Discovery of the Potent and Selective ATR Inhibitor Camonsertib (RP-3500)

ATR is a key kinase in the DNA-damage response (DDR) that is synthetic lethal with several other DDR proteins, making it an attractive target for the treatment of genetically selected solid tumors. Herein we describe the discovery of a novel ATR inhibitor guided by a pharmacophore model to position a key hydrogen bond. Optimization was driven by potency and selectivity over the related kinase mTOR, resulting in the identification of camonsertib (RP-3500) with high potency and excellent ADME properties. Preclinical evaluation focused on the impact of camonsertib on myelosuppression, and an exploration of intermittent dosing schedules to allow recovery of the erythroid compartment and mitigate anemia. Camonsertib is currently undergoing clinical evaluation both as a single agent and in combination with talazoparib, olaparib, niraparib, lunresertib, or gemcitabine (NCT04497116, NCT04972110, NCT04855656). A preliminary recommended phase 2 dose for monotherapy was identified as 160 mg QD given 3 days/week.

Detection of Biallelic Loss of DNA Repair Genes in Formalin-Fixed, Paraffin-Embedded Tumor Samples Using a Novel Tumor-Only Sequencing Panel

Patient selection for synthetic lethal-based cancer therapy may be improved by assessment of gene-specific loss of heterozygosity (LOH) and biallelic loss of function (LOF). This report describes SyNthetic lethal Interactions for Precision Diagnostics (SNiPDx), a targeted next-generation sequencing (NGS) panel for detection of LOH and biallelic LOF alterations in 26 target genes focused on DNA damage response pathways, in tumor-only formalin-fixed, paraffin-embedded (FFPE) samples. NGS was performed across all exons of these 26 genes and encompassed a total of 7632 genome-wide single-nucleotide polymorphisms on genomic DNA from 80 FFPE solid tumor samples. The Fraction and Allele-Specific Copy Number Estimates from Tumor Sequencing algorithm was optimized to assess tumor purity and copy number based on heterozygous single-nucleotide polymorphisms. SNiPDx demonstrated high sensitivity (95%) and specificity (91%) for LOH detection compared with whole genome sequencing. Positive agreement with local NGS-based testing in the detection of genetic alterations was 95%. SNiPDx detected 93% of biallelic ATM LOF mutations, 100% of ATM single-nucleotide variants and small insertions/deletions, and 100% of all ATM LOH status events identified by orthogonal NGS-based testing. SNiPDx is a novel, clinically feasible test for analysis of allelic status in FFPE tumor samples, which demonstrated high accuracy when compared with other NGS-based approaches in clinical use.

Guiding ATR and PARP inhibitor combinationswith chemogenomic screens

Combinations of ataxia telangiectasia- and Rad3-related kinase inhibitors (ATRis) and poly(ADP-ribose) polymerase inhibitors (PARPis) synergistically kill tumor cells through modulation of complementary DNA repair pathways, but their tolerability is limited by hematological toxicities. To address this, we performed a genome-wide CRISPR-Cas9 screen to identify genetic alterations that hypersensitize cells to a combination of the ATRi RP-3500 with PARPi, including deficiency in RNase H2, RAD51 paralog mutations, or the "alternative lengthening of telomeres" telomere maintenance mechanism. We show that RP-3500 and PARPi combinations kill cells carrying these genetic alterations at doses sub-therapeutic as single agents. We also demonstrate the mechanism of combination hypersensitivity in RNase H2-deficient cells, where we observe an irreversible replication catastrophe, allowing us to design a highly efficacious and tolerable in vivo dosing schedule. We present a comprehensive dataset to inform development of ATRi and PARPi combinations and an experimental framework applicable to other drug combination strategies.

Abstract 2801: Detection of biallelic loss of DNA repair genes in formalin-fixed, paraffin embedded (FFPE) tumor samples using a novel tumor-only sequencing panel with error correction

Background: Loss-of-function (LOF) mutations in DNA damage response (DDR) tumor suppressor genes are compensated for by functional redundancies, exposing synthetic lethal (SL) interactions and opportunities for targeted therapy. Patient selection for SL-based therapy may be improved by assessment of gene-specific loss of heterozygosity (LOH) and biallelic LOF, neither of which is routinely reported by existing targeted sequencing panels. The Synthetic Lethal Interactions for Precision Diagnostics (SNiPDx) targeted sequencing panel features a novel bioinformatic analysis pipeline that enables accurate genome-wide determination of allele-specific copy number, estimation of tumor ploidy and purity, and detection of single nucleotide and indel variants in target genes focused on DDR pathways, all from tumor-only samples. Here we describe the development and accuracy of SNiPDx for detection of LOH and bi-allelic LOF genetic alterations in FFPE samples.

Methods: Genomic DNA (>50 ng) was extracted from FFPE samples of multiple solid tumor types (n = 43). Next-generation sequencing was performed on anchored multiplex PCR libraries, constructed using probes that incorporate unique molecular identifiers and span 26 genes and 5,000 genome-wide common germline single-nucleotide polymorphisms (SNPs). Unmatched non-tumor samples (n = 24) were used to generate a reference baseline dataset. The FACETS algorithm, optimized to account for differential DNA fragmentation across samples, was used to assess copy number imbalance in heterozygous SNPs and to quantify tumor purity. Allele fractions at each heterozygous SNP were used to estimate allelic imbalances across chromosomal regions. A reference dataset was derived from matched FFPE tumor samples by whole genome sequencing (WGS) and analysis of sequence data using 3 complementary algorithms. Allele-specific copy number analysis and tumor purity estimation from SNiPDx and WGS data were compared.

Results: Copy number was evaluable in 605 genes from 24 matched tumor samples that passed quality control filters. Median sequencing depth across samples by SNiPDx and WGS were 1346x and 18.6x, respectively. LOH detection by SNiPDx was reproducible (100%) across 170 genes from 7 samples sequenced and analyzed in duplicate. A strong correlation was observed between sample purity estimates by WGS and SNiPDx (Pearson’s r = 0.81, p < 0.001). Compared with WGS-derived calls, the sensitivity and specificity of LOH detection by SNiPDx were 95% and 90%, respectively, rising to 97% and 91% in regions with LOH agreement by all 3 WGS algorithms, and to 99% and 97% in diploid regions with no subclonal alterations.

b The SNiPDx panel is a novel clinical test for biallelic loss in FFPE tumor-only samples with high accuracy as validated through concordance with a WGS-derived dataset.

Citation Format: Dominik Glodzik, Pier Selencia, Ryan Rogge, Ian M. Silverman, Michael Zinda, Maria Koehler, Robert D. Daber, Verity Johnson, Jorge S. Reis-Filho, Victoria Rimkunas. Detection of biallelic loss of DNA repair genes in formalin-fixed, paraffin embedded (FFPE) tumor samples using a novel tumor-only sequencing panel with error correction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2801.

CCNE1 amplification is synthetic lethal with PKMYT1 kinase inhibition

Amplification of the CCNE1 locus on chromosome 19q12 is prevalent in multiple tumour types, particularly in high-grade serous ovarian cancer, uterine tumours and gastro-oesophageal cancers, where high cyclin E levels are associated with genome instability, whole-genome doubling and resistance to cytotoxic and targeted therapies^1–4. To uncover therapeutic targets for tumours with CCNE1 amplification, we undertook genome-scale CRISPR–Cas9-based synthetic lethality screens in cellular models of CCNE1 amplification. Here we report that increasing CCNE1 dosage engenders a vulnerability to the inhibition of the PKMYT1 kinase, a negative regulator of CDK1. To inhibit PKMYT1, we developed RP-6306, an orally bioavailable and selective inhibitor that shows single-agent activity and durable tumour regressions when combined with gemcitabine in models of CCNE1 amplification. RP-6306 treatment causes unscheduled activation of CDK1 selectively in CCNE1-overexpressing cells, promoting early mitosis in cells undergoing DNA synthesis. CCNE1 overexpression disrupts CDK1 homeostasis at least in part through an early activation of the MMB–FOXM1 mitotic transcriptional program. We conclude that PKMYT1 inhibition is a promising therapeutic strategy for CCNE1-amplified cancers.

Genome-scale CRISPR–Cas9-based synthetic lethality screens identify PKMYT1 as a potential therapeutic target in tumours with CCNE1 amplification.

RP-3500: A Novel, Potent, and Selective ATR Inhibitor that is Effective in Preclinical Models as a Monotherapy and in Combination with PARP Inhibitors

Ataxia telangiectasia and Rad3-related (ATR) kinase protects genome integrity during DNA replication. RP-3500 is a novel, orally bioavailable clinical-stage ATR kinase inhibitor (NCT04497116). RP-3500 is highly potent with IC₅₀ values of 1.0 and 0.33 nmol/L in biochemical and cell-based assays, respectively. RP-3500 is highly selective for ATR with 30-fold selectivity over mammalian target of rapamycin (mTOR) and more than 2,000-fold selectivity over ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), and phosphatidylinositol 3-kinase alpha (PI3Kα) kinases. In vivo, RP-3500 treatment results in potent single-agent efficacy and/or tumor regression in multiple xenograft models at minimum effective doses (MED) of 5 to 7 mg/kg once daily. Pharmacodynamic assessments validate target engagement, with dose-proportional tumor inhibition of phosphorylated checkpoint kinase 1 (pCHK1) (IC₈₀ = 18.6 nmol/L) and induction of phosphorylated H2A.X variant histone (γH2AX), phosphorylated DNA-PK catalytic subunit (pDNA-PKcs), and phosphorylated KRAB-associated protein 1 (pKAP1). RP-3500 exposure at MED indicates that circulating free plasma levels above the in vivo tumor IC₈₀ for 10 to 12 hours are sufficient for efficacy on a continuous schedule. However, short-duration intermittent (weekly 3 days on/4 days off) dosing schedules as monotherapy or given concomitantly with reduced doses of olaparib or niraparib, maximize tumor growth inhibition while minimizing the impact on red blood cell depletion, emphasizing the reversible nature of erythroid toxicity with RP-3500 and demonstrating superior efficacy compared with sequential treatment. These results provide a strong preclinical rationale to support ongoing clinical investigation of the novel ATR inhibitor, RP-3500, on an intermittent schedule as a monotherapy and in combination with PARP inhibitors as a potential means of maximizing clinical benefit.

ATM Germline Mutated Gastroesophageal Junction Adenocarcinomas: Clinical Descriptors, Molecular Characteristics and Potential Therapeutic Implications

Background

Gastroesophageal junction (GEJ) adenocarcinoma is a rare cancer associated with poor prognosis. The genetic factors conferring predisposition to GEJ adenocarcinoma have yet to be identified.

Methods

We analyzed germline testing results from 23 381 cancer patients undergoing tumor-normal sequencing, of which 312 individuals had GEJ adenocarcinoma. Genomic profiles and clinico-pathologic features were analyzed for the GEJ adenocarcinomas. Silencing of ATM and ATR was performed using validated short-interfering RNA species in GEJ, esophageal, and gastric adenocarcinoma cell lines. All statistical tests were 2-sided.

Results

Pathogenic or likely pathogenic ATM variants were identified in 18 of 312 patients (5.8%), and bi-allelic inactivation of ATM through loss of heterozygosity of the wild-type allele was detected in all (16 of 16) samples with sufficient tumor content. Germline ATM-mutated GEJ adenocarcinomas largely lacked somatic mutations in TP53, were more likely to harbor MDM2 amplification, and harbored statistically significantly fewer somatic single nucleotide variants (2.0 mutations/Mb vs 7.9 mutations/Mb; P < .001). A statistically significantly higher proportion of germline ATM-mutated than ATM–wild-type GEJ adenocarcinoma patients underwent a curative resection (10 [100%] vs 92 [86.8%], P = .04; Fisher’s exact test.), A synthetic lethal interaction between short-interfering RNA silencing of ATM and ATR was observed in the models analyzed.

Conclusions

Our results indicate that germline pathogenic variants in ATM drive oncogenesis in GEJ adenocarcinoma and might result in a distinct clinical phenotype. Given the high prevalence of germline ATM-mutated GEJ adenocarcinomas, genetic testing for individuals with GEJ adenocarcinomas may be considered to better inform prognostication, treatment decisions, and future cancer risk.

The CIP2A-TOPBP1 axis safeguards chromosome stability and is a synthetic lethal target for BRCA-mutated cancer

BRCA1/2-mutated cancer cells adapt to the genome instability caused by their deficiency in homologous recombination (HR). Identification of these adaptive mechanisms may provide therapeutic strategies to target tumors caused by the loss of these genes. In the present study, we report genome-scale CRISPR-Cas9 synthetic lethality screens in isogenic pairs of BRCA1- and BRCA2-deficient cells and identify CIP2A as an essential gene in BRCA1- and BRCA2-mutated cells. CIP2A is cytoplasmic in interphase but, in mitosis, accumulates at DNA lesions as part of a complex with TOPBP1, a multifunctional genome stability factor. Unlike PARP inhibition, CIP2A deficiency does not cause accumulation of replication-associated DNA lesions that require HR for their repair. In BRCA-deficient cells, the CIP2A-TOPBP1 complex prevents lethal mis-segregation of acentric chromosomes that arises from impaired DNA synthesis. Finally, physical disruption of the CIP2A-TOPBP1 complex is highly deleterious in BRCA-deficient tumors, indicating that CIP2A represents an attractive synthetic lethal therapeutic target for BRCA1- and BRCA2-mutated cancers.

Synthetic Lethality in Cancer Therapeutics: The Next Generation

Synthetic lethality (SL) provides a conceptual framework for tackling targets that are not classically "druggable," including loss-of-function mutations in tumor suppressor genes required for carcinogenesis. Recent technological advances have led to an inflection point in our understanding of genetic interaction networks and ability to identify a wide array of novel SL drug targets. Here, we review concepts and lessons emerging from first-generation trials aimed at testing SL drugs, discuss how the nature of the targeted lesion can influence therapeutic outcomes, and highlight the need to develop clinical biomarkers distinct from those based on the paradigms developed to target activated oncogenes. SIGNIFICANCE: SL offers an approach for the targeting of loss of function of tumor suppressor and DNA repair genes, as well as of amplification and/or overexpression of genes that cannot be targeted directly. A next generation of tumor-specific alterations targetable through SL has emerged from high-throughput CRISPR technology, heralding not only new opportunities for drug development, but also important challenges in the development of optimal predictive biomarkers.

AZD4320, A Dual Inhibitor of Bcl-2 and Bcl-xL, Induces Tumor Regression in Hematologic Cancer Models without Dose-limiting Thrombocytopenia

PURPOSE

Targeting Bcl-2 family members upregulated in multiple cancers has emerged as an important area of cancer therapeutics. While venetoclax, a Bcl-2-selective inhibitor, has had success in the clinic, another family member, Bcl-x_L, has also emerged as an important target and as a mechanism of resistance. Therefore, we developed a dual Bcl-2/Bcl-x_L inhibitor that broadens the therapeutic activity while minimizing Bcl-x_L-mediated thrombocytopenia.

EXPERIMENTAL DESIGN

We used structure-based chemistry to design a small-molecule inhibitor of Bcl-2 and Bcl-x_L and assessed the activity against in vitro cell lines, patient samples, and in vivo models. We applied pharmacokinetic/pharmacodynamic (PK/PD) modeling to integrate our understanding of on-target activity of the dual inhibitor in tumors and platelets across dose levels and over time.

RESULTS

We discovered AZD4320, which has nanomolar affinity for Bcl-2 and Bcl-x_L, and mechanistically drives cell death through the mitochondrial apoptotic pathway. AZD4320 demonstrates activity in both Bcl-2- and Bcl-x_L-dependent hematologic cancer cell lines and enhanced activity in acute myeloid leukemia (AML) patient samples compared with the Bcl-2-selective agent venetoclax. A single intravenous bolus dose of AZD4320 induces tumor regression with transient thrombocytopenia, which recovers in less than a week, suggesting a clinical weekly schedule would enable targeting of Bcl-2/Bcl-x_L-dependent tumors without incurring dose-limiting thrombocytopenia. AZD4320 demonstrates monotherapy activity in patient-derived AML and venetoclax-resistant xenograft models.

CONCLUSIONS

AZD4320 is a potent molecule with manageable thrombocytopenia risk to explore the utility of a dual Bcl-2/Bcl-x_L inhibitor across a broad range of tumor types with dysregulation of Bcl-2 prosurvival proteins.

Endogenous DNA 3' Blocks Are Vulnerabilities for BRCA1 and BRCA2 Deficiency and Are Reversed by the APE2 Nuclease

The APEX2 gene encodes APE2, a nuclease related to APE1, the apurinic/apyrimidinic endonuclease acting in base excision repair. Loss of APE2 is lethal in cells with mutated BRCA1 or BRCA2, making APE2 a prime target for homologous recombination-defective cancers. However, because the function of APE2 in DNA repair is poorly understood, it is unclear why BRCA-deficient cells require APE2 for viability. Here we present the genetic interaction profiles of APE2, APE1, and TDP1 deficiency coupled to biochemical and structural dissection of APE2. We conclude that the main role of APE2 is to reverse blocked 3' DNA ends, problematic lesions that preclude DNA synthesis. Our work also suggests that TOP1 processing of genomic ribonucleotides is the main source of 3'-blocking lesions relevant to APEX2-BRCA1/2 synthetic lethality. The exquisite sensitivity of BRCA-deficient cells to 3' blocks indicates that they represent a tractable vulnerability in homologous recombination-deficient tumor cells.

Pharmacological Inhibition of PARP6 Triggers Multipolar Spindle Formation and Elicits Therapeutic Effects in Breast Cancer

: PARP proteins represent a class of post-translational modification enzymes with diverse cellular functions. Targeting PARPs has proven to be efficacious clinically, but exploration of the therapeutic potential of PARP inhibition has been limited to targeting poly(ADP-ribose) generating PARP, including PARP1/2/3 and tankyrases. The cancer-related functions of mono(ADP-ribose) generating PARP, including PARP6, remain largely uncharacterized. Here, we report a novel therapeutic strategy targeting PARP6 using the first reported PARP6 inhibitors. By screening a collection of PARP compounds for their ability to induce mitotic defects, we uncovered a robust correlation between PARP6 inhibition and induction of multipolar spindle (MPS) formation, which was phenocopied by PARP6 knockdown. Treatment with AZ0108, a PARP6 inhibitor with a favorable pharmacokinetic profile, potently induced the MPS phenotype, leading to apoptosis in a subset of breast cancer cells in vitro and antitumor effects in vivo. In addition, Chk1 was identified as a specific substrate of PARP6 and was further confirmed by enzymatic assays and by mass spectrometry. Furthermore, when modification of Chk1 was inhibited with AZ0108 in breast cancer cells, we observed marked upregulation of p-S345 Chk1 accompanied by defects in mitotic signaling. Together, these results establish proof-of-concept antitumor efficacy through PARP6 inhibition and highlight a novel function of PARP6 in maintaining centrosome integrity via direct ADP-ribosylation of Chk1 and modulation of its activity. SIGNIFICANCE: These findings describe a new inhibitor of PARP6 and identify a novel function of PARP6 in regulating activation of Chk1 in breast cancer cells.

BRD4 amplification facilitates an oncogenic gene expression program in high-grade serous ovarian cancer and confers sensitivity to BET inhibitors

BRD4 is a transcriptional co-activator functioning to recruit regulatory complexes to acetylated chromatin. A subset of High-grade Serous Ovarian Cancer (HGSOC) patients are typified by focal, recurrent BRD4 gene amplifications. Despite previously described cancer dependencies, it is unclear whether BRD4 amplification events are oncogenic in HGSOC. We find that physiologically relevant levels of expression of BRD4 isoforms in non-transformed ovarian cells result in cellular transformation. Transcriptional profiling of BRD4-transformed ovarian cells, and BRD4-amplified HGSOC patient samples revealed shared expression patterns, including enriched MYC, and E2F1 gene signatures. Furthermore, we demonstrate that a novel BET inhibitor, AZD5153, is highly active in BRD4-amplified patient derived xenografts and uncover Neuregulin-1 as a novel BRD4 effector. Experiments involving Neuregulin-1 inhibition and exogenous addition, demonstrate Neuregulin-1 as necessary and sufficient for BRD4-mediated transformation. This study demonstrates the oncogenic potential of BRD4 amplification in cancer and establishes BRD4-amplified HGSOC as a potential patient population that could benefit from BET inhibitors.

BRD4 facilitates replication stress-induced DNA damage response

Previous reports have demonstrated that select cancers depend on BRD4 to regulate oncogenic gene transcriptional programs. Here we describe a novel role for BRD4 in DNA damage response (DDR). BRD4 associates with and regulates the function of pre-replication factor CDC6 and plays an indispensable part in DNA replication checkpoint signaling. Inhibition of BRD4 by JQ1 or AZD5153 resulted in a rapid, time-dependent reduction in CHK1 phosphorylation and aberrant DNA replication re-initiation. Furthermore, BRD4 inhibition sensitized cancer cells to various replication stress-inducing agents, and synergized with ATR inhibitor AZD6738 to induce cell killing across a number of cancer cell lines. The synergistic interaction between AZD5153 and AZD6738 is translatable to in vivo ovarian cell-line and patient-derived xenograft models. Taken together, our study uncovers a new biological function of BRD4 and provides mechanistic rationale for combining BET inhibitors with DDR-targeted agents for cancer therapy.

Targeting KRAS-dependent tumors with AZD4785, a high-affinity therapeutic antisense oligonucleotide inhibitor of KRAS

Activating mutations in KRAS underlie the pathogenesis of up to 20% of human tumors, and KRAS is one of the most frequently mutated genes in cancer. Developing therapeutics to block KRAS activity has proven difficult, and no direct inhibitor of KRAS function has entered clinical trials. We describe the preclinical evaluation of AZD4785, a high-affinity constrained ethyl-containing therapeutic antisense oligonucleotide (ASO) targeting KRAS mRNA. AZD4785 potently and selectively depleted cellular KRAS mRNA and protein, resulting in inhibition of downstream effector pathways and antiproliferative effects selectively in KRAS mutant cells. AZD4785-mediated depletion of KRAS was not associated with feedback activation of the mitogen-activated protein kinase (MAPK) pathway, which is seen with RAS-MAPK pathway inhibitors. Systemic delivery of AZD4785 to mice bearing KRAS mutant non-small cell lung cancer cell line xenografts or patient-derived xenografts resulted in inhibition of KRAS expression in tumors and antitumor activity. The safety of this approach was demonstrated in mice and monkeys with KRAS ASOs that produced robust target knockdown in a broad set of tissues without any adverse effects. Together, these data suggest that AZD4785 is an attractive therapeutic for the treatment of KRAS-driven human cancers and warrants further development.

Effective combination therapies in preclinical endocrine resistant breast cancer models harboring ER mutations

Although endocrine therapy is successfully used to treat patients with estrogen receptor (ER) positive breast cancer, a substantial proportion of this population will relapse. Several mechanisms of acquired resistance have been described including activation of the mTOR pathway, increased activity of CDK4 and activating mutations in ER. Using a patient derived xenograft model harboring a common activating ER ligand binding domain mutation (D538G), we evaluated several combinatorial strategies using the selective estrogen receptor degrader (SERD) fulvestrant in combination with chromatin modifying agents, and CDK4/6 and mTOR inhibitors. In this model, fulvestrant binds WT and MT ER, reduces ER protein levels, and downregulated ER target gene expression. Addition of JQ1 or vorinostat to fulvestrant resulted in tumor regression (41% and 22% regression, respectively) though no efficacy was seen when either agent was given alone. Interestingly, although the CDK4/6 inhibitor palbociclib and mTOR inhibitor everolimus were efficacious as monotherapies, long-term delayed tumor growth was only observed when co-administered with fulvestrant. This observation was consistent with a greater inhibition of compensatory signaling when palbociclib and everolimus were co-dosed with fulvestrant. The addition of fulvestrant to JQ1, vorinostat, everolimus and palbociclib also significantly reduced lung metastatic burden as compared to monotherapy. The combination potential of fulvestrant with palbociclib or everolimus were confirmed in an MCF7 CRISPR model harboring the Y537S ER activating mutation. Taken together, these data suggest that fulvestrant may have an important role in the treatment of ER positive breast cancer with acquired ER mutations.

Generation of stable PDX derived cell lines using conditional reprogramming

Efforts to develop effective cancer therapeutics have been hindered by a lack of clinically predictive preclinical models which recapitulate this complex disease. Patient derived xenograft (PDX) models have emerged as valuable tools for translational research but have several practical limitations including lack of sustained growth in vitro. In this study, we utilized Conditional Reprogramming (CR) cell technology- a novel cell culture system facilitating the generation of stable cultures from patient biopsies- to establish PDX-derived cell lines which maintain the characteristics of the parental PDX tumor. Human lung and ovarian PDX tumors were successfully propagated using CR technology to create stable explant cell lines (CR-PDX). These CR-PDX cell lines maintained parental driver mutations and allele frequency without clonal drift. Purified CR-PDX cell lines were amenable to high throughput chemosensitivity screening and in vitro genetic knockdown studies. Additionally, re-implanted CR-PDX cells proliferated to form tumors that retained the growth kinetics, histology, and drug responses of the parental PDX tumor. CR technology can be used to generate and expand stable cell lines from PDX tumors without compromising fundamental biological properties of the model. It offers the ability to expand PDX cells in vitro for subsequent 2D screening assays as well as for use in vivo to reduce variability, animal usage and study costs. The methods and data detailed here provide a platform to generate physiologically relevant and predictive preclinical models to enhance drug discovery efforts.

Abstract 1026: Identify BRD4 as a facilitator of replication stress response signaling

BRD4 is a member of the BET (bromodomain and extraterminal domain) family of chromatin readers that recognize acetylated-lysines on histones and nuclear proteins. Previous reports have demonstrated that select cancers depend on BRD4 to regulate oncogenic gene transcriptional programs. However, whether BRD4 contributes to cancer malignancy through other mechanisms has not been extensively evaluated. Here, we show that BRD4 is important for maintaining an intact DNA replication checkpoint in cancers. Displacement of BRD4 by BET bromodomain inhibitor AZD5153 in cell lines under intrinsic or exogenous replication stress led to a time-dependent reduction in phospho-Chk1 first detected within 30 minutes, and reaching maximum phospho-Chk1 inhibition (~85%) at an hour after AZD5153 treatment in U2OS cells. The decrease in Chk1 phosphorylation was observed without a concomitant decrease in total Chk1, and this was not replicated by treatment with pan-transcriptional inhibitors, suggesting a non-transcriptional mechanism linked to BRD4. Furthermore, BRD4 interacts with the DNA pre-replication complex and inhibition of BRD4 leads to hyperactivation of the pre-replication complex and aberrant DNA replication re-initiation under replication stress conditions. Consistent with a role in S-phase signaling, BETi treatment sensitizes replicating cells to replication stress-inducing agents. Finally, we observed that ovarian cancer cell lines are highly-sensitive to the combined inhibition of BRD4 and ATR. Coadministration of AZD5153 and AZD6738 (ATR inhibitor) significantly inhibited tumor growth in OVCAR3 ovarian xenograft model (TGI after 21 day dosing: AZD5153, 52%; AZD6738, 46%; Combo, 84%). Sustained tumor growth delay was observed after combination treatment cessation. Together, our study uncovered a novel function for BRD4 in regulating DNA replication stress response, and provide mechanistic rational for combining BETi with DNA damage-targeted agents for cancer therapies.

Citation Format: Jingwen Zhang, Brandon Willis, Maureen Hattersley, Alan Lau, Corinne Reimer, Michael Zinda, Stephen Fawell, Gordon Mills, Austin Dulak, Huawei Chen. Identify BRD4 as a facilitator of replication stress response signaling [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 1026. doi:10.1158/1538-7445.AM2017-1026

Target Deconvolution Efforts on Wnt Pathway Screen Reveal Dual Modulation of Oxidative Phosphorylation and SERCA2

Wnt signaling is critical for development, cell proliferation and differentiation, and mutations in this pathway resulting in constitutive signaling have been implicated in various cancers. A pathway screen using a Wnt-dependent reporter identified a chemical series based on a 1,2,3-thiadiazole-5-carboxamide (TDZ) core with sub-micromolar potency. Herein we report a comprehensive mechanism-of-action deconvolution study toward identifying the efficacy target(s) and biological implication of this chemical series involving bottom-up quantitative chemoproteomics, cell biology, and biochemical methods. Through observing the effects of our probes on metabolism and performing confirmatory cellular and biochemical assays, we found that this chemical series inhibits ATP synthesis by uncoupling the mitochondrial potential. Affinity chemoproteomics experiments identified sarco(endo)plasmic reticulum Ca²⁺ -dependent ATPase (SERCA2) as a binding partner of the TDZ series, and subsequent validation studies suggest that the TDZ series can act as ionophores through SERCA2 toward Wnt pathway inhibition.

Comparative analysis of primary versus relapse/refractory DLBCL identifies shifts in mutation spectrum

Current understanding of the mutation spectrum of relapsed/refractory (RR) tumors is limited. We performed whole exome sequencing (WES) on 47 diffuse large B cell lymphoma (DLBCL) tumors that persisted after R-CHOP treatment, 8 matched to primary biopsies. We compared genomic alterations from the RR cohort against two treatment-naïve DLBCL cohorts (n=112). While the overall number and types of mutations did not differ significantly, we identified frequency changes in DLBCL driver genes. The overall frequency of MYD88 mutant samples increased (12% to 19%), but we noted a decrease in p.L265P (8% to 4%) and increase in p.S219C mutations (2% to 6%). CARD11 p.D230N, PIM1 p.K115N and CD79B p.Y196C mutations were not observed in the RR cohort, although these mutations were prominent in the primary DLBCL samples. We observed an increase in BCL2 mutations (21% to 38% of samples), BCL2 amplifications (3% to 6% of samples) and CREBBP mutations (31% to 42% of samples) in the RR cohort, supported by acquisition of mutations in these genes in relapsed compared to diagnostic biopsies from the same patient. These increases may reflect the genetic characteristics of R-CHOP RR tumors expected to be enriched for during clinical trial enrollment. These findings hold significance for a number of emerging targeted therapies aligned to genetic targets and biomarkers in DLBCL, reinforcing the importance of time-of-treatment biomarker screening during DLBCL therapy selection.

Abstract 1971: BRD4 amplification facilitates an oncogenic gene expression program in high-grade serous ovarian cancer

The bromodomain and extra-terminal (BET) protein, BRD4 functions as a transcriptional co-activator through recruitment of regulatory complexes to acetylated chromatin. Among all malignancies, the most focal, and recurrent BRD4 gene amplification occurs in high-grade serous ovarian cancer (HGSOC). Despite the elucidation of BRD4 dependencies in cancer, it is unclear whether BRD4 gene amplification can result in oncogenic activity, and hence serve as a patient selection strategy for BET bromodomain inhibitors. To assess the oncogenic potential of BRD4 amplification in HGSOC, we assayed enforced BRD4 expression in non-transformed immortalized surface ovarian cells (IOSE). Physiologically relevant expression of either long or short BRD4 spliced isoforms in IOSE (BRD4-IOSE) resulted in marked phenotypic changes indicative of cellular transformation, including altered growth kinetics, chromatin reorganization, and acquisition of colony formation potential. Transcriptional profiling of BRD4-IOSE and BRD4-amplified HGSOC patients revealed shared expression patterns, including enriched MYC, E2F1, and VEGF gene signatures. Interrogation of BRD4 inhibitor pharmacodynamic markers, and transcripts upregulated through enforced BRD4 expression uncovered Neuregulin-1 as a critical BRD4 transcriptional effector. RNAi-mediated Neuregulin-1 depletion was capable of abolishing the oncogenic activity of BRD4-IOSE, and exogenous Neuregulin-1 was sufficient to transform IOSE without BRD4. A novel BRD4-SWI/SNF interaction was required for driving the oncogenic activity of BRD4-IOSE through maintaining NRG1 expression. The sensitivity of patient-derived HGSOC xenografts to a novel clinical candidate BRD4 inhibitor, AZD5153, correlated with BRD4 amplification and a pharmacodynamic NRG1 response. This study demonstrates the oncogenic potential of BRD4 amplification, defines a relationship between BRD4 and NRG1, and further establishes HGSOC as an appropriate patient population in which to test the therapeutic potential of BET bromodomain inhibitors.

Citation Format: Garrett W. Rhyasen, Yi Yao, Austin Dulak, Lillian Castriotta, Kelly Jacques, Maureen Hattersley, Gordon B. Mills, Michael Zinda, Stephen Fawell, Paul Lyne, Edwin Clark, Huawei Chen. BRD4 amplification facilitates an oncogenic gene expression program in high-grade serous ovarian cancer. [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 1971.

Abstract 1150: Targeting MET Exon 14 mutations with the selective small molecule inhibitor Savolitinib

Alterations in the MET oncogene occurs across a broad range of tumor indications. Amplification or mutations in MET lead to increased activity of downstream pathways including PI3K and MAPK, eventually resulting in tumor formation. Several small molecule inhibitors are currently in clinical trials, including the selective inhibitor Savolitinib (HMP-504, Volitinib, AZD6094), which shows single digit nanomolar activity in MET-amplified cell lines. Newly emerging data suggest mutations in MET causing complete skipping of Exon 14 occur in approximately 4% of non-small cell lung cancer (NSCLC), and are more rare in other indications [1, 2]. MET exon 14 skipping mutations were shown to be mutually exclusive from EGFRm, ALK and KRAS and can occur in the context of MET gene amplification [3]. Exon 14 harbors the CBL binding site (Y1003), which is critical for receptor degradation after binding of its ligand, HGF, and suppression of downstream signaling events. Clinical trial results with less potent, pan RTK inhibitors Crizotinib (31nM GI50 vs 3nM for Savolitinib) and Cabozantinib show promising early results, but fall short in long term responses. Therefore, better therapies targeting MET are needed. Human cell line models with Exon 14 deletions are rare. Therefore, we used engineered cell lines to test the effect of Savolitinib on these mutations. To do this, we expressed MET-Y1003F mutants in NIH-3T3 and HEK293T cells. We found that Savolitinib potently inhibited phospho-MET in both models expressing this mutant (100% phospho-MET inhibition). In addition, we tested whether or not Savolitinib could inhibit HGF-dependent signaling and growth of a NSCLC cell line, NCI-H596. In the presence of FBS (10%), Savolitinib had no effect on the growth rate of these cells, however was highly efficient at blocking HGF-dependent growth in the absence of FBS. To test the effect of this mutation in the background of amplification, we also tested the gastric cancer cell line Hs746T, which harbors exon 14 skipping in addition to MET amplification. Savolitinib was highly efficacious at blocking the growth of this cell line. Future studies are aimed at looking at the in vivo effect of Savolitinib targeting exon 14 mutants. These data provide a platform of evidence for using Savolitinib to target exon 14 mutant MET in patients.

1.

Paik, P.K., et al., Response to MET inhibitors in patients with stage IV lung adenocarcinomas harboring MET mutations causing exon 14 skipping. Cancer Discov, 2015. 5(8): p. 842-9.

2.

Frampton, G.M., et al., Activation of MET via diverse exon 14 splicing alterations occurs in multiple tumor types and confers clinical sensitivity to MET inhibitors. Cancer Discov, 2015. 5(8): p. 850-9.

3.

Cancer Genome Atlas Research, N., Comprehensive molecular profiling of lung adenocarcinoma. Nature, 2014. 511(7511): p. 543-50.

Citation Format: Evan Barry, Elizabeth Maloney, Ryan Henry, Alexandra Borodovsky, Edwin Clark, Melanie Frigault, Michael Zinda, Celina D’Cruz. Targeting MET Exon 14 mutations with the selective small molecule inhibitor Savolitinib. [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 1150.

JAK2 inhibition sensitizes resistant EGFR-mutant lung adenocarcinoma to tyrosine kinase inhibitors

Lung adenocarcinomas with mutant epidermal growth factor receptor (EGFR) respond to EGFR-targeted tyrosine kinase inhibitors (TKIs), but resistance invariably occurs. We found that the Janus kinase (JAK)/signal transduction and activator of transcription 3 (STAT3) signaling pathway was aberrantly increased in TKI-resistant EGFR-mutant non-small cell lung cancer (NSCLC) cells. JAK2 inhibition restored sensitivity to the EGFR inhibitor erlotinib in TKI-resistant cell lines and xenograft models of EGFR-mutant TKI-resistant lung cancer. JAK2 inhibition uncoupled EGFR from its negative regulator, suppressor of cytokine signaling 5 (SOCS5), consequently increasing EGFR abundance and restoring the tumor cells' dependence on EGFR signaling. Furthermore, JAK2 inhibition led to heterodimerization of mutant and wild-type EGFR subunits, the activity of which was then blocked by TKIs. Our results reveal a mechanism whereby JAK2 inhibition overcomes acquired resistance to EGFR inhibitors and support the use of combination therapy with JAK and EGFR inhibitors for the treatment of EGFR-dependent NSCLC.

Identification of azabenzimidazoles as potent JAK1 selective inhibitors

We have identified a class of azabenzimidazoles as potent and selective JAK1 inhibitors. Investigations into the SAR are presented along with the structural features required to achieve selectivity for JAK1 versus other JAK family members. An example from the series demonstrated highly selective inhibition of JAK1 versus JAK2 and JAK3, along with inhibition of pSTAT3 in vivo, enabling it to serve as a JAK1 selective tool compound to further probe the biology of JAK1 selective inhibitors.

Tumors with AKT1E17K Mutations Are Rational Targets for Single Agent or Combination Therapy with AKT Inhibitors

AKT1(E17K) mutations occur at low frequency in a variety of solid tumors, including those of the breast and urinary bladder. Although this mutation has been shown to transform rodent cells in culture, it was found to be less oncogenic than PIK3CA mutations in breast epithelial cells. Moreover, the therapeutic potential of AKT inhibitors in human tumors with an endogenous AKT1(E17K) mutation is not known. Expression of exogenous copies of AKT1(E17K) in MCF10A breast epithelial cells increased phosphorylation of AKT and its substrates, induced colony formation in soft agar, and formation of lesions in the mammary fat pad of immunodeficient mice. These effects were inhibited by the allosteric and catalytic AKT inhibitors MK-2206 and AZD5363, respectively. Both AKT inhibitors caused highly significant growth inhibition of breast cancer explant models with AKT1(E17K) mutation. Furthermore, in a phase I clinical study, the catalytic Akt inhibitor AZD5363 induced partial responses in patients with breast and ovarian cancer with tumors containing AKT1(E17K) mutations. In MGH-U3 bladder cancer xenografts, which contain both AKT1(E17K) and FGFR3(Y373C) mutations, AZD5363 monotherapy did not significantly reduce tumor growth, but tumor regression was observed in combination with the FGFR inhibitor AZD4547. The data show that tumors with AKT1(E17K) mutations are rational therapeutic targets for AKT inhibitors, although combinations with other targeted agents may be required where activating oncogenic mutations of other proteins are present in the same tumor.

Abstract 1477: Pharmacodynamic response and anti-tumor activity of the MET inhibitor AZD6094 in papillary renal cell carcinoma patient derived xenograft models

Papillary renal cell carcinoma (PRCC) is the second most common cancer of the kidney and carries a poor prognosis for patients with non-localized disease. The central role of the hepatocyte growth factor (HGF) receptor MET in PRCC has been explored, demonstrating that MET aberrations, either through mutation, copy number gain, or trisomy of chromosome 7 (the location of MET and HGF) occur in the majority of PRCC cases. We sought to evaluate AZD6094 (HMPL-504), a potent and selective small molecule MET kinase inhibitor, in this disease setting. However, the development of effective therapies targeting MET and other targets in PRCC has been hampered in part by a lack of available preclinical models to test novel targeted therapies. Here we describe for the first time the pharmacodynamic (PD) response and anti-tumor activity of the selective MET inhibitor AZD6094 in two preclinical patient derived xenograft (PDX) models of PRCC (RCC-43b and RCC-47). Both PDX models have increased MET copy number of 8 and 9 copies by FISH in RCC-43b, and RCC-47 respectively, and robust MET protein staining by IHC. AZD6094 treatment resulted in dose dependent anti-tumor responses reaching ∼85% tumor growth inhibition (TGI) when dosed at 2.5 mg/kg daily (qd), stasis when dosed 10 mg/kg qd, and ∼20% regression when dosed at 25 mg/kg qd in the RCC-43b model and ∼63% TGI, ∼89% TGI, ∼64% regression, and ∼96% regression in the RCC-47 model when dosed 0.5, 2.5, 10, and 25 mg/kg qd respectively. The standard of care for RCC, sunitinib, showed no activity in RCC-43b when dosed at 10 mg/kg qd (∼10% TGI, p&gt;0.05 vs vehicle) and ∼60% TGI when dosed at 80 mg/kg qd. Pharmacodynamic analysis of RCC-47 tumors revealed that two hours after an acute dose of AZD6094 pMET levels were reduced &gt;95% at all dose levels tested (0.5 - 25 mg/kg). Eight hours after dosing, pMET levels returned to ∼50% in the 0.5 and 2.5 mg/kg dose groups whereas pMET was still inhibited &gt;90% in the 10 and 25 mg/kg dose groups indicating that the duration of target inhibition was dose related. AZD6094 inhibited multiple signaling nodes including MAPK, PI3K, and EGFR. Finally, at doses that induced tumor regression, AZD6094 resulted in a dose and time dependent induction of cleaved PARP, a marker of cell death. The finding that lower, sub-optimal doses of AZD6094 showed return of pMET 8 hours after a single administration, raised the question whether splitting the dose over a longer duration would increase anti-tumor activity. Indeed, twice a day dosing (bid, 8;16 hours) of AZD6094 at 1.25 mg/kg was more efficacious than daily administration of 2.5 mg/kg resulting in 8% regression compared to 89% TGI (p&lt;0.05). Taken together, these data provide the first report testing therapeutics in preclinical in vivo models of PRCC and support the clinical development of AZD6094 in this indication.

Citation Format: Alwin Schuller, Evan Barry, Rhys Jones, Melanie Frigault, Garry Beran, Ryan Henry, David Linsenmayer, Maureen Hattersley, Aaron Smith, Joanne Wilson, Ammar Adam, Michael Zinda, Corinne Reimer, Stephen Fawell, Edwin Clark, Celina D'Cruz. Pharmacodynamic response and anti-tumor activity of the MET inhibitor AZD6094 in papillary renal cell carcinoma patient derived xenograft models. [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 1477. doi:10.1158/1538-7445.AM2015-1477

Abstract 761: Changing the paradigm for treating drug resistance in NSCLC: Novel combinations of AZD6094, a selective MET inhibitor, and an irreversible, selective (EGFRm/T790M) EGFRTKI, AZD9291

Aberrant receptor tyrosine kinase (RTK) signaling is a well-documented driver of disease onset and progression across myriad cancer types, where the MET RTK contributes to tumor progression, maintenance and resistance to targeted therapies. Here we explore the therapeutic potential of AZD6094, a highly potent and selective MET inhibitor, in EGFR mutant (EGFRm) non-small cell lung cancer (NSCLC). Although many EGFRm NSCLC patients receiving first-line EGFR Tyrosine Kinase Inhibitors (TKI) benefit from therapy initially, the majority of patients will acquire resistance in 9-14 months1,2. Of this patient population, ∼10-15% of patients with emerging resistance to early generation EGFRm-TKI will have MET amplification3. Using xenograft models (HCC827) of resistance to erlotinib or gefitinib, both first-generation EGFRm-TKI, we assessed the efficacy of AZD6094 in models with varying copy number gain for MET. We demonstrate that the combination of AZD6094 with gefitinib, or AZD9291, an irreversible, selective (EGFRm/T790M) EGFR TKI, results in tumor growth inhibition (TGI) of &gt;100% in 3 models (HCC827-ER1, PCS030 clone 1 and 2)4, suggesting that the combination is necessary and sufficient to address acquired resistance due to MET gene amplification. Moreover, we explore efficacy of AZD6094 in models representative of resistance to first-line treatment with EGFRm-TKIs, harboring MET amplification and T790M EGFR mutations. In NCI-H820 xenografts (EGFRm/T790M/MET), we demonstrate for the first time that combining MET and EGFRm/T790M TKIs (AZD6094 with AZD9291) induces tumor regressions (TGI% &gt;100%, 94% regressions) and the loss of palpable tumors in 5/7 animals as compared to AZD9291 (TGI 48%) or AZD6094 treatment alone (TGI &gt;100%). Pharmacodynamic analysis of tumor lysates demonstrated potent and durable inhibition of pMET in all AZD6094 treatment groups. Due to the clinical importance of understanding acquired resistance to targeted TKIs, we then generated a model of resistance to AZD6094 in MET-amplified NSCLC NCI-H1993 cells and analyzed several resistant clones (H1993R). Interestingly, MET phosphorylation remains strongly inhibited in AZD6094-treated H1993R cells, while EGFR protein expression is upregulated and leads to co-dependency between both pathways. Enhanced expression and phosphorylation of EGFR, as well as AKT, MEK and ERK activation were commonly observed in H1993R cells. Taken together, our data support the potential of AZD6094 as a novel combination therapy for MET-driven NSCLC in the context of EGFRm TKI resistance, and highlight the clinical relevance of EGFR and MET signaling in the context of emerging TKI resistance mechanisms and coordinated pathways.

1. Mok et al. N Engl J Med 2009;361:947-957.

2. Rosell et al. Lancet Oncol 2012;13:239-246.

3. Engelman et al. Science 2007;316:1039-1043.

4. Models from Precos Ltd

Citation Format: Celina D'Cruz, Evan Barry, Ryan Henry, Lillian Castriotta, Alwin Schuller, Garry Beran, Susan Ashton, Cath Eberlein, Corinne Reimer, Melanie Frigault, Michael Zinda, Darren Cross, Stephen Fawell. Changing the paradigm for treating drug resistance in NSCLC: Novel combinations of AZD6094, a selective MET inhibitor, and an irreversible, selective (EGFRm/T790M) EGFRTKI, AZD9291. [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 761. doi:10.1158/1538-7445.AM2015-761

Abstract 1706: Whole exome sequencing of pre and post treatment diffuse large B cell lymphoma reveals the mutation spectrum of the relapse/refractory patient population

Our current understanding of the mutation spectrum of relapse/refractory patients is limited. Several published studies describing the mutational landscape of Diffuse Large B cell Lymphoma (DLBCL) have focused, by design, on diagnostic (pre-treatment) biopsies alone, while re-biopsy of patients who are refractory to first line therapy or who relapse on treatment is not standard of care in DLBCL. We have performed whole exome sequencing on 47 post treatment DLBCL core needle biopsies, 8 with matched diagnostic biopsies. Samples were obtained during a phase II trial prior to the start of treatment with the BCR targeted agent fostamatinib (1,2). Patients had progressed following therapy with an anthracycline-based regimen such as R-CHOP and had a median of 3 prior therapies (range 1-8). We compared the whole exome somatic variant and copy number calls from the post treatment and matched pairs to 2 cohorts of primary DLBCL (n = 112) analyzed with the same mutation caller (3,4). The average mutation rate between the pre and post treatment samples (n = 250, 282 respectively) and the paired diagnostic and post treatment biopsies were similar. However, we found that the mutation spectrum between the paired biopsies differed. Known DLBCL hotspot mutations such as MYD88 L265P remained consistent between pre and post treatment biopsies, however novel mutations in known DLBCL targets were found to emerge in the post treatment biopsies.

1. Veldman-Jones, M. et al. Reproducible, quantitative and flexible molecular sub-typing of clinical DLBCL samples using the NanoString nCounter system. Clin Cancer Res (2014)

2. Flinn I, B.N., Blum KA, et al. A Phase II Trial to Evaluate the Efficacy of Fostamatinib in Patients with Relapsed or Refractory Diffuse Large B-Cell Lymphoma (DLBCL). American Society of Hematology (San Francisco, 2014).

3. Zhang, J. et al. Genetic heterogeneity of diffuse large B-cell lymphoma. Proc Natl Acad Sci U S A 110, 1398-403 (2013).

4. Pasqualucci, L. et al. Analysis of the coding genome of diffuse large B-cell lymphoma. Nat Genet 43, 830-7 (2011).

Citation Format: Danielle Greenawalt, Kate Byth, Zhongwu Lai, Justin Johnson, Ambar Ahmed, Brian Dougherty, Kenneth Thress, Michael Zinda, Winnie S. Liang, John Carpten, Stephen Fawell, J. Carl Barrett. Whole exome sequencing of pre and post treatment diffuse large B cell lymphoma reveals the mutation spectrum of the relapse/refractory patient population. [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 1706. doi:10.1158/1538-7445.AM2015-1706

The MET Inhibitor AZD6094 (Savolitinib, HMPL-504) Induces Regression in Papillary Renal Cell Carcinoma Patient-Derived Xenograft Models

PURPOSE

Papillary renal cell carcinoma (PRCC) is the second most common cancer of the kidney and carries a poor prognosis for patients with nonlocalized disease. The HGF receptor MET plays a central role in PRCC and aberrations, either through mutation, copy number gain, or trisomy of chromosome 7 occurring in the majority of cases. The development of effective therapies in PRCC has been hampered in part by a lack of available preclinical models. We determined the pharmacodynamic and antitumor response of the selective MET inhibitor AZD6094 in two PRCC patient-derived xenograft (PDX) models.

EXPERIMENTAL DESIGN

Two PRCC PDX models were identified and MET mutation status and copy number determined. Pharmacodynamic and antitumor activity of AZD6094 was tested using a dose response up to 25 mg/kg daily, representing clinically achievable exposures, and compared with the activity of the RCC standard-of-care sunitinib (in RCC43b) or the multikinase inhibitor crizotinib (in RCC47).

RESULTS

AZD6094 treatment resulted in tumor regressions, whereas sunitinib or crizotinib resulted in unsustained growth inhibition. Pharmacodynamic analysis of tumors revealed that AZD6094 could robustly suppress pMET and the duration of target inhibition was dose related. AZD6094 inhibited multiple signaling nodes, including MAPK, PI3K, and EGFR. Finally, at doses that induced tumor regression, AZD6094 resulted in a dose- and time-dependent induction of cleaved PARP, a marker of cell death.

CONCLUSIONS

Data presented provide the first report testing therapeutics in preclinical in vivo models of PRCC and support the clinical development of AZD6094 in this indication.

Pharmacologic suppression of JAK1/2 by JAK1/2 inhibitor AZD1480 potently inhibits IL-6-induced experimental prostate cancer metastases formation

Metastatic prostate cancer is lethal and lacks effective strategies for prevention or treatment, requiring novel therapeutic approaches. Interleukin-6 (IL-6) is a cytokine that has been linked with prostate cancer pathogenesis by multiple studies. However, the direct functional roles of IL-6 in prostate cancer growth and progression have been unclear. In the present study, we show that IL-6 is produced in distant metastases of clinical prostate cancers. IL-6-activated signaling pathways in prostate cancer cells induced a robust 7-fold increase in metastases formation in nude mice. We further show that IL-6 promoted migratory prostate cancer cell phenotype, including increased prostate cancer cell migration, microtubule reorganization, and heterotypic adhesion of prostate cancer cells to endothelial cells. IL-6-driven metastasis was predominantly mediated by Stat3 and to lesser extent by ERK1/2. Most importantly, pharmacologic inhibition of Jak1/2 by AZD1480 suppressed IL-6-induced signaling, migratory prostate cancer cell phenotypes, and metastatic dissemination of prostate cancer in vivo in nude mice. In conclusion, we demonstrate that the cytokine IL-6 directly promotes prostate cancer metastasis in vitro and in vivo via Jak-Stat3 signaling pathway, and that IL-6-driven metastasis can be effectively suppressed by pharmacologic targeting of Jak1/2 using Jak1/2 inhibitor AZD1480. Our results therefore provide a strong rationale for further development of Jak1/2 inhibitors as therapy for metastatic prostate cancer.

Discovery of 1-methyl-1H-imidazole derivatives as potent Jak2 inhibitors

Structure based design, synthesis, and biological evaluation of a novel series of 1-methyl-1H-imidazole, as potent Jak2 inhibitors to modulate the Jak/STAT pathway, are described. Using the C-ring fragment from our first clinical candidate AZD1480 (24), optimization of the series led to the discovery of compound 19a, a potent, orally bioavailable Jak2 inhibitor. Compound 19a displayed a high level of cellular activity in hematopoietic cell lines harboring the V617F mutation and in murine BaF3 TEL-Jak2 cells. Compound 19a demonstrated significant tumor growth inhibition in a UKE-1 xenograft model within a well-tolerated dose range.

Abstract C144: MAPK1 mutation E322K modulates ERK pathway output and feedback

Mutations of MAPK1 E322K are observed in ∼8% of cervical ∼1% and head and neck cancer but there is currently little evidence of their impact on the ERK pathway. This study evaluated the impact of the E322K mutation on the ERK pathway output and feedback using an inducible system pTRIPZ in MCF10A immortalised cells. Expression of E322K MAPK1 following doxycycline induction reduced RSK phosphorylation on T359/S363 but increased pELK1 S383. DUSP6 protein levels were also increased in MCF10A expressing E322K mutant compared to WT. Pathway output was determined using the mRNA MEK signature (Dry et al. 2010). Following Dox induction, MCF10A E322K showed a 4-fold increase in DUSP2 mRNA and a 2-fold increase in DUSP6 mRNA while levels were unchanged in MCF10A expressing WT MAPK1. Conversely, &gt;2-fold decrease in ETV5 levels was observed in E322K MCF10A compared to WT cells. Exposure of WT and E322K MCF10A cells to an ATP competitive ERK inhibitor showed a greater reduction in pRSK T359/S363 levels in E322K cells compared to WT cells (likely due to lower baseline levels) but abrogation of pELK1 required higher concentrations of the inhibitor in mutant compared to WT cells. Consistent with its mechanism of action, the ERK inhibitor increased pERK levels. Interestingly, the combination of the MEK inhibitor selumetinib with the ERK inhibitor completely abrogated pERK in WT but not in E322K mutant MCF10 cells. Overall, the results suggest that the E322K mutation increases ERK-regulated genes such as DUSP2 which may only partially de-phosphorylate ERK due to the E322K mutation affecting substrates’ binding to the D site. The impact of E322K on the sensitivity to ERK and MEK inhibition is currently under evaluation.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C144.

Citation Format: Nin Guan, Oona Delpuech, Danielle Greenawalt, Kelly Jacques, Farzin Gharahdaghi, Michael Zinda, Paul J. Smith, Sylvie M. Guichard. MAPK1 mutation E322K modulates ERK pathway output and feedback. [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 C144.

Pharmacologic inhibition of Jak2-Stat5 signaling By Jak2 inhibitor AZD1480 potently suppresses growth of both primary and castrate-resistant prostate cancer

PURPOSE

Progression of prostate cancer to the lethal castrate-resistant stage coincides with loss of responsiveness to androgen deprivation and requires development of novel therapies. We previously provided proof-of-concept that Stat5a/b is a therapeutic target protein for prostate cancer. Here, we show that pharmacologic targeting of Jak2-dependent Stat5a/b signaling by the Jak2 inhibitor AZD1480 blocks castrate-resistant growth of prostate cancer.

EXPERIMENTAL DESIGN

Efficacy of AZD1480 in disrupting Jak2-Stat5a/b signaling and decreasing prostate cancer cell viability was evaluated in prostate cancer cells. A unique prostate cancer xenograft mouse model (CWR22Pc), which mimics prostate cancer clinical progression in patients, was used to assess in vivo responsiveness of primary and castrate-resistant prostate cancer (CRPC) to AZD1480. Patient-derived clinical prostate cancers, grown ex vivo in organ explant cultures, were tested for responsiveness to AZD1480.

RESULTS

AZD1480 robustly inhibited Stat5a/b phosphorylation, dimerization, nuclear translocation, DNA binding, and transcriptional activity in prostate cancer cells. AZD1480 reduced prostate cancer cell viability sustained by Jak2-Stat5a/b signaling through induction of apoptosis, which was rescued by constitutively active Stat5a/b. In mice, pharmacologic targeting of Stat5a/b by AZD1480 potently blocked growth of primary androgen-dependent as well as recurrent castrate-resistant CWR22Pc xenograft tumors, and prolonged survival of tumor-bearing mice versus vehicle or docetaxel-treated mice. Finally, nine of 12 clinical prostate cancers responded to AZD1480 by extensive apoptotic epithelial cell loss, concurrent with reduced levels of nuclear Stat5a/b.

CONCLUSIONS

We report the first evidence for efficacy of pharmacologic targeting of Stat5a/b as a strategy to inhibit castrate-resistant growth of prostate cancer, supporting further clinical development of Stat5a/b inhibitors as therapy for advanced prostate cancer.

Abstract 3133: Identification and functional validation of novel genetically-linked breast cancer targets through pooled gain-of-function screening

Breast cancer is one of the most common cancer types, with greater than 450,000 deaths reported per year worldwide. Through genome wide sequencing efforts, multiple genetic alterations have been identified, including mutations and amplifications in genes such as v-erb-b2 erythroblastic leukemia viral oncogene homolog 2 (ERBB2), GATA binding protein 3 (GATA3), phosphatidylinositol 3-kinase alpha catalytic subunit (PIK3CA) as well as novel genomic rearrangements such as the recently identified MAGI3-AKT3 fusion. Now that breast cancer can be characterized to an unprecedented level, one of the key challenges remaining is to identify and distinguish critical ‘driver’ events responsible for tumor progression, from neutral ‘passenger’ lesions. In order to achieve this, we utilized high resolution aCGH analysis of 50 purified breast cancer samples (made up of Her2+, estrogen receptor positive (ER+) and triple negative tumors with variable responses to SOC regimens), in combination with a Gain-of-Function transformation screen to identify and validate novel breast targets. 158 genomic regions were found to be recurrently amplified, consisting of 759 genes in total. The top 32 focally amplified genes, along with 12 cancer-relevant mutant alleles were prioritized and a library generated utilizing the pTRIPZ-tetracycline regulated inducible lentiviral vector system. These 44 genes were subsequently combined into 16 different target pools (5-13 targets per pool, co-expressing genes that were co-amplified in the same clinical specimen) and evaluated for their ability to transform immortalized breast epithelial MCF10A cells (both wild-type and p53 -/- cells). Through this screening approach, p21-activated kinase 1 (PAK1) was identified, whose kinase activity was required to robustly transform MCF10A cells through regulating multiple signalling pathways including MAPK. Several other putative oncogenes were also identified and will be presented here, including the glycosyltransferse asparagine-linked glycosylation 8 (ALG8). Interestingly, PAK1 and ALG8 are co-amplified in both breast (8%) and ovarian cancers (11%). Our target validation studies have suggested that ALG8 can support PAK1-induced transformation, as dramatic suppression of soft-agar colony growth was seen in co-amplified breast cancer cell lines upon combined siRNA treatment to both targets. Thus, this combined high resolution aCGH profiling and functional screening approach has enabled the successful identification of novel oncogenic targets in breast cancer.

Citation Format: Krishna Vasudevan, Axel Hernandez, Zhongwu Lai, Yonghong Xiao, Nin Guan, Carolyn Hardy, Robert Godin, Christopher Denz, Minwei Ye, Elizabeth Lenkiewicz, Stephanie Savage, Michael T. Barrett, Donna Prunkard, Peter Rabinovitch, Mark Basik, Ewa Przybytkowski, Kevin Webster, Michael Zinda, Emma-Louise Jenkins. Identification and functional validation of novel genetically-linked breast cancer targets through pooled gain-of-function screening. [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 3133. doi:10.1158/1538-7445.AM2013-3133

Antiangiogenic and antimetastatic activity of JAK inhibitor AZD1480

STAT3 has important functions in both tumor cells and the tumor microenvironment to facilitate cancer progression. The STAT regulatory kinase Janus-activated kinase (JAK) has been strongly implicated in promoting oncogenesis of various solid tumors, including the use of JAK kinase inhibitors such as AZD1480. However, direct evidence that JAK drives STAT3 function and cancer pathogenesis at the level of the tumor microenvironment is yet to be established clearly. In this study, we show that AZD1480 inhibits STAT3 in tumor-associated myeloid cells, reducing their number and inhibiting tumor metastasis. Myeloid cell-mediated angiogenesis was also diminished by AZD1480, with additional direct inhibition of endothelial cell function in vitro and in vivo. AZD1480 blocked lung infiltration of myeloid cells and formation of pulmonary metastases in both mouse syngeneic experimental and spontaneous metastatic models. Furthermore, AZD1480 reduced angiogenesis and metastasis in a human xenograft tumor model. Although the effects of AZD1480 on the tumor microenvironment were important for the observed antiangiogenic activity, constitutive activation of STAT3 in tumor cells themselves could block these antiangiogenic effects, showing the complexity of the JAK/STAT signaling network in tumor progression. Together, our results indicated that AZD1480 can effectively inhibit tumor angiogenesis and metastasis mediated by STAT3 in stromal cells as well as tumor cells.

Discovery of 5-chloro-N2-[(1S)-1-(5-fluoropyrimidin-2-yl)ethyl]-N4-(5-methyl-1H-pyrazol-3-yl)pyrimidine-2,4-diamine (AZD1480) as a novel inhibitor of the Jak/Stat pathway

The myeloproliferative neoplasms, polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis are a heterogeneous but related group of hematological malignancies characterized by clonal expansion of one or more myeloid lineages. The discovery of the Jak2 V617F gain of function mutation highlighted Jak2 as a potential therapeutic target in the MPNs. Herein, we disclose the discovery of a series of pyrazol-3-yl pyrimidin-4-amines and the identification of 9e (AZD1480) as a potent Jak2 inhibitor. 9e inhibits signaling and proliferation of Jak2 V617F cell lines in vitro, demonstrates in vivo efficacy in a TEL-Jak2 model, has excellent physical properties and preclinical pharmacokinetics, and is currently being evaluated in Phase I clinical trials.

The JAK2 inhibitor AZD1480 potently blocks Stat3 signaling and oncogenesis in solid tumors

Persistent activation of Stat3 is oncogenic and is prevalent in a wide variety of human cancers. Chronic cytokine stimulation is associated with Stat3 activation in some tumors, implicating cytokine receptor-associated Jak family kinases. Using Jak2 inhibitors, we demonstrate a central role of Jaks in modulating basal and cytokine-induced Stat3 activation in human solid tumor cell lines. Inhibition of Jak2 activity is associated with abrogation of Stat3 nuclear translocation and tumorigenesis. The Jak2 inhibitor AZD1480 suppresses the growth of human solid tumor xenografts harboring persistent Stat3 activity. We demonstrate the essential role of Stat3 downstream of Jaks by inhibition of tumor growth using short hairpin RNA targeting Stat3. Our data support a key role of Jak kinase activity in Stat3-dependent tumorigenesis.

Effects of the JAK2 inhibitor, AZ960, on Pim/BAD/BCL-xL survival signaling in the human JAK2 V617F cell line SET-2

The Janus-associated kinase 2 (JAK2) V617F mutation is believed to play a critical role in the pathogenesis of polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis. We have characterized a novel small molecule JAK2 inhibitor, AZ960, and used it as a tool to investigate the consequences of JAK2 V617F inhibition in the SET-2 cell line. AZ960 inhibits JAK2 kinase with a K(i) of 0.00045 microm in vitro and treatment of TEL-JAK2 driven Ba/F3 cells with AZ960 blocked STAT5 phosphorylation and potently inhibited cell proliferation (GI(50)=0.025 microm). AZ960 demonstrated selectivity for TEL-JAK2-driven STAT5 phosphorylation and cell proliferation when compared with cell lines driven by similar fusions of the other JAK kinase family members. In the SET-2 human megakaryoblastic cell line, heterozygous for the JAK2 V617F allele, inhibition of JAK2 resulted in decreased STAT3/5 phosphorylation and inhibition of cell proliferation (GI(50)=0.033 microm) predominately through the induction of mitochondrial-mediated apoptosis. We provide evidence that JAK2 inhibition induces apoptosis by direct and indirect regulation of the anti-apoptotic protein BCL-xL. Inhibition of JAK2 blocked BCL-XL mRNA expression resulting in a reduction of BCL-xL protein levels. Additionally, inhibition of JAK2 resulted in decreased PIM1 and PIM2 mRNA expression. Decreased PIM1 mRNA corresponded with a decrease in Pim1 protein levels and inhibition of BAD phosphorylation at Ser(112). Finally, small interfering RNA-mediated suppression of BCL-xL resulted in apoptotic cell death similar to the phenotype observed following JAK2 inhibition. These results suggest a model in which JAK2 promotes cell survival by signaling through the Pim/BAD/BCL-xL pathway.