Abstract P2-03-04: Application of digital-PCR technology to determine c-MET copy number variation in paired primary breast cancer and brain metastases

INTRODUCTION:

c-MET amplification/overexpression has been associated with treatment failure and progression in many cancers, including breast cancer (BC). c-MET showed amplification by fluorescent in situ hybridization (FISH) in 27% of trastuzumab-treated HER2-positive patients. These patients had a high trastuzumab failure rate and a shorter time to progression. Up to 50% of patients with metastatic HER2-positive disease will develop brain metastases (BM) during their disease course and in approximately one third, brain is the first site of progression. Amplification/copy number variations (CNVs) are mainly assessed by FISH whereas overexpression is assessed by immunohistochemistry (IHC). We present a PCR-based assay (digital-PCR) able to determine CNV in c-MET and HER2 in a cohort of patients with metastatic BC to the brain and demonstrate the correlation of CNV to protein expression.

METHODS:

DNA was isolated from paraffin-embedded tissues of 23 paired primary BC-BM cases. CNV was analysed by the QuantStudioTM 3D-Digital-PCR (QS3D) and real-time qPCR (both from ThermoFisher Scientific). The breast MCF7, T47D, BT474, AU565, SKBR3 and the gastric MKN45 cell lines were used as controls for the HER2 and c-MET CNV assays. Copy number per diploid genome was calculated using the absolute quantification number of FAM-labelled target and VIC-labelled RNaseP reference multiplied by 2. Cases with ≤2 copies are classified as normal whereas cases with >2 were classified as amplified. The HER2 positivity of the primary BC cases was routinely assessed by IHC. The c-MET protein expression was assessed by IHC using the c-MET(3D4) monoclonal antibody (ThermoFisher Scientific).

RESULTS:

CNV in c-MET by QS3D digital-PCR was detected in 69.6% of primary BC (ER-/HER2+:2, ER+/HER2+:5, ER+/HER2-:8, Triple-negatives:5, unknown:3) as well as 69.6% of BM, whereas HER2 CNV was observed in 39.1% primary BC and 52.2% BM. In the HER2-positive cases, the prevalence of HER2 CNV was 100% in both primary BC and BM. Within these cases, c-MET CNV was 85.7% in the primary BC and 71.43% in BM. CNVs in both genes were observed in 30.4 % of all primary and 39.1% of BM. The CNV data are presented in Table 1.

CNV data for c-MET and HER2 between primary breast cancer (BC) and corresponding brain metastatic (BM) casesc-MET CNVHER2 CNVBCBMBCBM>2: 16>2: 12≤2: 4>2: 9>2: 8≤2: 1≤2: 7>2: 4≤2: 3≤2: 14>2: 4≤2: 10

There was a high concordance between the QS3D and qPCR data with Pearson's R=0.74 (p<0.00001).

A significant correlation between HER2 protein expression and CNV was observed (Fisher's exact test p=0.0005). Data will be presented on c-MET protein expression in the pair samples.

CONCLUSIONS:

The prevalence of CNV is much higher than that reported by immunohistochemistry and FISH in the literature to date, possibly due to the sensitivity of the digital-PCR technology. The high level of c-MET CNV in primary and metastatic BC, and the concurrent CNV in both genes warrants further investigation. It also highlights the potential to use c-MET directed therapy particularly in HER2+ BC and reinforces the potential importance of precise detection methods in both the primary and metastatic setting. Analysis of a larger series is currently on-going.

Citation Format: Giannoudis A, Zakaria R, Platt-Higgins A, Syed KAR, Ashton K, Dawson T, Rudland PS, Holcombe C, Jenkinson MD, Palmieri C. Application of digital-PCR technology to determine c-MET copy number variation in paired primary breast cancer and brain metastases [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-03-04.

Systemic cobalt toxicity from total hip arthroplasties

As adverse events related to metal on metal hip arthroplasty have been better understood, there has been increased interest in toxicity related to the high circulating levels of cobalt ions. However, distinguishing true toxicity from benign elevations in cobalt levels can be challenging. The purpose of this review is to examine the use of cobalt alloys in total hip arthroplasty, to review the methods of measuring circulating cobalt levels, to define a level of cobalt which is considered pathological and to review the pathophysiology, risk factors and treatment of cobalt toxicity. To the best of our knowledge, there are 18 published cases where cobalt metal ion toxicity has been attributed to the use of cobalt-chromium alloys in hip arthroplasty. Of these cases, the great majority reported systemic toxic reactions at serum cobalt levels more than 100 μg/L. This review highlights some of the clinical features of cobalt toxicity, with the goal that early awareness may decrease the risk factors for the development of cobalt toxicity and/or reduce its severity.

Take home message: Severe adverse events can arise from the release of cobalt from metal-on-metal arthroplasties, and as such, orthopaedic surgeons should not only be aware of the presenting problems, but also have the knowledge to treat appropriately.

Cite this article: Bone Joint J 2016;98-B:14–20.

Systemic cobalt toxicity from total hip arthroplasties

Recently, the use of metal-on-metal articulations in total hip arthroplasty (THA) has led to an increase in adverse events owing to local soft-tissue reactions from metal ions and wear debris. While the majority of these implants perform well, it has been increasingly recognised that a small proportion of patients may develop complications secondary to systemic cobalt toxicity when these implants fail. However, distinguishing true toxicity from benign elevations in cobalt ion levels can be challenging.

The purpose of this two part series is to review the use of cobalt alloys in THA and to highlight the following related topics of interest: mechanisms of cobalt ion release and their measurement, definitions of pathological cobalt ion levels, and the pathophysiology, risk factors and treatment of cobalt toxicity. Historically, these metal-on-metal arthroplasties are composed of a chromium-cobalt articulation.

The release of cobalt is due to the mechanical and oxidative stresses placed on the prosthetic joint. It exerts its pathological effects through direct cellular toxicity.

This manuscript will highlight the pathophysiology of cobalt toxicity in patients with metal-on-metal hip arthroplasties.

Take home message: Patients with new or evolving hip symptoms with a prior history of THA warrant orthopaedic surgical evaluation. Increased awareness of the range of systemic symptoms associated with cobalt toxicity, coupled with prompt orthopaedic intervention, may forestall the development of further complications.

Cite this article: Bone Joint J 2016;98-B:6–13.

Characterization of a signal generated by oxidation of protein thiols that activates the heat shock transcription factor

The diazenecarbonyl derivative, diamide, was used to produce nonnative protein disulfides in Chinese hamster ovary cells in order to characterize the events that occur during thiol oxidation-induced denaturation that trigger induction of Hsp 70. We limit the term protein denaturation to a process involving a conformational rearrangement by which the ordered native structure of a protein changes to a more disordered structure. Protein thiol oxidation resulted in immediate destabilization of proteins, as assessed by differential scanning calorimetry (DSC). The DSC profile indicated both a decrease in the onset temperature for detection of denaturation and destabilization of a class of proteins with an average transition temperature (Tm) of 60 degrees C. Concomitant with destabilization was an increase in proteins associated with isolated nuclei. Thiol oxidation also induced heat shock transcription factor (HSF) binding activity, however, this was nearly undetectable immediately following diamide treatment: maximum activation occurred 3 hr following exposure. In contrast, heat shock denatured thermolabile proteins which exhibited a Tm of < or = 48 degrees C. Heat shock also resulted in a rapid increase in proteins associated with isolated nuclei and produced immediate and maximum activation of HSF binding. The accumulation of Hsp and Hsc 70 mRNA following thiol oxidation reflected the delay in HSF binding. Acquisition of HSF binding activity occurred immediately if diamide-treated cells were subsequently exposed to a heat shock, indicating that HSF was not inactivated by the diamide treatment. Ostensibly, the cellular system for detecting denatured/abnormal proteins failed to immediately recognize the signal generated by thiol oxidation. These results suggest that at least two processes are involved in the induction of Hsp 70 by nonnative disulfide bond formation: destabilization of protein structure resulting in denaturation and recognition of denatured protein.

Carboxanilide derivative non-nucleoside inhibitors of HIV-1 reverse transcriptase interact with different mechanistic forms of the enzyme

Researchers at the National Cancer Institute first recognized the anti-HIV potential of the carboxanilide compound oxathiin carboxanilide (UC84) [Bader, J. P., et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 6740-6744]. We have compared the inhibitory effect of UC84 and a second-generation thiocarboxanilide derivative, UC38, on HIV-1 reverse transcriptase (RT) RNA-dependent DNA polymerase activity. UC38 was a much better inhibitor (IC50 = 0.8 microM) than UC84 (IC50 = 4.3 microM). Inhibition by UC84 was competitive with respect to primer/template (P/T), whereas that by UC38 was uncompetitive. Both compounds were mixed noncompetitive inhibitors with respect to deoxynucleoside triphosphate (dNTP). Both compounds protected RT from irreversible photoinactivation by an azido derivative of nevirapine, implying that UC84 and UC38 bind to the same region of RT as nevirapine. UC84 photoprotected both free RT and the RT-P/T binary complex, but did not protect the RT-P/T-dNTP ternary complex. In contrast, UC38 completely photoprotected the RT-P/T-dNTP ternary complex, but not free RT or the RT-P/T binary complex. UC84 and UC38 thus appear to bind to different mechanistic forms of RT in the polymerase reaction sequence.