Abstract OT1-06-03: The plasmaMATCH trial: A multiple parallel cohort, open-label, multi-centre phase II clinical trial of ctDNA screening to direct targeted therapies in patients with advanced breast cancer (CRUK/15/010)

Introduction

Circulating tumour DNA (ctDNA) is found in the plasma of over 90% of patients with advanced breast cancer (BC). Screening for the presence of mutations in ctDNA provides a current assessment of the genetic profile of the patient's recurrent BC. The plasmaMATCH trial is designed to assess the potential of ctDNA screening to direct targeted therapies in patients with advanced breast cancer.

Methods

plasmaMATCH is a multi-centre phase IIa umbrella trial platform of ctDNA screening and a therapeutic trial. The study will screen 1000 women with advanced breast cancer, who have received prior systemic treatment in the advanced setting, with digital PCR ctDNA assays for hotspot mutations in ESR1, HER2, AKT1, and PIK3CA, with HER2 copy number assessment, in a central laboratory. The study will recruit from up to 50 sites in the UK. Patients with mutations identified will enter the matching treatment cohort, ESR1 – extended dose fulvestrant 500mg every two weeks, HER2 – neratinib +/- fulvestrant, AKT1 – AZD5363 +/- fulvestrant.

Mutation prevalence is presented with corresponding exact 95% confidence intervals (CIs) both overall and excluding 14 patients who were known to have mutations from a prior screening program. Patients with more than one mutation are included once in each relevant row.

Results

We report the results of prospective ctDNA mutation testing in the first 92 patients. plasmaMATCH opened to recruitment on 15/12/2016. As of 08/06/2017, 120 patients have been registered for ctDNA screening from 7 UK centres, of which 92 have ctDNA screening results available:

plasmaMATCH ctDNA screening resultsMutationPrevalence (95% CI)Prevalence excluding 14 patients with known mutations (95% CI)ESR134/92: 37% (27%-48%)26/78: 33% (23%-45%)HER25/90: 6% (2%-12%)2/76: 3% (0%-9%)AKT17/92: 8% (3%-15%)4/78: 5% (1%-13%)PIK3CA*22/92: 24% (16%-34%)21/78: 27% (18%-38%)*No corresponding plasmaMATCH treatment cohort

14 patients had more than one mutation detected (10 ESR1+PIK3CA, 3 ESR1+AKT1, 1 ESR1+ +HER2+AKT1). ctDNA results were reported in a median of 8 working days.

Of the 40 patients with one or more actionable mutation, 15 have entered a cohort, 16 are being screened for entry into a cohort, 5 are currently receiving further systemic treatment prior to cohort entry and 4 will not enter a cohort. One additional patient has entered a treatment cohort on the basis of a mutation detected in an alternative tumour sequencing initiative.

Conclusions

plasmaMATCH ctDNA demonstrates the feasibility and accuracy of ctDNA testing as a screening tool for patients with advanced BC, with a high rate of subsequent recruitment into matching therapeutic trials.

Citation Format: Turner N, Bye H, Kernaghan S, Proszek P, Fribbens C, Moretti L, Morden J, Snowdon C, Macpherson I, Wardley A, Roylance R, Baird R, Bliss J, Ring A. The plasmaMATCH trial: A multiple parallel cohort, open-label, multi-centre phase II clinical trial of ctDNA screening to direct targeted therapies in patients with advanced breast cancer (CRUK/15/010) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT1-06-03.

Abstract P2-02-17: Circulating tumor DNA analysis with ultra-high sensitivity sequencing in metastatic breast cancer

Introduction.

Circulating tumor DNA analysis has the potential to transform the clinical management of patients with breast cancer. We assessed the accuracy of ultra-high sensitivity ctDNA testing in patients with advanced breast cancer.

Methods.

From a prospective tissue collection study, we identified 25 patients with a contemporaneous metastatic tissue biopsy and plasma for ctDNA testing. Tumour DNA from the metastatic tissue biopsy was sequenced with a validated clinical hybrid capture panel, while plasma cell free DNA was sequenced with AVENIO ctDNA technology – a molecular barcoded duplex sequencing based on CAPPseq technology. Sample collection is on-going and results from the full concordance series will be presented at the conference.

Results.

Circulating tumour DNA was detectable in 87% (20/23) of patients, with at least one variant from tissue sequencing identified in plasma. There was overall high agreement between tissue and plasma sequencing. The sensitivity of plasma testing for variants identified in tumour, positive percent agreement, was 75% (24/32). Plasma testing revealed a diversity of sub-clonal mutations including polyclonal ESR1, polyclonal FGFR2 and FGFR3 mutations, rare KRAS mutations, and TSC1 and MSH2 inactivating mutations.

Conclusions.

Circulating tumour DNA testing with molecular barcoded duplex sequencing offers high sensitivity for tumour variant detection. The extent of sub-clonal resistance mutations identified emphasises the genetic diversity of advanced breast cancer.

Citation Format: Garcia-Murillas I, Proszek P, Fribbens C, Yuan L, Bye H, Hubank M, Jiang J, Yuang S, Palma J, Johnston S, Ring A, Turner N. Circulating tumor DNA analysis with ultra-high sensitivity sequencing in metastatic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-02-17.

Receptor localization, native tissue binding and ex vivo occupancy for centrally penetrant P2X7 antagonists in the rat

BACKGROUND AND PURPOSE

The P2X7 receptor is implicated in inflammation and pain and is therefore a potential target for therapeutic intervention. Here, the development of a native tissue radioligand binding, localization and ex vivo occupancy assay for centrally penetrant P2X7 receptor antagonists is described.

EXPERIMENTAL APPROACH

Autoradiography studies using the P2X7 antagonist radioligand [³H]-A-804598 were carried out in rat brain and spinal cord. Subsequent in vitro binding and ex vivo occupancy assays were performed using rat cortex homogenate.

KEY RESULTS

P2X7 expression was shown to be widespread throughout the rat brain, and in the grey matter of the spinal cord. In binding assays in rat cortex homogenate, ∼60% specific binding was achieved at equilibrium. In kinetic binding assays, k(on) and k(off) values of 0.0021·min⁻¹·nM⁻¹ and 0.0070·min⁻¹ were determined, and the K(d) derived from kinetic measurements was consistent with that derived from saturation analysis. Novel P2X7 antagonists inhibited the binding of [³H]-A-804598 to rat cortex P2X7 receptors with K(i) values of <40 nM. In an ex vivo occupancy assay, a P2X7 antagonist dosed orally to rats caused a concentration-dependent inhibition of the specific binding of [³H]-A-804598 to rat cortex.

CONCLUSIONS AND IMPLICATIONS

The present study describes the development of an assay that allows localization of P2X7 receptors, the measurement of the binding affinity of P2X7 receptor antagonists in native tissue, and provides a means of determining central P2X7 receptor occupancy. These assays could form an important part of a P2X7 drug discovery programme.