Cetuximab is a monoclonal antibody that targets the human epidermal growth factor receptor (EGFR). Although approved for use in EGFR-overexpressing advanced colorectal cancer, recent studies have shown a lack of association between EGFR overexpression and cetuximab response, requiring the identification of novel biomarkers predictive of response to this agent. To do so, 22 colon cancer cell lines were screened for cetuximab response in vitro and sensitive and resistant lines were identified. In sensitive cell lines, cetuximab induced a G 0 -G 1 arrest without inducing apoptosis. Notably, cetuximabsensitive but not cetuximab-resistant cell lines were preferentially responsive to EGF-stimulated growth. Whereas neither EGFR protein/mRNA expression nor gene copy number correlated with cetuximab response, examination of the mutation status of signaling components downstream of EGFR showed that cell lines with activating PIK3CA mutations or loss of PTEN expression (PTEN null) were more resistant to cetuximab than PIK3CA wild type (WT)/PTENexpressing cell lines (14 F 5.0% versus 38.5 F 6.4% growth inhibition, mean F SE; P = 0.008). Consistently, PIK3CA mutant isogenic HCT116 cells showed increased resistance to cetuximab compared with PIK3CA WT controls. Furthermore, cell lines that were PIK3CA mutant/PTEN null and Ras/BRAF mutant were highly resistant to cetuximab compared with those without dual mutations/PTEN loss (10.8 F 4.3% versus 38.8 F 5.9% growth inhibition, respectively; P = 0.002), indicating that constitutive and simultaneous activation of the Ras and PIK3CA pathways confers maximal resistance to this agent. A priori screening of colon tumors for PTEN expression status and PIK3CA and Ras/BRAF mutation status could help stratify patients likely to benefit from this therapy.

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Phosphorylation of Bcl-2 protein is a post-translational modification of unclear functional consequences. We studied the correlation between Bcl-2 phosphorylation, mitotic arrest, and apoptosis induced by the antitubulin agent paclitaxel. Continuous exposure of human cervical carcinoma HeLa cells to 50 ng/ml paclitaxel resulted in mitotic arrest with a symmetrical bell-shaped curve over time. The number of mitotic cells was highest at 24 h (82%), then declined as arrested cells progressed into apoptosis, and barely no mitotic cells were present at 48 -60 h. The time curves of paclitaxel-induced cyclin B1 accumulation and stimulation of Cdc2/cyclin B1 kinase activity were identical and superimposable to that of M phase arrest. In contrast, apoptosis was first detected at 12 h and steadily increased thereafter until the termination of the experiments at 48 -60 h, when about 80 -96% of cells were apoptotic. Bcl-2 phosphorylation was closely associated in time with M phase arrest, accumulation of cyclin B1, and activation of Cdc2/cyclin B1 kinase, but not with apoptosis. At 24 h, when about 82% of the cells were in mitosis, almost all Bcl-2 protein was phosphorylated, whereas at 48 h, when 70 -90% of the cells were apoptotic, all Bcl-2 protein was unphosphorylated. Similar results were obtained with SKOV3 cells, indicating that the association of paclitaxel-induced M phase arrest and Bcl-2 phosphorylation is not restricted to HeLa cells. We used short exposure to nocodazole and double thymidine to synchronize HeLa cells and investigate the association of Bcl-2 phosphorylation with mitosis. These studies demonstrated that Bcl-2 phosphorylation occurs in tight association with the number of mitotic cells in experimental conditions that do not lead to apoptosis. However, a continuous exposure to nocodazole resulted in a pattern of Bcl-2 phosphorylation, M phase arrest, and apoptosis similar to that observed with paclitaxel. The phosphatase inhibitor okadaic acid was found to inhibit the dephosphorylation of phosphorylated Bcl-2 and to delay the progression of nocodazole M phase-arrested cells into interphase. In contrast, the serine/threonine kinase inhibitor staurosporine, but not the tyrosine kinase inhibitor genistein, led to rapid dephosphorylation of phosphorylated Bcl-2 and accelerated the progression of nocodazole M phase-arrested cells into interphase. Immune complex kinase assays in cell-free systems demonstrated that Bcl-2 protein can be a substrate of Cdc2/ cyclin B1 kinase isolated from paclitaxel-treated cells arrested in M phase. Taken together, these studies suggest that Bcl-2 phosphorylation is tightly associated with mitotic arrest and fail to demonstrate that it is a determinant of progression into apoptosis after mitotic arrest induced by anti-tubulin agents.Apoptosis is controlled by a complex interplay between regulatory proteins (1). Bcl-2, a 26-kDa integral membrane oncoprotein, was the first anti-apoptosis gene product discovered (2). Several reports have demonstrated that overexpression of Bcl-...

Purpose: This study was undertaken to select the optimal combination schedule of erlotinib and pemetrexed for the treatment of relapsed non^small cell lung cancer (NSCLC) using a panel of human NSCLC lines. Experimental Design: Human NSCLC cell lines, with variable expression of the known molecular determinants of erlotinib sensitivity, were exposed to pemetrexed and erlotinib using different schedules. Antitumor effect was measured by growth inhibition by cell count and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, cell cycle distribution and apoptosis by flow cytometry, and expression of cell cycle mediators by immunoblots. The cytotoxic interaction between pemetrexed and erlotinib (i.e., synergistic, additive, or antagonistic) was determined by median effect analysis. Results: When cells were exposed to concurrent pemetrexed and erlotinib or sequential pemetrexed followed by erlotinib, cytotoxic synergism was observed in both erlotinib-sensitive and erlotinib-resistant human NSCLC cell lines. This was independent of the mutation status of epidermal growth factor receptor or K-Ras genes. Synergism was associated with a combination of cell cycle effects from both agents. In contrast, exposure of cells to erlotinib followed by pemetrexed was mostly antagonistic in erlotinib-sensitive cells and additive at best in erlotinib-resistant cells. Antagonism was associated with erlotinib-induced G 1 -phase blockade of erlotinib-sensitive cells, which protects cells from pemetrexed cytotoxicity. Pemetrexed induced an epidermal growth factor receptor^mediated activation of the phosphatidylinositol 3-kinase/AKT pathway, which was inhibited by erlotinib and a specific phosphatidylinositol 3-kinase inhibitor, LY294002. Conclusions: The combination of pemetrexed and erlotinib is synergistic in NSCLC in vitro if exposure to erlotinib before pemetrexed is avoided, particularly in tumors that are sensitive to erlotinib. Based on these findings, a randomized phase II study comparing the progression-free survival between an intermittent combination of erlotinib and pemetrexed (experimental arm) and pemetrexed alone (control arm) in patients with relapsing NSCLC has been initiated.

The binding interactions between two cyanine dyes, pseudoisocyanine (PIC) and pinacyanol (PIN), and the cucurbit[n]uril hosts, cucurbit[7]uril (CB7) and cucurbit[6]uril (CB6), were investigated by electronic absorption spectroscopy and DFT computational methods. The CB7 host forms more stable complexes with both dyes than CB6 and the computational studies suggest that the cavity of the smaller host CB6 is not threaded by the dyes. The equilibrium association constants (K) for complexation by CB7 were measured and found to be 2.05 x 10(4) and 3.84 x 10(5) M(-1) for PIC and PIN, respectively, in aqueous media at 23 degrees C. CB7 complexation was found to effectively disrupt the intermolecular forces responsible for the aggregation of both dyes. Thus, CB7 completely disrupts the J-aggregates formed by PIC and the H-aggregates (as well as lower concentrations of J-aggregates) formed by PIN. In both cases a competing guest, 1-aminoadamantane (AD), could be used to adjust the extent of aggregation of the cyanine dye. AD regulates aggregate formation because it forms an extremely stable complex with CB7 (K approximately = 10(12) M(-1)) and exerts a tight control on the CB7 concentration available to interact and bind with the dye.