Synthesis and Anticancer Activity Evaluation of Novel Carborane-Containing Isoflavonoid Analogues

Abstract

Isoflavonoids represent a privileged structure derived from natural products with diverse bioactivities. Carborane has been utilized as a three-dimensional mimetic of phenyl rings in medicinal chemistry. Herein, we replaced the phenyl group of isoflavonoids with carborane and prepared a series of carborane-containing isoflavonoid analogues. Compounds 1d, 1g, and 1m showed significantly enhanced antiproliferative activities on a broad scope of cancer cell lines. Further studies indicated that both 1d and 1m inhibited JAK/STAT5, PI3K/AKT, and p38 MAPK pathways, leading to G1 cell cycle phase arrest. Additionally, both compounds reduced the expression of P-glycoprotein (P-gp), a key mediator in multidrug resistance, and reversed the resistance of chemotherapeutic agents in multidrug-resistant cells in vitro. The biodistribution of compounds 1d and 1m was evaluated through ICP-mass and positron emission tomography imaging studies. Taken together, these results suggested promising pharmaceutical properties for the carborane-containing isoflavonoid analogues.

Figure 1

Structures of representative bioactive compounds with isoflavonoid scaffolds.

Figure 2

(A) Design of carborane-containing isoflavone derivatives. (B) Structures of carborane-containing isoflavone derivatives in this study.

Scheme 1. Synthesis of Compounds 1a–1g

Reagents and conditions: (a) N,N-dimethylformamide dimethyl acetal, DMF, 70 °C (b); I₂, MeOH, 40 °C; (c) trimethylsilylacetylene, Pd(PPh₃)₂Cl₂, CuI, Et₃N, rt; (d) CSA, TBAF, THF, rt; (e) B₁₀H₁₂(CH₃CN)₂, (Bmim)Cl, PhMe, 110 °C; (f) BBr₃, DCE, 40 °C or 70 °C.

Scheme 2. Synthesis of Compounds 1h–1k

Reagents and conditions: (a) NaBH₄, THF, rt; (b) MnO₂, DCM, rt; (c) polyphosphoric acid, DCE, reflux; (d) H₂, Pd/C, THF, rt.

Scheme 3. Synthesis of Compounds 1l and 1m

Reagents and conditions: (a) NaBH₄, THF, rt; (b) 1-(fluorosulfonyl)-2,3-dimethyl-1H-imidazol-3-ium trifluoromethanesulfonate, Et₃N, MeCN, rt.

Figure 3

Compounds 1d and 1m induce G1 cell cycle phase arrest. MDA-MB-231 and PC-3 cells were treated with 1d (A) or 1m (B) for 24 h. The cell cycle distribution was analyzed by PI staining via flow cytometry. Numbers on the vertical coordinate indicated the proportion of cells in each phase of the cell cycle. Western blot analyses of cell cycle-related proteins in MDA-MB-231 and PC-3 cell lines after 24 h of treatment with a concentration gradient of 1d (C) or 1m (D) were shown. Data were presented as means ± SD. Statistical significance was assessed using a two-tailed unpaired Student’s t test. *P < 0.05, **P < 0.01.

Figure 4

Compounds 1d and 1m inhibit the JAK/STAT5, PI3K/AKT, and p38 MAPK pathways. Western blot analyses of MDA-MB-231 and PC-3 cell lines after treatment with a concentration gradient of 1d (A) or 1m (B) for 24 h.

Figure 5

Compounds 1d and 1m reverse multidrug resistance in K562/ADR cells. (A, B) Western blot analyses of K562 and K562/ADR after treatment with a concentration gradient of 1d or 1m for 48 h. (C, D) IC₅₀ values of 1m and verapamil in reversing the resistance of K562/ADR to ADR or VRN.

Figure 6

(A) PET imaging results of compound ¹⁸F-1m at 1 h postinjection. (B) PET imaging results of compound ¹⁸F-1m at 3 h postinjection. (C) ¹⁸F-1m biodistribution at 1 and 3 h postinjection. (D) In vivo boron biodistribution analysis of compound 1d at 3 h postinjection.