Abstract P6-15-18: PELP1-KDM1 Axis: A Novel Therapeutic Target for Blocking Local Estrogen Synthesis

Background: Local estrogen production via deregulated expression of aromatase (Cyp19), the key enzyme in the biosynthesis of estrogen, contributes to tumor progression in post-menopausal women. Aromatase inhibitors (AI) are effective in enhancing patient survival although long term use is limited by systemic side effects and therapy resistance. Therefore, identifying novel pathways that contributes to in situ E2 in breast tumors and therapeutic agents to block these pathways are urgently needed. Recent studies from our lab demonstrated PELP1 proto-oncogene cooperates with HER2/neu and modulates epigenetic changes at aromatase promoter by interacting with lysine specific demethylase (KDM1) leading to local E2 synthesis. In this study, we examined the therapeutic efficacy of targeting the PELP-KDM1 axis in blocking local E2 production.

Methods: Three breast cancer model cells which exhibit local E2 were used: (a) MCF7 cells overexpressing HER2/neu onogene (MCF7-HER2), (b) MCF7 cells overexpressing proto-oncogene PELP1 (MCF7-PELP1), (c) MCF7 cells with acquired Letrozole resistance (MCF7-Ca-LTLT); parental MCF7 cells were used as controls. Therapeutic potential of KDM1 targeting drugs, (1) Pargyline, a monoamine oxidase inhibitor, (2) NCL-1, a KDM1-selective inhibitor to block PELP1-KDM1 axis were tested using proliferation, aromatase reporter, ChIP and RTqPCR assays. Efficacy of the KDM1 targeting drugs alone or in combination with Letrozole, and Dasatinib was also measured. Pre-clinical, post-memopausal nude mice based models were used to validate the drug effect in vivo.

Results: Depletion of PELP1 or KDM1 using siRNA substantially reduced proliferation of all three model cells and affected epigenetic modifications at the aromatase promoter. Reporter gene and ChIP assays showed growth factors and HER2/neu enhance PELP1 and KDM1 recruitment to the aromatase promoter. KDM1 inhibitors {pargyline (3mM) and NCL1 (10uM)} substantially inhibited growth of all three model cells. In postmenopausal xenograft based model, treatment with pargyline significantly inhibited the growth of local E2 producing tumor cells. IHC and ChIP analysis revealed alterations in histone methyl modifications in treated ER positive tumors. Combinatorial therapy of AI (Letrozole), Src kinaseinhibitor (Dasatinib) with Pargyline or NCL1 showed most promising therapeutic effect compared to single agent therapy to inhibit growth of therapy resistant cells.

Conclusions: Drugs targeting the PELP1-KDM1 are effective in reversing the methyl modifications at aromatase promoter that are affected by proto-oncogenes PELP1, HER2 and blocking growth of local E2 producing cells. Our results suggest targeting of PELP1-KDM1 axis in combination with current endocrine therapies will have a better therapeutic effect and may inhibit or delay development of AI resistance. This study is funded by Komen grant KG090447 and NIH grant CA095681.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-15-18.

Abstract P4-02-10: Significance of ER-Coregulator-Src Axis in Hormonal Resistance

Background: The estrogen receptor (ER) is implicated in the progression of breast cancer. Endocrine therapy using Tamoxifen, a selective estrogen receptor modulator (SERM), improves disease-free survival in postmenopausal women. Despite positive effects, initial or acquired resistance to endocrine therapies frequently occurs. Recent studies suggested the presence of alternative signaling pathways (including HER2 and c-Src kinase) that contribute to ER activation in the absence of estrogen. ER-coregulators play an essential role in hormonal responsiveness and coregulators such as PELP1 couples Src axis to ER thus representing a new pathway for targeted drug therapy. In this study, we examined the therapeutic efficacy of targeting the PELP-Src axis in blocking therapy resistance.

Methods: Three breast cancer model cell lines with resistance to Tamoxifen were used in this study: (1) MCF7-PELP1 (2) MCF7-HER2/neu and (3) MCF7-Tam. To establish the significance of ER-PELP1 coregulator-Src axis, we have generated additional model cells that stably express Src-ShRNA (MCF7-PELP1 -Src-shRNA and MCF7-HER2-SrcshRNA). Model cells were tested for proliferation using CellTiter-Glo assays, anchorage dependence and ER-extranuclear signaling by Western analysis using phospho-antibodies. Orally soluble Src inhibitor Dasatinib (SPRYCEL)was used to test whether it (a) blocks of ER-coactivator-Src signaling and (b) sensitizes the resistant breast cancer cells to endocrine therapy. Pre-clinical nude mice xenograft based studies were performed to validate the effect of Dasatinib alone or in combination with tamoxifen in vivo. IHC analysis of the tumors was performed to examine the effect of Dasatinib on ER signaling components.

Results: Src knock down or Dasatinib (100 nM) treatment substantially inhibited the growth of MCF7-PELP1, MCF7-HER2/neu and MCF7- Tam model cells in proliferation assays. Depletion of Src using siRNA substantially reduced E2 mediated activation of Src, MAPK and AKT in resistant model cells. In post-menopausal xenograft based studies, treatment with Dasatinib significantly inhibited the growth of therapy resistant cells. IHC analysis revealed that the tumors are ER positive, and Dasatinib (15 mg/kg/d) treated tumors exhibited alterations in Src and AKT pathways. Combinatorial therapy of Tamoxifen (100 μg/mouse/day) with Dasatinib showed better therapeutic effect compared to single agent therapy on the growth of therapy resistant tumors.

Conclusions: The results from this study showed that ER-PELP1 coregulator-Src axis play an important role in promoting hormonal resistance and blocking this axis prevents the development of hormonal independence in vivo. ER coregulator PELP1 and Src kinase are commonly deregulated in breast cancers therefore combination therapies using both endocrine agents and Dasatinib may have better therapeutic effect by delaying the development of hormonal resistance This study is supported by DOD grant W81XWH-08-1-0604.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-02-10.

Large pulmonary masses containing varicose veins: a rare presentation of benign metastasising leiomyomas

A 48-year-old woman presented with cough and chest pain. A chest radiograph and CT scans showed bilateral lung masses containing massive venous varices. A core biopsy specimen revealed benign metastasising leiomyoma with strong expression of progesterone receptors. A review of her medical history revealed a hysterectomy 11 years earlier. The lung masses showed significant reduction in size after induction of artificial menopause, although the pulmonary varices persisted.