High-resolution imaging for the detection and characterisation of circulating tumour cells from patients with oesophageal, hepatocellular, thyroid and ovarian cancers

Interest has increased in the potential role of circulating tumour cells in cancer management. Most cell‐based studies have been designed to determine the number of circulating tumour cells in a given volume of blood. Ability to understand the biology of the cancer cells would increase the clinical potential. The purpose of this study was to develop and validate a novel, widely applicable method for detection and characterisation of circulating tumour cells. Cells were imaged with an ImageStream^X imaging flow cytometer which allows detection of expression of multiple biomarkers on each cell and produces high‐resolution images. Depletion of haematopoietic cells was by red cell lysis, leukocyte common antigen CD45 depletion and differential centrifugation. Expression of epithelial cell adhesion molecule, cytokeratins, tumour‐type‐specific biomarkers and CD45 was detected by immunofluorescence. Nuclei were identified with DAPI or DRAQ5 and brightfield images of cells were collected. The method is notable for the dearth of cell damage, recoveries greater than 50%, speed and absence of reliance on the expression of a single biomarker by the tumour cells. The high‐quality images obtained ensure confidence in the specificity of the method. Validation of the methodology on samples from patients with oesophageal, hepatocellular, thyroid and ovarian cancers confirms its utility and specificity. Importantly, this adaptable method is applicable to all tumour types including those of nonepithelial origin. The ability to measure simultaneously the expression of multiple biomarkers will facilitate analysis of the cancer cell biology of individual circulating tumour cells.

What's new?

Circulating tumour cells (CTCs) are disseminated malignant cells from which biological and therapeutic information may be obtained non‐invasively. Detection of small CTC populations within the large number of normal blood cells is a challenge. This study describes a novel method for the detection and high‐resolution imaging of CTCs. Unlike most other studies, CTC detection is not reliant upon expression of a single biomarker. The method is applicable to all cancers; the authors present preliminary results from four tumour types. The high quality of the images allows biological characterisation of the tumour cells and increases the clinical potential of the approach.

Abstract 2448: Towards structure-based drug design of 3-phosphoglycerate dehydrogenase inhibitors

Background

The NAD+-requiring enzyme 3-phosphoglycerate dehydrogenase (PHGDH) diverts glycolytic flux into serine production and folate metabolism by catalyzing the oxidization of 3-phosphoglycerate to phosphohydroxypyruvate. The PHGDH gene is located on chromosome 1(1p12), a region frequently amplified in melanoma and certain breast cancer forms. PHGDH knockdown in cells with amplified PHGDH or overexpressing PHGDH at the protein level resulted in cell growth inhibition. In addition ectopic overexpression of PHGDH in a non-tumorigenic cell line induced morphological changes characteristic of transformation. Therefore, inhibitors of PHGDH may be therapeutically valuable.

No PHGDH inhibitors have been reported to date, our aim is to develop PHGDH inhibitors targeting the cofactor (and substrate) binding site.

Methods

Full length PHGDH and the catalytic subunit (sPHGDH) were expressed in, and isolated from E. coli. PHGDH was found to co-purify with its cofactor, making it necessary to abolish the cofactor-protein interaction to investigate inhibitor binding at the co-factor site. To accomplish this, site-directed sPHGDH mutants were constructed and purified. To characterize the mutants, their enzymatic activity and ability to bind to NADH (assessed by thermal stability and isothermal titration calorimetry (ITC)) were measured, and their structures were characterized by circular dichroism (CD) spectroscopy and on-going x-ray crystallographic studies.

Results sPHGDH retained 60% of the enzymatic activity of the full length protein whereas introduction of single or double point mutations around the cofactor or substrate binding site resulted in complete abolition of enzymatic activity. The binding of NADH (1mM) to PHGDH and sPHGDH resulted in increases in melting temperature (ΔTm) of 8.4 ± 0.2 °C and 9.3 ± 0.5 °C respectively. Mutation of the cofactor binding site resulted in reduced ability to bind NADH (ΔTm = 0.8 ± 0.2 °C, 2.3 ± 0.1 °C) whereas mutation at the substrate binding site, directly adjacent to the cofactor binding site, had no significant effect on the ability to bind NADH. Congruent findings were obtained via ITC determining a binding affinity (Kd) of 0.66 μM for wt sPHGDH and a reduced binding affinity of 3-30 fold for the mutated proteins. CD measurements showed that the proteins mutated at the co-factor binding site had undergone minor changes in the secondary structure compared to the wt sPHGDH whereas mutation at the substrate binding site had no effect on the secondary structure elements.

Conclusion Although the mutations carried out were single or double point mutations only, cofactor binding could be reduced substantially, giving rise to markedly lower catalytic activity. These investigations illustrate a promising way of making proteins with large, tight binding ligands accessible to structure-based drug-design.

Citation Format: Judith E. Unterlass, Nabila Aljufri, Sophie Bex, Celine Cano, Martin E M Noble, Nicola J. Curtin. Towards structure-based drug design of 3-phosphoglycerate dehydrogenase inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2448. doi:10.1158/1538-7445.AM2015-2448

Vasoactivity of rucaparib, a PARP-1 inhibitor, is a complex process that involves myosin light chain kinase, P2 receptors, and PARP itself

Therapeutic inhibition of poly(ADP-ribose) polymerase (PARP), as monotherapy or to supplement the potencies of other agents, is a promising strategy in cancer treatment. We previously reported that the first PARP inhibitor to enter clinical trial, rucaparib (AG014699), induced vasodilation in vivo in xenografts, potentiating response to temozolomide. We now report that rucaparib inhibits the activity of the muscle contraction mediator myosin light chain kinase (MLCK) 10-fold more potently than its commercially available inhibitor ML-9. Moreover, rucaparib produces additive relaxation above the maximal degree achievable with ML-9, suggesting that MLCK inhibition is not solely responsible for dilation. Inhibition of nitric oxide synthesis using L-NMMA also failed to impact rucaparib’s activity. Rucaparib contains the nicotinamide pharmacophore, suggesting it may inhibit other NAD+-dependent processes. NAD⁺ exerts P2 purinergic receptor-dependent inhibition of smooth muscle contraction. Indiscriminate blockade of the P2 purinergic receptors with suramin abrogated rucaparib-induced vasodilation in rat arterial tissue without affecting ML-9-evoked dilation, although the specific receptor subtypes responsible have not been unequivocally identified. Furthermore, dorsal window chamber and real time tumor vessel perfusion analyses in PARP-1^-/- mice indicate a potential role for PARP in dilation of tumor-recruited vessels. Finally, rucaparib provoked relaxation in 70% of patient-derived tumor-associated vessels. These data provide tantalising evidence of the complexity of the mechanism underlying rucaparib-mediated vasodilation.

PARP activity in peripheral blood lymphocytes as a predictive biomarker for PARP inhibition in tumor tissues - A population pharmacokinetic/pharmacodynamic analysis of rucaparib

PURPOSE

Rucaparib is a potent Poly (ADP-ribose) Polymerase (PARP) inhibitor currently under clinical development. The objectives of this analysis were to establish population PK and PK/PD models for rucaparib, and to evaluate the predictability of PARP activity in PBL for PARP activity in tumor tissues.

EXPERIMENTAL DESIGN

Rucaparib concentrations and PARP activity in human PBLs and tumor issues were obtained from 32 patients with solid tumors in a Phase 1 First-in-Patient study. Simulations were conducted to evaluate different dosing regimens.

RESULTS

A 3-compartment PK model best described the PK of rucaparib. An Emax model best described the exposure and PARP inhibition relationship. The maximum PARP inhibition (Imax) achieved in PBLs and in tumors were 90.9% and 90.0% of the baseline PARP activity, and the IC50 values were 1.05 ng/mL and 1.10 ng/mL, respectively. PAR polymer baseline value was found to be a covariate of Emin.

CONCLUSION

Population PK and PK/PD models have been established to describe population PK of rucaparib and the relationship between rucaparib plasma concentration and PARP inhibition in both PBLs and tumor issues. Results from this trial indicated that PARP inhibition in PBLs can be used as a substitute for PARP inhibition in melanoma tumor tissues.

DNA-PK-A candidate driver of hepatocarcinogenesis and tissue biomarker that predicts response to treatment and survival

PURPOSE

Therapy resistance and associated liver disease make hepatocellular carcinomas (HCC) difficult to treat with traditional cytotoxic therapies, whereas newer targeted approaches offer only modest survival benefit. We focused on DNA-dependent protein kinase, DNA-PKcs, encoded by PRKDC and central to DNA damage repair by nonhomologous end joining. Our aim was to explore its roles in hepatocarcinogenesis and as a novel therapeutic candidate.

EXPERIMENTAL DESIGN

PRKDC was characterized in liver tissues from of 132 patients [normal liver (n = 10), cirrhotic liver (n = 13), dysplastic nodules (n = 18), HCC (n = 91)] using Affymetrix U133 Plus 2.0 and 500 K Human Mapping SNP arrays (cohort 1). In addition, we studied a case series of 45 patients with HCC undergoing diagnostic biopsy (cohort 2). Histological grading, response to treatment, and survival were correlated with DNA-PKcs quantified immunohistochemically. Parallel in vitro studies determined the impact of DNA-PK on DNA repair and response to cytotoxic therapy.

RESULTS

Increased PRKDC expression in HCC was associated with amplification of its genetic locus in cohort 1. In cohort 2, elevated DNA-PKcs identified patients with treatment-resistant HCC, progressing at a median of 4.5 months compared with 16.9 months, whereas elevation of activated pDNA-PK independently predicted poorer survival. DNA-PKcs was high in HCC cell lines, where its inhibition with NU7441 potentiated irradiation and doxorubicin-induced cytotoxicity, whereas the combination suppressed HCC growth in vitro and in vivo.

CONCLUSIONS

These data identify PRKDC/DNA-PKcs as a candidate driver of hepatocarcinogenesis, whose biopsy characterization at diagnosis may impact stratification of current therapies, and whose specific future targeting may overcome resistance.

Untangling the ATR-CHEK1 network for prognostication, prediction and therapeutic target validation in breast cancer

ATR-CHEK1 signalling is critical for genomic stability. ATR-CHEK1 signalling may be deregulated in breast cancer and have prognostic, predictive and therapeutic significance. We investigated ATR, CHEK1 and phosphorylated CHEK1 (Ser345) protein (pCHEK1) levels in 1712 breast cancers. ATR and CHEK1 mRNA expression was evaluated in 1950 breast cancers. Pre-clinically, biological consequences of ATR gene knock down or ATR inhibition by the small molecule inhibitor (VE-821) were investigated in MCF7 and MDA-MB-231 breast cancer cell lines and in non-tumorigenic breast epithelial cells (MCF10A). High ATR and high cytoplasmic pCHEK1 levels were significantly associated with higher tumour stage, higher mitotic index, pleomorphism and lymphovascular invasion. In univariate analyses, high ATR and high cytoplasmic pCHEK1 levels were associated with poor breast cancer specific survival (BCSS). In multivariate analysis, high ATR level remains an independent predictor of adverse outcome. At the mRNA level, high CHEK1 remains associated with aggressive phenotypes including lymph node positivity, high grade, Her-2 overexpression, triple negative, aggressive molecular phenotypes and adverse BCSS. Pre-clinically, CHEK1 phosphorylation at serine(345) following replication stress was impaired in ATR knock down and in VE-821 treated breast cancer cells. Doxycycline inducible knockdown of ATR suppressed growth, which was restored when ATR was re-expressed. Similarly, VE-821 treatment resulted in a dose dependent suppression of cancer cell growth and survival (MCF7 and MDA-MB-231) but was less toxic in non-tumorigenic breast epithelial cells (MCF10A). We provide evidence that ATR and CHEK1 are promising biomarkers and rational drug targets for personalized therapy in breast cancer.

Development of pharmacodynamic biomarkers for ATR inhibitors

BACKGROUND

ATR, which signals DNA damage to S/G2 cell cycle checkpoints and for repair, is an attractive target in cancer therapy. ATR inhibitors are being developed and a pharmacodynamic assay is needed to support clinical studies.

METHODS

Phosphorylation of ATR targets, Chk1 and H2AX, was evaluated in MCF7 and K562 cells, human volunteer PBMCs and whole blood by Western blot, immunofluorescence microscopy and flow cytometry after DNA damage. The effect of cell cycle phase, ATR knockdown and inhibition on these phosphorylation events was determined.

RESULTS

Hydroxyurea, UV and 4NQO induced Chk1 and H2AX phosphorylation in MCF7 and K562 cells. UV/4NQO activation of ATR was detectable in non-cycling cells. Chk1 phosphorylation was reduced by ATR knockdown and reflects ATR activity for 3 h, H2AX phosphorylation after UV/4NQO is ATR-dependent for 1 h but increasingly ATM and DNA-PK-dependent at later time points. In isolated PBMCs both phospho-targets were detectable after UV/4NQO but in PBMCs from whole blood treated with 4NQO only H2AX was detectable.

CONCLUSION

PhosphoChk1 and H2AX are useful biomarkers for ATR inhibition using a variety of immuno-detection methods, but timing may be critical. Importantly, ATR activity is detectable in non-cycling PBMCs allowing them to be used as a surrogate tissue for biomarker measurement. In PBMCs from whole blood treated with 4NQO phosphoH2AX was the most useful biomarker of ATR activity and a clinically viable pharmacodynamic assay for ATR inhibitors has been developed.

Abstract 2418: Investigating p53 and other potential determinants of cell sensitivity to ATR inhibition by VE-821

Background: Defects in the multifactorial DNA damage response (DDR) are common in cancer, making them vulnerable to inhibitors of other components of the DDR. ATR is a key component of the DDR, signalling ssDNA, arising from stalled replication forks, resected double strand breaks (DSBs) and NER intermediates to activate cell cycle arrest at the S/G2 checkpoints and initiate homologous recombination repair (HRR). Tumors often have a dysfunctional G1 checkpoint e.g. due to p53 mutations or other DDR defects. ATR inhibition of the S/G2 checkpoints and HRR has the potential to exploit these defects and selectively target cancer. VE-821 is a potent ATR inhibitor under advanced pre-clinical investigation

Hypotheses: 1) Cells with dysfunctional p53 will be more sensitive to ATR inhibition. 2) Defects in other DDR components will sensitise cells to ATR inhibition.

Methods: The survival of isogenic p53 mutant/null and wt/corrected human cell lines (HCT116 p53+/+ and p53-/- or U2OS p53WT and p53DN (dominant negative)) and a panel of repair defective Chinese hamster ovary and lung fibroblast cells was determined using colony formation after 24 hours exposure VE-821 alone or in the presence of gemcitabine or ionising radiation.

Results: There was no significant difference in sensitivity to VE-821 between p53 wt or mutant/null cells in either HCT116 (LC50 = 2.13 and 4.56 µM, respectively) or U2OS pairs (LC50 = 2.54 and 3.34 µM, respectively). However, 1 µM VE-821 significantly potentiated the antimetabolite, gemcitabine, in HCT116 p53-/- (4.3-fold) but not p53+/+ cells (1.5-fold), and enhanced cell kill by 100 nM gemcitabine 40-fold in U2OS p53DN cells but only 3-fold in U2OS p53WT cells. Chinese hamster ovary cells defective in XRCC1 (single stranded break repair) were more sensitive to single agent VE-821 than the parental wt cells (35% and 55% survival at 10 µM, respectively). Data on other repair-defective cell lines will be presented.

Conclusions: p53 status is not a determinant of sensitivity to VE-821 as a single agent but VE-821 preferentially sensitises cells lacking functional p53 to gemcitabine. This supports the hypothesis that p53 status may be predictive of cellular response to ATR inhibition in combination with certain chemotherapies. Furthermore, data using Chinese hamster cell lines indicate that DDR defects may be exploited by ATR inhibition.

Citation Format: Fiona K. Middleton, Tao Chen, John R. Pollard, Nicola J. Curtin. Investigating p53 and other potential determinants of cell sensitivity to ATR inhibition by VE-821. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2418. doi:10.1158/1538-7445.AM2014-2418

Preferential potentiation of topoisomerase I poison cytotoxicity by PARP inhibition in S phase

BACKGROUND

Topoisomerase I (Topo I) poisons (e.g., camptothecin (CPT)), used to treat cancer, cause DNA breaks that are most cytotoxic during S phase. PARP-1 promotes DNA repair and PARP inhibitors (PARPi) sensitise cells to Topo I poisons. We aimed to determine whether chemosensitisation is also S phase specific using rucaparib, a potent PARPi in advanced clinical evaluation.

METHODS

The impact of rucaparib, on CPT-induced cytotoxicity was measured in human colon cancer (LoVo) and leukaemic (K562) cells in asynchronous and cell cycle phase-separated cultures. Topoisomerase I and PARP levels and activity and the effect of rucaparib on DNA single-strand breaks (SSBs), double-strand breaks (DSBs) and collapsed replication fork induction and repair were determined in cell cycle phase-separated cells.

RESULTS

The cytotoxicity of CPT was greatest during S phase, partially attributable to high Topo I activity, and rucaparib preferentially sensitised S-phase cells. Rucaparib increased CPT-induced DNA SSBs in all phases of the cell cycle, and increased DSB and γH2AX foci in S and G2, with γH2AX foci being highest in S-phase cells. Repair of SSBs and DSBs was most rapid during S then G2 phases and was substantially hindered by rucaparib.

CONCLUSIONS

Rucaparib preferentially sensitises S-phase cells by increasing the frequency of collapsed replication forks.

Assessing the function of homologous recombination DNA repair in malignant pleural effusion (MPE) samples

Background:

Patients with malignant pleural effusions (MPEs) generally have advanced disease with poor survival and few therapeutic options. Cells within MPEs may be used to stratify patients for targeted therapy. Targeted therapy with poly(ADP ribose) polymerase inhibitors (PARPi) depends on identifying homologous recombination DNA repair (HRR)-defective cancer cells. We aimed to determine the feasibility of assaying HRR status in MPE cells.

Methods:

A total of 15 MPE samples were collected from consenting patients with non-small-cell lung cancer (NSCLC), mesothelioma and ovarian and breast cancer. Primary cultures were confirmed as epithelial by pancytokeratin, and HRR status was determined by the detection of γH2AX and RAD51 foci following a 24-h exposure to rucaparib, by immunofluorescence microscopy. Massively parallel next-generation sequencing of DNA repair genes was performed on cultured MPE cells.

Results:

From 15 MPE samples, 13 cultures were successfully established, with HRR function successfully determined in 12 cultures. Four samples – three NSCLC and one mesothelioma – were HRR defective and eight samples – one NSCLC, one mesothelioma, one sarcomatoid, one breast and four ovarian cancers – were HRR functional. No mutations in DNA repair genes were associated with HRR status, but there was probable loss of heterozygosity of FANCG, RPA1 and PARP1.

Conclusions:

HRR function can be successfully detected in MPE cells demonstrating the potential to stratify patients for targeted therapy with PARPi.

Tumour cell retention of rucaparib, sustained PARP inhibition and efficacy of weekly as well as daily schedules

Background:

Poly(ADP-ribose) polymerase-1 (PARP) inhibitors (PARPi) exploit tumour-specific defects in homologous recombination DNA repair and continuous dosing is most efficacious. Early clinical trial data with rucaparib suggested that it caused sustained PARP inhibition. Here we investigate the mechanism of this durable inhibition and potential exploitation.

Methods:

Uptake and retention of rucaparib and persistence of PARP inhibition were determined by radiochemical and immunological assays in human cancer cell lines. The pharmacokinetics and pharmacodynamics of rucaparib were determined in tumour-bearing mice and the efficacy of different schedules of rucaparib was determined in mice bearing homologous recombination DNA repair-defective tumours.

Results:

Rucaparib accumulation is carrier mediated (Km=8.4±1.2 μM, Vmax=469±22 pmol per 10⁶ cells per 10 min), reaching steady-state levels >10 times higher than the extracellular concentration within 30 min. Rucaparib is retained in cells and inhibits PARP ⩾50% for ⩾72 h days after a 30-min pulse of 400 nM. In Capan-1 tumour-bearing mice rucaparib accumulated and was retained in the tumours, and PARP was inhibited for 7 days following a single dose of 10 mg kg⁻¹ i.p or 150 mg kg⁻¹ p.o. by 70% and 90%, respectively. Weekly dosing of 150 mg kg⁻¹ p.o once a week was as effective as 10 mg kg⁻¹ i.p daily for five days every week for 6 weeks in delaying Capan-1 tumour growth.

Conclusions:

Rucaparib accumulates and is retained in tumour cells and inhibits PARP for long periods such that weekly schedules have equivalent anticancer activity to daily dosing in a pre-clinical model, suggesting that clinical evaluation of alternative schedules of rucaparib should be considered.

Inhibiting the DNA damage response as a therapeutic manoeuvre in cancer

The DNA damage response (DDR), consisting of an orchestrated network of proteins effecting repair and signalling to cell cycle arrest, to allow time to repair, is essential for cell viability and to prevent DNA damage being passed on to daughter cells. The DDR is dysregulated in cancer with some pathways up-regulated and others down-regulated or lost. Up-regulated pathways can confer resistance to anti-cancer DNA damaging agents. Therefore, inhibitors of key components of these pathways have the potential to prevent this therapeutic resistance. Conversely, defects in a particular DDR pathway may lead to dependence on a complementary pathway. Inhibition of this complementary pathway may result in tumour-specific cell killing. Thus, inhibitors of the DDR have the potential to increase the efficacy of DNA damaging chemotherapy and radiotherapy and have single-agent activity against tumours with a specific DDR defect. This review describes the compounds that have been designed to inhibit specific DDR targets and summarizes the pre-clinical and clinical evaluation of these inhibitors of DNA damage signalling and repair.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Abstract A220: Inhibition of PBMC PARP activity with the novel PARP 1/2 inhibitor BMN 673 in patients with advanced solid tumors

Introduction: BMN 673 is a novel, potent (IC50 < 1.0 nM) inhibitor of Poly(ADP-ribose) polymerase (PARP) 1 and PARP 2 in clinical development for the treatment of genetically defined cancers.

Methods: The pharmacokinetics (PK) and pharmacodynamics (PD) of BMN 673 were evaluated in a Phase 1 dose-escalation study in patients with advanced solid tumors. Oral doses evaluated ranged from 0.025 to 1.1 mg/day, with 3-6 patients evaluated at each dose level in a standard 3+3 design. The first dose in Cycle 1 was followed for 7 days without dosing for collection of serial PK and PD samples. Thereafter BMN 673 was administered once daily on Days 8 to 35, with predose PK and PD samples collected on Days 15 and 22. Following the last dose in Cycle 1 on Day 35, serial PK and PD samples were collected for 7 and 3 days, respectively, without dosing. In subsequent cycles, BMN 673 was administered daily in contiguous 28-day cycles. The PD activity of BMN 673 was measured in peripheral blood mononuclear cells (PBMCs) using assay methods previously described (Clin Cancer Res 2008 14:7917023, Biochem J 2011 436:671-679). Correlations between systemic BMN 673 exposure and inhibition of PBMC PARP activity were investigated across dose levels.

Results: BMN 673 demonstrated good oral bioavailability and a long half-life supporting daily dosing (ASCO 2013 Abstract 2580). While variable across and within patients, overall PBMC PARP activity decreased in a dose-dependent manner. Within individual patients at higher dose levels, PBMC PARP activity decreased soon after the first dose of BMN 673, and activity remained at suppressed levels with daily dosing. PBMC PARP activity rebounded when dosing was stopped, indicating the return of PARP function. Correlations between the mean percent baseline PARP activity with daily BMN 673 dosing and measures of steady-state BMN 673 exposures within individuals (i.e., Day 35 Cmin, Cmax, and AUC0-24) showed decreased PARP activity with increasing exposure. This correlation was well described using an Imax model with IC50 values based on an interim analyses of 1140 pg/mL, 3090 pg/mL, and 26700 pg-hr/mL for Cmin, Cmax, and AUC0-24, respectively.

Conclusions: PBMC PARP activity was rapidly and continuously inhibited with daily dosing of BMN 673. A positive correlation between systemic BMN 673 exposure and inhibition of PARP activity in PBMCs was demonstrated. This effect on a relevant pharmacodynamic marker provides in vivo proof of an on-target effect of BMN 673 and may be an initial step with potential to inform BMN 673 dose selection.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A220.

Citation Format: Joshua W. Henshaw, Huiyu Zhou, Ashleigh Herriott, Miranda Patterson, Evelyn W. Wang, Don Musson, Johann de Bono, Lida A. Mina, Ramesh K. Ramanathan, Charles O'Neill, Andrew Dorr, Nicola J. Curtin. Inhibition of PBMC PARP activity with the novel PARP 1/2 inhibitor BMN 673 in patients with advanced solid tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A220.

Abstract C75: Rucaparib (CO-338) accumulation and persistence of PARP inhibition in vitro and in vivo and efficacy of intermittent vs continuous schedules

Background: Preclinical studies show that both duration and extent of PARP inhibition is critical for synthetically lethality in tumors with defects in homologous recombination repair (HRR). Rucaparib is undergoing clinical evaluation in HRR-defective tumors. Our aim was to determine whether multiple daily doses or an intermittent schedule will give the required “coverage” for anticancer activity.

Methods: The accumulation of 14C-rucaparib and duration of PARP inhibition was determined in SW620 and BRCA2 mutant Capan-1 cells after a 30 minute pulse. Rucaparib concentration in plasma brain and Capan-1 tumor xenografts and PARP inhibition in brain and tumor was determined at intervals up to 1 week after a single dose of rucaparib. The efficacy of continuous and discontinuous schedules of rucaparib was determined in mice bearing Capan-1 xenografts.

Results: Rucaparib accumulates in cells via a carrier-mediated transporter (Km of 8.4 ± 1.2 μM and Vmax of 469 ± 22 pmol/106cells/10 min) PARP activity in Capan-1 cells was suppressed by 80% for 72 hr after a pulse of 50 or 400 nM rucaparib, and still 40% reduced 7 days after 400 nM. Rucaparib was cleared rapidly from the plasma but it was detectable for up to 72 hr and suppressed PARP activity in the tumors for 7 days, being 25% and 10% of control after 10 mg/kg and 150 mg/kg, respectively. Peak levels in the brain were 2-10% of those in the tumor and only modest, transient PARP inhibition was observed in the brain. Tumor growth was suppressed by rucaparib at 150 mg/kg po on a weekly schedule as effectively as 10 mg/kg po on a daily x5 every week for 6 weeks.

Conclusion: Rucaparib accumulates in human tumor cells and PARP inhibition by rucaparib is durable after a 30 min pulse. PARP is inhibited in tumor xenografts for up to 1 week after a single dose and when the drug concentrations are no longer detectable. Weekly dosing with rucaparib inhibits tumor growth.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C75.

Citation Format: James C. Murray, Huw D. Thomas, Philip Berry, Suzanne Kyle, Christopher Jones, Ruth Plummer, Alan V. Boddy, Nicola J. Curtin. Rucaparib (CO-338) accumulation and persistence of PARP inhibition in vitro and in vivo and efficacy of intermittent vs continuous schedules. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C75.

Critical research gaps and translational priorities for the successful prevention and treatment of breast cancer

INTRODUCTION

Breast cancer remains a significant scientific, clinical and societal challenge. This gap analysis has reviewed and critically assessed enduring issues and new challenges emerging from recent research, and proposes strategies for translating solutions into practice.

METHODS

More than 100 internationally recognised specialist breast cancer scientists, clinicians and healthcare professionals collaborated to address nine thematic areas: genetics, epigenetics and epidemiology; molecular pathology and cell biology; hormonal influences and endocrine therapy; imaging, detection and screening; current/novel therapies and biomarkers; drug resistance; metastasis, angiogenesis, circulating tumour cells, cancer 'stem' cells; risk and prevention; living with and managing breast cancer and its treatment. The groups developed summary papers through an iterative process which, following further appraisal from experts and patients, were melded into this summary account.

RESULTS

The 10 major gaps identified were: (1) understanding the functions and contextual interactions of genetic and epigenetic changes in normal breast development and during malignant transformation; (2) how to implement sustainable lifestyle changes (diet, exercise and weight) and chemopreventive strategies; (3) the need for tailored screening approaches including clinically actionable tests; (4) enhancing knowledge of molecular drivers behind breast cancer subtypes, progression and metastasis; (5) understanding the molecular mechanisms of tumour heterogeneity, dormancy, de novo or acquired resistance and how to target key nodes in these dynamic processes; (6) developing validated markers for chemosensitivity and radiosensitivity; (7) understanding the optimal duration, sequencing and rational combinations of treatment for improved personalised therapy; (8) validating multimodality imaging biomarkers for minimally invasive diagnosis and monitoring of responses in primary and metastatic disease; (9) developing interventions and support to improve the survivorship experience; (10) a continuing need for clinical material for translational research derived from normal breast, blood, primary, relapsed, metastatic and drug-resistant cancers with expert bioinformatics support to maximise its utility. The proposed infrastructural enablers include enhanced resources to support clinically relevant in vitro and in vivo tumour models; improved access to appropriate, fully annotated clinical samples; extended biomarker discovery, validation and standardisation; and facilitated cross-discipline working.

CONCLUSIONS

With resources to conduct further high-quality targeted research focusing on the gaps identified, increased knowledge translating into improved clinical care should be achievable within five years.

1-substituted (Dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-ones endowed with dual DNA-PK/PI3-K inhibitory activity

Analogues of (dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one (NU7441), a potent inhibitor of DNA-dependent protein kinase (DNA-PK; IC50 = 42 ± 2 nM), have been synthesized in which water-solubilizing groups [NHCO(CH₂)nNR¹R², where n = 1 or 2 and the moiety R¹R²N was derived from a library of primary and secondary amines, e.g., morpholine] were placed at the 1-position. Several of the newly synthesized compounds exhibited high potency against DNA-PK and potentiated the cytotoxicity of ionizing radiation (IR) in vitro 10-fold or more (e.g., 2-(4-ethylpiperazin-1-yl)-N-(4-(2-morpholino-4-oxo-4H-chromen-8-yl)dibenzo[b,d]thio-phen-1-yl)acetamide, 39; DNA-PK IC₅₀ = 5.0 ± 1 nM, IR dose modification ratio = 13). Furthermore, 39 was shown to potentiate not only IR in vitro but also DNA-inducing cytotoxic anticancer agents, both in vitro and in vivo. Counter-screening against other members of the phosphatidylinositol 3-kinase (PI-3K) related kinase (PIKK) family unexpectedly revealed that some of the compounds were potent mixed DNA-PK and PI-3K inhibitors.

Preclinical evaluation of a novel ATM inhibitor, KU59403, in vitro and in vivo in p53 functional and dysfunctional models of human cancer

Ataxia telangiectasia mutated (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 radiosensitization. KU59403 is an ATM inhibitor with the potency, selectivity, and solubility for advanced preclinical 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 radiosensitization 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 hours in tumor xenografts. KU59403 significantly enhanced the antitumor activity of topoisomerase poisons in mice bearing human colon cancer xenografts (SW620 and HCT116) at doses that were nontoxic alone and well-tolerated in combination. Chemosensitization was both dose- and schedule-dependent. KU59403 represents a major advance in ATM inhibitor development, being the first compound to show good tissue distribution and significant chemosensitization in in vivo models of human cancer, without major toxicity. KU59403 provides the first proof-of-principle preclinical data to support the future clinical development of ATM inhibitors.

First-in-human trial of novel oral PARP inhibitor BMN 673 in patients with solid tumors

2580

Background: BMN 673 is the most potent and specific inhibitor of PARP1/2 in clinical development (IC50<1nM). In tumors genetically dependent on DNA repair by homologous recombination PARP inhibition induces synthetic lethality. Methods: Pharmacokinetics (PK), pharmacodynamics (PD), safety and anti-tumor activity of BMN 673 were evaluated in a 2-stage dose-escalation study with 3-6 patients (pts)/dose level. In dose escalation (Stage 1) cycle 1 was 6 wks, with drug taken on days 1 and 8-35, for PK and PD assays, followed by daily continuous dosing in 4-wk cycles. Stage 2 (expansion at MTD) recruits pts with tumors defective in DNA repair: Ewing sarcoma, small cell lung cancer or tumors associated with BRCA mutation (mut). Results: 39 pts (33F/6M) were enrolled in 9 cohorts from 25 to 1100 µg/d that defined a MTD of 1000 µg/d. Median (range) age was 58 (19-81), PS 0 (0-1) and # of prior therapies 4 (1-13). Tumors (# with deleterious BRCA 1/2 mut) included 23 ovarian/primary peritoneal (17); 8 breast (6); 3 pancreas; 2 colon; 1 prostate (1), and 1 mullerian carcinosarcoma. 17 and 8 pts had BRCA 1 and 2 mut, respectively. Dose-limiting thrombocytopenia occurred in 1/6 and 2/5 pts at 900 and 1100 µg/d, respectively. Potentially-related adverse events in >10% of pts (# grade 1 and 2/grade 3 and 4) included fatigue (10/0); nausea (10/0); flatulence (4/0); anemia (5/2); neutropenia (4/3); thrombocytopenia (1/3); and grade 1 alopecia (10). Inhibition of PARP activity in PBMCs was observed at doses ≥ 100 µg/d. BMN 673 plasma concentrations peaked 1-2 hrs post-dose; exposure increased dose proportionally. Steady state plasma concentrations were reached by the end of the 2nd week of daily dosing; mean Cmax: 0.30 - 25.4 ng/mL and AUC0-24: 3.96 - 203 ng-hr/mL across the 25 to 1100 µg/d dose range after 28d of daily dosing. RECIST and/or CA-125 responses occurred at doses ≥ 100 µg/d in 11/17 BRCA carrier ovarian/peritoneal cancer pts. Objective responses occurred in 2/6 BRCA-carrier breast cancer pts. Conclusions: BMN 673 is well tolerated with impressive anti-tumor activity in pts with BRCA mut with a single agent recommended Phase II trial dose of 1000 µg/d due to dose-limiting thrombocytopenia. Clinical trial information: NCT01286987.

DNA repair dysregulation from cancer driver to therapeutic target

Dysregulation of DNA damage repair and signalling to cell cycle checkpoints, known as the DNA damage response (DDR), is associated with a predisposition to cancer and affects responses to DNA-damaging anticancer therapy. Dysfunction of one DNA repair pathway may be compensated for by the function of another compensatory DDR pathway, which may be increased and contribute to resistance to DNA-damaging chemotherapy and radiotherapy. Therefore, DDR pathways make an ideal target for therapeutic intervention; first, to prevent or reverse therapy resistance; and second, using a synthetic lethal approach to specifically kill cancer cells that are dependent on a compensatory DNA repair pathway for survival in the context of cancer-associated oxidative and replicative stress. These hypotheses are currently being tested in the laboratory and are being translated into clinical studies.

Clinicopathological features of homologous recombination-deficient epithelial ovarian cancers: sensitivity to PARP inhibitors, platinum, and survival

Up to 50% of epithelial ovarian cancers (EOC) display defects in the homologous recombination (HR) pathway. We sought to determine the ramifications of the homologous recombination-deficient (HRD) status on the clinicopathologic features, chemotherapy response, and survival outcomes of patients with EOCs. HR status was determined in primary cultures from ascitic fluid in 50 chemotherapy-naïve patients by a functional RAD51 immunofluorescence assay and correlated with in vitro sensitivity to the PARP inhibitor (PARPi), rucaparib. All patients went on to receive platinum-based chemotherapy; platinum sensitivity, tumor progression, and overall survival were compared prospectively in HR-competent versus HRD patients. Compared with HR-competent patients, the HRD group was predominantly serous with a higher median CA125 at presentation. HRD was associated with higher ex vivo PARPi sensitivity and clinical platinum sensitivity. Median follow-up duration was 14 months; patients in the HRD group had lower tumor progression rates at 6 months, lower overall/disease-specific death rates at 12 months, and higher median survival. We therefore suggest that HRD as predicted by a functional RAD51 assay correlates with in vitro PARPi sensitivity, clinical platinum sensitivity, and improved survival outcome.

Chemosensitization of cancer cells by KU-0060648, a dual inhibitor of DNA-PK and PI-3K

DNA double-strand breaks (DSB) are the most cytotoxic lesions induced by topoisomerase II poisons. Nonhomologous end joining (NHEJ) is a major pathway for DSB repair and requires DNA-dependent protein kinase (DNA-PK) activity. DNA-PK catalytic subunit (DNA-PKcs) is structurally similar to PI-3K, which promotes cell survival and proliferation and is upregulated in many cancers. KU-0060648 is a dual inhibitor of DNA-PK and PI-3K in vitro. KU-0060648 was investigated in a panel of human breast and colon cancer cells. The compound inhibited cellular DNA-PK autophosphorylation with IC(50) values of 0.019 μmol/L (MCF7 cells) and 0.17 μmol/L (SW620 cells), and PI-3K-mediated AKT phosphorylation with IC(50) values of 0.039 μmol/L (MCF7 cells) and more than 10 μmol/L (SW620 cells). Five-day exposure to 1 μmol/L KU-0060648 inhibited cell proliferation by more than 95% in MCF7 cells but only by 55% in SW620 cells. In clonogenic survival assays, KU-0060648 increased the cytotoxicity of etoposide and doxorubicin across the panel of DNA-PKcs-proficient cells, but not in DNA-PKcs-deficient cells, thus confirming that enhanced cytotoxicity was due to DNA-PK inhibition. In mice bearing SW620 and MCF7 xenografts, concentrations of KU-0060648 that were sufficient for in vitro growth inhibition and chemosensitization were maintained within the tumor for at least 4 hours at nontoxic doses. KU-0060648 alone delayed the growth of MCF7 xenografts and increased etoposide-induced tumor growth delay in both in SW620 and MCF7 xenografts by up to 4.5-fold, without exacerbating etoposide toxicity to unacceptable levels. The proof-of-principle in vitro and in vivo chemosensitization with KU-0060648 justifies further evaluation of dual DNA-PK and PI-3K inhibitors.

Abstract 3122: The DNA-PK inhibitor NU7441 inhibits non-homologous end joining, enhances radio- and chemosensitivity and increases dependence on homologous recombination in hepatocellular carcinoma cell lines

Background DNA double-strand breaks (DSBs), the most cytotoxic lesions induced by ionizing radiation (IR) and anticancer drugs such as topoisomerase II poisons (e.g., doxorubicin), are repaired by non-homologous end joining (NHEJ) and homologous recombination (HR). DNA-dependent protein kinase (DNA-PK), which initiates NHEJ, is up-regulated in hepatocellular carcinoma (HCC) (GEO profiles), possibly contributing to anticancer therapy resistance. To assess DNA-PK as a potential therapeutic target for chemo- and radio-sensitisation in HCC we determined the effect of the DNA-PK inhibitor, NU7441, on DSB repair and cytotoxicity in HCC cells. Methods DNA-PK protein levels and activation by IR (Western blot), DSB levels (y-H2AX foci), HR (RAD51 foci), cell growth (DAPI fluorescence) and cytotoxicity (colony formation) following exposure to IR or doxorubicin was determined in a panel of 6 hepatoma cell lines (HepG2, Hep3B, Huh7, SNU-182, SNU475 and PLC/PRF/5). Results DNA-PK protein concentration and activity did not vary significantly across the panel (±24% and ±37%, respectively) but there were cell-specific sensitivities to IR and doxorubicin (e.g. HepG2 2-fold more resistant than Hep3B). NU7441 significantly sensitised all cells to both doxorubicin (average PF50 4.3±3.0) and IR (average PF50 3.9±1.1) in growth inhibition assays and significantly reduced survival (4.8 to 3.3-fold) in colony forming assays. Following exposure to IR, NU7441 significantly delayed yH2AX focus clearance in all cell lines (e.g. only 13% cleared at 4 hr compared to 50% in control), but increased RAD51 focus formation (3-fold). Conclusion While chemo- and radio-sensitivity in HCC cells was not dependent on DNA-PK expression or activity, NU7441 causes greater than 2-fold chemo- and radiosensitisation in all cells. This was accompanied by a substantial reduction in the rapid phase of DNA repair (NHEJ-dependent) and a shift to a greater reliance on the slower HR repair. DNA-PK inhibitors may have potential as chemo- and radio-sensitisors in hepatoma patients.

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 3122. doi:1538-7445.AM2012-3122

Visualization of a DNA-PK/PARP1 complex

The DNA-dependent protein kinase (DNA-PK) and Poly(ADP-ribose) polymerase-1 (PARP1) are critical enzymes that reduce genomic damage caused by DNA lesions. They are both activated by DNA strand breaks generated by physiological and environmental factors, and they have been shown to interact. Here, we report in vivo evidence that DNA-PK and PARP1 are equally necessary for rapid repair. We purified a DNA-PK/PARP1 complex loaded on DNA and performed electron microscopy and single particle analysis on its tetrameric and dimer-of-tetramers forms. By comparison with the DNA-PK holoenzyme and fitting crystallographic structures, we see that the PARP1 density is in close contact with the Ku subunit. Crucially, PARP1 binding elicits substantial conformational changes in the DNA-PK synaptic dimer assembly. Taken together, our data support a functional, in-pathway role for DNA-PK and PARP1 in double-strand break (DSB) repair. We also propose a NHEJ model where protein-protein interactions alter substantially the architecture of DNA-PK dimers at DSBs, to trigger subsequent interactions or enzymatic reactions.