Validation of the BRCA1 antibody MS110 and the utility of BRCA1 as a patient selection biomarker in immunohistochemical analysis of breast and ovarian tumours

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.

Concordance of ATM (ataxia telangiectasia mutated) immunohistochemistry between biopsy or metastatic tumor samples and primary tumors in gastric cancer patients

ATM (ataxia telangiectasia mutated) is one of several DNA repair proteins that are suggested to sensitize tumor cells to the poly(ADP-ribose) polymerase inhibitor olaparib when deficient. The aim of this study was to assess the spatiotemporal concordance of ATM immunohistochemistry (IHC) in gastric cancer in order to determine if measurements made at the level of various sample types and times could be inferred as having the potential to be relevant to treatment decisions made at the patient level. Two independent cohorts composed of 591 gastric cancer patients divided into a gastrectomy cohort (n = 450) and a metastasis cohort (n = 141) were used in this study. A total of 2,705 ATM IHC samples were examined, including 450 whole tissue, 3 sets of 450 tissue microarray (TMA), 301 biopsy, 222 metastatic tumor and 2 additional whole tissue samples of 50 cases from the gastrectomy cohort, and 141 pairs of primary and metastatic tumors from the metastasis cohort. The prevalence of ATM negativity was 13.1% in biopsies, 13.9, 15.1, and 16.0% in TMAs and 15.9% in whole tissue samples of the gastrectomy cohort, and 21.4% in primary tumor and 21.5% in metastatic tumor samples of the metastasis cohort. coefficients were 0.341 for biopsy, 0.572 as the average of 3 TMAs and 0.415 for the largely synchronous metastatic tumors of the gastrectomy cohort, and 0.153 for the largely asynchronous metastatic tumors of the metastasis cohort. Using whole tissue sections from tumor resections or primary tumor, respectively, as the reference standards, specificity and sensitivity were 91.6 and 41.0% for biopsy, 93.9 and 61.9% as the average of 3 TMAs, and 86.6 and 58.8% for metastatic tumors of the gastrectomy cohort and 81.7 and 33.3% for metastatic tumors of the metastasis cohort, respectively. Although we have demonstrated that the IHC assay for ATM was robust and reproducible in gastric tumor samples, we have also found that measurements were subject to significant discordance across multiple sample types from the same patient. Further work will be necessary to determine if classification may be made more consistent by multiple sampling. However, the lack of agreement between primary and asynchronous metastatic samples suggests that such sampling would need to be performed at the time of any treatment decision.

Abstract 3108: Exploring base excision repair variants as potential defining events in cancer patient populations and characterization of models for pre-clinical studies

Background Deficiencies in base excision repair (BER) may increase the cell's dependence on alternative repair pathways and so define a patient population for novel inhibitors of DNA damage repair. Notably, cancer associated molecular events in DNA polymerase beta (POLα) have been described in various disease backgrounds including colorectal cancer (CRC), gastric, breast and prostate (1-5). Although functional consequence has been linked to certain POLα mutations and splice variants, their prevalence in defined disease segments remains largely undefined. Aim We set out to ascertain the prevalence of POLα deficiencies in CRC, and subsequently investigated protein and gene expression profiling as alternative methods for defining BER defects in cancer. Methods/Results A comprehensive study of clinical (CRC; N=64), tumour explant (CRC; N=36) and cell line (mixed origin; N=280) samples revealed that cancer-associated mutations in the polymerase encoding domain of POLα (1-3) are not common events in CRC. Additionally, a previously described splice variant of POLα lacking part of the polymerase domain (3-4), was assayed and found to be expressed at similar levels in CRC and normal tissue. This would suggest that expression of the POLα splice variant is not a defining element of CRC in western populations. Expression profiling using Fluidigm Taqman revealed a subset of BER genes more highly expressed in CRC clinical samples and mixed cell lines compared with normal tissue. While protein expression profiles did not reflect relative gene expression in selected cell line models, we observed an additional low molecular weight band in a subset of cells profiled for POLB expression. Furthermore, we report variations in the expression of the scaffold protein XRCC1 in colorectal and breast cell lines and propose that this could also provide a mechanism for variation in DNA repair capacity. Summary Although from our studies sequencing and transcript analysis of POLα do not provide suitable markers of BER deficiency in CRC, we report aberrant banding patterns in POLα by Western blotting and variation in XRCC1 protein expression in a subset of cell lines analyzed. We hypothesize that these variants may confer a BER deficient phenotype. 1. Lang, T. et al. (2004Proc. Natl Acad. Sci. USA, 101, 6074-6079. 2. Tan, Xiao-Hui, et al Cancer Letters: 2005: 220: 101-114 3. Wang, L et al Cancer Research, 1992; 52:4824-4827 4. Bhattacharyya, N. et al. (1997) Proc. Natl Acad. Sci. USA, 94, 10324-10329

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3108. doi:1538-7445.AM2012-3108

Dynamic inhibition of ATM kinase provides a strategy for glioblastoma multiforme radiosensitization and growth control

Glioblastoma multiforme (GBM) is notoriously resistant to treatment. Therefore, new treatment strategies are urgently needed. ATM elicits the DNA damage response (DDR), which confers cellular radioresistance; thus, targeting the DDR with an ATM inhibitior (ATMi) is very attractive. Herein, we show that dynamic ATM kinase inhibition in the nanomolar range results in potent radiosensitization of human glioma cells, inhibits growth and does not conflict with temozolomide (TMZ) treatment. The second generation ATMi analog KU-60019 provided quick, reversible and complete inhibition of the DDR at sub-micromolar concentrations in human glioblastoma cells. KU-60019 inhibited the phosphorylation of the major DNA damage effectors p53, H2AX and KAP1 as well as AKT. Colony-forming radiosurvival showed that continuous exposure to nanomolar concentrations of KU-60019 effectively radiosensitized glioblastoma cell lines. When cells were co-treated with KU-60019 and TMZ, a slight increase in radiation-induced cell killing was noted, although TMZ alone was unable to radiosensitize these cells. In addition, without radiation, KU-60019 with or without TMZ reduced glioma cell growth but had no significant effect on the survival of human embryonic stem cell (hESC)-derived astrocytes. Altogether, transient inhibition of the ATM kinase provides a promising strategy for radiosensitizing GBM in combination with standard treatment. In addition, without radiation, KU-60019 limits growth of glioma cells in co-culture with human astrocytes that seem unaffected by the same treatment. Thus, inter-fraction growth inhibition could perhaps be achieved in vivo with minor adverse effects to the brain.

Activated germinal centre B cells undergo directed migration

Affinity maturation, the fundamental basis for adaptive immunity, is accomplished through somatic hypermutation of B-cell receptors followed by expansion of rare mutants with higher affinity for the immunising antigen. This process occurs over a period of weeks in unique micro-anatomic sites known as germinal centres. Two-photon microscopy has recently made it possible to track individual cells moving within germinal centres in living animals. Here we apply statistical approaches to test the hypothesis that B-cell motion is random. Our results show that activated B cells move in a directed manner that sharply contrasts with the behaviour of naïve B cells.

Inhibition of PARP-1 by olaparib (AZD2281) increases the radiosensitivity of a lung tumor xenograft

PARP-1 is a critical enzyme in the repair of DNA strand breaks. Inhibition of PARP-1 increases the effectiveness of radiation in killing tumor cells. However, although the mechanism(s) are well understood for these radiosensitizing effects in vitro, the underlying mechanism(s) in vivo are less clear. Nicotinamide, a drug structurally related to the first generation PARP-1 inhibitor, 3-aminobenzamide, reduces tumor hypoxia by preventing transient cessations in tumor blood flow, thus improving tumor oxygenation and sensitivity to radiotherapy. Here, we investigate whether olaparib, a potent PARP-1 inhibitor, enhances radiotherapy, not only by inhibiting DNA repair but also by changing tumor vascular hemodynamics in non-small cell lung carcinoma (NSCLC). In irradiated Calu-6 and A549 cells, olaparib enhanced the cytotoxic effects of radiation (sensitizer enhancement ratio at 10% survival = 1.5 and 1.3) and DNA double-strand breaks persisted for at least 24 hours after treatment. Combination treatment of Calu-6 xenografts with olaparib and fractionated radiotherapy caused significant tumor regression (P = 0.007) relative to radiotherapy alone. To determine whether this radiosensitization was solely due to effects on DNA repair, we used a dorsal window chamber model to establish the drug/radiation effects on vessel dynamics. Olaparib alone, when given as single or multiple daily doses, or in combination with fractionated radiotherapy, increased the perfusion of tumor blood vessels. Furthermore, an ex vivo assay in phenylephrine preconstricted arteries confirmed olaparib to have higher vasodilatory properties than nicotinamide. This study suggests that olaparib warrants consideration for further development in combination with radiotherapy in clinical oncology settings such as NSCLC.

Abstract 5088: Exploring ATM deficiency as a potential therapeutic target for the PARP inhibitor olaparib in head and neck squamous cell carcinoma

Background: Ataxia telangiectasia mutated (ATM) gene, localized in chromosome 11q22-23 is a key player in the signaling response to double strand breaks (DSBs). Impaired DSB repair due to ATM deficiency in tumor cells may lead to a wider application of the ‘‘synthetic lethality’’ approach seen with PARP inhibitors in BRCA-deficient tumors. Targeting DNA repair mechanisms with specific small molecule inhibitors will in principle sensitize tumor cells to DNA-damaging agents such as radiation. Radiation therapy remains the most common treatment of choice for head and neck cancers; however, there is still a large scope for improvement. Loss of distal 11q chromosome and subsequent ATM deficiency has been reported in primary head and neck tumors. Therefore, there are two aims to this work. First, we will establish the potential of targeting this cellular deficiency with the potent poly (ADP-ribose) polymerase (PARP) inhibitor olaparib; second, we will determine the prognostic significance of ATM deficiency in patients with head and neck squamous cell carcinoma (HNSCC) undergoing radiotherapy.

Methods: A panel of 10 HNSCC cell lines was screened for sensitivity to radiation in combination with olaparib by clonogenic survival assay in normoxic and anoxic conditions. The effect of olaparib as a single agent was also assessed in a PE/CA PJ34 (ATM deficient) xenograft model. A panel of 155 HNSCC biopsies taken prior to treatment with radiotherapy and where 5 year outcome data was available were used for ATM expression analysis by immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH).

Results: Olaparib enhanced the effect of ionizing radiation (IR) in all HNSCC cell lines. In vitro, the increase in sensitivity to 2Gy after olaparib treatment ranged between 1.5- and 8.4-fold in normoxia and between 1.2- and 3.9-fold in anoxia. In vivo, administration of olaparib (50mg/kg p.o) as a single agent in PE/CA PJ34 xenografts daily for 5 days caused a substantial increase in tumor growth delay compared to vehicle alone. The IHC and FISH studies of the 155 HNSCC biopsies showed a variable level of ATM deficiency and the prognostic significance (if any) of these observations are being established.

Conclusion: We demonstrate that olaparib is a promising candidate as a single agent in tumors with ATM deficiency, and given the radiosensitizing effects in vitro and in vivo it warrants consideration for combining with radiation for the treatment of HNSCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5088. doi:10.1158/1538-7445.AM2011-5088

Tumor growth inhibition by olaparib in BRCA2 germline-mutated patient-derived ovarian cancer tissue xenografts

PURPOSE

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.

EXPERIMENTAL DESIGN

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.

RESULTS

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.

CONCLUSIONS

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.

Micro-CT enables microlocalisation and quantification of Her2-targeted gold nanoparticles within tumour regions

OBJECTIVES

Gold nanoparticles are of interest as potential in vivo diagnostic and therapeutic agents, as X-ray contrast agents, drug delivery vehicles and radiation enhancers. The aim of this study was to quantitatively determine their targeting and microlocalisation in mouse tumour models after intravenous injection by using micro-CT.

METHODS

Gold nanoparticles (15 nm) were coated with polyethylene glycol and covalently coupled to anti-Her2 antibodies (Herceptin). In vitro, conjugates incubated with Her2+ (BT-474) and Her2- (MCF7) human breast cancer cells showed specific targeted binding with a Her2+ to Her2- gold ratio of 39.4±2.7:1. Nude mice, simultaneously bearing subcutaneous Her2+ and Her2- human breast tumours in opposite thighs were prepared. Gold nanoparticles alone, conjugated to Herceptin or to a non-specific antibody were compared. After intravenous injection of the gold nanoparticles, gold concentrations were determined by atomic absorption spectroscopy. Microlocalisation of gold was carried out by calibrated micro-CT, giving both the radiodensities and gold concentrations in tumour and non-tumour tissue.

RESULTS

All gold nanoparticle constructs showed accumulation, predominantly at tumour peripheries. However, the Herceptin-gold nanoparticles showed the best specific uptake in their periphery (15.8±1.7% injected dose per gram), 1.6-fold higher than Her2- tumours and 22-fold higher than surrounding muscle. Imaging readily enabled detection of small, 1.5 mm-thick tumours.

CONCLUSION

In this pre-clinical study, antibody-targeted 15 nm gold nanoparticles showed preferential uptake in cognate tumours, but even untargeted gold nanoparticles enhanced the visibility of tumour peripheries and enabled detection of millimetre-sized tumours. Micro-CT enabled quantification within various regions of a tumour.

Sensitivity to poly(ADP-ribose) polymerase (PARP) inhibition identifies ubiquitin-specific peptidase 11 (USP11) as a regulator of DNA double-strand break repair

DNA damage repair and checkpoint responses prevent genome instability and provide a barrier to the development of cancer. Inherited mutations in DNA damage response (DDR) genes such as those that encode the homologous recombination (HR) proteins BRCA1 and BRCA2 cause cancer predisposition syndromes. PARP inhibitors are an exciting new class of targeted therapy for treating patients with HR repair-defective tumors. In this study, we use an RNAi screen to identify genes that when silenced cause synthetic lethality with the PARP inhibitor AZD2281. This screen identified the deubiquitylating enzyme USP11 as a participant in HR repair of DNA double-strand breaks. Silencing USP11 with siRNA leads to spontaneous DDR activation in otherwise undamaged cells and hypersensitivity to PARP inhibition, ionizing radiation, and other genotoxic stress agents. Moreover, we demonstrate that HR repair is defective in USP11-silenced cells. Finally, the recruitment of a subset of double-strand break repair proteins including RAD51 and 53BP1 to repair foci is misregulated in the absence of USP11 catalytic activity. Thus, our synthetic lethal approach identified USP11 as a component of the HR double-strand break repair pathway.

ATM deficiency sensitizes mantle cell lymphoma cells to poly(ADP-ribose) polymerase-1 inhibitors

Poly(ADP-ribose) polymerase-1 (PARP-1) inhibition is toxic to cells with mutations in the breast and ovarian cancer susceptibility genes BRCA1 or BRCA2, a concept termed synthetic lethality. However, whether this approach is applicable to other human cancers with defects in other DNA repair genes has yet to be determined. The ataxia telangiectasia mutated (ATM) gene is altered in several human cancers including mantle cell lymphoma (MCL). Here, we characterize a panel of MCL cell lines for ATM status and function and investigate the potential for synthetic lethality in MCL in the presence of small-molecule inhibitors of PARP-1. We show that Granta-519 and UPN2 cells have low levels of ATM protein, are defective in DNA damage-induced ATM-dependent signaling, are radiation sensitive, and have cell cycle checkpoint defects: all characteristics of defective ATM function. Significantly, Granta-519 and UPN2 cells were more sensitive to PARP-1 inhibition than were the ATM-proficient MCL cell lines examined. Furthermore, the PARP-1 inhibitor olaparib (known previously as AZD2281/KU-0059436) significantly decreased tumor growth and increased overall survival in mice bearing s.c. xenografts of ATM-deficient Granta-519 cells while producing only a modest effect on overall survival of mice bearing xenografts of the ATM-proficient cell line, Z138. Thus, PARP inhibitors have therapeutic potential in the treatment of MCL, and the concept of synthetic lethality extends to human cancers with ATM alterations.

Abstract C119: Identification of gene expression biomarkers that predict sensitivity to the PARP inhibitor olaparib

Background: The oral PARP inhibitor olaparib (AZD2281, KU-0059436) is in Phase II clinical trials in patients with BRCA-mutated breast and ovarian cancer. Early results in these trials have provided positive clinical evidence for the targeted therapy concept of synthetic lethality using PARP inhibitors in molecularly-defined tumors with little effect on normal tissues. However, olaparib offers the potential to treat a broader range of patient tumors and pre-clinical studies have indicated that homologous recombination deficiency (HRD) due to loss of other DNA repair genes or through impaired cell-cycle checkpoints can also lead to sensitivity to PARP inhibitors. The ability to stratify patients whose tumors will respond to treatment will be critical to realise the potential of this targeted therapy approach. In order to identify predictive biomarkers of olaparib response and to provide further insights into mechanisms of olaparib sensitivity a study was undertaken using a panel of cell lines correlating response with molecular profiles.

Methods: A cross tumor-type panel of 95 cell lines (KU-95 panel) representing breast, ovarian, colorectal, lung, head & neck and pancreatic cancers was tested for sensitivity to olaparib using 2D-clonogenic survival assays. Baseline (untreated) gene expression profiles using Affymetrix genome-wide U133A 2.0 arrays together with protein expression and mutational status of genes, such as BRCA1, known to modify of olaparib response were determined for each cell line. Novel statistical, bioinformatics and pathway analysis approaches were used to identify genes that are predictive for olaparib response.

Results: Across the KU-95 cell-line panel, 30 cell lines were highly sensitive to olaparib (IC50 <1 M) treatment and 36 were resistant (IC50 >4 M). Deleterious mutations in BRCA1 or BRCA2 genes were associated with only a small subset of highly sensitive cell lines indicating the presence of other factors able to modulate olaparib responsiveness. Directed analysis of several other DNA repair genes showed correlations with response consistent with previous data. Genome-wide transcriptome and pathway mapping analysis revealed DNA repair and proliferation associated genes to be most consistently correlated with olaparib sensitivity. Based on results from all these approaches a candidate baseline gene expression profile predictive of olaparib response was established.

Conclusions: By profiling a large panel of cell lines we have determined that factors in addition to BRCA mutation can be linked with olaparib sensitivity. A list of candidate gene transcripts was identified that predicts sensitivity to olaparib across a broad range of tumor types in vitro and may have utility as predictive biomarkers in the clinic. Studies are already underway to determine whether this baseline transcript tumor profile can be correlated with patient responses to olaparib.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C119.

Improved ATM kinase inhibitor KU-60019 radiosensitizes glioma cells, compromises insulin, AKT and ERK prosurvival signaling, and inhibits migration and invasion

Ataxia telangiectasia (A-T) mutated (ATM) is critical for cell cycle checkpoints and DNA repair. Thus, specific small molecule inhibitors targeting ATM could perhaps be developed into efficient radiosensitizers. Recently, a specific inhibitor of the ATM kinase, KU-55933, was shown to radiosensitize human cancer cells. Herein, we report on an improved analogue of KU-55933 (KU-60019) with K(i) and IC(50) values half of those of KU-55933. KU-60019 is 10-fold more effective than KU-55933 at blocking radiation-induced phosphorylation of key ATM targets in human glioma cells. As expected, KU-60019 is a highly effective radiosensitizer of human glioma cells. A-T fibroblasts were not radiosensitized by KU-60019, strongly suggesting that the ATM kinase is specifically targeted. Furthermore, KU-60019 reduced basal S473 AKT phosphorylation, suggesting that the ATM kinase might regulate a protein phosphatase acting on AKT. In line with this finding, the effect of KU-60019 on AKT phosphorylation was countered by low levels of okadaic acid, a phosphatase inhibitor, and A-T cells were impaired in S473 AKT phosphorylation in response to radiation and insulin and unresponsive to KU-60019. We also show that KU-60019 inhibits glioma cell migration and invasion in vitro, suggesting that glioma growth and motility might be controlled by ATM via AKT. Inhibitors of MEK and AKT did not further radiosensitize cells treated with KU-60019, supporting the idea that KU-60019 interferes with prosurvival signaling separate from its radiosensitizing properties. Altogether, KU-60019 inhibits the DNA damage response, reduces AKT phosphorylation and prosurvival signaling, inhibits migration and invasion, and effectively radiosensitizes human glioma cells.

Inhibition of poly(ADP-ribose) polymerase in tumors from BRCA mutation carriers

BACKGROUND

The inhibition of poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) is a potential synthetic lethal therapeutic strategy for the treatment of cancers with specific DNA-repair defects, including those arising in carriers of a BRCA1 or BRCA2 mutation. We conducted a clinical evaluation in humans of olaparib (AZD2281), a novel, potent, orally active PARP inhibitor.

METHODS

This was a phase 1 trial that included the analysis of pharmacokinetic and pharmacodynamic characteristics of olaparib. Selection was aimed at having a study population enriched in carriers of a BRCA1 or BRCA2 mutation.

RESULTS

We enrolled and treated 60 patients; 22 were carriers of a BRCA1 or BRCA2 mutation and 1 had a strong family history of BRCA-associated cancer but declined to undergo mutational testing. The olaparib dose and schedule were increased from 10 mg daily for 2 of every 3 weeks to 600 mg twice daily continuously. Reversible dose-limiting toxicity was seen in one of eight patients receiving 400 mg twice daily (grade 3 mood alteration and fatigue) and two of five patients receiving 600 mg twice daily (grade 4 thrombocytopenia and grade 3 somnolence). This led us to enroll another cohort, consisting only of carriers of a BRCA1 or BRCA2 mutation, to receive olaparib at a dose of 200 mg twice daily. Other adverse effects included mild gastrointestinal symptoms. There was no obvious increase in adverse effects seen in the mutation carriers. Pharmacokinetic data indicated rapid absorption and elimination; pharmacodynamic studies confirmed PARP inhibition in surrogate samples (of peripheral-blood mononuclear cells and plucked eyebrow-hair follicles) and tumor tissue. Objective antitumor activity was reported only in mutation carriers, all of whom had ovarian, breast, or prostate cancer and had received multiple treatment regimens.

CONCLUSIONS

Olaparib has few of the adverse effects of conventional chemotherapy, inhibits PARP, and has antitumor activity in cancer associated with the BRCA1 or BRCA2 mutation. (ClinicalTrials.gov number, NCT00516373.)

Pre-clinical activity of the PARP inhibitor AZD2281 in human breast cancer cell lines and in combination with DNA damaging agents

Abstract #1038

Background: Deficiencies in DNA repair mechanisms have been associated with breast cancer. AZD2281, a potent, oral, PARP inhibitor has been shown to have clinical activity in patients with BRCA mutant breast cancers. Laboratory studies have suggested that non-BRCA mutant breast cancers may also be sensitive to PARP inhibition in tumors as a consequence of deficiencies in other homologous recombination (HR) repair components. Using a large panel of human breast cancer cell lines we tested the hypotheses that (1) there may be a subset of non-BRCA mutant breast cancers that are sensitive to single-agent AZD2281 and (2) AZD2281 would potentiate the cytotoxic effects of the DNA damaging agent cisplatin. Methods: 43 human cell lines representing known molecular subgroups of breast cancer (i.e. ER+, HER2 amplified, “triple-negative”), and 3 immortalized breast lines were treated in duplicate in adherent plates with AZD2281 using two-fold dilutions over 6 concentrations for 6 days. Dose response curves were generated using a cell count assay to calculate the IC50 of AZD2281. In addition, a subset of cell lines that grow under anchorage independent conditions were grown in triplicate in the presence and absence of 1 µM AZD2281 in soft agar for at least 3 weeks and growth inhibition was calculated as per cent of untreated control. Cell lines (both sensitive and resistant to single agent AZD2281) were also evaluated in combination with cisplatin in a cell count assay to assess the interaction between the two agents.
 Results: The majority of breast cancer cell lines evaluated in the short term 2-D growth assay did not show significant growth inhibition (IC50 < 1 µM) following AZD2281 treatment, including a known BRCA mutant cell line, suggesting this assay may not be ideal for determining sensitivity to AZD2281. However, in the longer term anchorage independent clonogenic assay, approximately half of the cell lines evaluated demonstrated an IC50 < 1 µM. Of note, the majority of the cell lines representing a “triple-negative” phenotype appeared sensitive to AZD2281 in this assay. In addition, pre-treatment with AZD2281 prior to cisplatin, potentiated the growth inhibition seen with cisplatin in both AZD2281 sensitive and resistant cell lines. Additional studies evaluating predictive markers other than BRCA status are ongoing. Conclusion: The PARP inhibitor AZD2281 has significant pre-clinical activity in human breast cancer cell lines. In a clonogenic assay, cell lines representing the “triple negative” subtype were especially sensitive to AZD2281 supporting clinical development in this population, regardless of BRCA status. In addition, these pre-clinical data support the hypothesis that PARP inhibition may potentiate the effects of chemotherapy induced DNA damage and provide further rationale for clinical development.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1038.

Selective inhibition of BRCA2-deficient mammary tumor cell growth by AZD2281 and cisplatin

PURPOSE

To assess efficacy of the novel, selective poly(ADP-ribose) polymerase-1 (PARP-1) inhibitor AZD2281 against newly established BRCA2-deficient mouse mammary tumor cell lines and to determine potential synergy between AZD2281 and cisplatin.

EXPERIMENTAL DESIGN

We established and thoroughly characterized a panel of clonal cell lines from independent BRCA2-deficient mouse mammary tumors and BRCA2-proficient control tumors. Subsequently, we assessed sensitivity of these lines to conventional cytotoxic drugs and the novel PARP inhibitor AZD2281. Finally, in vitro combination studies were done to investigate interaction between AZD2281 and cisplatin.

RESULTS

Genetic, transcriptional, and functional analyses confirmed the successful isolation of BRCA2-deficient and BRCA2-proficient mouse mammary tumor cell lines. Treatment of these cell lines with 11 different anticancer drugs or with gamma-irradiation showed that AZD2281, a novel and specific PARP inhibitor, caused the strongest differential growth inhibition of BRCA2-deficient versus BRCA2-proficient mammary tumor cells. Finally, drug combination studies showed synergistic cytotoxicity of AZD2281 and cisplatin against BRCA2-deficient cells but not against BRCA2-proficient control cells.

CONCLUSION

We have successfully established the first set of BRCA2-deficient mammary tumor cell lines, which form an important addition to the existing preclinical models for BRCA-mutated breast cancer. The exquisite sensitivity of these cells to the PARP inhibitor AZD2281, alone or in combination with cisplatin, provides strong support for AZD2281 as a novel targeted therapeutic against BRCA-deficient cancers.

4-[3-(4-cyclopropanecarbonylpiperazine-1-carbonyl)-4-fluorobenzyl]-2H-phthalazin-1-one: a novel bioavailable inhibitor of poly(ADP-ribose) polymerase-1

Poly(ADP-ribose) polymerase activation is an immediate cellular response to metabolic-, chemical-, or ionizing radiation-induced DNA damage and represents a new target for cancer therapy. In this article, we disclose a novel series of substituted 4-benzyl-2 H-phthalazin-1-ones that possess high inhibitory enzyme and cellular potency for both PARP-1 and PARP-2. Optimized compounds from the series also demonstrate good pharmacokinetic profiles, oral bioavailability, and activity in vivo in an SW620 colorectal cancer xenograft model. 4-[3-(4-Cyclopropanecarbonylpiperazine-1-carbonyl)-4-fluorobenzyl]-2 H-phthalazin-1-one (KU-0059436, AZD2281) 47 is a single digit nanomolar inhibitor of both PARP-1 and PARP-2 that shows standalone activity against BRCA1-deficient breast cancer cell lines. Compound 47 is currently undergoing clinical development for the treatment of BRCA1- and BRCA2-defective cancers.

Premature twins of a mother with Graves' disease with discordant thyroid function: a case report

Thyroid dysfunction is recognized in the newborns of mothers affected by Graves' disease during pregnancy. We describe the development of concurrent hyperthyroidism and hypothyroidism in the twin infants of a mother with Graves' disease diagnosed during pregnancy.

Deficiency in the Repair of DNA Damage by Homologous Recombination and Sensitivity to Poly(ADP-Ribose) Polymerase Inhibition

Deficiency in either of the breast cancer susceptibility proteins BRCA1 or BRCA2 induces profound cellular sensitivity to the inhibition of poly(ADP-ribose) polymerase (PARP) activity. We hypothesized that the critical role of BRCA1 and BRCA2 in the repair of double-strand breaks by homologous recombination (HR) was the underlying reason for this sensitivity. Here, we examine the effects of deficiency of several proteins involved in HR on sensitivity to PARP inhibition. We show that deficiency of RAD51, RAD54, DSS1, RPA1, NBS1, ATR, ATM, CHK1, CHK2, FANCD2, FANCA, or FANCC induces such sensitivity. This suggests that BRCA-deficient cells are, at least in part, sensitive to PARP inhibition because of HR deficiency. These results indicate that PARP inhibition might be a useful therapeutic strategy not only for the treatment of BRCA mutation-associated tumors but also for the treatment of a wider range of tumors bearing a variety of deficiencies in the HR pathway or displaying properties of 'BRCAness.'

Duplication 8q22.1-q24.1 associated with bipolar disorder and speech delay

OBJECTIVE

To report a case of a child with bipolar disorder found to have an unbalanced translocation involving the long arm of chromosome 8, a region that has been previously implicated in genome-wide linkage scans.

CASE REPORT

A 7-year-old boy with a complex psychiatric symptom presentation including attention deficits, distractibility, impulsivity, pressured speech, sleep disturbance, aggressive behavior, and hypersexuality diagnosed with bipolar disorder. He also showed evidence of borderline intellectual and adaptive functioning and had mild dysmorphic features with a duplication of distal 8q that arose as an unbalanced chromosomal translocation due to a maternal 15p;8q insertion.

CONCLUSION

This finding of an unbalanced translocation provides further evidence to support previous linkage studies of a potential causative gene on 8q for bipolar disorder.

A role for polymerase eta in the cellular tolerance to cisplatin-induced damage

Mutation of the POLH gene encoding DNA polymerase eta (pol eta) causes the UV-sensitivity syndrome xeroderma pigmentosum-variant (XP-V) which is linked to the ability of pol eta to accurately bypass UV-induced cyclobutane pyrimidine dimers during a process termed translesion synthesis. Pol eta can also bypass other DNA damage adducts in vitro, including cisplatin-induced intrastrand adducts, although the physiological relevance of this is unknown. Here, we show that independent XP-V cell lines are dramatically more sensitive to cisplatin than the same cells complemented with functional pol eta. Similar results were obtained with the chemotherapeutic agents, carboplatin and oxaliplatin, thus revealing a general requirement for pol eta expression in providing tolerance to these platinum-based drugs. The level of sensitization observed was comparable to that of XP-A cells deficient in nucleotide excision repair, a recognized and important mechanism for repair of cisplatin adducts. However, unlike in XP-A cells, the absence of pol eta expression resulted in a reduced ability to overcome cisplatin-induced S phase arrest, suggesting that pol eta is involved in translesion synthesis past these replication-blocking adducts. Subcellular localization studies also highlighted an accumulation of nuclei with pol eta foci that correlated with the formation of monoubiquitinated proliferating cell nuclear antigen following treatment with cisplatin, reminiscent of the response to UV irradiation and further indicating a role for pol eta in dealing with cisplatin-induced damage. Together, these data show that pol eta represents an important determinant of cellular responses to cisplatin, which could have implications for acquired or intrinsic resistance to this key chemotherapeutic agent.

hnRNP K: An HDM2 Target and Transcriptional Coactivator of p53 in Response to DNA Damage

In response to DNA damage, mammalian cells trigger the p53-dependent transcriptional induction of factors that regulate DNA repair, cell-cycle progression, or cell survival. Through differential proteomics, we identify heterogeneous nuclear ribonucleoprotein K (hnRNP K) as being rapidly induced by DNA damage in a manner that requires the DNA-damage signaling kinases ATM or ATR. Induction of hnRNP K ensues through the inhibition of its ubiquitin-dependent proteasomal degradation mediated by the ubiquitin E3 ligase HDM2/MDM2. Strikingly, hnRNP K depletion abrogates transcriptional induction of p53 target genes and causes defects in DNA-damage-induced cell-cycle-checkpoint arrests. Furthermore, in response to DNA damage, p53 and hnRNP K are recruited to the promoters of p53-responsive genes in a mutually dependent manner. These findings establish hnRNP K as a new HDM2 target and show that, by serving as a cofactor for p53, hnRNP K plays key roles in coordinating transcriptional responses to DNA damage.

The overexpression of specialized DNA polymerases in cancer

Specialized DNA polymerases are required to bypass DNA damage lesions that would otherwise cause replication arrest and cell death. When operating on non-canonical templates, such as undamaged DNA or on non-cognate lesions, these polymerases exhibit considerably reduced fidelity, resulting in the generation of mutations. Ectopic overexpression of these polymerases can also lead to an increased mutation rate and an enhanced capability of DNA repair, suggesting that they could potentially act as oncogenes if they were overexpressed in cancers. Here, we examine expression patterns of DNA polymerases in matched normal and tumor samples from a diverse range of tissues. As well as investigating the specialized polymerases beta, lambda, iota and kappa, we also investigate the expression of the replicative polymerases alpha, delta and epsilon. The data presented provide evidence for the overexpression of specialized polymerases in tumors, with more than 45% of the 68 tumor samples studied demonstrating greater than two-fold enhanced expression of at least one specialized polymerase. Of particular note, DNA polymerase beta (pol beta) was found to be overexpressed at both the mRNA and protein level in approximately one third of all tumor types studied, with overexpression being particularly frequent in uterus, ovary, prostate and stomach samples. Pols lambda, and iota were also found to be overexpressed to a significant extent in a range of tumor types, albeit less frequently than pol beta. In contrast, pol kappa was rarely found to be overexpressed in tumors but was found to be commonly underexpressed in many samples. Downregulation of pol beta expression by siRNA resulted in an increased sensitivity to the chemotherapeutic agent cisplatin, suggesting a role for this polymerase in providing tolerance to cisplatin-induced damage. These observations suggest that specialised DNA polymerases, and particularly pol beta, could be considered both as caretaker genes altered during tumorigenesis, and as potential drug targets to sensitise tumors to chemotherapy.

Suppression of HIV-1 infection by a small molecule inhibitor of the ATM kinase

Chemotherapy that is used to treat human immunodeficiency virus type-1 (HIV-1) infection focuses primarily on targeting virally encoded proteins. However, the combination of a short retroviral life cycle and high mutation rate leads to the selection of drug-resistant HIV-1 variants. One way to address this problem is to inhibit non-essential host cell proteins that are required for viral replication. Here we show that the activity of HIV-1 integrase stimulates an ataxia-telangiectasia-mutated (ATM)-dependent DNA damage response, and that a deficiency of this ATM kinase sensitizes cells to retrovirus-induced cell death. Consistent with these observations, we demonstrate that a novel and specific small molecule inhibitor of ATM kinase activity, KU-55933, is capable of suppressing the replication of both wild-type and drug-resistant HIV-1.

Suppression of retroviral infection by the RAD52 DNA repair protein

Reverse transcription of retroviral RNA into linear double-stranded DNA and its integration into the host cell genome are essential steps in the retroviral life cycle. The nonhomologous end-joining (NHEJ) DNA repair pathway has been implicated in protecting cells from retrovirus-induced apoptosis caused by strand breaks in host cell DNA or unintegrated linear viral DNA. In eukaryotes, both the NHEJ and homologous recombination (HR) pathways play important roles in repairing DNA double-strand breaks. Here we show that the HR repair protein RAD52 modulates the outcome of recombinant HIV-l vector infection by markedly reducing the efficiency of productive integration events. Increased retroviral integration is the first major phenotype described for a RAD52 deficiency in mammalian cells. Mutations in other HR proteins (XRCC2, XRCC3 and BRCA2) do not markedly affect retroviral transduction rates, suggesting that the HR repair pathway per se does not influence retroviral infection. Instead, the mechanism of attenuation of retroviral infection by RAD52 appears to be based upon competition between the RAD52 protein and active integration complexes for the retroviral cDNA genome.