Chemosensitizing Activity of Histone Deacetylases Inhibitory Cyclic Hydroxamic Acids for Combination Chemotherapy of Lymphatic Leukemia

BACKGROUND

Anti-tumor effect of hydroxamic acid derivatives is largely connected with its properties as efficient inhibitors of histone deacetylases, and other metalloenzymes involved in carcinogenesis.

OBJECTIVE

The work was aimed to (i) determine the anti-tumor and chemosensitizing activity of the novel racemic spirocyclic hydroxamic acids using experimental drug sensitive leukemia P388 of mice, and (ii) determine the structure-activity relationships as metal chelating and HDAC inhibitory agents.

METHOD

Outbreed male rat of 200-220 g weights were used in biochemical experiments. In vivo experiments were performed using the BDF1 hybrid male mice of 22-24 g weight. Lipid peroxidation, Fe (II) -chelating activity, HDAC fluorescent activity, anti-tumor and anti-metastatic activity, acute toxicity techniques were used in this study.

RESULTS

Chemosensitizing properties of water soluble cyclic hydroxamic acids (CHA) are evaluated using in vitro activities and in vivo methods and found significant results. These compounds possess iron (II) chelating properties, and slightly inhibit lipid peroxidation. CHA prepared from triacetonamine (1a-e) are more effective Fe (II) ions cheaters, as compared to CHA prepared from 1- methylpiperidone (2a-e). The histone deacetylase (HDAC) inhibitory activity, lipophilicity and acute toxicity were influenced by the length amino acids (size) (Glycine < Alanine < Valine < Leucine < Phenylalanine). All compounds bearing spiro-N-methylpiperidine ring (2a-e) are non-toxic up to 1250 mg/kg dose, while compounds bearing spiro-tetramethylpiperidine ring (1a-e) exhibit moderate toxicity which increases with increasing lipophility, but not excite at 400 mg/kg.

CONCLUSION

It was shown that the use of combination of non-toxic doses of cisplatin (cPt) or cyclophosphamide with CHA in most cases result in the appearance of a considerable anti-tumor effect of cytostatics. The highest chemosensitizing activity with respect to leukemia Р388 is demonstrated by the CHA derivatives of Valine 1c or 2c.

PXD101 analogs with L-phenylglycine-containing branched cap as histone deacetylase inhibitors

Histone deacetylases (HDACs) allow histones to wrap DNA more tightly and finally lead to the repression of some tumor suppressor genes. Histone deacetylase inhibitors (HDACIs) have been proved to have effects on tumorigenesis and tumor progression. In this study, we reported the design, synthesis, and in vitro activity evaluation of novel PXD101 analogs with L-phenylglycine-containing cap as HDACIs. Our results showed that HDACs inhibitory activities of compounds 10k, 10r, and 10s were not only superior to the first approved HDACI SAHA, but also comparable to their parent compound PXD101, a recently approved HDACI in 2014. However, all 6 selected PXD101 analogs exhibited moderate in vitro antiproliferative activities, less potent than PXD101 and SAHA. Representative compound 10s showed similar HDACs isoform selective profile to PXD101, which demonstrated that introduction of L-phenylglycine-containing branched cap group could not change the isoform selectivity of PXD101 dramatically.

Development of N-hydroxybenzamide derivatives with indole-containing cap group as histone deacetylases inhibitors

Histone deacetylases inhibitors (HDACIs) have captured more and more attention in many diseases therapies, of which cancer is the most intractable. A novel series of N-hydroxybenzamide derivatives containing indole cap group was designed and synthesized. Most compounds exhibited excellent HDACs inhibitory activity, especially 8q-8v with low nanomolar IC₅₀ values (1.5-13.0 nM), which were much more potent than the positive control SAHA. The most potent compound 8r showed slightly higher growth inhibitory activity than SAHA in multiple tumor cell lines, even though, antiproliferative activity of 8r seemed inferior to its HDAC inhibition activity. Poor transcellular permeability obtained from the result of HDAC class I cellular assay could explain the inferior antiproliferative activity. In addition, 8r displayed similar HDAC IIa cellular activity to class I, which indicated 8r might be a potent pan-HDAC inhibitor.