Design, Synthesis and Tumour-Selective Toxicity of Novel 1-[3-{3,5-Bis(benzylidene)-4-oxo-1-piperidino}-3-oxopropyl]-4-piperidone Oximes and Related Quaternary Ammonium Salts

Abstract

A novel series of 1-[3-{3,5-bis(benzylidene)-4-oxo-1-piperidino}-3-oxopropyl]-4-piperidone oximes 3a-h and related quaternary ammonium salts 4a-h were prepared as candidate antineoplastic agents. Evaluation against neoplastic Ca9-22, HSC-2 and HSC-4 cells revealed the compounds in series 3 and 4 to be potent cytotoxins with submicromolar CC₅₀ values in virtually all cases. In contrast, the compounds were less cytocidal towards HGF, HPLF and HPC non-malignant cells revealing their tumour-selective toxicity. Quantitative structure-activity relationships revealed that, in general, both cytotoxic potency and selectivity index figures increased as the magnitude of the Hammett sigma values rose. In addition, 3a-h are cytotoxic towards a number of leukemic and colon cancer cells. 4b,c lowered the mitochondrial membrane potential in CEM cells, and 4d induced transient G2/M accumulation in Ca9-22 cells. Five compounds, namely 3c,d and 4c-e, were identified as lead molecules that have drug-like properties.

Keywords: QSAR; conjugated unsaturated ketones; cytotoxins; mitochondrial membrane potential; oximes; quaternary ammonium salts.

Figure 1

Design of the compounds in series 4.

Scheme 1

Synthetic chemical route for the compounds in series 3 and 4.

Figure 2

Dose–response curves of the cytotoxicity of three representative compounds. Human oral squamous cell carcinoma cell lines (Ca9-22, HSC-2, HSC-4) and human normal oral cells (HGF, HPLF, HPC) were incubated for 48 h without (control) or with the indicated concentrations of 3d (A), 4c (B) and 4d (C), and the relative viable cell number was determined. Each value represents the mean ± S.D. of triplicate assays.

Figure 3

Comparison of the antitumor activity expressed as SI (A) and PSE (B) between series 3 (3a–h) and 4 (4a–h). These data are derived from Table 1 and Table 2.

Figure 4

4d induced cell spreading and transient accumulation of the G2/M phase cells. Ca9-22 cells were treated for 24 h without (A), or with actinomycin D (1 μM) (B), 4d (0.02, 0.1 or 0.5 μM) (C–E). (Upper column) Morphological changes. (Lower column) Cell cycle analysis.

Figure 5

Effect of 4b and 4c on the mitochondrial membrane potential of CEM cells. The concentrations of 4b and 4c are the CC₅₀ or twice the CC₅₀ values. The asterisks above the bar graphs indicate that the p-value is less than 0.05 compared to dimethylsulfoxide.