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.

Indazolylamino quinazolines and pyridopyrimidines as inhibitors of the EGFr and c-erbB-2

Described herein is the design and synthesis of indazolylaminopyridopyrimidines and quinazolines as inhibitors of the class 1 tyrosine kinase receptor family. Data is presented for N(4)-(1-benzyl-1H-indazol-5-yl)-N(6),N(6)-dimethylpyrido[3,4-d]pyrimidine-4,6-diamine 3B. This compound inhibited EGFr and c-erbB-2 enzymes selectively over other kinases. It inhibited the proliferation of a range of tumour cell lines in vitro and the growth of BT474 xenografts in SCID mice.

Isolation and characterisation of a prenylated p-terphenyl metabolite of Aspergillus candidus possessing potent and selective cytotoxic activity; studies on mechanism of action

We describe the discovery and properties of a prenylated p-terphenyl metabolite of the fungus Aspergillus candidus. The compound (1) possesses potent cytotoxic activity against a range of tumour and other hyper-proliferative cell lines. Cell cycle analysis shows that in mouse keratinocyte (BALB/MK) cells treated with 1, the cell cycle is arrested in early S phase, indicative of an antimetabolite effect. Furthermore, cellular cytotoxicity can be reversed by addition of exogenous pyrimidine but not purine nucleosides to the cell culture medium. It is therefore likely that compound 1 selectively inhibits pyrimidine biosynthesis, and it is this property which accounts for its potent cytotoxic properties.

EGFR blockade by tyrosine kinase inhibitor or monoclonal antibody inhibits growth, directs terminal differentiation and induces apoptosis in the human squamous cell carcinoma HN5

Human squamous cell carcinomas frequently overexpress the epidermal growth factor receptor (EGFR) and this is often associated with poor prognosis in patients with these cancers. The high level of expression of the EGFR provides an important target for therapy and we and others have shown that monoclonal antibodies (mAbs) which block the activation of the receptor by the EGF family of ligands inhibit the growth of EGFR overexpressing tumours in vitro and induce the regression of established tumours grown as xenografts in athymic mice. Inhibitors of the tyrosine kinase associated with the EGFR have also been shown to block receptor activation and prevent tumour cell proliferation. Using the EGFR-overexpressing head and neck carcinoma cell line HN5, we have compared the biological consequences of treatment with an inhibitor of EGFR tyrosine kinase (PD153035) with anti-EGFR monoclonal antibodies (mAbs) ICR63 or ICR80. We found that both the anti-EGFR mAbs and the TK inhibitor produce similar biological changes namely, they inhibit the EGF and TGFá-induced tyrosine phosphorylation of the receptor and the growth in culture of HN5 cells. At concentrations above 100 nM, the TK inhibitor prevented the growth in culture of HN5 cells completely with an IC50 of 40 nM. With the anti-EGFR mAbs, growth of HN5 cells was inhibited completely at concentrations above 4 nM with an IC50 of 1 nM. More importantly we found that, like the anti-EGFR mAbs, treatment with the TK inhibitor directs HN5 cells to undergo terminal differentiation as monitored by the expression of cytokeratin 10. In addition, our results indicate that the growth inhibitory effects of the anti-EGFR agents also lead to induction of apoptosis as determined by 7-amino actinomycin D staining (7-AAD). We conclude that EGFR blockade by anti-EGFR mAbs or TK inhibitor influences the growth in culture of EGFR overexpressing tumours by directing terminal differentiation and inducing apoptosis.

Early elemental and ionic changes in cultured cells after stimulation with epidermal growth factor

Stimulation of A431 cells (a human vulval epidermal cell line) with 50 ng/ml of epidermal growth factor (EGF) in the presence of 1.7 mM extracellular calcium produced a sharp and sustained rise in intracellular ionic Ca2+, increased elemental Na, decreased K and a rise in Ca. In the absence of extracellular calcium, the initial Ca2+ rise remained but the sustained elevation of intracellular Ca2+ was abolished, Na and K fluxes were variable and the Ca did not change. Increased Na and decreased K was marked at 2 minutes and returned to the control value after 60 minutes. The increase in Ca was an early event. Cells stimulated with EGF showed a pronounced morphological disruption, especially the mitochondria. The response of NR6/SA3 and NR6/DC7 cells (genetically engineered rodent fibroblast cell lines) to EGF stimulation was higher than that of the A431 cells, as was the resting cytoplasmic Ca2+. Untreated NR6/SA3 and NR6/DC7 cells possessed an increased Na/K ratio when compared with A431 cells.

Monoclonal antibody targeting of methotrexate (MTX) against MTX-resistant tumour cell lines

Several Methotrexate (MTX)-resistant sublines of the osteogenic sarcoma cell line 791T were derived by continuous selection in the presence of MTX and 12-O-tetradecanoylphorbol-13-acetate (TPA). Studies including assays of the uptake and binding of [3H]MTX and fluoresceinated-MTX, determined that these sublines showed diminished MTX transport, and that none of them appeared to overproduce the MTX-target enzyme dihydrofolate reductase. Conjugates of the anti-791T monoclonal antibody 791T/36 linked to MTX via human serum albumin (HSA) were prepared by Dr M.C. Garnett. These were cytotoxic selectively for cells bearing the 791T/36-defined antigen (gp72), and were found to be as cytotoxic to most of the MTX-resistant 791T sublines as they were to parental 791T cells. Furthermore, an anti-MTX/anti-gp72 bispecific antibody 516 augmented the cytotoxicity of HSA-MTX conjugate to the MTX-resistant 791T variant R120 apparently as efficiently as for parental 791T cells. It is suggested that acquired drug resistance caused by deficient transport mechanisms may be partially or wholly overcome by targeting the drug to a readily-internalised cell surface antigen.

Efficacy and selectivity of monoclonal-antibody-targeted drugs and free methotrexate in fluorescence-labelled mixed tumour-cell monolayer cultures and multicellular spheroids

Free methotrexate (MTX) and 2 monoclonal antibody (MAb)-MTX conjugates were tested against mixed human tumour-cell cultures, in which 2 cell lines of differing antigenicity or drug sensitivity, pre-labelled with fluorescent dyes, were added together in microtitre wells. Conjugates were selectively cytotoxic for cells bearing high concentrations of the relevant antigen, and MTX was preferentially cytotoxic for wild-type cells rather than MTX-resistant variants when tested on separate cultures. In mixed cultures these selectivities were substantially retained, although there was a varying tendency towards intermediate cytotoxicity for each cell line of the pair. MTX was cytotoxic for cell line 79 IT grown as multicellular spheroids, but a MAb-MTX conjugate and a MAb-RTA immunotoxin showed little cytotoxicity against spheroids at the highest concentrations tested, although they were highly effective against monolayer cells. Mixed spheroids could be formed efficiently from most cell lines, although in some cases cell distribution was non-random. In mixed spheroids prepared between wild-type and MTX-resistant 79 IT variants, relative MTX sensitivities conformed broadly to those seen in separate monolayer cultures. Fluorescence-labelling was a reliable method for determining cell behaviour under the above conditions. We conclude that (a) selectivity of therapeutic agents in mixed cultures was partially, but not completely, impaired compared to that observed in separate cultures, and (b) that low Mr drugs are effective against 3-dimensional tumour-cell structures but antibody-targeted conjugates are not.