The proteasome inhibitor bortezomib is a novel anticancer drug that has shown promise in the treatment of refractory multiple myeloma. However, its clinical efficacy has been hampered by the emergence of drug-resistance phenomena, the molecular basis of which remains elusive. Toward this end, we here developed high levels (45-to 129-fold) of acquired resistance to bortezomib in human myelomonocytic THP1 cells by exposure to stepwise increasing (2.5-200 nM) concentrations of bortezomib. Study of the molecular mechanism of bortezomib resistance in these cells revealed (1) an Ala49Thr mutation residing in a highly conserved bortezomib-binding pocket in the proteasome ␤5-subunit (PSMB5) protein, (2) a dramatic overexpression (up to 60-fold) of PSMB5 protein but not of other proteasome subunits including PSMB6, PSMB7, and PSMA7, (3) high levels of cross-resistance to ␤5 subunit-targeted cytotoxic peptides 4A6, MG132, MG262, and ALLN, but not to a broad spectrum of chemotherapeutic drugs, (4) no marked changes in chymotrypsin-like proteasome activity, and (5) IntroductionThe ubiquitin proteasome system (UPS) facilitates the degradation of ubiquitin-tagged intracellular proteins, many of which play a regulatory role in cell proliferation, cell survival, and signaling processes. [1][2][3] As such, proteasome inhibitors have been recognized as a new generation of chemotherapeutic agents and antiinflammatory drugs. [4][5][6][7][8][9][10][11][12][13] The boronic dipeptide bortezomib (PS341, Velcade) is the first proteasome inhibitor that has been approved for the treatment of refractory multiple myeloma. 6,14 Bortezomib is a reversible inhibitor that targets primarily the ␤5-subunit (PSMB5) subunit/chymotrypsin-like activity of the 26S proteasome and to a somewhat lesser extent also caspase-like activity harbored by the ␤1 (PSMB6) proteasome subunit. At higher concentrations, bortezomib inhibits trypsin-like proteolytic activity facilitated by ␤2 (PSMB7) proteasome subunits. [15][16][17] Despite promising clinical activity, some patients with multiple myeloma failed to respond to bortezomib therapy. 18 Moreover, the efficacy for bortezomib may differ between tumor types. 6,[19][20][21] Whether these observations are related to common mechanisms of drug resistance frequently seen for anticancer 22 or anti-inflammatory drugs 23 is largely unknown. However, their characterization is of key importance as it may pave the way for the overcoming of drug resistance, thereby enhancing the efficacy of this new class of proteasome-targeted drugs.One mode of primary resistance to bortezomib is conveyed by constitutively high levels of heat shock protein 27. 24 In the context of acquired resistance, studies aimed at delineating the mechanism of acquired resistance to the tripeptidyl aldehyde proteasome inhibitor ALLN (N-acetyl-leucyl-leucyl-norleucinal) revealed 2 possible molecular mechanisms: (a) enhanced cellular efflux via the multidrug resistance (MDR) transporter P-glycoprotein (Pgp; ABCC1) 25 or multidrug resistance-related pro...

Because the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor erlotinib and the multitargeted antifolate pemetrexed are registered in the treatment of second-line nonsmall-cell lung cancer (NSCLC), empirical combinations of these drugs are being tested. This study investigated molecular mechanisms underlying their combination in six NSCLC cell lines. Cells were characterized by heterogeneous expression of pemetrexed determinants, including thymidylate synthase (TS) and dihydrofolate reductase (DHFR), and mutations potentially affecting chemosensitivity. Pharmacological interaction was studied using the combination index (CI) method, whereas cell cycle, apoptosis induction, and EGFR, extracellular signalregulated kinases 1 and 2, and Akt phosphorylation were studied by flow cytometry, fluorescence microscopy, and enzyme-linked immunosorbent assays. Reverse-transcriptase polymerase chain reaction (RT-PCR), Western blot, and activity assays were performed to assess whether erlotinib influenced TS. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assays demonstrated that EGFR and k-Ras mutations were related to erlotinib sensitivity, whereas TS and DHFR expression were related to pemetrexed sensitivity. Synergistic cytotoxicity was found in all cells, most pronounced with pemetrexed ϩ erlotinib (24 h) 3 erlotinib (48 h) sequence (CI, 0.09 -0.40), which was associated with a significant induction of apoptosis. Pemetrexed increased EGFR phosphorylation and reduced Akt phosphorylation, which was additionally reduced by drug combination (Ϫ70.6% in H1650). Erlotinib significantly reduced TS expression and activity, possibly via E2F-1 reduction, as detected by RT-PCR and Western blot, and the combination decreased TS in situ activity in all cells. Erlotinib and pemetrexed showed a strong synergism in NSCLC cells, regardless of their genetic characteristics. Induction of apoptosis, modulation of EGFR and Akt phosphorylation, and changes in the expression of critical genes involved in pemetrexed activity contribute to this synergistic interaction and support the clinical investigation of these markers.Non-small-cell lung cancer (NSCLC) is the leading cause of cancer-related deaths in the Western world. Chemotherapy represents the backbone of treatment of advanced NSCLC, which represents more than 50% of cases diagnosed. Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org. doi:10.1124/mol.107.042382.ABBREVIATIONS: NSCLC, non-small-cell lung cancer; 5-FU, 5-fluorouracil; AI, apoptotic index; BCRP, breast cancer resistance protein; CI, combination index; DHFR, dihydrofolate reductase; EGFR, epidermal growth factor receptor; FA, fraction affected; FPGS, folyl-polyglutamate synthetase; GARFT, glycinamide ribonucleotide formyltransferase; MRPs, multidrug-related protein; PI3K, phosphatidylinositide 3-kinase; RFC, reduced folate carrier; TKI, tyrosine-kinase inhibitor; TS, thymidylate synthase; LY294002, (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one ...

Calcimycin restricts Wnt/β-catenin–regulated S100A4 expression, leading to reduced S100A4-mediated cell migration and invasion in colon cancer cells, as well as to inhibition of metastasis formation in xenografted mice.

Multidrug resistance is often associated with the (over)expression of drug efflux transporters of the ATP-binding cassette (ABC) protein family. This minireview discusses the role of one selected ABC-transporter family member, the breast cancer resistance protein (BCRP/ABCG2), in the (pre)clinical efficacy of novel experimental anticancer drugs, in particular tyrosine kinase inhibitors.

Serotonin plays important physiological functions at the intestinal level. However, nothing is known concerning its inactivation mechanisms in the human intestine. So, the aim of this work was to characterize the uptake of serotonin at the apical and basolateral membranes of human intestinal epithelial (Caco-2) cells. Uptake of [ 3 H]serotonin at the apical membrane of Caco-2 cells was specific and Na ϩ -, Cl Ϫ -, and potentialdependent. It was concentration dependently inhibited by several monoamines (with the following rank order of potency: serotonin Ͼ Ͼ dopamine Ն noradrenaline) and tricyclic and nontricyclic antidepressants (with the following rank order of potency: fluoxetine Ͼ desipramine Ͼ cocaine Ͼ GBR 12909). In contrast, it was not affected by corticosterone (0.01-100 M) and was only partially inhibited by decynium-22 (0.001-10 M). Transepithelial apparent permeability (P app ) to [ 3 H]serotonin in the apical-to-basolateral direction was reduced by desipramine (0.4 M) and fluoxetine (0.02 M), and it was not Na ϩ -dependent nor affected by corticosterone (100 M). Uptake of [3 H]serotonin at the basolateral membrane of Caco-2 cells was Na ϩ -dependent and reduced by desipramine (0.4 M) and fluoxetine (0.02 M), and it was not affected by corticosterone (100 M).The P app to [3 H]serotonin in the basolateral-to-apical direction was reduced by desipramine (0.4 M) and fluoxetine (0.02 M), and it was not affected by Na ϩ omission or by corticosterone (100 M). Reverse transcriptase-polymerase chain reaction indicates that mRNA of the neuronal serotonin transporter (SERT) is present in Caco-2 cells and in human small intestine. In conclusion, these results suggest that human intestinal epithelial Caco-2 cells functionally express SERT, both at their apical and basolateral cell membranes.The largest store of serotonin in the body is found in the gastrointestinal tract, corresponding to over 95% of the body's serotonin (Erspamer, 1966). Most of the gastrointestinal serotonin is contained in enterochromaffin (EC) cells of the mucosal epithelium, within which serotonin is synthesized from L-tryptophan and stored in secretory granules. Serotonin is also present in serotonergic neurons of the enteric nervous system. Several functions of enteric serotonin have been identified in the past years. First, serotonin acts as the neurotransmitter of a subset of myenteric interneurons (Wade et al., 1994). Second, serotonin contained in EC cells, being released in response to chemical or mechanical stimuli, affects gastrointestinal motility (it initiates peristaltic reflexes by acting on intrinsic sensory neurons and musculature) and intestinal electrolyte transport (it initiates secretory reflexes by acting on intrinsic sensory neurons and mucosal cells) (Engel et al., 1984;Imada-Shirakata et al., 1997). Moreover, extrinsic sensory neurons activated by serotonin initiate sensations from the bowel, which may include nausea, bloating, and pain (for review, see Gershon, 1999). Additionally, serotonin present in EC cells...

The ABCG2 -15622C/T polymorphism and ABCG2 (1143C/T, -15622C/T) haplotype resulted in a gefitinib-dependent, moderate-to-severe diarrhea suggesting that these pharmacogenetic markers should be considered to optimize NSCLC treatment.

Folate is a water-soluble B vitamin with a crucial role in the synthesis and methylation of DNA and in the metabolism of several amino acids. In the present study we investigated whether beverages like wine, beer and tea, or some of their specific constituents, affect the intestinal uptake of (3)H-folic acid or (3)H-methotrexate (an antifolate). All tested beverages significantly inhibited the uptake of (3)H-folic acid by Caco-2 cells. Most of these beverages, with the exception of wines (not tested), also inhibited (3)H-methotrexate uptake in these cells. Additionally, ethanol, when tested separately, inhibited the uptake of both compounds. Some of the tested phenolic compounds, namely myricetin, epigallocatechin gallate (EGCG) and isoxanthohumol, markedly inhibited (3)H-folic acid uptake. Myricetin and EGCG also had a concentration-dependent inhibitory effect upon the uptake of (3)H-methotrexate by Caco-2 cells. Resveratrol, quercetin and kaempferol were able to inhibit the transport of both compounds, but only in the concentration of 100 microM. In conclusion, dietary constituents may impact on intestinal folate uptake, as here shown for phenolic compounds.

Purpose: We have previously identified the gene MACC1 as a strong prognostic biomarker for colorectal cancer metastasis and patient survival. Here, we report for the first time the generation of transgenic mouse models for MACC1.Experimental Design: We generated mice with transgenic overexpression of MACC1 in the intestine driven by the villin promoter (vil-MACC1) and crossed them with Apc Min mice (vil-MACC1/Apc Min ). Results: vil-MACC1/ApcMin mice significantly increased the total number of tumors (P ¼ 0.0056). This was particularly apparent in large tumors (!3-mm diameter; P ¼ 0.0024). A detailed histopathologic analysis of these lesions demonstrated that the tumors from the vil-MACC1/Apc Min mice had a more invasive phenotype and, consequently, showed a significantly reduced survival time than Apc Min mice (P ¼ 0.03). Molecular analysis revealed an increased Wnt and pluripotency signaling in the tumors of vil-MACC1/Apc Min mice. Specifically, we observed a prominent upregulation of the pluripotency markers Oct4 and Nanog in these tumors compared with Apc Min controls. Finally, we could also validate that Oct4 and Nanog are regulated by MACC1 in vitro and strongly correlate with MACC1 levels in a cohort of 60 tumors of colorectal cancer patients (r ¼ 0.7005 and r ¼ 0.6808, respectively; P > 0.0001 and P > 0.0002, respectively).Conclusions: We provide proof of principle that MACC1-induced tumor progression in colorectal cancer acts, at least in part, via the newly discovered MACC1/Nanog/Oct4 axis. These findings might have important implications for the design of novel therapeutic intervention strategies to restrict tumor progression.