SYNTHESIS AND ANTICANCER ACTION OF NITRIC OXIDE-RELEASING LIPOSOMES

The implementation of nitric oxide (NO)-based therapeutics has been met with formidable challenges relating to NO’s gaseous, reactive nature and difficulties associated with controlled delivery. Although macromolecular vehicles have been developed for applications in NO release, a common limitation associated with these systems is exposure of the NO donor to the surrounding medium, resulting in unintended NO release. To overcome this issue, liposomes were investigated as new vehicles for NO delivery whereby the NO donor is encapsulated within the aqueous core, protected from the external solution by a lipid membrane. Liposomes with encapsulated N-diazeniumdiolate NO donors were first synthesized using a reverse-phase evaporation protocol. Encapsulation efficiencies for several molecular NO donors were in the range of 33–41%. Relative to the unencapsulated (free) NO donor, NO-release half-lives at pH 7.4 were up to 7-times greater upon encapsulation, yet the NO-releasing liposomes still exhibited their unique pH-sensitive release properties. The liposomes retained ~80% of the encapsulated NO concentrations after 3 months of storage at 4°C, indicating excellent stability. In order to determine if the liposomes held merit as therapeutic agents, cytotoxicity against human pancreatic cancer cells were performed that demonstrated the liposomal NO donors required less NO to kill versus the free NO donor (183 μM and 2.4 mM, respectively). The ability to tune NO-release kinetics of these liposomes was further studied. It was possible to vary the NO-release kinetics by altering the encapsulated NO donor molecule or the phospholipid composing the bilayer (independently or in combination). Phospholipid headgroup surface area was determined to be a main factor in controlling NO-release half-lives. As the surface area of the lipid headgroup was decreased from 0.660 nm2 to 0.420 nm2, a concomitant increase in NO-release half-life was also observed. The composition of the lipid bilayer is known to affect in vivo properties, so NO-release kinetics were also measured in serum and whole blood. Half-lives in serum were equivalent to those measured in buffer, while those measured in blood were ~60% faster. An investigation into the cytotoxicity of slow (t1/2 > 72 h) versus fast (t1/2 ~ 2.5 h) NO-releasing liposomes demonstrated how the biological consequences were dependent on the NO-release rate. Fast NO-releasing liposomes yielded consistently higher LD50 values (>230 μM NO), relative their slow-releasing counterparts (<230 μM NO), across 9 different cancer cell lines encompassing 3 different types of cancer (breast, colorectal, and pancreatic). The fast-release system was able to eradicate 50% of the cells much quicker (~36 h vs. 72 h for slow-release system). Flow cytometry studies suggest that this faster killing is due to a more rapid intracellular build-up of NO, which was observed for both the free and encapsulated NO donors. Western blotting revealed that both the slow and fast NO-release systems could induce apoptosis, albeit to different degrees.Doctor of Philosoph

Electrochemical Modulation of Nitric Oxide Release Using Diazeniumdiolated Species

Honors (Bachelor's)ChemistryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/96648/1/dsuchyta.pd

Encapsulation of <i>N</i>‑Diazeniumdiolates within Liposomes for Enhanced Nitric Oxide Donor Stability and Delivery

The rapid decomposition of nitric oxide (NO) donors in aqueous environments remains a limitation for applications requiring extended NO release. Herein, we report the synthesis of dipalmitoyl­phosphatidylcholine-based liposomes capable of extended NO release using low molecular weight NO donors and a reverse-phase evaporation technique. The encapsulation of the NO donors within the liposomes enabled both prolonged NO release and enhanced storage compared to free NO donors alone. The NO-releasing liposomes also demonstrated enhanced efficacy against human pancreatic cancer cells. These NO-release vehicles represent attractive anticancer therapeutics due to their potential to store the majority of their NO payload until reaching cancerous tissue at which time the lower pH inherent to such environments will trigger an avalanche of NO

Controlled Release of Nitric Oxide from Liposomes

We report the ability to readily tune NO release from <i>N</i>-diazeniumdiolate-encapsulated liposomal structures by altering the NO donor molecule structure and/or phospholipid composition (independently or in combination). While encapsulating more stable NO donors expectedly enhanced the NO release (up to 48 h) from the liposomes, the phospholipid headgroup surface area proved equally useful in controlling NO-release kinetics by influencing the proton uptake and concomitant <i>N</i>-diazeniumdiolate NO donor breakdown (to NO). The potential therapeutic utility of the NO-releasing liposomes was further assessed in biological/proteinaceous fluids. The NO-release kinetics were similar in buffer and serum

Antibacterial Activity of Nitric Oxide-Releasing Hyperbranched Polyamidoamines

Hyperbranched polyamidoamines (h-PAMAM) were prepared using a one-pot reaction to have similar molecular weight to third generation PAMAM (G3-PAMAM) dendrimers, and then functionalized with <i>N</i>-diazeniumdiolate nitric oxide (NO) donors. A wide range of NO storage capacities (∼1–2.50 μmol mg^–1) and NO-release kinetics (<i>t</i>_1/2 ∼30–80 min) were achieved by changing the extent of propylene oxide (PO) modification. The therapeutic potential of these materials was evaluated by studying their antibacterial activities and toxicity against common dental pathogens and human gingival fibroblast cells, respectively. Our results indicate that the combination of NO release and PO modification is necessary to yield h-PAMAM materials with efficient bactericidal action without eliciting unwarranted cytotoxicity. Of importance, NO-releasing PO-modified h-PAMAM polymers exhibited comparable biological properties (i.e., antibacterial action and cytotoxicity) to defect-free G3-PAMAM dendrimers, but at a substantially lower synthetic burden

Nitric Oxide-Releasing Alginates

Low and high molecular weight alginate biopolymers were chemically modified to store and release potentially therapeutic levels of nitric oxide (NO). Carbodiimide chemistry was first used to modify carboxylic acid functional groups with a series of small molecule alkyl amines. The resulting secondary amines were subsequently converted to <i>N</i>-diazeniumdiolate NO donors via reaction with NO gas under basic conditions. NO donor-modified alginates stored between 0.4–0.6 μmol NO·mg^–1. In aqueous solution, the NO-release kinetics were diverse (0.3–13 h half-lives), dependent on the precursor amine structure. The liberated NO showed bactericidal activity against <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i> with pathogen eradication efficiency dependent on both molecular weight and NO-release kinetics. The combination of lower molecular weight (∼5 kDa) alginates with moderate NO-release durations (half-life of ∼4 h) resulted in enhanced killing of both planktonic and biofilm-based bacteria. Toxicity against human respiratory epithelial (A549) cells proved negligible at NO-releasing alginate concentrations required to achieve a 5-log reduction in viability in the biofilm eradication assay

The CDK inhibitor CR8 acts as a molecular glue degrader that depletes cyclin K

Molecular glue compounds induce protein-protein interactions that, in the context of a ubiquitin ligase, lead to protein degradation; 1; . Unlike traditional enzyme inhibitors, these molecular glue degraders act substoichiometrically to catalyse the rapid depletion of previously inaccessible targets; 2; . They are clinically effective and highly sought-after, but have thus far only been discovered serendipitously. Here, through systematically mining databases for correlations between the cytotoxicity of 4,518 clinical and preclinical small molecules and the expression levels of E3 ligase components across hundreds of human cancer cell lines; 3-5; , we identify CR8-a cyclin-dependent kinase (CDK) inhibitor; 6; -as a compound that acts as a molecular glue degrader. The CDK-bound form of CR8 has a solvent-exposed pyridyl moiety that induces the formation of a complex between CDK12-cyclin K and the CUL4 adaptor protein DDB1, bypassing the requirement for a substrate receptor and presenting cyclin K for ubiquitination and degradation. Our studies demonstrate that chemical alteration of surface-exposed moieties can confer gain-of-function glue properties to an inhibitor, and we propose this as a broader strategy through which target-binding molecules could be converted into molecular glues