Yasemin Yuksel Durmaz

Enzyme-activated nanoconjugates for tunable release of doxorubicin in hepatic cancer cells

We report the synthesis of a series of aromatic azo-linkers (L1-L4), which are selectively recognized and cleaved by azoreductase enzymes present in the cytoplasm of hepatic cancer cells via a NADPH-dependent mechanism. We utilized L1-L4 azo-linkers to conjugate doxorubicin to generation 5 (G5) of poly(amidoamine) dendrimers to prepare G5-L(x)-DOX nanoconjugates. We incorporated electron-donating oxygen (O) or nitrogen (N) groups in the para and ortho positions of L1-L4 azo-linkers to control the electronegativity of G5-L(x)-DOX conjugates and investigated their cleavage by azoreductase enzymes and the associated release of loaded DOX molecules. Hammett σ values of G5-L(x)-DOX conjugates ranged from -0.44 to -1.27, which is below the reported σ threshold (-0.37) required for binding to azoreductase enzymes. Results show that incubation of G5-L1-DOX (σ = -0.44), G5-L2-DOX (σ = -0.71), G5-L3-DOX (σ = -1.00), and G5-L4-DOX (σ = -1.27) conjugates with human liver microsomal (HLM) enzymes and the S9 fraction isolated from HepG2 hepatic cancer cells results in release of 4%-8%, 17%, 60%, and 100% of the conjugated DOX molecules, respectively. These results show that increasing the electronegativity (i.e. lower σ value) of L1-L4 azo-linkers increases their susceptibility to cleavage by azoreductase enzymes. Intracellular cleavage of G5-L(x)-DOX nanoconjugates, release of conjugated DOX molecules, and cytotoxicity correlated with conjugates electronegativity (σ value) was investigated, with G5-L4-DOX conjugate exhibiting the highest toxicity towards hepatic cancer cells with an IC50 of 13 nm ± 5 nm in HepG2 cells. Cleavage of G5-L(x)-DOX conjugates was specific to hepatic cancer cells as shown by low non-specific DOX release upon incubation with non-enzymatic insect proteins and the S9 fraction isolated from rat cardiomyocytes. These enzyme-activated G5-L(x)-DOX conjugates represent a drug delivery platform that can achieve tunable and cell-specific release of the loaded cargo in hepatic cancer cells.

Nanodroplet-Mediated Histotripsy for Image-guided Targeted Ultrasound Cell Ablation

This paper is an initial work towards developing an image-guided, targeted ultrasound ablation technique by combining histotripsy with nanodroplets that can be selectively delivered to tumor cells. Using extremely short, high-pressure pulses, histotripsy generates a dense cloud of cavitating microbubbles that fractionates tissue. We hypothesize that synthetic nanodroplets that encapsulate a perfluoropentane (PFP) core will transition upon exposure to ultrasound pulses into gas microbubbles, which will rapidly expand and collapse resulting in disruption of cells similar to the histotripsy process but at a significantly lower acoustic pressure. The significantly reduced cavitation threshold will allow histotripsy to be selectively delivered to the tumor tissue and greatly enhance the treatment efficiency while sparing neighboring healthy tissue. To test our hypothesis, we prepared nanodroplets with an average diameter of 204±4.7 nm at 37°C by self-assembly of an amphiphilic triblock copolymer around a PFP core followed by cross-linkage of the polymer shell forming stable nanodroplets. The nanodroplets were embedded in agarose tissue phantoms containing a sheet of red blood cells (RBCs), which were exposed to 2-cycle pulses applied by a 500 kHz focused transducer. Using a high speed camera to monitor microbubble generation, the peak negative pressure threshold needed to generate bubbles >50 μm in agarose phantoms containing nanodroplets was measured to be 10.8 MPa, which is significantly lower than the 28.8 MPa observed using ultrasound pulses alone. High speed images also showed cavitation microbubbles produced from the nanodroplets displayed expansion and collapse similar to histotripsy alone at higher pressures. Nanodroplet-mediated histotripsy created consistent, well-defined fractionation of the RBCs in agarose tissue phantoms at 10 Hz pulse repetition frequency similar to the lesions generated by histotripsy alone but at a significantly lower pressure. These results support our hypothesis and demonstrate the potential of using nanodroplet-mediated histotripsy for targeted cell ablation.

Functionalization of Poly(divinylbenzene) Microspheres by Combination of Hydrobromination and Click Chemistry Processes: A Model Study

Fluorescent pyrene-functional poly(divinylbenzene) (PDVB) cross-linked core microspheres were synthesized using the click chemistry strategy as a model study. First, the core monodisperse microspheres were prepared by precipitation polymerization using 2,2′-azobisisobutronitrile (AIBN) as initiator in acetonitrile in the absence of any stabilizer. Residual double bonds were converted to azide-functions by hydrobrominated with hydrogen bromide followed by azidation with NaN3 in DMF solution. Propargyl pyrene was prepared independently as a fluorescent click component. Finally, azide-functionalized microspeheres were coupled with propargyl pyrene with high efficiency by click chemistry. The modified PDVB microspheres are characterized by using FT-IR spectroscopy, UV-Vis absorption spectroscopy, fluorescence spectroscopy and fluorescence microscopy.

Targeting Hepatic Cancer Cells with PEGylated Dendrimers Displaying N -Acetylgalactosamine and SP94 Peptide Ligands

Poly(amidoamine) (PAMAM) dendrimers are branched water-soluble polymers defined by consecutive generation numbers (Gn) indicating a parallel increase in size, molecular weight, and number of surface groups available for conjugation of bioactive agents. In this article, we compare the biodistribution of N-acetylgalactosamine (NAcGal)-targeted [(14) C]1 -G5-(NH2 )5 -(Ac)108 -(NAcGal)14 particles to non-targeted [(14) C]1 -G5-(NH2 )127 and PEGylated [(14) C]1 -G5-(NH2 )44 -(Ac)73 -(PEG)10 particles in a mouse hepatic cancer model. Results show that both NAcGal-targeted and non-targeted particles are rapidly cleared from the systemic circulation with high distribution to the liver. However, NAcGal-targeted particles exhibited 2.5-fold higher accumulation in tumor tissue compared to non-targeted ones. In comparison, PEGylated particles showed a 16-fold increase in plasma residence time and a 5-fold reduction in liver accumulation. These results motivated us to engineer new PEGylated G5 particles with PEG chains anchored to the G5 surface via acid-labile cis-aconityl linkages where the free PEG tips are functionalized with NAcGal or SP94 peptide to investigate their potential as targeting ligands for hepatic cancer cells as a function of sugar conformation (α versus β), ligand concentration (100-4000 nM), and incubation time (2 and 24 hours) compared to fluorescently (Fl)-labeled and non-targeted G5-(Fl)6 -(NH2 )122 and G5-(Fl)6 -(Ac)107 -(cPEG)15 particles. Results show G5-(Fl)6 -(Ac)107 -(cPEG[NAcGalβ ])14 particles achieve faster uptake and higher intracellular concentrations in HepG2 cancer cells compared to other G5 particles while escaping the non-specific adsorption of serum protein and phagocytosis by Kupffer cells, which make these particles the ideal carrier for selective drug delivery into hepatic cancer cells.

Synthesis, Characterization and Thermally-Activated Curing of Azobenzene-Containing Benzoxazines

Two new benzoxazine monomers with aliphatic and aromatic substituents, as well as azobenzene moieties were synthesized and characterized by spectroscopic methods. Their thermal curing behavior in the absence of any catalyst was investigated by differential scanning calorimetry. The thermal properties of the cross-linked structures were also studied by thermogravimetric analysis. While the monomeric forms gave some indication of thermally-induced isomerization, the azo groups were shown to be fixed in the disordered form in the densely cross-linked matrix.

Effects of Ultrasound Frequency on Nanodroplet-Mediated Histotripsy.

Nanodroplet-mediated histotripsy (NMH) is a targeted ultrasound ablation technique combining histotripsy with nanodroplets that can be selectively delivered to tumor cells for targeted tumor ablation. In a previous study, it was reported that by use of extremely short, high-pressure pulses, histotripsy cavitation bubbles were generated in regions containing nanodroplets at significantly lower pressure (∼10.8 MPa) than without nanodroplets (∼28 MPa) at 500 kHz. Furthermore, it was hypothesized that lower frequency would improve the effectiveness of NMH by increasing the size of the focal region, increasing bubble expansion, and decreasing the cavitation threshold. In this study, we investigated the effects of ultrasound frequency (345 kHz, 500 kHz, 1.5 MHz, and 3 MHz) on NMH. First, the NMH cavitation threshold was measured in tissue phantoms with and without nanodroplets, with results indicating that the NMH threshold was significantly below the histotripsy intrinsic threshold at all frequencies. Results also indicated that the NMH threshold decreased at lower frequency, ranging from 7.4 MPa at 345 kHz to 13.2 MPa at 3 MHz. In the second part of this study, the effects of frequency on NMH bubble expansion were investigated, with results indicating larger expansion at lower frequency, even at a lower pressure. In the final part of this study, the ability of perfluoropentane-encapsulated nanodroplets to act as sustainable cavitation nuclei over multiple pulses was investigated, with results indicating that the nanodroplets are destroyed by the cavitation process and only function as cavitation nuclei for the first few pulses, with this effect being most pronounced at higher frequencies. Overall, the results of this study support our hypothesis that using a lower frequency will improve the effectiveness of NMH by increasing the size of the focal region, increasing bubble expansion and decreasing the cavitation threshold.

Synthesis and Characterization of Polystyrene Possessing Triptycene Units in the Main Chain by Combination of ATRP and Click Chemistry Processes

Polystyrene with triptcyene units were synthesized by combination of Atom Transfer Radical Polymerization (ATRP) and “Click” chemistry processes and characterized. Well-defined precursor polystyrene with predetermined molecular weight and narrow polydispersity was prepared by ATRP in the presence of Cu(I)/pentamethyldiethylenetriamine (PMDETA) catalyst system and terminal bromine groups of the obtained polymer were converted to azide group by using NaN3. The click reaction between diazido compounds, namely diazido polystyrene (N3-PSt-N3) and diazidodecane (DAD) and dialkyne compounds, dipropargyloxytriptycene (DPT) and dipropargyloxydecane (DPD) resulted in the formation polystyrene with triptycene units in the main chain. Dialkyne compound without triptycene unit such as dipropargyloxybenzene (DPB) was used under the same click conditions for comparison. Characterization of the intermediates and the resulting polymers was performed by means of FT-IR and 1H-NMR spectral analysis, and GPC, DSC and TGA studies. The effect of the triptycene moiety on the thermal properties was evaluated.

Modification of polydivinylbenzene microspheres by a hydrobromination/click-chemistry protocol and their protein-adsorption properties.

Hydrophobic- and/or hydrophilic-polymer-grafted PDVB microspheres are synthesized by the combination of hydrobromination and click-chemistry processes. The modified-PDVB microspheres and the intermediates at various stages of synthesis are characterized using GPC, ¹H NMR and FTIR spectroscopy and TGA analysis. Use of the microspheres as a support matrix for reversible protein immobilization via adsorption is investigated. The system parameters such as the adsorption conditions (i.e., enzyme concentration, medium pH) and desorption are studied and evaluated with regards to the biocatalytic activity and adsorption capacity.

Development of nanodroplets for histotripsy-mediated cell ablation.

This report describes the synthesis of amphiphilic copolymers (ABC-1 and ABC-2) composed of a hydrophilic poly(ethylene glycol) (PEG) block, a central poly(acrylic acid) (PAA) block, and a random copolymer of heptadecafluorodecyl methacrylate (HDFMA) and methyl methacrylate (MMA) forming the hydrophobic block, which are used to form nanodroplets for ultrasound-mediated cell ablation. Specifically, the effect of molecular weight of PEG and P(HDFMA-co-MMA) blocks on polymers ability to self-assemble around a variable amount (0%, 1%, and 2% v/v) of perfluoropentane (PFP) forming nanodroplets is investigated. The ability of different nanodroplets formulations embedded with a monolayer of red blood cells (RBCs) in tissue-mimicking agarose phantoms to initiate and sustain a bubble cloud in response to ultrasound treatments with different acoustic pressures and the associated ablation of RBCs were also investigated. Results show that ABC-1 polymer composed of a 2 kDa PEG block and a 6.7 kDa P(HDFMA-co-MMA) block better encapsulate the PFP core compared to ABC-2 polymer composed of a 5 kDa PEG block and 11.4 kDa P(HDFMA-co-MMA) block. Further, the ablative capacity indicated by the damage area in the RBCs monolayer increased with the increase in PFP content and reached its maximum with the nanodroplets formulated using ABC-1 polymer and encapsulating 2% v/v PFP. The nanodroplets formulated using ABC-1 polymer and loaded with 2% PFP produced the cavitation cloud and exhibited their ablative effect at an acoustic pressure that is 2.5-fold lower than the acoustic pressure needed to generate the same effect using a histotripsy (ultrasound) pulse alone, which indicates the ability of these nanodroplets to achieve targeted and self-limiting fractionation of disease cells while sparing neighboring healthy ones. Results also show that effective nanodroplets maintained their size and concentration upon incubation with bovine serum albumin at 37 °C for 24 h, which indicates their stability in physiologic conditions and their promise for in vivo cancer cell ablation.

Light Induced Processes for the Synthesis of Polymers With Complex Structures

Light induced reactions are based on the absorption of light that excites the electrons of a molecule and can, under favorable circumstances, lead to dissociation, isomerization, abstraction, electron or energy transfer, and bond formation. These reactions have been the subject of many studies in various fields including organic chemistry, molecular biology, electronics etc. Light induced reactions can advantageously be utilized in the field of polymer chemistry. Among them, light induced polymerization is of enormous commercial importance. Techniques such as curing of coatings on wood, metal and paper, adhesives, printing inks and photoresists are based on photopolymerization. There are some other interesting applications, including production of laser video discs and curing of acrylate dental fillings. In this chapter, general methods for the light induced polymerization processes involving radical and ionic reactions are described. Special emphasize is devoted to their application to more complex macromolecular structures such as block, graft and star copolymers, and polymer nanocomposites based on clay and metal.