Discovery and preclinical pharmacology of a selective ATP-competitive Akt inhibitor (GDC-0068) for the treatment of human tumors

The discovery and optimization of a series of 6,7-dihydro-5H-cyclopenta[d]pyrimidine compounds that are ATP-competitive, selective inhibitors of protein kinase B/Akt is reported. The initial design and optimization was guided by the use of X-ray structures of inhibitors in complex with Akt1 and the closely related protein kinase A. The resulting compounds demonstrate potent inhibition of all three Akt isoforms in biochemical assays and poor inhibition of other members of the cAMP-dependent protein kinase/protein kinase G/protein kinase C extended family and block the phosphorylation of multiple downstream targets of Akt in human cancer cell lines. Biological studies with one such compound, 28 (GDC-0068), demonstrate good oral exposure resulting in dose-dependent pharmacodynamic effects on downstream biomarkers and a robust antitumor response in xenograft models in which the phosphatidylinositol 3-kinase-Akt-mammalian target of rapamycin pathway is activated. 28 is currently being evaluated in human clinical trials for the treatment of cancer.

Chk1 inhibition and Wee1 inhibition combine synergistically to impede cellular proliferation

Inhibition of the checkpoint kinase Chk1, both as a monotherapy and in combination with DNA damaging cytotoxics, is a promising therapeutic approach for the treatment of a wide array of human cancers. However, much remains to be elucidated in regard to the patient populations that will respond best to a Chk1 inhibitor and the optimal therapeutics to combine with a Chk1 inhibitor. In an effort to discover sensitizing mutations and novel combination strategies for Chk1 inhibition, an siRNA screen was performed in combination with the selective Chk1 inhibitor AR458323. This screen employed a custom made library of siRNAs targeting 195 genes, most of which are involved in cell-cycle control or DNA damage repair. One of the most prominent and consistent hits across runs of the screen performed in three different cancer cell lines was Wee1 kinase. MK-1775 is a small molecule inhibitor of Wee1 that is currently in early stage clinical trials. In confirmation of the results obtained from the siRNA screen, AR458323 and MK-1775 synergistically inhibited proliferation in multiple cancer cell types. This antiproliferative effect correlated with a synergistic induction of apoptosis. In cellular mechanistic studies, the combination of the two molecules resulted in dramatic decreases in inhibitory phosphorylation of cyclin-dependent kinases, an increase in DNA damage, alterations in cell-cycle profile, and collapse of DNA synthesis. In conclusion, the clinical combination of a Chk1 inhibitor and a Wee1 inhibitor holds promise as an effective treatment strategy for cancer.

Pyrazolopyridine Inhibitors of B-Raf(V600E). Part 1: The Development of Selective, Orally Bioavailable, and Efficacious Inhibitors

The V600E mutation of B-Raf kinase results in constitutive activation of the MAPK signaling pathway and is present in approximately 7% of all cancers. Using structure-based design, a novel series of pyrazolopyridine inhibitors of B-Raf(V600E) was developed. Optimization led to the identification of 3-methoxy pyrazolopyridines 17 and 19, potent, selective, and orally bioavailable agents that inhibited tumor growth in a mouse xenograft model driven by B-Raf(V600E) with no effect on body weight. On the basis of their in vivo efficacy and preliminary safety profiles, 17 and 19 were selected for further preclinical evaluation.

Abstract 2939: Chk1 inhibition and Wee1 inhibition combine synergistically to inhibit cellular proliferation

Inhibition of the checkpoint kinase Chk1, both as a monotherapy and in combination with DNA damaging cytotoxics, is a promising therapeutic strategy for human cancer. However, much remains to be learned in regard to the patient populations that will respond best to a Chk1 inhibitor and the optimal therapeutics to combine with a Chk1 inhibitor. In an effort to discover sensitizing mutations and novel combination strategies for Chk1 inhibition, we performed a synthetic lethality siRNA screen with the selective Chk1 inhibitor Chk1-A. This screen employed a custom made library of siRNAs against 197 genes (3 siRNAs per gene), most of which are involved in cell-cycle control or DNA damage repair. One of the most prominent and consistent hits across runs of the screen performed in PC3, LNCaP, and A549 cell lines was Wee1 kinase. MK-1775 is a small molecule inhibitor of Wee1 that is currently in early stage clinical trials. In confirmation of the results obtained from the siRNA screen, we found that Chk1-A and MK-1775 synergistically inhibited proliferation in multiple cell types. The combination of the two molecules resulted in up to a 5-fold enhancement of anti-proliferative activity compared to what would be expected from pure additivity. This anti-proliferative synergy correlated with a synergistic induction of apoptosis. We explored the mechanism of the impressive synergy by examining the cellular and biochemical effects of the Chk1-A and MK-1775 combination. We found that co-treatment with the two inhibitors resulted in dramatic decreases in inhibitory phosphorylation of cyclin-dependent kinases 1 and 2, increases in DNA damage, and the collapse of DNA replication. In conclusion, the combination of a Chk1 inhibitor and a Wee1 inhibitor may be an effective treatment strategy for cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2939. doi:10.1158/1538-7445.AM2011-2939

Microautoradiographic quantitation of vascular endothelial growth factor mRNA levels in human prostate specimens containing normal and neoplastic epithelium

Human prostate specimens commonly contain a spectrum of epithelial changes, including normal acinar and ductal structures, hyperplasia, intraepithelial neoplasia (dysplasia), and carcinoma. Since vascular endothelial growth factor (VEGF) expression is dependent on cell type and tissue microenvironment, meaningful quantitation of the levels of this mRNA in pathological specimens requires analysis at the microscopic level. Phosphorimage analysis of the binding of radiolabeled cRNA probes to tissue sections allows quantitation of mRNA levels, but the resolution is limited. Alternatively, emulsion autoradiography allows visualization of mRNA levels at cellular resolution, but quantitation is difficult. We have developed a method of quantitating steady state mRNA levels in tissue sections at the microscopic level, using autoradiography and quantitative image analysis. In this study, we describe the method and apply it to quantitation of VEGF mRNA in human prostate specimens. The VEGF mRNA level was low in nonepithelial stromal tissue (0.8 dpm/mm2), high in normal and benign hyperplastic epithelium (17-18 dpm/mm2), and significantly decreased in intraepithelial neoplasia (6.4 dpm/mm2) and in microacinar carcinoma that had invaded the stroma (3.5 dpm/mm2). Immunohistochemical staining detected VEGF protein in epithelial and stromal cells, with highest levels on the luminal surface of normal epithelium and in stromal cells, and lower levels in benign hyperplasia, intraepithelial neoplasia, and carcinoma. No correlation between VEGF expression in epithelium and nearby vessel density was observed. The results indicate a decrease in the steady state level of VEGF mRNA when prostate epithelial cells become transformed, escape the confines of glandular structure and invade the stroma, and suggest that the progression of prostatic carcinoma through the stages examined in this study is not associated with increased VEGF expression, in contrast to the elevated VEGF expression associated with progression of several other tumor types.

Decreased vascular endothelial growth factor expression associated with tumor regression induced by (E)-2'-deoxy-2'-(fluoromethylene)cytidine (MDL 101,731)

The effect of the antitumor drug MDL 101,731 [(E)-2'-deoxy-2'-(fluoromethylene)cytidine] on tumor growth and on steady-state vascular endothelial growth factor (VEGF) mRNA levels in MDA-MB-231, PC-3, MCF-7, and HT-29 human tumor xenografts grown in nude mice was examined, using quantitative in situ hybridization. MDL 101,731 caused regression of MDA-MB-231 and PC-3 tumor xenografts, but only inhibition of growth (without regression) of MCF-7 xenografts. The drug caused inhibition of growth of HT-29 xenografts at low doses, and regression at high doses. When treatment with MDL 101,731 led to tumor regression, VEGF mRNA levels were decreased. When treatment led only to inhibition of growth, there was no significant change in VEGF mRNA. Further examination of the tumor xenografts revealed that elevated VEGF mRNA was associated with hypoxic zones surrounding areas of necrosis in the tumors, and that the drop in VEGF mRNA observed in tumors from mice treated with MDL 101,731 correlated with a loss of zones of necrosis. In contrast, treatment with cisplatin led to either an increase (PC-3) or no change (MDA-MB-231) in VEGF mRNA levels, and no loss of necrotic zones. Quantitative analysis of changes in VEGF mRNA levels was supported by immunohistochemical analysis of VEGF protein in the same tumor specimens. In vitro, MDL 101,731 was a potent inhibitor of VEGF secretion in cells exposed to hypoxia, whereas there was no effect of cisplatin on VEGF secretion by three of the four cell lines tested. These findings suggest that inhibition of VEGF expression by MDL 101,731 may distinguish this compound from other classes of cytotoxic agents, such as cisplatin.

Quantitation of vascular endothelial growth factor mRNA levels in human breast tumors and metastatic lymph nodes

In situ hybridization analysis provides a means to qualitatively study the heterogeneity of primary tumors and metastases based on the types of genes transcribed. In this study, we have tested some parameters for quantitative analysis of in situ hybridizations with paraffin-embedded human breast tumors and measured mRNA levels for the angiogenic protein, vascular endothelial growth factor (VEGF). VEGF mRNAs were highly tumor specific, with the highest levels near necrotic regions within the tissues (0.1 to 2.7 dpm/mm2). Normal cells within the tissue sections did not have detectable levels of VEGF mRNA. For comparison, tumor levels of c-myc (4 to 46 dpm/mm2) and glyceraldehyde-3-phosphate dehydrogenase mRNAs (48 to 214 dpm/mm2) were measured. The mRNAs for both of these genes were more broadly expressed across the tissue sections. The hybridization pattern for VEGF mRNAs was consistent with hypoxia-induced VEGF mRNA steady-state levels and supports the hypothesis that oxidative stress regulates VEGF expression in breast tumors.

Proliferation- and cell cycle-dependent differences in expression of the 170 kilodalton and 180 kilodalton forms of topoisomerase II in NIH-3T3 cells

The cellular content of 170kD and 180kD topoisomerase II was studied as a function of the proliferation state and cell cycle position in NIH-3T3 cells. When the cells were synchronized by serum starvation and then stimulated to enter the cell cycle by addition of fresh growth medium, the amount of 170kD topoisomerase II present was undetectable until the cells reached late S phase, peaked in G2-M phase cells, and decreased as the cells completed mitosis. The amount of 180kD topoisomerase II was constant once the cells entered the cell cycle. When exponentially growing cells were induced to enter G0 by serum starvation, the amount of 170kD topoisomerase II decreased in parallel with the loss of cells from the S and G2-M phases of the cell cycle and was undetectable once all of the cells reached G0. In contrast, the 180kD enzyme was still present after all of the cells had entered G0. The tightness of association of the two enzymes with chromatin was measured by determining the concentration of salt required to extract them from isolated nuclei. The 180kD enzyme required a higher concentration of NaCl for extraction than did the 170kD enzyme. The different patterns of expression of the two forms of topoisomerase II suggest that they perform different functions in cells.

Inhibition of endothelin-mediated topoisomerase I activation by pertussis toxin

Cultured rat mesangial cells contain high affinity endothelin (ET) receptors at high densities. Exposure of these cells to ET resulted in a transient activation of topoisomerase I extractable activity, which reached its maximum value at approximately 2 min and returned to basal value after approximately 10 min of treatment. The activation of this enzyme was dependent upon the concentration of ET added. Incubation of the cells with pertussis toxin inhibited ET-induced increases in topoisomerase I activity in a concentration-dependent manner, suggesting that involvement of pertussis toxin-sensitive GTP-binding protein in ET-mediated action. Endothelin had no detectable effect upon extractable topoisomerase II activity.

Development of a stable camptothecin-resistant subline of P388 leukemia with reduced topoisomerase I content

A camptothecin-resistant subline of P388 leukemia (P388/CPT) was developed by repeated transplantation of P388 cells in mice treated with therapeutic doses of camptothecin. In mice bearing the resistant tumor, a maximally tolerated dose of camptothecin produced no net reduction in tumor cell burden, in contrast to a 5-log cell kill in the parental P388 (P388/S). The IC50 of camptothecin, as determined by colony formation assays of cultured cells, was 8 times greater for the cloned P388/CPT cell line than for P388/S. P388/CPT cells were not cross-resistant to other antineoplastic agents, including topoisomerase II inhibitors. The type I topoisomerases purified from P388/CPT and P388/S cells were identical with respect to molecular weight, specific activity, in vitro camptothecin sensitivity, and DNA cleavage specificity. Camptothecin induced fewer protein-associated DNA single-strand breaks in the resistant cells than in the wild-type P388 cells. Topoisomerase I mRNA, immunoreactivity, and extractable enzymatic activity were 2-4 times lower for P388/CPT cells than for P388/S cells. As resistance to camptothecin developed, topoisomerase I extractable activity decreased, concomitant with an increase in topoisomerase II extractable activity. Furthermore, the appearance of camptothecin resistance was associated with specific rearrangements of the topoisomerase I gene. These results suggest that development of resistance to inhibitors of topoisomerase I can occur by down-regulation of the target enzyme, thus reducing the production of lethal enzyme-mediated DNA damage. The enhanced topoisomerase II activity in these cells suggests that resistance to camptothecin may be overcome by co-treatment with topoisomerase II inhibitors.

Differences between normal and ras-transformed NIH-3T3 cells in expression of the 170kD and 180kD forms of topoisomerase II

The activity of topoisomerase II and the cellular content of the 170kD and 180kD forms of the enzyme were studied as functions of transformation and growth state by using normal and ras-transformed NIH-3T3 cells. Total topoisomerase II activity, as measured by the unknotting of P4 DNA, was higher in ras-transformed than in normal cells in similar growth states, and was higher in exponentially growing than in plateau cells for both cell lines. Total topoisomerase II levels, as measured by immunoblotting, showed a similar dependence on transformation and growth state. The relative amounts of the 170kD and 180kD forms of the enzyme varied as a function of transformation and growth state. The proportion of 170kD topoisomerase II was higher in ras-transformed than in untransformed cells and depended much less on growth state in the ras-transformed cells. The topoisomerase II activity in extracts of ras-transformed cells was more sensitive to inhibition by teniposide and merbarone, drugs which selectively inhibit the 170kD form of topoisomerase II. The ras-transformed cells were also more sensitive to the cytotoxic effects of these drugs. An increase in the relative cellular content of 170kD topoisomerase II is characteristic of ras-transformed 3T3 cells, and the levels of this form of the enzyme appear to be less dependent on proliferation state than in untransformed cells. The susceptibility of certain tumors to killing by topoisomerase II-directed drugs may be due to a higher proportion of 170kD enzyme as well as a higher level of total topoisomerase II activity.

The effect of lithium on the membrane molecular dynamics of normal human erythrocytes

Erythrocytes from normal adults with no personal or family history of bipolar affective disorder were analyzed by fluorescence spectroscopy to determine what effect, if any, acute in vitro incubation with lithium had on erythrocyte membrane dynamics. The effects on erythrocyte membrane molecular dynamics of varying concentrations of Li2CO3 (0.25-2.0 meq/liter), varying incubation temperatures (25-40 degrees C), and varying incubation times (5-185 min) were investigated. Following incubation with Li2CO3, the erythrocytes were labeled with either 4-phenylspiro-[furan-2(3H),--1'phthalan]--3,3'-dione (fluorescamine), which binds to membrane surface primary amines, or 12(9)anthroyl stearate [12(9)AS], which inserts deep in the membrane hydrocarbon core. The membrane molecular dynamics were then determined by fluorescence anisotropy measurements. These studies demonstrate that clinically relevant concentrations of Li+ incubated with intact normal human erythrocytes significantly alters molecular dynamics on the erythrocyte membrane surface, with less striking changes in the hydrocarbon core. A possible interpretation of these findings is that hydrated Li+ alters the electrostatic interaction of membrane surface molecules, as well as the surrounding solvent (water) structure, with a resultant increase in the molecular motion of these molecules. Alterations in membrane receptor motion could potentially alter receptor functional activity. If similar motional alterations were to occur in the interior of a membrane channel, such as an ionophore, the functional activity of the channel could also be potentially altered. These findings provide additional insight into possible biological actions of Li+, as well as potential molecular alterations in bipolar affective disorder erythrocytes.