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Inhibition of Akt Enhances the Chemopreventive Effects of Topical Rapamycin in Mouse Skin.

Abstract
The PI3Kinase/Akt/mTOR pathway has important roles in cancer development for multiple tumor types, including UV-induced nonmelanoma skin cancer. Immunosuppressed populations are at increased risk of aggressive cutaneous squamous cell carcinoma (SCC). Individuals who are treated with rapamycin (sirolimus, a classical mTOR inhibitor) have significantly decreased rates of developing new cutaneous SCCs compared with those that receive traditional immunosuppression. However, systemic rapamycin use can lead to significant adverse events. Here, we explored the use of topical rapamycin as a chemopreventive agent in the context of solar-simulated light (SSL)-induced skin carcinogenesis. In SKH-1 mice, topical rapamycin treatment decreased tumor yields when applied after completion of 15 weeks of SSL exposure compared with controls. However, applying rapamycin during SSL exposure for 15 weeks, and continuing for 10 weeks after UV treatment, increased tumor yields. We also examined whether a combinatorial approach might result in more significant tumor suppression by rapamycin. We validated that rapamycin causes increased Akt (S473) phosphorylation in the epidermis after SSL, and show for the first time that this dysregulation can be inhibited in vivo by a selective PDK1/Akt inhibitor, PHT-427. Combining rapamycin with PHT-427 on tumor prone skin additively caused a significant reduction of tumor multiplicity compared with vehicle controls. Our findings indicate that patients taking rapamycin should avoid sun exposure, and that combining topical mTOR inhibitors and Akt inhibitors may be a viable chemoprevention option for individuals at high risk for cutaneous SCC.
AuthorsSally E Dickinson, Jaroslav Janda, Jane Criswell, Karen Blohm-Mangone, Erik R Olson, Zhonglin Liu, Christy Barber, Emanuel F Petricoin 3rd, Valerie S Calvert, Janine Einspahr, Jesse E Dickinson, Steven P Stratton, Clara Curiel-Lewandrowski, Kathylynn Saboda, Chengcheng Hu, Ann M Bode, Zigang Dong, David S Alberts, G Timothy Bowden
JournalCancer prevention research (Philadelphia, Pa.) (Cancer Prev Res (Phila)) Vol. 9 Issue 3 Pg. 215-24 (Mar 2016) ISSN: 1940-6215 [Electronic] United States
PMID26801880 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
Copyright©2016 American Association for Cancer Research.
Chemical References
  • 4-dodecyl-N-(1,3,4-thiadiazol-2-yl)benzenesulfonamide
  • Antibiotics, Antineoplastic
  • Sulfonamides
  • Thiadiazoles
  • MTOR protein, human
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • Sirolimus
Topics
  • Administration, Topical
  • Animals
  • Antibiotics, Antineoplastic (administration & dosage, pharmacology)
  • Apoptosis (drug effects, radiation effects)
  • Blotting, Western
  • Female
  • Keratinocytes (cytology, drug effects, metabolism, radiation effects)
  • Mice
  • Mice, Hairless
  • Phosphorylation (drug effects, radiation effects)
  • Proto-Oncogene Proteins c-akt (antagonists & inhibitors, metabolism)
  • Signal Transduction (drug effects, radiation effects)
  • Sirolimus (administration & dosage, pharmacology)
  • Skin Neoplasms (etiology, metabolism, pathology, prevention & control)
  • Sulfonamides (pharmacology)
  • Sunlight (adverse effects)
  • TOR Serine-Threonine Kinases (metabolism)
  • Thiadiazoles (pharmacology)

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