Image-Guided Surgery: Breast Cancer Detection Using Monoclonal Antibodies Conjugated to a Near-Infrared Fluorescent Dye in a Syngeneic Rat Model

Background: Incomplete tumor resections occur frequently in patients undergoing breast-conserving surgery. As the surgeon can only rely on palpation and visual inspection, real-time visualization of cancer cells during surgery is needed to increase the number of complete tumor resections. Near-infrared fluorescence (NIRF) imaging using an intra-operative camera system is a novel technique to assess the extent of disease during surgery. Advantages of NIRF light (700-900 nm) include high tissue penetration up to several centimeters deep and low autofluorescence providing sufficient signal-to-noise ratio. Currently, several NIRF dyes are available for chemical conjugation to molecules that can target tumors, e.g. antibodies. This study aimed to investigate whether monoclonal antibodies conjugated to a NIRF dye could detect primary breast carcinomas in a syngeneic rat model.Methods: The hormone-dependent syngeneic breast cancer rat model EMR86 and its derived cell line MCR86 were used. Tumors were induced by orthotopic implantation of fresh EMR86 tumor fragments of 1 mm3 into the flanks at four sites in female WAG/Rij rats (Harlan, the Netherlands). The mouse monoclonal antibody MG1 was used for tumor cell detection. MG1 (IgG2a) recognizes a membrane epitope of rat cancer cells of epithelial origin and is developed by our research group. MG1 was conjugated to the NIRF dye CW-800 (LI-COR, USA) and dye/protein ratio was determined using absorbance measurements (UltroSpec, Amersham, UK). Fluorescence imaging of cells, animals and organs was performed using IVIS Spectrum (Caliper, USA) and Odyssey (LI-COR, USA) equipment.Results: Conjugated antibodies MG1-CW800 bound specifically to cultured MCR86 cells. The signal intensity was linearly correlated with the number of cells and concentration of MG1-CW800 (R2=0.99, p<0.00001). Addition of unconjugated MG1 lowered the fluorescent signal in a competitive binding assay, showing that labeling did not influence binding properties. Intravenous injection of unconjugated MG1 (200 μg/rat) in 3 Wag/Rij rats and subsequent immunohistochemical analysis of tissue sections revealed a specific and exclusive binding of MG1 to the EMR86 tumors and no difference in staining intensity between 24 and 48hrs after injection. Intravenous injection of conjugated MG1-CW800 (200 μg/rat) demonstrated a clear fluorescent demarcation of EMR86 tumors and the surrounding tissue after spectral unmixing (paired t-test 8.17, p<0.00001). Mean fluorescence did not differ between 24 and 48hrs after injection (t=1.85, p=0.11). However, a two-fold increase of the dye/protein ratio led to a two-fold increase of the in vivo fluorescence (t=-6.40, p=0.0001).Conclusion: Intravenous injection of monoclonal antibodies MG1 conjugated to the NIRF dye CW800 enabled detection of primary breast carcinomas in the syngeneic hormone-dependent EMR86 rat model. This study demonstrates proof-of-concept for future labeling of clinically relevant antibodies (e.g. HER2/neu, EGF, VEGF). Translation of this technique to breast cancer patients can lead to intra-operative identification of optimal resection margins in order to increase the comple tumor resection rate.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5006.

Intra-Operative Imaging of the Invasive Tumor Border by a Cathepsin-Sensing Near-Infrared Fluorescence Probe in a Syngeneic Breast Cancer Rat Model

Background: An incomplete tumor resection occurs in 5-45% of the patients undergoing breast-conserving surgery. As the surgeon can only rely on palpation and visual inspection, real-time visualization of cancer cells at the time of surgery is needed to increase the number of complete tumor resections. Near-infrared fluorescence (NIRF) imaging is a promising technique to assess the extent of disease during surgery. This study aimed to validate NIRF imaging in a breast cancer rat model.Methods: The hormone-dependent syngeneic breast cancer rat model EMR86 and its derived cell line MCR86 were used. Tumor cells were detected with the cathepsin-activatable (mainly cathepsin-B) NIRF probe ProSense® (VisEn Medical, USA). Fluorescence imaging of the animals, organs and tissue sections was performed using IVIS Spectrum (Caliper, USA), Odyssey (LI-COR, USA) and SP5 microscope (Leica, Germany). Intra-operative fluorescence imaging was performed using the Fluobeam700 system equipped with a 690 nm class 3B laser and a CCD camera (Fluoptics, France).Results: ProSense was activated by cleavage in MCR86 cells. The signal intensity was linearly correlated with the number of cells, the concentration of ProSense and the incubation time (all R2>0.93, p<0.0001). The influence of ProSense concentration and tumor volume on fluorescent intensity was confirmed in nine rats each bearing four tumors (mean volume=0.38 ±0.36 cm3). In contrast to the in vitro data, no difference in fluorescence intensity was found between 24hr and 48hr after injection of ProSense (paired t=-0.27, p=0.80). Therefore, subsequent experiments were conducted 24hr after injection. Calibration of the intra-operative camera system demonstrated a strong correlation of fluorescence intensity and activated ProSense concentration (R2=0.9903). Using the intra-operative NIRF camera, all 64 mammary tumors (0.01-1.8 cm3) were successfully detected. Histological assessment of residual fluorescent hotspots confirmed the presence of breast cancer cells indicating incomplete resections of the primary tumor (margin positivity). The signal intensity of the tumor was 60-fold higher than the surrounding tissue (p<0.0001). Fluorescence scanning microscopy of 2-mm thick tumor sections revealed a significantly two-fold higher signal intensity at the tumor border compared to the tumor center (t=-8.12, p<0.00001). Fluorescent microscopy of 10 um frozen tissue sections confirmed the higher intensity at the border, which was mainly located in the tumor-associated stroma.Conclusion: We demonstrated that it is possible to detect and resect sub-mm breast tumor depositions under fluorescent guidance in a syngeneic rat model. The higher fluorescent signal at the tumor border likely reflects the extra-cellular matrix degradation induced by increased cathepsin-B activity. Intra-operative imaging of cathepsin activity at the invasive border facilitates clear demarcation of tumor margins. Clinical introduction of this technique has the potential to substantially improve breast-conserving surgery.Acknowledgement: We want to thank Fluoptics for providing us with the Fluobeam700 system to perform the above described experiments.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5007.

Whole body optical imaging in small animals and its translation to the clinic: intra-operative optical imaging guided surgery

Whole body optical imaging using bioluminescence or fluorescence is one of the most rapidly emerging technologies to non-invasively follow all kinds of molecular and cellular processes in small animals. Using tomographic approaches it is now also possible to get better quantitative data. Due to its sensitivity and simplicity it is now also widely used in drug development and drug screening. Finally, using near infrared fluorescent probes that have much deeper penetration also opens up new exciting applications such as intra-operative image guided surgery for sentinel lymph node mapping and radical resection of tumours. Recent advances in imaging strategies that reveal cellular and molecular biological events in real-time facilitate our understanding of biological processes occurring in living animals. The development of molecular tags, such as green fluorescent protein (GFP) from the jellyfish Aequorea victoria, red fluorescent proteins (RFP) from the Discosoma species (dsRed2) and luciferase (Luc) from the firefly Photinus pyralis (fLuc) and the sea pansy Renilla (rLuc), has revolutionised research over the past decade, allowing complex biochemical processes to be associated with the functioning of proteins in living cells. Optical technologies, both microscopic and macroscopic, are developing fast. Recent technical advances for imaging weak visible light sources using cooled charged coupled device (CCCD) cameras, peltier cooled detectors and micro-plate channel intensifiers allow detection of photon emission from inside the tissues of small animals. Whole body fluorescent imaging (FLI) and bioluminescent imaging (BLI) are now applied to study cell- and tissue-specific gene promoter activity and also to follow trafficking, differentiation and fate of i.e. GFP or RFP and/or luciferase expressing cells, or biological processes like apoptosis, protein-protein interaction, angiogenesis, proteolysis and gene-transfer. Optical imaging (OI) and optical reporter systems are also very cost-effective and time-efficient and they are particularly well suited for small animal imaging and for in vitro assays to validate different reporter systems.

Morphological appearance, content of extracellular matrix and vascular density of lung metastases predicts permissiveness to infiltration by adoptively transferred natural killer and T cells

We have recently shown that adoptively transferred, IL-2-activated natural killer (A-NK) cells are able to eliminate well-established B16-F10.P1 melanoma lung metastases. However, some B16-F10.P1 lung metastases were resistant to infiltration by the A-NK cells and also resistant to the A-NK cell treatment. The infiltration-resistant (I-R) B16-F10.P1 metastases had a unique "compact" morphology compared to the "loose" morphology of the infiltration-permissive (I-P) metastases. Here, we show that I-P loose tumors and I-R compact tumors are also found in lung metastases of mouse Lewis lung carcinoma (3LL), MCA-102 sarcoma, and MC38 colon carcinoma as well as rat MADB106 mammary carcinoma origin. Furthermore, the infiltration resistance of the compact tumors is not restricted to A-NK cells, since PHA and IL-2 stimulated CD8+ T-cells (T-LAK cells) also infiltrated the compact tumors poorly. Analyses of tumors for extracellular matrix (ECM) components and PECAM-1(+) vasculature, revealed that the I-R lesions are hypovascularized and contain very little laminin, collagen and fibronectin. In contrast, the I-P loose tumors are well-vascularized and they contain high amounts of ECM components. Interestingly, the distribution pattern of ECM components in the I-P loose tumors is almost identical to that of the normal lung tissue, indicating that these tumors develop around the alveolar walls which provide the loose tumors with both a supporting tissue and a rich blood supply. In conclusion, tumor infiltration by activated NK and T cells correlates with the presence of ECM components and PECAM-1(+) vasculature in the malignant tissue. Thus, analysis of the distribution of ECM and vasculature in tumor biopsies may help select patients most likely to benefit from cellular adoptive immunotherapy.

Morphological studies of effector cell-microvessel interactions in adoptive immunotherapy in tumor-bearing animals

Murine lymphokine-activated natural killer (A-NK) cells are able to migrate to and accumulate in tumor metastases. However, the exact migratory pattern is as yet unknown. In the present study, we have investigated the migration from the vasculature towards malignant tissues of various effector cells. Our results indicate that murine A-NK cells seem to be arrested for an extended period of time in the microvasculature and also, although infrequently, to adhere to the endothelial lining of larger vessels close to tumor tissues before extravasation. While murine T lymphokine-activated killer and rat A-NK cells accumulate significantly in the subendothelial areas of larger venules in normal tissues, no such accumulation is observed with respect to murine A-NK cells. Electron microscopy reveals that the murine A-NK cells undergo an extreme deformation during extravasation and tumor infiltration. Furthermore, the cells are shown to be in an activated stage probably facilitating their migration, and hence, the elimination of tumor cells.

Effect of irradiation on hepatic natural killer cells

The rat liver contains a population of natural killer cells consisting of two morphologically and functionally different subsets, a low-density and a high-density fraction. In this work we describe the influence of low-dose radiation on hepatic natural killer activity. The effect on the cytotoxicity against YAC-1 lymphoma and CC531 colon adenocarcinoma tumor cells was measured in chromium-51 assays, and morphological changes were analyzed by means of electron microscopy. The low-density natural killer fraction showed increased cytotoxicity against YAC-1 which was associated with an increased binding of natural killer cells to the YAC-1 tumor cells shortly after irradiation. These phenomena were paralleled by an increased number of multivesicular bodies and cytoplasmic granules with an electron-lucent halo. In contrast, the other hepatic natural killer cell fraction, the high-density natural killer cells, did not show increased cytotoxicity, binding or morphological alterations. The radiation-stimulated lysis of YAC-1 cells was also observed when in vivo irradiated cells were isolated and tested immediately for in vitro lysis of YAC-1 cells. Sixteen hours after in vitro or in vivo irradiation, the cytotoxicity of hepatic natural killer cells against YAC-1 was no longer enhanced. The cytolysis of and binding of hepatic natural killer cells to CC531 colon adenocarcinoma cells was not stimulated by in vitro irradiation. From these experiments, we conclude that low-dose radiation stimulates the cytotoxicity of hepatic low-density natural killer cells against YAC-1 lymphoma cells immediately after irradiation as the result of enhanced binding of the cells to the tumor cells, in addition to the synthesis of new cytotoxic granules.