16 research outputs found
A bypass mechanism of abiraterone-resistant prostate cancer: Accumulating CYP17A1 substrates activate androgen receptor signaling
Background: Intratumoral steroidogenesis and its potential relevance in castrationâ
resistant prostate cancer (CRPC) and in cytochrome P450, family 17, subfamily A,
polypeptide 1 (CYP17A1)âinhibitor treated hormoneânaĂŻve and patients with CRPC are not
well established. In this study, we tested if substrates for de novo steroidogenesis
accumulating during CYP17A1 inhibition may drive cell growth in relevant preclinical
models.
Methods: PCa cell lines and their respective CRPC sublines were used to model CRPC in
vitro. Precursor steroids pregnenolone (Preg) and progesterone (Prog) served as substrate
for de novo steroid synthesis. TAK700 (orteronel), abiraterone, and small interfering RNA
(siRNA) against CYP17A1 were used to block CYP17A1 enzyme activity. The antiandrogen
RD162 was used to assess androgen receptor (AR) involvement. Cell growth was
measured by 3â(4,5âdimethylthiazolâ2âyl)â2,5âdiphenyltetrazolium bromide assay. ARâ
target gene expression was quantified by reverse transcription polymerase chain reaction
(RTâPCR). Nuclear import studies using cells with green fluorescent protein (GFP)âtagged
AR were performed to assess the potential of precursor steroids to directly activate AR.
Results: Preg and Prog stimulated cell proliferation and AR target gene expression in VCaP, DuCaP, LNCaP, and their respective CRPC sublines. The antiandrogen RD162,
but not CYP17A1 inhibition with TAK700, abiraterone or siRNA, was able to block
Pregâ and Progâinduced proliferation. In contrast to TAK700, abiraterone also
affected dihydrotestosteroneâinduced cell growth, indicating direct AR binding.
Furthermore, Progâinduced AR translocation was not affected by treatment with
TAK700 or abiraterone, while it was effectively blocked by the AR antagonist
enzalutamide, further demonstrating the direct AR activation by Prog.
Conclusion: Activation of the AR by clinically relevant levels of Preg and Prog
accumulating in abirateroneâtreated patients may act as a driver for CRPC. These
data provide a scientific rationale for combining CYP17A1 inhibitors with antiandrogens, particularly in patients with overexpressed or mutatedâAR