Therapeutic targeting of cellular senescence in diabetic macular edema: preclinical and phase 1 trial results

Compromised vascular endothelial barrier function is a salient feature of diabetic complications such as sight-threatening diabetic macular edema (DME). Current standards of care for DME manage aspects of the disease, but require frequent intravitreal administration and are poorly effective in large subsets of patients. Here we provide evidence that an elevated burden of senescent cells in the retina triggers cardinal features of DME pathology and conduct an initial test of senolytic therapy in patients with DME. In cell culture models, sustained hyperglycemia provoked cellular senescence in subsets of vascular endothelial cells displaying perturbed transendothelial junctions associated with poor barrier function and leading to micro-inflammation. Pharmacological elimination of senescent cells in a mouse model of DME reduces diabetes-induced retinal vascular leakage and preserves retinal function. We then conducted a phase 1 single ascending dose safety study of UBX1325 (foselutoclax), a senolytic small-molecule inhibitor of BCL-xL, in patients with advanced DME for whom anti-vascular endothelial growth factor therapy was no longer considered beneficial. The primary objective of assessment of safety and tolerability of UBX1325 was achieved. Collectively, our data suggest that therapeutic targeting of senescent cells in the diabetic retina with a BCL-xL inhibitor may provide a long-lasting, disease-modifying intervention for DME. This hypothesis will need to be verified in larger clinical trials. ClinicalTrials.gov identifier: NCT04537884 .

Revealing the mechanism of action of a first-in-class covalent inhibitor of KRASG12C (ON) and other functional properties of oncogenic KRAS by 31P NMR

Individual oncogenic KRAS mutants confer distinct differences in biochemical properties and signaling for reasons that are not well understood. KRAS activity is closely coupled to protein dynamics and is regulated through two interconverting conformations: state 1 (inactive, effector binding deficient) and state 2 (active, effector binding enabled). Here, we use 31P NMR to delineate the differences in state 1 and state 2 populations present in WT and common KRAS oncogenic mutants (G12C, G12D, G12V, G13D, and Q61L) bound to its natural substrate GTP or a commonly used nonhydrolyzable analog GppNHp (guanosine-5'-[(β,γ)-imido] triphosphate). Our results show that GppNHp-bound proteins exhibit significant state 1 population, whereas GTP-bound KRAS is primarily (90% or more) in state 2 conformation. This observation suggests that the predominance of state 1 shown here and in other studies is related to GppNHp and is most likely nonexistent in cells. We characterize the impact of this differential conformational equilibrium of oncogenic KRAS on RAF1 kinase effector RAS-binding domain and intrinsic hydrolysis. Through a KRAS G12C drug discovery, we have identified a novel small-molecule inhibitor, BBO-8956, which is effective against both GDP- and GTP-bound KRAS G12C. We show that binding of this inhibitor significantly perturbs state 1-state 2 equilibrium and induces an inactive state 1 conformation in GTP-bound KRAS G12C. In the presence of BBO-8956, RAF1-RAS-binding domain is unable to induce a signaling competent state 2 conformation within the ternary complex, demonstrating the mechanism of action for this novel and active-conformation inhibitor.

Small-molecule inhibition of kinesin KIF18A reveals a mitotic vulnerability enriched in chromosomally unstable cancers

Chromosomal instability (CIN) is a hallmark of cancer, caused by persistent errors in chromosome segregation during mitosis. Aggressive cancers like high-grade serous ovarian cancer (HGSOC) and triple-negative breast cancer (TNBC) have a high frequency of CIN and TP53 mutations. Here, we show that inhibitors of the KIF18A motor protein activate the mitotic checkpoint and selectively kill chromosomally unstable cancer cells. Sensitivity to KIF18A inhibition is enriched in TP53-mutant HGSOC and TNBC cell lines with CIN features, including in a subset of CCNE1-amplified, CDK4-CDK6-inhibitor-resistant and BRCA1-altered cell line models. Our KIF18A inhibitors have minimal detrimental effects on human bone marrow cells in culture, distinct from other anti-mitotic agents. In mice, inhibition of KIF18A leads to robust anti-cancer effects with tumor regression observed in human HGSOC and TNBC models at well-tolerated doses. Collectively, our results provide a rational therapeutic strategy for selective targeting of CIN cancers via KIF18A inhibition.

OncoVEXmGM-CSFexpands tumor antigen-specific CD8+ T-cell response in preclinical models

BACKGROUND

Checkpoint inhibitors targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) have demonstrated clinical efficacy in advanced melanoma, but only a subset of patients with inflamed tumors are responsive. Talimogene laherparepvec (T-VEC), a modified herpes simplex virus type 1 (HSV-1) expressing granulocyte-macrophage colony-stimulating factor (GM-CSF), is a first-in-class oncolytic immunotherapy approved for the treatment of melanoma and has been shown to inflame the tumor microenvironment. To evaluate the potential and mechanisms of T-VEC to elicit systemic antitumor immunity and overcome resistance to checkpoint inhibitors in murine tumor models, OncoVEX^mGM-CSF was developed similarly to T-VEC, except the human GM-CSF transgene was replaced with murine GM-CSF. Previous work had demonstrated that OncoVEX^mGM-CSF generated systemic antitumor immunity dependent on CD8+ T cells in an immune checkpoint-sensitive tumor cell model.

METHODS

A novel B16F10 syngeneic tumor model with both HSV-1-permissive subcutaneous tumors and HSV-1-refractory experimental lung metastasis was used to study the local and systemic effects of OncoVEX^mGM-CSF treatment alone or in combination with checkpoint inhibitors.

RESULTS

Intratumoral injection of OncoVEX^mGM-CSF in combination with an anti-CTLA-4 or anti-PD-1 blocking antibody led to increased tumor growth inhibition, a reduction in the number of lung metastases, and prolonged animal survival. OncoVEX^mGM-CSF induced both neoantigen-specific and tumor antigen-specific T-cell responses. Furthermore, cured mice from the combination treatment of OncoVEX^mGM-CSF and anti-CTLA-4 antibody rejected tumor rechallenges.

CONCLUSIONS

These data support the concept that T-VEC and checkpoint inhibition may be an effective combination to treat patients with advanced melanoma.

Modulation of Glucose Production by Central Insulin Requires IGF-1 Receptors in AgRP Neurons

Similar to insulin, central administration of IGF-1 can suppress hepatic glucose production (HGP), but it is unclear whether this effect is mediated via insulin receptors (InsRs) or IGF-1 receptors (IGF-1Rs) in the brain. To this end, we used pharmacologic and genetic approaches in combination with hyperinsulinemic-euglycemic clamps to decipher the role of these receptors in mediating central effects of IGF-1 and insulin on HGP. In rats, we observed that intracerebroventricular (ICV) administration of IGF-1 or insulin markedly increased the glucose infusion rate (GIR) by >50% and suppressed HGP (P < 0.001). However, these effects were completely prevented by preemptive ICV infusion with an IGF-1R and InsR/IGF-1R hybrid (HybridR) blocking antibody. Likewise, ICV infusion of the InsR antagonist, S961, which also can bind HybridRs, interfered with the ability of central insulin, but not IGF-1, to increase the GIR. Furthermore, hyperinsulinemic clamps in mice lacking IGF-1Rs in AgRP neurons revealed ∼30% reduction in the GIR in knockout animals, which was explained by an impaired ability of peripheral insulin to completely suppress HGP (P < 0.05). Signaling studies further revealed an impaired ability of peripheral insulin to trigger ribosomal S6 phosphorylation or phosphatidylinositol (3,4,5)-trisphosphate production in AgRP neurons lacking IGF-1Rs. In summary, these data suggest that attenuation of IGF-1R signaling in the mediobasal hypothalamus, and specifically in AgRP neurons, can phenocopy impaired regulation of HGP as previously demonstrated in mice lacking InsRs in these cells, suggesting a previously unappreciated role for IGF-1Rs and/or HybridRs in the regulation of central insulin/IGF-1 signaling in glucose metabolism.

AMG 757, a Half-Life Extended, DLL3-Targeted Bispecific T-Cell Engager, Shows High Potency and Sensitivity in Preclinical Models of Small-Cell Lung Cancer

PURPOSE

Small-cell lung cancer (SCLC) is an aggressive neuroendocrine tumor with a high relapse rate, limited therapeutic options, and poor prognosis. We investigated the antitumor activity of AMG 757, a half-life extended bispecific T-cell engager molecule targeting delta-like ligand 3 (DLL3)-a target that is selectively expressed in SCLC tumors, but with minimal normal tissue expression.

EXPERIMENTAL DESIGN

AMG 757 efficacy was evaluated in SCLC cell lines and in orthotopic and patient-derived xenograft (PDX) mouse SCLC models. Following AMG 757 administration, changes in tumor volume, pharmacodynamic changes in tumor-infiltrating T cells (TILs), and the spatial relationship between the appearance of TILs and tumor histology were examined. Tolerability was assessed in nonhuman primates (NHPs).

RESULTS

AMG 757 showed potent and specific killing of even those SCLC cell lines with very low DLL3 expression (<1,000 molecules per cell). AMG 757 effectively engaged systemically administered human T cells, induced T-cell activation, and redirected T cells to lyse tumor cells to promote significant tumor regression and complete responses in PDX models of SCLC and in orthotopic models of established primary lung SCLC and metastatic liver lesions. AMG 757 was well tolerated with no AMG 757-related adverse findings up to the highest tested dose (4.5 mg/kg weekly) in NHP. AMG 757 exhibits an extended half-life in NHP, which is projected to enable intermittent administration in patients.

CONCLUSIONS

AMG 757 has a compelling safety and efficacy profile in preclinical studies making it a viable option for targeting DLL3-expressing SCLC tumors in the clinical setting.

Abstract 2219: OnxoVEXmGM-CSF promotes systemic response to PD-L1 /PD-1 blockade in multiple mouse syngeneic tumor models

Inhibition of the immune-checkpoint axis that involves PD-L1/PD-1 has improved responses and outcomes for certain cancer patients, but there remains unmet need as only a fraction of patients respond to these therapies. Talimogene laherparepvec (T-VEC) is an FDA-approved, first-in-class oncolytic immunotherapy based on a modified herpes simplex virus type 1 (HSV-1) designed to selectively replicate in tumors and produce granulocyte-macrophage stimulating factor (GM-CSF) to enhance a tumor-antigen specific adaptive immune response. Intratumoral treatment with T-VEC has been shown to promote an inflammatory tumor microenvironment both preclinically and clinically. Combining T-VEC with immune checkpoint inhibitors is of high interest to potentially broaden and deepen the clinical responses in checkpoint-resistant tumors. In the current study, we evaluated the efficacy of OncoVEXmGM-CSF (an HSV modified like T-VEC, except that it produces murine GM-CSF) in combination with anti-PD-1/PD-L1 treatment in multiple syngeneic mouse tumor models. Bilateral tumor models were used, where only one tumor was treated with OncoVEXmGM-CSF (representing the local oncolytic effect), allowing the evaluation of systemic abscopal effect in the uninjected contralateral tumors. OncoVEXmGM-CSF in combination with anti-PD-L1/PD-1 enhanced tumor growth inhibition in both treated and contralateral tumors in the A20 and MC38 syngeneic models and overcame anti-PD-L1 resistance in the CT26 model. The combination treatment also led to a significant increase in median overall survival compared to either agent as a monotherapy. In addition, tumor antigen epitopes were identified by combining exome sequencing and MHC/HLA-binding prediction algorithms. Antigen-specific T cell response was measured in an IFN-γ ELISPOT assay using splenocytes from treated mice. OncoVEXmGM-CSF induced and /or enhanced systemic T cell responses directed against both tumor neoantigens and tumor-associated antigens. Together, these data reveal that OncoVEXmGM-CSF treatment can cause direct tumor lysis along with the potentiation of an adaptive, systemic T cell-mediated anti-tumor immune response that can be enhanced by the addition of PD-L1/PD-1. Our study provides a strong rationale for the ongoing clinical evaluation of the combination of T-VEC and PD1-/PD-L1-targeted therapy in cancer patients.

Citation Format: Keegan Cooke, Juan Estrada, Petia Mitchell, Jinghiu Zhan, Pedro J. Beltran, Jing Qing, Jude Canon. OnxoVEXmGM-CSF promotes systemic response to PD-L1 /PD-1 blockade in multiple mouse syngeneic tumor models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2219.

Local Delivery of OncoVEXmGM-CSF Generates Systemic Antitumor Immune Responses Enhanced by Cytotoxic T-Lymphocyte-Associated Protein Blockade

Purpose: Talimogene laherparepvec, a new oncolytic immunotherapy, has been recently approved for the treatment of melanoma. Using a murine version of the virus, we characterized local and systemic antitumor immune responses driving efficacy in murine syngeneic models.Experimental Design: The activity of talimogene laherparepvec was characterized against melanoma cell lines using an in vitro viability assay. Efficacy of OncoVEX^mGM-CSF (talimogene laherparepvec with the mouse granulocyte-macrophage colony-stimulating factor transgene) alone or in combination with checkpoint blockade was characterized in A20 and CT-26 contralateral murine tumor models. CD8⁺ depletion, adoptive T-cell transfers, and Enzyme-Linked ImmunoSpot assays were used to study the mechanism of action (MOA) of systemic immune responses.Results: Treatment with OncoVEX^mGM-CSF cured all injected A20 tumors and half of contralateral tumors. Viral presence was limited to injected tumors and was not responsible for systemic efficacy. A significant increase in T cells (CD3⁺/CD8⁺) was observed in injected and contralateral tumors at 168 hours. Ex vivo analyses showed these cytotoxic T lymphocytes were tumor-specific. Increased neutrophils, monocytes, and chemokines were observed in injected tumors only. Importantly, depletion of CD8⁺ T cells abolished all systemic efficacy and significantly decreased local efficacy. In addition, immune cell transfer from OncoVEX^mGM-CSF-cured mice significantly protected from tumor challenge. Finally, combination of OncoVEX^mGM-CSF and checkpoint blockade resulted in increased tumor-specific CD8⁺ anti-AH1 T cells and systemic efficacy.Conclusions: The data support a dual MOA for OncoVEX^mGM-CSF that involves direct oncolysis of injected tumors and activation of a CD8⁺-dependent systemic response that clears injected and contralateral tumors when combined with checkpoint inhibition. Clin Cancer Res; 23(20); 6190-202. ©2017 AACR.

Abstract 3632: BiTE® antibody constructs for the treatment of SCLC

Small cell lung cancer (SCLC) is a highly aggressive neuroendocrine tumor with a poor prognosis and limited therapeutic options. Most patients present with extensive stage disease, where recent advances in immunotherapies, including bi-specific T cell engager (BiTE®) antibody constructs, represent a promising new therapeutic approach. BiTE® molecules have demonstrated durable complete responses in the clinic in hematological malignancies. Similar to hematological malignancies, SCLC is also a widely-disseminated malignancy that shows very high response rate to first line therapies with high rates of disease recurrence, features which may support efficacy of the BiTE® modality. Next generation sequencing (NGS) identified Delta-like Ligand 3 (DLL3) as a highly specific tumor associated antigen for SCLC, with consistent expression in tumors and very low expression in normal tissues. Tumor expression of DLL3 protein was confirmed by IHC, with 30 of 35 SCLC tumors staining positive for DLL3. DLL3 BiTE® antibody constructs showed low pM potency in vitro and also demonstrated significant inhibition of tumor growth in vivo in an orthotopic model of SCLC. A half-life extended (HLE) BiTE® targeting DLL3 demonstrated antibody-like pharmacokinetic properties in single-dose studies in non-human primates (NHP), with a half-life of 11 days. This is predicted to support every other week dosing in humans. The combination of high potency and excellent PK properties suggests that HLE BiTE® molecules may provide a useful tool for targeting residual disease in SCLC patients whose tumors express DLL3.

Citation Format: Michael J. Giffin, Ed K. Lobenhofer, Keegan Cooke, Tobias Raum, Jennitte Stevens, Pedro J. Beltran, Angela Coxon, Paul E. Hughes. BiTE® antibody constructs for the treatment of SCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3632. doi:10.1158/1538-7445.AM2017-3632

Abstract 4566: OncoVEXmGM-CSF (HSV-1 modified similarly to Talimogene Laherparepvec) in combination with CTLA-4 blockade leads to both local and systemic efficacy in a murine syngeneic model of metastatic melanoma

Talimogene laherparepvec is an oncolytic immunotherapy based on a modified herpes simplex virus type 1 (HSV-1) designed to kill cancer cells through two mechanisms: a) direct viral-mediated lysis and b) stimulation of a tumor antigen-specific adaptive immune response. We developed a mouse model of metastatic melanoma using the B16F10 cell line to study local and systemic responses following treatment with talimogene laherparepvec alone or in combination with CTLA-4 blockade. OncoVEXmGM-CSF, an HSV-1 modified similarly to talimogene laherparepvec (murine GM-CSF is expressed instead of human GM-CSF) was used in these studies.

B16F10 cells have been reported to be resistant to HSV-1 infection due to a lack of requisite entry receptors. To overcome resistance, we transduced B16F10 cells with a lentiviral vector expressing mouse nectin1 (mNectin1) or eGFP as a control. Expression was confirmed by ddPCR and sensitivity to OncoVEXmGM-CSF evaluated in an in vitro viability assay. B16F10-mNectin1 cells were highly sensitive to OncoVEXmGM-CSF with a multiplicity of infection (MOI) IC50 of 0.001 (B16F10-eGFP were insensitive at MOI of 100). In vivo, B16F10-mNectin1 and B16F10-eGFP cells showed similar growth when injected subcutaneously. OncoVEXmGM-CSF treatment of B16F10-mNectin1 tumors (intratumoral, 5x106 PFU/dose, 3X) caused a significant (p&lt;0.0001) inhibition of tumor growth and prolonged median overall survival compared to control animals. To assess the local and systemic effect of OncoVEXmGM-CSF in combination with CTLA-4 blockade, we developed a model of experimental metastatic melanoma by delivering the B16F10-eGFP cells intravenously (systemic, non-injectable tumors) on day 0 and implanting the B16F10-mNectin1 cells SC (local, injectable tumors) on day 2. Mice were dosed with OncoVEXmGM-CSF and anti-CTLA-4 antibody 9D9 (100ug/dose) every 3 days between days 12 and 19. Subcutaneous tumor growth inhibition was assessed and lung metastasis were quantified on day 28. Both OncoVEXmGM-CSF and CTLA-4 treatment significantly inhibited subcutaneous tumor growth and lung metastasis. The combination of both therapeutics resulted in significantly greater local and systemic efficacy than either agent alone. The strong local and systemic anti-tumor activity of the combination resulted in a significant increase in median overall survival (p&lt;0.0001) compared to control mice that received intravenous B16F10-eGFP cells only.

In conclusion, OncoVEXmGM-CSF in combination with CTLA-4 blockade significantly reduced systemic tumor burden and prolonged median overall survival in a B16F10 mouse model of metastatic melanoma. These data support the proposed MOA by which OncoVEXmGM-CSF treatment can cause direct tumor lysis along with potentiation of an adaptive, systemic anti-tumor immune response.

Citation Format: Keegan Cooke, Juan Estrada, Jinghui Zhan, David Hill, Andrea Boden, Jon Werner, Pedro J. Beltran. OncoVEXmGM-CSF (HSV-1 modified similarly to Talimogene Laherparepvec) in combination with CTLA-4 blockade leads to both local and systemic efficacy in a murine syngeneic model of metastatic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4566. doi:10.1158/1538-7445.AM2017-4566

Antibody-mediated neutralization of autocrine Gas6 inhibits the growth of pancreatic ductal adenocarcinoma tumors in vivo

Gas6 and its receptors Axl, Mer and Tyro-3 (TAM) are highly expressed in human malignancy suggesting that signaling through this axis may be tumor-promoting. In pancreatic ductal adenocarcinoma (PDAC), Gas6 and the TAM receptor Axl are frequently co-expressed and their co-expression correlates with poor survival. A strategy was devised to generate fully human neutralizing antibodies against Gas6 using XenoMouse® technology. Hybridoma supernatants were selected based on their ability to inhibit Gas6 binding to the receptor Axl and block Gas6-induced Axl phosphorylation in human cells. Two purified antibodies isolated from the screened hybridomas, GMAB1 and GMAB2, displayed optimal cellular potency which was comparable to that of the soluble extracellular domain of the receptor Axl (Axl-Fc). In vivo characterization of GMAB1 was conducted using a pharmacodynamic assay that measured inhibition of Gas6-induced Akt activation in the mouse spleen. Treatment of mice with a single dose (100-1000 µg) of GMAB1 led to greater than 90% inhibition of Gas6-induced phosphorylated Akt (pAkt) for up to 72 hr. Based on the target coverage observed in the PD assay, the efficacy of GMAB1 was tested against human pancreatic adenocarcinoma xenografts. At doses of 50 µg and 150 µg, twice weekly, GMAB1 was able to inhibit 55% and 76% of tumor growth, respectively (p < 0.001 for both treatments vs. control Ig). When combined with gemcitabine, GMAB1 significantly inhibited tumor growth compared to either agent alone (p < 0.001). Together, the data suggest that Gas6 neutralization may be important as a potential strategy for the treatment of PDAC.

Abstract 2968: A novel bispecific CD3/CDH19 antibody construct (CDH19 BiTE) directs potent killing of melanoma cells in vitro and in vivo and is enhanced by blockade of PD-L1

CDH19 is an unconventional type 2 cadherin widely expressed in malignant melanoma with limited expression in normal tissues. RNAseq and immunohistochemical analysis of

CDH19 in human samples confirmed its over-expression in &gt;60% of melanoma, whereas normal expression primarily occurred in tissues derived from the neural crest such as nerve fibers and autonomic ganglia. CD3 based bi-specific T-cell engagers (BiTEs) were used to determine if redirected lysis of T-cells against CDH19 would drive anti-tumor efficacy. In vitro, the CDH19 BiTEs were high affinity binders to both human and cyno CDH19, and were able to induce specific T-cell activation and cytotoxicity against a panel of melanoma cell lines. In addition, soluble CDH19 levels were detected in human serum and the effects of BiTE cytotoxicity toward melanoma cells in the presence of soluble CDH19 was investigated. In vivo studies were conducted to confirm the specificity and activity of CDH19 BiTEs in xenograft models of melanoma. The CDH19 BiTE AMG-CDH19X was able to cause tumor growth inhibition in models expressing as few as 250 receptors per cell, and inhibition of tumor growth was enhanced by the addition of a blocking antibody against PD-L1. Immunohistochemical analysis of post-treatment xenograft samples suggested that anti-PD-L1 the persistence of tumor reactive T cells, and provided rationale for combining a BiTE against CDH19 with a PD-1 or PD-L1 blocking antibody in melanoma. In summary, targeting CDH19 presents a promising novel opportunity for BiTEs in the treatment of melanoma, both alone and in combination with current standard of care.

Citation Format: Gordon E. Moody, Jodi Moriguchi, Shyun Li, Fei Lee, Brendon Frank, Amy Gilbert, Ryan Case, Khue Dang, Beth Hinkle, Suzanne Coberly, James Rottman, Kim Merriam, Julie Bailis, Pedro J. Beltran. A novel bispecific CD3/CDH19 antibody construct (CDH19 BiTE) directs potent killing of melanoma cells in vitro and in vivo and is enhanced by blockade of PD-L1. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2968.

Oxopyrido[2,3-d]pyrimidines as Covalent L858R/T790M Mutant Selective Epidermal Growth Factor Receptor (EGFR) Inhibitors

In nonsmall cell lung cancer (NSCLC), the threonine(790)-methionine(790) (T790M) point mutation of EGFR kinase is one of the leading causes of acquired resistance to the first generation tyrosine kinase inhibitors (TKIs), such as gefitinib and erlotinib. Herein, we describe the optimization of a series of 7-oxopyrido[2,3-d]pyrimidinyl-derived irreversible inhibitors of EGFR kinase. This led to the discovery of compound 24 which potently inhibits gefitinib-resistant EGFR(L858R,T790M) with 100-fold selectivity over wild-type EGFR. Compound 24 displays strong antiproliferative activity against the H1975 nonsmall cell lung cancer cell line, the first line mutant HCC827 cell line, and promising antitumor activity in an EGFR(L858R,T790M) driven H1975 xenograft model sparing the side effects associated with the inhibition of wild-type EGFR.

A novel calcium-dependent mechanism of acquired resistance to IGF-1 receptor inhibition in prostate cancer cells

Inhibition of the mitogenic insulin-like growth factor receptor 1 (IGF-1R) signaling axis is a compelling treatment strategy for prostate cancer. Combining the IGF-1R inhibitor ganitumab (formerly AMG 479) with standard of care androgen-deprivation therapy greatly delays prostate cancer recurrence in xenograft models; however, a significant proportion of these tumors ultimately acquire resistance to ganitumab. Here we describe the development of a stable and reproducible ganitumab-resistant VCaP human prostate cancer cell derivative termed VCaP/GanR to investigate the mechanism of acquired resistance to IGF-1R inhibition. Unlike parental VCaP, VCaP/GanR did not undergo apoptosis following ganitumab treatment. VCaP/GanR did not express increased levels of IGF-1R, insulin receptor, or phospho-AKT compared to parental VCaP. VCaP/GanR exhibited increased levels of phospho-S6 indicative of increased mTOR activity. However, acquired resistance to ganitumab was not dependent on increased mTOR activity in VCaP/GanR. Phospho-proteomic arrays revealed alterations in several calcium-regulated signaling components in VCaP/GanR compared to VCaP. Reduction of intracellular calcium using cell-permeable calcium-specific chelators restored ganitumab sensitivity to VCaP/GanR through inhibition of cell-cycle progression. These data suggest a new mechanism of resistance to IGF-1R inhibition involving calcium-mediated proliferation effects. Such pathways should be considered in future clinical studies of IGF-1R inhibitors in prostate cancer.

Abstract 2587: A novel covalent inhibitor of mutant but not wild-type (WT) epidermal growth factor receptor (EGFR) has activity in vitro and in vivo in non-small cell lung cancer (NSCLC) models

Background: Mutations in the EGFR kinase are common in NSCLC. Patients with first-line EGFR mutations (exon 19 deletions, L858R mutations, exon 20 variants, codon 719 variants) initially respond to the reversible EGFR inhibitors erlotinib and gefitinib, but then relapse as additional mutations emerge. EGFR T790M is the most common of these mutations and is found in &gt; 50% of refractory tumors. We assessed the in vitro and in vivo activity of CPD 24, a newly developed, covalent, small-molecule inhibitor of both first-line and T790M mutant EGFR, but not WT EGFR. Inhibition of WT EGFR in normal tissues can be a source of dose-limiting toxicities.

Methods: The effects of CPD 24 were evaluated on H1975 (EGFR T790M/L858R), HCC827 (EGFR exon 19 deletion), and A431 (WT) cell lines. Inhibition of EGFR phosphorylation was measured in serum-starved cells using an MSD assay. Viability was assessed by measuring ATP in cells using a CellTiter-Glo® assay. Dose- and time-dependent pharmacodynamic effects were evaluated by treating mice bearing matrigel plugs containing H1975 cells. Drug levels were measured in plasma samples by LC-MS. CPD 24 was administered to athymic nude mice bearing H1975, HCC827, or A431 xenografts (3, 10, and 30 mg/kg, QD, PO) and tumor growth was measured twice per week with digital calipers. CPD 24 was also formulated in PLGA microspheres and administered subcutaneously (SC) as a sustained release formulation to mice bearing H1975 or A431 xenografts (30 and 100 mg/kg, Q3D, SC). Proliferation of H1975 and HCC827 cells in the presence of CPD 24, growth factors, and a MET inhibitor was measured with an IncuCyte live-cell imaging system.

Results: The IC50 of CPD 24 for p-EGFR inhibition was 4 nM on L858R/T790M mutant EGFR (H1975 cells), 17 nM on the exon 19 deletion EGFR (HCC827 cells), and 510 nM on WT EGFR (A431 cells). CPD 24 inhibited the growth of tumor cells in vitro and led to both dose- and time-dependent p-EGFR inhibition in vivo. Phosphorylation of EGFR in H1975 cells growing in matrigel plugs was inhibited by &gt; 75% for 12 hours by a single 30 mg/kg dose. Tumor growth inhibition (TGI) was observed in two EGFR mutant NSCLC xenograft models (H1975, 89% TGI; HCC827, 139% TGI) but not in a WT EGFR model (A431). CPD 24 formulated in PLGA microspheres achieved drug levels above the IC50 for 72 hours after a single SC dose. Tumor regression was observed with this formulation in H1975 xenografts but not in WT tumors. HGF was able to confer resistance to CPD 24 inhibition in both H1975 and HCC827 cells in vitro. This resistance was prevented by the addition of a selective MET inhibitor.

Conclusion: CPD 24 is a covalent inhibitor of both first-line and T790M mutant EGFR while maintaining &gt; 100-fold selectivity over WT EGFR. The antiproliferative effects of CPD 24 can be reversed by HGF, and this resistance can be prevented by treatment with a MET inhibitor.

Citation Format: Pedro J. Beltran, Jinghui Zhan, Petia Mitchell, Ryan P. Wurz, Liping Pettus, Tian Wu, Mary Chaves, Darren L. Reid, Robert Radinsky, Keegan Cooke, Andrew Tasker. A novel covalent inhibitor of mutant but not wild-type (WT) epidermal growth factor receptor (EGFR) has activity in vitro and in vivo in non-small cell lung cancer (NSCLC) models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2587. doi:10.1158/1538-7445.AM2015-2587

Discovery of N-(4-(3-(2-aminopyrimidin-4-yl)pyridin-2-yloxy)phenyl)-4-(4-methylthiophen-2-yl)phthalazin-1-amine (AMG 900), a highly selective, orally bioavailable inhibitor of aurora kinases with activity against multidrug-resistant cancer cell lines

Efforts to improve upon the physical properties and metabolic stability of Aurora kinase inhibitor 14a revealed that potency against multidrug-resistant cell lines was compromised by increased polarity. Despite its high in vitro metabolic intrinsic clearance, 23r (AMG 900) showed acceptable pharmacokinetic properties and robust pharmacodynamic activity. Projecting from in vitro data to in vivo target coverage was not practical due to disjunctions between enzyme and cell data, complex and apparently contradictory indicators of binding kinetics, and unmeasurable free fraction in plasma. In contrast, it was straightforward to relate pharmacokinetics to pharmacodynamics and efficacy by following the time above a threshold concentration. On the basis of its oral route of administration, a selectivity profile that favors Aurora-driven pharmacology and its activity against multidrug-resistant cell lines, 23r was identified as a potential best-in-class Aurora kinase inhibitor. In phase 1 dose expansion studies with G-CSF support, 23r has shown promising single agent activity.

Abstract 3683: Targeting PIK3CA mutant breast cancer with the combination of PIK3CA-specific inhibitor, BYL719, and IGF1-R antibody, ganitumab

Background: PI3K/AKT signaling is a critical growth and survival pathway in many human cancers. PI3Ks are lipid kinases that are important in controlling signaling pathways involved in cell proliferation, motility, cell death and cell invasion. The α isoform of PI3K (PIK3CA) is linked upstream mainly to receptor tyrosine kinases. Various solid tumor types such as colorectal cancers, gastric cancers, brain cancers, glioblastomas, breast and lung cancers have been found to contain gain-of-function mutations of PIK3CA. The existing scientific evidence strongly supports the concept of targeting PIK3CA in human cancers, especially those harboring PIK3CA mutations. Sustained PIK3CA inhibition may lead to aberrant RTK signaling to attenuate PIK3CA inhibition. IGF1R is a RTK commonly expressed in human neoplasia. Its signaling, primarily through AKT, has been implicated in tumor cell survival. Additionally, IGF1R/IRS signaling has been shown to be a feedback pathway to down-modulate mTOR inhibition by RAD001 in cancer cells. We speculate that the efficacy of PIK3CA inhibition might be enhanced if PIK3CA inhibitor is combined with a targeted agent against a key RTK in pAKT signaling.

Methods: With pATK signaling closely linked to mTOR signaling, we set out to examine whether PIK3CA inhibition would also trigger IGF1-R/IRS signaling. In addition, we explored the combination of PIK3CA-specific inhibitor, BYL719, and a fully human antibody against IGF1-R, AMG 479 (ganitumab), preclinically against a PIK3CA mutant breast cancer model, MCF7.

Results: Our data indicate that IGF1-R/IRS signaling is activated upon PIK3CA inhibition. BYL719 exhibited concentration-dependent tumor growth inhibition in vitro. Ganitumab alone had modest inhibitory activity. The combination of BYL719 and ganitumab inhibited MCF7 growth synergistically in vitro. This combination was further tested in an MCF7 xenograft in mice. BYL719 monotherapy resulted in tumor stasis. Ganitumab alone had marginal growth inhibition. The combination of BYL719 and ganitumab led to tumor regression. Further more, the combination of BYL719 and Ganitumumab lead to increased suppression of pS6RP in vivo.

Conclusions: Our data suggest that the combination of BYL719 and ganitumab would act synergistically to inhibit PIK3CA mutant breast cancer cells by blocking two inter-connected pathways. The combination of BYL719 and ganitumab has now entered into clinical trial (NCT01708161). It represents a promising approach against PI3KCA mutant breast cancers.

Citation Format: Z. Alexander Cao, Maria Pinzon-Ortiz, Yan Chen, Xiaoyan Li, Pedro J. Beltran, Jennifer Gansert, Malte Peters, Robert Schlegel, Karl M. Schumacher, Alan Huang. Targeting PIK3CA mutant breast cancer with the combination of PIK3CA-specific inhibitor, BYL719, and IGF1-R antibody, ganitumab. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3683. doi:10.1158/1538-7445.AM2014-3683

Ganitumab (AMG 479) inhibits IGF-II-dependent ovarian cancer growth and potentiates platinum-based chemotherapy

PURPOSE

Insulin-like growth factor 1 receptor (IGF-IR) has been implicated in the pathogenesis of ovarian cancer. Ganitumab is an investigational, fully human monoclonal antibody against IGF-IR. Here, we explore the therapeutic potential of ganitumab for the treatment of ovarian cancer.

EXPERIMENTAL DESIGN

The effects of ganitumab were tested in vitro against a panel of 23 established ovarian cancer cell lines. The ability of ganitumab to inhibit IGF-I-, IGF-II-, and insulin-mediated signaling was examined in vitro and in tumor xenografts using ovarian cancer models displaying IGF-IR/PI3K/AKT pathway activation by two distinct mechanisms, PTEN loss and IGF-II overexpression. Drug interactions between ganitumab and cisplatin, carboplatin, or paclitaxel were studied in vitro and in vivo.

RESULTS

In vitro, growth inhibition varied significantly among individual ovarian cancer cell lines. IGF-II mRNA and phospho-IGF-IR protein expression were quantitatively correlated with response to ganitumab, and PTEN mutations conferred resistance to ganitumab. Ganitumab potently inhibited baseline and IGF-I-, IGF-II-, and insulin-induced IGF-IR and IGF-IR/insulin hybrid receptor signaling in vitro and in vivo. Synergistic and additive drug interactions were seen for ganitumab and carboplatin or paclitaxel in vitro. Furthermore, ganitumab significantly increased the efficacy of cisplatin in ovarian cancer xenograft models in vivo.

CONCLUSIONS

These observations provide a biologic rationale to test ganitumab as a single agent or in combination with carboplatin/cisplatin and paclitaxel in patients with ovarian cancer. Moreover, assessment of tumor expression of IGF-II, phospho-IGF-IR, or PTEN status may help select patients with ovarian cancer who are most likely to benefit from ganitumab. Clin Cancer Res; 20(11); 2947-58. ©2014 AACR.

IGF1R blockade with ganitumab results in systemic effects on the GH-IGF axis in mice

Ganitumab is a fully human MAB to the human type 1 IGF receptor (IGF1R). Binding assays showed that ganitumab recognized murine IGF1R with sub-nanomolar affinity (KD=0.22 nM) and inhibited the interaction of murine IGF1R with IGF1 and IGF2. Ganitumab inhibited IGF1-induced activation of IGF1R in murine lungs and CT26 murine colon carcinoma cells and tumors. Addition of ganitumab to 5-fluorouracil resulted in enhanced inhibition of tumor growth in the CT26 model. Pharmacological intervention with ganitumab in naïve nude mice resulted in a number of physiological changes described previously in animals with targeted deletions of Igf1 and Igf1r, including inhibition of weight gain, reduced glucose tolerance and significant increase in serum levels of GH, IGF1 and IGFBP3. Flow cytometric analysis identified GR1/CD11b-positive cells as the highest IGF1R-expressing cells in murine peripheral blood. Administration of ganitumab led to a dose-dependent, reversible decrease in the number of peripheral neutrophils with no effect on erythrocytes or platelets. These findings indicate that acute IGF availability for its receptor plays a critical role in physiological growth, glucose metabolism and neutrophil physiology and support the presence of a pituitary IGF1R-driven negative feedback loop that tightly regulates serum IGF1 levels through Gh signaling.

Targeting PIK3CA mutant breast cancer with the combination of PIK3CA-specific inhibitor, BYL719, and IGF1-R antibody, ganitumab

e13525

Background: PI3K/AKT signaling is a critical growth and survival pathway in many human cancers. PI3Ks are lipid kinases that are important in controlling signaling pathways involved in cell proliferation, motility, cell death and cell invasion. The α isoform of PI3K (PIK3CA) is linked upstream mainly to receptor tyrosine kinases and is commonly mutated in various solid tumor types. The existing scientific evidence strongly supports the concept of targeting PIK3CA in human cancers, especially those harboring PIK3CA mutations. Sustained PIK3CA inhibition may lead to aberrant RTK signaling to attenuate PIK3CA inhibition. IGF1R is a RTK commonly expressed in human neoplasia. Its signaling has been implicated in tumor cell survival. Additionally, IGF1R/IRS signaling has been shown to be a feedback pathway to down-modulate mTOR inhibition by RAD001 in cancer cells. We reason that the efficacy of PIK3CA inhibition would be enhanced if PIK3CA inhibitor is combined with a targeted agent against a key RTK in pAKT signaling. Methods: We set out to examine whether PIK3CA inhibition would also trigger IGF1-R/IRS signaling. In addition, we explored the combination of PIK3CA-specific inhibitor, BYL719, and a fully human antibody against IGF1-R, ganitumab, preclinically against a PIK3CA mutant breast cancer model, MCF7. Results: Our data indicate that IGF1-R/IRS signaling is activated upon PIK3CA inhibition. BYL719 exhibited concentration-dependent tumor growth inhibition in vitro. Ganitumab alone had modest inhibitory activity. The combination of BYL719 and ganitumab inhibited MCF7 growth synergistically in vitro. This combination was further tested in an MCF7 xenograft in mice. BYL719 monotherapy resulted in tumor stasis. Ganitumab alone had marginal growth inhibition. The combination of BYL719 and ganitumab led to tumor regression. Conclusions: Our data suggest that the combination of BYL719 and ganitumab would act synergistically to inhibit PIK3CA mutant breast cancer cells by blocking two inter-connected pathways. The combination of BYL719 and ganitumab has now entered into clinical trial (NCT01708161). It represents a promising approach against PI3KCA mutant breast cancers.

MRI apparent diffusion coefficient in a murine orthotopic glioblastoma model as a clinically translatable early readout of efficacy for AMG 595, an antibody drug conjugate targeting EGFRvIII

11095

Background: Epidermal growth factor receptor variant III (EGFRvIII) is a constitutively active mutant of EGFR present in thirty to fifty percent of glioblastoma (GBM) patients. AMG 595, currently in Phase I trials, is composed of a fully human anti-EGFRvIII-specific antibody conjugated to the maytansinoid DM1 via a non-cleavable linker. The MRI apparent diffusion coefficient (MRI ADC) has been shown to correlate with tissue cellularity, and changes in MRI ADC can be an early indicator of therapeutic efficacy. The aim of this work is to evaluate MRI ADC as a clinically translatable early readout of tissue changes due to AMG 595 treatment in a murine orthotopic GBM model. Methods: D317 human GBM cells were intracranially injected into in female CB17 SCID mice at Day 0. Mice were randomized at Day 7, using tumor volumes calculated by MRI, and were treated with vehicle, 6.5, 11, or 22 mg/kg AMG 595 i.v. twice per week, or temozolomide 10 mg/kg p.o. daily five days per week (N=8/group). MRI was repeated at days 14 and 21. Tumor volumes were manually traced on multi-slice T2-weighted RARE images covering the entire tumor volume. The mean MRI apparent diffusion coefficients for each tumor in the vehicle and 22 mg/kg AMG 595-treated groups were calculated from diffusion-weighted spin echo images (b = 100-1200 s/mm2). Results: A dose-dependent effect of AMG 595 on tumor volume was observed at Day 21; growth was inhibited in both the temozolomide and AMG 595-treated groups (22 and 11 mg/kg) relative to vehicle (p<0.0001). At Day 14, this significant treatment effect on tumor volume was not yet detectable. However, mean MRI ADC values were already significantly higher in the AMG 595 (22 mg/kg) treated group than in the vehicle group (23% higher at Day 14, p<0.01 vs vehicle; 32% higher at Day 21, p<0.0001 vs vehicle). The increase in MRI ADC in the AMG 595-treated group preceded observable tumor growth inhibition in the AMG 595-treated animals. Conclusions: Increases in tumor MRI ADC in response to AMG 595 treatment precede measurable inhibition of tumor growth, supporting the use of MRI ADC as a clinically relevant early biomarker for therapeutic efficacy.

Abstract 5158: Generation of a fully human Gas6 neutralizing antibody with anti-tumor activity in vivo

Growth arrest specific 6 (Gas6) is a vitamin-K dependent protein that is involved in the regulation of a wide array of cellular activities, including adhesion, migration, immune evasion, and apoptosis. Gas6 as well as its receptors Axl, Mer, and Tyro3 are highly expressed in multiple malignancies suggesting that signaling through this axis may be tumor promoting in human disease. A strategy was devised to generate fully human neutralizing antibodies against Gas6 using XenoMouse technology. Hybridoma supernatants were first screened for their ability to bind Gas6, then for their ability to inhibit Gas6 binding to the Axl receptor and block Gas6-induced Axl phosphorylation in human cells. Two purified antibodies isolated from the screened hybridomas, 1D9.1 and 1G9.1, maintained potency in all 3 assays and also inhibited Gas6-induced cellular migration and proliferation. In the scratch wound migration assay, the antibodies inhibited both basal and Gas6-induced wound closure to a greater extent than the soluble extracellular domain of the receptor Axl (Axl- Fc). In the proliferation assay, the antibody 1D9.1 completely inhibited Gas6-induced proliferation with a half maximal effective concentration (EC50) of 0.15nM. In vivo characterization of one of the antibodies, 1D9.1, was conducted using a pharmacodynamic (PD) assay that measured the ability of the antibody to inhibit Gas6-induced Akt activation in the mouse spleen. Treatment of mice with a single dose (100-1000 μg) of 1D9.1 led to greater than 90% inhibition of Gas6-induced phosphorylated Akt (pAkt) for up to 72 hours. Based on the target coverage observed in the PD assay, we tested the efficacy of 1D9.1 against Panc-1 human pancreatic adenocarcinoma xenografts implanted in athymic nu/nu female mice. At doses of 50 and 150 μg, twice weekly, the Gas6 neutralizing antibody 1D9.1 was able to inhibit 55% and 76% of tumor growth, respectively. (p&lt;0.001 for both treatments vs. control Ig). When combined with gemcitabine, 1D9.1 was able to inhibit tumor growth to a greater extent than either agent alone (p&lt;0.001 vs. either monotherapy). Together, the data suggest that Gas6 neutralization should be further explored as a potential strategy for the treatment of pancreatic cancer.

Citation Format: Gordon E. Moody, Brian Belmontes, Chadwick King, Shuying Liu, Stephanie Masterman, Chris Murawsky, Trace Tsuruda, Wei Wang, Robert Radinsky, Pedro J. Beltran. Generation of a fully human Gas6 neutralizing antibody with anti-tumor activity in vivo. [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 5158. doi:10.1158/1538-7445.AM2013-5158

Targeting IGF-IR with ganitumab inhibits tumorigenesis and increases durability of response to androgen-deprivation therapy in VCaP prostate cancer xenografts

Prostate cancer is the most commonly diagnosed malignancy in men. While tumors initially respond to androgen-deprivation therapy, the standard care for advanced or metastatic disease, tumors eventually recur as castration-resistant prostate cancer (CRPC). Upregulation of the insulin-like growth factor receptor type I (IGF-IR) signaling axis drives growth and progression of prostate cancer by promoting proliferation, survival, and angiogenesis. Ganitumab (formerly AMG 479) is a fully human antibody that inhibits binding of IGF-I and IGF-II to IGF-IR. We evaluated the therapeutic value of ganitumab in several preclinical settings including androgen-dependent prostate cancer, CRPC, and in combination with androgen-deprivation therapy. Ganitumab inhibited IGF-I-induced phosphorylation of the downstream effector AKT and reduced proliferation of multiple androgen-dependent and castration-resistant human prostate cancer cell lines in vitro. Ganitumab inhibited androgen-dependent VCaP xenograft growth and increased tumor-doubling time from 2.3 ± 0.4 weeks to 6.4 ± 0.4 weeks. Ganitumab blocked growth of castration-resistant VCaP xenografts for over 11.5 weeks of treatment. In contrast, ganitumab did not have appreciable effects on the castration-resistant CWR-22Rv1 xenograft model. Ganitumab was most potent against VCaP xenografts when combined with complete androgen-deprivation therapy (castration). Tumor volume was reduced by 72% after 4 weeks of treatment and growth suppression was maintained over 16 weeks of treatment. These data suggest that judicious use of ganitumab particularly in conjunction with androgen-deprivation therapy may be beneficial in the treatment of prostate cancer.

Effect of a low-fat diet combined with IGF-1 receptor blockade on 22Rv1 prostate cancer xenografts

In preclinical models, both dietary fat reduction and insulin-like growth factor I receptor (IGF-1R) blockade individually inhibit prostate cancer xenograft growth. We hypothesized that a low-fat diet combined with IGF-1R blockade would cause additive inhibition of prostate cancer growth and offset possible untoward metabolic effects of IGF-1R blockade antibody therapy. Fifty severe combined immunodeficient mice were injected with 22Rv1 cells subcutaneously. Ten days postinjection, the animals were randomized to four groups: (i) high-fat diet + saline (HF); (ii) high-fat diet + IGF-1R blocking antibody, ganitumab (HF/Ab); (iii) low-fat diet + saline (LF); and (iv) low-fat diet + ganitumab (LF/Ab). After 19 days of treatment, the animals were euthanized, serum was collected, and tumors were weighed. Tumor Ki67, Akt and extracellular signal-regulated kinase (ERK) activation, serum insulin, IGF-I and TNF-α were measured. In vitro, ganitumab treatment inhibited growth and induced apoptosis in several prostate cancer cell lines. In vivo, tumor weights and volumes were unaffected by the different treatments. The LF/Ab therapy significantly reduced proliferation (Ki67) and ERK activation in tumors. The HF/Ab group had significantly higher serum insulin levels than the HF group. However, LF/Ab combination significantly reduced serum insulin back to normal levels as well as normalizing serum TNF-α level. Whereas the combination of low-fat diet and IGF-1R blockade did not have additive inhibitory effects on tumor weight, it led to reduced tumor cell proliferation and a reduction in serum insulin and TNF-α levels.

Abstract C55: Ganitumab (AMG 479) inhibits the development and progression of castration-resistant VCaP human prostate cancer xenografts

Prostate tumors are initially dependent on androgens for growth; thus the standard of care for advanced or metastatic prostate cancer is androgen deprivation therapy. While this treatment strategy diminishes tumor burden and growth, prostate cancer invariably recurs in a castration-resistant form for which therapeutic options are extremely limited. Therefore, new therapeutic regimens are needed that are effective against castration-resistant prostate cancer (CRPC) and its development. The insulin-like growth factor 1 (IGF-1) signaling axis drives both anti-apoptotic and proliferative signals and is dysregulated in prostate cancer. Ganitumab (AMG 479), a fully human monoclonal antibody (IgG1) against the type 1 insulin-like growth factor receptor (IGF-1R), is currently in a phase III clinical trial for treatment of metastatic pancreatic cancer. Since the IGF-1 signaling axis is thought to be instrumental in prostate cancer growth and development, we evaluated the therapeutic potential of ganitumab in a human model of prostate cancer, alone and in combination with androgen deprivation therapy. We used the human prostate cancer cell line, VCaP, which expresses wild type PTEN and grows readily as xenografts that are initially androgen-dependent but progress to castration-resistance in vivo. VCaP is unique among prostate cancer cell lines in that they express the TMPRSS-ERG fusion protein characteristic of a substantial proportion of clinical prostate cancer specimens. In vitro, we found that IGF-1 stimulated phosphorylation of AKT and cell proliferation in VCaP cells, and ganitumab treatment effectively inhibited both. Ganitumab treatment of androgen-dependent VCaP xenografts (300 μg/dose, 2×/week, ip) increased the mean tumor doubling time from 2.9 to 6.3 weeks resulting in significant (p&lt;0.005) tumor growth inhibition of 85% after 4 weeks of treatment. When castration-resistant VCaP xenografts were treated with ganitumab, stasis was achieved over an 11 week treatment period. Most importantly, when ganitumab treatment was combined with androgen deprivation therapy (castration), tumor regression occurred and progression to CRPC was significantly (p&lt;0.0001) delayed in all mice. After 2 weeks of treatment, tumor volume was reduced by 72% in ganitumab-treated as compared to control (androgen deprivation only)-treated mice. After 16 weeks of ganitumab treatment, 60% of tumors had not recurred in the combination arm. Serum levels of the clinically relevant biomarker, prostate specific antigen (PSA), followed similar trends as tumor volumes in all experiments. Together, these studies suggest that ganitumab could be an important therapeutic strategy for many stages of prostate cancer, especially when combined with androgen deprivation therapy.

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 C55.

Efficacy of ganitumab (AMG 479), alone and in combination with rapamycin, in Ewing's and osteogenic sarcoma models

Ewing's and osteogenic sarcoma are two of the leading causes of cancer deaths in children and adolescents. Recent data suggest that sarcomas may depend on the insulin-like growth factor type 1 (IGF-1) receptor (IGF1R) and/or the insulin receptor (INSR) to drive tumor growth, survival, and resistance to mammalian target of rapamycin complex 1 (mTORC1) inhibitors. We evaluated the therapeutic value of ganitumab (AMG 479; C(6472)H(10028)N(1728)O(2020)S(42)), an anti-IGF1R, fully human monoclonal antibody, alone and in combination with rapamycin (mTORC1 inhibitor) in Ewing's (SK-ES-1 and A673) and osteogenic (SJSA-1) sarcoma models. IGF1R was activated by IGF-1 but not by insulin in each sarcoma model. INSR was also activated by IGF-1 in the SJSA-1 and SK-ES-1 models, but not in the A673 model where insulin was the preferred INSR ligand. Ganitumab significantly inhibited the growth of SJSA-1 and SK-ES-1 xenografts; inhibition was associated with decreased IGF1R and Akt phosphorylation, reduced total IGF1R and bromodeoxyuridine detection, and increased caspase-3 expression. Ganitumab inhibited rapamycin-induced IGF1R, Akt, and glycogen synthase kinase-3β hyperphosphorylation in each sarcoma model. However, ganitumab in combination with rapamycin also resulted in a marked increase in INSR expression and activity in the SJSA-1 and A673 models. The in vivo efficacy of ganitumab in the two ganitumab-sensitive models (SJSA-1 and SK-ES-1) was significantly enhanced in combination with rapamycin. Our results support studying ganitumab in combination with mTORC1 inhibitors for the treatment of sarcomas and suggest that INSR signaling is an important mechanism of resistance to IGF1R blockade.

Selective and potent Raf inhibitors paradoxically stimulate normal cell proliferation and tumor growth

Raf inhibitors are under clinical investigation, specifically in patients with tumor types harboring frequent activating mutations in B-Raf. Here, we show that cell lines and tumors harboring mutant B-Raf were sensitive to a novel series of Raf inhibitors (e.g., (V600E)B-Raf A375, IC(50) on cells = 2 nmol/L; ED(50) on tumor xenografts = 1.3 mg/kg). However, in cells and tumors with wild-type B-Raf, exposure to Raf inhibitors resulted in a dose-dependent and sustained activation of mitogen-activated protein kinase signaling. In some of these cell lines, Raf inhibition led to entry into the cell cycle, enhanced proliferation, and significantly stimulated tumor growth in vivo. Inhibition with structurally distinct Raf inhibitors or isoform-specific small interfering RNA knockdown of Raf showed that these effects were mediated directly through Raf. Either A-Raf or C-Raf mediated the Raf inhibitor-induced mitogen-activated protein kinase pathway activation in an inhibitor-specific manner. These paradoxical effects of Raf inhibition were seen in malignant and normal cells in vitro and in vivo. Hyperplasia of normal epithelial cells in the esophagus and the stomach was evident in mice with all efficacious Raf inhibitors (n = 8) tested. An implication of these results is that Raf inhibitors may induce unexpected normal cell and tumor tissue proliferation in patients.

Abstract 2519: Efficacy of a potent and selective Raf inhibitor against human xenograft models displaying specific genetic mutations in the MAPK signaling pathway

Background: A significant percentage of human melanomas as well as colon, ovarian and thyroid carcinomas display missense mutations in B-Raf which can drive cellular transformation through constitutive activation of the MAPK signaling pathway. Thus, mutant B-Raf represents an attractive target to develop new oncology therapeutics. Here we describe the in vivo potency and efficacy of a novel Raf inhibitor (cmpd 1) against xenograft models displaying mutations in the MAPK signaling pathway.

Methods: Established human xenograft models implanted in athymic female nude mice were used to examine the effects of cmpd 1 on P-ERK basal level and tumor growth. For examination of pharmacodynamic effect, cmpd 1 was dosed orally, once for 6-8 hours prior to collection of the xenograft and peripheral blood. Collected xenografts were lysed and levels of P-ERK analyzed by Meso Scale Detection Assay (MSD). Plasma concentrations of cmpd 1 were determined using Quantitative Liquid Chromatography-Tandem Mass Spectometry (LC-MS/MS). In order to study the effects of cmpd 1 on tumor growth inhibition (TGI), mice with established xenografts (∼ 200-250 cubic mm) were randomized into 4 groups (n=10) on day 0. Mice were dosed orally, once (QD) or twice (BID) per day starting on day 1 until completion of the experiment. Tumor volume and body weight were measured twice per week. Significant TGI was determined using repeated measures ANOVA (RMANOVA) followed by the Dunnett's test.

Results: Models expressing B-Raf activating mutations (A375, WM-266 and Colo-205) showed significant decreased expression of P-ERK (&gt;70%) and significant TGI, including complete stasis (100% TGI) and regression at 5 mg/kg QD (ED50 1-3 mg/kg). Models with activating NRAS mutations also showed sensitivity to cmpd 1 but higher doses were required to achieve significant reduction of P-ERK level and tumor growth inhibition (ED50 11 mg/kg). Models with activating KRAS mutations displayed responses ranging from stimulation of tumor growth (MiaPaCa-2) to lack of effect (A549) or 40% TGI (HCT-116). These suboptimal responses in KRAS mutant models were observed even when cmpd 1 was dosed at 10 mg/kg BID. Finally, BxPC-3, a xenograft model with a wild-type (WT) MAPK signaling pathway, displayed sensitivity to cmpd 1 albeit to a lesser extend than observed in B-Raf mutant models (ED50 6.0 mg/kg). In most models, TGI was directly correlated to the ability of cmpd 1 to reduce P-ERK levels in vivo. Plasma exposures of cmpd 1 were approximately proportional to the administered dose.

Conclusion: These results show that inhibition of P-ERK by this Raf inhibitor can result in significant TGI in mutant B-Raf, NRAS and WT models while significant sensitivity can be lost in KRAS mutant models. In addition, the data also show that under certain circumstances, the inhibition of Raf in KRAS mutant cell lines can result in stimulation of tumor growth.

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 2519.

Abstract 2681A: Structure-guided design of potent and selective inhibitors of B-Raf kinase displaying on-mechanism in vivo activity

The Ras-Raf-MAPK signaling pathway plays a central role in diverse cellular processes including differentiation, proliferation and survival. This pathway is activated in a large percentage of cancers as a result of mutations in Ras or in B-Raf Ser/Thr kinase. The activating mutation V600E in B-Raf is present in approximately 60% of melanomas and occurs with lower, yet still significant, frequency in human colon and thyroid cancers. Hence, V600EB-Raf has received considerable interest as a small-molecule drug discovery target within the pharmaceutical industry. A high-throughput screen of Amgen's internal kinase preferred library against a recombinant V600EB-Raf kinase domain enzyme identified a class of biarylamide compounds as potent inhibitors of this kinase, and potential starting points for medicinal chemistry efforts. However, these compounds suffered from poor kinase selectivity, particularly against tyrosine kinases from the Src-, VEGFR and PDGFR-families. Crystal structures of representative examples of this scaffold in B-Raf and other tyrosine kinases identified a unique pocket in B-Raf that could be accessed to achieve selective inhibitors of this enzyme. Consequently a novel series of isoquinoline-based compounds was derived which demonstrated potent inhibition against V600EB-Raf enzyme and inhibition of MAPK pathway signaling in cell lines harboring V600EB-Raf. Further optimization within this inhibitor class yielded compounds with favorable in vivo properties as demonstrated by robust inhibition of ERK phosphorylation in V600EB-Raf driven pharmacodynamic models. Crystallographic work supporting the optimization of this series of selective B-Raf inhibitors will be presented.

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 2681A.

Dimerization of tyrosine phosphatase PTPRO decreases its activity and ability to inactivate TrkC

Receptor-protein tyrosine phosphatases (RPTPs), like receptor tyrosine kinases, regulate neuronal differentiation. While receptor tyrosine kinases are dimerized and activated by extracellular ligands, the extent to which RPTPs dimerize, and the effects of dimerization on phosphatase activity, are poorly understood. We have examined a neuronal type III RPTP, PTPRO; we find that PTPRO can form dimers in living cells, and that disulfide linkages in PTPROs intracellular domain likely regulate dimerization. Dimerization of PTPROs transmembrane and intracellular domains, achieved by ligand binding to a chimeric fusion protein, decreases activity toward artificial peptides and toward a putative substrate, tropomyosin-related kinase C (TrkC). Dephosphorylation of TrkC by PTPRO may be physiologically relevant, as it is efficient, and TrkC and PTPRO can be co-precipitated from transfected cells. Inhibition of PTPROs phosphatase activity by dimerization is interesting, as dimerization of a related RPTP, CD148/PTPRJ, increases activity. Thus, our results suggest a complex relationship between dimerization and activity in type III RPTPs.

AMG 479, a fully human anti-insulin-like growth factor receptor type I monoclonal antibody, inhibits the growth and survival of pancreatic carcinoma cells

Pancreatic carcinoma is a leading cause of cancer deaths, and recent clinical trials of a number of oncology therapeutics have not substantially improved clinical outcomes. We have evaluated the therapeutic potential of AMG 479, a fully human monoclonal antibody against insulin-like growth factor (IGF) type I receptor (IGF-IR), in two IGF-IR-expressing pancreatic carcinoma cell lines, BxPC-3 and MiaPaCa2, which also differentially express insulin receptor (INSR). AMG 479 bound to IGF-IR (K(D) 0.33 nmol/L) and blocked IGF-I and IGF-II binding (IC(50) < 0.6 nmol/L) without cross-reacting to INSR. AMG 479 completely inhibited ligand-induced (IGF-I, IGF-II, and insulin) activation of IGF-IR homodimers and IGF-IR/INSR hybrids (but not INSR homodimers) leading to reduced cellular viability in serum-deprived cultures. AMG 479 inhibited >80% of basal IGF-IR activity in BxPC-3 and MiaPaCa2 xenografts and prevented IGF-IR and IGF-IR/INSR hybrid activation following challenge with supraphysiologic concentrations of IGF-I. As a single agent, AMG 479 inhibited (∼ 80%) the growth of pancreatic carcinoma xenografts, and long-term treatment was associated with reduced IGF-IR signaling activity and expression. Efficacy seemed to be the result of two distinct biological effects: proapoptotic in BxPC-3 and antimitogenic in MiaPaCa2. The combination of AMG 479 with gemcitabine resulted in additive inhibitory activity both in vitro and in vivo. These results indicate that AMG 479 is a clinical candidate, both as a single agent and in combination with gemcitabine, for the treatment of patients with pancreatic carcinoma

Expression of PTPRO during mouse development suggests involvement in axonogenesis and differentiation of NT-3 and NGF-dependent neurons

Competition and cooperation between type II and type III receptor protein tyrosine phosphatases (RPTPs) regulate axon extension and pathfinding in Drosophila. The first step to investigate whether RPTPs influence axon growth in the more complex vertebrate nervous system is to identify which neurons express a particular RPTP. We studied the expression of mouse PTPRO, a type III RPTP with an extracellular region containing eight fibronectin type III domains, during embryogenesis and after birth. Mouse PTPRO mRNA is expressed exclusively in two cell types: neurons and kidney podocytes. Maximal expression in the brain was coincident with mid to late gestation and axonogenesis in the brain. We cloned two cDNAs, including a splice variant without sequence coding of 28 amino acids within the juxtamembrane domain that was found mostly in kidney. In situ hybridization detected mPTPRO mRNA in the cerebral cortex, olfactory bulb and nucleus, hippocampus, motor neurons, and the spinal cord midline. In addition, mPTPRO mRNA was found throughout dorsal root, cranial, and sympathetic ganglia and within kidney glomeruli. Mouse PTPRO mRNA was observed in neuron populations expressing TrkA, the high-affinity nerve growth factor receptor, or TrkC, the neurotrophin-3 receptor, and immunoreactive mPTPRO and TrkC colocalized in large dorsal root ganglia proprioceptive neurons. Our results suggest that mPTPRO is involved in the differentiation and axonogenesis of central and peripheral nervous system neurons, where it is in a position to modulate intracellular responses to neurotrophin-3 and/or nerve growth factor.

Receptor protein tyrosine phosphatases as mediators of cellular adhesion

Receptor protein tyrosine phosphatases (RPTPs) are structurally characterized by the diversity of their extracellular domains (ECDs). These domains display Ig-like, fibronectin type III (FNIII), MAM (meprin, A5, PTPmu), and carbonic anhydrase (CAH) motifs that resemble those present in many cell adhesion molecules (CAMs). However, in contrast to most CAMs, RPTPs also contain an intracellular domain possessing phosphatase activity. This combination makes RPTPs unusual in their ability to directly couple extracellular adhesion mediated events to intracellular signaling pathways. Even though identifying physiologically relevant ligands for RPTPs has proven difficult, recent experiments have shown that RPTPs can bind to themselves (homophilic) as well as to other proteins (heterophilic). For example, the type IIb RPTP, PTPmu? acts as a homophilic cell adhesion protein for epithelial and neural cells while the type V RPTP, PTPbeta/zeta binds a variety of CAMs and ECM components such as N-CAM and pleiotrophin. Interestingly, both PTPmu and PTPbeta/zeta interact with and regulate the tyrosine phosphorylation level of catenins, which are critical in physiological and pathological events such as cell migration, adhesion and transformation. In addition to their role as CAMs, RPTPs directly interact with intracellular adhesion regulators such as the cadherin/catenin complex, p130cas and GIT1. In summary, RPTPs represent a diverse family of transmembrane proteins that act as adhesion receptors and directly translate this engagement into intracellular signaling by modulating phosphotyrosine levels. Discovering the specific roles of RPTPs as receptors and identifying their ligands may lead to a better understanding of human illnesses whose underlying mechanisms involve cellular adhesion.

Intratumoral heterogeneity for and epigenetic modulation of mdr-1 expression in murine melanoma

We determined whether tumour size in vivo and cell density in vitro modulate the expression of the mdr-1 gene in B16 melanoma cells. Cells were injected subcutaneously into syngeneic mice. Small (5 mm in diameter) and large (15-20 mm in diameter) tumours were harvested. Tumour cells from small subcutaneous tumours exhibited higher levels of mdr-1 mRNA (measured using Northern blot and in situ hybridization) and P-glycoprotein (P-gp) (measured using immunohistochemistry and fluorescent activated cell sorter analysis), as well as greater. In vitro resistance to doxorubicin (DXR) than cells from large subcutaneous tumours. immunohistochemical studies using an antibody against proliferating cell nuclear antigen revealed that the small subcutaneous tumours contained a larger fraction of proliferating cells than the large tumours. To determine whether cell proliferation correlated with expression of mdr-1, we plated B16-F10 cells to yield sparse and confluent monolayer cultures. The levels of mdr-1 mRNA and P-gp and resistance to DXR and phosphotyrosine activity were higher in the sparse cultures than in the confluent cultures. These results demonstrate an intratumoral heterogeneity for the expression of mdr-1 that directly correlates with intratumoral heterogeneity for cell division.

Chemosensitization of cancer cells by the staurosporine derivative CGP 41251 in association with decreased P-glycoprotein phosphorylation

The multidrug resistance (MDR) phenotype of cancer cells often correlates with the level and activity of protein kinase C (PKC). We studied the ability of the staurosporine derivative PKC inhibitor CGP 41251 to reverse the MDR phenotype in MCF-7 human breast carcinoma and CT-26 murine colon adenocarcinoma cells and their doxorubicin (DXR)-selected MDR variants. Nontoxic concentrations of CGP 41251 significantly enhanced the cytotoxic properties of DXR, actinomycin D, vinblastine, and vincristine but not those of 5-fluorouracil. CGP 41251 increased intracellular concentrations of [14C]DXR but did not cause significant differences in P-glycoprotein (P-gp) expression. Pretreatment of MCF-7adr cells with phorbol 12-myristate 13-acetate reduced the CGP 41251 mediated intracellular accumulation of [14C]DXR. At concentrations that induced drug uptake, CGP 41251 significantly decreased the level of P-gp phosphorylation in the cells but did not compete with [3H]azidopine for photoaffinity labeling of P-gp. These data provide evidence that CGP 41251 reverses the MDR phenotype by modulating the phosphorylation of P-gp and/or other PKC substrates critical to the maintenance of the MDR phenotype.

Bcl-2 protects cells from cytokine-induced nitric-oxide-dependent apoptosis

Cytokine-mediated cell death in tumor cells can be achieved through endogenous nitric oxide (NO) from within tumor cells or exogenous NO from either activated macrophages or endothelial cells. The purpose of this study was to determine the role of Bcl-2 in NO-mediated apoptosis. The incubation of murine L929 and NIH3T3 cells with interleukin-1 alpha (IL-1 alpha) and interferon gamma (IFN gamma) induced high endogenous NO production only in the L929 cells that also underwent apoptosis. NIH3T3 cells were not resistant to NO-mediated apoptosis. In fact, the incubation of L929 and NIH3T3 cells with exogenous NO derived from NO donors, sodium nitroprusside, or S-nitroso-N-acetyl-DL-penicillamine (SNAP) induced death, characterized by typical apoptotic morphology and DNA fragmentation, in both cell types, but to a higher degree in NIH3T3 cells than in the L929 cells. We then measured the effect of Bcl-2 expression on exogenous NO-induced apoptosis. At both the mRNA and protein levels, L929 fibroblasts expressed higher levels of endogenous mouse Bcl-2 than did NIH3T3 cells. At the same time, L929 cells were much more resistant to exogenous NO-induced cell death than were NIH3T3 cells. The inverse correlation between mouse Bcl-2 expression and sensitivity to exogenous NO-mediated cell death was also found in the murine K-1735 melanoma C-23 and X-21 clonal populations. Transfection of both NIH3T3 cells and L929 cells with the human bcl-2 gene led to resistance to both exogenous and endogenous NO-mediated apoptosis. These data demonstrate that NO-mediated apoptosis can be suppressed by expression of Bcl-2, suggesting that abnormal expression of Bcl-2 may influence the efficacy of tumor immunotherapy.

Treatment of nude mice with 4-amidinoindan -1- one2 '- amidinohydrazone, a new S-adenosylmethionine decarboxylase inhibitor, delays growth and inhibits metastasis of human melanoma cells

CGP 48664A (4-amidinoindan-1-one2'-amidinohydrazone) is a novel inhibitor of S-adenosyl-methionine decarboxylase (SAMDC), a key enzyme in the biosynthesis of polyamines, which are themselves essential for proliferation of mammalian cells. Seven different human melanoma cell lines were treated in vitro with CGP 48664A. High, intermediate and low levels of cytostasis were induced in four, one and two melanoma lines, respectively. This cytostasis was reversed by the addition of exogenous spermidine or spermine to the culture medium. The heterogeneous low metastatic (CGP 48664A-resistant) A375P cells and highly metastatic (CGP 48664A-sensitive) A375SM cells were implanted into the subcutis or injected intravenously into nude mice. Systemic daily administration of CGP 48664A significantly reduced the size of cutaneous lesions and the number of lung metastases in mice implanted with A375SM cells. No beneficial effects were found in mice injected with A375P cells. Drug activity was dose dependent, and maximal effects were observed when treatment began in mice with small tumour burdens. The data suggest that CGP 48664A is effective against melanoma metastasis in nude mice and that its activity should be tested in combination with other cytoreductive agents.

Transcriptional induction of the melanocyte-stimulating hormone receptor in brain metastases of murine K-1735 melanoma

Metastatic K-1735 murine melanoma cells are amelanotic in culture or in the subcutis of syngeneic mice. When injected into the internal carotid artery, these cells produce melanotic brain metastases. The production of melanin in tumor cells growing in the brain was directly correlated with induction of melanocyte-stimulating hormone receptor (MSH-R) steady-state mRNA transcripts. K-1735 cells isolated from brain lesions and implanted into the subcutis or grown in culture lose MSH-R transcripts and become amelanotic. In contrast to K-1735 cells, B16-BL6 melanoma cells constitutively produce melanin and express high levels of MSH-R mRNA regardless of the site of growth. Somatic cell hybrids between K-1735 and B16 cells produced melanin and expressed high levels of MSH-R mRNA transcripts, regardless of the site of growth, suggesting the dominance of the B16 phenotype. Treatment with alpha-MSH failed to upregulate MSH-R expression in cultured K-1735 cells or to maintain MSH-R expression in K-1735 cells isolated from brain metastases to be grown in culture. Responsiveness to alpha-MSH as determined by cell proliferation, melanin production, and intracellular accumulation of cyclic AMP directly correlated with MSH-R expression. These data demonstrate that a specific organ environment influences the phenotype of metastatic cells by regulation of specific genes that encode for cell surface receptors.