Chee-Onn Leong

Tumor-Specific p73 Up-regulation Mediates p63 Dependence in Squamous Cell Carcinoma

p63 is essential for normal epithelial development and is overexpressed in the vast majority of squamous cell carcinomas (SCC). Recent work had shown that DeltaNp63alpha is essential for survival of SCC cells, raising the possibility that the p63 pathway may be an attractive therapeutic target in these tumors. Nevertheless, it is unknown whether a therapeutic window exists for inhibiting p63 in tumor cells versus normal epithelia. Here, we show that SCC cells are uniquely dependent on DeltaNp63alpha for survival, unlike normal p63-expressing epithelial cells, and that dependence is mediated through tumor-specific up-regulation of the related protein p73. In normal primary human keratinocytes, we find that inhibition of endogenous p63 by RNA interference (RNAi) induces p21(CIP1) expression, inhibits cell cycle progression, and ultimately promotes cellular senescence. In contrast, p63 inhibition in SCC cells induces proapoptotic bcl-2 family members and rapidly triggers apoptosis. Expression of p73 is low in uncultured basal keratinocytes but is markedly up-regulated in both SCC cell lines and primary tumors in vivo. Whereas p21(CIP1) induction following loss of p63 in normal cells is independent of p53 and p73, both proapoptotic gene induction and cell death following p63 RNAi in tumor cells are p73 dependent. Finally, ectopic p73 expression in primary keratinocytes does not affect baseline cell proliferation but is sufficient to trigger cell death following loss of p63. Together, these findings define a specific molecular mechanism of p63 dependence through p73 up-regulation, and they provide a rationale for targeting the p63 pathway as a therapeutic strategy in SCCs.

HOXB13 promotes ovarian cancer progression

Deregulated expression of HOXB13 in a subset of estrogen receptor-positive breast cancer patients treated with tamoxifen monotherapy is associated with an aggressive clinical course and poor outcome. Because the ovary is another hormone-responsive organ, we investigated whether HOXB13 plays a role in ovarian cancer progression. We show that HOXB13 is expressed in multiple human ovarian cancer cell lines and tumors and that knockdown of endogenous HOXB13 by RNA interference in human ovarian cancer cell lines is associated with reduced cell proliferation. Ectopic expression of HOXB13 is capable of transforming p53−/− mouse embryonic fibroblasts and promotes cell proliferation and anchorage-independent growth in mouse ovarian cancer cell lines that contain genetic alterations in p53, myc, and ras. In this genetically defined cell line model of ovarian cancer, we demonstrate that HOXB13 collaborates with activated ras to markedly promote tumor growth in vivo and that HOXB13 confers resistance to tamoxifen-mediated apoptosis. Taken together, our results support a pro-proliferative and pro-survival role for HOXB13 in ovarian cancer.

6-Shogaol inhibits breast and colon cancer cell proliferation through activation of peroxisomal proliferator activated receptor γ (PPARγ).

6-Shogaol has been shown to possess many antitumor properties including inhibition of cancer cell growth, inhibition of cancer metastasis, induction of apoptosis in cancer cells and induction of cancer cell differentiation. Despite its prominent antitumor effects, the direct molecular target of 6-shogaol has remained elusive. To identify the direct targets of 6-shogaol, a comprehensive antitumor profile of 6-shogaol (NSC752389) was tested in the NCI-60 cell line in an in vitro screen. The results show that 6-shogaol is COMPARE negative suggesting that it functions via a mechanism of action distinct from existing classes of therapeutic agents. Further analysis using microarray gene profiling and Connectivity Map analysis showed that MCF-7 cells treated with 6-shogaol display gene expression signatures characteristic of peroxisome proliferator activated receptor γ (PPARγ) agonists, suggesting that 6-shogaol may activate the PPARγ signaling pathway for its antitumor effects. Indeed, treatment of MCF-7 and HT29 cells with 6-shogaol induced PPARγ transcriptional activity, suppressed NFκB activity, and induced apoptosis in breast and colon cancer cells in a PPARγ-dependent manner. Furthermore, 6-shogaol is capable of binding to PPARγ with a binding affinity comparable to 15-delta prostaglandin J2, a natural ligand for PPARγ. Together, our findings suggest that the antitumor effects of 6-shogaol are mediated through activation of PPARγ and imply that activation of PPARγ might be beneficial for breast and colon cancer treatment.

Functional roles of fibroblast growth factor receptors (FGFRs) signaling in human cancers

The fibroblast growth factor receptors (FGFRs) regulate important biological processes including cell proliferation and differentiation during development and tissue repair. Over the past decades, numerous pathological conditions and developmental syndromes have emerged as a consequence of deregulation in the FGFRs signaling network. This review aims to provide an overview of FGFR family, their complex signaling pathways in tumorigenesis, and the current development and application of therapeutics targeting the FGFRs signaling for treatment of refractory human cancers.

Rapamycin synergizes cisplatin sensitivity in basal-like breast cancer cells through up-regulation of p73

Recent gene expression profiling studies have identified five breast cancer subtypes, of which the basal-like subtype is the most aggressive. Basal-like breast cancer poses serious clinical challenges as there are currently no targeted therapies available to treat it. Although there is increasing evidence that these tumors possess specific sensitivity to cisplatin, its success is often compromised due to its dose-limiting nephrotoxicity and the development of drug resistance. To overcome this limitation, our goal was to maximize the benefits associated with cisplatin therapy through drug combination strategies. Using a validated kinase inhibitor library, we showed that inhibition of the mTOR, TGFβRI, NFκB, PI3K/AKT, and MAPK pathways sensitized basal-like MDA-MB-468 cells to cisplatin treatment. Further analysis demonstrated that the combination of the mTOR inhibitor rapamycin and cisplatin generated significant drug synergism in basal-like MDA-MB-468, MDA-MB-231, and HCC1937 cells but not in luminal-like T47D or MCF-7 cells. We further showed that the synergistic effect of rapamycin plus cisplatin on basal-like breast cancer cells was mediated through the induction of p73. Depletion of endogenous p73 in basal-like cells abolished these synergistic effects. In conclusion, combination therapy with mTOR inhibitors and cisplatin may be a useful therapeutic strategy in the treatment of basal-like breast cancers.

CYP2S1 and CYP2W1 Mediate 2-(3,4-Dimethoxyphenyl)-5-Fluorobenzothiazole (GW-610, NSC 721648) Sensitivity in Breast and Colorectal Cancer Cells

Both 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F-203; NSC 703786) and 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole (GW-610; NSC 721648) are antitumor agents with novel mechanism(s). Previous studies have indicated that cytochrome (CYP) P450 1A1 is crucial for 5F-203 activity. In the present study, we investigated the functional role of 2 newly identified CYP P450 enzymes, CYP2S1 and CYP2W1, in mediating antitumor activity of benzothiazole compounds. We generated isogenic breast cancer (MDA-MB-468, MCF-7) and colorectal cancer (CRC; KM12 and HCC2998) cell lines depleted for CYP1A1, CYP2S1, or CYP2W1. The sensitivity of these cells to 5F-203 and GW-610 was then compared with vector control cells. 5F-203 exhibited potent activity against breast cancer cells, whereas GW-610 was effective against both breast and colorectal cancer cells. CYP1A1 was induced in both breast cancer and CRC cells, while CYP2S1 and CYP2W1 were selectively induced in breast cancer cells only following treatment with 5F-203 or GW-610. Depletion of CYP1A1 abrogated the sensitivity of breast cancer and CRC cells to 5F-203 and GW-610. Although depletion of CYP2S1 sensitized both breast cancer and CRC cells toward 5F-203 and GW-610, CYP2W1 knockdown caused marked resistance to GW-610 in CRC cells. Our results indicate that CYP-P450 isoforms, with the exception of CYP1A1, play an important role in mediating benzothiazole activity. CYP2S1 appears to be involved in deactivation of benzothiazoles, whereas CYP2W1 is important for bioactivation of GW-610 in CRC cells. Because CYP2W1 is highly expressed in colorectal tumors, GW-610 represents a promising agent for CRC therapy. Mol Cancer Ther; 10(10); 1982–92. ©2011 AACR.

Toxicity of single-walled carbon nanotubes

Carbon nanotubes (CNTs) are an important class of nanomaterials, which have numerous novel properties that make them useful in technology and industry. Generally, there are two types of CNTs: single-walled nanotubes (SWNTs) and multi-walled nanotubes. SWNTs, in particular, possess unique electrical, mechanical, and thermal properties, allowing for a wide range of applications in various fields, including the electronic, computer, aerospace, and biomedical industries. However, the use of SWNTs has come under scrutiny, not only due to their peculiar nanotoxicological profile, but also due to the forecasted increase in SWNT production in the near future. As such, the risk of human exposure is likely to be increased substantially. Yet, our understanding of the toxicological risk of SWNTs in human biology remains limited. This review seeks to examine representative data on the nanotoxicity of SWNTs by first considering how SWNTs are absorbed, distributed, accumulated and excreted in a biological system, and how SWNTs induce organ-specific toxicity in the body. The contradictory findings of numerous studies with regards to the potential hazards of SWNT exposure are discussed in this review. The possible mechanisms and molecular pathways associated with SWNT nanotoxicity in target organs and specific cell types are presented. We hope that this review will stimulate further research into the fundamental aspects of CNTs, especially the biological interactions which arise due to the unique intrinsic characteristics of CNTs.

Suppression of BCL-2 synergizes cisplatin sensitivity in nasopharyngeal carcinoma cells

The efficacy of cisplatin for treating nasopharyngeal carcinoma (NPC) is limited by the dose-related toxicities and the development of resistance to cisplatin. Recent studies have shown that B cell lymphoma-2 (BCL-2) is overexpressed and confers chemoresistance in NPC. Thus, targeted therapy against BCL-2 may enhance the antitumour effects of chemotherapy by sensitizing the tumor cells to undergo apoptosis. This study evaluated the combined effects of BCL-2 inhibition and cisplatin in NPC cells. Our results demonstrate that inhibition of BCL-2 by small-hairpin RNA (shRNA) or the BCL-2 inhibitor YC137, synergizes cisplatin sensitivity in NPC cells that overexpress BCL-2. We also show that YC137 enhance cisplatin-induced apoptosis in HK1 and CNE1 cells through suppression of BCL-2 protein expression, induction of mitochondrial depolarization and activation of caspase 9 and caspase 3/7. These findings suggest that the combination of BCL-2 inhibition and cisplatin represents a promising strategy for treating NPC.

Metformin synergizes 5-fluorouracil, epirubicin, and cyclophosphamide (FEC) combination therapy through impairing intracellular ATP production and DNA repair in breast cancer stem cells

Metformin, an AMPK activator, has been reported to improve pathological response to chemotherapy in diabetic breast cancer patients. To date, its mechanism of action in cancer, especially in cancer stem cells (CSCs) have not been fully elucidated. In this study, we demonstrated that metformin, but not other AMPK activators (e.g. AICAR and A-769662), synergizes 5-fluouracil, epirubicin, and cyclophosphamide (FEC) combination chemotherapy in non-stem breast cancer cells and breast cancer stem cells. We show that this occurs through an AMPK-dependent mechanism in parental breast cancer cell lines. In contrast, the synergistic effects of metformin and FEC occurred in an AMPK-independent mechanism in breast CSCs. Further analyses revealed that metformin accelerated glucose consumption and lactate production more severely in the breast CSCs but the production of intracellular ATP was severely hampered, leading to a severe energy crisis and impairs the ability of CSCs to repair FEC-induced DNA damage. Indeed, addition of extracellular ATP completely abrogated the synergistic effects of metformin on FEC sensitivity in breast CSCs. In conclusion, our results suggest that metformin synergizes FEC sensitivity through distinct mechanism in parental breast cancer cell lines and CSCs, thus providing further evidence for the clinical relevance of metformin for the treatment of cancers.

Triple-negative breast cancer is associated with EGFR, CK5/6 and c-KIT expression in Malaysian women

BackgroundTriple-negative breast cancer (TNBC) is a heterogeneous subgroup of breast cancer characterized by the lack of estrogen receptor (ER), progesterone receptor (PR) and the human epidermal growth factor receptor 2 (HER2) expressions. This subgroup of refractory disease tends to have aggressive clinical behavior, high frequency of metastasis and lack of response to current hormonal or targeted therapies. Despite numerous studies reporting the clinicopathological features of TNBC and its association with the basal-like phenotype in the Western population, only limited data are available in the Asian population. Therefore, the aim of this study was to investigate the clinicopathological characteristics of TNBC and its association with epidermal growth factor receptor (EGFR), cytokeratin 5/6 (CK5/6) and mast/stem cell growth factor receptor (c-KIT or CD117) expression in Malaysian women.MethodsA total of 340 patients diagnosed with primary breast cancer between 2002 and 2006 in Malaysia were reviewed and analyzed.ResultsThe incidence of TNBC was 12.4% (42/340). Bivariate analysis revealed that TNBC was strongly associated with a younger age, higher grade tumor and p53 expression. Further immunohistochemical analysis suggested that TNBC in Malaysian women was strongly associated with EGFR, CK5/6 and c-KIT expression with high a Ki-67 proliferation index.ConclusionIn conclusion, our study confirms the association of TNBC with basal-like marker expression (EGFR, CK5/6 and c-KIT) in Malaysian women, consistent with studies in other populations.