[Show abstract][Hide abstract] ABSTRACT: ATR and ATM are DNA damage signaling kinases that phosphorylate several thousand substrates. ATR kinase activity is increased at damaged replication forks and resected DNA double-strand breaks (DSBs). ATM kinase activity is increased at DSBs. ATM has been widely studied since ataxia telangiectasia individuals who express no ATM protein are the most radiosensitive patients identified. Since ATM is not an essential protein, it is widely believed that ATM kinase inhibitors will be well-tolerated in the clinic. ATR has been widely studied, but advances have been complicated by the finding that ATR is an essential protein and it is widely believed that ATR kinase inhibitors will be toxic in the clinic. We describe AZD6738, an orally active and bioavailable ATR kinase inhibitor. AZD6738 induces cell death and senescence in non-small cell lung cancer (NSCLC) cell lines. AZD6738 potentiates the cytotoxicity of cisplatin and gemcitabine in NSCLC cell lines with intact ATM kinase signaling, and potently synergizes with cisplatin in ATM-deficient NSCLC cells. In contrast to expectations, daily administration of AZD6738 and ATR kinase inhibition for 14 consecutive days is tolerated in mice and enhances the therapeutic efficacy of cisplatin in xenograft models. Remarkably, the combination of cisplatin and AZD6738 resolves ATM-deficient lung cancer xenografts.
[Show abstract][Hide abstract] ABSTRACT: Purpose:
Glioblastoma multiforme (GBM) is the most lethal form of brain cancer with a median survival of only 12 to 15 months. Current standard treatment consists of surgery followed by chemoradiation. The poor survival of patients with GBM is due to aggressive tumor invasiveness, an inability to remove all tumor tissue, and an innate tumor chemo- and radioresistance. Ataxia-telangiectasia mutated (ATM) is an excellent target for radiosensitizing GBM because of its critical role in regulating the DNA damage response and p53, among other cellular processes. As a first step toward this goal, we recently showed that the novel ATM kinase inhibitor KU-60019 reduced migration, invasion, and growth, and potently radiosensitized human glioma cells in vitro.
Using orthotopic xenograft models of GBM, we now show that KU-60019 is also an effective radiosensitizer in vivo. Human glioma cells expressing reporter genes for monitoring tumor growth and dispersal were grown intracranially, and KU-60019 was administered intratumorally by convection-enhanced delivery or osmotic pump.
Our results show that the combined effect of KU-60019 and radiation significantly increased survival of mice 2- to 3-fold over controls. Importantly, we show that glioma with mutant p53 is much more sensitive to KU-60019 radiosensitization than genetically matched wild-type glioma.
Taken together, our results suggest that an ATM kinase inhibitor may be an effective radiosensitizer and adjuvant therapy for patients with mutant p53 brain cancers.
Full-text · Article · Apr 2013 · Clinical Cancer Research
[Show abstract][Hide abstract] ABSTRACT: ATM kinase signals DNA double strand breaks (DSB) to cell cycle arrest via p53 and DNA repair. ATM-defective cells are sensitive to DSB-inducing agents, making ATM an attractive target for anticancer chemo- and radio-sensitisation. KU59403 is an ATM inhibitor with the potency, selectivity and solubility for advanced pre-clinical evaluation. KU59403 was not cytotoxic to human cancer cell lines (SW620, LoVo, HCT116 and MDA-MB-231) per se but significantly increased the cytotoxicity of topoisomerase I and II poisons: camptothecin, etoposide and doxorubicin. Chemo- and radio-sensitisation by ATM inhibition was not p53-dependent. Following administration to mice, KU59403 distributed to tissues and concentrations exceeding those required for in vitro activity were maintained for at least 4 hr in tumour xenografts. KU59403 significantly enhanced the antitumour activity of topoisomerase poisons in mice bearing human colon cancer xenografts (SW620 and HCT116) at doses that were non-toxic alone and well tolerated in combination. Chemosensitisation was both dose and schedule-dependent. KU59403 represents a major advance in ATM inhibitor development, being the first compound to demonstrate good tissue distribution and significant chemo-sensitisation in in vivo models of human cancer, without major toxicity. KU59403 provides the first proof-of-principle pre-clinical data to support the future clinical development of ATM inhibitors.
Full-text · Article · Mar 2013 · Molecular Cancer Therapeutics
[Show abstract][Hide abstract] ABSTRACT: BRCA1 protein measurement has previously been evaluated as a potential diagnostic marker without reaching a conclusive recommendation. In this study, we applied current best practice in antibody validation to further characterize MS110, a widely used antibody targeting BRCA1. Antibody specificity was investigated using different biochemical validation techniques. We found that BRCA1 could not be reliably detected using immunoprecipitation and Western blot in endogenously expressing cells. We used immunohistochemistry on formalin-fixed paraffin-embedded cell pellets to establish compatibility with formalin-fixed paraffin-embedded samples. We demonstrated that in transfected cells and cell lines with known genetic BRCA1 status, MS110 successfully detected BRCA1 giving the expected level of staining in immunohistochemistry. Following this, we investigated the use of BRCA1 protein measurement by immunohistochemistry in a cohort of triple negative breast and serous ovarian tumour samples to explore the use of BRCA1 protein measurement by immunohistochemistry for patient stratification. Using MS110 in repeated standardized experiments, on serial sections from a panel of patient samples, results demonstrated considerable run-to-run variability. We concluded that in formalin-fixed tissue samples, MS110 does detect BRCA1; however, using standard methodologies, BRCA1 expression levels in tissue samples is incompatible with the use of this protein as a statistically robust patient selection marker in immunohistochemistry. These results demonstrate the need for further development to deliver BRCA1 protein quantification by immunohistochemistry as a patient stratification marker.
No preview · Article · Jan 2013 · Archiv für Pathologische Anatomie und Physiologie und für Klinische Medicin
[Show abstract][Hide abstract] ABSTRACT: Unlabelled:
Inhibition of PARP is a promising therapeutic strategy for homologous recombination-deficient tumors, such as BRCA1-associated cancers. We previously reported that BRCA1-deficient mouse mammary tumors may acquire resistance to the clinical PARP inhibitor (PARPi) olaparib through activation of the P-glycoprotein drug efflux transporter. Here, we show that tumor-specific genetic inactivation of P-glycoprotein increases the long-term response of BRCA1-deficient mouse mammary tumors to olaparib, but these tumors eventually developed PARPi resistance. In a fraction of cases, this resistance is caused by partial restoration of homologous recombination due to somatic loss of 53BP1. Importantly, PARPi resistance was minimized by long-term treatment with the novel PARP inhibitor AZD2461, which is a poor P-glycoprotein substrate. Together, our data suggest that restoration of homologous recombination is an important mechanism for PARPi resistance in BRCA1-deficient mammary tumors and that the risk of relapse of BRCA1-deficient tumors can be effectively minimized by using optimized PARP inhibitors.
In this study, we show that loss of 53BP1 causes resistance to PARP inhibition in mouse mammary tumors that are deficient in BRCA1. We hypothesize that low expression or absence of 53BP1 also reduces the response of patients with BRCA1-deficient tumors to PARP inhibitors.
[Show abstract][Hide abstract] ABSTRACT: Impaired DNA damage response pathways may create vulnerabilities of cancer cells that can be exploited therapeutically. One such selective vulnerability is the sensitivity of BRCA1- or BRCA2-defective tumors (hence defective in DNA repair by homologous recombination, HR) to inhibitors of the poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme critical for repair pathways alternative to HR. While promising, treatment with PARP-1 inhibitors (PARP-1i) faces some hurdles, including (1) acquired resistance, (2) search for other sensitizing, non-BRCA1/2 cancer defects and (3) lack of biomarkers to predict response to PARP-1i. Here we addressed these issues using PARP-1i on 20 human cell lines from carcinomas of the breast, prostate, colon, pancreas and ovary. Aberrations of the Mre11-Rad50-Nbs1 (MRN) complex sensitized cancer cells to PARP-1i, while p53 status was less predictive, even in response to PARP-1i combinations with camptothecin or ionizing radiation. Furthermore, monitoring PARsylation and Rad51 foci formation as surrogate markers for PARP activity and HR, respectively, supported their candidacy for biomarkers of PARP-1i responses. As to resistance mechanisms, we confirmed the role of the multidrug resistance efflux transporters and its reversibility. More importantly, we demonstrated that shRNA lentivirus-mediated depletion of 53BP1 in human BRCA1-mutant breast cancer cells increased their resistance to PARP-1i. Given the preferential loss of 53BP1 in BRCA-defective and triple-negative breast carcinomas, our findings warrant assessment of 53BP1 among candidate predictive biomarkers of response to PARPi. Overall, this study helps characterize genetic and functional determinants of cellular responses to PARP-1i and contributes to the search for biomarkers to exploit PARP inhibitors in cancer therapy.
[Show abstract][Hide abstract] ABSTRACT: Most patients with ovarian carcinomas succumb to their disease and there is a critical need for improved therapeutic approaches. Carcinomas arising in BRCA mutation carriers display defective DNA double-strand break repair that can be therapeutically exploited by inhibition of PARP-1, a key enzyme in the repair of DNA single-strand breaks, creating synthetic lethality in tumor cells.
To investigate synthetic lethality in vivo, we established a BRCA2 germline-mutated xenograft model that was developed directly from human ovarian cancer tissue, treated with the PARP inhibitor olaparib (AZD2281) alone and in combination with carboplatin.
We show that olaparib alone and in combination with carboplatin greatly inhibit growth in BRCA2-mutated ovarian serous carcinoma. This effect was not observed in a serous carcinoma with normal BRCA function, showing a specific antitumor effect of olaparib in mutation carriers. Immunohistochemistry (cleaved caspase-3 and Ki-67 stains) of remnant tissue after olaparib treatment revealed significantly decreased proliferation and increased apoptotic indices in these tumors compared with untreated controls. Furthermore, olaparib-treated tumors showed highly reduced PARP-1 activity that correlated with olaparib levels.
We established a BRCA2-mutated human ovarian cancer xenograft model suitable for experimental drug testing. The demonstrated in vivo efficacy of olaparib extends on the preclinical rationale for further clinical trials targeting ovarian cancer patients with BRCA mutations.
Full-text · Article · Feb 2011 · Clinical Cancer Research