Substitutional Diversity-Oriented Synthesis and In Vitro Anticancer Activity of Framework-Integrated Estradiol-Benzisoxazole Chimeras

Abstract

Hybridization of steroids and other pharmacophores often modifies the bioactivity of the parent compounds, improving selectivity and side effect profile. In this study, estradiol and 3′-(un)substituted benzisoxazole moieties were combined into novel molecules by structural integration of their aromatic rings. Simple estrogen starting materials, such as estrone, estradiol and estradiol-3-methylether were used for the multistep transformations. Some of the heterocyclic derivatives were prepared from the estrane precursor by a formylation or Friedel–Crafts acylation—oximation—cyclization sequence, whereas others were obtained by a functional group interconversion strategy. The antiproliferative activities of the synthesized compounds were assessed on various human cervical, breast and prostate cancer cell lines (HeLa, MCF-7, PC3, DU-145) and non-cancerous MRC-5 fibroblast cells. Based on the primary cytotoxicity screens, the most effective cancer-selective compounds were selected, their IC50 values were determined and their apoptosis-inducing potential was evaluated by quantitative real-time PCR. Pharmacological studies revealed a strong structure–function relationship, where derivatives with a hydroxyl group on C-17 exhibited stronger anticancer activity compared to the 17-acetylated counterparts. The present study concludes that novel estradiol-benzisoxazole hybrids exert remarkable cancer cell-specific antiproliferative activity and trigger apoptosis in cancer cells.

Medicinal‐Chemistry‐Driven Approach to 2‐Substituted Benzoxazole–Estradiol Chimeras: Synthesis, Anticancer Activity, and Early ADME Profile

“…In addition, the presence of a heteroring in a lipid-soluble sterane backbone that allows cell membrane penetration may be advantageous as it may interact with targets other than the estrogen receptor through H-bond formation. This concept seems to be supported by the fact that among the various estradiol-heterocycle chimeras we have reported recently, [17][18][19][20] several compounds exerted remarkable cancer cell-specific antiproliferative activity and induced apoptosis in cancer cells, and among them, the estradiol-benzisoxazole hybrids [20] were found to be the most effective agents. The main objective of the present study was to expand our compound library with estradiol-benzoxazole derivatives, as well as to compare their biological effect with previously synthesized regioisomeric benzisoxazoles [20] in order to obtain more information about the structure-effect relationships.…”

“…This concept seems to be supported by the fact that among the various estradiol-heterocycle chimeras we have reported recently, [17][18][19][20] several compounds exerted remarkable cancer cell-specific antiproliferative activity and induced apoptosis in cancer cells, and among them, the estradiol-benzisoxazole hybrids [20] were found to be the most effective agents. The main objective of the present study was to expand our compound library with estradiol-benzoxazole derivatives, as well as to compare their biological effect with previously synthesized regioisomeric benzisoxazoles [20] in order to obtain more information about the structure-effect relationships. Since sterane-based molecules may have a very complex mechanism of action in the human body, [21] e. g., at least five different aspects of the anticancer mechanism of action of 2ME2 have been elucidated so far, [16,22] the identification of the biological target was beyond the scope of the present study.…”