Role of human nucleoside transporters in the cellular uptake of two inhibitors of IMP dehydrogenase, tiazofurin and benzamide

Further studies are warranted to determine if this finding can be generalized to other cell types

Synergistic activity of troxacitabine (Troxatyl™) and gemcitabine in pancreatic cancer

<p>Abstract</p> <p>Background</p> <p>Gemcitabine, a deoxycytidine nucleoside analog, is the current standard chemotherapy used as first-line treatment for patients with locally advanced or metastatic cancer of the pancreas, and extends life survival by 5.7 months. Advanced pancreatic cancer thus remains a highly unmet medical need and new therapeutic agents are required for this patient population. Troxacitabine (Troxatyl™) is the first unnatural L-nucleoside analog to show potent preclinical antitumor activity and is currently under clinical investigation. Troxacitabine was recently evaluated as a first-line therapy in 54 patients with advanced adenocarcinoma of the pancreas and gave comparable overall results to those reported with gemcitabine in recently published randomized trials.</p> <p>Methods</p> <p>The human pancreatic adenocarcinoma cell lines, AsPC-1, Capan-2, MIA PaCa-2 and Panc-1, were exposed to troxacitabine or gemcitabine alone or in combination, for 72 h, and the effects on cell growth were determined by electronic particle counting. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Mechanistic studies addressed incorporation of troxacitabine into DNA and intracellular levels of troxacitabine and gemcitabine metabolites. For <it>in vivo </it>studies, we evaluated the effect of both drugs, alone and in combination, on the growth of established human pancreatic (AsPC-1) tumors implanted subcutaneously in nude mice. Statistical analysis was calculated by a one-way ANOVA with Dunnett as a post-test and the two-tailed unpaired <it>t </it>test using GraphPad prism software.</p> <p>Results</p> <p>Synergy, evaluated using the CalcuSyn Software, was observed in all four cell-lines at multiple drug concentrations resulting in combination indices under 0.7 at Fa of 0.5 (50% reduction of cell growth). The effects of drug exposures on troxacitabine and gemcitabine nucleotide pools were analyzed, and although gemcitabine reduced phosphorylation of troxacitabine when cells were exposed at equal drug concentrations, there was no effect on phosphorylated pools at drug combinations that were synergistic. The amount of troxacitabine incorporated into DNA was also not affected by the presence of gemcitabine. <it>In vivo </it>testing against a human pancreatic (AsPC-1) xenograft mouse tumor model indicated that both drugs were more than additive at well-tolerated doses and schedule. The biological basis for this synergy is unclear as we did not observe changes in apoptosis, DNA repair, troxacitabine incorporation into DNA or troxacitabine metabolism in the presence of gemcitabine.</p> <p>Conclusion</p> <p>These data, together with phase I clinical data showing tolerability of both agents when combined, suggest combination therapy with troxacitabine and gemcitabine warrants further evaluation in advanced pancreatic cancer patients.</p

Tyrosine Kinase Inhibitors Reduce Glucose Uptake by Binding to an Exofacial Site on hGLUT‐1: Influence on 18F‐FDG PET Uptake

Positron emission tomography (PET) using 2‐deoxy‐2‐[18F]fluoro‐d‐glucose ([18F]FDG), a marker of energy metabolism and cell proliferation, is routinely used in the clinic to assess patient response to chemotherapy and to monitor tumor growth. Treatment with some tyrosine kinase inhibitors (TKIs) causes changes in blood glucose levels in both nondiabetic and diabetic patients. We evaluated the interaction of several classes of TKIs with human glucose transporter‐1 (hGLUT‐1) in FaDu and GIST‐1 cells by measuring [3H]2‐deoxy‐d‐glucose ([3H]2‐DG) and [3H]FDG uptake. Uptake of both was inhibited to varying extents by the TKIs, and representative TKIs from each class showed competitive inhibition of [3H]2‐DG uptake. In GIST‐1 cells, [3H]FDG uptake inhibition by temsirolimus and nilotinib was irreversible, whereas inhibition by imatinib, gefitinib, and pazopanib was reversible. Molecular modeling studies showed that TKIs form multiple hydrogen bonds with polar residues of the sugar binding site (i.e., Q161, Q282, Q283, N288, N317, and W388), and van der Waals interactions with the H‐pocket site. Our results showed interaction of TKIs with amino acid residues at the glucose binding site to inhibit glucose uptake by hGLUT‐1. We hypothesize that inhibition of hGLUT‐1 by TKIs could alter glucose levels in patients treated with TKIs, leading to hypoglycemia and fatigue, although further studies are required to evaluate roles of other SLC2 and SLC5 members. In addition, TKIs could affect tumor [18F]FDG uptake, increasingly used as a marker of tumor response. The hGLUT‐1 inhibition by TKIs may have implications for routine [18F]FDG‐PET monitoring of tumor response in patients

2-Nitroimidazole-Furanoside Derivatives for Hypoxia Imaging—Investigation of Nucleoside Transporter Interaction, ¹⁸F-Labeling and Preclinical PET Imaging

The benefits of PET imaging of tumor hypoxia in patient management has been demonstrated in many examples and with various tracers over the last years. Although, the optimal hypoxia imaging agent has yet to be found, 2-nitroimidazole (azomycin) sugar derivatives&#8212;mimicking nucleosides&#8212;have proven their potential with [18F]FAZA ([18F]fluoro-azomycin-&#945;-arabinoside) as a prominent representative in clinical use. Still, for all of these tracers, cellular uptake by passive diffusion is postulated with the disadvantage of slow kinetics and low tumor-to-background ratios. We recently evaluated [18F]fluoro-azomycin-&#946;-deoxyriboside (&#946;-[18F]FAZDR), with a structure more similar to nucleosides than [18F]FAZA and possible interaction with nucleoside transporters. For a deeper insight, we comparatively studied the interaction of FAZA, &#946;-FAZA, &#945;-FAZDR and &#946;-FAZDR with nucleoside transporters (SLC29A1/2 and SLC28A1/2/3) in vitro, showing variable interactions of the compounds. The highest interactions being for &#946;-FAZDR (IC50 124 &#177; 33 &#181;M for SLC28A3), but also for FAZA with the non-nucleosidic &#945;-configuration, the interactions were remarkable (290 &#177; 44 &#181;M {SLC28A1}; 640 &#177; 10 &#181;M {SLC28A2}). An improved synthesis was developed for &#946;-FAZA. For a PET study in tumor-bearing mice, &#945;-[18F]FAZDR was synthesized (radiochemical yield: 15.9 &#177; 9.0% (n = 3), max. 10.3 GBq, molar activity &gt; 50 GBq/&#181;mol) and compared to &#946;-[18F]FAZDR and [18F]FMISO, the hypoxia imaging gold standard. We observed highest tumor-to-muscle ratios (TMR) for &#946;-[18F]FAZDR already at 1 h p.i. (2.52 &#177; 0.94, n = 4) in comparison to [18F]FMISO (1.37 &#177; 0.11, n = 5) and &#945;-[18F]FAZDR (1.93 &#177; 0.39, n = 4), with possible mediation by the involvement of nucleoside transporters. After 3 h p.i., TMR were not significantly different for all 3 tracers (2.5&#8315;3.0). Highest clearance from tumor tissue was observed for &#946;-[18F]FAZDR (56.6 &#177; 6.8%, 2 h p.i.), followed by &#945;-[18F]FAZDR (34.2 &#177; 7.5%) and [18F]FMISO (11.8 &#177; 6.5%). In conclusion, both isomers of [18F]FAZDR showed their potential as PET hypoxia tracers. Differences in uptake behavior may be attributed to a potential variable involvement of transport mechanisms

Synergistic activity of troxacitabine (Troxatyl™) and gemcitabine in pancreatic cancer-3

<p><b>Copyright information:</b></p><p>Taken from "Synergistic activity of troxacitabine (Troxatyl™) and gemcitabine in pancreatic cancer"</p><p>http://www.biomedcentral.com/1471-2407/7/121</p><p>BMC Cancer 2007;7():121-121.</p><p>Published online 3 Jul 2007</p><p>PMCID:PMC1948004.</p><p></p>xacitabine or gemcitabine either alone or in combination at a ratio of 1:100 of gemcitabine vs. troxacitabine, for 72 h, after which cells were harvested by trypsinization and their numbers determined using electronic particle counting. Each data point represents the mean ± SD of three determinations. Gemcitabine (open squares), troxacitabine (open inverted triangle), gemcitabine + troxacitabine (open circle). The GIvalues for exposures to troxacitabine and gemcitabine alone are given in Table 2