Design, Synthesis of Novel Tetrandrine-14-l-Amino Acid and Tetrandrine-14-l-Amino Acid-Urea Derivatives as Potential Anti-Cancer Agents

Abstract

Tetrandrine, a dibenzyltetrahydroisoquinoline alkaloid isolated from the root of the traditional Chinese medicinal plant Stephania tetrandra S. Moore, a member of the Menispermaceae, showed anti-cancer activity by inhibiting cell proliferation, preventing cell cycle progress and induction of cell death and autophagy. In this study, twelve tetrandrine-l-amino acid derivatives and twelve tetrandrine-14-l-amino acid-urea derivatives were designed and synthesized, using C14-aminotetrandrine as raw material. Then the preliminary in vitro anti-cancer activities of these derivatives against human breast cancer cell line MDA-MB-231, human leukemia cell lines HEL and K562 were evaluated. The in vitro cytotoxicity results showed that these derivatives exhibited potent inhibitory effects on cancer cell growth, and the primary structure-activity relationships were evaluated. Notably, compound 3f exhibited satisfactory anticancer activity against all three cancer cell lines, especially the HEL cell line, with the IC₅₀ value of 0.23 µM. Further research showed that 3f could induce G1/S cycle arrest and apoptosis in a dose- and time- dependent manner on the leukemia cell line HEL. The results suggested that 3f may be used as a potential anti-cancer agent for human leukemia.

Keywords: anti-cancer activity; l-amino acid; tetrandrine derivatives; urea.

Figure 1

The structure of tetrandrine.

Figure 2

The structures of floxuridine prodrug (a) and brivanib (b).

Scheme 1

The synthetic routes of tetrandrine derivatives. Reagents and Conditions: (a) mixed acid (20 eq, HNO₃: acetic anhydride = 7:10 v/v), DCM, 0 °C to r.t., 4 h (93%); (b) Pd/C (5%), hydrazine hydrate (80 eq), MeOH, 65 °C, 3.5 h (84%); (c) Boc-l-amino acid (1.1 eq), EDCI (1.1 eq), HOBT (0.4 eq), DCM, r.t., 1.5–3 h (78-88%); (d) TFA (1.0 eq), DCM, 0 °C to r.t., 4 h (97%); (e) isocyanate (1.1 eq), triethylamine (0.2 eq), DCM, r.t., 0.5–1.5 h (90–95%).

Figure 3

The inhibitory activity on proliferation of human leukemia HEL cell of 3f. (A) Cellular morphological alteration of HEL cell at different concentrations of 3f after 24 h of drug treatment. (B) The inhibition of 3f on HEL cell growth after 72 h.

Figure 4

Apoptosis induced by compound 3f in HEL cell line. (A) Compound 3f had effect in retardation of cell cycle progression in HEL cell line. The cell cycle progression was retarded in the G1/S phase. HEL cell line was treated with compound 3f for 24 h. (B) Compound 3f induced apoptosis in HEL cell line. The HEL cell line was treated with compound 3f for 24 h and analyzed by flow cytometry, using Annexin V/PI staining.