PARP Inhibitor Efficacy Depends on CD8+ T-cell Recruitment via Intratumoral STING Pathway Activation in BRCA-Deficient Models of Triple-Negative Breast Cancer

Combinatorial clinical trials of PARP inhibitors with immunotherapies are ongoing, yet the immunomodulatory effects of PARP inhibition have been incompletely studied. Here, we sought to dissect the mechanisms underlying PARP inhibitor-induced changes in the tumor microenvironment of BRCA1-deficient triple-negative breast cancer (TNBC). We demonstrate that the PARP inhibitor olaparib induces CD8⁺ T-cell infiltration and activation in vivo, and that CD8⁺ T-cell depletion severely compromises antitumor efficacy. Olaparib-induced T-cell recruitment is mediated through activation of the cGAS/STING pathway in tumor cells with paracrine activation of dendritic cells and is more pronounced in HR-deficient compared with HR-proficient TNBC cells and in vivo models. CRISPR-mediated knockout of STING in cancer cells prevents proinflammatory signaling and is sufficient to abolish olaparib-induced T-cell infiltration in vivo. These findings elucidate an additional mechanism of action of PARP inhibitors and provide a rationale for combining PARP inhibition with immunotherapies for the treatment of TNBC. SIGNIFICANCE: This work demonstrates cross-talk between PARP inhibition and the tumor microenvironment related to STING/TBK1/IRF3 pathway activation in cancer cells that governs CD8⁺ T-cell recruitment and antitumor efficacy. The data provide insight into the mechanism of action of PARP inhibitors in BRCA-associated breast cancer.This article is highlighted in the In This Issue feature, p. 681.

Olaparib and α-specific PI3K inhibitor alpelisib for patients with epithelial ovarian cancer: a dose-escalation and dose-expansion phase 1b trial

BACKGROUND

Based on preclinical work, we found that combination of poly (ADP-ribose) polymerase (PARP) inhibitors with drugs that inhibit the homologous recombination repair (HRR) pathway (such as PI3K inhibitors) might sensitise HRR-proficient epithelial ovarian cancers to PARP inhibitors. We aimed to assess the safety and identify the recommended phase 2 dose of the PARP inhibitor olaparib in combination with the PI3K inhibitor alpelisib in patients with epithelial ovarian cancer and in patients with breast cancer.

METHODS

In this multicentre, open-label, phase 1b trial following a 3 + 3 dose-escalation design, we recruited patients aged 18 years or older with the following key eligibility criteria: confirmed diagnosis of either recurrent ovarian, fallopian tube, or primary peritoneal cancer of high-grade serous histology; confirmed diagnosis of either recurrent ovarian, fallopian tube, or primary peritoneal cancer of any histology with known germline BRCA mutations; confirmed diagnosis of recurrent breast cancer of triple-negative histology; or confirmed diagnosis of recurrent breast cancer of any histology with known germline BRCA mutations. Additional patients with epithelial ovarian cancer were enrolled in a dose-expansion cohort. Four dose levels were planned: the starting dose level of alpelisib 250 mg once a day plus olaparib 100 mg twice a day (dose level 0); alpelisib 250 mg once a day plus olaparib 200 mg twice a day (dose level 1); alpelisib 300 mg once a day plus olaparib 200 mg twice a day (dose level 2); and alpelisib 200 mg once a day plus olaparib 200 mg twice a day (dose level 3). Both drugs were administered orally, in tablet formulation. The primary objective was to identify the maximum tolerated dose and the recommended phase 2 dose of the combination of alpelisib and olaparib for patients with epithelial ovarian cancer and patients with breast cancer. Analyses included all patients who received at least one dose of the study drugs. The trial is active, but closed to enrolment; follow-up for patients who completed treatment is ongoing. This trial is registered with ClinicalTrials.gov, number NCT01623349.

FINDINGS

Between Oct 3, 2014, and Dec 21, 2016, we enrolled 34 patients (28 in the dose-escalation cohort and six in the dose-expansion cohort); two in the dose-escalation cohort were ineligible at the day of scheduled study initiation. Maximum tolerated dose and recommended phase 2 dose were identified as alpelisib 200 mg once a day plus olaparib 200 mg twice a day (dose level 3). Considering all dose levels, the most common treatment-related grade 3-4 adverse events were hyperglycaemia (five [16%] of 32 patients), nausea (three [9%]), and increased alanine aminotransferase concentrations (three [9%]). No treatment-related deaths occurred. Dose-limiting toxic effects included hyperglycaemia and fever with decreased neutrophil count. Of the 28 patients with epithelial ovarian cancer, ten (36%) achieved a partial response and 14 (50%) had stable disease according to Response Evaluation Criteria in Solid Tumors 1.1.

INTERPRETATION

Combining alpelisib and olaparib is feasible with no unexpected toxic effects. The observed activity provides preliminary clinical evidence of synergism between olaparib and alpelisib, particularly in epithelial ovarian cancer, and warrants further investigation.

FUNDING

Ovarian Cancer Dream Team (Stand Up To Cancer, Ovarian Cancer Research Alliance, National Ovarian Cancer Coalition), Breast Cancer Research Foundation, Novartis.

Identifying and Targeting Sporadic Oncogenic Genetic Aberrations in Mouse Models of Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBC) are genetically characterized by aberrations in TP53 and a low rate of activating point mutations in common oncogenes, rendering it challenging in applying targeted therapies. We performed whole-exome sequencing (WES) and RNA sequencing (RNA-seq) to identify somatic genetic alterations in mouse models of TNBCs driven by loss of Trp53 alone or in combination with Brca1 Amplifications or translocations that resulted in elevated oncoprotein expression or oncoprotein-containing fusions, respectively, as well as frameshift mutations of tumor suppressors were identified in approximately 50% of the tumors evaluated. Although the spectrum of sporadic genetic alterations was diverse, the majority had in common the ability to activate the MAPK/PI3K pathways. Importantly, we demonstrated that approved or experimental drugs efficiently induce tumor regression specifically in tumors harboring somatic aberrations of the drug target. Our study suggests that the combination of WES and RNA-seq on human TNBC will lead to the identification of actionable therapeutic targets for precision medicine-guided TNBC treatment.Significance: Using combined WES and RNA-seq analyses, we identified sporadic oncogenic events in TNBC mouse models that share the capacity to activate the MAPK and/or PI3K pathways. Our data support a treatment tailored to the genetics of individual tumors that parallels the approaches being investigated in the ongoing NCI-MATCH, My Pathway Trial, and ESMART clinical trials. Cancer Discov; 8(3); 354-69. ©2017 AACR.See related commentary by Natrajan et al., p. 272See related article by Matissek et al., p. 336This article is highlighted in the In This Issue feature, p. 253.

Serial-omics of P53-/-, Brca1-/- Mouse Breast Tumor and Normal Mammary Gland

This study demonstrates a liquid-liquid extraction for the sequential tandem mass spectrometry (LC-MS/MS) analysis of non-polar lipids, polar metabolites, proteins and phosphorylation sites from a single piece of tissue. Extraction of 10 mg BRCA-/-, p53-/- breast tumor tissue or normal mammary gland tissue with methyl-tert-butyl ether (MTBE) results in three phases: an upper non-polar phase containing 1,382 lipids, a lower polar phase with 805 metabolites and a precipitated protein pellet with 4,792 proteins with 1,072 phosphorylation sites. Comparative analysis revealed an activated AKT-mTOR pathway in tumors. Tumors also showed a reduction of phosphorylation sites involved in transcription and RNA splicing and decreased abundance of enzymes in lipid synthesis. Analysis of polar metabolites revealed a reduction in glycolysis, pentose phosphate pathway, polyamines and nucleotides, but an increase in TCA and urea cycle intermediates. Analysis of lipids revealed a shift from high triglycerides in mammary gland to high phospholipid levels in tumors. The data were integrated into a model showing breast tumors exhibit features on the proteomic, lipidomic and metabolomic level that are distinct from normal breast tissue. Our integrative technique lends itself to samples such as tumor biopsies, dried blood spots and fluids including urine and CSF to develop biomarkers of disease.

Abstract CT008: Phase I study of the alpha specific PI3-Kinase inhibitor BYL719 and the poly (ADP-Ribose) polymerase (PARP) inhibitor olaparib in recurrent ovarian and breast cancer: Analysis of the dose escalation and ovarian cancer expansion cohort

Background: In vivo synergy with concurrent PI3-Kinase inhibition and PARP inhibition has been observed in BRCA-deficient and BRCA-proficient preclinical models of triple negative breast cancer (TNBC) and ovarian cancer (OC). A phase I trial of the oral pan-class I PI3-Kinase inhibitor BKM120 and the PARP inhibitor olaparib demonstrated anti-cancer activity in TNBC and OC, both in patients with and without germline BRCA1 and BRCA2 (BRCA) mutations. However, CNS toxicity (depression) and liver function test abnormalities limited dose escalation of BKM120 prompting evaluation of the alpha specific PI3-Kinase inhibitor BYL719 (which has no CNS toxicity) in combination with olaparib.

Methods: Olaparib was administered twice daily (tablet formulation) and BYL719 daily on a 28-day cycle, both orally. A 3 + 3 dose-escalation design was employed with primary objectives of defining the maximum tolerated dose (MTD) and recommended phase 2 dose of the combination of BYL719 and olaparib, and secondary objectives of defining toxicity, activity, and pharmacokinetic profiles of both agents. Eligibility included recurrent TNBC or high grade serous (HGS) OC, or any histology OC or breast cancer (BC) with presence of a known germline BRCA mutation, performance status of 0-1 and measurable/evaluable cancer. Patients with platinum sensitive or resistant or refractory OC were eligible and prior PARP inhibitor use was allowed. Dose-expansion cohorts at the MTD were enrolled for both BC and OC.

Results: 46 patients (16 BC and 30 OC) have been enrolled in the study; 28 patients participated in the dose escalation portion of the study (4 BC and 24 OC). Two patients with OC did not receive study drugs because of ineligibility. MTD was defined as BYL719 200mg once daily and olaparib 200mg twice daily. Dose limiting toxicities included hyperglycemia, rash and fever with decreased neutrophil count. Four patients (3 OC and 1 BC) discontinued protocol therapy because of toxicity (2 for hyperglycemia, 1 for nausea and 1 for allergic reaction). Most common toxicities included nausea, hyperglycemia, fatigue, diarrhea and vomiting. At the MTD, 6 patients with OC and 12 patients with BC were enrolled into a dose expansion cohort. The OC expansion cohort has completed enrollment, while the BC cohort is still enrolling. Among patients with OC who received study drugs (28 patients, 26 (93%) with platinum resistant disease), objective response rate (ORR) by RECIST 1.1 was 36% (10/28 patients, all partial responses (PRs)). Median duration of response was 167 days (range 16-398 days); 5 of 10 patients with PR remain on treatment. ORR was 33% for patients with germline BRCA mutations and 31% for patients without germline BRCA mutations. Among patients without germline BRCA mutations with platinum resistant OC, ORR was 29%.

Conclusions: Combined BYL719 and olaparib is feasible, and similar clinical benefit was observed in patients with and without germline BRCA mutations. The activity of this combination in OC patients without germline BRCA mutations and with platinum resistant disease was higher than expected from olaparib monotherapy and warrants further investigation. This work was funded in part by the Stand Up To Cancer Ovarian Dream Team. Clinical trial: NCT01623349.

Citation Format: Panagiotis A. Konstantinopoulos, William T. Barry, Michael Birrer, Shannon N. Westin, Sarah Farooq, Karen Cadoo, Christin Whalen, Weixiu Luo, Hui Liu, Carol Aghajanian, David B. Solit, Gordon B. Mills, Barry S. Taylor, Helen Won, Michael F. Berger, Sangeetha Palakurthi, Joyce F. Liu, Lew Cantley, Scott H. Kaufmann, Elizabeth M. Swisher, Alan D. D'Andrea, Eric Winer, Gerburg M. Wulf, Ursula A. Matulonis. Phase I study of the alpha specific PI3-Kinase inhibitor BYL719 and the poly (ADP-Ribose) polymerase (PARP) inhibitor olaparib in recurrent ovarian and breast cancer: Analysis of the dose escalation and ovarian cancer expansion cohort [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 CT008. doi:10.1158/1538-7445.AM2017-CT008

Establishment of Patient-Derived Tumor Xenograft Models of Epithelial Ovarian Cancer for Preclinical Evaluation of Novel Therapeutics

Purpose: Ovarian cancer is the leading cause of death from gynecologic malignancy in the United States, with high rates of recurrence and eventual resistance to cytotoxic chemotherapy. Model systems that allow for accurate and reproducible target discovery and validation are needed to support further drug development in this disease.Experimental Design: Clinically annotated patient-derived xenograft (PDX) models were generated from tumor cells isolated from the ascites or pleural fluid of patients undergoing clinical procedures. Models were characterized by IHC and by molecular analyses. Each PDX was luciferized to allow for reproducible in vivo assessment of intraperitoneal tumor burden by bioluminescence imaging (BLI). Plasma assays for CA125 and human LINE-1 were developed as secondary tests of in vivo disease burden.Results: Fourteen clinically annotated and molecularly characterized luciferized ovarian PDX models were generated. Luciferized PDX models retain fidelity to both the nonluciferized PDX and the original patient tumor, as demonstrated by IHC, array CGH, and targeted and whole-exome sequencing analyses. Models demonstrated diversity in specific genetic alterations and activation of PI3K signaling pathway members. Response of luciferized PDX models to standard-of-care therapy could be reproducibly monitored by BLI or plasma markers.Conclusions: We describe the establishment of a collection of 14 clinically annotated and molecularly characterized luciferized ovarian PDX models in which orthotopic tumor burden in the intraperitoneal space can be followed by standard and reproducible methods. This collection is well suited as a platform for proof-of-concept efficacy and biomarker studies and for validation of novel therapeutic strategies in ovarian cancer. Clin Cancer Res; 23(5); 1263-73. ©2016 AACR.

Abstract 159: Analysis of resistance to the combination of a PI3K- and Parp-inhibitor using a genomic sequencing approach

The objective of this study is to investigate the genomic and transcriptonal changes that are associated with resistance to treatment with the combination of a PI3K-inhibitor (NVP-BKM120) and a PARP-inhibitor (Olaparib). Previous studies have shown that the combination of a PI3K-inhibitor and a PARP-inhibitor synergistically reduced the growth of BRCA-related xenograft tumors derived from patients with TNBC. However, in clinical practice, primary and secondary resistance to this combination is observed. We hypothesize that acquired resistance is the result of a genomic evolution resulting from the selection pressure exerted by the drug treatment.

We used a genetically engineered mouse model, K14-Cre BRCA1f/fp53f/f, where primary tumors had been propagated in Cre-negative littermates and treated to point of resistance with NVP-BKM120 or NVP-BKM120 plus Olaparib. For each of the three tumors, we analyzed exome sequencing and RNA-seq using Illumina technology at the stage of sensitivity (C), resistance to PI3K-inhibition (B) and resistance to the combination (BO); i.e. for each individual tumor a parental clone and its drug-resistant subclones, obtained in vivo, were analyzed. We used the Mutect software tool to call somatic mutations, VarScan2 to call somatic copy number variations, Cuffdiff for differential expression analysis, and TophatFusion. Data were integrated to identify genes for functional analyses using MetaCore and MSigDB software tools.

We found that tumors resistant to the combination drug treatment in general had fewer gross genomic alterations (CNVs) than parental tumors, indicative of evolution of a less variable subclone. However, these tumors also displayed a higher number of non-synonymous mutations than their parental clone. Pathway analysis showed that somatically mutated genes in PI3K-inhibitor resistant tumors were highly enriched for antigen processing and presentation, while those of tumors resistant to the combination treatment were enriched for histone modification pathways. Notably, the tumors resistant to PI3K-inhibitor alone were enriched for Insulin-processing pathways. Genomic losses in PI3K-inhibitor treated tumors enriched for the estrogen receptor pathway (ESR) in breast cancer and DNA damage pathways.

In conclusion, our experimental design of analyzing isogenic tumors resistant to PI3K- or combined PI3K- and Parp-inhibitors enabled us to identify genomic alterations and pathways that explain the evolution to drug resistance.

Citation Format: Sheida Nabavi, Ashish Juvekar, Nicholas Wang, Lewis C. Cantley, Gerburg M. Wulf. Analysis of resistance to the combination of a PI3K- and Parp-inhibitor using a genomic sequencing approach. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 159.

Epstein-Barr Virus Infection of Mammary Epithelial Cells Promotes Malignant Transformation

Whether the human tumor virus, Epstein-Barr Virus (EBV), promotes breast cancer remains controversial and a potential mechanism has remained elusive. Here we show that EBV can infect primary mammary epithelial cells (MECs) that express the receptor CD21. EBV infection leads to the expansion of early MEC progenitor cells with a stem cell phenotype, activates MET signaling and enforces a differentiation block. When MECs were implanted as xenografts, EBV infection cooperated with activated Ras and accelerated the formation of breast cancer. Infection in EBV-related tumors was of a latency type II pattern, similar to nasopharyngeal carcinoma (NPC). A human gene expression signature for MECs infected with EBV, termed EBVness, was associated with high grade, estrogen-receptor-negative status, p53 mutation and poor survival. In 11/33 EBVness-positive tumors, EBV-DNA was detected by fluorescent in situ hybridization for the viral LMP1 and BXLF2 genes. In an analysis of the TCGA breast cancer data EBVness correlated with the presence of the APOBEC mutational signature. We conclude that a contribution of EBV to breast cancer etiology is plausible, through a mechanism in which EBV infection predisposes mammary epithelial cells to malignant transformation, but is no longer required once malignant transformation has occurred.

Phosphoinositide 3-Kinase Regulates Glycolysis through Mobilization of Aldolase from the Actin Cytoskeleton

The phosphoinositide 3-kinase (PI3K) pathway regulates multiple steps in glucose metabolism and also cytoskeletal functions, such as cell movement and attachment. Here, we show that PI3K directly coordinates glycolysis with cytoskeletal dynamics in an AKT-independent manner. Growth factors or insulin stimulate the PI3K-dependent activation of Rac, leading to disruption of the actin cytoskeleton, release of filamentous actin-bound aldolase A, and an increase in aldolase activity. Consistently, PI3K inhibitors, but not AKT, SGK, or mTOR inhibitors, cause a significant decrease in glycolysis at the step catalyzed by aldolase, while activating PIK3CA mutations have the opposite effect. These results point toward a master regulatory function of PI3K that integrates an epithelial cell's metabolism and its form, shape, and function, coordinating glycolysis with the energy-intensive dynamics of actin remodeling.

Abstract IA08: PI3K- and PARP-inhibitors for the treatment of women cancers

Amplification of PIK3CA is highly prevalent in ovarian cancer and isoform-specific and pan-PI3K inhibitors have entered clinical trials. However, identifying tumor subtypes and biological mechanisms that predict for response to PI3K inhibitors as single agents or in combination has been a challenge.

We previously reported that combining a phophoinositide 3-kinase (PI3K) inhibitor with a poly ADP ribose polymerase (PARP)-inhibitor enhanced DNA damage and cell death in breast cancers that have genetic aberrations in BRCA1 and TP53. We now show that the enhanced DNA damage induced by PI3K inhibitors in this mutational background is a consequence of impaired production of deoxynucleotides needed for DNA synthesis and DNA repair. Inhibition of PI3K causes a reduction in all four deoxynucleotide triphosphates (dATP, dTTP, dGTP and dCTP), while inhibition of AKT is less effective than inhibition of PI3K in suppressing nucleotide synthesis and inducing DNA damage. Carbon flux studies reveal that PI3K-inhibition disproportionately affects the non-oxidative pentose phosphate pathway (non-ox PPP) that delivers ribose-5-posphate required for base ribosylation. In vivo in a mouse model of BRCA1-linked triple-negative breast cancer combined PI3K- and PARP-inhibition was superior to either agent alone to induce durable remissions of established tumors. Our data indicate that PI3K inhibitors induce DNA damage in tumors that have defects in DNA damage repair pathways and that they do so by impairing the production of Ribose-5-phosphate and amino acids needed for deoxynucleotide synthesis. An ongoing phase I/II study (NCT01623349, PI: Matulonis) examines the safety and toxicity of a PI3K/Parp-inhibitor combination in ovarian and breast cancer.

Citation Format: Gerburg M. Wulf, Ashish Juvekar, Lewis C. Cantley, Ursula A. Matulonis. PI3K- and PARP-inhibitors for the treatment of women cancers. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr IA08.

Abstract 1081: Non-random genomic alterations in BRCA1-related breast cancer

BRCA1-related breast cancer is characterized by a high degree of genomic instability. However, to which extent this instability is a random result of the homologous recombination defect or the selection of the tumor phenotype, is unknown. The objective of this study is to investigate the genomic aberrations (copy number variation and somatic mutations) of BRCA1-related breast cancer, using a mouse model, to identify likely nonrandom aberrations and their biological functions.

We examined genomic aberrations of three independent BRCA1-related tumors from a genetically engineered mouse model, K14-Cre BRCA1f/fp53f/f. Tumors had been propagated in Cre-negative littermates and liver tissue of the recipient mice from the controls were used as a germline control. Fresh frozen tumors and normal samples were used for exome sequencing and RNA-seq using Illumina technology. A commonly used workflow, GATK, was used for the sequence alignment, preprocessing and calling somatic mutations. VarScan2 was used for calling somatic copy number variations. We investigate the prevalence of common aberrations among these mouse in human BRCA1-related breast and ovarian cancer from The Cancer Genome Atlas (TCGA). We used the BioMart software tool to map mouse genes to human genes for the cross species analysis. After identifying common aberrant regions and genes across human and mouse we applied enrichment analysis using GOSeq, MetaCore and MSigDB software tools to identify the biological functions of the genetic alterations observed in BRCA1-related breast cancer across species.

The analysis of exome sequencing data from BRCA1-related mouse tumors revealed surprisingly similar patterns of CNVs and rates of non-synonymous mutations. Correspondingly, distinct pattern were identified with regard to CNVs in human BRCA1-related breast and ovarian cancer. The cross species analysis of BRCA1-related TCGA ovarian and breast cancer tumors and BRCA1-related mouse tumors identified commonly aberrant regions that mapped to the long arms of human chromosomes 1, 8, 17 and 20 in both breast and ovarian cancer. Functionally, the blocks of genes that were commonly amplified in BRCA1-related breast or ovarian cancer included genes that transduce mitogenic signaling and ligand independent activation of estrogen receptors ESR1 and ESR2 as well as genes of the renin-angiotensin system.

To conclude, copy number aberrations in BRCA1-related breast or ovarian cancers are not random and enrich for genes that enforce mitogenic signaling. The data support the notion that in addition to loss of cell cycle checkpoint control, tumor development requires activation of a mitogenic signaling program that could potentially be targeted for treatment.

Citation Format: Sheida Nabavi, Kristina M. Holton, Ashish Juvekar, Nicholas Wang, Olivier Elemento, Lewis C. Cantley, Gerburg M. Wulf. Non-random genomic alterations in BRCA1-related breast cancer. [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 1081. doi:10.1158/1538-7445.AM2015-1081

Abstract IA21: Combination treatments that include PI3K-inhibitors for the treatment of triple-negative breast cancer

Alterations in the PI3K pathway are highly prevalent in triple-negative breast and high grade ovarian cancer, including BRCA1- and BRCA2-related disease. On the cellular level, loss of BRCA1 increases genomic instability and reliance on single strand break repair, hence creating an opportunity to treat BRCA-related TNBC or OC with PARP-inhibitors. In addition, loss of BRCA1 and/or p53 lead to relaxation of negative feed-back loops in mitogenic signaling, resulting in highly proliferative malignancies. For these reasons PARP-inhibitor Olaparib and PI3K-inhibitor NVP-BKM120 were tested in combination and found to be synergistic in mouse models of BRCA1-related BC. Surprisingly, PI3K-inhibition enhanced a DNA damage phenotype, caused by a profound decrease in DNA synthesis that could be observed after treatment with NVP-BKM120 in vivo and in vitro. The decrease in DNA synthesis was due to reduced Nucleoside synthesis resulting from a block in glycolysis that led to a drop in flux through the non-oxidative pentose phosphate pathway. In a preclinical mouse model (K14-Cre BRCA1f/fp53f/f), the combination of NVP-BKM120 and Olaparib could induce complete remissions, while PI3K-inhibitor alone marginally slowed disease progression and PARP-inhibitor alone stabilized the disease. This concept was translated into a clinical trial: BKM120/Olaparib for Triple Negative Breast Cancer or High Grade Serous Ovarian Cancer (NCT01623349; PI: Ursula Matulonis). Dose escalation for this study and accrual to an extension cohort at the MTD (NVP-BKM120 50 mg once a day in combination with Olaparib 300 mg twice a day) have been completed and a second dose escalation arm with NVP-BYL719 and Olaparib is ongoing.

Citation Format: Gerburg M. Wulf, Ashish Juvekar, Costas M. Lyssiotis, Hai Hu, Kim Baek, Sina Yadegarynia, Ralph Scully, Eric Winer, John Asara, Lewis C. Cantley, Ursula Matulonis. Combination treatments that include PI3K-inhibitors for the treatment of triple-negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr IA21.

Abstract NG05: Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53 null tumors

The phosphoinositide family of lipids includes seven derivatives of phosphatidylinositol (PI) that are formed through the phosphorylation of the 3-, 4-, and 5-positions on the inositol ring. Phosphoinositides have distinct biological roles and regulate many cellular processes, including proliferation, survival, glucose uptake, and migration. Phosphoinositide kinases, phosphatases, and phospholipases spatially and temporally regulate the generation of the different phosphoinositide species, which localize to different subcellular compartments. Phosphatidylinositol-3,4,5-trisphosphate (PI-3,4,5-P3) is synthesized by phosphoinositide 3-kinase (PI3K) and serves as the plasma membrane docking site for a subset of proteins that have pleckstrin-homology (PH) domains that bind this lipid, including the serine/threonine protein kinase AKT (also known as protein kinase B or PKB). AKT is a proto-oncogene that has critical regulatory roles in insulin signaling and cancer progression. Phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) is the major substrate for Class I PI3Ks and has a significant role itself in mediating the localization of proteins to the plasma membrane and in nucleating cortical actin polymerization (1).

Until 1997 it was thought that PI-4,5-P2 was produced exclusively by phosphorylation of phosphatidylinositol-4-phosphate (PI-4-P) at the 5 position of the inositol ring, a reaction catalyzed by the Type 1 PI-4-P 5-kinases (encoded by the genes PIP5K1A, B and C). Unexpectedly, a second highly-related family of PIP kinases (called Type 2) was found to produce PI-4,5-P2 by phosphorylating the 4 position of phosphatidylinositol-5-phosphate (PI-5-P), a lipid that had been previously overlooked due to its co-migration with the much more abundant PI-4-P (2-3). The Type 2 PIP kinases are not present in yeast but are conserved in higher eukaryotes from worms and flies to mammals. Humans and mice have three distinct genes, PIP4K2A, B and C encoding enzymes called PI5P4Kα, β, and γ, respectively. The bulk of PI-4,5-P2 in most tissues is almost certainly derived from the Type 1 PIP5Ks, yet recent quantitative proteomic studies on cell lines have revealed a higher abundance of PI5P4Ks than PI4P5Ks (4). This high abundance of the Type 2 enzymes may, in part, explain why the substrate, PI-5-P is present at very low levels. While the Type 1 PIP kinases generate PI-4,5-P2 at the plasma membrane, the Type 2 kinases are located at internal membranes, including the ER, Golgi and nucleus and probably generate PI-4,5-P2 at those locations (5-8). The vast majority of PI-4,5-P2 is located at the plasma membrane and it is not clear whether the critical function of the Type 2 PIP kinases is to generate PI-4,5-P2 at intracellular sites or to maintain low levels of PI-5-P (or both).

In a previous study we generated mice in which one of the Type 2 PIP kinase genes (PIP4K2B) was deleted in the germline. These mice were viable, exhibited enhanced insulin sensitivity and enhanced insulin-dependent activation of AKT in skeletal muscle (9). Paradoxically, despite increased AKT activation the mice were smaller and had decreased adiposity on a high fat diet. Cell based assays revealed that PI5P4Kβ (encoded by PIP4K2B) becomes phosphorylated by p38 at Ser326 in response to cellular stresses, such as UV and H2O2, and that this causes inhibition of the PI5P 4-kinase activity and results in increased cellular PI-5-P levels (10). These studies suggest that the Type 2 PIP kinases mediate cellular stress responses downstream of p38 (presumably by altering the PI-5-P/PI-4,5-P2 ratio at intracellular locations) and that under conditions of low stress, these enzymes suppress the PI3K/AKT signaling pathway. It should be pointed out that the Type 2 PIP kinases are unlikely to supply PI-4,5-P2 as a substrate for PI3K since activation of AKT correlates with loss of PI5P4K activity rather than gain.

In this study we have interrogated the potential role of Type 2 PIP kinases in cancers. We found high levels of either PI5P4Kα or PI5P4Kβ enzymes or both in a number of breast cancer cell lines, and more importantly, found amplification of the PIP4K2B gene and high levels of both the PI5P4Kα and PI5P4Kβ proteins in a subset of human breast tumors. We found that knocking down the levels of both PI5P4Kα and PI5P4Kβ in a TP53 deficient breast cancer cell line blocked growth on plastic and in xenografts. This impaired growth correlated with impaired glucose metabolism and enhanced levels of reactive oxygen species (ROS) leading to senescence. The impaired glucose metabolism, despite activation of the PI3K-AKT pathway (which typically enhances glucose metabolism) was paradoxical. The results indicate that PI3K activation is not driving the ROS production, but may be an inadequate feedback attempt to restore glucose uptake and metabolism.

To assess the role of Type 2 PIP kinases in tumor formation, we generated mice with germline deletions of PIP4K2A and PIP4K2B and crossed these with TP53-/- mice and evaluated tumor formation in all the viable genotypes. We found that mice with homozygous deletion of both TP53 and PIP4K2B were not viable, indicating a synthetic lethality for loss of these two genes. Importantly, mice with the genotype PIP4K2A-/-, PIP4KB+/-, TP53-/- were viable and had a dramatic reduction in tumor formation compared to siblings that were TP53-/- and wild type for PIP4K2B and/or PIP4K2A genes. The decreased tumor incidence in the background of PIP4K2A-/-, PIP4K2B+/-, TP53-/- compared to TP53-/- alone is particularly interesting in respect to Li Fraumeni Syndrome (germline TP53 mutations). Our results indicate that expression of PI5P4Kα and/or β is critical for the growth of tumors with TP53 mutations or deletions. Thus, co-amplification of PIP4K2B with ERBB2 might explain why breast cancers in patients with Li Fraumeni syndrome show ERBB2 amplifications (HER2-positive) in over 83% of cases as opposed to 16% of age-matched patients with wild type TP53 (11).

The results that we present here suggest that PI5P4Kα and β play a critical role in mediating changes in metabolism in response to stress, and in particular ROS stress that occurs in the absence of p53. Germ-line deletion of either PIP4K2A or PIP4K2B alone resulted in mice with normal lifespans, and germ-line deletion of both PIP4K2A and PIP4K2B resulted in full-term embryos of normal size and appearance at birth, indicating that these genes do not play a major role in normal embryonic growth and development. Yet the PIP4K2A-/-, PIP4K2B-/- pups die shortly after birth, consistent with these genes having a role in mediating stress responses known to occur following birth. Importantly, germ-line deletion of both PIP4K2B and TP53 resulted in lethality while germ-line deletion of either gene alone resulted in Mendelian ratios of viable pups. Thus, the genetic studies suggest that TP53 and PIP4K2B have overlapping roles in mediating cellular responses to stress and that, while neither gene alone is essential, loss of both genes is not tolerated.

The most exciting observation from these studies in regard to potentially new therapies for p53 mutant tumors is that germ-line deletion of both alleles of PIP4K2A and one allele of PIP4K2B in the context of TP53-/- results in a viable mouse with a dramatic reduction in tumor-dependent death compared to TP53-/- mice that are wild type for PIP4K2A and B. These results (and studies of the PIP4K2A-/-, PIP4K2B+/- or PIP4K2A+/-, PIP4K2B-/- mice in the context of wild type TP53) indicate that normal tissues tolerate well the loss of three out of four alleles of the PIP4K2A and PIP4K2B genes, but that tumors are not viable in this context. PI5P4Kα and β are kinases and pharmaceutical companies have shown that it is possible to develop highly specific inhibitors of both protein kinases and lipid kinases. The synthetic lethality that we observe between TP53 loss and loss of these kinases indicates that drugs that target either the enzyme PI5P4Kβ alone or that target both PI5P4Kα and β are likely to be well-tolerated and very effective on tumors that have loss of function mutations or deletions of TP53. Our observations with BT474 cells suggest that HER2 positive tumors that have amplifications of PIP4K2B and mutations in TP53 may be particularly sensitive to PI5P4Kα,β inhibitors. The ERBB2 (Her2) amplicon on chromosome 17 is variable in size and can contain a number of cancer-related genes in addition to the ERBB2 locus. Clinically, patients who have tumors with small amplicons confined to the ERBB2 locus have the greatest benefit from ERBB2-directed therapies such as Trastuzumab, while tumors with wider ERBB2 amplicons have poor responses, suggesting co-amplification of genes that contribute to Trastuzumab resistance (11). PIP4K2B, which is located in a chromosomal region (17q12) close to ERBB2, may be a candidate for an adjacent co-amplified gene that confers Trastuzumab resistance, and, conversely, concomitant inhibition of ERBB2 and PIP4K2B could be a highly effective treatment option for ERBB2 (Her2) positive tumors that are p53-mutant and PIP4K2B-amplified.

References

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3. Rameh, L.E., Tolias, K.F., Duckworth, B.C., and Cantley, L.C. A new pathway for synthesis of phosphatidylinositol-4,5-bisphosphate. Nature 1997;390:192-196.

4. Nagaraj, N., Wisniewski, J.R., Geiger, T., Cox, J., Kircher, M., Kelso, J., Paabo, S., and Mann, M. Deep proteome and transcriptome mapping of a human cancer cell line. Mol Syst Biol 2011;7: 548.

5. Fruman, D.A., Meyers, R.E., and Cantley, L.C. Phosphoinositide kinases. Annu Rev Biochem 1998;67:481-507.

6. Sarkes, D., and Rameh, L.E. A novel HPLC-based approach makes possible the spatial characterization of cellular PtdIns5P and other phosphoinositides. Biochem J 2010;428:375-384.

7. Schaletzky, J., Dove, S.K., Short, B., Lorenzo, O., Clague, M.J., and Barr, F.A. Phosphatidylinositol-5-phosphate activation and conserved substrate specificity of the myotubularin phosphatidylinositol 3-phosphatases. Curr Biol 2003;13:504-509.

8. Walker, D.M., Urbe, S., Dove, S.K., Tenza, D., Raposo, G., and Clague, M.J. Characterization of MTMR3. an inositol lipid 3-phosphatase with novel substrate specificity. Curr Biol 2001;11:1600-1605.

9. Lamia, K.A., Peroni, O.D., Kim, Y.B., Rameh, L.E., Kahn, B.B., and Cantley, L.C. Increased insulin sensitivity and reduced adiposity in phosphatidylinositol 5-phosphate 4-kinase beta-/- mice. Mol Cell Biol 2004;24:5080-5087.

10. Jones, D.R., Bultsma, Y., Keune, W.J., Halstead, J.R., Elouarrat, D., Mohammed, S., Heck, A.J., D'Santos, C.S., and Divecha, N. Nuclear PtdIns5P as a transducer of stress signaling: an in vivo role for PIP4Kbeta. Mol Cell 2006;23:685-695.

11. Morrison, L.E., Jewell, S.S., Usha, L., Blondin, B.A., Rao, R.D., Tabesh, B., Kemper, M., Batus, M., and Coon, J.S. Effects of ERBB2 amplicon size and genomic alterations of chromosomes 1, 3, and 10 on patient response to trastuzumab in metastatic breast cancer. Genes Chromosomes Cancer 2007;46:397-405.

Citation Format: Brooke M. Emerling, Jonathan B. Hurov, George Poulogiannis, Rayman Choo-Wing, Gerburg M. Wulf, Hye-Seok Shim, Katja A. Lamia, Lucia E. Rameh, Xin Yuan, Andrea Bullock, Gina M. DeNicola, Jiaxi Song, Sabina Signoretti, Lewis C. Cantley. Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53 null tumors. [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 NG05. doi:10.1158/1538-7445.AM2014-NG05

Abstract CT338: Combination of a PI3K- and a PARP-inhibitor to treat high-grade serous ovarian or triple-negative breast cancer

Clinical trials have shown promising responses of BRCA-linked breast and ovarian cancers to PARP inhibitor therapy, but remissions are often short-lived and incomplete. The PI3K pathway is frequently activated in these malignancies. Recently, we reported in vivo synergy of a PI3K- and a PARP-inhibitor in a mouse model of BRCA1-related breast cancer. While the PARP-inhibitor olaparib alone attenuated tumor growth modestly, a dramatic reduction in tumor growth was observed when olaparib was combined with the PI3K-inhibitor BKM120. In BRCA1-mutant HCC1937 BC cells, PI3K- (but not akt-) inhibition increased indicators of DNA damage, such as poly-ADP-ribosylation and γH2AX, suggesting a critical role of PI3K activity for the maintenance of genomic stability. Here, we report on the molecular mechanism underlying this synergy, on treatment outcomes in an improved mouse model system and the development of an early-phase clinical study. Pre-clinical modeling was done in BRCA1-mutant HCC1937 cells and in a mouse model based on the syngenic transplantation of tumors derived on the K14-Cre BRCA1f/fp53f/f background. Metabolic profiling in vitro and in vivo showed that PI3K-inhibition decreased flux through glycolysis and specifically through the non-oxidative pentose-phosphate pathway, the main source of ribose-5-phosphate required for the de novo synthesis of nucleotides in HCC1937 cells. Within 3 hours and preceding cell cycle changes, BKM120 caused a decrease in nucleotide pools that was further exacerbated by the addition of olaparib. Nucleotide shortage led to to replication stress with the appearance of γH2AX and increased poly-ADP-ribosylation. Tumors with complete loss of BRCA1 and p53 proved particularly vulnerable to this treatment strategy. We were able to induce complete and durable remissions of murine tumors arising on the K14-Cre BRCA1f/fp53f/f background with a 28-day course of BKM120 and Olaparib. These preclinical data have served as the rationale for a phase I, multi-center study (NCT01623349) combining the oral PARP inhibitor olaparib with the oral PI3-kinase inhibitor BKM120 in patients with recurrent HGSC or recurrent TNBC. The study is being conducted through the Stand Up to Cancer (SU2C)'s Targeting PI3-kinase in Women's Cancers Dream Team. It has a 3 + 3 design, escalating if 0/3 or 1/6 participants have a DLT during the first cycle of therapy. The study objectives are to determine the recommended phase II dose (RP2D) of daily continuous oral olaparib (using the tablet formulation) and BKM120, assess toxicities, safety, and preliminary activity of this combination, and determine pharmacokinetic profiles of both agents as well as translational endpoints. The study serves as an example for the development of a clinical trials concept for TNBC and HGSC based on a close collaboration of basic and clinical scientists through the SU2C mechanism.

Citation Format: Gerburg M. Wulf, Ashish Juvekar, Costas A. Lyssiotis, Hai Hu, Sina Yadegarynia, Hui Liu, Baek Kim, Eric Winter, Ralph Scully, John Asara, Lewis C. Cantley, Ursula Matulonis. Combination of a PI3K- and a PARP-inhibitor to treat high-grade serous ovarian or triple-negative 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 CT338. doi:10.1158/1538-7445.AM2014-CT338

Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53-null tumors

Here, we show that a subset of breast cancers express high levels of the type 2 phosphatidylinositol-5-phosphate 4-kinases α and/or β (PI5P4Kα and β) and provide evidence that these kinases are essential for growth in the absence of p53. Knocking down PI5P4Kα and β in a breast cancer cell line bearing an amplification of the gene encoding PI5P4K β and deficient for p53 impaired growth on plastic and in xenografts. This growth phenotype was accompanied by enhanced levels of reactive oxygen species (ROS) leading to senescence. Mice with homozygous deletion of both TP53 and PIP4K2B were not viable, indicating a synthetic lethality for loss of these two genes. Importantly however, PIP4K2A(-/-), PIP4K2B(+/-), and TP53(-/-) mice were viable and had a dramatic reduction in tumor formation compared to TP53(-/-) littermates. These results indicate that inhibitors of PI5P4Ks could be effective in preventing or treating cancers with mutations in TP53.

PKM2 isoform-specific deletion reveals a differential requirement for pyruvate kinase in tumor cells

The pyruvate kinase M2 isoform (PKM2) is expressed in cancer and plays a role in regulating anabolic metabolism. To determine whether PKM2 is required for tumor formation or growth, we generated mice with a conditional allele that abolishes PKM2 expression without disrupting PKM1 expression. PKM2 deletion accelerated mammary tumor formation in a Brca1-loss-driven model of breast cancer. PKM2 null tumors displayed heterogeneous PKM1 expression, with PKM1 found in nonproliferating tumor cells and no detectable pyruvate kinase expression in proliferating cells. This suggests that PKM2 is not necessary for tumor cell proliferation and implies that the inactive state of PKM2 is associated with the proliferating cell population within tumors, whereas nonproliferating tumor cells require active pyruvate kinase. Consistent with these findings, variable PKM2 expression and heterozygous PKM2 mutations are found in human tumors. These data suggest that regulation of PKM2 activity supports the different metabolic requirements of proliferating and nonproliferating tumor cells.

Closing escape routes: inhibition of IL-8 signaling enhances the anti-tumor efficacy of PI3K inhibitors

The phosphoinositide 3-kinase (PI3K) pathway serves as a relay where signals that emanate from the cell membrane are received and converted into intracellular signals that promote proliferation and survival. Inhibitors of PI3K hold promise for the treatment of breast cancer because activation of this pathway is highly prevalent. However, as is increasingly observed with inhibitors of cell signaling, there appear to be mechanisms of primary and secondary resistance. Britschgi and colleagues report that compensatory activation of the IL-8 signaling axis is a mechanism of primary resistance to PI3K inhibitors in some triple-negative breast cancers. In a set of experiments that carefully emulate the clinical scenario in a mouse model, they show that simultaneous inhibition of Janus kinase 2 enhances the efficacy of PI3K/mammalian target of rapamycin inhibition. Their paper lends further support to the concept that successful design of treatments with signal transduction inhibitors must anticipate potential escape routes - and include agents to simultaneously block them.

Combining a PI3K inhibitor with a PARP inhibitor provides an effective therapy for BRCA1-related breast cancer

There is a need to improve treatments for metastatic breast cancer. Here, we show the activation of the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways in a MMTV-CreBrca1(f/f)Trp53(+/-) mouse model of breast cancer. When treated with the pan-class IA PI3K inhibitor NVP-BKM120, tumor doubling was delayed from 5 to 26 days. NVP-BKM120 reduced AKT phosphorylation, tumor cell proliferation, and angiogenesis. Resistant tumors maintained suppression of AKT phosphorylation but exhibited activation of the MAPK pathway at the "pushing margin." Surprisingly, PI3K inhibition increased indicators of DNA damage, poly-ADP-ribosylation (PAR), and γ-H2AX, but decreased Rad51 focus formation, suggesting a critical role of PI3K activity for Rad51 recruitment. The PARP inhibitor olaparib alone attenuated tumor growth modestly; however, the combination of NVP-BKM120 and olaparib delayed tumor doubling to more than 70 days in the mouse model and more than 50 days in xenotransplants from human BRCA1-related tumors, suggesting that combined PI3K and PARP inhibition might be an effective treatment of BRCA1-related tumors.

SIGNIFICANCE

Current treatment options for triple-negative breast cancer are limited to chemotherapeutic regimens that have considerable toxicity and are not curative. We report here that the combination of a PI3K inhibitor with a PARP inhibitor provides in vivo synergy for treatment of an endogenous mouse model for BRCA1-related breast cancers, making this a candidate combination to be tested in human clinical trials.

The amplifier effect: how Pin1 empowers mutant p53

Mutation of p53 occurs in 15 to 20% of all breast cancers, and with higher frequency in estrogen-receptor negative and high-grade tumors. Certain p53 mutations contribute to malignant transformation not only through loss of wild-type p53 but also through a gain of function of specific p53 mutations. How these hotspot mutations turn p53 from a tumor suppressor into an oncogene had until now remained incompletely understood. In an elegant paper published in the July 12 issue of Cancer Cell, Girardini and colleagues show how Pin1-mediated prolylisomerization, a regulatory mechanism intended by evolution to support p53's function as a guardian of the genome, can go haywire and accelerate malignant transformation when p53 carries a dominant-negative mutation.

Phase I/II Study of Trastuzumab in Combination With Everolimus (RAD001) in Patients With HER2-Overexpressing Metastatic Breast Cancer Who Progressed on Trastuzumab-Based Therapy

Purpose

Trastuzumab resistance has been linked to activation of the phosphoinositol 3-kinase (PI3K) pathway. Phosphatase and tensin homolog (PTEN) is a dual phosphatase that counteracts the PI3K function; PTEN loss leads to activation of the Akt cascade and the downstream mammalian target of rapamycin (mTOR). Preclinical studies demonstrated that mTOR inhibition sensitized the response to trastuzumab in mice with HER2 overexpressing and PTEN-deficient breast xenografts. Our trial evaluated the safety and efficacy of the combination of everolimus and trastuzumab in women with HER2-overexpressing metastatic breast cancer (MBC) that progressed on trastuzumab-based therapy.

Patients and Methods

This represents a pooled analysis (n = 47), stemming from two trials that occurred concurrently in The University of Texas MD Anderson Cancer Center, Beth Israel Deaconess Medical Center, and Dana-Farber Cancer Institute. Patients with HER2-overexpressing MBC who had progressed on trastuzumab-based therapy received trastuzumab every 3 weeks in combination with daily everolimus.

Results

Among 47 patients, the combination of everolimus and trastuzumab provided partial responses in seven patients (15%) and persistent stable disease (lasting 6 months or longer) in nine patients (19%), resulting in a clinical benefit rate of 34%. The median progression-free survival (PFS) was 4.1 month. Fatigue, infection, and mucositis were the predominant nonhematologic toxicities. Trastuzumab did not have significant influence on the pharmacokinetic profile of everolimus. Patients with PTEN loss demonstrated decreased overall survival (P = .048). However, PFS was not affected by PTEN loss.

Conclusion

Inhibition of mTOR results in clinical benefit and disease response in patients with trastuzumab-resistant HER2-overexpressing MBC.

Phase I/II study of trastuzumab in combination with everolimus (RAD001) in patients with HER2-overexpressing metastatic breast cancer who progressed on trastuzumab-based therapy

PURPOSE

Trastuzumab resistance has been linked to activation of the phosphoinositol 3-kinase (PI3K) pathway. Phosphatase and tensin homolog (PTEN) is a dual phosphatase that counteracts the PI3K function; PTEN loss leads to activation of the Akt cascade and the downstream mammalian target of rapamycin (mTOR). Preclinical studies demonstrated that mTOR inhibition sensitized the response to trastuzumab in mice with HER2 overexpressing and PTEN-deficient breast xenografts. Our trial evaluated the safety and efficacy of the combination of everolimus and trastuzumab in women with HER2-overexpressing metastatic breast cancer (MBC) that progressed on trastuzumab-based therapy.

PATIENTS AND METHODS

This represents a pooled analysis (n = 47), stemming from two trials that occurred concurrently in The University of Texas MD Anderson Cancer Center, Beth Israel Deaconess Medical Center, and Dana-Farber Cancer Institute. Patients with HER2-overexpressing MBC who had progressed on trastuzumab-based therapy received trastuzumab every 3 weeks in combination with daily everolimus.

RESULTS

Among 47 patients, the combination of everolimus and trastuzumab provided partial responses in seven patients (15%) and persistent stable disease (lasting 6 months or longer) in nine patients (19%), resulting in a clinical benefit rate of 34%. The median progression-free survival (PFS) was 4.1 month. Fatigue, infection, and mucositis were the predominant nonhematologic toxicities. Trastuzumab did not have significant influence on the pharmacokinetic profile of everolimus. Patients with PTEN loss demonstrated decreased overall survival (P = .048). However, PFS was not affected by PTEN loss.

CONCLUSION

Inhibition of mTOR results in clinical benefit and disease response in patients with trastuzumab-resistant HER2-overexpressing MBC.