Improved performance by replacing iminodiacetic residues with glyceryl residues in symmetrically branched oligoglycerols

[Conjugation to Branched Glycerol Oligomers, a Novel Strategy for Extremely Hydrophobic Agents]

Ascertaining the absorption, distribution, metabolism, and excretion (ADME) profile of drugs is one of the most crucial factors in the process of drug discovery. Since it is important to combine water solubility and cell permeability within the compound to achieve the desired ADME properties, an appropriate balance between lipophilicity and hydrophilicity is required. It is often necessary to facilitate hydrophilicity of very hydrophobic candidates, because quite lipophobic molecules are rarely hit as positive in molecular-targeted or cell-based screenings. For that purpose, it has been popular to conjugate hydrophobic molecules with polyethylene glycol (PEG). However, PEG is a polymer, and PEG-conjugated molecules are not uniform. Besides, the dosage should be much increased compared with the original molecule due to the increase in molecular weight. Therefore we have been developing alternative ways to endow hydrophobic compounds with extra hydrophilicity by conjugating with symmetrically branched glycerol oligomers. This technology is versatile and easily applicable to various hydrophobic compounds. Water-solubility of fenofibrate, one of the most hydrophobic medicines in clinical use, was facilitated by a factor of more than 2000, and its lipid-lowering effect in vivo improved more than ten-fold, by simply conjugating with branched glycerol trimer, for instance. Here we will briefly introduce the basic concepts and our successful experiences of applying branched glycerol oligomers including antitumor agents in terms of water-solubility, pharmacological effects, and pharmacokinetics, and merits and current issues will be discussed in this review.

Acute oral toxicity evaluation of symmetrically branched glycerol trimer in ddY mice

Lipophilic-hydrophilic balance is a quite important determinant of pharmacokinetic properties of pharmaceuticals. Thus it is a key step to successfully manage lipophilic-hydrophilic balance in drug design. We have designed unique modular molecules, symmetrically branched oligoglycerols (BGL) as an alternative means to endow hydrophobic molecules with much hydrophilicity. We have succeeded in improving the water-solubility of several hydrophobic medicinal small molecules and thermal stability of artificial protein by covalent conjugation to BGL. We have also demonstrated that a representative BGL, symmetrically branched glycerol trimer (BGL003) does not exhibit significant cytotoxicity against human hepatocarcinoma HepG2 cells. However, there have been no reports suggesting whether BGL could be used in safety in vivo. Therefore, evaluation of acute oral toxicity of BGL003 in healthy mice was conducted. Here we demonstrate that an oral administration of BGL003 did not exhibit acute lethal toxicity up to 3,000 mg/kg. Body weight, food intake, blood glucose levels and weights of tissues were not affected by a short-term repetitive administration of increasing doses of BGL003. Biochemical indications related to hepatic disorders and tissue damage were unchanged, either. A single administration study revealed that 50% lethal dose of BGL003 should be more than 2,000 mg/kg. BGL003 will be safe and suitable approach to improve hydrophilicity of hydrophobic compounds.

A novel prodrug strategy for extremely hydrophobic agents: conjugation to symmetrically branched glycerol trimer improves pharmacological and pharmacokinetic properties of fenofibrate

Management of a lipophilic-hydrophilic balance is a key element in drug design to achieve desirable pharmacokinetic characters. Therefore we have created unique modular molecules, symmetrically branched oligoglycerols (BGL), as an alternative way to endow hydrophobic molecules with sufficient hydrophilicity. We have successfully demonstrated amelioration of the water solubility and thermal stability of several hydrophobic agents by covalent conjugation to BGL so far. However, it has not been clarified whether the molecular modification by BGL also improves the pharmacological and/or pharmacokinetic properties indeed. Recently, we synthesized a novel BGL-prodrug derivative of fenofibrate, which is an antihyperlipidemic agent and one of the most hydrophobic medicinal compounds currently used clinically, by conjugating fenofibric acid to symmetrically branched glycerol trimer (BGL003), the simplest BGL. We have previously demonstrated that the hydrophilicity and water solubility of fenofibrate are improved more than 2000 times just by conjugation to the BGL003. To verify our hypothesis that the prodrug strategy with BGL should improve pharmacological efficacy and pharmacokinetic properties of extremely hydrophobic agents such as fenofibrate by the rise in hydrophilicity, we evaluated the BGL003-prodrug derivative of fenofibrate (FF-BGL) using rodent models. Here we demonstrate that the lipid-lowering effects of fenofibrate are much potentiated by chemical conjugation to BGL003 without exhibiting significant toxicity. Plasma concentration of fenofibric acid, an active metabolite of fenofibrate, after single oral administration of FF-BGL was more than 3 times higher than that of fenofibrate, in accordance. In fasting rats, plasma concentration of fenofibric acid after fenofibrate administration was curtailed into less than half of that in ad libitum-fed rats, while FF-BGL showed about the same plasma level even in the starving rats. This is the first report showing that BGL-prodrug improves pharmacological and pharmacokinetic properties as well as hydrophilicity of highly hydrophobic compounds. Furthermore, prodrug strategy using BGL suggests the possibility of diminishing the food-drug interaction effects, which should be advantageous for promoting drug compliance. BGL will be a suitable prodrug strategy to ameliorate physical, pharmacological, and pharmacokinetic characteristics of extremely hydrophobic compounds.

Cytotoxicity evaluation of symmetrically branched glycerol trimer in human hepatocellular carcinoma HepG2 cells

An appropriate balance between lipophilicity and hydrophilicity is necessary for pharmaceuticals to achieve fine Absorption, Distribution, Metabolism and Excretion (ADME) properties including absorption and distribution, in particular. We have designed and proposed symmetrically branched oligoglycerols (BGL) as an alternative approach to improve the lipophilic-hydrophilic balance. We have previously shown that stability in circulation and water-solubility of such molecules as proteins, liposomes and hydrophobic compounds are much improved by conjugation to BGL. Albeit these successful applications of BGL, little was known whether BGL could be used in safety. Thus we conducted evaluation of the cytotoxicity of a representative BGL, symmetrically branched glycerol trimer (BGL003) in the cultured cells to clarify its biological safeness. Here we demonstrate that water-solubility of an extremely hydrophobic agent, fenofibrate was more than 2,000-fold improved just by conjugated with BGL003. BGL003 did not exhibit any significant cytotoxicity in human hepatocarcinoma HepG2 cells. Thus BGL003 should be safe and suitable strategy to endow hydrophobic molecules with much hydrophilicity.

Synthesis of paclitaxel-BGL conjugates

Four kinds of symmetrically branched oligoglyceryl trimeric (BGL003)-paclitaxel conjugates and a corresponding heptameric (BGL007) conjugate were synthesized. Molecular weights of all the compounds were less than two times that of paclitaxel. The anti-tumor activity of the most water-soluble BGL003 conjugate was examined and found to be preserved in spite of the chemical modification that is displacement of the N3'-debenzoyl residue with the BGL003 succinyl residue.