Efficient Synthesis of Exo-<i>N</i>-carbamoyl Nucleosides: Application to the Synthesis of Phosphoramidate Prodrugs

An efficient protection protocol for the 6-<i>exo</i>-amino group of purine nucleosides with various chloroformates was developed utilizing <i>N</i>-methylimidazole (NMI). The reaction of an <i>exo</i>-<i>N</i>⁶-group of adenosine analogue <b>1</b> with alkyl/and aryl chloroformates under optimized conditions provided the <i>N</i>⁶-carbamoyl adenosines (<b>2a</b>–<b>j</b>) in good to excellent yields. The reaction of <i>N</i>⁶-Cbz-protected nucleosides (<b>5a</b>–<b>c</b>) with phenyl phosphoryl chloride (<b>7</b>) using <i>t</i>-BuMgCl followed by catalytic hydrogenation afforded the corresponding phosphoramidate pronucleotides (<b>8a</b>–<b>c</b>) in excellent yield

Synthesis of Cyclopentanyl Carbocyclic 5‑Fluorocytosine ((−)-5-Fluorocarbodine) Using a Facially Selective Hydrogenation Approach

An efficient synthetic route to biologically relevant (−)-5-fluorocarbodine <b>6</b> was developed. Direct coupling of N⁶-protected 5-fluorouracil <b>15</b> with cyclopentenyl intermediate <b>13</b>, followed by formation of a macrocycle between the base and the carbocyclic sugar moiety, via ring-closing metathesis, allowed for a facial selective hydrogenation of the sugar double bond to give, exclusively, the desired 4′-β stereoisomer

Restriction sites and sequences of primers used for cloning.

<p>Restriction sites and sequences of primers used for cloning.</p

DZNep alters histone lysine methylation and methyltransferase and demethylase expressions in pancreatic cancer.

<p>A. Changes in methylation levels of H3K4, H3K9, H3K27, and H4K20 in HPDE and MIA PaCa-2 treated with DZNep (0–100 µM). Cells were treated with DZNep for 24 h, and whole cell lysates (50 µg) were subjected to Western blotting analysis. β-actin, the internal loading control, is shown with a representative blot. B. Western blotting analysis of histone lysine methyltransferases and demethylases in MIA PaCa-2 treated with DZNep (1 µM) for up to 48 h. C. Histone methylation dynamics in MIA PaCa-2 treated with DZNep (1 µM) for up to 72 h.</p

Physiochemical Characterization of NPs.

<p>Physiochemical Characterization of NPs.</p

Acyl modifications of DZNep further enhance cytotoxicity.

<p>A. The chemical structures of DZNep and its two acyl prodrugs (Prodrug 1: C₂₀H₂₉ClN₄O₄, and Prodrug 2: C₁₈H₂₄N₄O₄). B. Cytotoxicity of DZNep versus its prodrugs in HPDE and MIA PaCa-2. IC₅₀ values are designated in each legend. Significance between each prodrug and DZNep was identified using the Student’s t test. C. Average IC₅₀ values of the various drug combinations in HPDE, Capan-1, and MIA PaCa-2. Twenty-four hours after 3×10³ cells/well were seeded in a 96-well plate, cells were treated for 72 h. Cellular viabilities were measured using MTT assays. IC₅₀ values are plotted. Significance of each prodrug combination was compared with Gem+DZNep using one-way ANOVA followed by Tukey’s post-hoc test. <i>Bars</i>, SD. <i>n</i> = 3. *<i>p</i><0.05, **<i>p</i><0.01.</p

Short priming of DZNep demonstrated superior cytotoxicity and synergy with gemcitabine than co-exposure of the two drugs.

<p>A. Short exposure with DZNep for 4–8 h produced maximal cytotoxic effects. Cells were exposed with DZNep at 1 µM for varying time intervals followed by increasing concentrations of gemcitabine (0–0.1 µM). Significance between 0 and 4 h is indicated. B. Superior cytotoxicity and synergism between gemcitabine and DZNep were observed when cells were primed with DZNep, as opposed to cotreatment with gemcitabine. Representative growth inhibition curves are shown. Twenty-four hours after 3×10³ cells/well were seeded in a 96-well plate, cells were exposed to gemcitabine and DZNep concentrations at a 1∶10 ratio either as a co-treatment for 72 h (C) or a primed treatment (with DZNep for 8 h followed by gemcitabine for 72 h) (P). Cellular viabilities were measured using MTT assays. Significance between co-treatment and priming is indicated. Combination index (CI) plots (insets) show the interactions between the two drugs. CI>1, antagonism; CI = 1, additivity; CI<1, synergism. <i>Bars</i>, SD. <i>n</i> = 3. *<i>p</i><0.05, **<i>p</i><0.01. C. Apoptosis levels were significantly greater in Capan-1 and MIA PaCa-2 cells with priming compared with co-treatment, while apoptosis levels in HPDE decreased with priming. Cells were either co-treated with 10 µM DZNep and 1 µM gemcitabine or primed with 10 µM DZNep for 8 h followed by 1 µM gemcitabine. Fluorescence values were background-subtracted and are indicated as fold-change from co-treatment to priming. Significant differences between co-treatment and priming were identified using the Student’s t test. <i>Bars</i>, SD. <i>n</i> = 3. *<i>p</i><0.05, **<i>p</i><0.01. D. Maximal reduction in H3K27 trimethylation was seen with priming schedules at 1∶10 DZNep:gemcitabine. MIA PaCa-2 was treated with vehicle, gemcitabine for 72 h, DZNep for 8 h, DZNep and gemcitabine for 72 h, or DZNep for 8 h followed by gemcitabine for 72 h. 100 µg of whole cell lysates were subjected to Western blotting analysis. Blots were stripped and re-probed for β-actin, the internal loading control. Densitometry ratios are indicated.</p

DZNep and gemcitabine sensitivity, singly or in combination, and interactions within a panel of pancreatic cell lines.

<p>A. All cancerous cell lines excluding the normal HPDE are DZNep-responsive and reduced cellular viability. B. DZNep and gemcitabine displayed antagonistic effects in HPDE. C. DZNep and gemcitabine displayed additive or synergistic effects in many of the cancerous pancreatic cell lines. Twenty-four hours after 3×10³ cells/well were seeded in a 96-well plate, cells were treated with either DZNep, gemcitabine, or a combination of both at an equimolar ratio for 72 h. Cellular viability was measured using an MTT assay. Cytotoxic IC₅₀ values are indicated. Significances between gemcitabine and DZNep as well as DZNep+Gemcitabine and DZNep were identified using one-way ANOVA followed by Tukey’s post-hoc test. Combination index (CI) plots (insets) show the interactions between the two drugs. CI>1, antagonism; CI = 1, additivity; CI<1, synergism. Bar graphs to the right indicate the relative caspase-3 activity (RCA) of each treatment as measured by fluorescence intensity. Values were background-subtracted and are presented as fold-change from the control. Significance between a single drug versus the drug combination was identified via one-way ANOVA followed by Tukey’s post-hoc analysis. Cells were treated with 1 µM DZNep, 100 nM gemcitabine, or both. <i>Bars</i>, SD. <i>n</i> = 3. *<i>p</i><0.05, **<i>p</i><0.01.</p

DZNep partially competes with the uptake of purine nucleosides by hENT1 and hCNT3.

<p>A. DZNep hindered the uptake of radiolabeled purine nucleosides in PANC-1 and MIA PaCa-2. Twenty-four hours after 5×10⁴ cells/well were seeded in a 24-well plate, cells were allowed to uptake the indicated radiolabeled nucleoside in the presence of DZNep or its respective unlabeled nucleoside. B. Inhibition of adenosine transport in <i>Xenopus</i> oocytes with DZNep. C. Pharmacological inhibition of hENT1 and excess uridine decreased the cytotoxicity of DZNep in MIA PaCa-2. Twenty-four hours after 3×10³ cells/well were seeded in a 96-well plate, cells were treated with increasing concentrations of DZNep in the presence of DMSO (control), 10 µM NBMPR, or 200 µM uridine. Cellular viability was measured using an MTT assay. IC₅₀ values are indicated. Significant differences between the control and each treatment were determined using the Student’s t test. <i>Bars</i>, SD. <i>n</i> = 3. *<i>p</i><0.05, **<i>p</i><0.01.</p

Spatiotemporal release of DZNep and gemcitabine using engineered nanoparticles reduced drug dose while potentiating chemosensitivity.

<p>A. Spatial distribution of DZNep and gemcitabine within NPs. Co-encapsulating double-emulsion formulations were created using PLGA-<i>b</i>-PEG-OH (<i>left</i>), DSPE-PEG-OH (<i>middle</i>), and PLGA-<i>b</i>-PEG-TPP (<i>right</i>). B and E. TEM illustrates the inner core and outer shell of all the double-emulsion NPs created. Insets show the NPs at higher magnification. <i>Bars</i>, SD. <i>n</i> = 3. C. Release kinetics indicates the similarity between DZNep and gemcitabine release using the PLGA-<i>b</i>-PEG-OH formulation. D. Gemcitabine (<i>top</i>) and DZNep (<i>bottom</i>) in individual PLGA-<i>b</i>-PEG-OH formulations distinctly increased cytotoxicity in MIA PaCa-2. Significance between nanoparticles and free formulation is shown. F. HPLC analyses demonstrate the rapid and sequential release of DZNep compared with gemcitabine in both DSPE (<i>top</i>) and TPP (<i>bottom</i>) formulations.G. Both engineered DSPE (<i>top</i>) and TPP (<i>bottom</i>) delayed-release NPs increased the cytotoxicity of MIA PaCa-2 even further compared with PLGA-<i>b</i>-PEG-OH NPs. Twenty-four hours after 5×10³ cells/well were seeded in a 96-well plate, cells were treated for 72 h. Cellular viabilities were measured using MTT assays. Cytotoxic IC₅₀ values are indicated. Significance between simultaneous and delayed NPs using the Student’s t test is shown. Bar graphs to the right indicate the relative levels of caspase-3 activity as measured by fluorescence intensity. Values were background-subtracted and are indicated as fold-change from simultaneous NPs to delayed NPs. <i>Bars</i>, SD. <i>n</i> = 3. *<i>p</i><0.05, **<i>p</i><0.01. H. H3K27 trimethylation decreases with simultaneous and delayed-release NPs. MIA PaCa-2 was treated with empty, simultaneous, or delayed NPs as above and total cell lysates were analyzed for H3K27 trimethylation using Western Blotting. A clear reduction in H3K27 trimethylation was noticed in both simultaneous and delayed NPs, with DSPE (<i>left</i>) and TPP (<i>right</i>) delayed NPs producing a slightly greater reduction compared with simultaneous NPs.</p