Alterations in cholesterol regulation contribute to the production of intratumoral androgens during progression to castration-resistant prostate cancer in a mouse xenograft model.
BACKGROUND
Emerging evidence suggests that androgens and the androgen receptor (AR) are important mediators of castration-resistant prostate cancer (CRPC) progression. Increased expression of several enzymes responsible for cholesterol synthesis and conversion into downstream androgens has been documented in human CRPC tumors in comparison to primary tumors. Based on these observations it is hypothesized that cholesterol and its overall regulation within the cell are altered, thus modifying precursor levels for de novo androgen synthesis within the castrate tumoral environment.


METHODS
Tumoral steroid levels were assessed by LC-MS. Free and esterified cholesterol was quantified by LC-MS and a fluorescent assay. Gene and protein expression were assessed by RT-PCR and immunoblotting.


RESULTS
Herein, using a prostate cancer xenograft mouse model it is demonstrated by Western blot analysis that proteins responsible for cholesterol regulation (LDL-r, SR-B1, HMG-CoA reductase, ACAT1,2, ABCA1) are altered during disease progression to increase influx and synthesis of cholesterol as well as free cholesterol formation from cholesteryl ester stores. In turn this can provide increased amounts of precursor for intratumoral steroidogenesis after castration. Androgens- testosterone and dihydrotestosterone- coincidently increase at CRPC to physiologically relevant levels leading to the induction of AR expression and PSA production. Furthermore, cellular cholesterol homeostasis is maintained by increased cholesterol efflux at CRPC so that excess free cholesterol does not cause toxicity to the tumor cells.


CONCLUSIONS
Cellular cholesterol regulation processes are altered during progression to CRPC. Free cholesterol from increased biosynthesis or uptake is likely a precursor for intratumoral de novo androgen synthesis.
Leon
Carlos G
CG
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada. cleon@interchange.ubc.ca
Locke
Jennifer A
JA
Adomat
Hans H
HH
Etinger
Susan L
SL
Twiddy
Alexis L
AL
Neumann
Rachel D
RD
Nelson
Colleen C
CC
Guns
Emma S
ES
Wasan
Kishor M
KM
D000101:Acetyl-CoA C-Acetyltransferase / Q000378:metabolism; D000728:Androgens / Q000096:biosynthesis*; D000818:Animals; D002784:Cholesterol / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D018450:Disease Progression; D015972:Gene Expression Regulation, Neoplastic; D006706:Homeostasis; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009919:Orchiectomy; D017430:Prostate-Specific Antigen / Q000235:genetics / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D011944:Receptors, Androgen / Q000378:metabolism*; D023041:Xenograft Model Antitumor Assays
D000728:Androgens; D008565:Membrane Proteins; D012333:RNA, Messenger; D011944:Receptors, Androgen; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D000101:Acetyl-CoA C-Acetyltransferase; D017430:Prostate-Specific Antigen