Characterization of the molecular pathways that are required for the viability and maintenance of self-renewing tumor-initiating cells may ultimately lead to improved therapies for cancer. In this study, we show that a CD133 ؉ /CD44 ؉ population of cells enriched in prostate cancer progenitors (PCaPs) has tumor-initiating potential and that these progenitors can be expanded under nonadherent, serum-free, sphere-forming conditions. Cells grown under these conditions have increased in vitro clonogenic and in vivo tumorigenic potential. mRNA expression analysis of cells grown under sphere-forming conditions, compared with long-term monolayer cultures, revealed preferential activation of the PI3K/AKT signaling pathway. PI3K p110␣ and ␤-protein levels were higher in cells grown under sphere-forming conditions, and phosphatase and tensin homolog (PTEN) knockdown by shRNA led to an increase in sphere formation as well as increased clonogenic and tumorigenic potential. Similarly, shRNA knockdown of FoxO3a led to an increase in tumorigenic potential. Consistent with these results, inhibition of PI3K activity by the dual PI3K/mTOR inhibitor NVP-BEZ235 led to growth inhibition of PCaPs. Taken together, our data strongly suggest that the PTEN/PI3K/Akt pathways are critical for prostate cancer stem-like cell maintenance and that targeting PI3K signaling may be beneficial in prostate cancer treatment by eliminating prostate cancer stem-like cells.FoxO3a ͉ PI3Kinase ͉ prostate cancer progenitors

Purpose: The cancer stem cell hypothesis predicts that standard prostate cancer monotherapy eliminates bulk tumor cells but not a tumor-initiating cell population, eventually leading to relapse. Many studies have sought to determine the underlying differences between bulk tumor and cancer stem cells.Experimental Design: Our previous data suggest that the PTEN/PI3K/AKT pathway is critical for the in vitro maintenance of CD133 þ /CD44 þ prostate cancer progenitors and, consequently, that targeting PI3Ksignaling may be beneficial in treatment of prostate cancer.Results: Here, we show that inhibition of PI3K activity by the dual PI3K/mTOR inhibitor NVP-BEZ235 leads to a decrease in the population of CD133þ prostate cancer progenitor cells in vivo. Moreover, the combination of the PI3K/mTOR modulator NVP-BEZ235, which eliminates prostate cancer progenitor populations, and the chemotherapeutic drug Taxotere, which targets the bulk tumor, is significantly more effective in eradicating tumors in a prostate cancer xenograft model than monotherapy.Conclusion: This combination treatment ultimately leads to the expansion of cancer progenitors with a PTEN E91D mutation, suggesting that the analysis of PTEN mutations could predict therapeutic response to the dual therapy. Clin Cancer Res; 16(23); 5692-702. Ó2010 AACR.

Tumor progenitor cells represent a population of drug-resistant cells that can survive conventional chemotherapy and lead to tumor relapse. However, little is known of the role of tumor progenitors in prostate cancer metastasis. The studies reported herein show that the CXCR4/CXCL12 axis, a key regulator of tumor dissemination, plays a role in the maintenance of prostate cancer stem-like cells. The CXCL4/CXCR12 pathway is activated in the CD44+/CD133+ prostate progenitor population and affects differentiation potential, cell adhesion, clonal growth and tumorigenicity. Furthermore, prostate tumor xenograft studies in mice showed that a combination of the CXCR4 receptor antagonist AMD3100, which targets prostate cancer stem-like cells, and the conventional chemotherapeutic drug Taxotere, which targets the bulk tumor, is significantly more effective in eradicating tumors as compared to monotherapy.

Lung cancer is the most common cause of cancer-related mortality worldwide. Here, we report elevated expression of tribbles homolog 2 (TRIB2) in primary human lung tumors and in non-small cell lung cancer cells that express low levels of differentiation-inducing transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα). In approximately 10–20% of cases, elevated TRIB2 expression resulted from gene amplification. TRIB2 knockdown was found to inhibit cell proliferation and in vivo tumor growth. In addition, TRIB2 knockdown led to morphological changes similar to C/EBPα overexpression and correlated with increased expression and activity of C/EBPα. TRIB2-mediated regulation of C/EBPα was found to occur through the association of TRIB2 with the E3 ligase TRIM21. Together, these data identify TRIB2 as a potential driver of lung tumorigenesis through a mechanism that involves downregulation of C/EBPα.

Emerging evidence suggests that some cancers contain a population of stem-like TICs (tumor-initiating cells) and eliminating TICs may offer a new strategy to develop successful anti-cancer therapies. As molecular mechanisms underlying the maintenance of the TIC pool are poorly understood, the development of TIC-specific therapeutics remains a major challenge. We first identified and characterized TICs and non-TICs isolated from a mouse breast cancer model. TICs displayed increased tumorigenic potential, self-renewal, heterogeneous differentiation, and bipotency. Gene expression analysis and immunostaining of TICs and non-TICs revealed that FGFR2 was preferentially expressed in TICs. Loss of FGFR2 impaired self-renewal of TICs, thus resulting in marked decreases in the TIC population and tumorigenic potential. Restoration of FGFR2 rescued the defects in TIC pool maintenance, bipotency, and breast tumor growth driven by FGFR2 knockdown. In addition, pharmacological inhibition of FGFR2 kinase activity led to a decrease in the TIC population which resulted in suppression of breast tumor growth. Moreover, human breast TICs isolated from patient tumor samples were found enriched in a FGFR2+ population that was sufficient to initiate tumor growth. Our data suggest that FGFR2 is essential in sustaining the breast TIC pool through promotion of self-renewal and maintenance of bipotent TICs, and raise the possibility of FGFR2 inhibition as a strategy for anti-cancer therapy by eradicating breast TICs.

<div>Abstract<p><b>Purpose:</b> The cancer stem cell hypothesis predicts that standard prostate cancer monotherapy eliminates bulk tumor cells but not a tumor-initiating cell population, eventually leading to relapse. Many studies have sought to determine the underlying differences between bulk tumor and cancer stem cells.</p><p><b>Experimental Design:</b> Our previous data suggest that the PTEN/PI3K/AKT pathway is critical for the <i>in vitro</i>maintenance of CD133⁺/CD44⁺ prostate cancer progenitors and, consequently, that targeting PI3K signaling may be beneficial in treatment of prostate cancer.</p><p><b>Results:</b> Here, we show that inhibition of PI3K activity by the dual PI3K/mTOR inhibitor NVP-BEZ235 leads to a decrease in the population of CD133⁺/CD44⁺ prostate cancer progenitor cells <i>in vivo</i>. Moreover, the combination of the PI3K/mTOR modulator NVP-BEZ235, which eliminates prostate cancer progenitor populations, and the chemotherapeutic drug Taxotere, which targets the bulk tumor, is significantly more effective in eradicating tumors in a prostate cancer xenograft model than monotherapy.</p><p><b>Conclusion:</b> This combination treatment ultimately leads to the expansion of cancer progenitors with a PTEN E91D mutation, suggesting that the analysis of PTEN mutations could predict therapeutic response to the dual therapy. <i>Clin Cancer Res; 16(23); 5692–702. ©2010 AACR.</i></p></div>

<p>Supplementary Figures S1-S7; Supplementary Materials and Methods; Supplementary Table S1.</p>

<div>Abstract<p><b>Purpose:</b> The cancer stem cell hypothesis predicts that standard prostate cancer monotherapy eliminates bulk tumor cells but not a tumor-initiating cell population, eventually leading to relapse. Many studies have sought to determine the underlying differences between bulk tumor and cancer stem cells.</p><p><b>Experimental Design:</b> Our previous data suggest that the PTEN/PI3K/AKT pathway is critical for the <i>in vitro</i>maintenance of CD133⁺/CD44⁺ prostate cancer progenitors and, consequently, that targeting PI3K signaling may be beneficial in treatment of prostate cancer.</p><p><b>Results:</b> Here, we show that inhibition of PI3K activity by the dual PI3K/mTOR inhibitor NVP-BEZ235 leads to a decrease in the population of CD133⁺/CD44⁺ prostate cancer progenitor cells <i>in vivo</i>. Moreover, the combination of the PI3K/mTOR modulator NVP-BEZ235, which eliminates prostate cancer progenitor populations, and the chemotherapeutic drug Taxotere, which targets the bulk tumor, is significantly more effective in eradicating tumors in a prostate cancer xenograft model than monotherapy.</p><p><b>Conclusion:</b> This combination treatment ultimately leads to the expansion of cancer progenitors with a PTEN E91D mutation, suggesting that the analysis of PTEN mutations could predict therapeutic response to the dual therapy. <i>Clin Cancer Res; 16(23); 5692–702. ©2010 AACR.</i></p></div>