Natarajan Venkatesan

University of California, Los Angeles, Los Angeles, CA, United States

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Publications (6)35.86 Total impact

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    ABSTRACT: Here, we investigate the potential role of the PARP inhibitor rucaparib (CO-338, formerly known as AG014699 and PF-01367338) for the treatment of sporadic ovarian cancer. We studied the growth inhibitory effects of rucaparib in a panel of 39 ovarian cancer cell lines that were each characterized for mutation and methylation status of BRCA1/2, baseline gene expression signatures, copy number variations of selected genes, PTEN status, and sensitivity to platinum-based chemotherapy. To study interactions with chemotherapy, we used multiple drug effect analyses and assessed apoptosis, DNA fragmentation, and γH2AX formation. Concentration-dependent antiproliferative effects of rucaparib were seen in 26 of 39 (67%) cell lines and were not restricted to cell lines with BRCA1/2 mutations. Low expression of other genes involved in homologous repair (e.g., BCCIP, BRCC3, ATM, RAD51L1), amplification of AURKA or EMSY, and response to platinum-based chemotherapy was associated with sensitivity to rucaparib. Drug interactions with rucaparib were synergistic for topotecan, synergistic, or additive for carboplatin, doxorubicin or paclitaxel, and additive for gemcitabine. Synergy was most pronounced when rucaparib was combined with topotecan, which resulted in enhanced apoptosis, DNA fragmentation, and γH2AX formation. Importantly, rucaparib potentiated chemotherapy independent of its activity as a single agent. PARP inhibition may be a useful therapeutic strategy for a wider range of ovarian cancers bearing deficiencies in the homologous recombination pathway other than just BRCA1/2 mutations. These results support further clinical evaluation of rucaparib either as a single agent or as an adjunct to chemotherapy for the treatment of sporadic ovarian cancer. Mol Cancer Ther; 12(6); 1-14. ©2013 AACR.
    Molecular Cancer Therapeutics 05/2013; · 5.60 Impact Factor
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    ABSTRACT: The recent identification of activating fibroblast growth factor receptor 2 (FGFR2) mutations in endometrial cancer (EC) has generated an opportunity for a novel target-based therapy. Here we explore the therapeutic potential of two FGFR inhibitors, the multi-kinase inhibitor dovitinib (TKI258) and the more selective FGFR inhibitor NVP-BGJ398 for the treatment of EC. We examined the effects of both inhibitors on tumor cell growth, FGFR2 signaling, cell cycle and apoptosis using a panel of 20 molecularly characterized human EC cell lines. Anchorage independent growth was studied using soft agar assays. In vivo studies were conducted using EC xenograft models. Cell lines with activating FGFR2 mutations (S252W, N550K) were more sensitive to dovitinib or NVP-BGJ398 when compared to their FGFR2 wild-type counterparts (p=0.073 and p=0.021, respectively). Both agents inhibited FGFR2 signaling, induced cell cycle arrest and significantly increased apoptosis in FGFR2 mutant lines. In vitro, dovitinib and NVP-BGJ398 were both potent at inhibiting cell growth of FGFR2 mutant EC cells but the activity of dovitinib was less restricted to FGFR2 mutant lines when compared to NVP-BGJ398. In vivo, dovitinib and NVP-BGJ398 significantly inhibited the growth of FGFR2 mutated EC xenograft models. In addition, dovitinib showed significant antitumor activity in FGFR2 wild-type EC xenograft models including complete tumor regressions in a long term in vivo study. Dovitinib and NVP-BGJ398 warrant further clinical evaluation in patients with FGFR2 mutated EC. Dovitinib may have antitumor activity in EC beyond FGFR2 mutated cases and may permit greater flexibility in patient selection.
    Molecular Cancer Therapeutics 02/2013; · 5.60 Impact Factor
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    ABSTRACT: Approximately 25,000 ovarian cancers are diagnosed in the United States annually, and 75% of cases are in the advanced stage when they are largely incurable. There is a critical need for improved early detection tools and development of novel treatments. Recently, we showed that among 20q13-amplified genes in ovarian cancer, ADRM1 overexpression was the most highly correlated with amplification and was significantly upregulated with respect to stage, recurrence, and metastasis. In addition, overexpression of ADRM1 correlated significantly with shorter time to recurrence and overall survival. Herein, array-CGH and microarray expression of ovarian cancer cell lines provides evidence consistent with the primary tumor data that ADRM1 is a 20q13 amplification target. Knockdown of ADRM1 in amplified ovarian cell-line OAW42 results in downregulation of growth factor GIPC1 and upregulation of tumor-suppressor RECK RNA and protein. In our dataset of 141 ovarian primary tumors, ADRM1 overexpression significantly correlates with GIPC1 overexpression. In addition, there is a significant anticorrelation between ADRM1 overexpression and RECK expression. Further research is necessary to determine whether targeting knockdown of ADRM1 in 20q13-amplified ovarian cancers results in growth inhibition and tumor suppression via downstream targets GIPC1 and RECK.
    Genes Chromosomes and Cancer 03/2011; 50(6):434-41. · 3.55 Impact Factor
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    ABSTRACT: although trastuzumab has improved the prognosis for HER-2-positive breast cancer patients, not all HER-2-positive breast tumours respond to trastuzumab treatment and those that initially respond frequently develop resistance. Insulin-like growth factor-1 receptor (IGF1R) signalling has been previously implicated in trastuzumab resistance. We tested IGF1R inhibition to determine if dual targeting of HER-2 and IGF1R improves response in cell line models of acquired trastuzumab resistance. HER-2, IGF1R, phospho-HER-2, and phospho-IGF1R levels were measured by enzyme-linked immunosorbent assays in parental and trastuzumab-resistant SKBR3 and BT474 cells. IGF1R signalling was targeted in these cells using both small interfering RNA (siRNA) and the tyrosine kinase inhibitor, NVP-AEW541. IGF1R levels were significantly increased in the trastuzumab-resistant model, SKBR3/Tr, compared with the parental SKBR3 cell line. In both the SKBR3/Tr and BT474/Tr cell lines, inhibition of IGF1R expression with siRNA or inhibition of tyrosine kinase activity by NVP-AEW541 significantly increased response to trastuzumab. The dual targeting approach also improved response in the parental SKBR3 cells but not in the BT474 parental cells. our results confirm that IGF1R inhibition improves response to trastuzumab in HER-2-positive breast cancer cells and suggest that dual targeting of IGF1R and HER-2 may improve response in HER-2-positive tumours.
    Annals of Oncology 01/2011; 22(1):68-73. · 7.38 Impact Factor
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    ABSTRACT: In this study, we explore the therapeutic potential of lapatinib a selective inhibitor of both the EGFR and HER2 tyrosine kinases for the treatment of endometrial cancer. The effect of lapatinib on tumour cell growth and receptor activation was studied in a panel of human endometrial cancer cell lines. Candidate molecular markers predicting sensitivity were assessed by baseline gene expression profiling, ELISA, and western blot analyses. Multiple drug effect/combination index (CI) isobologram analysis was used to study the interactions between chemotherapeutic drugs and lapatinib. Concentration-dependent anti-proliferative effects of lapatinib were seen in all endometrial cancer cell lines tested, but varied significantly between individual cell lines (IC(50) range: 0.052-10.9 micromol). HER2 overexpression or increased expression of EGFR was significantly associated with in vitro sensitivity (P=0.024 or 0.011, respectively). Lapatinib exerts growth inhibition in a PTEN-independent manner. Sensitive cell lines also exhibited increased expression of EGFR ligands or HER3. In contrast, lapatinib-resistant cell lines exhibited high androgen receptor (AR) levels or epithelial-to-mesenchymal transition (post-EMT) features. In endometrial cancer cells, at a wide range of clinically achievable drug concentrations, additive and synergistic interactions were observed for lapatinib plus carboplatin, paclitaxel, docetaxel, and doxorubicin. These observations provide a clear biologic rational to test lapatinib as a single agent or in combination with chemotherapy in endometrial cancer with HER2 overexpression. Expression of EGFR, its ligands, HER3, AR, and post-EMT markers warrant further evaluation to help define patients with HER2-nonoverexpressing endometrial cancer most likely to benefit from lapatinib.
    British Journal of Cancer 04/2008; 98(6):1076-84. · 5.08 Impact Factor
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    ABSTRACT: Lapatinib (GW572016) is a selective inhibitor of both epidermal growth factor receptor (EGFR) and HER-2 tyrosine kinases. Here, we explore the therapeutic potential of lapatinib by testing its effect on tumor cell growth in a panel of 31 characterized human breast cancer cell lines, including trastuzumab-conditioned HER-2-positive cell lines. We further characterize its activity in combination with trastuzumab and analyze whether EGFR and HER-2 expression or changes induced in the activation of EGFR, HER-2, Raf, AKT, or extracellular signal-regulated kinase (ERK) are markers of drug activity. We report that concentration-dependent antiproliferative effects of lapatinib were seen in all breast cancer cell lines tested but varied significantly between individual cell lines with up to 1,000-fold difference in the IC(50)s (range, 0.010-18.6 micromol/L). Response to lapatinib was significantly correlated with HER-2 expression and its ability to inhibit HER-2, Raf, AKT, and ERK phosphorylation. Long-term in vivo lapatinib studies were conducted with human breast cancer xenografts in athymic mice. Treatment over 77 days resulted in a sustained and significant reduction in xenograft volume compared with untreated controls. For the combination of lapatinib plus trastuzumab, synergistic drug interactions were observed in four different HER-2-overexpressing cell lines. Moreover, lapatinib retained significant in vitro activity against cell lines selected for long-term outgrowth (>9 months) in trastuzumab-containing (100 microg/mL) culture medium. These observations provide a clear biological rationale to test lapatinib as a single agent or in combination with trastuzumab in HER-2-overexpressing breast cancer and in patients with clinical resistance to trastuzumab.
    Cancer Research 02/2006; 66(3):1630-9. · 8.65 Impact Factor