Evaluation of a novel monoclonal antibody against tumor-associated MUC1 for diagnosis and prognosis of breast cancer
Natascha Stergiou et al., International Journal of Medical Sciences, 2019
Breast cancer is the most common cancer among women worldwide and the leading cause of cancer death among women. Due to the heterogeneity of breast cancer, the traditional diagnostic markers are often not sufficient either for a precise prognosis or a sufficient statement about an adjuvant or neoadjuvant therapy. It is therefore essential to look for additional prognostic and predictive breast cancer markers that will be complementary in predicting clinical response to the available therapeutic modalities. In addition, there is a need to develop additional markers for such tumors that do not express ER, PR and or HER-2/neu (triple-negative breast cancer [TNBC]). A very promising marker to support breast cancer diagnosis and prognosis is the tumor-associated MUC1 ((TA)MUC1). It is expressed in over 90 % of all breast cancers and even in 94 % of TNBCs. Due to its characteristic aberrant glycosylation as a result of reduced activity of glycosyltransferases and accelerated activity of sialyltransferases in the MUC1 biosynthesis in breast cancer cells, breast-(TA)MUC1 represents a tumor-specific marker and target for therapy. Based on the aberrant glycan pattern, the authors synthesized human (TA)MUC1 (hu(TA)MUC1) glycopeptides derived from the tandem repeat (VNTR) region of this glycoprotein that correspond to the aberrant glycosylation pattern of (TA)MUC1. One specific hu(TA)MUC1 glycopeptide, 22mer huMUC1 peptide sequence of the VNTR region glycosylated with STN on serine-17 located in the highly immune reactive GSTA motif, was conjugated to tetanus toxoid (TTox) forming an unique vaccine. Monoclonal antibodies (mAbs) were generated utilizing this vaccine. Among these, mAb GGSK-1/30 was identified that specifically recognized the hu(TA)MUC1-glycopeptide pattern on human breast cancer cells whereas fully glycosylated huMUC1 expressed by healthy breast epithelial cells was not recognized. The authors could also demonstrate that GGSK-1/30 showed stronger binding to these breast cancer cells than the commonly used and commercially available mAbs (SM3, HMFG1). The aim of the current study was to evaluate the mAb GGSK-1/30 as a diagnostic and prognostic tool for breast cancer.
Small animal PET studies were carried out 72 h after application of radioconjugates regarding the highest enrichment of the mAbs in the tumors at this time point. All scans were performed in head-first-prone position in a PET-MRI 1T scanner. In some experiments MRI measurements (Material Map) were first performed for co-registration of the PET scan (3D Gradient Echo External Averaging (GRE-EXT), Multi Field of View (FOV); slice thickness: 0,6 mm; TE: 2 ms; TR: 15 ms; flip angle: 25 deg) followed by a static PET scan (collecting 20 million events). PET data were reconstructed with Teratomo 3D (4 iterations, 6 subsets, voxel size 0.4 mm), co-registered to the MR and analyzed with PMOD software (version 3.6, PMOD Technologies LLC). Figure 5C. shows PET imaging after 72 hours demonstrated a strong accumulation of [89Zr]Zr-Df'-GGSK-1/30 in the tumor. The highest amount of [89Zr]Zr-Df'-GGSK-1/30 was detected after 72 hours in the tumor (>55 %ID/g). Uptake values in other tissues (lung, heart, spleen, pancreas, stomach, intestines, kidneys, lymph nodes, mammary glands, muscle) were below 20 %ID/g(tissue). The concentration of the [89Zr]Zr-Df'-GGSK-1/30 in blood decreased steadily while increasing amounts of [89Zr]Zr-Df'-GGSK-1/30 accumulated in the tumor. The radioconjugate showed predominant hepatobiliary excretion with increasing uptake values over time from 22 to 38 %ID/g (liver). The uptake values in bone tissues steadily increased due to the slight degradation of the Zr-Df'-complex in vivo, which is known for 89Zr-radiolabeled Df'-conjugated antibodies. An exact calculation of the tumor-to-tissue ratio revealed a comparatively high tumor accumulation.
Figure 6C. shows Selective binding of [89Zr]Zr-Df'-GGSK-1/30 to hu(TA)MUC1 expressed by PyMTxhuMUC1 tumors. HuMUC1-transgenic mice bearing a PyMTxhuMUC1 breast tumor transplant subcutaneously on the right flank were treated i.p. with [89Zr]Zr-Df'-GGSK-1/30 (80 µg, 2.5 MBq) - left image -, previously saturated with 1200 molar excess of the corresponding glycopeptide: [89Zr]Zr-Df'-GGSK-1/30 blocked (50 µg, 0,46 MBq) - right image -:
Hu(TA)MUC1 is a tumor-specific antigen on breast cancer cells with an exceptionally high diagnostic and potential prognostic value/importance. The radiolabeled derivative [89Zr]Zr-Df'-GGSK-1/30 demonstrated high in vivo stability and highly selective and tumor-specific accumulation which resulted in high contrast PET imaging. Thus, GGSK-1/30 represents a promising PET-tracer for clinical studies on molecular imaging in early diagnosis and/or in therapy-accompanying control examinations of breast cancer patients undergoing systemic therapies.
The mAb GGSK-1/30 represents a platform, which can be used (i) as a diagnostic tool for the detection of hu(TA)MUC1 in early breast cancer diagnosis, (ii) as a prognostic biomarker, (iii) as a companion diagnostic during therapy and (iv) in future perspective in radioimmunotherapy.