation of the phosphatidylinositol 3-kinase (PI3K) pathway may be involved in ALK inhibitor resistance, suggesting that combining ceritinib with a PI3K inhibitor may provide synergistic antitumor activity in ALK-rearranged NSCLC. Here, we assess the synergy and antiproliferative activity of PI3K inhibitor/ceritinib combinations in crizotinib-naive primary preclinical models of NSCLC. Methods: In vitro experiments used the EML4−ALK-translocated lung cancer cell line H2228 to screen for synergistic combinations of ceritinib with 18 other compounds (PI3K, MEK, and CDK4/6 inhibitors, among others). In vivo experiments used a human-mouse primary xenograft lung cancer model with similar EML4−ALK translocation (LUF1656). Tumor fragments (diameter 2−3 mm) from stock mice inoculated with LUF1656 lung cancer tissue were harvested and used for inoculation into nu/nu mice for tumor development. Once mean tumor size had reached ∼150 mm3, treatment was initiated with single-agent or combination regimens of buparlisib (pan-PI3K inhibitor; 35 mg/kg QD), alpelisib (PI3Kα inhibitor; 30 mg/kg QD), or ceritinib (25 mg/kg [low dose] or 50 mg/kg [full dose] QD). All doses used were equivalent to known therapeutic doses in patients. Results: In vitro experiments revealed the strongest antiproliferative activity when ceritinib was combined with either buparlisib or alpelisib versus the other compounds tested. In vivo, low-dose ceritinib in combination with buparlisib improved tumor growth delay over single-agent, full-dose ceritinib. Full-dose ceritinib plus alpelisib showed no significant difference in tumor growth delay versus full-dose ceritinib alone. Low-dose ceritinib plus alpelisib appeared to be better tolerated than full-dose ceritinib plus alpelisib, but with similar efficacy to low-dose ceritinib alone. A delayed tumor growth rate after treatment interruption was noted in all ceritinib combinations. Conclusion: Synergy was observed between ceritinib and PI3K inhibitors in a crizotinib-naive ALK-translocated lung model in vitro. In the in vivo EML4−ALK lung preclinical cancer models, low-dose ceritinib (25 mg/kg) combined with buparlisib showed improved efficacy versus full-dose ceritinib (50 mg/kg) alone. Preclinical experiments exploring combinations of PI3K- and ALK-targeted therapies in crizotinib-resistant ALK-rearranged tumors are also ongoing. Citation Format: Emmanuelle Di Tomaso, Ronald Linnartz, Fang Li, Cristian Massacesi, Samit Hirawat. Combination of ceritinib (LDK378) with PI3K inhibitors (buparlisib [BKM120] and alpelisib [BYL719]) demonstrates synergistic preclinical antitumor activity in ALK-rearranged non-small cell lung cancer (NSCLC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4698. doi:10.1158/1538-7445.AM2015-4698