Synthesis of D‑Ring Annulated Pyridosteroids from β‑Formyl Enamides and Their Biological Evaluations

Herein, we report
the synthesis of a novel class of substituted
androst­[17,16-b]­pyridines (pyridosteroids) from the
reaction of β-formyl enamides with alkynes in high yields. The
optimized reaction protocol was extended to acyclic and cyclic β-formyl
enamides to afford nonsteroidal pyridines. Cell survival assay of
all compounds were carried against prostate cancer PC-3 cells wherein
3-hydroxy-5-en-2′,3′-dicarbethoxy-androst­[17,16-b]­pyridine showed the highest cytotoxic activity. Phase
contrast microscopy and flow cytometry studies exhibited marked morphological
features characteristic of apoptosis in 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst­[17,16-b]­pyridine and abiraterone treated PC-3 cells. The treatment
of 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst­[17,16-b]­pyridine induces G2/M phase cell cycle arrest
in prostate cancer PC-3 cells. Enhancement of apoptotic inductions
of PC-3 cells by 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst­[17,16-b]­pyridine and abiraterone through the activation of caspases-6,
-7, and -8 pathways were supported by qRT-PCR. In silico study of
the compound 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst­[17,16-b]­pyridine showed stable and promising interaction with
the key caspase proteins. Our studies revealed that the pyridosteroid
3-hydroxy-5-en-2′,3′-dicarbethoxy-androst­[17,16-b]­pyridine, bearing pyridine-2,3-dicarbethoxy pharmacophore,
facilitated initiation of caspase-8 and activates downstream effectors
caspase-6 and caspase-7 and thereby triggering apoptosis of PC-3 cancer
cells.