Synthesis and evaluation of aniline headgroups for alkynyl thienopyrimidine dual EGFR/ErbB-2 kinase inhibitors

Aniline 'headgroups' were synthesized and incorporated into an alkynyl thienopyrimidine series of EGFR and ErbB-2 inhibitors. Potent inhibition of enzyme activity and cellular proliferation was observed. In certain instances, protein binding was reduced and oral exposure was found to be somewhat improved relative to compounds containing the reference aniline.

Dual EGFR/ErbB-2 inhibitors from novel pyrrolidinyl-acetylenic thieno[3,2-d]pyrimidines

A novel class of substituted pyrrolidinyl-acetylenic thieno[3,2-d]pyrimidines has been identified that are potent and selective inhibitors of both EGFR/ErbB-2 receptor tyrosine kinases. The inhibitors are found to display a range of enzyme and cellular potency and also to display a varying level of covalent modification of the kinase targets. Selected molecules, including compound 15h, were found to be potent in enzymatic and cellular assays while also demonstrating exposure in the mouse from an oral dose.

Assessment of epidermal growth factor receptor (EGFR, ErbB1) and HER2 (ErbB2) protein expression levels and response to lapatinib (Tykerb, GW572016) in an expanded panel of human normal and tumour cell lines

OBJECTIVE

Lapatinib (Tykerb, GW572016), a potent inhibitor of the catalytic activities of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) (ErbB2), inhibits population growth of selected EGFR and HER2 overexpressing cell lines. Previous studies with a small number of cell lines suggest a correlation between overexpression of EGFR and/or HER2 and sensitivity to growth inhibition by lapatinib; however, the precise determinants of lapatinib selectivity for tumour and/or other cells remain unclear.

MATERIALS AND METHODS

To clarify the determinants of its selectivity in cultured cells, lapatinib-induced cell population growth inhibition and relative EGFR and HER2 protein expression were quantified in 61 different human tumour cell lines from 12 tumour types, two oncogene transformed human cell lines and two normal human cell cultures. Using statistical tools to analyse the data, a model describing the relationship between lapatinib IC(50) (the response variable) and EGFR and HER2 expression and tissue type (explanatory variables) was derived.

CONCLUSION

The results suggest that simultaneous consideration of EGFR and HER2 expression, as well as tissue type yields the best determinant of lapatinib selectivity in cultured cells.

Demonstration of a genetic therapeutic index for tumors expressing oncogenic BRAF by the kinase inhibitor SB-590885

Oncogenic BRAF alleles are both necessary and sufficient for cellular transformation, suggesting that chemical inhibition of the activated mutant protein kinase may reverse the tumor phenotype. Here, we report the characterization of SB-590885, a novel triarylimidazole that selectively inhibits Raf kinases with more potency towards B-Raf than c-Raf. Crystallographic analysis revealed that SB-590885 stabilizes the oncogenic B-Raf kinase domain in an active configuration, which is distinct from the previously reported mechanism of action of the multi-kinase inhibitor, BAY43-9006. Malignant cells expressing oncogenic B-Raf show selective inhibition of mitogen-activated protein kinase activation, proliferation, transformation, and tumorigenicity when exposed to SB-590885, whereas other cancer cell lines and normal cells display variable sensitivities or resistance to similar treatment. These studies support the validation of oncogenic B-Raf as a target for cancer therapy and provide the first evidence of a correlation between the expression of oncogenic BRAF alleles and a positive response to a selective B-Raf inhibitor.

Optimization and SAR for dual ErbB-1/ErbB-2 tyrosine kinase inhibition in the 6-furanylquinazoline series

Synthetic modifications on a 6-furanylquinazoline scaffold to optimize the dual ErbB-1/ErbB-2 tyrosine kinase inhibition afforded consistent SAR whereby a 4-(3-fluorobenzyloxy)-3-haloanilino provided the best enzyme potency and cellular selectivity. Changes made to the 6-furanyl group had little impact on the enzyme activity, but appeared to dramatically affect the cellular efficacy. The discovery of lapatinib emerged from this work.

Activity of the dual kinase inhibitor lapatinib (GW572016) against HER-2-overexpressing and trastuzumab-treated breast cancer cells

Lapatinib (GW572016) is a selective inhibitor of both epidermal growth factor receptor (EGFR) and HER-2 tyrosine kinases. Here, we explore the therapeutic potential of lapatinib by testing its effect on tumor cell growth in a panel of 31 characterized human breast cancer cell lines, including trastuzumab-conditioned HER-2-positive cell lines. We further characterize its activity in combination with trastuzumab and analyze whether EGFR and HER-2 expression or changes induced in the activation of EGFR, HER-2, Raf, AKT, or extracellular signal-regulated kinase (ERK) are markers of drug activity. We report that concentration-dependent antiproliferative effects of lapatinib were seen in all breast cancer cell lines tested but varied significantly between individual cell lines with up to 1,000-fold difference in the IC(50)s (range, 0.010-18.6 micromol/L). Response to lapatinib was significantly correlated with HER-2 expression and its ability to inhibit HER-2, Raf, AKT, and ERK phosphorylation. Long-term in vivo lapatinib studies were conducted with human breast cancer xenografts in athymic mice. Treatment over 77 days resulted in a sustained and significant reduction in xenograft volume compared with untreated controls. For the combination of lapatinib plus trastuzumab, synergistic drug interactions were observed in four different HER-2-overexpressing cell lines. Moreover, lapatinib retained significant in vitro activity against cell lines selected for long-term outgrowth (>9 months) in trastuzumab-containing (100 microg/mL) culture medium. These observations provide a clear biological rationale to test lapatinib as a single agent or in combination with trastuzumab in HER-2-overexpressing breast cancer and in patients with clinical resistance to trastuzumab.

Alkynyl pyrimidines as dual EGFR/ErbB2 kinase inhibitors

Anilinoalkynylpyrimidines were prepared and evaluated as dual EGFR/ErbB2 kinase inhibitors. A preference was found for substituted phenyl and heteroaromatic rings attached to the alkyne. In addition, the presence of a potential hydrogen bond donor appended to this ring was favored. Selected molecules in the series demonstrated some activity against human tumor cell lines.

Inhibition of colony-stimulating-factor-1 signaling in vivo with the orally bioavailable cFMS kinase inhibitor GW2580

Colony-stimulating-factor-1 (CSF-1) signaling through cFMS receptor kinase is increased in several diseases. To help investigate the role of cFMS kinase in disease, we identified GW2580, an orally bioavailable inhibitor of cFMS kinase. GW2580 completely inhibited human cFMS kinase in vitro at 0.06 microM and was inactive against 26 other kinases. GW2580 at 1 microM completely inhibited CSF-1-induced growth of mouse M-NFS-60 myeloid cells and human monocytes and completely inhibited bone degradation in cultures of human osteoclasts, rat calvaria, and rat fetal long bone. In contrast, GW2580 did not affect the growth of mouse NS0 lymphoblastoid cells, human endothelial cells, human fibroblasts, or five human tumor cell lines. GW2580 also did not affect lipopolysaccharide (LPS)-induced TNF, IL-6, and prostaglandin E2 production in freshly isolated human monocytes and mouse macrophages. After oral administration, GW2580 blocked the ability of exogenous CSF-1 to increase LPS-induced IL-6 production in mice, inhibited the growth of CSF-1-dependent M-NFS-60 tumor cells in the peritoneal cavity, and diminished the accumulation of macrophages in the peritoneal cavity after thioglycolate injection. Unexpectedly, GW2580 inhibited LPS-induced TNF production in mice, in contrast to effects on monocytes and macrophages in vitro. In conclusion, GW2580's selective inhibition of monocyte growth and bone degradation is consistent with cFMS kinase inhibition. The ability of GW2580 to chronically inhibit CSF-1 signaling through cFMS kinase in normal and tumor cells in vivo makes GW2580 a useful tool in assessing the role of cFMS kinase in normal and disease processes.

A unique structure for epidermal growth factor receptor bound to GW572016 (Lapatinib): relationships among protein conformation, inhibitor off-rate, and receptor activity in tumor cells

GW572016 (Lapatinib) is a tyrosine kinase inhibitor in clinical development for cancer that is a potent dual inhibitor of epidermal growth factor receptor (EGFR, ErbB-1) and ErbB-2. We determined the crystal structure of EGFR bound to GW572016. The compound is bound to an inactive-like conformation of EGFR that is very different from the active-like structure bound by the selective EGFR inhibitor OSI-774 (Tarceva) described previously. Surprisingly, we found that GW572016 has a very slow off-rate from the purified intracellular domains of EGFR and ErbB-2 compared with OSI-774 and another EGFR selective inhibitor, ZD-1839 (Iressa). Treatment of tumor cells with these inhibitors results in down-regulation of receptor tyrosine phosphorylation. We evaluated the duration of the drug effect after washing away free compound and found that the rate of recovery of receptor phosphorylation in the tumor cells reflected the inhibitor off-rate from the purified intracellular domain. The slow off-rate of GW572016 correlates with a prolonged down-regulation of receptor tyrosine phosphorylation in tumor cells. The differences in the off-rates of these drugs and the ability of GW572016 to inhibit ErbB-2 can be explained by the enzyme-inhibitor structures.

A simple method for predicting serum protein binding of compounds from IC 50 shift analysis for in vitro assays

The shift in apparent IC(50) that attends addition of serum proteins to in vitro cellular, enzymatic, and receptor binding assays can be used to determine the dissociation constant for compound-serum protein complexes. We show here that a simple linear relationship exists between the apparent IC(50) in the presence of serum protein and the inverse of the apparent K(d) for the compound-serum protein complex. Using a series of cell-active kinase inhibitors we demonstrate that the K(d) value derived in this way can be used to predict the extent of protein binding in serum for various compounds. This method should provide a simple means of assessing the relative serum protein binding propensity of compounds early in the compound optimization phase of drug discovery campaigns.

Discovery and biological evaluation of potent dual ErbB-2/EGFR tyrosine kinase inhibitors: 6-thiazolylquinazolines

We have identified a novel class of 6-thiazolylquinazolines as potent and selective inhibitors of both ErbB-2 and EGFR tyrosine kinase activity, with IC(50) values in the nanomolar range. These compounds inhibited the growth of both EGFR (HN5) and ErbB-2 (BT474) over-expressing human tumor cell lines in vitro. Using xenograft models of the same cell lines, we found that the compounds given orally inhibited in vivo tumor growth significantly compared with control animals.

Anti-tumor activity of GW572016: a dual tyrosine kinase inhibitor blocks EGF activation of EGFR/erbB2 and downstream Erk1/2 and AKT pathways

Dual EGFR/erbB2 inhibition is an attractive therapeutic strategy for epithelial tumors, as ligand-induced erbB2/EGFR heterodimerization triggers potent proliferative and survival signals. Here we show that a small molecule, GW572016, potently inhibits both EGFR and erbB2 tyrosine kinases leading to growth arrest and/or apoptosis in EGFR and erbB2-dependent tumor cell lines. GW572016 markedly reduced tyrosine phosphorylation of EGFR and erbB2, and inhibited activation of Erk1/2 and AKT, downstream effectors of proliferation and cell survival, respectively. Complete inhibition of activated AKT in erbB2 overexpressing cells correlated with a 23-fold increase in apoptosis compared with vehicle controls. EGF, often elevated in cancer patients, did not reverse the inhibitory effects of GW572016. These observations were reproduced in vivo, where GW572016 treatment inhibited activation of EGFR, erbB2, Erk1/2 and AKT in human tumor xenografts. Erk1/2 and AKT represent potential biomarkers to assess the clinical activity of GW572016. Inhibition of activated AKT in EGFR or erbB2-dependent tumors by GW572016 may lead to tumor regressions when used as a monotherapy, or may enhance the anti-tumor activity of chemotherapeutics, since constitutive activation of AKT has been linked to chemo-resistance.

The effects of the novel, reversible epidermal growth factor receptor/ErbB-2 tyrosine kinase inhibitor, GW2016, on the growth of human normal and tumor-derived cell lines in vitro and in vivo

The epidermal growth factor receptor (EGFR) and ErbB-2 transmembrane tyrosine kinases are currently being targeted by various mechanisms in the treatment of cancer. GW2016 is a potent inhibitor of the ErbB-2 and EGFR tyrosine kinase domains with IC50 values against purified EGFR and ErbB-2 of 10.2 and 9.8 nM, respectively. This report describes the efficacy in cell growth assays of GW2016 on human tumor cell lines overexpressing either EGFR or ErbB-2: HN5 (head and neck), A-431 (vulva), BT474 (breast), CaLu-3 (lung), and N87 (gastric). Normal human foreskin fibroblasts, nontumorigenic epithelial cells (HB4a), and nonoverexpressing tumor cells (MCF-7 and T47D) were tested as negative controls. After 3 days of compound exposure, average IC50 values for growth inhibition in the EGFR- and ErbB-2-overexpressing tumor cell lines were < 0.16 microM. The average selectivity for the tumor cells versus the human foreskin fibroblast cell line was 100-fold. Inhibition of EGFR and ErbB-2 receptor autophosphorylation and phosphorylation of the downstream modulator, AKT, was verified by Western blot analysis in the BT474 and HN5 cell lines. As a measure of cytotoxicity versus growth arrest, the HN5 and BT474 cells were assessed in an outgrowth assay after a transient exposure to GW2016. The cells were treated for 3 days in five concentrations of GW2016, and cell growth was monitored for an additional 12 days after removal of the compound. In each of these tumor cell lines, concentrations of GW2016 were reached where outgrowth did not occur. Furthermore, growth arrest and cell death were observed in parallel experiments, as determined by bromodeoxyuridine incorporation and propidium iodide staining. GW2016 treatment inhibited tumor xenograft growth of the HN5 and BT474 cells in a dose-responsive manner at 30 and 100 mg/kg orally, twice daily, with complete inhibition of tumor growth at the higher dose. Together, these results indicate that GW2016 achieves excellent potency on tumor cells with selectivity for tumor versus normal cells and suggest that GW2016 has value as a therapy for patients with tumors overexpressing either EGFR or ErbB-2.

The characterization of novel, dual ErbB-2/EGFR, tyrosine kinase inhibitors: potential therapy for cancer

The type I receptor tyrosine kinases constitute a family of transmembrane proteins involved in various aspects of cell growth and survival and have been implicated in the initiation and progression of several types of human malignancies. The best characterized of these proteins are the epidermal growth factor receptor (EGFR) and ErbB-2 (HER-2/neu). We have developed potent quinazoline and pyrido-[3,4-d]-pyrimidine small molecules that are dual inhibitors of ErbB-2 and EGFR. The compounds demonstrate potent in vitro inhibition of the ErbB-2 and EGFR kinase domains with IC(50)s <80 nM. Growth of ErbB-2- and EGFR-expressing tumor cell lines is inhibited at concentrations <0.5 microM. Selectivity for tumor cell growth inhibition versus normal human fibroblast growth inhibition ranges from 10- to >75-fold. Tumor growth in mouse s.c. xenograft models of the BT474 and HN5 cell lines is inhibited in a dose-responsive manner using oral doses of 10 and 30 mg/kg twice per day. In addition, the tested compounds caused a reduction of ErbB-2 and EGFR autophosphorylation in tumor fragments from these xenograft models. These data indicate that these compounds have potential use as therapy in the broad population of cancer patients overexpressing ErbB-2 and/or EGFR.

The formation of a covalent complex between a dipeptide ligand and the src SH2 domain

The X-ray crystal structure of the src SH2 domain revealed the presence of a thiol residue (Cys 188) located proximal to the phosphotyrosine portion of a dipeptide ligand. An aldehyde bearing ligand (1) was designed to position an electrophilic carbonyl group in the vicinity of the thiol. X-ray crystallographic and NMR examination of the complex formed between (1) and the src SH2 domain revealed a hemithioacetal formed by addition of the thiol to the aldehyde group with an additional stabilizing hydrogen bond between the acetal hydroxyl and a backbone carbonyl.

The production and characterization of murine monoclonal antibodies to human Gadd45 raised against a recombinant protein

The production of two different murine monoclonal antibodies to human Gadd45, a protein that is induced in response to DNA damage, is reported. Antibodies were generated in a SJL mouse using a recombinant form of the human Gadd45 protein. Monoclonal antibody 4TCYA1, which recognizes the denatured form of human Gadd45 in Western blots, was selected based upon the recognition of Gadd45 induced by functional p53 in the human myeloid leukemia cell line, ML-1. A second monoclonal antibody, designated 30T.14, immunoprecipitates native human Gadd45 in lysates produced from RKO cells, a colorectal carcinoma cell line that expresses relatively high basal levels of Gadd45, as well as from cell lysates made from ML-1 cells after exposure to ionizing irradiation (IR). Since 4TCYA1 fails to immunoprecipitate Gadd45, and 30T.14 fails to bind to IR-induced Gadd45 in immunoblotting, these two monoclonal antibodies probably recognize different epitopes.

Alterations in the localization of F-actin, fibronectin, and thrombospondin occur prior to neoplastic transformation in rat tracheal epithelial cells

Structural glycoproteins and cytoskeletal proteins play a major role in the regulation of cellular organization and function. Changes in the structure and function of these proteins are involved in the cascade of events which lead to neoplastic transformation. We evaluated RNA levels, protein localization, and organization of selected proteins in an in vitro model system of respiratory carcinogenesis to examine alterations in cell architecture. Localization of fibronectin (Fn), thrombospondin (Tsp), and F-actin was examined in (1) primary rat tracheal epithelial (RTE) cells; (2) spontaneously immortalized nonneoplastic cells (SPOC-1); and (3) neoplastic cells (EGV5T) derived from tumors arising following transplantation of an N-methyl-N'-nitro-N-nitrosoguanidine-transformed RTE cell line into nude mice. Proteins were stained with fluorescein-labeled antibodies or phalloidin compound and analysis was performed with a confocal laser scanning microscope. Primary RTE cells display organized F-actin stress fibers, perinuclear Fn and Tsp, and pericellular Fn in fibrillar arrays. In larger colonies, Tsp occurs between cells and occasionally in fibrillar arrays. SPOC-1 cells, unlike primary RTE cells and neoplastic EGV5T cells, seldom form junctions and exhibit few cell surface extensions. F-actin stress fibers are reduced in these immortalized cells. F-actin in SPOC-1 cells occurs in the perinuclear region, scattered diffusely throughout the cell and in punctate adhesions. Fn and Tsp are localized to the perinuclear region with Fn staining more intensely. EGV5T neoplastic cells also display a dramatic loss of stress fibers and F-actin is concentrated mainly near the cell periphery. Perinuclear staining of Fn and Tsp occurs in some cells within the colony. Levels of Tsp RNA and Fn RNA and protein are significantly reduced in both cell lines compared to primary RTE cells. We conclude that structural protein disruptions are early events in the transformation of these respiratory epithelial cells.

Epidermal growth factor dependence and TGF alpha autocrine growth regulation in primary rat tracheal epithelial cells

We have examined dependence of primary rat tracheal epithelial (RTE) on exogenous epidermal growth factor (EGF) and determined whether a TGF alpha autocrine pathway is operating in these cells. Primary RTE cells plated in serum free media (SFM) without EGF and bovine pituitary factor (BPE) show little proliferation compared to cultures propagated in media containing EGF/BPE (CSFM). Removal of EGF/BPE shortly after plating, however, results in significant proliferation, although plateau cell densities are reduced and cell morphology is significantly altered compared to cells propagated in CSFM. Addition of EGF and/or BPE to cultures propagated in SFM minus EGF/BPE restores maximum cell density. The concentration of TGF alpha peptide in media conditioned by cells propagated without EGF/BPE is lower than the concentration in the media of CSFM cultures. TGF alpha mRNA and protein levels are also significantly lower in cells late in culture compared to logarithmically growing cells regardless of the presence or absence of EGF/BPE. The proliferation of primary RTE cells propagated without EGF/BPE is inhibited by neutralizing TGF alpha antiserum and by a tyrphostin compound that blocks TGF alpha/EGF receptor tyrosine kinase activity. These results indicate that primary RTE cells utilize TGF alpha as an autocrine growth factor and that the autocrine pathway is regulated as a function of growth state of the cells. However, this pathway does not provide growth autonomy to primary RTE cells, since cultures remain dependent on exogenous EGF/BPE for sustained proliferation.

Altered growth factor dependence and transforming growth factor gene expression in transformed rat tracheal epithelial cells

The role of peptide growth factors in neoplastic progression of transformed rat tracheal epithelial (RTE) cells was assessed by examining growth factor requirements and expression of growth factor and growth factor receptor genes in normal and transformed RTE cells. Neoplastically transformed cell lines showed decreased requirements for bovine pituitary extract, insulin, and epidermal growth factor compared to normal primary RTE cells. Neoplastic RTE cell lines expressed significantly increased levels of transforming growth factor alpha (TGF alpha) RNA and secreted TGF alpha into the media, suggesting an autocrine role for this growth factor. Increased levels of TGF alpha RNA were also observed in the preneoplastic stages of the same cell lines, indicating that increased TGF alpha expression is an early event in the multistage process of neoplastic transformation of RTE cells. TGF beta transcripts were also overexpressed in neoplastically transformed cell lines. Our studies suggest that aberrant expression of growth factors may play an important role in the development and/or maintenance of the transformed phenotype in RTE cells.