Torc1/Torc2 inhibitor, Palomid 529, enhances radiation response modulating CRM1-mediated survivin function and delaying DNA repair in prostate cancer models.
BACKGROUND
P529, a Torc1/Torc2 inhibitor, has demonstrated its potential as a radiosensitizer. However the molecular mechanisms underlying this phenomenon still need to be elucidated. Aim of this study is to dissect molecular mechanisms regulating the radiosensitizing properties of P529 in a wide panel of prostate cancer models.


METHODS
Six tumor cell lines and xenograft models were used for in vitro and in vivo studies. Clonogenic survival, apoptotic, autophagic, and senescence assays were used to examine the effects of ionizing radiation (IR) alone and in combination with P529. CRM1, survivin, GSK-3β, and DNA-DSBs expression and modulation, upon P529 and RT, were monitored by western blot. In vivo treatment response upon P529, irradiation or combination of P529 with IR was monitored by tumor volume, time to progression (TTP), and immunohistochemical analysis.


RESULTS
P529 treatment induced significantly more apoptosis and DNA double-strand break (DSB) when combined with radiotherapy resulting in cellular radiosensitization and growth delay of irradiated tumor xenografts. Upon P529 treatment Rad51, DNA-PKcs, and Ku70 protein expression was downregulated, indicating delayed DNA double-strand damage repair. The radiosensitizing properties of P529 were partially linked to GSK-3β, cyclin-D1, and c-myc modulation with associated inhibition of CRM1-mediated nuclear export of survivin. Importantly, autophagy and tumor senescence were involved in the enhanced P529 radioresponse.


CONCLUSIONS
Impaired DNA double-strand damage repair, inhibition of CRM1-mediated nuclear export of survivin, modulation of cyclin-D1 and c-myc with associated pro-apoptotic and autophagic and senescent events explain the radiosensitizing properties of P529 in preclinical models of prostate cancer.
Division of Radiation Oncology, Department of Clinical and Applied Sciences and Biotechnologies, University of L'Aquila, L'Aquila, Italy; Department of Clinical and Applied Sciences and Biotechnologies, Laboratory of Radiobiology, University of L'Aquila, L'Aquila, Italy; Department of Experimental Medicine, Section of Medical Pathophysiology, Food Science and Endocrinology, Sapienza University of Rome, Rome, Italy; Department of Clinical and Applied Sciences and Biotechnologies, School of Sexology, University of L'Aquila, L'Aquila, Italy.
Giovanni Luca
GL
Gravina
Francesco
F
Marampon
David
D
Sherris
Francesca
F
Vittorini
Ernesto
E
Di Cesare
Vincenzo
V
Tombolini
Andrea
A
Lenzi
Emmanuele A
EA
Jannini
Claudio
C
Festuccia
D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D004260:DNA Repair / Q000187:drug effects / Q000502:physiology; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism / Q000502:physiology*; D028884:Karyopherins / Q000378:metabolism / Q000502:physiology*; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D008819:Mice, Nude; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000532:radiotherapy; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology* / Q000627:therapeutic use; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology*; D000077022:Survivin; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays / Q000379:methods; D000097606:Exportin 1 Protein
D001578:Benzopyrans; D051034:Inhibitor of Apoptosis Proteins; D028884:Karyopherins; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D046912:Multiprotein Complexes; D011838:Radiation-Sensitizing Agents; D018160:Receptors, Cytoplasmic and Nuclear; D000077022:Survivin; D058570:TOR Serine-Threonine Kinases; D000097606:Exportin 1 Protein; C107489:BIRC5 protein, human; C533469:palomid 529
CRM1; GSK-3β; P529; TORC1/TORC2; prostate cancer; radiotherapy; survivin