Preparation and evaluation of polyvinyl alcohol-co-oleylvinyl ether derivatives as tumor-specific cytotoxic systems

D-α-Tocopherol-Based Micelles for Successful Encapsulation of Retinoic Acid

All-trans-retinoic acid (ATRA) represents the first-choice treatment for several skin diseases, including epithelial skin cancer and acne. However, ATRA's cutaneous side effects, like redness and peeling, and its high instability limit its efficacy. To address these drawbacks and to improve ATRA solubilization, we prepared ATRA-loaded micelles (ATRA-TPGSs), by its encapsulation in D-α-tocopheryl-polyethylene-glycol-succinate (TPGS). First, to explore the feasibility of the project, a solubility study based on the equilibrium method was performed; then, six ATRA-TPGS formulations were prepared by the solvent-casting method using different TPGS amounts. ATRA-TPGSs showed small sizes (11-20 nm), low polydispersity, slightly negative zeta potential, and proved good encapsulation efficiency, confirmed by a chemometric-assisted Fourier transform infrared spectroscopy (FTIR) investigation. ATRA-TPGS stability was also investigated to choose the most stable formulation. Using Carbopol^® 980 as gelling agent, ATRA-TPGS-loaded gels were obtained and analyzed for their rheological profiles. Ex vivo release studies from ATRA-TPGSs were performed by Franz cells, demonstrating a permeation after 24 h of 22 ± 4 µ cm^-2. ATRA-TPGSs showed enhanced cytotoxic effects on melanoma cells, suggesting that these formulations may represent a valid alternative to improve patient compliance and to achieve more efficacious therapeutic outcomes.

Enhancement of Oleyl Alcohol Anti Tumor Activity through Complexation in Polyvinylalcohol Amphiphilic Derivatives

Oleyl alcohol was complexed with new amphiphilic polyvinylalcohol derivatives with the aim of increasing its aqueous solubility, thus improving bioavailability and favoring its antitumor activity. Water-soluble amphiphilic polymers were prepared by polyvinyl alcohol (PVA) substitution with oleyl chains through a succinyl spacer at 2% and 3% substitution degree. The complexes were obtained by spray-drying hydroalcoholic solutions of the substituted polymers and free oleyl alcohol at different weight ratios (3:1; 5:1; 10:1 w/w). The main physicochemical characteristics of the complexes were analyzed and correlated to the cytotoxic activity of oleyl alcohol toward tumor cell lines. The complexes strongly increased the aqueous solubility of oleyl alcohol and provided oleyl alcohol release in the presence of extractive conditions (simulating in vivo absorption). The complexes obtained by 10:1 polymer:fatty alcohol weight ratio offered higher release rates than the 5:1 and 3:1 ratios, respectively. Complexation also increased oleyl alcohol cytotoxicity toward tumor cells due to increased availability of the active molecule in the aqueous phase. Pure polymers were found to be biocompatible and no toxic effect was detected up to the highest concentration used in the present study (500 mu g/ml). The complexation of oleyl alcohol with the polymers analyzed here efficiently increased the availability of the fatty alcohol in aqueous environment. The enhanced cytotoxicity toward tumor cells of the complexed oleyl alcohol and the polymer biocompatibility make these amphiphilic PVA derivatives interesting candidates for soluble pharmaceutical formulations containing hydrophobic drugs whose therapeutic potential is often underestimated due to unsuitable levels of their aqueous solubilization.

Amphiphilic poly(vinyl alcohol) derivatives as complexing agents for fenretinide

Poly(vinyl alcohol) (PVA) substituted with oleyl chains and tetraethyleneglycol monoethyl ether chains (TEGMEE) at 1.5% and 1% degrees of substitution respectively (mol of substituent to mol of hydroxyvinyl monomer) has previously been shown to self-assemble in water, providing aggregates selectively cytotoxic toward tumor cells vs normal cells. These polymers have also been shown to increase the long-term survival of nude mice injected with both human and murine neuroblastoma cell lines. In the present work, we changed the substitution degree of the oleyl chains on the poly(vinyl alcohol) backbone and maintained constant at 1% the degree of TEGMEE substitution. We evaluated the main physicochemical characteristics of the final polymers, their cytotoxicity toward tumor cells, and their complexing ability for hydrophobic molecules. The aim was to investigate the possibility of improving intrinsic antitumor efficacy of the polymer by changing the degree of oleyl chain substitution and further increase activity by complexation with antitumor drugs. The polymers were prepared at oleyl chain substitution degrees ranging from 0.5 to 3% (mol of substituent to mol of hydroxyvinyl monomer). The most active was again the 1.5% substituted polymer. It was further characterized by exhibiting the highest complexing ability toward hydrophobic molecules allowing the formation of a complex with fenretinide (HPR). The polymer-HPR complex was stable in aqueous environment and released the free drug prevalently in the presence of fluid hydrophobic phases. It was cytotoxic toward tumor cells with minimal activity toward normal cells. Antitumor activity exceeded that of the separate complex components resulting from the concomitant effect of the polymer and the HPR solubilized by complexation.

In vitro and In vivo Antitumor Activity of the Novel Derivatized Polyvinyl Alcohol-Based Polymer P10(4)

PURPOSE

The major limitation to successful chemotherapy of neuroblastoma is the toxicity of traditional antitumor drugs. Hence, less toxic and more effective drugs are to be found, and novel formulations of conventional compounds allowing a more favorable biodistribution should be sought for. In an attempt to pursue this task, we recently synthesized an amphiphilic polymer based on a polyvinyl alcohol backbone [P10(4)].

EXPERIMENTAL DESIGN

The cytotoxic activity of P10(4) was evaluated both in vitro on neuroblastoma and melanoma cell lines and in vivo in pseudometastatic neuroblastoma models. Apoptosis was assessed by morphology, cytofluorimetric analysis of DNA content, and DNA fragmentation assay. Caspases activation was investigated by kits specific for caspase-1, caspase-2, caspase-3, caspase-4, caspase-6, caspase-7, caspase-8, caspase-9, caspase-10, and caspase-13. Colony formation was evaluated by soft agar assay.

RESULTS

P10(4) exerted a potent cytotoxic activity on different neuroblastoma and melanoma cell lines through induction of both extrinsic and intrinsic caspase cascades and subsequent apoptosis. Moreover, the clonogenic potential of cells that survived P10(4) treatment was strongly reduced. Next, we tested the effects of P10(4) in nude mice injected with both a human and a murine neuroblastoma cell lines i.v. P10(4) significantly increased the life span and the long-term survival of treated mice over controls. No side effects were observed, even at doses higher than those used for therapeutic purposes.

CONCLUSIONS

Our data suggest that P10(4) holds promise as an anticancer compound and, because of its lack of interaction with DNA, is unlikely to give rise to drug resistance.