AN-113, a novel prodrug of 4-phenylbutyrate with increased anti-neoplastic activity in glioma cell lines

Targeting post-translational histone modifying enzymes in glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor in adults, and the most lethal form of glioma, characterized by variable histopathology, aggressiveness and poor clinical outcome and prognosis. GBMs constitute a challenge for oncologists because of their molecular heterogeneity, extensive invasion, and tendency to relapse. Glioma cells demonstrate a variety of deregulated genomic pathways and extensive interplay with epigenetic alterations. Epigenetic modifications have emerged as essential players in GBM research, with biomarker potential for tumor classification and prognosis and for drug targeting. Histone posttranslational modifications (PTMs) are crucial regulators of chromatin architecture and gene expression, playing a pivotal role in malignant transformation, tumor development and progression. Alteration in the expression of genes coding for lysine and arginine methyltransferases (G9a, SUV39H1 and SETDB1) and acetyltransferases and deacetylases (KAT6A, SIRT2, SIRT7, HDAC4, 6, 9) contribute to GBM pathogenesis. In addition, proteins of the sumoylation pathway are upregulated in GBM cell lines, including E1 (SAE1), E2 (Ubc9) components, and a SUMO-specific protease (SENP1). Preclinical and clinical studies are currently in progress targeting epigenetic enzymes in gliomas, including a new generation of histone deacetylase (HDAC), protein arginine methyltransferase (PRMT) and bromodomain (BRD) inhibitors. Herein, we provide an update on recent advances in glioma epigenetic research, focusing on the role of histone modifications and the use of epigenetic therapy as a valid treatment option for glioblastoma.

Histone deacetylase inhibitor based prodrugs

Histone deacetylases (HDACs) are a family of enzymes which play important roles in the development and progression of cancers. Inhibition of HDACs has been widely studied as a therapeutic strategy in the discovery of anticancer drugs. HDAC inhibitors (HDACIs) have exhibited potency against a variety of cancer types, and four of them have been approved by the US FDA for cancer treatment. However, the clinical benefits of current HDACIs is limited by the insufficient physicochemical property, selectivity and potency. To improve the clinical potential of HDACIs, the prodrug strategy had been utilized to improve the in vivo pharmacokinetic and pharmacodynamic performances of HDACIs. Enhancements in the stability, water solubility, lipophilicity, oral bioavailability and tumor cell selectivity were reported by various studies. Herein, the development of different kinds of HDACI-based prodrug is summarized for the further structural modification of HDACIs with high potential to be drug candidates.

Species Differences in the Binding of Sodium 4-Phenylbutyrate to Serum Albumin

Sodium 4-phenylbutyrate (PB) is clinically used as a drug for treating urea cycle disorders. Recent research has shown that PB also has other pharmacologic activities, suggesting that it has the potential for use as a drug for treating other disorders. In the process of drug development, preclinical testing using experimental animals is necessary to verify the efficacy and safety of PB. Although the binding of PB to human albumin has been studied, our knowledge of its binding to albumin from the other animal species is extremely limited. To address this issue, we characterized the binding of PB to albumin from several species (human, bovine, rabbit, and rat). The results indicated that PB interacts with 1 high-affinity site of albumin from these species, which corresponds to site II of human albumin. The affinities of PB to human and bovine albumins were higher than those to rabbit and rat albumin, and that to rabbit albumin was the lowest. Binding and molecular docking studies using structurally related compounds of PB suggested that species differences in the affinity are attributed to differences in the structural feature of the PB-binding sites on albumins (e.g., charge distribution, hydrophobicity, shape, or size).

Acylation or phosphorylation of hydroxyurea unexpectedly takes place on N rather than on O, leading to the formation of amides instead of the expected esters

Attempted acylation of the anticancer agent hydroxyurea (HU) with acyl chlorides or anhydrides led to acylation on the NH group rather than on the OH.

Physicochemical property trends of marketed prodrugs

Many prodrug reviews describe specific examples of the successful application of prodrug technology to produce blockbuster drugs, such as simvastatin, omeprazole, acyclovir and enalapril. These reviews are helpful to understand the previous success stories and case histories of prodrug technology. The aim of the current review seeks to more clearly define quantitative trends in the changes in the physicochemical property parameters between the successful prodrug and the active parent molecule. This information can serve to guide medicinal chemists toward more successful pharmaceutical prodrugs in the future.