Abstract 1646: IK-930, a paralog-selective TEAD inhibitor for treating YAP/TAZ-TEAD dependent cancers

The Hippo signaling cascade regulates cell proliferation and survival, as well as overall tissue homeostasis. These functions are mediated by the TEAD family of transcription factors which, when bound to the co-activators YAP or TAZ, induce expression of pro-growth and anti-apoptotic genes. This pathway is frequently dysregulated across tumor types, with genetic alterations along with other mechanisms driving hyper-active YAP/TAZ-TEAD. In addition, Hippo signaling mediates resistance to therapies targeting key oncogenic pathways such as EGFR and RAS. As a result, TEAD transcription factors are promising therapeutic targets. The TEAD family comprises four paralogs (TEAD1-4) that have both over-lapping and non-redundant functions. Given the essential roles of the Hippo pathway in normal physiology, it may be beneficial to target a subset of TEADs to minimize potential on-target toxicity while maintaining anti-tumor efficacy.

Although highly homologous, the lipid-binding pocket of TEADs harbor some sequence divergence, highlighting an opportunity to design paralog-specific compounds. We developed IK-930 as a novel, selective inhibitor that potently blocks TEAD transcriptional activity by disrupting the auto-palmitoylation required for its interaction with YAP/TAZ. To demonstrate the selectivity profile of IK-930, a suite of biochemical assays was employed, all of which showed preferential compound binding to an individual paralog. A novel NanoBRETTM system that enabled quantitative, high-throughput measurements of cellular TEAD engagement also documented selective inhibitor interaction with the same family member.

To assess how differences in selectivity affect therapeutic index, the in vivo efficacy and toxicity of IK-930 was compared to a pan-TEAD inhibitor. In several Hippo-mutated xenograft models, both compounds displayed potent anti-tumor activity. Moreover, IK-930 exhibited synergy with targeted agents, including EGFR inhibitors, indicating that its selectivity profile could drive robust efficacy in diverse tumor types. Previous studies in genetically engineered mouse models reported that perturbation of YAP/TAZ results in kidney toxicity. Treatment with a pan-TEAD inhibitor in rats and non-human primates led to substantial proteinuria and kidney pathology at exposures similar to those needed for antitumor activity in mouse models. In contrast, IK-930 demonstrated limited kidney toxicity in rats above efficacious doses and no signs of renal problems in non-human primates. Collectively, these results suggest that paralog selectivity with IK-930 broadens the therapeutic window of this novel compound class. With its distinct TEAD inhibitory profile, IK-930 offers unique therapeutic index advantages, further supporting its development as a first-in-class paralog-selective TEAD inhibitor.

Citation Format: Nathan Young, George Punkosdy, Jill Cavanaugh, Collin Bantle, Alex Constan, Bin Li, James Conley, Marta Sanchez-Martin, Lan Xu, Karen McGovern, Alfredo Castro, Michelle Zhang, Jeffrey Ecsedy. IK-930, a paralog-selective TEAD inhibitor for treating YAP/TAZ-TEAD dependent cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1646.

The Ah Receptor from Toxicity to Therapeutics: Report from the 5th AHR Meeting at Penn State University, USA, June 2022

The aryl hydrocarbon receptor (AHR) is a sensor of low-molecular-weight molecule signals that originate from environmental exposures, the microbiome, and host metabolism. Building upon initial studies examining anthropogenic chemical exposures, the list of AHR ligands of microbial, diet, and host metabolism origin continues to grow and has provided important clues as to the function of this enigmatic receptor. The AHR has now been shown to be directly involved in numerous biochemical pathways that influence host homeostasis, chronic disease development, and responses to toxic insults. As this field of study has continued to grow, it has become apparent that the AHR is an important novel target for cancer, metabolic diseases, skin conditions, and autoimmune disease. This meeting attempted to cover the scope of basic and applied research being performed to address possible applications of our basic knowledge of this receptor on therapeutic outcomes.

Bypassing evolutionary dead ends and switching the rate-limiting step of a human immunotherapeutic enzyme

The Trp metabolite kynurenine (KYN) accumulates in numerous solid tumours and mediates potent immunosuppression. Bacterial kynureninases (KYNases), which preferentially degrade kynurenine, can relieve immunosuppression in multiple cancer models, but immunogenicity concerns preclude their clinical use, while the human enzyme (HsKYNase) has very low activity for kynurenine and shows no therapeutic effect. Using fitness selections, we evolved a HsKYNase variant with 27-fold higher activity, beyond which exploration of >30 evolutionary trajectories involving the interrogation of >109 variants led to no further improvements. Introduction of two amino acid substitutions conserved in bacterial KYNases reduced enzyme fitness but potentiated rapid evolution of variants with ~500-fold improved activity and reversed substrate specificity, resulting in an enzyme capable of mediating strong anti-tumour effects in mice. Pre-steady-state kinetics revealed a switch in rate-determining step attributable to changes in both enzyme structure and conformational dynamics. Apart from its clinical significance, our work highlights how rationally designed substitutions can potentiate trajectories that overcome barriers in protein evolution.

Discovery and Characterization of a Novel Aryl Hydrocarbon Receptor Inhibitor, IK-175, and Its Inhibitory Activity on Tumor Immune Suppression

Aryl hydrocarbon receptor (AHR) is a transcription factor that regulates the activity of multiple innate and adaptive immune cells subsequent to binding to numerous endogenous and exogenous ligands. For example, AHR is activated by the metabolite kynurenine, which is secreted into the tumor microenvironment by cancer cells leading to broad immunosuppression. Therefore, AHR inhibition provides a novel and ideal approach to stimulate immune-mediated recognition and subsequent eradication of tumor cells. We report here the discovery and characterization of IK-175, a novel, potent and selective AHR antagonist with favorable ADME and pharmacokinetic profiles in preclinical species. IK-175 inhibits AHR activity in experimental systems derived from multiple species including mouse, rat, monkey, and humans. In human primary immune cells, IK-175 decreased AHR target gene expression and anti-inflammatory cytokine release and increased proinflammatory cytokine release. Moreover, IK-175 led to a decrease in suppressive IL17A-, IL-22+ expressing T cells in a Th17 differentiation assay. IK-175 dose dependently blocks ligand-stimulated AHR activation of Cyp1a1 transcription in mouse liver and spleen, demonstrating on-target in vivo activity. IK-175 increases proinflammatory phenotype of the tumor microenvironment in mouse syngeneic tumors and in adjacent tumor-draining lymph nodes. As a monotherapy and combined with an anti-PD-1 antibody, IK-175 demonstrates antitumor activity in syngeneic mouse models of colorectal cancer and melanoma. IK-175 also demonstrates antitumor activity combined with liposomal doxorubicin in syngeneic mouse tumors. These studies provide rationale for targeting AHR in patients with cancer. IK-175 is being evaluated in a phase I clinical trial in patients with advanced solid tumors.

Abstract 2156: IK-930 is a novel TEAD inhibitor for the treatment of cancers harboring mutations in the Hippo signal transduction pathway

The Hippo pathway is critical to cancer progression, biogenesis, metastasis, and therapeutic resistance. Many cancer indications have a high frequency of mutations in the Hippo pathway. These pro-tumor mutations lead to constitutive TEAD transcription factor activation, which drives gene expression involved in cell growth and pro-survival signaling. To target cancers harboring mutations in the Hippo pathway, we have discovered and are developing IK-930, a novel small molecule that selectively inhibits TEAD-dependent transcription by directly blocking autopalmitoylation. IK-930 prevents this critical post-translational modification that is required for the functional interaction of TEAD with two transcriptional activators, YAP1 and TAZ (WWTR1). IK-930 inhibits in vitro proliferation of Hippo pathway-deficient cancer cell lines, but not Hippo pathway wild type cells. In human mesothelioma xenografts, IK-930 downregulates TEAD-dependent genes. Daily oral administration of IK-930 resulted in antitumor activity in Hippo-dysregulated mesothelioma xenograft models. In EGFR or KRAS mutated tumors, IK-930 enhanced apoptosis and in vivo antitumor activity in combination with EGFR and MEK inhibitors, respectively. IK-930 is inactive in a broad panel of kinases, receptors, and transporters, furthering evidence of selectivity. Multispecies pharmacokinetic analysis and additional in vitro ADME properties imply favorable pharmacokinetic properties, with a low potential for clinically significant drug-drug interactions. To identify indications that may be dependent on TEAD we evaluated tumor types for the incidence of gene alterations in the Hippo pathway, as well as for YAP1 and TAZ activation. YAP1 and TAZ activation was assessed by evaluating nuclear protein expression in tumor tissue microarrays. These analyses showed high YAP1 nuclear expression in tumors with frequent genetic alterations, that may help guide the development of IK-930. Mesothelioma ranks top among tumor types evaluated, due to high prevalence of YAP1 nuclear expression and Hippo pathway genetic alterations, which are predominantly mutations and copy number alterations in the tumor suppressor NF2. In summary, Hippo pathway dysregulation has been implicated in the etiology of multiple tumor types, including mesothelioma. IK-930 is a selective and potent TEAD inhibitor expected to enter the clinic in early 2022. Our analysis pointed to tumors with genetic alterations driving aberrant Hippo signaling. IK-930 demonstrates efficacy in tumor models representing these indications and beneficial combination activity with other targeted therapies. Taken together, these data have informed the clinical development plan for IK-930.

Citation Format: Benjamin S. Amidon, Marta Sanchez-Martin, Wilmin Bartolini, Sakeena Syed, Karen McGovern, Lan Xu, Jeffrey Ecsedy, X. Michelle Zhang, Alex Constan, Alfredo C. Castro. IK-930 is a novel TEAD inhibitor for the treatment of cancers harboring mutations in the Hippo signal transduction pathway [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 2156.

Abstract P212: Systems biology-guided indication selection to inform the clinical development of a novel TEAD inhibitor

TEAD transcription factors are the final effectors of the Hippo pathway, a signaling cascade comprising multiple tumor suppressors (NF2, MST1/2, LATS1/2) critical in regulating proliferation, survival, and tissue homeostasis. Activated Hippo signaling suppresses TEAD-dependent transcription through the phosphorylation and degradation of TEAD co-activators YAP1 and TAZ in the cytosol. Consistently, genetic alterations in NF2, LATS1/2, YAP1 or TAZ lead to aberrant TEAD activation and are implicated in tumor initiation, progression, and therapeutic resistance in cancer. Here we present a unique systems biology approach integrating genomic, transcriptional and tissue-based analysis, to inform clinical development, indication and patient selection biomarkers for a novel inhibitor of TEAD being developed by Ikena. To identify cancers dependent on TEAD activity, tumor types were evaluated based on the cumulative incidence of genetic alterations in Hippo pathway genes including NF2, LATS1/2, YAP1, TAZ and others. This novel analysis pointed to a subset of tumors with high frequency of genetic alterations driving aberrant Hippo signaling including mesothelioma and NSCLC. This same subset was found to highly express a transcriptional signature indicative of YAP1/TEAD-dependency, confirming increased activation of TEAD transcription and pointing to the dependency of these tumors on TEAD activity. A proprietary IHC method was used to further assess YAP1/TAZ activation by assessing expression of either protein in the nucleus in multiple tumor tissue microarrays. Tissue-based analysis showed high YAP1 nuclear expression in tumors with frequent genetic alterations and high YAP1/TEAD-signature. Mesothelioma in particular ranks top among these indications, due to high frequency of NF2 deficiency and other Hippo pathway alterations. Consistently, TEAD inhibition showed single agent activity in two xenograft models of mesothelioma with NF2 deficiency and LAST1/2 alterations respectively. Hippo pathway alterations frequently co-occur with mutations in other oncogenic signaling pathways, e.g. EGFR. Importantly, YAP1/TAZ have been implicated in acquired resistance to targeted therapies in cancer including EGFR inhibitors in EGFR mutant tumors. Indeed, PDX models derived from patients who relapsed on osimertinib treatment showed high YAP1 protein expression in the nucleus. In addition, combination of TEAD and EGFR inhibitors induced apoptosis in vitro and greater antitumor activity than either drug as a single agent in vivo in EGFR mutant cancer models. In summary, the integration of multi-disciplinary bioinformatics, pharmacologic and tissue-based approaches enabled the identification of cancer types with high dependency on Hippo signaling. Moreover, these studies support the for monotherapy and combination of TEAD inhibitors with other targeted therapies including EGFR inhibitors. Altogether this unique approach has identified cancer patients who may benefit from TEAD inhibition and has informed the clinical development plan of a novel TEAD inhibitor.

Citation Format: Marta Sanchez-Martin, Sakeena Syed, Hyejin Frosch, Chelsea Turcotte, Benjamin Amidon, Karen McGovern, Jeffrey Ecsedy, Michelle X. Zhang. Systems biology-guided indication selection to inform the clinical development of a novel TEAD inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P212.

Abstract P216: IK-930 mediated TEAD inhibition decreases and delays tumor growth and enhances targeted apoptosis in lung and colon cancer xenografts when combined with MEK or EGFR inhibitors

The Hippo signaling cascade is an important pathway that plays a role in controlling cell proliferation and limiting apoptosis, but when dysregulated can contribute to cancer initiation, progression, and therapeutic resistance. The TEAD family of transcription factors, in conjunction with YAP1 or WWTR1/TAZ, are regulated by Hippo pathway signaling and modulate cell growth and proliferation. IK-930 inhibits the growth of TEAD-dependent human cancer xenografts. By exploiting synthetic lethality, the IK-930 single agent activity in TEAD-dependent cancers could expand to other indications upon inhibition of certain oncogenic pathways. Literature indicates that activation of TEAD-dependent transcription by other oncogenes such as mutant EGFR or KRAS mediates resistance to multiple targeted therapies. Additionally, genetic loss of YAP1 leads to increased apoptosis in osimertinib and trametinib treated mutant EGFR NSCLC cell lines (Kurppa, 2020). Here, we present preclinical data that support the use of IK-930 combination therapies to enhance anti-tumor impact of EGFR and MEK blockade in mutant EGFR NSCLC, or with MEK inhibition in several BRAF and KRAS mutant cancers. In these studies, EGFR and MEK1/2 were inhibited and IK-930 used to enhance anti-tumor activity in EGFR-mutant NSCLC cells. These NSCLC cell lines that are largely insensitive to osimertinib and/or trametinib, were observed to have a marked increase in apoptosis in vitro when treated with the combination of osimertinib, trametinib, and IK-930. We also observed increased nuclear accumulation of YAP1 after treatment of NSCLC cells with osimertinib alone, or osimertinib and trametinib and upregulation of TEAD-dependent transcription. In NSCLC xenografts, the combination of osimertinib and IK-930 prevented tumor growth and the triple combination of osimertinib, IK-930, and trametinib drove complete tumor regression and demonstrated greater efficacy than any single agent or double combination. A second set of studies tested the synthetic lethality effect of IK-930 and MEK inhibition in RAF- and RAS-mutant tumors. The combination of TEAD inhibition with MEK inhibition enhanced apoptosis in several KRAS-mutant NSCLC, PDAC, CRC KRAS-mutant cell lines and BRAF-mutant melanoma. The combination of trametinib and IK-930 prevented tumor growth in these xenografts, where either single agent had either modest or little activity. In summary, the Hippo pathway has been implicated in multiple tumor types, including those with resistance mechanisms to EGFR and MEK blockade. IK-930-mediated TEAD inhibition has been investigated to suppress the bypass pathway activation mechanism to the targeted therapies. These data demonstrated the potential to further expand single agent patient benefit by combining IK-930 with MEK and/or EGFR inhibition in a wide variety of cancer indications, including mutant EGFR-driven NSCLC and mutant KRAS colon, lung, and pancreatic cancers. Taken together, these data are informing the clinical development plan and combination strategy for IK-930, a novel TEAD inhibitor.

Citation Format: Benjamin Amidon, Hyejin Frosch, Sakeena Syed, Jill Cavanaugh, Chelsea Turcotte, Katie O'Callaghan, Prabitha Natarajan, Jeffrey Ecsedy, Karen McGovern, Alfredo Castro. IK-930 mediated TEAD inhibition decreases and delays tumor growth and enhances targeted apoptosis in lung and colon cancer xenografts when combined with MEK or EGFR inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P216.

Enteric permeability and inflammation associated with day of hatch Enterobacteriaceae inoculation

Early exposure to Enterobacteriaceae may result in inappropriate microbial colonization of the gastrointestinal (GI) tract, induce mild GI inflammation, alter immune system development, and predispose poultry to opportunistic infection. Four experiments were conducted to test Enterobacteriaceae isolates Escherichia coli LG strain (LG), E. coli Huff strain (Huff), Salmonella Enteritidis LB (SE) and Salmonella Typhimurium (ST) on ability to induce GI inflammation. All 4 experiments included a noninoculated control, and day of hatch (DOH) oral inoculation of LG, Huff, SE and ST in experiment 1, LG and SE in experiment 2, and LG, Huff, SE, and ST in experiment 3. Experiment 4 included LG, Huff, a noninoculated control (NIC), and Clostridium perfringens only (NCP) wherein birds received oral C. perfringens challenge on d15-16 to induce necrotic enteritis. Body weight was measured, yolk sacs and spleens were collected, and blood was obtained for serum fluorescein isothiocyanate dextran (FITC-d) recovery and alpha-1-acid glycoprotein (A1GP) concentrations. Samples were taken weekly through 2 wk of age in experiments 1 and 2, or 4 wk of age in experiments 3 and 4. Increased FITC-d recovery was observed for LG and SE on d13 in experiment 2 (P < 0.05), and C. perfringens only birds on d27 in experiment 4 (P < 0.05) as compared to noninoculated controls. Each experiment resulted in notable differences in A1GP serum concentrations over time, with fluctuations in A1GP patterns through d14 based on DOH inoculation (P < 0.05). Over time, A1GP was increased for DOH inoculated birds from d 22 to 29, the fourth wk of life, and d 2-29, the entire experiment, vs. noninoculated controls in experiment 3 (P < 0.05). Similarly, NCP and LGCP showed increased A1GP from d 20 to 27 and d 6 to 27, vs. NIC in experiment 4 (P < 0.05). In experiment 4, C. perfringens challenge resulted in earlier A1GP response in DOH inoculated birds, d 17-20, as compared to NCP birds, d 20-27 (P < 0.05). These results suggest early Enterobacteriaceae exposure may influence early inflammatory state in the GI tract and may also alter patterns of inflammation and responsiveness to pathogens.

Evaluation of day of hatch exposure to various Enterobacteriaceae on inducing gastrointestinal inflammation in chicks through two weeks of age

Inappropriate microbial colonization can induce gastrointestinal (GI) inflammation may predispose poultry to opportunistic infections and reduce growth performance. Four independent experiments were completed to test ability of select Enterobacteriaceae isolates to induce GI inflammation. Experiments 1 and 2 included a non-inoculated control (NC), and a low (L), medium (M), or high (H) day of hatch (DOH) oral inoculation level. In experiment 1, birds in L1, M1, and H1 received 102 to 104 CFU of a mixed dose of 2 species of Citrobacter and Salmonella Enteritidis LB (SE). In experiment 2, birds in L2, M2, and H2 received 103 to 105 CFU of E. coli LG (LG) and included NC. Body weight was recorded on d 0, 7, and 14, with blood collected for chicken serum alpha-1-acid glycoprotein (A1GP) measurements on d14. Neither experiment resulted in differences in BWG, however, A1GP was increased (P < 0.05) on d 14 when DOH inoculation dose 103 CFU/chick was used compared to NC. This observed increase in A1GP resulted in selection of 103 CFU/chick for DOH inoculation in experiments 3 and 4. Experiment 3 consisted of NC, E. coli Huff (Huff), and SE. On d 0, 7 and 15, BW was measured, with blood collected on d 15 for A1GP. Both d 15 A1GP and BWG from d 7 to 15 were reduced in inoculated chicks, Huff and SE, in experiment 3 (P < 0.05). Experiment 4 evaluated NC and LG with BW measured on d 0, 2, 7 and 14. Yolk sacs were evaluated for retention and bacterial enumeration, and blood for serum A1GP were collected on d 2 and 14. Experiment 4 resulted in no differences in yolk sac parameters or A1GP, whereas there was an increase in BWG for LG from d 0 to 14 (P < 0.05). When evaluated over time, serum A1GP increased between d 2 and d 14 by nearly 46% in LG, compared to negligible changes in NC (P = 0.111). Mild GI inflammation induced by early Enterobacteriaceae exposure may not drastically impact growth or inflammation parameters but may increase susceptibility to opportunistic infection necessitating further study of this model.

Abstract PR05: Blockade of AHR activation by IDO/TDO-derived kynurenine restricts cancer immune suppression

Immune checkpoint blockade (ICB) has been shown to convey significant clinical activity across a spectrum of malignancies, yet there is now recognition that multiple mechanisms of resistance can impair response. The catabolism of tryptophan into metabolites known as kynurenines (Kyn) by enzymes such as indoleamine 2,3-dioxygenase (IDO) or tryptophan 2,3-dioxygenase (TDO) plays a major suppressive role. Recently it was shown that Kyn acts as an endogenous agonist of the Aryl hydrocarbon receptor (AhR). In order to gain a better understanding of this pathway, we sought to characterize the mechanisms of immunosuppression associated with AhR and evaluate its potential as therapeutic target. Gene-expression analysis of IDO-overexpressing melanomas (B16-IDO vs. B16-WT) demonstrated reduced expression levels of Type 1 inflammatory genes, including IFNy, TNF, GzmB, and CD40. In addition, B16-IDO presents higher infiltration of tumor-associated macrophages TAMs, which upregulate the AHR as well as classic AhR-regulated genes (Cyp1a1 and Cyp1b1) and are differentially skewed towards an immunosuppressive M2 phenotype. Tumor-antigen specific CD8+T cells show reduced expression of activation markers (GzmB and CD44) and proliferation rate when primed by Kyn-treated antigen-presenting cells. In addition, TAMs from B16-IDO tumors suppressed activation of CD8+T cells in vitro and their depletion delayed tumor growth. When B16-IDO cells are implanted in mice depleted of Foxp3 expressing cells, TAMs do not accumulate. Treatment of B16-IDO tumors with an AhR-specific antagonist (CH-223191) upregulates MHC II in APCs, activation markers in CD8s, and reduced frequency of T-regs in B16-IDO tumors. AhR inhibition slows tumor growth and prolongs survival of tumors with active IDO/TDO/Kyn pathway (B16-IDO and B16-TDO), and this is enhanced when PD-1 blockade is used in combination. In summary, our findings demonstrate that targeting the Kyn pathway through AhR inhibition could overcome key suppressive mechanisms and sensitize tumors to ICB.

This abstract is also being presented as Poster A57.

Citation Format: Luis F. Campesato, Sadna Budhu, Mathieu Gigoux, Jeremy Tchaicha, Stephane Pourpe, Cailian Liu, Dmitriy Zamarin, Mark G. Manfredi, Karen McGovern, Jedd D. Wolchok, Taha Merghoub. Blockade of AHR activation by IDO/TDO-derived kynurenine restricts cancer immune suppression [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr PR05.

Abstract 4131: Overcoming aryl hydrocarbon receptor mediated tumor immunosuppression

Checkpoint inhibitors (CPIs) have become the cornerstone of immune-based oncology therapy; still many cancer patients do not benefit from these agents. Resistance to checkpoint inhibitors is due in part to the presence of immunosuppressive molecules which prevent immune activation despite T cell checkpoint inhibition. Aryl Hydrocarbon Receptor (AHR) is a transcription factor that mediates the immune response in multiple innate and adaptive immune cells subsequent to binding of a diverse set of endogenous and exogenous ligands. One such AHR agonist is kynurenine. Kynurenine, metabolized from tryptophan by indoleamine-pyrrole 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2), binds to AHR and leads to a net immunosuppressive tumor microenvironment.

Given that kynurenine can be synthesized by both IDO1 and TDO2 and that AHR is activated by endogenous ligands other than kynurenine, AHR inhibition provides a novel approach to reverse immunosuppression in a broad range of tumor types. We demonstrated that AHR antagonism affects multiple immune cell types and can lead to pro-inflammatory phenotypes in human T cells and myeloid cells in vitro and in murine tumor models. AHR antagonism inhibits growth in the B16-IDO, CT26 and MC38 models and reverses the immunosuppressive microenvironment as indicated by changes in T cell and myeloid cell populations. Immune signature changes characterized via Nanostring in multiple tumor models treated with AHR antagonists were also assessed.

Oral dosing of AHR antagonists led to tumor growth inhibition as a single agent and increased anti-tumor activity when combined with checkpoint inhibitors. In addition, beneficial anti-tumor activity occurred with AHR antagonists combined with chemotherapy or with radiation therapy in syngeneic mouse tumor models. Our data indicate that reversing AHR-mediated immune suppression in the tumor microenvironment drives anti-tumor activity alone and in combination with other therapeutic modalities.

Overall, our data demonstrates that AHR is an attractive target for reversing immune suppression in tumors. Therefore, we are developing AHR antagonists and translational insights to treat patients most likely to benefit from this approach.

Citation Format: Jeremy Tchaicha, Silvia Coma, Meghan Walsh, Jill Cavanaugh, Marta Sanchez-Martin, X. Michelle Zhang, Alfredo Castro, Jeff Ecsedy, Mark Manfredi, Karen McGovern. Overcoming aryl hydrocarbon receptor mediated tumor immunosuppression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4131.

Blockade of IDO/TDO downstream effectors restricts cancer immune suppression

Immune checkpoint blockade (ICB) results in clinical benefit for a subset of cancer patients, yet multiple mechanisms of resistance can impair optimal response. The catabolism of tryptophan into metabolites known as kynurenines (Kyn) by the expression of enzymes such as IDO or TDO is a frequent phenomenon that plays a suppressive role in tumor immunity. Recently it was shown that Kyn acts as agonist of the aryl hydrocarbon receptor (AHR). Here we sought to characterize the mechanisms of immune suppression associated with the AHR pathway and to evaluate its potential as therapeutic target. RNAseq analysis of human cancers revealed a correlation between the expressions of AHR-related genes with markers associated with immunotherapy resistance (PD-1, FOXP3, CD206). By using IDO or TDO-overexpressing variants of a melanoma cell model (B16-F10), we found that myeloid cells, such as tumor-associated macrophages (TAMs) and dendritic cells (DCs), present up-regulation of the AHR. IDO-expressing tumors (B16-IDO) show higher myeloid cell infiltration, which present a tolerogenic phenotype. Tumor-antigen specific CD8T cells present reduced expression of activation markers and proliferation rate when primed by Kyn-treated BMDCs. Treatment of B16-IDO-bearing mice with an AHR-specific antagonist (CH-223191) leads to an increase of MHC II in TAMs, of activation markers in CD8 T cells and reduced frequency of T-regs. AHR inhibition delays progression of tumors with an active IDO/TDO/Kyn pathway (B16-IDO and B16-TDO), and efficacy is further improved when ICB is used in combination. In summary, our findings demonstrate that targeting the Kyn pathway through AHR inhibition could overcome key suppressive mechanisms and sensitize tumors to ICB.

Abstract B008: Treatment of IDO1 and TDO2 positive tumors with a kynurenine-degrading enzyme: A highly differentiated approach from IDO1 inhibition

Despite the sustained clinical benefit demonstrated by immune checkpoint inhibitors, a majority of patients derive minimal or no appreciable benefit, indicating the urgent need to incorporate novel immunomodulatory targets and therapeutic strategies. Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) catalyze the first and rate-limiting step in the immunosuppressive tryptophan/kynurenine pathway and are both upregulated in a number of tumor types. Although small-molecule IDO1 inhibitors are being clinically evaluated in several tumor types, so far they have not demonstrated significant clinical benefits either as a single agent or in combination with immune checkpoint inhibition. We are developing pegylated kynureninase (Kynase), a kynurenine degrading enzyme, to treat a broader population with IDO1 and/or TDO2 expressing tumors. We believe that a more robust antitumor immune response can be achieved by depleting kynurenine, produced by both IDO1 and TDO2, with Kynase, than by inhibiting only IDO1. The human Kynase (HsKYN) has been successfully engineered to exhibit vastly improved catalytic activity and stability toward kynurenine over the wild-type human enzyme. HsKYN achieved durable and near complete plasma kynurenine depletion in mice, rats and non-human primates. HsKYN demonstrated single agent efficacy in CT26, MC38 and B16-IDO syngeneic mouse models. Tumor gene expression analysis using NanoString revealed that HsKYN treatment upregulated T-cell and NK cell activation signature. More importantly, HsKYN significantly increased the tumor-infiltrating CD8 T-cells and their activation/polyfunctionality, and reduced the Treg population. As a direct comparison, the lead IDO1 inhibitor epacadostat did not impose any meaningful effects on the same immune cell populations. Furthermore, HsKYN showed beneficial combination efficacy with anti-PD-1 that was superior to combined Epacadostat / anti-PD-1. Evidence to date suggest that HsKYN is well tolerated in multiple species. Therefore, immunoprofiling, efficacy and safety results strongly support that Kynase is a more effective therapeutic approach than IDO1 inhibition. HsKYN is moving toward clinical development for treatment of cancers where IDO1 and/or TDO2 pathways play a significant immunosuppressive role.

Citation Format: Silvia Coma, Jillian Cavanaugh, James Nolan, Jeremy Tchaicha, Karen McGovern, Everett Stone, John Blazeck, Candice Lamb, George Georgiou, Mark G Manfredi, Michelle Zhang. Treatment of IDO1 and TDO2 positive tumors with a kynurenine-degrading enzyme: A highly differentiated approach from IDO1 inhibition [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B008.

The phosphoinositide-3 kinase (PI3K)-δ,γ inhibitor, duvelisib shows preclinical synergy with multiple targeted therapies in hematologic malignancies

Duvelisib is an orally active dual inhibitor of PI3K-δ and PI3K-γ in clinical development in hematologic malignancies (HM). To identify novel pairings for duvelisib in HM, it was evaluated alone and in combination with 35 compounds comprising a diverse panel of standard-of-care agents and emerging drugs in development for HM. These compounds were tested in 20 cell lines including diffuse large B-cell, follicular, T-cell, and mantle cell lymphomas, and multiple myeloma. Single agent activity was seen in fourteen cell lines, with a median GI50 of 0.59 μM. A scalar measure of the strength of synergistic drug interactions revealed a synergy hit rate of 19.3% across the matrix of drug combinations and cell lines. Synergy with duvelisib was prominent in lymphoma lines with approved and emerging drugs used to treat HM, including dexamethasone, ibrutinib, and the BCL-2 inhibitor venetoclax. Western blotting revealed that certain duvelisib-treated cell lines showed inhibition of phosphorylated (p) AKT at serine 473 only out to 12 hours, with mTORC2 dependent re-phosphorylation of pAKT evident at 24 hours. Combination with dexamethasone or ibrutinib, however, prevented this reactivation leading to durable inhibition of pAKT. The combination treatments also inhibited downstream signaling effectors pPRAS40 and pS6. The combination of duvelisib with dexamethasone also significantly reduced p-4EBP1, which controls cap dependent translation initiation, leading to decreased levels of c-MYC 6 hours after treatment. In support of the in vitro studies, in vivo xenograft studies revealed that duvelisib in combination with the mTOR inhibitor everolimus led to greater tumor growth inhibition compared to single agent administration. These data provide a rationale for exploring multiple combinations in the clinic and suggest that suppression of mTOR-driven survival signaling may be one important mechanism for combination synergy.

Abstract 3757: Targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine

The tryptophan/kynurenine pathway has been clinically validated in several tumor types with small-molecule IDO1 inhibitors in combination with checkpoint inhibition. Indoleamine-pyrrole 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) are upregulated in a number of tumor types, metabolizing tryptophan to form immunosuppressive kynurenine. We are developing Kynureninase (Kynase), a kynurenine depleting enzyme, to treat IDO1 and TDO2 positive tumors. The human Kynase has been successfully engineered to vastly increase catalytic activity and stability toward kynurenine over the wild type enzyme. In mice, Kynase achieved prolonged Kynurenine degradation (≥5 days) in plasma and tumor draining lymph node (TDLN), leading to anti-tumor activity as a single agent and in combination with check point inhibitors in mouse syngeneic tumor models. Kynase demonstrated superior tumor growth inhibition and survival benefit relative to a leading IDO1 inhibitor epacadostat in these models. The effects of Kynase on a number of immune cell types, both in vitro and in vivo, are being investigated. Human Kynase has also shown a favorable PK profile and kynurenine degradation in non-human primates, and Kynase variants are now moving toward development candidate selection for treatment of cancers where both IDO/TDO pathways play a significant immunosuppressive role.

Citation Format: Silvia Coma, Jill Cavanaugh, James Nolan, Jeremy Tchaicha, Karen McGovern, Everett Stone, Candice Lamb, Christos Karamitros, John Blazek, Kendra Garrison, George Georgiou, Mark Manfredi, Xiaoyan Michelle Zhang. Targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3757.

Interaction between Kynurenine and the AhR is an effector mechanism of tumor immunosuppression and represents a potential immunotherapy target

Although with notable impact on cancer treatment, immune-checkpoint blockade (ICB) have multiple mechanisms of resistance. The catabolism of Tryptophan into metabolites known as Kynurenines (Kyn) by enzymes such as IDO or TDO plays a major suppressive role in different tumor types. Recently it was shown that Kyn acts as an endogenous agonist of the Aryl-hydrocarbon Receptor (AhR). In order to gain a better understanding of this pathway, we sought to characterize the mechanisms of immunosuppression associated with AhR and evaluate its potential as therapeutic target. Gene-expression analysis of IDO-overexpressing melanomas (B16-IDO vs B16-WT) present reduced expression levels of Type-1 inflammatory genes, including IFNy, TNFa, Granzyme B and CD40. In addition, B16-IDO presents higher infiltration of TAMs, which up-regulate classic AhR-regulated genes (Cyp1a1 and Cyp1b1) and are differentially skewed towards an immunosuppressive M2-phenotype. Tumor-antigen specific CD8+T cells present reduced expression of activation markers (GzmB and CD44) and proliferation rate when primed by Kyn-treated BMDMs. Also, B16-IDO TAMs suppressed activation of CD8+T cells in vitro and their depletion abrogated tumor growth. Implantation of B16-IDOs in FoxP3-depleted mice prevents TAMs accumulation. Treatment of B16-IDO tumors with an AhR-specific antagonist (CH-223191) up-regulates MHC II in APCs, activation markers in CD8s and reduced frequency of T-regs. AhR inhibition slows down tumor growth and prolongs survival, which is improved in combination with PD-1 blockade. In summary, our findings demonstrate that targeting the Kyn pathway through AhR-inhibition represents a promising approach in cancer patients who are resistant to ICB.

The Selective Phosphoinoside-3-Kinase p110δ Inhibitor IPI-3063 Potently Suppresses B Cell Survival, Proliferation, and Differentiation

The class I phosphoinoside-3-kinases (PI3Ks) are important enzymes that relay signals from cell surface receptors to downstream mediators driving cellular functions. Elevated PI3K signaling is found in B cell malignancies and lymphocytes of patients with autoimmune disease. The p110δ catalytic isoform of PI3K is a rational target since it is critical for B lymphocyte development, survival, activation, and differentiation. In addition, activating mutations in PIK3CD encoding p110δ cause a human immunodeficiency known as activated PI3K delta syndrome. Currently, idelalisib is the only selective p110δ inhibitor that has been FDA approved to treat certain B cell malignancies. p110δ inhibitors can suppress autoantibody production in mouse models, but limited clinical trials in human autoimmunity have been performed with PI3K inhibitors to date. Thus, there is a need for additional tools to understand the effect of pharmacological inhibition of PI3K isoforms in lymphocytes. In this study, we tested the effects of a potent and selective p110δ inhibitor, IPI-3063, in assays of B cell function. We found that IPI-3063 potently reduced mouse B cell proliferation, survival, and plasmablast differentiation while increasing antibody class switching to IgG1, almost to the same degree as a pan-PI3K inhibitor. Similarly, IPI-3063 potently inhibited human B cell proliferation in vitro. The p110γ isoform has partially overlapping roles with p110δ in B cell development, but little is known about its role in B cell function. We found that the p110γ inhibitor AS-252424 had no significant impact on B cell responses. A novel dual p110δ/γ inhibitor, IPI-443, had comparable effects to p110δ inhibition alone. These findings show that p110δ is the dominant isoform mediating B cell responses and establish that IPI-3063 is a highly potent molecule useful for studying p110δ function in immune cells.

Abstract B032: The PI3K-γ inhibitor, IPI-549, increases antitumor immunity by targeting tumor-associated myeloid cells and remodeling the immune-suppressive tumor microenvironment

The PI3 kinases (PI3K) belong to a family of signal-transducing enzymes that mediate key cellular functions in cancer and immunity. The PI3K-gamma (γ) isoform plays an important role in macrophage/myeloid cell function and migration, and a role for PI3K-γ in tumor growth and immune tolerance has been established in studies utilizing PI3K-γ knockout (KO) mice (Schmid et al., Cancer Cell, 2011; Gunderson et al., Cancer Discovery, 2015). We propose that pharmacological inhibition of PI3K-γ in myeloid cells can alter the tumor-immune microenvironment leading to enhanced antitumor T-cell responses. IPI-549 is an oral, potent, and selective inhibitor of PI3K-γ. Prior studies showed single agent antitumor activity in multiple murine tumor models, and enhanced antitumor activity and improved survival when combined with immune-checkpoint blockade. This antitumor activity is dependent on the presence of both immune-suppressive tumor-associated CD11b+ myeloid cells and CD8+ cytotoxic T cells. IPI-549 can reduce the T-cell-suppressive activity of both murine and human myeloid-derived suppressor cells in vitro (Kutok et al, 2015 CRI-CIMT-EATI-AACR Cancer Immunotherapy Meeting; De Henau et al, 2016 AACR Annual Meeting). We now show that IPI‑549 treatment of tumor‑bearing mice leads to a shift in tumor-associated myeloid cells from an immunosuppressive M2 phenotype to a proinflammatory M1 phenotype, characterized by reduced CD206 expression and enhanced expression of MHC class II and NOS2. Compared to vehicle-treated controls, short-term (9 days) treatment of CT26 tumor‑bearing animals with IPI‑549 revealed an increased frequency of circulating tumor-specific T cells, an increased percentage of tumor-infiltrating CD8+IFNγ+ T cells, and a reduced percentage of CD4+Foxp3+ regulatory T cells, leading to a trend towards increasing the CD8+/T-reg cell ratio. Treatment of 4T1 and B16GM tumor-bearing mice with IPI-549 for 14 days led to a significant increase in the CD8+/T-reg cell ratio. Together these data show that IPI-549 treatment leads to a proinflammatory tumor microenvironment. Importantly, gene and protein expression analysis of whole tumor tissue collected from IPI-549-treated mice revealed a cytotoxic T-cell signature characterized by increased production of proinflammatory cytokines, and enhanced expression costimulatory and coinhibitory genes relative to vehicle-treated animals. These findings indicate that IPI-549 increases antitumor immunity by remodeling the tumor-immune microenvironment via blockade of tumor-associated myeloid cells. In addition, the up-regulation of costimulatory and coinhibitory genes with IPI-549 treatment provides a mechanistic rationale for the observed combination activity with immune checkpoint inhibition. IPI-549 is currently in Phase I development, both as a single agent and in combination with an anti-PD-1 antibody, in solid tumors (ClinicalTrials.gov NCT02637531).

Citation Format: Matthew Rausch, Jeremy Tchaicha, Thomas Tibbitts, Olivier De Henau, Sujata Sharma, Melissa Pink, Joseph Gladstone, Jennifer Proctor, Mark Douglas, Howard Stern, Taha Merghoub, Jedd Wolchok, Karen McGovern, Jeff Kutok, David Winkler. The PI3K-γ inhibitor, IPI-549, increases antitumor immunity by targeting tumor-associated myeloid cells and remodeling the immune-suppressive tumor microenvironment [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B032.

PI3Kγ is a molecular switch that controls immune suppression

Macrophages play critical, but opposite, roles in acute and chronic inflammation and cancer. In response to pathogens or injury, inflammatory macrophages express cytokines that stimulate cytotoxic T cells, whereas macrophages in neoplastic and parasitic diseases express anti-inflammatory cytokines that induce immune suppression and may promote resistance to T cell checkpoint inhibitors. Here we show that macrophage PI 3-kinase γ controls a critical switch between immune stimulation and suppression during inflammation and cancer. PI3Kγ signalling through Akt and mTor inhibits NFκB activation while stimulating C/EBPβ activation, thereby inducing a transcriptional program that promotes immune suppression during inflammation and tumour growth. By contrast, selective inactivation of macrophage PI3Kγ stimulates and prolongs NFκB activation and inhibits C/EBPβ activation, thus promoting an immunostimulatory transcriptional program that restores CD8⁺ T cell activation and cytotoxicity. PI3Kγ synergizes with checkpoint inhibitor therapy to promote tumour regression and increased survival in mouse models of cancer. In addition, PI3Kγ-directed, anti-inflammatory gene expression can predict survival probability in cancer patients. Our work thus demonstrates that therapeutic targeting of intracellular signalling pathways that regulate the switch between macrophage polarization states can control immune suppression in cancer and other disorders.

Integration of Hedgehog and mutant FLT3 signaling in myeloid leukemia

FMS-like tyrosine kinase 3 (FLT3) internal tandem duplication (ITD) mutations resulting in constitutive kinase activity are common in acute myeloid leukemia (AML) and carry a poor prognosis. Several agents targeting FLT3 have been developed, but their limited clinical activity suggests that the inhibition of other factors contributing to the malignant phenotype is required. We examined gene expression data sets as well as primary specimens and found that the expression of GLI2, a major effector of the Hedgehog (Hh) signaling pathway, was increased in FLT3-ITD compared to wild-type FLT3 AML. To examine the functional role of the Hh pathway, we studied mice in which Flt3-ITD expression results in an indolent myeloproliferative state and found that constitutive Hh signaling accelerated the development of AML by enhancing signal transducer and activator of transcription 5 (STAT5) signaling and the proliferation of bone marrow myeloid progenitors. Furthermore, combined FLT3 and Hh pathway inhibition limited leukemic growth in vitro and in vivo, and this approach may serve as a therapeutic strategy for FLT3-ITD AML.

Abstract B029: The potent and selective phosphoinositide-3-kinase-gamma inhibitor, IPI-549, inhibits tumor growth in murine syngeneic solid tumor models through alterations in the immune suppressive microenvironment

Introduction: The phosphoinositide-3-kinase (PI3K) lipid kinases are a family of kinase isoforms that transduce signals in response to various stimuli in different cell types. The PI3K-γ isoform is expressed in immune cells and has limited, if any, expression in epithelial cancer cells. Genetic deletion and kinase-dead knock-in studies highlight a key role for PI3K-γ in the development and function of myeloid-derived cells that constitute a key component of the immune suppressive tumor microenvironment (Joshi Mol Canc Res 2014; Schmid Canc Cell 2011). Targeting PI3K-γ in these tumor-associated myeloid cells could therefore inhibit the immune suppressive tumor microenvironment, enabling the immune system to attack tumor cells more effectively. To date, potent and selective PI3K-γ inhibitors with drug-like properties have not been available to test this hypothesis. We now report the structure, biochemical, cellular, and in vivo properties of a potent and selective, small molecule inhibitor of PI3K-γ, IPI-549, and provide data to support the therapeutic potential of breaking tumor immune tolerance through PI3K-γ inhibition.

Results: Discovery efforts identified a highly selective inhibitor of PI3K-γ, IPI-549, with pharmaceutical properties suitable for further development. Binding studies with IPI-549 revealed a KD value of 0.29 nM for PI3K-γ with &gt;58-fold weaker binding affinity for the other Class I PI3K isoforms. Enzymatic assays utilizing physiological ATP concentrations (3 mM) confirmed the selectivity of IPI-549 for PI3K-γ (&gt;200-fold) over other Class I PI3K isoforms. Cellular assays designed to assess individual Class I PI3K isoform activity demonstrated that IPI-549 is highly potent and specific for PI3K-γ (IC50 of 1.2 nM; &gt;140-fold selectivity). Further selectivity screening revealed that IPI-549 is selective for PI3K-γ over other protein and lipid kinases, receptors, ion channels, and transporters.

In vitro functional assays demonstrated that IPI-549 blocked bone marrow derived M2 murine macrophage polarization in response to IL-4 and MCSF1, but did not inhibit ConA-induced T-cell activation. These data indicate the potential for IPI-549 to block immune suppressive macrophage development but not T-cell activity. Pharmacokinetic studies in mice demonstrated IPI-549 to be orally bioavailable with a long plasma half-life enabling selective inhibition of the PI3K-γ isoform relative to the other Class I PI3K isoforms. In an in vivo PI3K-γ-dependent neutrophil migration murine model, IPI-549 blocked neutrophil migration in a dose dependent manner.

To evaluate the effect of PI3K-γ inhibition on tumor growth in an immunocompetent animal, IPI-549 was tested in murine syngeneic solid tumor models. Mice treated with IPI-549 demonstrated significant tumor growth inhibition in multiple syngeneic models. Studies to elucidate the mechanism of tumor growth inhibition indicated that IPI-549 affects immune suppressive myeloid cell numbers and/or function, leading to an increase in cytotoxic T-cell activity. Studies in nude or CD8 T-cell depleted mice demonstrated the T-cell dependence of IPI-549 mediated tumor growth inhibition. Finally, in vivo studies with IPI-549 in combination with immune checkpoint inhibitors showed increased tumor growth inhibition compared to either monotherapy.

Conclusions: IPI-549 is a potent and selective inhibitor of PI3K-γ with pharmaceutical properties that allow for the selective inhibition of PI3K-γ in vivo. Our findings provide evidence that targeted inhibition of PI3K-γ by IPI-549 can restore antitumor immune responses and inhibit solid tumor growth in preclinical models. IND-enabling studies with IPI-549 are ongoing to support its initial clinical exploration in the setting of solid tumors.

Citation Format: Jeffery Kutok, Janid Ali, Erin Brophy, Alfredo Castro, Jonathan DiNitto, Catherine Evans, Kerrie Faia, Stanley Goldstein, Nicole Kosmider, Andre Lescarbeau, Tao Liu, Christian Martin, Karen McGovern, Somarajan Nair, Melissa Pink, Jennifer Proctor, Matthew Rausch, Sujata Sharma, John Soglia, Jeremy Tchaicha, Martin Tremblay, Vivian Villegas, Katherine Walsh, Kerry White, David Winkler, Vito Palombella. The potent and selective phosphoinositide-3-kinase-gamma inhibitor, IPI-549, inhibits tumor growth in murine syngeneic solid tumor models through alterations in the immune suppressive microenvironment. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B029.

Abstract A192: The potent and selective phosphoinositide-3-kinase-γ inhibitor, IPI-549, inhibits tumor growth in murine syngeneic solid tumor models through alterations in the immune suppressive microenvironment

Introduction

The phosphoinositide-3-kinase (PI3K) lipid kinases transduce signals in response to various stimuli in different cell types. PI3K-γ is expressed in immune cells and has limited expression in epithelial cancer cells. Genetic inactivation of PI3K-γ highlights its role in the development and function of myeloid-derived cells that constitute a key component of the suppressive tumor microenvironment (Schmid 2011). Targeting PI3K-γ in tumor-associated myeloid cells could potentially relieve tumor immune tolerance, enabling the immune system to attack tumor cells more effectively. To date, potent and selective PI3K-γ inhibitors with drug-like properties have not been available to test this hypothesis. We now report the structure, biochemical, cellular, and in vivo properties of a potent and selective, small molecule inhibitor of PI3K-γ, IPI-549, and provide data to support the therapeutic potential of breaking tumor immune tolerance through PI3K-γ inhibition.

Results

Discovery efforts identified a highly selective inhibitor of PI3K-γ, IPI-549, with pharmaceutical properties suitable for further development. Binding studies with IPI-549 revealed a KD of 0.29 nM for PI3K-γ and enzymatic assays confirmed the selectivity of IPI-549 for PI3K-γ (&gt;200-fold) over the other Class I PI3K isoforms. Comparison of IPI-549 to previously reported PI3K-γ inhibitors in this enzymatic confirmed its unique potency and selectivity for PI3K-γ. Cellular assays for individual Class I PI3K isoform activity demonstrated that IPI-549 is highly potent and specific for PI3K-γ (IC50 of 1.2 nM; &gt;140-fold selectivity). In kinase screens, IPI-549 is selective for PI3K-γ over other kinases, receptors, ion channels, and transporters.

In vitro assays demonstrated that IPI-549 blocked immune suppressive M2 murine macrophage polarization in response to IL-4 and MCSF1. Pharmacokinetic studies in mice demonstrated IPI-549 to be orally bioavailable with a long plasma half-life enabling selective inhibition of PI3K-γ relative to other Class I PI3K isoforms. To characterize IPI-549's ability to inhibit PI3K-γ in vivo, mice with air pouches treated with IPI-549 showed dose responsive inhibition of PI3K-γ-dependent neutrophil migration.

The effect of IPI-549 on tumor growth was tested in murine syngeneic solid tumor models. Mice treated with IPI-549 demonstrated significant tumor growth inhibition in multiple models. Studies to elucidate the mechanism of tumor growth inhibition indicated that IPI-549 affects suppressive myeloid cell numbers and/or function, leading to an increase in cytotoxic T-cell numbers and activity, as assessed by marker studies. Nude or CD8 T-cell depleted mice studies demonstrated a T-cell dependence of IPI-549-mediated tumor growth inhibition. Finally, in vivo studies with IPI-549 in combination with immune checkpoint inhibitors or following chemotherapy showed increased tumor growth inhibition compared to monotherapies.

Conclusions

IPI-549 is a potent and selective inhibitor of PI3K-γ with pharmaceutical properties that allow for the selective inhibition of PI3K-γ in vivo. Our findings provide evidence that targeted inhibition of PI3K-γ by IPI-549 can restore antitumor immune responses and inhibit solid tumor growth in preclinical models.

Citation Format: Karen McGovern, Janid Ali, Erin Brophy, Alfredo Castro, Jonathan DiNitto, Catherine Evans, Kerrie Faia, Stanley Goldstein, Nicole Kosmider, Andre Lescarbeau, Tao Liu, Christian Martin, Somarajan Nair, Melissa Pink, Jennifer Proctor, Matthew Rausch, Sujata Sharma, John Soglia, Jeremy Tchaicha, Martin Tremblay, Vivian Villegas, Kerry White, David Winkler, Vito Palombella, Jeffery Kutok. The potent and selective phosphoinositide-3-kinase-γ inhibitor, IPI-549, inhibits tumor growth in murine syngeneic solid tumor models through alterations in the immune suppressive microenvironment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A192.

HSP90 inhibition enhances antimitotic drug-induced mitotic arrest and cell death in preclinical models of non-small cell lung cancer

HSP90 inhibitors are currently undergoing clinical evaluation in combination with antimitotic drugs in non-small cell lung cancer (NSCLC), but little is known about the cellular effects of this novel drug combination. Therefore, we investigated the molecular mechanism of action of IPI-504 (retaspimycin HCl), a potent and selective inhibitor of HSP90, in combination with the microtubule targeting agent (MTA) docetaxel, in preclinical models of NSCLC. We identified a subset of NSCLC cell lines in which these drugs act in synergy to enhance cell death. Xenograft models of NSCLC demonstrated tumor growth inhibition, and in some cases, regression in response to combination treatment. Treatment with IPI-504 enhanced the antimitotic effects of docetaxel leading to the hypothesis that the mitotic checkpoint is required for the response to drug combination. Supporting this hypothesis, overriding the checkpoint with an Aurora kinase inhibitor diminished the cell death synergy of IPI-504 and docetaxel. To investigate the molecular basis of synergy, an unbiased stable isotope labeling by amino acids in cell culture (SILAC) proteomic approach was employed. Several mitotic regulators, including components of the ubiquitin ligase, anaphase promoting complex (APC/C), were specifically down-regulated in response to combination treatment. Loss of APC/C by RNAi sensitized cells to docetaxel and enhanced its antimitotic effects. Treatment with a PLK1 inhibitor (BI2536) also sensitized cells to IPI-504, indicating that combination effects may be broadly applicable to other classes of mitotic inhibitors. Our data provide a preclinical rationale for testing the combination of IPI-504 and docetaxel in NSCLC.

Phthalate exposure and pubertal development in a longitudinal study of US girls

STUDY QUESTION

Does phthalate exposure during early childhood alter the timing of pubertal development in girls?

SUMMARY ANSWER

Urinary concentrations of high-molecular weight phthalate (high-MWP) metabolites are associated with later pubarche.

WHAT IS KNOWN ALREADY

Phthalates are anti-androgenic environmental agents known to alter early development, with possible effects on pubertal onset.

STUDY DESIGN, SIZE, AND DURATION

This multi-ethnic study included 1239 girls from New York City, greater Cincinnati, and the San Francisco Bay Area who were 6-8 years old at enrollment (2004-2007) and who were followed until 2011. PARTICIPANTS/MATERIALS, SETTING, METHODS Phthalate metabolites were measured in urine collected at enrollment from 1170 girls; concentrations ranged from <1 to >10,000 µg/l. Breast and pubic hair stages and body size were assessed one to two times annually to determine the age at transition from stage 1 to 2 for breast and pubic hair development. Associations between exposures and pubertal ages were estimated using Cox proportional hazard ratios (HR) with 95% confidence intervals (CI) and survival analyses. Associations were examined with respect to age-specific body mass-index percentile, one of the strongest predictors of pubertal onset.

MAIN RESULTS AND THE ROLE OF CHANCE

Urinary concentrations of high-MWP including di(2-ethylhexyl) phthalate (ΣDEHP) metabolites were associated with later pubic hair development during 7 years of observation. The relationship was linear and was stronger among normal-weight girls. Among normal-weight girls, age at pubic hair stage 2 (PH2) was 9.5 months older for girls in the fifth compared with the first quintile of urinary ΣDEHP (medians: 510 and 59 µg/g creatinine, respectively; adjusted HR 0.70, CI 0.53-0.93, P-trend 0.005. Age at first breast development was older for fifth quintile of mono-benzyl phthalate versus first (HR 0.83, CI 0.68-1.02; P-trend 0.018). No associations were observed between low-molecular weight phthalate urinary metabolite concentrations and age at pubertal transition in adjusted analyses.

LIMITATIONS, REASONS FOR CAUTION

While there is evidence that phthalate exposures are fairly consistent over time, the exposure measure in this study may not reflect an earlier, more susceptible window of exposure. We investigated alternative explanations that might arise from exposure misclassification or confounding.

WIDER IMPLICATIONS OF THE FINDINGS

Phthalates are widespread, hormonally active pollutants that may alter pubertal timing. Whether exposures delay or accelerate pubertal development may depend on age at exposure as well as other factors such as obesity and exposures earlier in life. Whether exposures act independently or as part of real life mixtures may also change their effects on maturation from birth through childhood.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported by the US National Institutes of Health, Environmental Protection Agency, New York State Empire Clinical Research Investigator Program and the Avon Foundation. L.H.K. is employed by Kaiser Permanente. The remaining authors declare they have no actual or potential competing financial interests.

Impact of the Smoothened inhibitor, IPI-926, on smoothened ciliary localization and Hedgehog pathway activity

A requisite step for canonical Hedgehog (Hh) pathway activation by Sonic Hedgehog (Shh) ligand is accumulation of Smoothened (Smo) to the primary cilium (PC). Activation of the Hh pathway has been implicated in a broad range of cancers, and several Smo antagonists are being assessed clinically, one of which is approved for the treatment of advanced basal cell carcinoma. Recent reports demonstrate that various Smo antagonists differentially impact Smo localization to the PC while still exerting inhibitory activity. In contrast to other synthetic small molecule Smo antagonists, the natural product cyclopamine binds to and promotes ciliary accumulation of Smo and “primes” cells for Hh pathway hyper-responsiveness after compound withdrawal. We compared the properties of IPI-926, a semi-synthetic cyclopamine analog, to cyclopamine with regard to potency, ciliary Smo accumulation, and Hh pathway activity after compound withdrawal. Like cyclopamine, IPI-926 promoted accumulation of Smo to the PC. However, in contrast to cyclopamine, IPI-926 treatment did not prime cells for hyper-responsiveness to Shh stimulation after compound withdrawal, but instead demonstrated continuous inhibition of signaling. By comparing the levels of drug-induced ciliary Smo accumulation with the degree of Hh pathway activity after compound withdrawal, we propose that a critical threshold of ciliary Smo is necessary for “priming” activity to occur. This “priming” appears achievable with cyclopamine, but not IPI-926, and is cell-line dependent. Additionally, IPI-926 activity was evaluated in a murine tumor xenograft model and a pharmacokinetic/pharmacodynamic relationship was examined to assess for in vivo evidence of Hh pathway hyper-responsiveness. Plasma concentrations of IPI-926 correlated with the degree and duration of Hh pathway suppression, and pathway activity did not exceed baseline levels out to 96 hours post dose. The overall findings suggest that IPI-926 possesses unique biophysical and pharmacological properties that result in Hh pathway inhibition in a manner that differentiates it from cyclopamine.

Involvement and targeted intervention of dysregulated Hedgehog signaling in osteosarcoma

BACKGROUND

During development, the Hedgehog pathway plays important roles regulating the proliferation and differentiation of chondrocytes, providing a template for growing bone. In this study, the authors investigated the components of dysregulated Hedgehog signaling as potential therapeutic targets for osteosarcoma.

METHODS

Small-molecule agonists and antagonists that modulate the Hedgehog pathway at different levels were used to investigate the mechanisms of dysregulation and the efficacy of Hedgehog blockade in osteosarcoma cell lines. The inhibitory effect of a small-molecule Smoothened (SMO) antagonist, IPI-926 (saridegib), also was examined in patient-derived xenograft models.

RESULTS

An inverse correlation was identified in osteosarcoma cell lines between endogenous glioma-associated oncogene 2 (GLI2) levels and Hedgehog pathway induction levels. Cells with high levels of GLI2 were sensitive to GLI inhibition, but not SMO inhibition, suggesting that GLI2 overexpression may be a mechanism of ligand-independent activation. In contrast, cells that expressed high levels of the Hedgehog ligand gene Indian hedgehog (IHH) and the target genes patched 1 (PTCH1) and GLI1 were sensitive to modulation of both SMO and GLI, suggesting ligand-dependent activation. In 2 xenograft models, active autocrine and paracrine, ligand-dependent Hedgehog signaling was identified. IPI-926 inhibited the Hedgehog signaling interactions between the tumor and the stroma and demonstrated antitumor efficacy in 1 of 2 ligand-dependent models.

CONCLUSIONS

The current results indicate that both ligand-dependent and ligand-independent Hedgehog dysregulation may be involved in osteosarcoma. It is the first report to demonstrate Hedgehog signaling crosstalk between the tumor and the stroma in osteosarcoma. The inhibitory effect of IPI-926 warrants additional research and raises the possibility of using Hedgehog pathway inhibitors as targeted therapeutics to improve treatment for osteosarcoma.

Abstract 3433: Deciphering the mechanism of synergy between the Heat Shock Protein 90 inhibitor retaspimycin HCl and docetaxel in preclinical models of non-small cell lung cancer

Heat Shock Protein 90 (Hsp90) has emerged as an attractive target in cancer therapy given its role in promoting the activity and stability of a host of oncogenic client proteins. Due to the functional diversity of client proteins, Hsp90 inhibitors have the potential to disrupt multiple oncogenic signaling pathways to mediate cancer cell death.

Retaspimycin HCl (IPI-504) is a potent, selective inhibitor of Hsp90 that has single agent activity predominantly in EML4-ALK positive non-small cell lung cancers (NSCLC). Retaspimycin HCl also recently demonstrated clinical activity in a Phase Ib trial when combined with docetaxel in patients with previously treated NSCLC without prospective selection for mutations or rearrangements. This trial demonstrated an overall response rate (ORR) of 26% (n=23) to combination therapy (Riely et al., ASCO, 2011), indicating an enhanced response compared to historical data with single agent docetaxel (ORR of 8%) (Hanna et al., JCO, 2004). To further evaluate activity of this drug combination, a double-blind, randomized Phase II trial is being conducted in NSCLC patients with a smoking history.In support of this trial, preclinical studies are being performed to determine the mechanism of action (MOA) of retaspimycin HCl and docetaxel in combination. To this end, a panel of NSCLC cell lines was screened for sensitivity to combination treatment, leading to identification of a subset of cell lines in which these drugs act in synergy to enhance cell death. Synergy with fixed and non-fixed drug ratios was assessed using the Chou-Talalay method to determine the combination index (CI). To then investigate the mechanism of synergy, an unbiased “stable isotope labeling by amino acids in cell culture” (SILAC) proteomic approach was employed to identify Hsp90 client proteins depleted by combination treatment. Several mitotic regulators, including components of the anaphase promoting complex (APC), were specifically downregulated in response to combination treatment, leading to the hypothesis that combination treatment mediates cell death by prolonging mitosis. Supporting this hypothesis, cells treated with retaspimycin HCl/docetaxel demonstrated a synergistic increase in the percentage of mitotic cells, as assessed by phospho-histone H3 staining, and accumulation of the APC substrates, securin and Cyclin B. Xenograft models of NSCLC demonstrated tumor regression in response to combination treatment, and pharmacodynamic studies are underway to examine the molecular basis for this regression. These preclinical data, together with biomarker investigation in the ongoing Phase II trial, may lead to an improved ability to identify NSCLC patients that are more likely to respond to combination treatment with retaspimycin HCl and docetaxel, and may inform the use of retaspimycin HCl in other combinations and indications.

Citation Format: Katie O'Callaghan, Brenda C. O'Connell, Bonnie Tillotson, Mark Douglas, Howard Stern, Kip A. West, Janid A. Ali, Paul Changelian, Karen McGovern, Vito J. Palombella, Christian C. Fritz, Jeff L. Kutok. Deciphering the mechanism of synergy between the Heat Shock Protein 90 inhibitor retaspimycin HCl and docetaxel in preclinical models of non-small cell lung cancer. [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 3433. doi:10.1158/1538-7445.AM2013-3433

The pre-clinical absorption, distribution, metabolism and excretion properties of IPI-926, an orally bioavailable antagonist of the hedgehog signal transduction pathway

1. IPI-926 is a novel semisynthetic cyclopamine derivative that is a potent and selective Smoothened inhibitor that blocks the hedgehog signal transduction pathway. 2. The in vivo clearance of IPI-926 is low in mouse and dog and moderate in monkey. The volume of distribution is high across species. Oral bioavailability ranges from moderate in monkey to high in mouse and dog. Predicted human clearance using simple allometry is low (24 L h(-1)), predicted volume of distribution is high (469 L) and predicted half-life is long (20 h). 3. IPI-926 is highly bound to plasma proteins and has minimal interaction with human α-1-acid glycoprotein. 4. In vitro metabolic stability ranges from stable to moderately stable. Twelve oxidative metabolites were detected in mouse, rat, dog, monkey and human liver microsome incubations and none were unique to human. 5. IPI-926 is not a potent reversible inhibitor of CYP1A2, 2C8, 2C9 or 3A4 (testosterone). IPI-926 is a moderate inhibitor of CYP2C19, 2D6 and 3A4 (midazolam) with KI values of 19, 16 and 4.5 µM, respectively. IPI-926 is both a substrate and inhibitor (IC50 = 1.9 µM) of P-glycoprotein. 6. In summary, IPI-926 has desirable pre-clinical absorption, distribution, metabolism and excretion properties.

Synthetic silvestrol analogues as potent and selective protein synthesis inhibitors

Misregulation of protein translation plays a critical role in human cancer pathogenesis at many levels. Silvestrol, a cyclopenta[b]benzofuran natural product, blocks translation at the initiation step by interfering with assembly of the eIF4F translation complex. Silvestrol has a complex chemical structure whose functional group requirements have not been systematically investigated. Moreover, silvestrol has limited development potential due to poor druglike properties. Herein, we sought to develop a practical synthesis of key intermediates of silvestrol and explore structure-activity relationships around the C6 position. The ability of silvestrol and analogues to selectively inhibit the translation of proteins with high requirement on the translation-initiation machinery (i.e., complex 5'-untranslated region UTR) relative to simple 5'UTR was determined by a cellular reporter assay. Simplified analogues of silvestrol such as compounds 74 and 76 were shown to have similar cytotoxic potency and better ADME characteristics relative to those of silvestrol.

Abstract 979: The anti-tumor activity of the Smoothened inhibitor IPI-926 in models of residual disease is time dependent

Although response rates can be high for some solid tumors and hematologic malignancies following treatment, cure rates are low and there is a need to extend the duration of response and overall survival after remission. This relapse is attributed to the presence of residual malignant cells that remain undetected after primary treatment and in many instances the presence of these residual tumor cells eventually leads to disease recurrence and shortened survival. The role of the Hedgehog (Hh) pathway in cancer has been well established, with both ligand-independent signaling due to genetic mutations, as well as ligand-dependent signaling, in which Hh signaling occurs either directly to the tumor cells or to the tumor microenvironment being observed. Moreover, it has been shown that Hh ligand produced by tumor cells acts on stromal cells and inhibition of this interaction results in alterations to the tumor-associated stroma and significant inhibition of tumor growth. IPI-926 is a potent and selective Hh pathway antagonist that inhibits the key signaling membrane protein Smoothened (Smo). IPI-926 delays tumor regrowth post-cytoreduction with either standard of care chemotherapy or targeted therapy in pre-clinical xenograft models of small cell lung (SCLC), non-small cell lung (NSCLC) and prostate cancer. Data reported here show that the activity of IPI-926 in this post-therapy setting exhibits a strict time-dependence, or “efficacy window”. In both the Lx-22 SCLC and H1650 NSCLC models, delaying the time between cytoreductive therapy and initiation of IPI-926 treatment resulted in significant loss of anti-tumor activity. To investigate the molecular consequences underlying this loss of activity, RT-PCR analysis of tumors from different time points post therapy was performed. These results showed upregulation of human Hh ligand in the tumors in response to cytoreductive therapy with subsequent increased Hh signaling in the murine-derived stromal cells. IPI-926 abrogated this signaling. In addition, histological and immunohistochemical analysis demonstrated that IPI-926 induced significant changes in the tumor microenvironment post therapy. Taken together, these data suggest that the administration of IPI-926 post cytoreductive therapy could potentially be beneficial in the residual disease setting in multiple cancer types and warrants further investigation. Moreover, the timing of IPI-926 administration post therapy is critical for this benefit. IPI-926 is currently being evaluated in three Phase 2 clinical trials designed to explore multiple approaches to target ligand-dependent activation of the Hh pathway: 1) a randomized Phase 2 trial in combination with gemcitabine in patients with metastatic pancreatic cancer; 2) a randomized Phase 2 in patients with metastatic or locally advanced chondrosarcoma; and 3) a single-arm Phase 2 trial in patients with myelofibrosis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 979. doi:1538-7445.AM2012-979

Abstract B145: The novel Hedgehog pathway inhibitor IPI-926 delays metastatic spread and provides a survival benefit in an experimental model of pancreatic liver metastasis

Metastasis, or the spread of disseminated tumor cells to and colonization of distal sites, is a major cause of cancer mortality. The Hedgehog (Hh) signaling pathway is normally involved in embryogenesis; however recent evidence suggests a role for this pathway in cancer and metastasis. Thus, inhibitors of Hh signaling may have potential utility as novel targeted anti-tumor therapies. IPI-926 is a novel, selective, small molecule that antagonizes the Hh pathway by binding to the Smoothened receptor, the major upstream facilitator of Hh signal transduction, and is currently in phase 2 clinical trials for pancreatic cancer, chondrosarcoma and primary myelofibrosis. Administration of IPI-926 in combination with gemcitabine inhibits incidence of metastases in a KRAS/p53 transgenic model of pancreatic cancer (Olive et al., 2009), supporting an integral role for the Hh pathway in this process.

To further explore the activity of IPI-926 in the setting of metastasis, we developed an experimental model of pancreatic cancer liver metastasis where luciferase-tagged tumor cells were implanted in the liver via an intra-splenic injection, followed by splenectomy, resulting in liver metastases. Tumor burden, as assessed by bioluminescence and survival were employed to evaluate IPI-926 activity utilizing different dosing regimens. While treatment of tumor-bearing animals with established disease provided no survival benefit, IPI-926 administered on the day of cell implant provided modest but reproducible increase in survival. However, prophylactic administration of IPI-926 beginning 14 days (d) prior to cell implant resulted in a significant decrease in disease burden and enhanced survival. The activity was dependent on the schedule of IPI-926 administration. Treatment initiated 14d prior to cell implant was more effective than 7d before cell implant, and treatment started only 2d prior to cell implantation showed no difference compared to treatment initiated on the day of cell implant. Histological analysis of pre-treated vs control livers confirmed decreased metastatic nodule formation. In addition, analysis of serum harvested from IPI-926 14d pre-treated vs control animals showed down-regulation of components of the VEGF, PDGF and MMP pathways, suggesting that IPI-926 modulation of these pathways may be involved in the observed effects on metastatic spread. The activity of IPI-926 was also evaluated in the setting of sunitinib enhancement of metastases (Ebos et al., 2010) in the above model. As has been shown previously, short, high-dose sunitinib administration resulted in striking increases in disease burden and shortening of survival compared to control animals. However, when IPI-926 was administered 14d prior to cell implant and sunitinib treatment, disease burden and survival were returned to the levels observed in the control group.

In summary, IPI-926 administration delays metastasis in an experimental model of pancreatic liver metastasis and in response to high-dose anti-angiogenic therapy. These results provide rationale for the evaluation of IPI-926 as adjuvant/neoadjuvant therapy to help control metastatic spread post surgical resection in pancreatic cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B145.

Self-renewal of acute lymphocytic leukemia cells is limited by the Hedgehog pathway inhibitors cyclopamine and IPI-926

Conserved embryonic signaling pathways such as Hedgehog (Hh), Wingless and Notch have been implicated in the pathogenesis of several malignancies. Recent data suggests that Hh signaling plays a role in normal B-cell development, and we hypothesized that Hh signaling may be important in precursor B-cell acute lymphocytic leukemia (B-ALL). We found that the expression of Hh pathway components was common in human B-ALL cell lines and clinical samples. Moreover, pathway activity could be modulated by Hh ligand or several pathway inhibitors including cyclopamine and the novel SMOOTHENED (SMO) inhibitor IPI-926. The inhibition of pathway activity primarily impacted highly clonogenic B-ALL cells expressing aldehyde dehydrogenase (ALDH) by limiting their self-renewal potential both in vitro and in vivo. These data demonstrate that Hh pathway activation is common in B-ALL and represents a novel therapeutic target regulating self-renewal and persistence of the malignant clone.

Abstract PR2: Therapeutic intervention targeting a Hedgehog-dependent barrier to drug delivery in pancreatic cancer

Ductal pancreatic tumors are unusually resistant to chemotherapy, exhibiting primary resistance to each of the numerous regimens tested to date. These tumors are also unusually desmoplastic and harbor a sparse and inefficient vasculature. The resulting lack of perfusion appears to play a role in the inefficient delivery of numerous chemotherapeutic agents to the parenchyma of pancreatic tumors. Recent evidence has implicated the sonic hedgehog pathway in promoting desmoplasia through a paracrine signaling mechanism active in pancreatic tumors of both humans and the Kras/p53/PdxCre (KPC) mouse model. We sought to evaluate the dependence of stromal desmoplasia on Hedgehog (Hh) pathway signaling and, by extension, assess the effects of Hh pathway inhibition on drug delivery and chemoresistance.

Using IPI-926, a semisynthetic inhibitor of the Smoothened protein, we found that stromal contribution was markedly diminished within 10 days of inhibition of the Hh pathway. Paradoxically, the depletion of stromal cells was coincident with an increase in microvessel density, despite previous data indicating a pro-angiogenic role for the Hh pathway. These non-cell autonomous changes resulted in an increase in the delivery of small molecules to KPC pancreatic tumors and an increase in apoptosis when administered in combination with gemcitabine. Ultimately, mice treated with both IPI-926 and gemcitabine had a significant extension of survival and a decrease in the incidence of liver metastases. We conclude that the Hh pathway plays an important role in the maintenance of pancreatic tumor stroma and that this contributes to the primary chemoresistance of pancreatic tumors. These data also support the clinical evaluation of agents that target the stroma in pancreatic cancer.

Citation Information: Clin Cancer Res 2010;16(14 Suppl):PR2.

Abstract 5045: The Hh inhibitor IPI-926 inhibits relapse of a non-small cell lung cancer xenograft model following treatment with an EGF-R targeted tyrosine kinase inhibitor

The Hedgehog (Hh) pathway plays a key role in multiple types of cancer, either by mutational activation of the pathway in tumor cells or by ligand-dependent signaling to the tumor cells or paracrine signaling between tumor cells and the tumor microenvironment. We have previously shown in a primary model of SCLC that the Hh pathway inhibitor IPI-926 prevents tumor relapse after regression of the tumor with chemotherapy (Travaglione et al., AACR 2009). To investigate whether tumor regression with a targeted agent could elicit a similar response as that seen with chemotherapy, two NSCLC lines (H1650 and HCC827), with activating mutations in the EGFR were evaluated. NSCLC cell lines bearing mutant EGFR are exquisitely sensitive to EGFR kinase inhibitors. Upon treatment with gefitinib in vitro, HCC827 increased the expression of Indian and Sonic hedgehog ligands 10-fold, as measured by qRT-PCR. When grown in mice as subcutaneous xenografts, H1650 tumors regressed following treatment with the EGFR inhibitor gefitinib (40 mg/kg every day) for 7 days. The gefitinib-treated mice were then administered either vehicle or IPI-926 at 40 mg/kg every other day for three weeks, and in this setting IPI-926 treatment led to a 65% decrease (p=0.0104) in tumor volume compared to vehicle-treated mice. Conversely, tumors that had not been regressed with the EGFR TKI showed no response to the Hh pathway inhibitor, similar to our previous results in SCLC with chemotherapy. Studies are ongoing to define the mechanism of action of IPI-926 in this setting. When grown in mice as subcutaneous xenografts, these tumor cells produce Shh ligand in conjunction with stromal Gli-1 expression in the murine stroma. Stromal Gli-1 expression is inhibited by treatment with IPI-926, indicating that Hh ligand produced by NSCLC tumor cells signals to stroma in a paracrine manner. Together with our previous results in SCLC, these data suggest that therapeutic inhibition of the Hh signaling pathway might be an important strategy to extend progression free survival in patients who initially respond to therapy but later relapse, and that this paradigm is applicable to multiple cancer types and treatment modalities.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5045.

Abstract 3857: Hedgehog signaling in primary prostate tumors and associated metastases

Malignant activation of the Hedgehog (Hh) pathway is associated with multiple tumor types. The Hh pathway can promote growth of certain cancers via three modes of malignant activation: ligand-dependent signaling either to the tumor cell itself or between the tumor and its microenvironment, and ligand-independent signaling activated by genetic mutations. In certain cancers, tumor-derived Hh ligand signals in a paracrine manner to the stromal cells in the microenvironment that support tumor cell growth. Using a sensitive immunohistochemistry method for detecting Hh ligand, 83 percent of 105 human prostate tumor samples, including lymph and bone metastases from the same patients, were found to express high levels of Sonic Hedgehog (SHh) ligand. LuCaP 23.1 and LuCaP 35v xenografts were derived from lymph node metastasis from patients with prostate cancer. Paracrine Hh signaling is detected in both xenograft models, where the human tumor cells produce Hh ligand and the surrounding stromal cells respond with Hh pathway activation, as measured by Gli1 levels. IPI-926, a novel, small molecule Hh inhibitor that acts by blocking Smoothened, inhibits signaling between the tumor and stromal cells in both castration sensitive and castration resistant tumor models. Inhibition of Hh signaling with IPI-926 was then evaluated as a potential means to reduce growth of prostate cancer tumors and metastases. IPI-926 significantly delays relapse and slows the growth rate of castration resistant primary human prostate tumors post-docetaxel treatment. Additional preclinical studies with IPI-926 in combination with chemotherapy and targeted therapies in castration resistant tumor models are in progress. These pre-clinical results provide a rationale for testing Hh inhibitors in patients with castration resistant prostate cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3857.

Abstract LB-374: The Hh inhibitor IPI-926 enhances tumor perfusion and nab-paclitaxel activity in a pancreatic xenograft model

Malignant activation of the Hedgehog (Hh) pathway is associated with multiple tumor types. In certain cancers, such as pancreatic, a paracrine role for the Hh ligand has been described, wherein cancer cells produce Hh ligand that activates the Hh pathway in the surrounding stroma. Consistent with this model, IPI-926, a potent and selective Smoothened (Smo) inhibitor, blocks Hh signaling in the mouse stroma -but not in the cancer cells- of several pancreatic xenograft models. We recently published (Olive, Science 2009) that IPI-926 increases vascular perfusion and enhances gemcitabine drug delivery to tumors in a genetically engineered mouse model of pancreatic cancer (KPC) leading to an increase in overall survival. To determine if similar effects could be observed in xenograft models of human pancreatic cancer, experiments were designed to study the combination of IPI-926 with nab-paclitaxel, an agent that has recently demonstrated anti-tumor activity in pancreatic cancer (Van Hoff, ASCO 2009). While IPI-926 had no single agent activity in the L3.6pl human pancreatic xenograft model, it enhanced the activity of nab-paclitaxel from 61% tumor growth inhibition (nab-paclitaxel alone) to 83% tumor growth inhibition (nab-paclitaxel plus IPI-926, p=0.0048). Tumor IHC analysis of phosphohistone 3 showed a higher frequency of cells arrested at the late G2/M phase in the IPI-926 plus nab-paclitaxel group versus nab-paclitaxel alone (p=0.02). One possible explanation for the synergistic effect of a combination of IPI-926 and nab-paclitaxel is that IPI-926 affects the mouse stroma and increases tumor perfusion and nab-paclitaxel accessibility to the tumor. Tumor perfusion was directly measured in IPI-926 treated and untreated animals using contrast enhanced ultrasound. In tumor bearing animals treated with IPI-926 for 7 days, the ultrasound data showed greater tumor perfusion with IPI-926. On average, the peak time for contrast agent levels decreased from 11.0 seconds to 4.75 seconds in the vehicle versus IPI-926 treated animals, respectively, (p=0.0321).

These data suggest that the mechanism of synergy between IPI-926 and nab-paclitaxel is likely enhanced drug delivery to the tumor through the effect of IPI-926 on the stroma. Studies are ongoing to measure nab-paclitaxel and paclitaxel levels in IPI-926 treated and untreated tumors, and to investigate these findings with the KPC in situ mouse model of pancreatic cancer. These preclinical data provide a strong rationale for evaluating the Hh inhibitor IPI-926 not only with the current standard of care, gemcitabine, but with emerging new potential therapies like nab-paclitaxel in pancreatic cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-374.

Discovery of a potent and orally active hedgehog pathway antagonist (IPI-926)

Recent evidence suggests that blocking aberrant hedgehog pathway signaling may be a promising therapeutic strategy for the treatment of several types of cancer. Cyclopamine, a plant Veratrum alkaloid, is a natural product antagonist of the hedgehog pathway. In a previous report, a seven-membered D-ring semisynthetic analogue of cyclopamine, IPI-269609 (2), was shown to have greater acid stability and better aqueous solubility compared to cyclopamine. Further modifications of the A-ring system generated three series of analogues with improved potency and/or solubility. Lead compounds from each series were characterized in vitro and evaluated in vivo for biological activity and pharmacokinetic properties. These studies led to the discovery of IPI-926 (compound 28), a novel semisynthetic cyclopamine analogue with substantially improved pharmaceutical properties and potency and a favorable pharmacokinetic profile relative to cyclopamine and compound 2. As a result, complete tumor regression was observed in a Hh-dependent medulloblastoma allograft model after daily oral administration of 40 mg/kg of compound 28.

Inhibition of Hedgehog signaling enhances delivery of chemotherapy in a mouse model of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is among the most lethal human cancers in part because it is insensitive to many chemotherapeutic drugs. Studying a mouse model of PDA that is refractory to the clinically used drug gemcitabine, we found that the tumors in this model were poorly perfused and poorly vascularized, properties that are shared with human PDA. We tested whether the delivery and efficacy of gemcitabine in the mice could be improved by coadministration of IPI-926, a drug that depletes tumor-associated stromal tissue by inhibition of the Hedgehog cellular signaling pathway. The combination therapy produced a transient increase in intratumoral vascular density and intratumoral concentration of gemcitabine, leading to transient stabilization of disease. Thus, inefficient drug delivery may be an important contributor to chemoresistance in pancreatic cancer.

Inhibition of Hedgehog signaling enhances delivery of chemotherapy in a mouse model of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is among the most lethal human cancers in part because it is insensitive to many chemotherapeutic drugs. Studying a mouse model of PDA that is refractory to the clinically used drug gemcitabine, we found that the tumors in this model were poorly perfused and poorly vascularized, properties that are shared with human PDA. We tested whether the delivery and efficacy of gemcitabine in the mice could be improved by coadministration of IPI-926, a drug that depletes tumor-associated stromal tissue by inhibition of the Hedgehog cellular signaling pathway. The combination therapy produced a transient increase in intratumoral vascular density and intratumoral concentration of gemcitabine, leading to transient stabilization of disease. Thus, inefficient drug delivery may be an important contributor to chemoresistance in pancreatic cancer.

Inhibition of Hedgehog signaling enhances delivery of chemotherapy in a mouse model of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is among the most lethal human cancers in part because it is insensitive to many chemotherapeutic drugs. Studying a mouse model of PDA that is refractory to the clinically used drug gemcitabine, we found that the tumors in this model were poorly perfused and poorly vascularized, properties that are shared with human PDA. We tested whether the delivery and efficacy of gemcitabine in the mice could be improved by coadministration of IPI-926, a drug that depletes tumor-associated stromal tissue by inhibition of the Hedgehog cellular signaling pathway. The combination therapy produced a transient increase in intratumoral vascular density and intratumoral concentration of gemcitabine, leading to transient stabilization of disease. Thus, inefficient drug delivery may be an important contributor to chemoresistance in pancreatic cancer.

An orally bioavailable small-molecule inhibitor of Hedgehog signaling inhibits tumor initiation and metastasis in pancreatic cancer

Recent evidence suggests that blockade of aberrant Hedgehog signaling can be exploited as a therapeutic strategy for pancreatic cancer. Our previous studies using the prototype Hedgehog small-molecule antagonist cyclopamine had shown the striking inhibition of systemic metastases on Hedgehog blockade in spontaneously metastatic orthotopic xenograft models. Cyclopamine is a natural compound with suboptimal pharmacokinetics, which impedes clinical translation. In the present study, a novel, orally bioavailable small-molecule Hedgehog inhibitor, IPI-269609, was tested using in vitro and in vivo model systems. In vitro treatment of pancreatic cancer cell lines with IPI-269609 resembled effects observed using cyclopamine (i.e., Gli-responsive reporter knockdown, down-regulation of the Hedgehog target genes Gli1 and Ptch, as well as abrogation of cell migration and colony formation in soft agar). Single-agent IPI-269609 profoundly inhibited systemic metastases in orthotopic xenografts established from human pancreatic cancer cell lines, although Hedgehog blockade had minimal effect on primary tumor volume. The only discernible phenotype observed within the treated primary tumor was a significant reduction in the population of aldehyde dehydrogenase-bright cells, which we have previously identified as a clonogenic tumor-initiating population in pancreatic cancer. Selective ex vivo depletion of aldehyde dehydrogenase-bright cells with IPI-269609 was accompanied by significant reduction in tumor engraftment rates in athymic mice. Pharmacologic blockade of aberrant Hedgehog signaling might prove to be an effective therapeutic strategy for inhibition of systemic metastases in pancreatic cancer, likely through targeting subsets of cancer cells with tumor-initiating ("cancer stem cell") properties.

Tamoxifen for retroperitoneal fibrosis

Retroperitoneal fibrosis is characterised by diffuse inflammatory proliferation of fibroblasts and the deposition of collagen fibrils throughout the retroperitoneum, especially in perivascular sites. This results in blockage of the ureters and other tubular retroperitoneal structures such as the vasculature and lymphatic channels. Left untreated, it typically follows a progressive and fatal course. The condition responds favourably to tamoxifen and several case reports describe an improvement in renal function on this therapy. This case report describes a subjective and objective functional improvement of lymphoedema secondary to retroperitoneal fibrosis with the use of tamoxifen.

Novel small-molecule inhibitors of RNA polymerase III

A genetic approach utilizing the yeast Saccharomyces cerevisiae was used to identify the target of antifungal compounds. This analysis led to the identification of small molecule inhibitors of RNA polymerase (Pol) III from Saccharomyces cerevisiae. Three lines of evidence show that UK-118005 inhibits cell growth by targeting RNA Pol III in yeast. First, a dominant mutation in the g domain of Rpo31p, the largest subunit of RNA Pol III, confers resistance to the compound. Second, UK-118005 rapidly inhibits tRNA synthesis in wild-type cells but not in UK-118005 resistant mutants. Third, in biochemical assays, UK-118005 inhibits tRNA gene transcription in vitro by the wild-type but not the mutant Pol III enzyme. By testing analogs of UK-118005 in a template-specific RNA Pol III transcription assay, an inhibitor with significantly higher potency, ML-60218, was identified. Further examination showed that both compounds are broad-spectrum inhibitors, displaying activity against RNA Pol III transcription systems derived from Candida albicans and human cells. The identification of these inhibitors demonstrates that RNA Pol III can be targeted by small synthetic molecules.