Implantable HDAC-inhibiting chemotherapeutics derived from hydrophobic amino acids for localized anticancer therapy

Abstract

Epigenetic targeting of different cancers by inhibiting particular histone deacetylase (HDAC) isozymes is a promising treatment approach against cancer. Development of locally-implantable molecular inhibitors of HDAC (henceforth called HDACi) promises high tumour site concentration and reduced systemic degradation of the HDACi. Herein, we report the design of such implantable HDACi based on amphiphilic derivatives of hydrophobic amino acids endowed with a hydroxamic acid (hxa)-based zinc-binding residue. The amino acids present in HDACi influenced the HDAC isozyme that could be inhibited most effectively; the L-phenylalanine derivative 4e inhibited the HDAC6 isozyme most potently (IC₅₀ ∼ 88 nM), while the L-isoleucine derivative 4h was most effective against the isozyme HDAC2 (IC₅₀ ∼ 94 nM). We also noticed that the L-Phe derivative 4e was up to 5× more potent towards inhibiting HDAC6 than its optical antipode 4f derived from D-Phe. This was rationalized in terms of the varying extent of penetration of the enantiomeric inhibitors inside the catalytic tunnel of the enzyme. Since the isozymes HDAC6 and HDAC2 are overexpressed in different cancer cells, 4e and 4h elicited selective anticancer activity in different cancer cell lines. Additive therapeutic action of the combination therapy of 4e and 4h was observed on lung cancer cells that overexpress both these isozymes. Further, 4e formed implantable self-assembled hydrogels that achieved sustained and selective killing of cancer cells in the vicinity of implantation.