The HIV protease inhibitor Nelfinavir down-regulates p70S6K/S6 signaling, induce autophagy and apoptosis in thyroid cancer cells

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 414-436-HPT Axis Biology & Action
Basic/Translational
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-436
Yevgeniya Kushchayeva*1, John Costello2, Erin Felger1, Lisa Boyle3, Kenneth Burman1 and Vasyl Vasko2
1MedStar Washington Hospital Center, Washington, DC, 2Uniformed Services University of the Health Sciences, Bethesda, MD, 3MedStar Georgetown University Hospital, Washington, DC
Background:Hsp90 (heat shock protein 90) is a molecular chaperone that assists in protein folding and degradation, and stabilization of signaling molecules including PI3K and AKT proteins. The HIV protease inhibitor Nelfinavir (NFV) causes side effects that can be associated with Hsp90-mediated Akt inhibition, an emerging target in thyroid cancers (TC). We assessed the potential utility of NFV to inhibit anti-apoptotic Akt signaling in TC cells.

Experimental Design: NFV at concentrations 5-20 uM was tested in RET/PTC1 positive (TPC1), PTEN deficient (FTC133) and BRAF mutant (BCPAP) TC cells. The effects of NFV were determined in vitro using assays that measure cellular proliferation, apoptotic cell death, DNA damage, activation of anti-apoptotic signaling, endoplasmic reticulum (ER) stress and autophagy. Expression of NFV molecular targets was examined in 45 human TC tissue samples.

Results: At concentrations achievable in HIV patients, NFV inhibited growth and induced cell death in all examined TC cells regardless of their mutation status. Treatment with NFV was associated with loss of pRB, over-expression of cell cycle suppressors (p53 and p21) and down-regulation of Cyclin D1. NFV had no effect on Hsp90 expression and did not influence the levels of total and pAKT and pERK. However, NFV induced pAMPK and inhibited p70S6K/pS6 signaling. NFV treatment was associated with ER stress as shown by gain of pELFL2a. NFV treated cells showed vacuolization of cytoplasm suggesting autophagy. Western Blot analysis with autophagy markers (LC3B and Atg12) confirmed induction of autophagy. Treatment with NFV was also associated with DNA damage and activation of DNA damage repair signaling as demonstrated by gain of γH2AX. In all examined thyroid cancer cells NFV induced caspase 3 cleavage indicating apoptosis. Rescue experiments showed that pharmacological inhibition of mitochondrial activity attenuated NFV-induced DNA damage and prevented apoptosis. Since NFV treatment was associated with inhibition of p70S6K/pS6 signaling in TC cell lines, we next performed immunostaining with anti-p-p70S6K in human TCs. Compared to the corresponding normal thyroid in the same patients, p70S6K was over-activated in 12/35 papillary and in 8/10 follicular TCs. 

Conclusions: NFV has a wide spectrum of activity against thyroid cancer cells in vitro. Our data suggest that a commonly used and well tolerated anti-HIV drug NFV has a potential to become a new thyroid cancer therapeutic agent.

Nothing to Disclose: YK, JC, EF, LB, KB, VV

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

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