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Title: Inhibition of phosphatidylinositol-3-kinase causes increased sensitivity to radiation through a PKB-dependent mechanism

Abstract

Purpose: To identify whether inhibition of phosphatidylinositol-3-kinase (PI3K) causes increased radiosensitivity through inhibition of protein kinase B (PKB), implicating PKB as an important therapeutic target in prostate cancer. Methods and Materials: The prostate cancer cell line LNCaP was treated with the PI3K inhibitor LY294002, radiation, and combinations of the two therapies. Apoptosis and survival were measured by cell cycle analysis, Western blot analysis for cleaved poly (ADP-ribose) polymerase, and clonogenic survival. To test the hypothesis that inhibition of PKB is responsible for LY294002-induced radiosensitivity, LNCaP cells expressing a constitutively active form of PKB were used. Results: The combination of PI3K inhibition and radiation caused an increase in apoptosis and a decrease in clonogenic survival when compared to either modality alone. The expression of constitutively activated PKB blocked apoptosis induced by combination of PI3K inhibition and radiation and prevented radiosensitization by LY294002. Conclusion: These data indicate that PI3K inhibition increases sensitivity of prostate cancer cell lines to ionizing radiation through inactivation of PKB. Therefore, PTEN mutations, which lead to PKB activation, may play an important role in the resistance of prostate cancer to radiation therapy. Targeted therapy against PKB could be beneficial in the management of prostate cancer patients.

Authors:
 [1];  [2];  [2];  [3];  [2];  [4]
  1. Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA (United States) and Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA (United States). E-mail: gottschalk@radonc17.ucsf.edu
  2. Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA (United States)
  3. Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA (United States)
  4. (United States)
Publication Date:
OSTI Identifier:
20706269
Resource Type:
Journal Article
Resource Relation:
Journal Name: International Journal of Radiation Oncology, Biology and Physics; Journal Volume: 63; Journal Issue: 4; Other Information: DOI: 10.1016/j.ijrobp.2005.08.014; PII: S0360-3016(05)02381-3; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ADP; APOPTOSIS; CARCINOMAS; CELL CYCLE; INHIBITION; IONIZING RADIATIONS; MUTATIONS; PROSTATE; PROTEINS; RADIOSENSITIVITY; RADIOTHERAPY; RIBOSE; SENSITIVITY

Citation Formats

Gottschalk, Alexander R., Doan, Albert, Nakamura, Jean L., Stokoe, David, Haas-Kogan, Daphne A., and Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA. Inhibition of phosphatidylinositol-3-kinase causes increased sensitivity to radiation through a PKB-dependent mechanism. United States: N. p., 2005. Web. doi:10.1016/j.ijrobp.2005.08.014.
Gottschalk, Alexander R., Doan, Albert, Nakamura, Jean L., Stokoe, David, Haas-Kogan, Daphne A., & Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA. Inhibition of phosphatidylinositol-3-kinase causes increased sensitivity to radiation through a PKB-dependent mechanism. United States. doi:10.1016/j.ijrobp.2005.08.014.
Gottschalk, Alexander R., Doan, Albert, Nakamura, Jean L., Stokoe, David, Haas-Kogan, Daphne A., and Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA. Tue . "Inhibition of phosphatidylinositol-3-kinase causes increased sensitivity to radiation through a PKB-dependent mechanism". United States. doi:10.1016/j.ijrobp.2005.08.014.
@article{osti_20706269,
title = {Inhibition of phosphatidylinositol-3-kinase causes increased sensitivity to radiation through a PKB-dependent mechanism},
author = {Gottschalk, Alexander R. and Doan, Albert and Nakamura, Jean L. and Stokoe, David and Haas-Kogan, Daphne A. and Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA},
abstractNote = {Purpose: To identify whether inhibition of phosphatidylinositol-3-kinase (PI3K) causes increased radiosensitivity through inhibition of protein kinase B (PKB), implicating PKB as an important therapeutic target in prostate cancer. Methods and Materials: The prostate cancer cell line LNCaP was treated with the PI3K inhibitor LY294002, radiation, and combinations of the two therapies. Apoptosis and survival were measured by cell cycle analysis, Western blot analysis for cleaved poly (ADP-ribose) polymerase, and clonogenic survival. To test the hypothesis that inhibition of PKB is responsible for LY294002-induced radiosensitivity, LNCaP cells expressing a constitutively active form of PKB were used. Results: The combination of PI3K inhibition and radiation caused an increase in apoptosis and a decrease in clonogenic survival when compared to either modality alone. The expression of constitutively activated PKB blocked apoptosis induced by combination of PI3K inhibition and radiation and prevented radiosensitization by LY294002. Conclusion: These data indicate that PI3K inhibition increases sensitivity of prostate cancer cell lines to ionizing radiation through inactivation of PKB. Therefore, PTEN mutations, which lead to PKB activation, may play an important role in the resistance of prostate cancer to radiation therapy. Targeted therapy against PKB could be beneficial in the management of prostate cancer patients.},
doi = {10.1016/j.ijrobp.2005.08.014},
journal = {International Journal of Radiation Oncology, Biology and Physics},
number = 4,
volume = 63,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}
  • Purpose: To identify whether inhibition of phosphatidylinositol-3-kinase (PI3K) causes apoptosis through inhibition of protein kinase B (PKB), implicating PKB as an important therapeutic target in prostate cancer. Methods and materials: After treatment with the PI3K inhibitor, LY294002, proliferation and apoptosis of the prostate cancer cell line, LNCaP, were measured by cell cycle analysis and cleavage of poly (ADP-ribose) polymerase. To test the hypothesis that inhibition of PKB is responsible for the LY294002-induced apoptosis, LNCaP cells expressing a constitutively active form of PKB were generated. Results: Treatment of LNCaP cells with the PI3K inhibitor, LY294002, caused inactivation of PKB, growth arrest,more » and apoptosis. LY294002-induced apoptosis was increased in the absence of serum. The G1 growth arrest was associated with an increase in p27{sup kip1} expression. Cells expressing constitutively active PKB were protected from apoptosis induced by LY294002, but not from the G1 growth arrest induced by PI3K inhibition. Conclusion: These data suggest that PKB activity regulates apoptosis, but not G1 arrest, and identify PKB as a potential critical target for cancer therapy. Targeted therapy against kinases might complement more conventional therapies, including androgen suppression for prostate cancer.« less
  • In normal epithelial cells, cell-matrix interaction is required for cell survival and proliferation, whereas disruption of this interaction causes epithelial cells to undergo apoptosis called anoikis. Here we show that the small GTPase RhoG plays an important role in the regulation of anoikis. HeLa cells are capable of anchorage-independent cell growth and acquire resistance to anoikis. We found that RNA interference-mediated knockdown of RhoG promoted anoikis in HeLa cells. Previous studies have shown that RhoG activates Rac1 and induces several cellular functions including promotion of cell migration through its effector ELMO and the ELMO-binding protein Dock180 that function as amore » Rac-specific guanine nucleotide exchange factor. However, RhoG-induced suppression of anoikis was independent of the ELMO- and Dock180-mediated activation of Rac1. On the other hand, the regulation of anoikis by RhoG required phosphatidylinositol 3-kinase (PI3K) activity, and constitutively active RhoG bound to the PI3K regulatory subunit p85{alpha} and induced the PI3K-dependent phosphorylation of Akt. Taken together, these results suggest that RhoG protects cells from apoptosis caused by the loss of anchorage through a PI3K-dependent mechanism, independent of its activation of Rac1.« less
  • Approaches to overcome chemoresistance in cancer cells have involved targeting specific signaling pathways such as the phosphatidylinositol 3-kinase (PI3K) pathway, a stress response pathway known to be involved in the regulation of cell survival, apoptosis and growth. The present study determined the effect of PI3K inhibition on the clonogenic survival of human cancer cells following exposure to various chemotherapeutic agents. Treatment with the PI3K inhibitors LY294002 or Compound 15e resulted in increased survival of MDA-MB-231 breast carcinoma cells after exposure to doxorubicin, etoposide, 5-fluorouracil, and vincristine. Increased survival following PI3K inhibition was also observed in DU-145 prostate, HCT-116 colon andmore » A-549 lung carcinoma cell lines exposed to doxorubicin. Increased cell survival mediated by LY294002 was correlated with a decrease in cell proliferation, which was linked to an increase in the proportion of cells in the G{sub 1} phase of the cell cycle. Inhibition of PI3K signaling also resulted in higher levels of the cyclin-dependent kinase inhibitors p21{sup Waf1/Cip1} and p27{sup Kip1}; and knockdown of p27{sup kip1} with siRNA attenuated resistance to doxorubicin in cells treated with LY294002. Incubation in the presence of LY294002 after exposure to doxorubicin resulted in decreased cell survival. These findings provide evidence that PI3K inhibition leads to chemoresistance in human cancer cells by causing a delay in cell cycle; however, the timing of PI3K inhibition (either before or after exposure to anti-cancer agents) may be a critical determinant of chemosensitivity.« less
  • Glucocorticoids induce COX-2 expression in rat cardiomyocytes. While investigating whether phosphatidylinositol 3 kinase (PI3K) plays a role in corticosterone (CT)-induced COX-2, we found that LY294002 (LY29) but not wortmannin (WM) attenuates CT from inducing COX-2 gene expression. Expression of a dominant-negative mutant of p85 subunit of PI3K failed to inhibit CT from inducing COX-2 expression. CT did not activate PI3K/AKT signaling pathway whereas LY29 and WM decreased the activity of PI3K. LY303511 (LY30), a structural analogue and a negative control for PI3K inhibitory activity of LY29, also suppressed COX-2 induction. These data suggest PI3K-independent mechanisms in regulating CT-induced COX-2 expression.more » LY29 and LY30 do not inhibit glucocorticoid receptor transactivity. Both compounds have been reported to inhibit Casein Kinase 2 activity and modulate potassium and calcium levels independent of PI3K, while LY29 has been reported to inhibit mammalian Target of Rapamycin (mTOR), and DNA-dependent Protein Kinase (DNA-PK). Inhibitor of Casein Kinase 2 (CK2), mTOR or DNA-PK failed to prevent CT from inducing COX-2 expression. Tetraethylammonium (TEA), a potassium channel blocker, and nimodipine, a calcium channel blocker, both attenuated CT from inducing COX-2 gene expression. CT was found to increase intracellular Ca{sup 2+} concentration, which can be inhibited by LY29, TEA or nimodipine. These data suggest a possible role of calcium instead of PI3K in CT-induced COX-2 expression in cardiomyocytes.« less
  • 4-vinylcyclohexene diepoxide (VCD) is an ovotoxicant that specifically destroys primordial and small primary follicles in the ovaries of mice and rats. In contrast, 7,12-dimethylbenz[a]anthracene (DMBA) is ovotoxic to all ovarian follicle classes. This study investigated phosphatidylinositol-3 kinase signaling involvement in VCD- and DMBA-induced ovotoxicity. Postnatal day (PND) 4 Fischer 344 (F344) rat whole ovaries were cultured for 2-12 days in vehicle control, VCD (30 muM), or DMBA (1 muM), +- PI3 kinase inhibitor LY294002 (20 muM) or its inactive analog LY303511 (20 muM). Following culture, ovaries were histologically evaluated, and healthy follicles were classified and counted. PI3 kinase inhibition hadmore » no effect on primordial follicle number, but reduced (P < 0.05) small primary and larger follicles beginning on day 4. VCD caused primordial and small primary follicle loss (P < 0.05) beginning on day 6. With PI3 kinase inhibition, VCD did not affect primordial follicles (P > 0.05) at any time, but did cause loss (P < 0.05) of small primary follicles. DMBA exposure caused primordial and small primary follicle loss (P < 0.05) on day 6. Further, DMBA-induced primordial and small primary follicle loss was greater with PI3 kinase inhibition (P < 0.05) than with DMBA alone. These results support that (1) PI3 kinase mediates primordial to small primary follicle recruitment, (2) VCD, but not DMBA, enhances ovotoxicity by increasing primordial to small primary follicle recruitment, and (3) in addition to xenobiotic-induced ovotoxicity, VCD is also a useful model chemical with which to elucidate signaling mechanisms involved in primordial follicle recruitment.« less