Targeting amino acid transport in metastatic castration-resistant prostate cancer: effects on cell cycle, cell growth, and tumor development.
BACKGROUND
L-type amino acid transporters (LATs) uptake neutral amino acids including L-leucine into cells, stimulating mammalian target of rapamycin complex 1 signaling and protein synthesis. LAT1 and LAT3 are overexpressed at different stages of prostate cancer, and they are responsible for increasing nutrients and stimulating cell growth.


METHODS
We examined LAT3 protein expression in human prostate cancer tissue microarrays. LAT function was inhibited using a leucine analog (BCH) in androgen-dependent and -independent environments, with gene expression analyzed by microarray. A PC-3 xenograft mouse model was used to study the effects of inhibiting LAT1 and LAT3 expression. Results were analyzed with the Mann-Whitney U or Fisher exact tests. All statistical tests were two-sided.


RESULTS
LAT3 protein was expressed at all stages of prostate cancer, with a statistically significant decrease in expression after 4-7 months of neoadjuvant hormone therapy (4-7 month mean = 1.571; 95% confidence interval = 1.155 to 1.987 vs 0 month = 2.098; 95% confidence interval = 1.962 to 2.235; P = .0187). Inhibition of LAT function led to activating transcription factor 4-mediated upregulation of amino acid transporters including ASCT1, ASCT2, and 4F2hc, all of which were also regulated via the androgen receptor. LAT inhibition suppressed M-phase cell cycle genes regulated by E2F family transcription factors including critical castration-resistant prostate cancer regulatory genes UBE2C, CDC20, and CDK1. In silico analysis of BCH-downregulated genes showed that 90.9% are statistically significantly upregulated in metastatic castration-resistant prostate cancer. Finally, LAT1 or LAT3 knockdown in xenografts inhibited tumor growth, cell cycle progression, and spontaneous metastasis in vivo.


CONCLUSIONS
Inhibition of LAT transporters may provide a novel therapeutic target in metastatic castration-resistant prostate cancer, via suppression of mammalian target of rapamycin complex 1 activity and M-phase cell cycle genes.
Affiliations of authors: Origins of Cancer Laboratory (QW, JT, JH) and Gene & Stem Cell Therapy Program (QW, JT, CGB, WR, CM, YF, JEJR, JH), Centenary Institute, Camperdown, Australia; Sydney Medical School, University of Sydney, Sydney, Australia (QW, JT, CGB, WR, CM, YF, JEJR, JH); Vancouver Prostate Centre, Department of Urologic Sciences, University of British Columbia, Vancouver, BC, Canada (MLL, LF, EL, MG, CCN); Cancer Biology Group, Basil Hetzel Institute for Translational Health Research, University of Adelaide, Adelaide, Australia (GB); Australian Prostate Cancer Research Centre-Queensland, Queensland University of Technology, Brisbane, Australia (CCN, MLL); Cell and Molecular Therapies, Royal Prince Alfred Hospital, Camperdown, Australia (JEJR).
Qian
Q
Wang
Jessamy
J
Tiffen
Charles G
CG
Bailey
Melanie L
ML
Lehman
William
W
Ritchie
Ladan
L
Fazli
Cynthia
C
Metierre
Yue Julie
YJ
Feng
Estelle
E
Li
Martin
M
Gleave
Grant
G
Buchanan
Colleen C
CC
Nelson
John E J
JE
Rasko
Jeff
J
Holst
D051701:Activating Transcription Factor 4 / Q000187:drug effects / Q000378:metabolism*; D026923:Amino Acid Transport Systems, Basic / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology* / Q000627:therapeutic use; D001692:Biological Transport / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D003198:Computer Simulation; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055785:Gene Knockdown Techniques; D006801:Humans; D007930:Leucine / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008163:Luminescent Measurements; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism; D020360:Neoadjuvant Therapy / Q000379:methods*; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy / Q000503:physiopathology; D009919:Orchiectomy; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D040081:Protein Array Analysis; D011944:Receptors, Androgen / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
C410798:AR protein, human; C497109:ATF4 protein, human; D026923:Amino Acid Transport Systems, Basic; D000596:Amino Acids; D018931:Antineoplastic Agents, Hormonal; D046912:Multiprotein Complexes; D011944:Receptors, Androgen; C469951:SLC7A6 protein, human; D051701:Activating Transcription Factor 4; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D007930:Leucine