Dissecting mechanisms of resistance to targeted drug combination therapy in human colorectal cancer.

Genomic alterations in cancer cells result in vulnerabilities that clinicians can exploit using molecularly targeted drugs, guided by knowledge of the tumour genotype. However, the selective activity of these drugs exerts an evolutionary pressure on cancers that can result in the outgrowth of resistant clones. Use of rational drug combinations can overcome resistance to targeted drugs, but resistance may eventually develop to combinatorial therapies. We selected MAPK- and PI3K-pathway inhibition in colorectal cancer as a model system to dissect out mechanisms of resistance. We focused on these signalling pathways because they are frequently activated in colorectal tumours, have well-characterised mutations and are clinically relevant. By treating a panel of 47 human colorectal cancer cell lines with a combination of MEK- and PI3K-inhibitors, we observe a synergistic inhibition of growth in almost all cell lines. Cells with KRAS mutations are less sensitive to PI3K inhibition, but are particularly sensitive to the combined treatment. Colorectal cancer cell lines with inherent or acquired resistance to monotherapy do not show a synergistic response to the combination treatment. Cells that acquire resistance to an MEK-PI3K inhibitor combination treatment still respond to an ERK-PI3K inhibitor regimen, but subsequently also acquire resistance to this combination treatment. Importantly, the mechanisms of resistance to MEK and PI3K inhibitors observed, MEK1/2 mutation or loss of PTEN, are similar to those detected in the clinic. ERK inhibitors may have clinical utility in overcoming resistance to MEK inhibitor regimes; however, we find a recurrent active site mutation of ERK2 that drives resistance to ERK inhibitors in mono- or combined regimens, suggesting that resistance will remain a hurdle. Importantly, we find that the addition of low concentrations of the BCL2-family inhibitor navitoclax to the MEK-PI3K inhibitor regimen improves the synergistic interaction and blocks the acquisition of resistance.

Discovery of potent, orally bioavailable, small-molecule inhibitors of WNT signaling from a cell-based pathway screen.

WNT signaling is frequently deregulated in malignancy, particularly in colon cancer, and plays a key role in the generation and maintenance of cancer stem cells. We report the discovery and optimization of a 3,4,5-trisubstituted pyridine 9 using a high-throughput cell-based reporter assay of WNT pathway activity. We demonstrate a twisted conformation about the pyridine-piperidine bond of 9 by small-molecule X-ray crystallography. Medicinal chemistry optimization to maintain this twisted conformation, cognisant of physicochemical properties likely to maintain good cell permeability, led to 74 (CCT251545), a potent small-molecule inhibitor of WNT signaling with good oral pharmacokinetics. We demonstrate inhibition of WNT pathway activity in a solid human tumor xenograft model with evidence for tumor growth inhibition following oral dosing. This work provides a successful example of hypothesis-driven medicinal chemistry optimization from a singleton hit against a cell-based pathway assay without knowledge of the biochemical target.

Dual targeting of ErbB2 and MUC1 in breast cancer using chimeric antigen receptors engineered to provide complementary signaling.

PURPOSE: Chimeric antigen receptor (CAR) engineered T-cells occupy an increasing niche in cancer immunotherapy. In this context, CAR-mediated CD3ζ signaling is sufficient to elicit cytotoxicity and interferon-γ production while the additional provision of CD28-mediated signal 2 promotes T-cell proliferation and interleukin (IL)-2 production. This compartmentalisation of signaling opens the possibility that complementary CARs could be used to focus T-cell activation within the tumor microenvironment. METHODS: Here, we have tested this principle by co-expressing an ErbB2- and MUC1-specific CAR that signal using CD3ζ and CD28 respectively. Stoichiometric co-expression of transgenes was achieved using the SFG retroviral vector containing an intervening Thosea asigna peptide. RESULTS: We found that "dual-targeted" T-cells kill ErbB2(+) tumor cells efficiently and proliferate in a manner that requires co-expression of MUC1 and ErbB2 by target cells. Notably, however, IL-2 production was modest when compared to control CAR-engineered T-cells in which signaling is delivered by a fused CD28 + CD3ζ endodomain. CONCLUSIONS: These findings demonstrate the principle that dual targeting may be achieved using genetically targeted T-cells and pave the way for testing of this strategy in vivo.

Silencing of HSP90 cochaperone AHA1 expression decreases client protein activation and increases cellular sensitivity to the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin.

AHA1 (activator of HSP90 ATPase) is a cochaperone of the ATP-dependent molecular chaperone, HSP90, which is involved in the maturation, stabilization/degradation, and function of oncogenic proteins. HSP90 operates in a multimeric complex driven by the binding and hydrolysis of ATP. Treatment of cells with the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) results in the degradation of client proteins via the ubiquitin-proteasome pathway. As AHA1 increases the ATPase activity of HSP90, we hypothesized that modulation of AHA1 expression could influence the activity of client proteins and/or the cellular response to 17-AAG. We show that the basal expression of AHA1 is different across a panel of human cancer cell lines, and that treatment with 17-AAG resulted in sustained AHA1 up-regulation. Increasing the expression of AHA1 did not affect the sensitivity to 17-AAG, but did increase C-RAF activity and the levels of phosphorylated MEK1/2 and ERK1/2 without affecting total levels of these proteins or of client proteins C-RAF, ERBB2, or CDK4. Conversely, small interfering RNA-selective knockdown of >80% of AHA1 expression decreased C-RAF activity and reduced the levels of MEK1/2 and ERK1/2 phosphorylation. Moreover, the AHA1 knockdown resulted in a significant (P < 0.05) increase in sensitivity to 17-AAG, due in part to a 2- to 3-fold increase in apoptosis. These results show that the reduction of AHA1 levels could decrease the phosphorylation of key signal transduction proteins, and for the first time, separate the activation and stabilization functions of HSP90. Furthermore, AHA1 knockdown could sensitize cancer cells to 17-AAG. We conclude that modulation of AHA1 might be a potential therapeutic strategy to increase sensitivity to HSP90 inhibitors.

Micro parallel liquid chromatography: enabling technology for discovery analytical chemistry.

Since the introduction of combinatorial chemistry, compound libraries have undergone a significant increase in size and diversity. The ensuing expansion and diversification of compound libraries have resulted in increased demand for analytical throughput. Following the evolution of new technologies for generating lead compounds and targets and the desire to increase research and development productivity, analytical chemistry is now gaining attention as a bottleneck that would benefit from advances in instrumentation for increased analytical throughput. The commercial introduction of the Veloce trade mark micro parallel liquid chromatography system from Nanostream offers discovery analytical chemists the capability to analyze 24 samples in parallel with as little as 0.5 microl of sample. The system offers a scalable analytical approach to address bottlenecks in historically underserved areas, such as compound library purity screening, as well as higher value-added applications, such as log P determination and aqueous solubility assessment. This article describes the Veloce system and presents representative data from several discovery analytical applications.

Nursing workforce supply data trends in Hawaii.

Surveys of the nursing workforce in Hawaii over the last six years point to an increasing shortage of nurses. Data trends reveal a nursing workforce that is older than the rest of the U.S. with more ethnic and gender diversity. Strategies are needed to ensure adequate numbers and levels of nurses to meet the health care needs of the people of Hawaii.

Viral delivery of P450 reductase recapitulates the ability of constitutive overexpression of reductase enzymes to potentiate the activity of mitomycin C in human breast cancer xenografts.

Indolequinones such as mitomycin C (MMC) require enzymatic bioreduction to yield cytotoxic moieties. An attractive approach to overcome the potential variability in reductive bioactivation between tumors is to exploit specific enzyme-bioreductive drug combinations in an enzyme-directed gene therapy (GDEPT) approach. To this end, human breast cancer cell lines (T47D, MDA468, and MDA231) that overexpress either DT-diaphorase (DTD) or NADPH:cytochrome P450 reductase (P450R) have been developed. Cytotoxicity of MMC was evaluated in the panel of cell lines following aerobic or anoxic exposure in vitro. DTD and/or P450R overexpression sensitized cells to MMC in air with no further increase in the cytotoxicity of MMC under anoxia. The most profound effect was seen in the MDA468 cells, where a 27-fold increase in potency was observed for MMC in the DTD-overexpressing cell line. The MMC sensitization achieved through DTD and P450R overexpression in MDA468 cells was maintained in vivo. Xenografts established from the clonal lines exhibited significant tumor control following MMC treatment (treated/control [T/C] 17% and 51% for DTD and P450R xenografts, respectively) that was not seen in wild-type tumors (T/C 102%). Delivery of a clinically relevant adenoviral vector encoding P450R to MDA468 wild-type tumors yielded comparable P450R activity to that seen in the P450R clonal xenografts and resulted in greater MMC sensitization (T/C 46%). The model systems developed will facilitate the identification of novel indolequinone agents that are targeted toward a specific enzyme for bioactivation and are consequently of potential use in a GDEPT approach.

Overexpression of BclXL in a human ovarian carcinoma cell line: paradoxic effects on chemosensitivity in vitro versus in vivo.

The effect of overexpressing the antiapoptotic protein BclXL in a human ovarian carcinoma cell line has been investigated in terms of sensitivity to the 2 major drugs used to treat this disease, paclitaxel and cisplatin. Stable transfection of BclXL into CH1 cells, which are relatively sensitive to cisplatin, resulted in around 2.7-fold higher expression in comparison with empty vector controls. However, this level of overexpression did not result in significant resistance in vitro to paclitaxel or cisplatin at the 50% inhibition level, using either short-term (4-day) growth inhibition or longer term colony-forming assays. By contrast, parallel subcutaneous xenograft models of these isogenic ovarian carcinoma cells in vivo, differing only in BclXL status, showed that this low-level BclXL overexpression conferred significant resistance to both paclitaxel and cisplatin in comparison with parent, nontransfected tumours. Whereas parent non-BclXL transfected tumours were highly responsive, with the disappearance of tumours for at least 50 days post treatment, tumours overexpressing BclXL grew back after 30 and 20 days after treatment with paclitaxel and cisplatin, respectively. These differences in responsiveness to paclitaxel in vivo were not attributable to any significant changes in the delivery of drug to the tumour. These data suggest that the responsiveness of ovarian cancer to paclitaxel and cisplatin in vivo, and therefore perhaps clinically, is influenced by levels of the antiapoptotic protein BclXL. Such effects may be missed in vitro when using short-term growth inhibition or clonogenic assays.