Inhibition of platelet-derived growth factor receptor α by MEDI-575 reduces tumor growth and stromal fibroblast content in a model of non-small cell lung cancer.

Platelet-derived growth factor receptor α (PDGFRα) is a receptor tyrosine kinase that promotes cell survival and is expressed in both the tumor and the stromal components of human cancers. We have developed a fully human monoclonal antibody, MEDI-575, that selectively binds to human PDGFRα with high affinity, with no observable affinity for murine PDGFRα. To more fully characterize the role of PDGFRα in the regulation of tumor stroma, we evaluated the in vivo antitumor effects of MEDI-575 in tumor-bearing severe combined immunodeficient (SCID) mice and in genetically altered SCID mice expressing human PDGFRα in place of murine PDGFRα. We used the Calu-6 non-small cell lung cancer model because it lacks an in vitro proliferative response to PDGFRα activation. Antitumor activity was observed when the study was performed in mice expressing the human receptor, but no activity was observed in the mice expressing the murine receptor. Immunohistologic analysis of the tumors from mice expressing human PDGFRα showed a highly significant reduction in stromal fibroblast content and only minor changes in tumor proliferative index in tumors exposed to MEDI-575 compared with the results seen in vehicle-treated tumors or in tumors from mice expressing murine PDGFRα. Additional in vitro studies indicated that exposure of primary cancer-associated fibroblasts to MEDI-575 can directly affect proliferation and key signaling pathways in these cells. These results highlight the potential for observing antitumor activity with MEDI-575 through modulation of the stromal component of tumors and confirm that the PDGFRα pathway can play a role in maintaining a tumor microenvironment conducive to tumor growth.

A PKPD Case Study: Achieving Clinically Relevant Exposures of AZD5991 in Oncology Mouse Models.

Capturing human equivalent drug exposures preclinically is a key challenge in the translational process. Motivated by the need to recapitulate the pharmacokinetic (PK) profile of the clinical stage Mcl-1 inhibitor AZD5991 in mice, we describe the methodology used to develop a refined mathematical model relating clinically relevant concentration profiles to efficacy. Administration routes were explored to achieve target exposures matching the clinical exposure of AZD5991. Intravenous infusion using vascular access button (VAB) technology was found to best reproduce clinical target exposures of AZD5991 in mice. Exposure-efficacy relationships were evaluated, demonstrating that dissimilar PK profiles result in differences in target engagement and efficacy outcomes. Thus, these data underscore the importance of accurately ascribing key PK metrics in the translational process to enable clinically meaningful predictions of efficacy.

Design and optimisation of dendrimer-conjugated Bcl-2/xL inhibitor, AZD0466, with improved therapeutic index for cancer therapy.

Dual Bcl-2/Bcl-xL inhibitors are expected to deliver therapeutic benefit in many haematological and solid malignancies, however, their use is limited by tolerability issues. AZD4320, a potent dual Bcl-2/Bcl-xL inhibitor, has shown good efficacy however had dose limiting cardiovascular toxicity in preclinical species, coupled with challenging physicochemical properties, which prevented its clinical development. Here, we describe the design and development of AZD0466, a drug-dendrimer conjugate, where AZD4320 is chemically conjugated to a PEGylated poly-lysine dendrimer. Mathematical modelling was employed to determine the optimal release rate of the drug from the dendrimer for maximal therapeutic index in terms of preclinical anti-tumour efficacy and cardiovascular tolerability. The optimised candidate is shown to be efficacious and better tolerated in preclinical models compared with AZD4320 alone. The AZD4320-dendrimer conjugate (AZD0466) identified, through mathematical modelling, has resulted in an improved therapeutic index and thus enabled progression of this promising dual Bcl-2/Bcl-xL inhibitor into clinical development.

STAT3 Antisense Oligonucleotide Remodels the Suppressive Tumor Microenvironment to Enhance Immune Activation in Combination with Anti-PD-L1.

PURPOSE: Danvatirsen is a therapeutic antisense oligonucleotide (ASO) that selectively targets STAT3 and has shown clinical activity in two phase I clinical studies. We interrogated the clinical mechanism of action using danvatirsen-treated patient samples and conducted back-translational studies to further elucidate its immunomodulatory mechanism of action. EXPERIMENTAL DESIGN: Paired biopsies and blood samples from danvatirsen-treated patients were evaluated using immunohistochemistry and gene-expression analysis. To gain mechanistic insight, we used mass cytometry, flow cytometry, and immunofluorescence analysis of CT26 tumors treated with a mouse surrogate STAT3 ASO, and human immune cells were treated in vitro with danvatirsen. RESULTS: Within the tumors of treated patients, danvatirsen uptake was observed mainly in cells of the tumor microenvironment (TME). Gene expression analysis comparing baseline and on-treatment tumor samples showed increased expression of proinflammatory genes. In mouse models, STAT3 ASO demonstrated partial tumor growth inhibition and enhanced the antitumor activity when combined with anti-PD-L1. Immune profiling revealed reduced STAT3 protein in immune and stromal cells, and decreased suppressive cytokines correlating with increased proinflammatory macrophages and cytokine production. These changes led to enhanced T-cell abundance and function in combination with anti-PD-L1. CONCLUSIONS: STAT3 ASO treatment reverses a suppressive TME and promotes proinflammatory gene expression changes in patients' tumors and mouse models. Preclinical data provide evidence that ASO-mediated inhibition of STAT3 in the immune compartment is sufficient to remodel the TME and enhance the activity of checkpoint blockade without direct STAT3 inhibition in tumor cells. Collectively, these data provide a rationale for testing this combination in the clinic.

Small molecule AZD4635 inhibitor of A2AR signaling rescues immune cell function including CD103+ dendritic cells enhancing anti-tumor immunity.

Accumulation of extracellular adenosine within the microenvironment is a strategy exploited by tumors to escape detection by the immune system. Adenosine signaling through the adenosine 2A receptor (A2AR) on immune cells elicits a range of immunosuppressive effects which promote tumor growth and limit the efficacy of immune checkpoint inhibitors. Preclinical data with A2AR inhibitors have demonstrated tumor regressions in mouse models by rescuing T cell function; however, the mechanism and role on other immune cells has not been fully elucidated. METHODS: We report here the development of a small molecule A2AR inhibitor including characterization of binding and inhibition of A2AR function with varying amounts of a stable version of adenosine. Functional activity was tested in both mouse and human T cells and dendritic cells (DCs) in in vitro assays to understand the intrinsic role on each cell type. The role of adenosine and A2AR inhibition was tested in DC differentiation assays as well as co-culture assays to access the cross-priming function of DCs. Syngeneic models were used to assess tumor growth alone and in combination with alphaprogrammed death-ligand 1 (αPD-L1). Immunophenotyping by flow cytometry was performed to examine global immune cell changes upon A2AR inhibition. RESULTS: We provide the first report of AZD4635, a novel small molecule A2AR antagonist which inhibits downstream signaling and increases T cell function as well as a novel mechanism of enhancing antigen presentation by CD103+ DCs. The role of antigen presentation by DCs, particularly CD103+ DCs, is critical to drive antitumor immunity providing rational to combine a priming agent AZD4635 with check point blockade. We find adenosine impairs the maturation and antigen presentation function of CD103+ DCs. We show in multiple syngeneic mouse tumor models that treatment of AZD4635 alone and in combination with αPD-L1 led to decreased tumor volume correlating with enhanced CD103+ function and T cell response. We extend these studies into human DCs to show that adenosine promotes a tolerogenic phenotype that can be reversed with AZD4635 restoring antigen-specific T cell activation. Our results support the novel role of adenosine signaling as an intrinsic negative regulator of CD103+ DCs maturation and priming. We show that potent inhibition of A2AR with AZD4635 reduces tumor burden and enhances antitumor immunity. This unique mechanism of action in CD103+ DCs may contribute to clinical responses as AZD4635 is being evaluated in clinical trials with IMFINZI (durvalumab, αPD-L1) in patients with solid malignancies. CONCLUSION: We provide evidence implicating suppression of adaptive and innate immunity by adenosine as a mechanism for immune evasion by tumors. Inhibition of adenosine signaling through selective small molecule inhibition of A2AR using AZD4635 restores T cell function via an internal mechanism as well as tumor antigen cross-presentation by CD103+ DCs resulting in antitumor immunity.

Discovery and pharmacological characterization of AZD3229, a potent KIT/PDGFRα inhibitor for treatment of gastrointestinal stromal tumors.

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma driven by mutations in KIT or platelet-derived growth factor α (PDGFRα). Although first-line treatment, imatinib, has revolutionized GIST treatment, drug resistance due to acquisition of secondary KIT/PDGFRα mutations develops in a majority of patients. Second- and third-line treatments, sunitinib and regorafenib, lack activity against a plethora of mutations in KIT/PDGFRα in GIST, with median time to disease progression of 4 to 6 months and inhibition of vascular endothelial growth factor receptor 2 (VEGFR2) causing high-grade hypertension. Patients with GIST have an unmet need for a well-tolerated drug that robustly inhibits a range of KIT/PDGFRα mutations. Here, we report the discovery and pharmacological characterization of AZD3229, a potent and selective small-molecule inhibitor of KIT and PDGFRα designed to inhibit a broad range of primary and imatinib-resistant secondary mutations seen in GIST. In engineered and GIST-derived cell lines, AZD3229 is 15 to 60 times more potent than imatinib in inhibiting KIT primary mutations and has low nanomolar activity against a wide spectrum of secondary mutations. AZD3229 causes durable inhibition of KIT signaling in patient-derived xenograft (PDX) models of GIST, leading to tumor regressions at doses that showed no changes in arterial blood pressure (BP) in rat telemetry studies. AZD3229 has a superior potency and selectivity profile to standard of care (SoC) agents-imatinib, sunitinib, and regorafenib, as well as investigational agents, avapritinib (BLU-285) and ripretinib (DCC-2618). AZD3229 has the potential to be a best-in-class inhibitor for clinically relevant KIT/PDGFRα mutations in GIST.

Differential Activity of ATR and WEE1 Inhibitors in a Highly Sensitive Subpopulation of DLBCL Linked to Replication Stress.

DNA damage checkpoint kinases ATR and WEE1 are among key regulators of DNA damage response pathways protecting cells from replication stress, a hallmark of cancer that has potential to be exploited for therapeutic use. ATR and WEE1 inhibitors are in early clinical trials and success will require greater understanding of both their mechanism of action and biomarkers for patient selection. Here, we report selective antitumor activity of ATR and WEE1 inhibitors in a subset of non-germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL) cell lines, characterized by high MYC protein expression and CDKN2A/B deletion. Activity correlated with the induction of replication stress, indicated by increased origin firing and retardation of replication fork progression. However, ATR and WEE1 inhibitors caused different amounts of DNA damage and cell death in distinct phases of the cell cycle, underlying the increased potency observed with WEE1 inhibition. ATR inhibition caused DNA damage to manifest as 53BP1 nuclear bodies in daughter G1 cells leading to G1 arrest, whereas WEE1 inhibition caused DNA damage and arrest in S phase, leading to earlier onset apoptosis. In vivo xenograft DLBCL models confirmed differences in single-agent antitumor activity, but also showed potential for effective ATR inhibitor combinations. Importantly, insights into the different inhibitor mechanisms may guide differentiated clinical development strategies aimed at exploiting specific vulnerabilities of tumor cells while maximizing therapeutic index. Our data therefore highlight clinical development opportunities for both ATR and WEE1 inhibitors in non-GCB DLBCL subtypes that represent an area of unmet clinical need. SIGNIFICANCE: ATR and WEE1 inhibitors demonstrate effective antitumor activity in preclinical models of DLBCL associated with replication stress, but new mechanistic insights and biomarkers of response support a differentiated clinical development strategy.

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.

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.

Comparison of biochemical and biological effects of ML858 (salinosporamide A) and bortezomib.

Strains within the genus Salinospora have been shown to produce complex natural products having antibiotic and antiproliferative activities. The biochemical basis for the cytotoxic effects of salinosporamide A has been linked to its ability to inhibit the proteasome. Synthetically accessible salinosporamide A (ML858) was used to determine its biochemical and biological activities and to compare its effects with those of bortezomib. ML858 and bortezomib show time- and concentration-dependent inhibition of the proteasome in vitro. However, unlike bortezomib, which is a reversible inhibitor, ML858 covalently binds to the proteasome, resulting in the irreversible inhibition of 20S proteasome activity. ML858 was equipotent to bortezomib in cell-based reporter stabilization assays, but due to intramolecular instability is less potent in long-term assays. ML858 failed to maintain levels of proteasome inhibition necessary to achieve efficacy in tumor models responsive to bortezomib. Our results show that ML858 and bortezomib exhibit different kinetic and pharmacologic profiles and suggest that additional characterization of ML858 is warranted before its therapeutic potential can be fully appreciated.

Longitudinally quantitative 2-deoxy-2-[18F]fluoro-D-glucose micro positron emission tomography imaging for efficacy of new anticancer drugs: a case study with bortezomib in prostate cancer murine model.

PURPOSE: The aim of this study was to validate quantitative metabolic response of tumors to a treatment measured by longitudinal 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) micro positron emission tomography (microPET) as a robust tool for preclinical evaluation of new anticancer agents. PROCEDURES: Severe combined immunodeficiency mice with CWR22 xenografts were intravenously treated with bortezomib (Velcade) at 0.8 mg/kg on days 0, 3, 7, 10, and 14 and imaged with FDG microPET before, during and after treatment. Quantitative indices of tumor FDG uptake were developed. RESULTS: FDG microPET images successfully revealed the gradual reduction of tumor FDG uptake on day 4 onward despite no absolute tumor shrinkage. The standardized uptake values of FDG in tumors was reduced to 43% of the baseline values. Using the total tumor FDG uptake as the viable tumor burden, we found 86% tumor inhibition, compared to a 55% tumor growth inhibition in tumor volume measurement. CONCLUSION: FDG microPET imaging can provide an additional dimension of the efficacy of anticancer therapies that may otherwise be underestimated by tumor volume measurement.

Antineoplastic effects of chemotherapeutic agents are potentiated by NM-3, an inhibitor of angiogenesis.

Antiangiogenic therapy, although effective in shrinking tumors, has not yet been established as a standalone treatment for cancer. This therapeutic limitation can be overcome by combining angiogenesis inhibitors with chemotherapeutic agents. NM-3, a small molecule isocoumarin, is a recently discovered angiogenesis inhibitor. Here we demonstrate that NM-3 inhibits the proliferation of human umbilical vein endothelial cells in vitro, at concentrations 10-fold less than those required to inhibit normal fibroblasts or tumor cells (HT29, MKN28, and MCF-7). NM-3 alone inhibits endothelial sprouting and tube formation in vitro. The results also show that synergistic antiproliferative activity is observed when human umbilical vein endothelial cells are treated with NM-3 in combination with 5-fluorouracil. The effects of treatment with NM-3 and various chemotherapeutic agents were also evaluated in tumor xenografts. The results demonstrate that combined treatment with NM-3 and chemotherapeutic agents significantly reduced mean tumor volume compared with either treatment alone, with no effects on body weight changes. Taken together, these findings demonstrate that NM-3 is a well-tolerated angiogenesis inhibitor that significantly increases the efficacy of existing antineoplastic agents.

Acquired savolitinib resistance in non-small cell lung cancer arises via multiple mechanisms that converge on MET-independent mTOR and MYC activation.

Lung cancer is the most common cause of cancer death globally with a significant, unmet need for more efficacious treatments. The receptor tyrosine kinase MET has been implicated as an oncogene in numerous cancer subtypes, including non-small cell lung cancer (NSCLC). Here we explore the therapeutic potential of savolitinib (volitinib, AZD6094, HMPL-504), a potent and selective MET inhibitor, in NSCLC. In vitro, savolitinib inhibits MET phosphorylation with nanomolar potency, which correlates with blockade of PI3K/AKT and MAPK signaling as well as MYC down-regulation. In vivo, savolitinib causes inhibition of these pathways and significantly decreases growth of MET-dependent xenografts. To understand resistance mechanisms, we generated savolitinib resistance in MET-amplified NSCLC cell lines and analyzed individual clones. We found that upregulation of MYC and constitutive mTOR pathway activation is a conserved feature of resistant clones that can be overcome by knockdown of MYC or dual mTORC1/2 inhibition. Lastly, we demonstrate that mechanisms of resistance are heterogeneous, arising via a switch to EGFR dependence or by a requirement for PIM signaling. This work demonstrates the efficacy of savolitinib in NSCLC and characterizes acquired resistance, identifying both known and novel mechanisms that may inform combination strategies in the clinic.

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.

AZD5153: A Novel Bivalent BET Bromodomain Inhibitor Highly Active against Hematologic Malignancies.

The bromodomain and extraterminal (BET) protein BRD4 regulates gene expression via recruitment of transcriptional regulatory complexes to acetylated chromatin. Pharmacological targeting of BRD4 bromodomains by small molecule inhibitors has proven to be an effective means to disrupt aberrant transcriptional programs critical for tumor growth and/or survival. Herein, we report AZD5153, a potent, selective, and orally available BET/BRD4 bromodomain inhibitor possessing a bivalent binding mode. Unlike previously described monovalent inhibitors, AZD5153 ligates two bromodomains in BRD4 simultaneously. The enhanced avidity afforded through bivalent binding translates into increased cellular and antitumor activity in preclinical hematologic tumor models. In vivo administration of AZD5153 led to tumor stasis or regression in multiple xenograft models of acute myeloid leukemia, multiple myeloma, and diffuse large B-cell lymphoma. The relationship between AZD5153 exposure and efficacy suggests that prolonged BRD4 target coverage is a primary efficacy driver. AZD5153 treatment markedly affects transcriptional programs of MYC, E2F, and mTOR. Of note, mTOR pathway modulation is associated with cell line sensitivity to AZD5153. Transcriptional modulation of MYC and HEXIM1 was confirmed in AZD5153-treated human whole blood, thus supporting their use as clinical pharmacodynamic biomarkers. This study establishes AZD5153 as a highly potent, orally available BET/BRD4 inhibitor and provides a rationale for clinical development in hematologic malignancies. Mol Cancer Ther; 15(11); 2563-74. ©2016 AACR.

Aurora kinase inhibitor nanoparticles target tumors with favorable therapeutic index in vivo.

Efforts to apply nanotechnology in cancer have focused almost exclusively on the delivery of cytotoxic drugs to improve therapeutic index. There has been little consideration of molecularly targeted agents, in particular kinase inhibitors, which can also present considerable therapeutic index limitations. We describe the development of Accurin polymeric nanoparticles that encapsulate the clinical candidate AZD2811, an Aurora B kinase inhibitor, using an ion pairing approach. Accurins increase biodistribution to tumor sites and provide extended release of encapsulated drug payloads. AZD2811 nanoparticles containing pharmaceutically acceptable organic acids as ion pairing agents displayed continuous drug release for more than 1 week in vitro and a corresponding extended pharmacodynamic reduction of tumor phosphorylated histone H3 levels in vivo for up to 96 hours after a single administration. A specific AZD2811 nanoparticle formulation profile showed accumulation and retention in tumors with minimal impact on bone marrow pathology, and resulted in lower toxicity and increased efficacy in multiple tumor models at half the dose intensity of AZD1152, a water-soluble prodrug of AZD2811. These studies demonstrate that AZD2811 can be formulated in nanoparticles using ion pairing agents to give improved efficacy and tolerability in preclinical models with less frequent dosing. Accurins specifically, and nanotechnology in general, can increase the therapeutic index of molecularly targeted agents, including kinase inhibitors targeting cell cycle and oncogenic signal transduction pathways, which have to date proved toxic in humans.

Biological characterization of MLN944: a potent DNA binding agent.

MLN944 (XR5944) is a novel bis-phenazine that has demonstrated exceptional efficacy against a number of murine and human tumor models. The drug was reported originally as a dual topoisomerase I/II poison, but a precise mechanism of action for this compound remains to be determined. Several lines of evidence, including the marginal ability of MLN944 to stabilize topoisomerase-dependent cleavage, and the sustained potency of MLN944 in mammalian cells with reduced levels of both topoisomerases, suggest that other activities of the drug exist. In this study, we show that MLN944 intercalates into DNA, but has no effect on the catalytic activity of either topoisomerase I or II. MLN944 displays no significant ability to stimulate DNA scission mediated by either topoisomerase I or II compared with camptothecin or etoposide, respectively. In addition, yeast genetic models also point toward a topoisomerase-independent mechanism of action. To examine cell cycle effects, synchronized human HCT116 cells were treated with MLN944, doxorubicin, camptothecin, or a combination of the latter two to mimic a dual topoisomerase poison. MLN944 treatment was found to induce a G(1) and G(2) arrest in cells that is unlike the typical G(2)-M arrest noted with known topoisomerase poisons. Finally, transcriptional profiling analysis of xenograft tumors treated with MLN944 revealed clusters of regulated genes distinct from those observed in irinotecan hydrochloride (CPT-11)-treated tumors. Taken together, these findings suggest that the primary mechanism of action of MLN944 likely involves DNA binding and intercalation, but does not appear to involve topoisomerase inhibition.

Resistance to everolimus driven by epigenetic regulation of MYC in ER+ breast cancers.

Acquired resistance to PI3K/mTOR/Akt pathway inhibitors is often associated with compensatory feedback loops involving the activation of oncogenes. Here, we have generated everolimus resistance in ER+ breast cancer cells and in long-term estrogen deprived (LTED) models that mimic progression on anti-estrogens. This allowed us to uncover MYC as a driver of mTOR inhibitor resistance. We demonstrate that both everolimus resistance and acute treatment of everolimus can lead to the upregulation of MYC mRNA, protein expression and, consequently, the enrichment of MYC signatures as revealed by RNA sequencing data. Depletion of MYC resulted in resensitization to everolimus, confirming its functional importance in this setting. Furthermore, ChIP assays demonstrate that MYC upregulation in the everolimus resistant lines is mediated by increased association of the BRD4 transcription factor with the MYC gene. Finally, JQ1, a BRD4 inhibitor combined with everolimus exhibited increased tumor growth inhibition in 3D Matrigel models and an in vivo xenograft model. These data suggest that MYC plays an important role in mediating resistance to everolimus in ER+ and ER+/LTED models. Furthermore, given the regulation ofMYCby BRD4 in this setting, these data have implications for increased therapeutic potential of combining epigenetic agents with mTOR inhibitors to effectively downregulate otherwise difficult to target transcription factors such as MYC.

AZD9150, a next-generation antisense oligonucleotide inhibitor of STAT3 with early evidence of clinical activity in lymphoma and lung cancer.

Next-generation sequencing technologies have greatly expanded our understanding of cancer genetics. Antisense technology is an attractive platform with the potential to translate these advances into improved cancer therapeutics, because antisense oligonucleotide (ASO) inhibitors can be designed on the basis of gene sequence information alone. Recent human clinical data have demonstrated the potent activity of systemically administered ASOs targeted to genes expressed in the liver. We describe the preclinical activity and initial clinical evaluation of a class of ASOs containing constrained ethyl modifications for targeting the gene encoding the transcription factor STAT3, a notoriously difficult protein to inhibit therapeutically. Systemic delivery of the unformulated ASO, AZD9150, decreased STAT3 expression in a broad range of preclinical cancer models and showed antitumor activity in lymphoma and lung cancer models. AZD9150 preclinical activity translated into single-agent antitumor activity in patients with highly treatment-refractory lymphoma and non-small cell lung cancer in a phase 1 dose-escalation study.

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.