Promising perspectives for the application of inPROBE® technology platform for protein expression determination

An inherent feature of modern oncology is personalization, manifested in conversion from the fit-to-all strategy based on applying the same chemotherapy regimens to all patients with a specific type of cancer to therapy tailored to the individual patient’s situation.
An integral part of personalization is the development of molecularly targeted therapies, acting on specific molecular targets related to the cancer cell, which are very often proteins expressed on the cell surface.

One of the earliest identified proteins is the human epidermal growth factor receptor 2 (HER2), a protein from the epidermal growth factor receptor (EGFR) family. Overexpression of the HER2 protein has been found on breast cancer cells, but also on stomach cancer cells and some rare subtypes of lung cancer [1].

In breast cancer, HER2 overexpression is associated with more aggressive tumor growth and poor prognosis (unfavorable prognostic factor), while enabling the use of targeted therapy with monoclonal antibody directed against this protein (favorable predictive factor).

Currently, HER2 expression on breast cancer cells is determined using immunohistochemistry (IHC) and – in doubtful cases – in situ hybridization (FISH) in tumor tissue samples collected during biopsy or surgery. The IHC method uses a chemical dye and evaluates the reaction result in the range of 0-3+. In the case of 0-1, HER2 expression is considered negative, a result of 2+ means that HER2 status of the tumor is not clear and is called “equivocal” and the HER2 status needs to be tested with FISH to clarify the result (a positive FISH result qualifies the tumor as HER2 positive), and a value of 3+ means positive HER2 expression.

Recently, the concept of HER2-low expression has been proposed, indicating low expression of the HER2 protein, undetectable by standard methods, but still being a positive predictive factor, and therefore justifying the use of targeted therapy. The change in the classification of HER2 protein expression is shown in the figure below [2].

Grafika paradygmatu oceny nadekspresji HER2  na graficznej prezentacji próbek tkanki z różnym stopniem nadekspresji białka.Fig. 1 Aktualny paradygmat oceny nadekspresji HER2 [2]

The recently made (April 5, 2024) decision of the US Food and Drug Administration (FDA) to register the medicinal product fam-trastuzumab deruxtecan-nxki (Enhertu, Daiichi Sankyo, Inc.) in an accelerated mode “for adult patients with unresectable or metastatic HER2-positive (IHC3+) solid tumors who have previously received systemic therapy and have no satisfactory alternative therapeutic options” further emphasizes the need to use reliable methods for determining HER2 expression [3].

It should be also emphasized that regardless of HER expression classification, the result obtained is subjective, which obviously increases the risk of obtaining imprecise results, which in turn may lead to either insufficient/suboptimal treatment of patients with false negative results, or unnecessary overtreatment in the case of a false positive result.

Urządzenie diagnostyczne inPROBE: analizator i mikrosonda światłowodowaSDS Optic Inc. from Lublin has developed the inPROBE® technological platform designed to determine protein expression in a way different from the standard one. Firstly, the determination is performed in vivo, i.e. directly in the patient’s body, without the need to collect tissue, secondly, the determination is possible both in the tumor itself and in its immediate surroundings, thirdly, the result is obtained in real time, i.e. after about 30 minutes and finally, fourthly, the result is quantitative, so it is an objective result, expressed in numbers.

The technological platform developed by SDS Optic Inc. is based on fiber optic technology using sensors functionalized with proteins recognizing a specific diagnostic marker, e.g. HER2 protein. The optical signal caused by the interaction of the protein with the sensor surface, after conversion using a mathematical algorithm, is translated into a numerical value of protein expression level.

The first protein for which an appropriate inPROBE® probe was developed was HER2. In order to confirm the possibility of using inPROBE® in clinical practice and to determine the safety of this new technology, an “An open-label, multicenter, single-arm, safety and efficacy clinical investigation of diagnostic microprobe (inPROBE) for the assessment of HER2 receptor expression in population of women at high risk of breast cancer” was conducted ( SDS-HER-01-2018), the first part of which was recently completed.

Overall, 22 patients with diagnosed breast cancer and known HER2 expression status, determined using standard methods, i.e. immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) were included in the study, and ultimately 18 adult patients, were included in the statistical analysis. The study group included 6 patients with HER2-positive and 12 patients with HER2-negative breast cancer according to IHC/FISH assessment.

The primary endpoint was the initial determination of the range of HER2 receptor concentrations measured with inPROBE® which would correspond to the HER2 receptor status determined by a standard diagnostic method (IHC and FISH).

The ranges of HER2 receptor concentrations determined using the inPROBE® (for which the median, mean, minimum and maximum values were calculated) were compared with the HER2-positive and HER2-negative status determined using standard methods. There was a clear numerical trend towards higher values in the HER2-positive group compared to the HER2-negative group, despite the small size of the entire study population (which is typical for early-phase studies) and the larger number of patients with HER2-negative cancer. For the minimum values of the concentration ranges determined using the inPROBE®, statistical significance was obtained (Wilcoxon rank sum test; p=0.041). These observations were confirmed in an analysis using linear mixed models for repeated measures.

When analyzing the obtained results, the influence of small overall sample size and individual subgroups should be highlighted. Moreover, according the state of the art, it could be expected, that the group of HER2-negative patients probably accounted for a heterogeneous population, which also included patients with HER2-low expression. It can therefore be assumed that the inPROBE® technology enabled the detection of a certain biological feature of breast cancer, which was subsequently confirmed in large, international studies [2, 4]. For this reason, in the second part of the study, appropriate modifications will be introduced to the protocol, enabling a more precise assessment of IHC staining and adapting HER2 expression determinations using inPROBE® probe to the current HER2 expression classification.

The secondary endpoint was to compare the correlation of HER2 concentrations detected with one inPROBE® microprobe located in the tumor and a second one in the immediate tumor vicinity in HER2-positive patients. Although this endpoint was not achieved, probably due to the small number of patients with HER2-positive tumors (n=6), a statistically significant correlation was demonstrated in the concentrations of HER2 receptors detected using inPROBE® in the tumor and in the immediate tumor vicinity for the entire study population (HER2-positive and HER2-negative patients) (p=0.046).

In part I of the clinical trial the safety of the procedure was also assessed. During the diagnostic examination, no defects, damages, failures or cracks of inPROBE® were found. There were also no safety events related to the device itself and no adverse events was reported in study patients.
The results of I part of this study in breast cancer patients justify the initiation of further research projects. These will include other cancers expressing HER2, assessing levels of proteins associated with viral infections, and examining other types of biological material such as tissues sampled during biopsy (ex vivo) and body fluids.

The data collected so far indicate that inPROBE® technological platform is a multipotent, effective and safe method for quantitative determination of various proteins in biological material. It also seems that it may find wider application not only in medicine, where it can also be used to develop drugs and determine their pharmacokinetics, but also in other areas of science benefiting from the progress of molecular biology and genetics, such as agriculture, veterinary medicine, forensics or food and chemical industry.

1. Iqbal Ni, Iqbal Na. Human Epidermal Growth Factor Receptor 2 (HER2) in Cancers: Overexpression and Therapeutic Implications. Mol Biol Int 2014; 2014: 852748.
2. Zhang H, Peng Y. Current Biological, Pathological and Clinical Landscape of HER2-Low Breast Cancer. Cancers 2023, 15, 126.
3. [access: 07/04/2024]
4. Tarantino P, Hamilton E, Tolaney SM, et al. HER2-Low Breast Cancer: Pathological and Clinical Landscape. J Clin Oncol 2020; 38(17): 1951.