Antitumor agents. 272. Structure-activity relationships and in vivo selective anti-breast cancer activity of novel neo-tanshinlactone analogues

Abstract

Neo-tanshinlactone (1) and its previously reported analogues, such as 2, are potent and selective in vitro antibreast cancer agents. The synthetic pathway to 2 was optimized from seven to five steps, with a better overall yield. Structure-activity relationships studies on these compounds revealed some key molecular determinants for this family of antibreast agents. Several derivatives (19-21 and 24) exerted potent and selective antibreast cancer activity with IC(50) values of 0.3, 0.2, 0.1, and 0.1 microg/mL, respectively, against the ZR-75-1 cell lines. Compound 24 was 2- to 3-fold more potent than 1 against SK-BR-3 and ZR-75-1. Importantly, 21 exhibited high selectivity; it was 23 times more active against ZR-75-1 than MCF-7. Compound 20 had an approximately 12-fold ratio of SK-BR-3/MCF-7 selectivity. In addition, analogue 2 showed potent activity against a ZR-75-1 xenograft model, but not PC-3 and MDA-MB-231 xenografts, as well as high selectivity against breast cancer cell line compared with normal breast tissue-derived cell lines. Further development of lead compounds 19-21 and 24 as clinical trial candidates is warranted.

Figure 1

Structures of tamoxifen, neo-tanshinlactone (1) and its analogs 2-3

Figure 2

Structures designed for future study

Figure 3

Selective in vitro anticancer activity of 2 against SK-BR-3 breast cancer versus normal breast tissue-derived cell lines (MCF10A and 184A1). Legend: Cell line description, source and activity determination using the MTT-dye assay are described in the experimental section. Graphical data are the mean and standard deviation of values obtained from replicates in a single experiment.

Figure 4. Anticancer activity of 2

The efficacy of 2 on the growth of human PC-3, MDA-MB-231, and ZR-75-1 xenografts in SCID mice. Treatment with compound 2 selectively abrogated the hormone-dependent breast cancer. Tumor growth is presented as the mean tumor volume (mm³) ± SE. Tumor volume was determined by caliper measurements and was calculated as the product of 1/2 × length × width². Each value represents the mean of at least five animals.

Scheme 1

Reagents and conditions: (a) EtMgBr, ZnCl₂, THF, rt; (b) Pd/C, triglyme, reflux; (c) BBr₃, CH₂Cl₂; (d) malonic acid, PPA (85% P₂O₅), 75 °C, 3 h; (e) chloroacetone, HOAc/NH₄OAc, toluene/EtOH, reflux, 24 h; (f) NBS, dibenzoyl peroxide, toluene, reflux; (g) BBr₃, CH₂Cl₂, reflux, 3 h; (h) Ac₂O, Et₃N, 10 h; (i) 2-chloro-N,N-dimethylethanamine, K₂CO₃, acetone, 12h.

Scheme 2

Reagents and conditions: (a) diethyl malonate, 220°C, 8h; (b) chloroacetone, HOAc/NH₄OAc, toluene/EtOH, reflux, 24 h.

Scheme 3

Reagents and conditions: (a) malonic acid, PPA (85% P₂O₅), 75 °C, 3 h; (b) chloroacetone, HOAc/NH₄OAc, toluene, EtOH, reflux, 24 h; (c) diethyl malonate, PPA (85% P₂O₅), 170 °C, 2h; (d) Lawesson's reagent, toluene, reflux, 5h; (e) NH₂OH HCl, NaOAc, MeOH, reflux, 12 h.

Scheme 4

Reagents and conditions: (a) HOAc/NH₄OAc, toluene, EtOH, reflux, 24 h; (b) Et₃N, formic acid, Pd/C, acetone, 12 h; (c) 2-bromo-4-methylbenzoyl chloride, DMAP, DIEA, THF, rt, 12h; (d) Pd(OAc)₂, PPh₃, NaOAc, DMF, reflux, 3h.