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Thesis - Venkatesh Chari.pdf (7.31 MB)

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Drug Targets to Improve the Outcome of Hormonal Adjuvant Therapy in Breast and Prostate Cancers

Chari, Venkatesh Vasu
http://rave.ohiolink.edu/etdc/view?acc_num=mco1384738922

Abstract Details

2013, Doctor of Philosophy (PhD), University of Toledo, College of Medicine.
Tamoxifen and aromatase inhibitors (AI) are a mainstay in the treatment of estrogen receptor (ER)-positive breast cancer. However, long-term treatment of women at high risk for breast cancer leads to development of resistance against the drug and reduces the incidence of both invasive and non-invasive ER-positive breast cancer in only approximately 50% of cases. For resistance to develop during either hormone depletion (AI) treatment or tamoxifen adjuvant therapy, there must be a fraction of cells that must maintain a basal level of cell cycling. Growth and proliferation of these latent tumor cells later lead to the development of resistance. Our lab has shown that: “Under conditions of hormonal adjuvant treatment the estrogen receptor apoprotein supports breast cancer cell cycling through the retinoic acid receptor (RAR) -a1 apoprotein”. RARa1 is the only isoform expressed in breast tumor cells and it being genetically redundant, targeting it specifically may lead to improved outcome of current hormonal adjuvant therapies with minimal side effects. We have synthesized a high affinity RARa-specific antagonist, AGN194301, as a carrier molecule to selectively target RARa. AGN194301 by itself did not affect the ability of RARa1 to support basal cell proliferation and did not alter the level of RARa1 protein. Structure-activity-relationship (SAR) studies showed the functional group(s) of the compound that could be modified without abrogating its ability to bind to RARa. Further studies and strategies for attaining downregulation of RARa1 at the protein level using modified versions of this compound are discussed. The androgen receptor (AR) is essential for diverse aspects of prostate development and function. Molecular mechanisms by which prostate cancer (PC) cells redirect AR signaling to genes that primarily support growth are unclear. A systematic search for critical AR-tethering proteins led to ELK1, an ETS transcrip- tion factor of the ternary complex factor subfamily. Although genetically redundant, ELK1 was obligatory for AR-dependent growth and clonogenic survival in both hormone-dependent PC and castration-recurrent PC cells but not for AR-negative cell growth. This study discusses detailed mapping of the peptide sequences within AR and Elk1 that are required for the interaction between them. We found that the N-terminal A/B domain of AR is alone sufficient for its interaction with Elk1 and for Elk1-dependent transactivation by AR. We further mapped the AR-A/B domain using deletion analysis and demonstrated that aa 156-329 within the A/B domain selectively inhibits Elk1-dependent gene activation by androgen as well as androgen-dependent growth of LNCaP cells. Synthetic peptides corresponding to sequence aa 156-206 and aa 181-231 inhibited the binding of the AR A/B domain to Elk1 and also inhibited the androgen-dependent growth of LNCaP cells. Simultaneously, deletion mapping of Elk1 and the use of mammalian two-hybrid assays identified the sequence aa 287-317 of the N-terminus and aa 387-428 of C-terminus as essential for the binding of Elk1 to AR. We also tested a phosphorylation mutant of Elk1 which was found to retain its ability to associate with AR. The results suggest that major splice variants of AR that lack the C-terminal ligand binding domain and that are known to support hormone-independent growth of prostate cancer cells may utilize Elk1 for growth signaling. Further, these results also confirm that phosphorylation of Elk1 is not involved in the Elk1-AR synergy. Finally, the results from this study led to identification of peptides that may be used to selectively disrupt the synergy between Elk1 and AR without interfering with other aspects of AR signaling.
Stephan Patrick, Ph.D. (Committee Member)
Manohar Ratnam, Ph.D. (Advisor)
Mark Wooten, Ph.D. (Committee Member)
Kandace Williams, Ph.D. (Committee Member)
196 p.
Biomedical Research

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Citations

  • Chari, V. V. (2013). Drug Targets to Improve the Outcome of Hormonal Adjuvant Therapy in Breast and Prostate Cancers [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=mco1384738922

    APA Style (7th edition)

  • Chari, Venkatesh. Drug Targets to Improve the Outcome of Hormonal Adjuvant Therapy in Breast and Prostate Cancers. 2013. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=mco1384738922.

    MLA Style (8th edition)

  • Chari, Venkatesh. "Drug Targets to Improve the Outcome of Hormonal Adjuvant Therapy in Breast and Prostate Cancers." Doctoral dissertation, University of Toledo, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=mco1384738922

    Chicago Manual of Style (17th edition)

mco1384738922
522
© 2013, all rights reserved.
This open access ETD is published by University of Toledo Health Science Campus and OhioLINK.