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Metachromatic leukodystrophy (MLD) is a rare, inherited, demyelinating lysosomal storage disorder caused by mutations in the arylsulfatase-A gene (ARSA). In patients, levels of functional ARSA enzyme are diminished and lead to deleterious accumulation of sulfatides. Herein, we demonstrate that intravenous administration of HSC15/ARSArestored the endogenous murine biodistribution of the corresponding enzyme, and overexpression ofARSAcorrected disease biomarkers and ameliorated motor deficits inArsaKO mice of either sex. In treatedArsaKO mice, when compared with intravenously administered AAV9/ARSA,significant increases in brain ARSA activity, transcript levels, and vector genomes were observed with HSC15/ARSA. Durability of transgene expression was established in neonate and adult mice out to 12 and 52 weeks, respectively. Levels and correlation between changes in biomarkers and ARSA activity required to achieve functional motor benefit was also defined. Finally, we demonstrated blood–nerve, blood–spinal and blood–brain barrier crossing as well as the presence of circulating ARSA enzyme activity in the serum of healthy nonhuman primates of either sex. Together, these findings support the use of intravenous delivery of HSC15/ARSA-mediated gene therapy for the treatment of MLD.SIGNIFICANCE STATEMENTHerein, we describe the method of gene therapy adeno-associated virus (AAV) capsid and route of administration selection leading to an efficacious gene therapy in a mouse model of metachromatic leukodystrophy. We demonstrate the therapeutic outcome of a new naturally derived clade F AAV capsid (AAVHSC15) in a disease model and the importance of triangulating multiple end points to increase the translation into higher species via ARSA enzyme activity and biodistribution profile (with a focus on the CNS) with that of a key clinically relevant biomarker.

Supplementary Figure 10 - PDF file 333K, Analysis of multiple EGFR-related signaling pathways in parental NCI-H1975 and COR resistant clones by Western blotting

Supplementary Figure 6 - PDF file 112K, Impact of CO-1686, erlotinib and afatinib administration on mouse body-weight

Supplementary Figure 9 - PDF file 168K, NCI-H1975 parental and CO-1686 resistant clones cluster into distinct groups using an RNA-based EMT signature

Supplementary Figure 3 - PDF file 295K, Activity of CO-1686 against rare lung-cancer associated EGFR mutants

PDF - 252K, Supplemental Table 1. Mass spectrometry on EGFR-L858R/T790M protein. Supplemental Table 2. EGFR modulation in A431, H1975 and HCC827 cells by compound 3. Supplemental Table 3. Kinase selectivity profile of compound 3, afatinib and WZ4002 at 1 ?M. Supplemental Table 4.Multi-dose level PK/PD study in H1975 tumor-bearing mice. Supplemental Figure 1. Signaling inhibition in EGFR wild-type (A431) and mutant EGFR NSCLC cells (H1975 and HCC827). Supplemental Figure 2. Prolonged duration of action on EGFR-L858R/T790M (A) and EGFR-DelE746-A750 (B) proteins. Supplemental Figure 3. Protein degradation (t1/2) of EGFR-L858R/T790M (A) and EGFR-DelE746-A750 (B) in H1975 and HCC827 cells, respectively. Supplemental Figure 4. Prolonged duration of action on EGFR-DelE746-A750 protein by erlotinib. Supplemental Figure 5. Time-dependent inhibition in EGFR mutant H1975 (A) and HCC827 (B) cells.

Supplementary Table 1 - PDF file 114K, Kinase selectivity profiling of CO-1686

Supplementary Figure 1 - PDF file 596K, Covalent binding of the EGFR L858R/T790M protein by CO-1686

Patients with non–small cell lung carcinoma (NSCLC) with activating mutations in epidermal growth factor receptor (EGFR) initially respond well to the EGFR inhibitors erlotinib and gefitinib. However, all patients relapse because of the emergence of drug-resistant mutations, with T790M mutations accounting for approximately 60% of all resistance. Second-generation irreversible EGFR inhibitors are effective against T790M mutations in vitro, but retain affinity for wild-type EGFR (EGFRWT). These inhibitors have not provided compelling clinical benefit in T790M-positive patients, apparently because of dose-limiting toxicities associated with inhibition of EGFRWT. Thus, there is an urgent clinical need for therapeutics that overcome T790M drug resistance while sparing EGFRWT. Here, we describe a lead optimization program that led to the discovery of four potent irreversible 2,4-diaminopyrimidine compounds that are EGFR mutant (EGFRmut) selective and have been designed to have low affinity for EGFRWT. Pharmacokinetic and pharmacodynamic studies in H1975 tumor–bearing mice showed that exposure was dose proportional resulting in dose-dependent EGFR modulation. Importantly, evaluation of normal lung tissue from the same animals showed no inhibition of EGFRWT. Of all the compounds tested, compound 3 displayed the best efficacy in EGFRL858R/T790M-driven tumors. Compound 3, now renamed CO-1686, is currently in a phase I/II clinical trial in patients with EGFRmut-advanced NSCLC that have received prior EGFR-directed therapy. Mol Cancer Ther; 13(6); 1468–79. ©2014 AACR.

Supplementary Figure 7 - PDF file 352K, H&E and immunohistochemical (Ki67) staining of tumors derived from EGFR mutant GEM models

Supplementary Figure 8 - PDF file 215K, Photomicrographs of CO-1686 resistant NCI-H1975 cell (COR) clones and quantification of EGFR siRNA knockdown in COR clones

Supplementary Figure 4 - PDF file 103K, Pharmacokinetic analysis of CO-1686 in nu/nu mice

Supplementary Figure 11 - PDF file 255K, Analysis of the role of AXL in mediating CO-1686 resistance in COR cell clones.

Supplementary Materials and Methods - PDF file 179K, Supplemental materials and methods for Walter et al. manuscript

Supplementary Figure 5 - PDF file 134K, Schedule dependence of CO-1686 antitumor activity in NCI-H1975 mode

Supplementary Table 2 - PDF file 113K, Mutant EGFR cell panel profiling of CO-1686

PDF - 91K, Supplemental Materials and Methods and Legends for Supplementary Figures 1 through 5.

Supplementary Table 3 - PDF file 119K, Comparison of differentially expressed genes in COR cell lines with the EMT signature of Byers et al. (2013)

Supplementary Figure 2 - PDF file 111K, CO-1686 inhibits cell growth in EGFR-mutant erlotinib-resistant cell lines

The precise correction of genetic mutations at the nucleotide level is an attractive permanent therapeutic strategy for human disease. However, despite significant progress, challenges to efficient and accurate genome editing persist. Here, we report a genome editing platform based upon a class of hematopoietic stem cell (HSC)-derived clade F adeno-associated virus (AAV), which does not require prior nuclease-mediated DNA breaks and functions exclusively through BRCA2-dependent homologous recombination. Genome editing is guided by complementary homology arms and is highly accurate and seamless, with no evidence of on-target mutations, including insertion/deletions or inclusion of AAV inverted terminal repeats. Efficient genome editing was demonstrated at different loci within the human genome, including a safe harbor locus, AAVS1, and the therapeutically relevant IL2RG gene, and at the murine Rosa26 locus. HSC-derived AAV vector (AAVHSC)-mediated genome editing was robust in primary human cells, including CD34+ cells, adult liver, hepatic endothelial cells, and myocytes. Importantly, high-efficiency gene editing was achieved in vivo upon a single i.v. injection of AAVHSC editing vectors in mice. Thus, clade F AAV-mediated genome editing represents a promising, highly efficient, precise, single-component approach that enables the development of therapeutic in vivo genome editing for the treatment of a multitude of human gene-based diseases.

PI3Kα has been identified as an oncogene in human tumors. By use of rational drug design, a targeted covalent inhibitor 3 (CNX-1351) was created that potently and specifically inhibits PI3Kα. We demonstrate, using mass spectrometry and X-ray crystallography, that the selective inhibitor covalently modifies PI3Kα on cysteine 862 (C862), an amino acid unique to the α isoform, and that PI3Kβ, -γ, and -δ are not covalently modified. 3 is able to potently (EC(50) < 100 nM) and specifically inhibit signaling in PI3Kα-dependent cancer cell lines, and this leads to a potent antiproliferative effect (GI(50) < 100 nM). A covalent probe, 8 (CNX-1220), which selectively bonds to PI3Kα, was used to investigate the duration of occupancy of 3 with PI3Kα in vivo. This is the first report of a PI3Kα-selective inhibitor, and these data demonstrate the biological impact of selectively targeting PI3Kα.

Netrin-4 is a 628 amino acid basement membrane component that promotes neurite elongation at low concentrations but inhibits neurite extension at high concentrations. There is a growing body of literature suggesting that several molecules, including netrins, are regulators of both neuronal and vascular growth. It is believed that molecules that guide neural growth and development are also involved in regulating morphogenesis of the vascular tree. Further, netrins have recently been implicated in controlling epithelial cell branching morphogenesis in the breast, lung and pancreas. Characterization of purified netrin-4 in in vitro angiogenesis assays demonstrated that netrin-4 markedly inhibits HMVEC migration and tube formation. Moreover, netrin-4 inhibits proliferation of a variety of human tumor cells in vitro. Netrin-4 has only modest effects on proliferation of endothelial and other non-transformed cells. Netrin-4 treatment results in phosphorylation changes of proteins that are known to control cell growth. Specifically, Phospho-Akt-1, Phospho-Jnk-2, and Phospho-c-Jun are reduced in tumor cells that have been treated with netrin-4. Together, these data suggest a potential role for netrin-4 in regulating tumor growth.

The molecular signature that defines tumor microvasculature will likely provide clues as to how vascular-dependent tumor proliferation is regulated. Using purified endothelial cells, we generated a database of gene expression changes accompanying vascular proliferation in invasive breast cancer. In contrast to normal mammary vasculature, invasive breast cancer vasculature expresses extracellular matrix and surface proteins characteristic of proliferating and migrating endothelial cells. We define and validate the up-regulated expression of VE-cadherin and osteonectin in breast tumor vasculature. In contrast to other tumor types, invasive breast cancer vasculature induced a high expression level of specific transcription factors, including SNAIL1 and HEYL, that may drive gene expression changes necessary for breast tumor neovascularization. We demonstrate the expression of HEYL in tumor endothelial cells and additionally establish the ability of HEYL to both induce proliferation and attenuate programmed cell death of primary endothelial cells in vitro. We also establish that an additional intracellular protein and previously defined metastasis-associated gene, PRL3, appears to be expressed predominately in the vasculature of invasive breast cancers and is able to enhance the migration of endothelial cells in vitro. Together, our results provide unique insights into vascular regulation in breast tumors and suggest specific roles for genes in driving tumor angiogenesis.

Malignant gliomas are uniformly lethal tumors whose morbidity is mediated in large part by the angiogenic response of the brain to the invading tumor. This profound angiogenic response leads to aggressive tumor invasion and destruction of surrounding brain tissue as well as blood-brain barrier breakdown and life-threatening cerebral edema. To investigate the molecular mechanisms governing the proliferation of abnormal microvasculature in malignant brain tumor patients, we have undertaken a cell-specific transcriptome analysis from surgically harvested nonneoplastic and tumor-associated endothelial cells. SAGE-derived endothelial cell gene expression patterns from glioma and nonneoplastic brain tissue reveal distinct gene expression patterns and consistent up-regulation of certain glioma endothelial marker genes across patient samples. We define the G-protein-coupled receptor RDC1 as a tumor endothelial marker whose expression is distinctly induced in tumor endothelial cells of both brain and peripheral vasculature. Further, we demonstrate that the glioma-induced gene, PV1, shows expression both restricted to endothelial cells and coincident with endothelial cell tube formation. As PV1 provides a framework for endothelial cell caveolar diaphragms, this protein may serve to enhance glioma-induced disruption of the blood-brain barrier and transendothelial exchange. Additional characterization of this extensive brain endothelial cell gene expression database will provide unique molecular insights into vascular gene expression.

Patients with non–small cell lung carcinoma (NSCLC) with activating mutations in epidermal growth factor receptor (EGFR) initially respond well to the EGFR inhibitors erlotinib and gefitinib. However, all patients relapse because of the emergence of drug-resistant mutations, with T790M mutations accounting for approximately 60% of all resistance. Second-generation irreversible EGFR inhibitors are effective against T790M mutations in vitro, but retain affinity for wild-type EGFR (EGFRWT). These inhibitors have not provided compelling clinical benefit in T790M-positive patients, apparently because of dose-limiting toxicities associated with inhibition of EGFRWT. Thus, there is an urgent clinical need for therapeutics that overcome T790M drug resistance while sparing EGFRWT. Here, we describe a lead optimization program that led to the discovery of four potent irreversible 2,4-diaminopyrimidine compounds that are EGFR mutant (EGFRmut) selective and have been designed to have low affinity for EGFRWT. Pharmacokinetic and pharmacodynamic studies in H1975 tumor–bearing mice showed that exposure was dose proportional resulting in dose-dependent EGFR modulation. Importantly, evaluation of normal lung tissue from the same animals showed no inhibition of EGFRWT. Of all the compounds tested, compound 3 displayed the best efficacy in EGFRL858R/T790M-driven tumors. Compound 3, now renamed CO-1686, is currently in a phase I/II clinical trial in patients with EGFRmut-advanced NSCLC that have received prior EGFR-directed therapy. Mol Cancer Ther; 13(6); 1468–79. ©2014 AACR.

Designing selective inhibitors of proteases has proven problematic, in part because pharmacophores that confer potency exploit the conserved catalytic apparatus. We developed a fundamentally different approach by designing irreversible inhibitors that target noncatalytic cysteines that are structurally unique to a target in a protein family. We have successfully applied this approach to the important therapeutic target HCV protease, which has broad implications for the design of other selective protease inhibitors.

Patients with non–small cell lung cancer (NSCLC) with activating EGF receptor (EGFR) mutations initially respond to first-generation reversible EGFR tyrosine kinase inhibitors. However, clinical efficacy is limited by acquired resistance, frequently driven by the EGFRT790M mutation. CO-1686 is a novel, irreversible, and orally delivered kinase inhibitor that specifically targets the mutant forms of EGFR, including T790M, while exhibiting minimal activity toward the wild-type (WT) receptor. Oral administration of CO-1686 as single agent induces tumor regression in EGFR-mutated NSCLC tumor xenograft and transgenic models. Minimal activity of CO-1686 against the WT EGFR receptor was observed. In NSCLC cells with acquired resistance to CO-1686 in vitro, there was no evidence of additional mutations or amplification of the EGFR gene, but resistant cells exhibited signs of epithelial–mesenchymal transition and demonstrated increased sensitivity to AKT inhibitors. These results suggest that CO-1686 may offer a novel therapeutic option for patients with mutant EGFR NSCLC. Significance: We report the preclinical development of a novel covalent inhibitor, CO-1686, that irreversibly and selectively inhibits mutant EGFR, in particular the T790M drug-resistance mutation, in NSCLC models. CO-1686 is the first drug of its class in clinical development for the treatment of T790M-positive NSCLC, potentially offering potent inhibition of mutant EGFR while avoiding the on-target toxicity observed with inhibition of the WT EGFR. Cancer Discov; 3(12); 1404–15. ©2013 AACR. This article is highlighted in the In This Issue feature, p. 1317

Antiangiogenesis has been validated as a therapeutic strategy to treat cancer, however, a need remains to identify new targets and therapies for specific diseases and to improve clinical benefit from antiangiogenic agents. Tumor endothelial marker 7 (TEM-7) was investigated as a possible target for therapeutic antiangiogenic intervention in cancer. TEM-7 expression was assessed by in situ hybridization or by immunohistochemistry (IHC) in 130 formalin-fixed paraffin-embedded (FFPE) and 410 frozen human clinical specimens of cancer plus 301 normal tissue samples. In vitro TEM-7 expression was evaluated in 4 human endothelial cell models and in 32 human cancer cell lines by RT-PCR and flow cytometry. An anti-TEM-7 antibody was tested in vitro on human SKOV3 ovarian and MDA-MB-231 breast carcinoma cells that expressed TEM-7 in antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis assays. In frozen tumor tissues, TEM-7 mRNA and protein was detected in all but one of the cancer types tested and was infrequently expressed in normal frozen tissues. In FFPE tumor tissues, TEM-7 protein was detected by IHC in colon, breast, lung, bladder, ovarian and endometrial cancers and in sarcomas. TEM-7 protein was not detected in head and neck, prostate or liver cancers. TEM-7 expression was restricted to the vasculature and was absent from tumor cells. In vitro, TEM-7 was not detected in human microvascular endothelial cells (HMVEC) or human umbilical vein endothelial cells (HUVEC) but was induced in endothelial precursor/progenitor cells (EPC) in the presence of the mitogen phorbol ester PMA. An anti-TEM-7 antibody mediated ADCC and phagocytosis in SKOV3 and MDA-MB-231 cell lines infected with an adenovirus expressing TEM-7. These data demonstrate that TEM-7 is a vascular protein associated with angiogenic states. TEM-7 is a novel and attractive target for antiangiogenic therapy.

Angiogenesis occurs during normal physiologic processes as well as under pathologic conditions such as tumor growth. Serial analysis of gene expression profiling revealed genes [tumor endothelial markers (TEM)] that are overexpressed in tumor endothelial cells compared with normal adult endothelial cells. Because blood vessel development of malignant tumors under certain conditions may include endothelial precursor cells (EPC) recruited from bone marrow, we investigated TEM expression in EPC. The expression of TEM1 or endosialin (CD248) and other TEM has been discovered in a population of vascular endothelial growth factor receptor 2+/CD31+/CD45−/VE-cadherin+ EPC derived from human CD133+/CD34+ cells. EPC share some properties with fully differentiated endothelial cells from normal tissue, yet reverse transcription-PCR and flow cytometry reveal that EPC express higher levels of endosialin at the molecular and protein levels. The elevated expression of endosialin in EPC versus mature endothelial cells suggests that endosialin is involved in the earlier stages of tumor angiogenesis. Anti-endosialin antibodies inhibited EPC migration and tube formation in vitro. In vivo, immunohistochemistry indicated that human EPC continued to express endosialin protein in a Matrigel plug angiogenesis assay established in nude mice. Anti-endosialin antibodies delivered systemically at 25 mg/kg were also able to inhibit circulating murine EPC in nude mice bearing s.c. SKNAS tumors. EPC and bone marrow–derived cells have been shown previously to incorporate into malignant blood vessels in some instances, yet they remain controversial in the field. The data presented here on endothelial genes that are up-regulated in tumor vasculature and in EPC support the hypothesis that the angiogenesis process in cancer can involve EPC. [Mol Cancer Ther 2008;7(8):2536–46]

Protein tyrosine phosphatase PRL-3 mRNA was found highly expressed in colon cancer endothelium and metastases. We sought to associate a function with PRL-3 expression in both endothelial cells and malignant cells using in vitro models. PRL-3 mRNA levels were determined in several normal human endothelial cells exposed or unexposed to the phorbol ester phorbol 12-myristate 13-acetate (PMA) and in 27 human tumor cell lines. In endothelial cells, PRL-3 mRNA expression was increased in human umbilical vascular endothelial cells and human microvascular endothelial cells (HMVEC) exposed to PMA. An oligonucleotide microarray analysis revealed that PRL-3 was among the 10 genes with the largest increase in expression on PMA stimulation. Phenotypically, PMA-treated HMVEC showed increased invasion, tube formation, and growth factor–stimulated proliferation. A flow cytometric analysis of cell surface markers showed that PMA-treated HMVEC retained endothelial characteristics. Infection of HMVEC with an adenovirus expressing PRL-3 resulted in increased tube formation. In tumor cells, PRL-3 mRNA levels varied markedly with high expression in SKNAS neuroblastoma, MCF-7 and BT474 breast carcinoma, Hep3B hepatocellular carcinoma, and HCT116 colon carcinoma. Western blotting analysis of a subset of cell line lysates showed a positive correlation between PRL-3 mRNA and protein levels. PRL-3 was stably transfected into DLD-1 colon cancer cells. PRL-3-overexpressing DLD-1 subclones were assessed for doubling time and invasion. Although doubling time was similar among parental, empty vector, and PRL-3 subclones, invasion was increased in PRL-3-expressing subclones. In models of endogenous expression, we observed that the MCF-7 cell line, which expresses high levels of PRL-3, was more invasive than the SKBR3 cell line, which expresses low levels of PRL-3. However, the MDA-MB-231 cell line was highly invasive with low levels of PRL-3, suggesting that in some models invasion is PRL-3 independent. Transfection of a PRL-3 small interfering RNA into MCF-7 cells inhibited PRL-3 expression and cell invasion. These results indicate that PRL-3 is functional in both endothelial cells and malignant cells and further validate PRL-3 as a potentially important molecular target for anticancer therapy. [Mol Cancer Ther 2006;5(2):219–29]

Introduction: Non-small cell lung cancer (NSCLC) patients with activating EGFR mutations initially respond well to the EGFR tyrosine kinase inhibitors (TKIs) erlotinib and gefitinib. However, clinical efficacy is limited by the development of resistance. The most common mechanism of resistance is a second site mutation within exon 20 of EGFR (T790M), observed in ∼50% of cases. CO-1686 is an irreversible kinase inhibitor that targets the mutant forms of EGFR by inhibiting the common activating mutations (L858R, delE746-A750) and the gatekeeper mutation (T790M) but not the wild-type receptor. Therefore, CO-1686 has the potential to effectively treat first- and second-line NSCLC patients with EGFR mutations without causing the dose limiting toxicities associated with approved EGFR kinase inhibitors or those in clinical development. Experimental procedures: Using structure-based drug design, CO-1686, a covalent, irreversible small molecule, which selectively inhibits mutant EGFR, was identified. CO-1686 potency was assessed against four common EGFR mutations (L858R, delE746-A750, L858R/T790M and delE746-A750/T790M) using in vitro biochemical and cell-based assays. Antitumor activity of CO-1686 as a single agent was assessed in NSCLC xenograft models harboring EGFR mutations: H1975 (L858R/T790M) and HCC827 (delE746-A750). Pharmacodynamic studies were performed to evaluate effects on cell survival and EGFR signaling. Results: In vitro and in vivo pharmacology studies focused on evaluating CO-1686 potency in four EGFR mutations common in NSCLC patients: L858R, delE746-A750, L858R/T790M and delE746-A750/T790M. CO-1686 was shown to be active against all four EGFR mutants. Effects of CO-1686 on cell proliferation and EGFR signaling were evaluated in HCC827 cells (delE746-A750) and its erlotinib-resistant clone, HCC827-EPR harboring the second site mutation T790M (delE746-A750/T790M). CO-1686 inhibited cell proliferation in both cell lines equally (GI50 values of 12 nM in the parental line and 19 nM in the T790M-positive clone). In mouse xenograft studies, oral dosing of CO-1686 in H1975 double mutant (L858R/T790M) and in HCC827 single mutant (delE746-A750) models caused tumor shrinkage as a single agent in a dose-dependent manner. Different dosing schedules were explored. Conclusions: Our results establish CO-1686 as a potent, mutant-selective EGFR inhibitor with excellent in vivo activity in mice bearing tumors with activating EGFR mutations as well as the resistance mutation T790M. These data suggest that treatment with CO-1686 as a single agent can overcome T790M-mediated drug resistance in NSCLC. Initially, clinical development will focus on NSCLC patients with mutant EGFR. 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 1791. doi:1538-7445.AM2012-1791

Recently, the importance of targeted covalent inhibitors in addressing potency, selectivity and drug resistance has become of great interest, especially in the area of non-small cell lung cancer (NSCLC). Although several covalent EGFR TKIs that are advancing in NSCLC clinical development are active against mutations which are refractory to the reversible TKI drugs Tarceva and Iressa, limited chemical diversity has been explored; all of the irreversible and reversible clinical compounds share the same quinazoline scaffold. We describe the design of a novel pyrimidine-based irreversible inhibitor of EGFR (CNX17) which is active against both the WT EGFR as well as the resistance mutation L858R/T790M in biochemical assays. The inhibitor is also a potent inhibitor of EGFR signaling, including the L858R/T790M resistance mutation in cells (H1975 cell line, EC50 441 nM). Importantly, it also potently inhibits proliferation in both HCC827 (EGFRΔ746–750 EC50 < 5 nM) and H1975 (EC50 134 nM). This novel chemical scaffold may be an important addition to the armamentarium in overcoming drug resistance to current EGFR therapies.

Introduction: Non-small cell lung cancer (NSCLC) patients with activating EGFR mutations initially respond well to EGFR tyrosine kinase inhibitors. However, clinical efficacy is limited by the development of resistance. The most common mechanism of resistance is a second site mutation within exon 20 of EGFR (T790M), observed in ∼50% of cases. Our goal was to develop a mutant-selective EGFR inhibitor that potently inhibits activating EGFR mutations as well as the T790M resistance mutation while sparing wild-type EGFR for the treatment of NSCLC patients. Such a drug has the potential to effectively treat first- and second-line NSCLC patients with EGFR mutations without causing the dose limiting toxicities associated with EGFR kinase inhibitors currently in clinical development. Experimental procedures: Using structure-based drug design, we identified CO-1686, a covalent, irreversible small molecule, which selectively inhibits mutant EGFR. We assessed antitumor activity of CO-1686 both in vitro and in vivo in two NSCLC cell lines harboring EGFR mutations: H1975 (EGFR L858R/T790M) and HCC827 (EGFR delE746-A750). We evaluated inhibition of EGFR phosphorylation and downstream signaling by immunoblot analysis in cells and tissue samples. IHC staining on skin samples was performed to address effects on wild-type EGFR. Results: CO-1686 is a potent inhibitor of cell proliferation and EGFR signaling in NSCLC cells harboring the single activating mutation EGFR delE746-A750 as well as the double mutation EGFR L858R/T790M. When administered orally, CO-1686 (3 − 100 mg/kg) significantly suppresses tumor growth of H1975 cells (L858R/T790M) in a dose-dependent manner causing tumor regressions at the highest dose (100 mg/kg) without affecting body weight. Erlotinib at the same dose exhibits no effect against H1975 xenografts. In HCC827 (delE746-A750) xenografts, both agents cause tumor shrinkage. In both NSCLC mouse models, inhibition of EGFR phosphorylation in tumors correlate with the observed anti-tumor activity, while no effect on EGFR signaling is observed in normal lung or skin tissues with CO-1686 treatment, confirming that CO-1686 does not inhibt wild-type EGFR. Conclusions: Our results establish CO-1686 as a mutant-selective, wild-type sparing EGFR inhibitor with in vivo efficacy against tumors with activating EGFR mutations as well as the resistance mutation T790M. These data suggest that treatment with CO-1686 as a single agent can overcome T790M-mediated drug resistance in NSCLC. This hypothesis will be tested clinically. 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 C189.

B-cell receptor (BCR) signaling is essential for normal B cell development and proliferation. In addition, functional BCR signaling contributes to the proliferation and survival of many B cell lymphomas through constitutive low level or tonic signaling. Disruption of this tonic signaling pathway results in cell death or decreased viability in many B cell lymphoma cells. Bruton’s tyrosine kinase (Btk) is a member of the Tec family of protein tyrosine kinases and plays a crucial role in the development and activation of B cells through association with the BCR signalosome. We have developed a novel, potent, irreversible inhibitor of Btk that selectively disrupts the BCR signaling pathway as measured by inhibition of both Btk Y223 autophosphorylation and phosphorylation of the Btk substrate PLCg2. AVL101 inhibits Btk but leaves upstream BCR kinase activity intact; both Syk phosphorylation at Y525/526 and transphosphorylation of Btk on residue Y551 are unaltered. By mass spectrometry, we have shown that AVL101 covalently modifies Btk specifically at Cys-481, and in cell-based assays, this irreversible binding leads to prolonged inhibition of Btk kinase activity. After removal of the compound, inhibition of Btk activity is maintained in cultured B cell lymphoma cells for > 8 hours. This prolonged inhibition correlates with the half-life of the Btk protein, which we have found to be greater than 8 hours, irrespective of BCR activation state or modification by the inhibitor. We have demonstrated that AVL101 functionally inhibits BCR signaling in vitro and in vivo. In vitro, AVL101 inhibits BCR ligand-induced calcium flux as well as proliferation of the B cell lymphoma cell lines DOHH2 and WSU-DLCL2. In vivo, we have shown AVL101 is orally bioavailable and can inhibit Btk-dependent B cell function. Our data demonstrate that Btk is a valid therapeutic target for B cell lymphomas and other disorders dependent on BCR signaling. Furthermore, irreversible inhibition of Btk enables complete and prolonged inactivation of the target kinase, and suggests that clinically, a rapid and sustained therapeutic response may be possible using an orally available, irreversible Btk inhibitor.