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Stratford A.L.,University of British Columbia | Reipas K.,University of British Columbia | Hu K.,University of British Columbia | Fotovati A.,University of British Columbia | And 11 more authors.
Stem Cells | Year: 2012

Y-box binding protein-1 (YB-1) is the first reported oncogenic transcription factor to induce the tumor-initiating cell (TIC) surface marker CD44 in triple-negative breast cancer (TNBC) cells. In order for CD44 to be induced, YB-1 must be phosphorylated at S102 by p90 ribosomal S6 kinase (RSK). We therefore questioned whether RSK might be a tractable molecular target to eliminate TICs. In support of this idea, injection of MDA-MB-231 cells expressing Flag-YB-1 into mice increased tumor growth as well as enhanced CD44 expression. Despite enrichment for TICs, these cells were sensitive to RSK inhibition when treated ex vivo with BI-D1870. Targeting RSK2 with small interfering RNA (siRNA) or small molecule RSK kinase inhibitors (SL0101 and BI-D1870) blocked TNBC monolayer cell growth by ∼100%. In a diverse panel of breast tumor cell line models RSK2 siRNA predominantly targeted models of TNBC. RSK2 inhibition decreased CD44 promoter activity, CD44 mRNA, protein expression, and mammosphere formation. CD44+ cells had higher P-RSK S221/227, P-YB-1S102, and mitotic activity relative to CD44- cells. Importantly, RSK2 inhibition specifically suppressed the growth of TICs and triggered cell death. Moreover, silencing RSK2 delayed tumor initiation in mice. In patients, RSK2 mRNA was associated with poor disease-free survival in a cohort of 244 women with breast cancer that had not received adjuvant treatment, and its expression was highest in the basal-like breast cancer subtype. Taking this further, we report that P-RSK S221/227 is present in primary TNBCs and correlates with P-YB-1 S102as well as CD44. In conclusion, RSK2 inhibition provides a novel therapeutic avenue for TNBC and holds the promise of eliminating TICs. © AlphaMed Press. Source

Ang J.E.,Institute of Cancer Research | Gourley C.,University of Edinburgh | Powell C.B.,University of California at San Francisco | High H.,Prince of Wales Clinical School | And 28 more authors.
Clinical Cancer Research | Year: 2013

Purpose: Preclinical data suggest that exposure to PARP inhibitors (PARPi) may compromise benefit to subsequent chemotherapy, particularly platinum-based regimens, in patients with BRCA1/2 mutation carrier ovarian cancer (PBMCOC), possibly through the acquisition of secondary BRCA1/2 mutations. The efficacy of chemotherapy in the PARPi-resistant setting was therefore investigated. Experimental Design: We conducted a retrospective review of PBMCOC who received chemotherapy following disease progression on olaparib, administered at -200 mg twice daily for one month or more. Tumor samples were obtained in the post-olaparib setting where feasible and analyzed by massively parallel sequencing. Results: Data were collected from 89 patients who received a median of 3 (range 1-11) lines of preolaparib chemotherapy. The overall objective response rate (ORR) to post-olaparib chemotherapy was 36% (24 of 67 patients) by Response Evaluation Criteria in Solid Tumors (RECIST) and45%(35 of 78) by RECIST and/or Gynecologic Cancer InterGroup (GCIG) CA125 criteria with median progression-free survival (PFS) and overall survival (OS) of 17 weeks [95% confidence interval (CI), 13-21] and 34 weeks (95% CI, 26-42), respectively. For patients receiving platinum-based chemotherapy, ORRs were 40% (19 of 48) and 49% (26/53), respectively, with a median PFS of 22 weeks (95% CI, 15-29) and OSof 45 weeks (95% CI, 15-75). An increased platinum-to-platinum interval was associated with an increased OS and likelihood of response following post-olaparib platinum. No evidence of secondary BRCA1/2 mutation was detected in tumor samples of six PARPi-resistant patients [estimated frequency of such mutations adjusted for sample size: 0.125 (95%-CI: 0-0.375)]. Conclusions: Heavily pretreated PBMCOC who are PARPi-resistant retain the potential to respond to subsequent chemotherapy, including platinum-based agents. These data support the further development of PARPi in PBMCOC. © 2013 American Association for Cancer Research. Source

Shen Y.,BioMarin Pharmaceutical | Rehman F.L.,Cancer Research UK Gene Function Laboratory | Rehman F.L.,Institute of Cancer Research | Feng Y.,BioMarin Pharmaceutical | And 12 more authors.
Clinical Cancer Research | Year: 2013

Purpose: PARP1/2 inhibitors are a class of anticancer agents that target tumor-specific defects in DNA repair. Here, we describe BMN 673, a novel, highly potent PARP1/2 inhibitor with favorable metabolic stability, oral bioavailability, and pharmacokinetic properties. Experimental Design: Potency and selectivity of BMN 673 was determined by biochemical assays. Anticancer activity either as a single-agent or in combination with other antitumor agents was evaluated both in vitro and in xenograft cancer models. Results: BMN 673 is a potent PARP1/2 inhibitor (PARP1 IC50 = 0.57 nmol/L), but it does not inhibit other enzymes that we have tested.BMN673 exhibits selective antitumor cytotoxicity and elicitsDNArepair biomarkers at much lower concentrations than earlier generation PARP1/2 inhibitors (such as olaparib, rucaparib, and veliparib). In vitro, BMN 673 selectively targeted tumor cells with BRCA1, BRCA2, or PTEN gene defects with 20-to more than 200-fold greater potency than existing PARP1/2 inhibitors. BMN 673 is readily orally bioavailable, with more than 40% absolute oral bioavailability in rats when dosed in carboxylmethyl cellulose. Oral administration of BMN 673 elicited remarkable antitumor activity in vivo; xenografted tumors that carry defects in DNA repair due to BRCA mutations or PTEN deficiency were profoundly sensitive to oral BMN 673 treatment at well-tolerated doses in mice. Synergistic or additive antitumor effects were also found when BMN 673 was combined with temozolomide, SN38, or platinum drugs. Conclusion: BMN 673 is currently in early-phase clinical development and represents a promising PARP1/2 inhibitor with potentially advantageous features in its drug class. © 2013 American Association for Cancer Research. Source

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