Heterogeneity of circulating tumor cell dissemination and lung metastases in a subcutaneous Lewis lung carcinoma model

Two-color diffuse in vivo flow cytometer

Significance

Hematogenous metastasis is mediated by circulating tumor cells (CTCs) and CTC clusters (CTCCs). We recently developed "diffuse in vivo flow cytometry" (DiFC) to detect fluorescent protein (FP) expressing CTCs in small animals. Extending DiFC to allow detection of two FPs simultaneously would allow concurrent study of different CTC sub-populations or heterogeneous CTCCs in the same animal.

Aim

The goal of this work was to develop and validate a two-color DiFC system capable of non-invasively detecting circulating cells expressing two distinct FPs.

Approach

A DiFC instrument was designed and built to detect cells expressing either green FP (GFP) or tdTomato. We tested the instrument in tissue-mimicking flow phantoms in vitro and in multiple myeloma bearing mice in vivo.

Results

In phantoms, we could accurately differentiate GFP+ and tdTomato+ CTCs and CTCCs. In tumor-bearing mice, CTC numbers expressing both FPs increased during disease. Most CTCCs (86.5%) expressed single FPs with the remainder both FPs. These data were supported by whole-body hyperspectral fluorescence cryo-imaging of the mice.

Conclusions

We showed that two-color DiFC can detect two populations of CTCs and CTCCs concurrently. This instrument could allow study of tumor development and response to therapies for different sub-populations in the same animal.

In Vivo Labeling and Detection of Circulating Tumor Cells in Mice Using OTL38

PURPOSE

We recently developed an optical instrument to non-invasively detect fluorescently labeled circulating tumor cells (CTCs) in mice called 'Diffuse in vivo Flow Cytometry' (DiFC). OTL38 is a folate receptor (FR) targeted near-infrared (NIR) contrast agent that is FDA approved for use in fluorescence guided surgery of ovarian and lung cancer. In this work, we investigated the use OTL38 for in vivo labeling and detection of FR + CTCs with DiFC.

PROCEDURES

We tested OTL38 labeling of FR + cancer cell lines (IGROV-1 and L1210A) as well as FR- MM.1S cells in suspensions of Human Peripheral Blood Mononuclear cells (PBMCs) in vitro. We also tested OTL38 labeling and NIR-DIFC detection of FR + L1210A cells in blood circulation in nude mice in vivo.

RESULTS

62% of IGROV-1 and 83% of L1210A were labeled above non-specific background levels in suspensions of PBMCs in vitro compared to only 2% of FR- MM.1S cells. L1210A cells could be labeled with OTL38 directly in circulation in vivo and externally detected using NIR-DiFC in mice with low false positive detection rates.

CONCLUSIONS

This work shows the feasibility of labeling CTCs in vivo with OTL38 and detection with DiFC. Although further refinement of the DiFC instrument and signal processing algorithms and testing with other animal models is needed, this work may eventually pave the way for human use of DiFC.

Lipid nanoparticle encapsulated large peritoneal macrophages migrate to the lungs via the systemic circulation in a model of clodronate-mediated lung-resident macrophage depletion

Rationale: A mature tissue resident macrophage (TRM) population residing in the peritoneal cavity has been known for its unique ability to migrate to peritoneally located injured tissues and impart wound healing properties. Here, we sought to expand on this unique ability of large peritoneal macrophages (LPMs) by investigating whether these GATA6+ LPMs could also intravasate into systemic circulation and migrate to extra-peritoneally located lungs upon ablating lung-resident alveolar macrophages (AMs) by intranasally administered clodronate liposomes in mice. Methods: C12-200 cationic lipidoid-based nanoparticles were employed to selectively deliver a small interfering RNA (siRNA)-targeting CD-45 labeled with a cyanine 5.5 (Cy5.5) dye to LPMs in vivo via intraperitoneal injection. We utilized a non-invasive optical technique called Diffuse In Vivo Flow Cytometry (DiFC) to then systemically track these LPMs in real time and paired it with more conventional techniques like flow cytometry and immunocytochemistry to initially confirm uptake of C12-200 encapsulated siRNA-Cy5.5 (siRNA-Cy5.5 (C12-200)) into LPMs, and further track them from the peritoneal cavity to the lungs in a mouse model of AM depletion incited by intranasally administered clodronate liposomes. Also, we stained for LPM-specific marker zinc-finger transcription factor GATA6 in harvested cells from biofluids like broncho-alveolar lavage as well as whole blood to probe for Cy5.5-labeled LPMs in the lungs as well as in systemic circulation. Results: siRNA-Cy5.5 (C12-200) was robustly taken up by LPMs. Upon depletion of lung-resident AMs, these siRNA-Cy5.5 (C12-200) labeled LPMs rapidly migrated to the lungs via systemic circulation within 12-24 h. DiFC results showed that these LPMs intravasated from the peritoneal cavity and utilized a systemic route of migration. Moreover, immunocytochemical staining of zinc-finger transcription factor GATA6 further confirmed results from DiFC and flow cytometry, confirming the presence of siRNA-Cy5.5 (C12-200)-labeled LPMs in the peritoneum, whole blood and BALF only upon clodronate-administration. Conclusion: Our results indicate for the very first time that selective tropism, migration, and infiltration of LPMs into extra-peritoneally located lungs was dependent on clodronate-mediated AM depletion. These results further open the possibility of therapeutically utilizing LPMs as delivery vehicles to carry nanoparticle-encapsulated oligonucleotide modalities to potentially address inflammatory diseases, infectious diseases and even cancer.

Circulating tumor cells reveal early predictors of disease progression in patients with stage III NSCLC undergoing chemoradiation and immunotherapy

Circulating tumor cells (CTCs) are early signs of metastasis and can be used to monitor disease progression well before radiological detection by imaging. Using an ultrasensitive graphene oxide microfluidic chip nanotechnology built with graphene oxide sheets, we were able to demonstrate that CTCs can be specifically isolated and molecularly characterized to predict future progression in patients with stage III non-small cell lung cancer (NSCLC). We analyzed CTCs from 26 patients at six time points throughout the treatment course of chemoradiation followed by immune checkpoint inhibitor immunotherapy. We observed that CTCs decreased significantly during treatment, where a larger decrease in CTCs predicted a significantly longer progression-free survival time. Durvalumab-treated patients who have future progression were observed to have sustained higher programmed death ligand 1+ CTCs compared to stable patients. Gene expression profiling revealed phenotypically aggressive CTCs during chemoradiation. By using emerging innovative bioengineering approaches, we successfully show that CTCs are potential biomarkers to monitor and predict patient outcomes in patients with stage III NSCLC.

Ratiometric fluorescence sensing and quantification of circulating blood sodium sensors in mice in vivo

In this work, we introduce ratiometric diffuse in vivo flow cytometry (R-DiFC) for quantitative measurement of circulating fluorescent red blood cell (fRBC) sensors for systemic blood sodium levels. Unlike in our previous work in measuring circulating fRBC sensors, R-DiFC allows simultaneous measurement of two fluorophores encapsulated in the sensor, the ratio of which enables self-calibration of the fluorescence signal with different fRBC depths in biological tissue. We show that the R-DiFC signal varies significantly less than either fluorescence signal alone. This work holds promise for personalized monitoring of systemic sodium for bipolar patients in the future.

Models to study CTCs and CTC culture methods

The vast majority of cancer-related deaths are due to the presence of disseminated disease. Understanding the metastatic process is key to achieving a reduction in cancer mortality. Particularly, there is a need to understand the molecular mechanisms that drive cancer metastasis, which will allow the identification of curative treatments for metastatic cancers. Liquid biopsies have arisen as a minimally invasive approach to gain insights into the biology of metastasis. Circulating tumour cells (CTCs), shed to the circulation from the primary tumour or metastatic lesions, are a key component of liquid biopsy. As metastatic precursors, CTCs hold the potential to unravel the mechanisms involved in metastasis formation as well as new therapeutic strategies for treating metastatic disease. However, the complex biology of CTCs together with their low frequency in circulation are factors hampering an in-depth mechanistic investigation of the metastatic process. To overcome these problems, CTC-derived models, including CTC-derived xenograft (CDX) and CTC-derived ex vivo cultures, in combination with more traditional in vivo models of metastasis, have emerged as powerful tools to investigate the biological features of CTCs facilitating cancer metastasis and uncover new therapeutic opportunities. In this chapter, we provide an up to date view of the diverse models used in different cancers to study the biology of CTCs, and of the methods developed for CTC culture and expansion, in vivo and ex vivo. We also report some of the main challenges and limitations that these models are facing.

Elemental profiles in distant tissues during tumor progression

BACKGROUND

Essential elements have functions in tumor progression by promoting protumoral cellular processes, such as proliferation, and migration, among others. Obtaining an understanding of how these elements relate to tumor progression processes is of great importance for research. Elemental profile studies in distant tissues, which can be modulated by tumor cells to promote metastasis, have not been sufficiently investigated. The main goal of this study is to evaluate multielemental distribution during tumor progression, focusing on tumor tissue and distant tissues that may be affected.

METHODS

Tumor progression in vivo was simulated by inoculating C57BL/6 mice with Lewis Lung Carcinoma (LLC) cells. Samples of the primary tumor and distant tissues were collected during 5 weeks of tumor progression for the control and experimental (tumor-bearing) groups. The biological samples were analyzed using the synchrotron radiation X-Ray fluorescence technique. Data on the concentration of P, S, K, Ca, Mn, Fe, Cu, and Zn in the samples were obtained and statistically analyzed to evaluate the distribution of the elements during tumor progression in the primary tumor as well as distant tissues.

RESULTS

It was possible to observe significant changes in the concentrations' distribution of P, S, K, Ca, Mn, Fe, and Cu in distant tissues caused by the presence of tumor cells. It was also possible to detect a greater similarity between tumor tissue (which has the lung as tissue of origin) and a tissue of non-origin, such as the liver, which is an unprecedented result. Moreover, changes in the distributions of concentrations were detected and studied over time for the different tissues analyzed, such as primary tumor, liver and lung, in Control and Tumor groups.

CONCLUSIONS

Among other results, this paper could explore the modulation of distant tissues caused by the presence of a primary tumor. This could be achieved by the evaluation of several elements of known biological importance allowing the study of different biological processes involved in cancer. The role of essential elements as modulators of the tumor microenvironment is a relevant aspect of tumor progression and this work is a contribution to the field of tumoral metallomics.

Trends in Subcutaneous Tumour Height and Impact on Measurement Accuracy

Tumour volume is typically calculated using only length and width measurements, using width as a proxy for height in a 1:1 ratio. When tracking tumour growth over time, important morphological information and measurement accuracy is lost by ignoring height, which we show is a unique variable. Lengths, widths, and heights of 9522 subcutaneous tumours in mice were measured using 3D and thermal imaging. The average height:width ratio was found to be 1:3 proving that using width as a proxy for height overestimates tumour volume. Comparing volumes calculated with and without tumour height to the true volumes of excised tumours indeed showed that using the volume formula including height produced volumes 36X more accurate (based off of percentage difference). Monitoring the height:width relationship (prominence) across tumour growth curves indicated that prominence varied, and that height could change independent of width. Twelve cell lines were investigated individually; the scale of tumour prominence was cell line-dependent with relatively less prominent tumours (MC38, BL2, LL/2) and more prominent tumours (RENCA, HCT116) detected. Prominence trends across the growth cycle were also dependent on cell line; prominence was correlated with tumour growth in some cell lines (4T1, CT26, LNCaP), but not others (MC38, TC-1, LL/2). When pooled, invasive cell lines produced tumours that were significantly less prominent at volumes >1200 mm³ compared to non-invasive cell lines (P < .001). Modelling was used to show the impact of the increased accuracy gained by including height in volume calculations on several efficacy study outcomes. Variations in measurement accuracy contribute to experimental variation and irreproducibility of data, therefore we strongly advise researchers to measure height to improve accuracy in tumour studies.

Maternally transferred mAbs protect neonatal mice from HSV-induced mortality and morbidity

Neonatal herpes simplex virus (nHSV) infections often result in significant mortality and neurological morbidity despite antiviral drug therapy. Maternally transferred herpes simplex virus (HSV)-specific antibodies reduce the risk of clinically overt nHSV, but this observation has not been translationally applied. Using a neonatal mouse model, we tested the hypothesis that passive transfer of HSV-specific human mAbs can prevent mortality and morbidity associated with nHSV. The mAbs were expressed in vivo via vectored immunoprophylaxis or recombinantly. Through these maternally derived routes or through direct administration to pups, diverse mAbs to HSV glycoprotein D protected against neonatal HSV-1 and HSV-2 infection. Using in vivo bioluminescent imaging, both pre- and post-exposure mAb treatment significantly reduced viral load in mouse pups. Together these studies support the notion that HSV-specific mAb-based therapies could prevent or improve HSV infection outcomes in neonates.

In vivo growth of subclones derived from Lewis lung carcinoma is determined by the tumor microenvironment

Heterogeneity is a fundamental feature of human tumors and plays a major role in drug resistance and disease progression. In the present study, we selected single-cell-derived cell lines (SCDCLs) derived from Lewis lung carcinoma (LLC1) cells to investigate tumorigenesis and heterogeneity. SCDCLs were generated using limiting dilution. Five SCDCLs were subcutaneously injected into wild-type C57BL/6N mice; however, they displayed significant differences in tumor growth. Subclone SCC1 grew the fastest in vivo, whereas it grew slower in vitro. The growth pattern of SCC2 was the opposite to that of SCC1. Genetic differences in these two subclones showed marked differences in cell adhesion and proliferation. Pathway enrichment results indicate that signal transduction and immune system responses were the most significantly altered functional categories in SCC2 cells compared to those in SCC1 cells in vitro. The number and activation of CD3⁺ and CD8⁺ T cells and NK cells in the tumor tissue of tumor-bearing mice inoculated with SCC2 were significantly higher, whereas those of myeloid cells were significantly lower, than those in the SCC1 and LLC1 groups. Our results suggest that the in vivo growth of two subclones derived from LLC1 was determined by the tumor microenvironment rather than their intrinsic proliferative cell characteristics.

Near-infrared diffuse in vivo flow cytometry

Significance

Diffuse in vivo flow cytometry (DiFC) is an emerging technique for enumerating rare fluorescently labeled circulating cells noninvasively in the bloodstream. Thus far, we have reported red and blue-green versions of DiFC. Use of near-infrared (NIR) fluorescent light would in principle allow use of DiFC in deeper tissues and would be compatible with emerging NIR fluorescence molecular contrast agents.

Aim

We describe the design of a NIR-DiFC instrument and demonstrate its use in optical flow phantoms in vitro and in mice in vivo.

Approach

We developed an improved optical fiber probe design for efficient collection of fluorescence from individual circulating cells and efficient rejection of instrument autofluorescence. We built a NIR-DiFC instrument. We tested this with NIR fluorescent microspheres and cell lines labeled with OTL38 fluorescence contrast agent in a flow phantom model. We also tested NIR-DiFC in nude mice injected intravenously with OTL38-labeled L1210A cells.

Results

NIR-DiFC allowed detection of circulating tumor cells (CTCs) in flow phantoms with mean signal-to-noise ratios (SNRs) of 19 to 32 dB. In mice, fluorescently labeled CTCs were detectable with mean SNR of 26 dB. NIR-DiFC also exhibited orders significantly lower autofluorescence and false-alarm rates than blue-green DiFC.

Conclusions

NIR-DiFC allows use of emerging NIR contrast agents. Our work could pave the way for future use of NIR-DiFC in humans.

Signal and measurement considerations for human translation of diffuse in vivo flow cytometry

SIGNIFICANCE

"Diffuse in vivo flow cytometry" (DiFC) is an emerging technology for fluorescence detection of rare circulating cells directly in large deep-seated blood vessels in mice. Because DiFC uses highly scattered light, in principle, it could be translated to human use. However, an open question is whether fluorescent signals from single cells would be detectable in human-scale anatomies.

AIM

Suitable blood vessels in a human wrist or forearm are at a depth of ∼2 to 4 mm. The aim of this work was to study the impact of DiFC instrument geometry and wavelength on the detected DiFC signal and on the maximum depth of detection of a moving cell.

APPROACH

We used Monte Carlo simulations to compute fluorescence Jacobian (sensitivity) matrices for a range of source and detector separations (SDS) and tissue optical properties over the visible and near infrared spectrum. We performed experimental measurements with three available versions of DiFC (488, 640, and 780 nm), fluorescent microspheres, and tissue mimicking optical flow phantoms. We used both computational and experimental data to estimate the maximum depth of detection at each combination of settings.

RESULTS

For the DiFC detection problem, our analysis showed that for deep-seated blood vessels, the maximum sensitivity was obtained with NIR light (780 nm) and 3-mm SDS.

CONCLUSIONS

These results suggest that-in combination with a suitable molecularly targeted fluorescent probes-circulating cells and nanosensors could, in principle, be detectable in circulation in humans.

Prevention of Melanoma Extravasation as a New Treatment Option Exemplified by p38/MK2 Inhibition

Melanoma releases numerous tumor cells into the circulation; however, only a very small fraction of these cells is able to establish distant metastasis. Intravascular survival of circulating tumor cells is limited through hemodynamic forces and by the lack of matrix interactions. The extravasation step is, thus, of unique importance to establish metastasis. Similar to leukocyte extravasation, this process is under the control of adhesion molecule pairs expressed on melanoma and endothelial cells, and as for leukocytes, ligands need to be adequately presented on cell surfaces. Based on melanoma plasticity, there is considerable heterogeneity even within one tumor and one patient resulting in a mixture of invasive or proliferative cells. The molecular control for this switch is still ill-defined. Recently, the balance between two kinase pathways, p38 and JNK, has been shown to determine growth characteristics of melanoma. While an active JNK pathway induces a proliferative phenotype with reduced invasive features, an active p38/MK2 pathway results in an invasive phenotype and supports the extravasation step via the expression of molecules capable of binding to endothelial integrins. Therapeutic targeting of MK2 to prevent extravasation might reduce metastatic spread.

Short-Term Circulating Tumor Cell Dynamics in Mouse Xenograft Models and Implications for Liquid Biopsy

MOTIVATION

Circulating tumor cells (CTCs) are widely studied using liquid biopsy methods that analyze fractionally-small peripheral blood (PB) samples. However, little is known about natural fluctuations in CTC numbers that may occur over short timescales in vivo, and how these may affect detection and enumeration of rare CTCs from small blood samples.

METHODS

We recently developed an optical instrument called "diffuse in vivo flow cytometry" (DiFC) that uniquely allows continuous, non-invasive counting of rare, green fluorescent protein expressing CTCs in large blood vessels in mice. Here, we used DiFC to study short-term changes in CTC numbers in multiple myeloma and Lewis lung carcinoma xenograft models. We analyzed CTC detections in over 100 h of DiFC data, and considered intervals corresponding to approximately 1%, 5%, 10%, and 20% of the PB volume. In addition, we analyzed changes in CTC numbers over 24 h (diurnal) periods.

RESULTS

For rare CTCs (fewer than 1 CTC per ml of blood), the use of short DiFC intervals (corresponding to small PB samples) frequently resulted in no detections. For more abundant CTCs, CTC numbers frequently varied by an order of magnitude or more over the time-scales considered. This variance in CTC detections far exceeded that expected by Poisson statistics or by instrument variability. Rather, the data were consistent with significant changes in mean numbers of CTCs on the timescales of minutes and hours.

CONCLUSIONS

The observed temporal changes can be explained by known properties of CTCs, namely, the continuous shedding of CTCs from tumors and the short half-life of CTCs in blood. It follows that the number of cells in a blood sample are strongly impacted by the timing of the draw. The issue is likely to be compounded for multicellular CTC clusters or specific CTC subtypes, which are even more rare than single CTCs. However, we show that enumeration can in principle be improved by averaging multiple samples, analysis of larger volumes, or development of methods for enumeration of CTCs directly in vivo.