PDK1 is a potential therapeutic target against angiosarcoma cells.
BACKGROUND
Angiosarcoma is a rare and aggressive malignant neoplasm of endothelial cells. Recent studies have shown that the mTOR pathway is also aberrantly activated in cutaneous angiosarcoma. New therapeutic strategies are required because the prognosis of this disease is still poor.


OBJECTIVE
The aim of the present study was to determine the driver gene of angiosarcoma useful for the screening of small molecule inhibitors.


METHODS
We investigated the sensitivity of inhibitors for the PI3K/AKT/mTOR pathway in ISOS-1 and ISO-HAS cutaneous angiosarcoma cell lines. Flow cytometric analysis was conducted to evaluate cell-cycle progression and apoptosis. Western blot analyses were performed to elucidate the possible underlying mechanisms of growth inhibition. The colony formation assay was conducted to evaluate the clonogenic potential. We used the siRNA for PDK1 to examine the role of PDK1 on the growth of angiosarcoma cells.


RESULTS
The PI3K inhibitor and mTOR inhibitor inhibited the growth of both cell lines in a dose-dependent manner. The PI3K inhibitor more effectively induced cell-cycle arrest at the G1 phase with the downregulated expression of cyclin D in ISOS-1 cells than the mTOR inhibitor. The PI3K inhibitor and mTOR inhibitor weakly but significantly induced G1 cell cycle arrest at the same degree in ISO-HAS cells. The expression of cyclin D was downregulated by the treatment with siRNA for PDK1, but not by the AKT inhibitor in ISOS-1 and ISO-HAS cells. The knock down of PDK1 with siRNA was more effective at reducing colony numbers than the mTOR inhibitor in ISOS-1 cells.


CONCLUSIONS
These data showed that PDK1 played a pivotal role in the growth of angiosarcoma cells. Therefore, inhibition of PDK1, but not AKT, may be a more appropriate strategy than that of mTORC1 for the treatment of cutaneous angiosarcoma; the PDK1 inhibitor is promising as a therapeutic agent.
Department of Dermatology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan; Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan. Electronic address: wada-102@koto.kpu-m.ac.jp.
Makoto
M
Wada
Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Mano
M
Horinaka
Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Shusuke
S
Yasuda
Department of Regulation Biochemistry, Kitasato University School of Allied Health Sciences, Kanagawa, Japan.
Mikio
M
Masuzawa
Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Toshiyuki
T
Sakai
Department of Dermatology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Norito
N
Katoh
D064413:3-Phosphoinositide-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D056741:Cyclin D / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D006394:Hemangiosarcoma / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D006801:Humans; D058990:Molecular Targeted Therapy; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects; D012878:Skin Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014162:Transfection
D000970:Antineoplastic Agents; D056741:Cyclin D; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; C546842:MTOR protein, human; D058539:Phosphatidylinositol 3-Kinase; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases
AKT-independent; Cyclin D; PDK1