Micellar complexes of all-trans retinoic acid with polyvinylalcohol-nicotinoyl esters as new parenteral formulations in neuroblastoma.

All-trans-retinoic acid (ATRA) is now included in many antitumor therapeutic schemes for the treatment of acute promyelocytic leukemia, Kaposi's sarcoma, head and neck squamous cell carcinoma, ovarian carcinoma, bladder cancer, and neuroblastoma. Unfortunately, its poor aqueous solubility hampers its parenteral formulation, whereas oral administration of ATRA is associated with progressively diminishing drug levels in plasma, which is related to induction of retinoic acid-binding proteins and increased drug catabolism by cytochrome P450-mediated reactions. An ATRA formulation, obtained by complexation of the drug into polymeric micelles, might be suitable for parenteral administration overcoming these unwanted effects. To this purpose, amphiphilic polymers were prepared by polyvinylalcohol (PVA) partial esterification with nicotinoyl moieties and their functional properties evaluated with regard to ATRA complexation. The physicochemical characteristics of the polymers and the complexes were analyzed by 1H-NMR, Dynamic Light Scattering (DLS), Capillary Electophoresis (CE), and were correlated with the complex ability to improve the drug solubilization and release the free drug in an aqueous environment. Subsequently, the best complex, providing the highest ATRA solubilization and release, was evaluated in vitro to test its cytotoxicity towards neuroblastoma cell lines. The PVA substitution degree calculated from 1H-NMR was found to be 5.0%, 8.2%, 15.3% (nicotinoyl moiety:PVA monomer molar ratio), while capillary electrophoresis analysis on the complexes revealed that the drug loadings were 0.95%, 1.20%, 4.76% (ATRA:polymer w:w) for PVA substitution degrees of 5.0%, 8.2%, and 15.3%, respectively. Complexation strongly increased ATRA aqueous solubility, which reached 1.20 +/- 0.25 mg/mL. The DLS measurements of the polymers and the complexes in aqueous solutions revealed mean sizes always below 400 nm, low polydispersity (min 0.202 +/- 0.013, max 0.450 +/- 0.032), and size almost unaffected by concentration. Drug fractional release did not exceed 8% after 48 h. The cytotoxicity studies against neuroblastoma cell lines outlined a significant growth inhibition effect of complexed ATRA with respect to free ATRA. These data suggest that the systems analyzed may be suitable carriers for parenteral administration of ATRA and other hydrophobic antitumor drugs, where the carriers are required to improve drug aqueous solubility and delay drug release almost after their accumulation in solid tumors.

Fenretinide-polyvinylalcohol conjugates: new systems allowing fenretinide intravenous administration.

N-(4-hydroxyphenyl)retinamide (fenretinide, 4-HPR) has been shown to be active toward many tumors without appreciable side effects. However its in vitro activity does not match a correspondent efficacy in vivo. The main reason is that the drug's hydrophobicity hinders its bioavailability in the body fluids. Even if the drug is previously dissolved in organic solvents, such as ethanol or DMSO, the subsequent dilution in body fluids trigger its precipitation in fine aggregates characterized by very low dissolution efficiency, never reaching amounts suitable for therapeutic response. To date no intravenous formulation of 4-HPR exists on the market. The 4-HPR linkage to a hydrophilic polymer by a covalent bond easily hydrolyzable in aqueous environment is expected to increase the drug's aqueous solubility, providing the free drug after hydrolysis of the covalent bond. This may be a useful tool for the preparation of aqueous intravenous formulations of 4-HPR. For this purpose, we linked 4-HPR to polyvinylalcohol (PVA) by a carbonate bond at different drug/hydroxy vinyl monomer molar ratios. We demonstrated that conjugation increased 4-HPR aqueous solubility and strongly inhibited neuroblastoma cell proliferation. In addition, in an in vivo neuroblastoma metastatic model, we obtained a significant antitumor effect as a consequence of the improved drug bioavailability.

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.

Mucoadhesive tablets for buccal administration containing sodium nimesulide.

The possibility of improving the flux of nimesulide across the buccal mucosa using the drug in the form of a sodium salt was investigated in our study. The salt form may increase to flux across buccal membrane, starting from a suspension; its lower permeation coefficient is compensated by a higher concentration gradient. The salt was inserted into a mucoadhesive tablet for buccal administration. The tablets were designed to prevent the loss of the drug into the saliva by means of a protective layer and placed on the area not in contact with the mucosa. Ten volunteers were used. The in vitro release from mucoadhesive tablets was examined through a porcine buccal mucosa, using a standard Franz cell, modified for present purposes. The advantages of a higher concentration gradient for the flux, related to a higher solubility of the salt, and to a sufficiently high permeation coefficient of the drug, despite the ionized form, could not be completely exploited, because the composition of the formulation destroys the chemical form of the drug.