Targeting serine/glycine metabolism improves radiotherapy response in non-small cell lung cancer

BACKGROUND

Lung cancer is the most lethal cancer, and 85% of cases are classified as non-small cell lung cancer (NSCLC). Metabolic rewiring is a cancer hallmark that causes treatment resistance, and lacks insights into serine/glycine pathway adaptations upon radiotherapy.

METHODS

We analyzed radiotherapy responses using mass-spectrometry-based metabolomics in NSCLC patient's plasma and cell lines. Efficacy of serine/glycine conversion inhibitor sertraline with radiotherapy was investigated by proliferation, clonogenic and spheroid assays, and in vivo using a serine/glycine dependent NSCLC mouse model by assessment of tumor growth, metabolite and cytokine levels, and immune signatures.

RESULTS

Serine/glycine pathway metabolites were significantly consumed in response to radiotherapy in NSCLC patients and cell models. Combining sertraline with radiotherapy impaired NSCLC proliferation, clonogenicity and stem cell self-renewal capacity. In vivo, NSCLC tumor growth was reduced solely in the sertraline plus radiotherapy combination treatment group. Tumor weights linked to systemic serine/glycine pathway metabolite levels, and were inhibited in the combination therapy group. Interestingly, combination therapy reshaped the tumor microenvironment via cytokines associated with natural killer cells, supported by eradication of immune checkpoint galectin-1 and elevated granzyme B levels.

CONCLUSION

Our findings highlight that targeting serine/glycine metabolism using sertraline restricts cancer cell recovery from radiotherapy and provides tumor control through immunomodulation in NSCLC.

Caffeic Acid Phenethyl Ester (CAPE), a natural polyphenol to increase the therapeutic window for lung adenocarcinomas

BACKGROUND AND PURPOSE

Lung cancers are highly resistant to radiotherapy, necessitating the use of high doses, which leads to radiation toxicities such as radiation pneumonitis and fibrosis. Caffeic Acid Phenethyl Ester (CAPE) has been suggested to have anti-proliferative and pro-apoptotic effects in tumour cells, while radioprotective anti-inflammatory and anti-oxidant effects in the normal tissue. We investigated the radiosensitizing and radioprotective effects of CAPE in lung cancer cell lines and normal tissue in vitro and ex vivo, respectively.

MATERIALS AND METHODS

The cytotoxic and radiosensitizing effects of CAPE in lung cancer were investigated using viability and clonogenic survival assays. The radioprotective effects of CAPE were assessed in vitro and ex vivo using precision cut lung slices (PCLS). Potential underlying molecular mechanisms of CAPE focusing on cell cycle, cell metabolism, mitochondrial function and pro-inflammatory markers were investigated.

RESULTS

Treatment with CAPE decreased cell viability in a dose-dependent manner (IC50 57.6 ± 16.6 μM). Clonogenic survival assays showed significant radiosensitization by CAPE in lung adenocarcinoma lines (p < 0.05), while no differences were found in non-adenocarcinoma lines (p ≥ 0.13). Cell cycle analysis showed an increased S-phase (p < 0.05) after incubation with CAPE in the majority of cell lines. Metabolic profiling showed that CAPE shifted cellular respiration towards glycolysis (p < 0.01), together with mitochondrial membrane depolarization (p < 0.01). CAPE induced a decrease in NF-κB activity in adenocarcinomas and decreased pro-inflammatory gene expression in PCLS.

CONCLUSION

The combination of CAPE and radiotherapy may be a potentially effective approach to increase the therapeutic window in lung cancer patients.

A deep-learning assisted bioluminescence tomography method to enable radiation targeting in rat glioblastoma

OBJECTIVE

A novel solution is required for accurate 3D Bioluminescence Tomography (BLT) based glioblastoma (GBM) targeting. The provided solution should be computationally efficient to support real-time treatment planning, thus reducing the X-ray imaging dose imposed by high-resolution micro cone-beam CT.&#xD;Approach: A novel deep-learning approach is developed to enable BLT-based tumor targeting and treatment planning for orthotopic rat GBM models. The proposed framework is trained and validated on a set of realistic Monte Carlo simulations. Finally, the trained deep learning model is tested on a limited set of BLI measurements of real rat GBM models.&#xD;Significance: Bioluminescence Imaging (BLI) is a 2D non-invasive optical imaging modality geared toward preclinical cancer research. It can be used to monitor tumor growth in small animal tumor models effectively and without radiation burden. However, the current state-of-the-art does not allow accurate radiation treatment planning using BLI, hence limiting BLI's value in preclinical radiobiology research. &#xD;Results: The proposed solution can achieve sub-millimeter targeting accuracy on the simulated dataset, with a median dice similarity coefficient (DSC) of 61%. The provided BLT-based planning volume achieves a median encapsulation of more than 97% of the tumor while keeping the median geometrical brain coverage below 4.2%. For the real BLI measurements, the proposed solution provided median geometrical tumor coverage of 95% and a median DSC of 42%. Dose planning using a dedicated small animal treatment planning system indicated good BLT-based treatment planning accuracy compared to ground-truth CT-based planning, where dose-volume metrics for the tumor fall within the limit of agreement for more than 95% of cases.&#xD;Conclusion: The combination of flexibility, accuracy, and speed of the deep learning solutions make them a viable option for the BLT reconstruction problem and can provide BLT-based tumor targeting for the rat GBM models.

Treating colorectal peritoneal metastases with an injectable cytostatic loaded supramolecular hydrogel in a rodent animal model

Patients with peritoneal metastases (PM) of colorectal cancer have a very poor outcome. Intraperitoneal delivery of chemotherapy is the preferred route for PM treatment. The main limitation of the treatment options is the short residence time of the cytostatic, with subsequent short exposure of the cancer cells. To address this, a supramolecular hydrogel has been developed that allows both local and slow release of its encapsulated drug, mitomycin C (MMC) or cholesterol-conjugated MMC (cMMC), respectively. This experimental study investigates if drug delivery using this hydrogel improves the therapeutic efficacy against PM. PM was induced in WAG/Rij rats (n = 72) by intraperitoneally injecting syngeneic colon carcinoma cells (CC531) expressing luciferase. After seven days, animals received a single intraperitoneal injection with saline (n = 8), unloaded hydrogel (n = 12), free MMC (n = 13), free cMMC (n = 13), MMC-loaded hydrogel (n = 13), or cMMC-loaded hydrogel (n = 13). Primary outcome was overall survival with a maximum follow-up of 120 days. Intraperitoneal tumor development was non-invasive monitored via bioluminescence imaging. Sixty-one rats successfully underwent all study procedures and were included to assess therapeutic efficacy. After 120 days, the overall survival in the MMC-loaded hydrogel and free MMC group was 78% and 38%, respectively. A trend toward significance was found when comparing the survival curves of the MMC-loaded hydrogel and free MMC (p = 0.087). No survival benefit was found for the cMMC-loaded hydrogel compared to free cMMC. Treating PM with our MMC-loaded hydrogel, exhibiting prolonged MMC exposure, seems effective in improving survival compared to treatment with free MMC.

A deep learning and Monte Carlo based framework for bioluminescence imaging center of mass-guided glioblastoma targeting

Objective. Bioluminescence imaging (BLI) is a valuable tool for non-invasive monitoring of glioblastoma multiforme (GBM) tumor-bearing small animals without incurring x-ray radiation burden. However, the use of this imaging modality is limited due to photon scattering and lack of spatial information. Attempts at reconstructing bioluminescence tomography (BLT) using mathematical models of light propagation show limited progress. Approach. This paper employed a different approach by using a deep convolutional neural network (CNN) to predict the tumor’s center of mass (CoM). Transfer-learning with a sizeable artificial database is employed to facilitate the training process for, the much smaller, target database including Monte Carlo (MC) simulations of real orthotopic glioblastoma models. Predicted CoM was then used to estimate a BLI-based planning target volume (bPTV), by using the CoM as the center of a sphere, encompassing the tumor. The volume of the encompassing target sphere was estimated based on the total number of photons reaching the skin surface. Main results. Results show sub-millimeter accuracy for CoM prediction with a median error of 0.59 mm. The proposed method also provides promising performance for BLI-based tumor targeting with on average 94% of the tumor inside the bPTV while keeping the average healthy tissue coverage below 10%. Significance. This work introduced a framework for developing and using a CNN for targeted radiation studies for GBM based on BLI. The framework will enable biologists to use BLI as their main image-guidance tool to target GBM tumors in rat models, avoiding delivery of high x-ray imaging dose to the animals.

'On the Spot' Digital Pathology of Breast Cancer Based on Single-Cell Mass Spectrometry Imaging

The molecular pathology of breast cancer is challenging due to the complex heterogeneity of cellular subtypes. The ability to directly identify and visualize cell subtype distribution at the single-cell level within a tissue section enables precise and rapid diagnosis and prognosis. Here, we applied mass spectrometry imaging (MSI) to acquire and visualize the molecular profiles at the single-cell and subcellular levels of 14 different breast cancer cell lines. We built a molecular library of genetically well-characterized cell lines. Multistep processing, including deep learning, resulted in a breast cancer subtype, the cancer's hormone status, and a genotypic recognition model based on metabolic phenotypes with cross-validation rates of up to 97%. Moreover, we applied our single-cell-based recognition models to complex tissue samples, identifying cell subtypes in tissue context within seconds during measurement. These data demonstrate "on the spot" digital pathology at the single-cell level using MSI, and they provide a framework for fast and accurate high spatial resolution diagnostics and prognostics.

Automatic contouring of normal tissues with deep learning for preclinical radiation studies

Objective.Delineation of relevant normal tissues is a bottleneck in image-guided precision radiotherapy workflows for small animals. A deep learning (DL) model for automatic contouring using standardized 3D micro cone-beam CT (μCBCT) volumes as input is proposed, to provide a fully automatic, generalizable method for normal tissue contouring in preclinical studies.Approach.A 3D U-net was trained to contour organs in the head (whole brain, left/right brain hemisphere, left/right eye) and thorax (complete lungs, left/right lung, heart, spinal cord, thorax bone) regions. As an important preprocessing step, Hounsfield units (HUs) were converted to mass density (MD) values, to remove the energy dependency of theμCBCT scanner and improve generalizability of the DL model. Model performance was evaluated quantitatively by Dice similarity coefficient (DSC), mean surface distance (MSD), 95th percentile Hausdorff distance (HD_95p), and center of mass displacement (ΔCoM). For qualitative assessment, DL-generated contours (for 40 and 80 kV images) were scored (0: unacceptable, manual re-contouring needed - 5: no adjustments needed). An uncertainty analysis using Monte Carlo dropout uncertainty was performed for delineation of the heart.Main results.The proposed DL model and accompanying preprocessing method provide high quality contours, with in general median DSC > 0.85, MSD < 0.25 mm, HD_95p < 1 mm and ΔCoM < 0.5 mm. The qualitative assessment showed very few contours needed manual adaptations (40 kV: 20/155 contours, 80 kV: 3/155 contours). The uncertainty of the DL model is small (within 2%).Significance.A DL-based model dedicated to preclinical studies has been developed for multi-organ segmentation in two body sites. For the first time, a method independent of image acquisition parameters has been quantitatively evaluated, resulting in sub-millimeter performance, while qualitative assessment demonstrated the high quality of the DL-generated contours. The uncertainty analysis additionally showed that inherent model variability is low.

Inter-observer variability of organ contouring for preclinical studies with cone beam Computed Tomography imaging

Background and purpose

In preclinical radiation studies, there is great interest in quantifying the radiation response of healthy tissues. Manual contouring has significant impact on the treatment-planning because of variation introduced by human interpretation. This results in inconsistencies when assessing normal tissue volumes. Evaluation of these discrepancies can provide a better understanding on the limitations of the current preclinical radiation workflow. In the present work, interobserver variability (IOV) in manual contouring of rodent normal tissues on cone-beam Computed Tomography, in head and thorax regions was evaluated.

Materials and methods

Two animal technicians performed manually (assisted) contouring of normal tissues located within the thorax and head regions of rodents, 20 cases per body site. Mean surface distance (MSD), displacement of center of mass (ΔCoM), DICE similarity coefficient (DSC) and the 95th percentile Hausdorff distance (HD₉₅) were calculated between the contours of the two observers to evaluate the IOV.

Results

For the thorax organs, right lung had the lowest IOV (ΔCoM: 0.08 ± 0.04 mm, DSC: 0.96 ± 0.01, MSD:0.07 ± 0.01 mm, HD₉₅:0.20 ± 0.03 mm) while spinal cord, the highest IOV (ΔCoM:0.5 ± 0.3 mm, DSC:0.81 ± 0.05, MSD:0.14 ± 0.03 mm, HD₉₅:0.8 ± 0.2 mm). Regarding head organs, right eye demonstrated the lowest IOV (ΔCoM:0.12 ± 0.08 mm, DSC: 0.93 ± 0.02, MSD: 0.15 ± 0.04 mm, HD₉₅: 0.29 ± 0.07 mm) while complete brain, the highest IOV (ΔCoM: 0.2 ± 0.1 mm, DSC: 0.94 ± 0.02, MSD: 0.3 ± 0.1 mm, HD₉₅: 0.5 ± 0.1 mm).

Conclusions

Our findings reveal small IOV, within the sub-mm range, for thorax and head normal tissues in rodents. The set of contours can serve as a basis for developing an automated delineation method for e.g., treatment planning.

Selectively Targeting Tumor Hypoxia With the Hypoxia-Activated Prodrug CP-506

Hypoxia-activated prodrugs (HAP) are a promising class of antineoplastic agents that can selectively eliminate hypoxic tumor cells. This study evaluates the hypoxia-selectivity and antitumor activity of CP-506, a DNA alkylating HAP with favorable pharmacologic properties. Stoichiometry of reduction, one-electron affinity, and back-oxidation rate of CP-506 were characterized by fast-reaction radiolytic methods with observed parameters fulfilling requirements for oxygen-sensitive bioactivation. Net reduction, metabolism, and cytotoxicity of CP-506 were maximally inhibited at oxygen concentrations above 1 μmol/L (0.1% O₂). CP-506 demonstrated cytotoxicity selectively in hypoxic 2D and 3D cell cultures with normoxic/anoxic IC₅₀ ratios up to 203. Complete resistance to aerobic (two-electron) metabolism by aldo-keto reductase 1C3 was confirmed through gain-of-function studies while retention of hypoxic (one-electron) bioactivation by various diflavin oxidoreductases was also demonstrated. In vivo, the antitumor effects of CP-506 were selective for hypoxic tumor cells and causally related to tumor oxygenation. CP-506 effectively decreased the hypoxic fraction and inhibited growth of a wide range of hypoxic xenografts. A multivariate regression analysis revealed baseline tumor hypoxia and in vitro sensitivity to CP-506 were significantly correlated with treatment response. Our results demonstrate that CP-506 selectively targets hypoxic tumor cells and has broad antitumor activity. Our data indicate that tumor hypoxia and cellular sensitivity to CP-506 are strong determinants of the antitumor effects of CP-506.

Pharmacological inhibition of 17β-hydroxysteroid dehydrogenase impairs human endometrial cancer growth in an orthotopic xenograft mouse model

Endometrial cancer (EC) is the most common gynaecological tumor in developed countries and its incidence is increasing. Approximately 80% of newly diagnosed EC cases are estrogen-dependent. Type 1 17β-hydroxysteroid dehydrogenase (17β-HSD-1) is the enzyme that catalyzes the final step in estrogen biosynthesis by reducing the weak estrogen estrone (E1) to the potent estrogen 17β-estradiol (E2), and previous studies showed that this enzyme is implicated in the intratumoral E2 generation in EC. In the present study we employed a recently developed orthotopic and estrogen-dependent xenograft mouse model of EC to show that pharmacological inhibition of the 17β-HSD-1 enzyme inhibits disease development. Tumors were induced in one uterine horn of athymic nude mice by intrauterine injection of the well-differentiated human endometrial adenocarcinoma Ishikawa cell line, modified to express human 17β-HSD-1 in levels comparable to EC, and the luciferase and green fluorescent protein reporter genes. Controlled estrogen exposure in ovariectomized mice was achieved using subcutaneous MedRod implants that released either the low active estrone (E1) precursor or vehicle. A subgroup of E1 supplemented mice received daily oral gavage of FP4643, a well-characterized 17β-HSD-1 inhibitor. Bioluminescence imaging (BLI) was used to measure tumor growth non-invasively. At sacrifice, mice receiving E1 and treated with the FP4643 inhibitor showed a significant reduction in tumor growth by approximately 65% compared to mice receiving E1. Tumors exhibited metastatic spread to the peritoneum, to the lymphovascular space (LVI), and to the thoracic cavity. Metastatic spread and LVI invasion were both significantly reduced in the inhibitor-treated group. Transcriptional profiling of tumors indicated that FP4643 treatment reduced the oncogenic potential at the mRNA level. In conclusion, we show that 17β-HSD-1 inhibition represents a promising novel endocrine treatment for EC.

Releasing the brakes of tumor immunity with anti-PD-L1 and pushing its accelerator with L19-IL2 cures poorly immunogenic tumors when combined with radiotherapy

BACKGROUND

Poorly immunogenic tumors are hardly responsive to immunotherapies such as immune checkpoint blockade (ICB) and are, therefore, a therapeutic challenge. Combination with other immunotherapies and/or immunogenic therapies, such as radiotherapy (RT), could make these tumors more immune responsive. We have previously shown that the immunocytokine L19-IL2 combined with single-dose RT resulted in 75% tumor remission and a 20% curative abscopal effect in the T cell-inflamed C51 colon carcinoma model. This treatment schedule was associated with the upregulation of inhibitory immune checkpoint (IC) molecules on tumor-infiltrating T cells, leading to only tumor growth delay in the poorly immunogenic Lewis lung carcinoma (LLC) model.

METHODS

We aimed to trigger curative therapeutic responses in three tumor models (LLC, C51 and CT26) by "pushing the accelerator" of tumor immunity with L19-IL2 and/or "releasing the brakes" with ICB, such as antibodies directed against cytotoxic T lymphocyte associated protein 4 (CTLA-4), programmed death 1 (PD-1) or its ligand (PD-L1), combined with single-dose RT (10 Gy or 5 Gy). Primary tumor endpoint was defined as time to reach four times the size of tumor volume at start of treatment (4T×SV). Multivariate analysis of 4T×SV was performed using the Cox proportional hazards model comparing each treatment group with controls. Causal involvement of T and natural killer (NK) cells in the anti-tumor effect was assessed by in vivo depletion of T, NK or both cell populations. Immune profiling was performed using flow cytometry on single cell suspensions from spleens, bone marrow, tumors and blood.

RESULTS

Combining RT, anti-PD-L1 and L19-IL2 cured 38% of LLC tumors, which was both CD8+ T and NK cell dependent. LLC tumors were resistant to RT +anti-PD-L1 likely explained by the upregulation of other IC molecules and increased T regulatory cell tumor infiltration. RT+L19-IL2 outperformed RT+ICB in C51 tumors; effects were comparable in CT26 tumors. Triple combinations were not superior to RT+L19-IL2 in both these models.

CONCLUSIONS

This study demonstrated that combinatorial strategies rationally designed on biological effects can turn immunotherapy-resistant tumors into immunologically responsive tumors. This hypothesis is currently being tested in the international multicentric randomized phase 2 trial: ImmunoSABR (NCT03705403).

Mitochondrial Dysfunction Inhibits Hypoxia-Induced HIF-1α Stabilization and Expression of Its Downstream Targets

mtDNA variations often result in bioenergetic dysfunction inducing a metabolic switch toward glycolysis resulting in an unbalanced pH homeostasis. In hypoxic cells, expression of the tumor-associated carbonic anhydrase IX (CAIX) is enhanced to maintain cellular pH homeostasis. We hypothesized that cells with a dysfunctional oxidative phosphorylation machinery display elevated CAIX expression levels. Increased glycolysis was observed for cytoplasmic 143B mutant hybrid (m.3243A>G, >94.5%) cells (p < 0.05) and 143B mitochondrial DNA (mtDNA) depleted cells (p < 0.05). Upon hypoxia (0.2%, 16 h), genetic or pharmacological oxidative phosphorylation (OXPHOS) inhibition resulted in decreased CAIX (p < 0.05), vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1-alpha (HIF-1α) expression levels. Reactive oxygen species (ROS) and prolyl-hydroxylase 2 (PHD2) levels could not explain these observations. In vivo, tumor take (>500 mm³) took longer for mutant hybrid xenografts, but growth rates were comparable with control tumors upon establishment. Previously, it has been shown that HIF-1α is responsible for tumor establishment. In agreement, we found that HIF-1α expression levels and the pimonidazole-positive hypoxic fraction were reduced for the mutant hybrid xenografts. Our results demonstrate that OXPHOS dysfunction leads to a decreased HIF-1α stabilization and subsequently to a reduced expression of its downstream targets and hypoxic fraction in vivo. In contrast, hypoxia-inducible factor 2-alpha (HIF-2α) expression levels in these xenografts were enhanced. Inhibition of mitochondrial function is therefore an interesting approach to increase therapeutic efficacy in hypoxic tumors.

Evofosfamide sensitizes esophageal carcinomas to radiation without increasing normal tissue toxicity

BACKGROUND AND PURPOSE

Esophageal cancer incidence is increasing and is rarely curable. Hypoxic tumor areas cause resistance to conventional therapies, making them susceptible for treatment with hypoxia-activated prodrugs (HAPs). We investigated in vivo whether the HAP evofosfamide (TH-302) could increase the therapeutic ratio by sensitizing esophageal carcinomas to radiotherapy without increasing normal tissue toxicity.

MATERIALS AND METHODS

To assess therapeutic efficacy, growth of xenografted esophageal squamous cell (OE21) or adeno (OE19) carcinomas was monitored after treatment with TH-302 (50 mg/kg, QD5) and irradiation (sham or 10 Gy). Short- and long-term toxicity was assessed in a gut mucosa and lung fibrosis irradiation model, sensitive to acute and late radiation injury respectively. Mice were injected with TH-302 (50 mg/kg, QD5) and the abdominal area (sham, 8 or 10 Gy) or the upper part of the right lung (sham, 20 Gy) was irradiated. Damage to normal tissues was assessed 84 hours later by histology and blood plasma citrulline levels (gut) and for up to 1 year by non-invasive micro CT imaging (lung).

RESULTS

The combination treatment of TH-302 with radiotherapy resulted in significant tumor growth delay in OE19 (P = 0.02) and OE21 (P = 0.03) carcinomas, compared to radiotherapy only. Irradiation resulted in a dose-dependent decrease of crypt survival (P < 0.001), mucosal surface area (P < 0.01) and citrulline levels (P < 0.001) in both tumor and non-tumor bearing animals. On the long-term, irradiation increased CT density in the lung, indicating fibrosis, over time. TH-302 did not influence the radiation-induced short-term and long-term toxicity, confirmed by histological evaluation.

CONCLUSION

The combination of TH-302 and radiotherapy might be a promising approach to improve the therapeutic index for esophageal cancer patients.

The immunocytokine L19-IL2: An interplay between radiotherapy and long-lasting systemic anti-tumour immune responses

Recently, we have shown that the administration of the tumour-targeted antibody-based immunocytokine L19-IL2 after radiotherapy (RT) resulted in synergistic anti-tumour effect. Here we show that RT and L19-IL2 can activate a curative abscopal effect, with a long-lasting immunological memory. Ionizing radiation (single dose of 15Gy, 5 × 2Gy or 5 × 5Gy) was delivered to primary C51 colon tumour-bearing immunocompetent mice in combination with L19-IL2 and response of secondary non-irradiated C51 or CT26 colon tumours was evaluated. 15Gy + L19-IL2 triggered a curative (20%) abscopal effect, which was T cell dependent. Moreover, 10Gy + L19-IL2 treated and cured mice were re-injected after 150 days with C51 tumour cells and tumour uptake was assessed. Age-matched controls (matrigel injected mice treated with 10Gy + L19-IL2, mice cured after treatment with surgery + L19-IL2 and mice cured after high dose RT 40Gy + vehicle) were included. Several immunological parameters in blood, tumours, lymph nodes and spleens were investigated. Treatment with 10Gy + L19-IL2 resulted in long-lasting immunological memory, associated with CD44⁺CD127⁺ expression on circulating T cells. This combination treatment can induce long-lasting curative abscopal responses, and therefore it has also great potential for treatment of metastatic disease. Preclinical findings have led to the initiation of a phase I clinical trial (NCT02086721) in our institute investigating stereotactic ablative radiotherapy with L19-IL2 in patients with oligometastatic solid tumours.

Detection of Localized Hepatocellular Amino Acid Kinetics by using Mass Spectrometry Imaging of Stable Isotopes

Mass spectrometry imaging (MSI) simultaneously detects and identifies the spatial distribution of numerous molecules throughout tissues. Currently, MSI is limited to providing a static and ex vivo snapshot of highly dynamic systems in which molecules are constantly synthesized and consumed. Herein, we demonstrate an innovative MSI methodology to study dynamic molecular changes of amino acids within biological tissues by measuring the dilution and conversion of stable isotopes in a mouse model. We evaluate the method specifically on hepatocellular metabolism of the essential amino acid l-phenylalanine, associated with liver diseases. Crucially, the method reveals the localized dynamics of l-phenylalanine metabolism, including its in vivo hydroxylation to l-tyrosine and co-localization with other liver metabolites in a time course of samples from different animals. This method thus enables the dynamics of localized biochemical synthesis to be studied directly from biological tissues.

The Sulfamate Small Molecule CAIX Inhibitor S4 Modulates Doxorubicin Efficacy

Carbonic anhydrase IX (CAIX) is a tumor-specific protein that is upregulated during hypoxic conditions where it is involved in maintaining the pH balance. CAIX causes extracellular acidification, thereby limiting the uptake of weak basic chemotherapeutic agents, such as doxorubicin, and decreasing its efficacy. The aim of this study was to determine if doxorubicin efficacy can be increased when combined with the selective sulfamate CAIX inhibitor S4. The effect of S4 on doxorubicin efficacy was tested in vitro using cell viability assays with MDA-MB-231, FaDu, HT29 –CAIX high and HT29 –CAIX low cell lines. In addition, the efficacy of this combination therapy was investigated in tumor xenografts of the same cell lines. The addition of S4 in vitro increased the efficacy of doxorubicin in the MDA-MB-231 during hypoxic exposure (IC50 is 0.25 versus 0.14 µM, p = 0.0003). Similar results were observed for HT29—CAIX high with S4 during normoxia (IC50 is 0.20 versus 0.08 µM, p<0.0001) and in the HT29 –CAIX low cells (IC50 is 0.09 µM, p<0.0001). In vivo doxorubicin treatment was only effective in the MDA-MB-231 xenografts, but the efficacy of doxorubicin was decreased when combined with S4. In conclusion, the efficacy of doxorubicin treatment can be increased when combined with the selective sulfamate CAIX inhibitor S4 in vitro in certain cell lines. Nevertheless, in xenografts S4 did not enhance doxorubicin efficacy in the FaDu and HT29 tumor models and decreased doxorubicin efficacy in the MDA-MB-231 tumor model. These results stress the importance of better understanding the role of CAIX inhibitors in intratumoral pH regulation before combining them with standard treatment modalities, such as doxorubicin.

In vivo optical imaging of MMP2 immuno protein antibody: tumor uptake is associated with MMP2 activity

Matrix metalloproteinase-2 (MMP2) is important in tumorigenesis, angiogenesis and tumor invasion. In this study, we investigated if the Cy5-tagged small immuno protein targeting the catalytic domain of human MMP2 (aMMP2-SIP) detects MMP2 in tumors non-invasively. For this purpose, we generated MMP2 expressing (empty vector EV) and knock-down (KD) HT1080, U373 and U87 cells, which were injected subcutaneously in the lateral flank of NMRI-nu mice. Optical imaging (Optix MX2) performed at 0.5, 2, 4, 8, 24 and 48 hour post injection (h.p.i.) of Cy5 tagged aMMP2-SIP, indicated significantly lower tumor to background ratios at both 24 (P = 0.0090) and 48 h.p.i. (P < 0.0001) for the U87 MMP2-KD compared to control tumors. No differences were found for HT1080 and U373 models. U87 MMP2-KD tumors had significantly lower MMP2 activity (P < 0.0001) than EV tumors as determined by gelatin zymography in tumor sections and lysates, while no differences were observed between EV and MMP2-KD in HT1080 and U373. In line with these data, only U87 MMP2-KD tumors had a reduced tumor growth compared to control tumors (P = 0.0053). aMMP2-SIP uptake correlates with MMP2 activity and might therefore be a potential non-invasive imaging biomarker for the evaluation of MMP2 activity in tumors.

Complementary use of bioluminescence imaging and contrast-enhanced micro-computed tomography in an orthotopic brain tumor model

Small animal models are crucial to link molecular discoveries and implementation of clinically relevant therapeutics in oncology. Using these models requires noninvasive imaging techniques to monitor disease progression and therapy response. Micro-computed tomography (CT) is less studied for the in vivo monitoring of murine intracranial tumors and traditionally suffers from poor soft tissue contrast, whereas bioluminescence imaging (BLI) is known for its sensitivity but is not frequently employed for quantifying tumor volume. A widely used orthotopic glioblastoma multiforme (GBM) tumor model was applied in nude mice, and tumor growth was evaluated by BLI and contrast-enhanced microCT imaging. A strong correlation was observed between CT volume and BLI-integrated intensity (Pearson coefficient (r)  =  .85, p  =  .0002). Repeated contouring of contrast-enhanced microCT-delineated tumor volumes achieved an intraobserver average pairwise overlap ratio of 0.84 and an average tumor volume coefficient of variance of 0.11. MicroCT-delineated tumor size was found to correlate with tumor size obtained via histologic analysis (Pearson coefficient (r)  =  .88, p  =  .005). We conclude that BLI intensity can be used to derive tumor volume but that the use of both contrast-enhanced microCT and BLI provides complementary tumor growth information, which is particularly useful for modern small animal irradiation devices that make use of microCT and BLI for treatment planning, targeting, and monitoring.

Combination of radiotherapy with the immunocytokine L19-IL2: Additive effect in a NK cell dependent tumour model

BACKGROUND AND PURPOSE

Recently, we have shown that radiotherapy (RT) combined with the immunocytokine L19-IL2 can induce long-lasting antitumour effects, dependent on ED-B expression and infiltration of cytotoxic T cells. On the other hand, in certain tumours, IL2 treatment can trigger a natural killer cell (NK) immune response. The aim of this study is to investigate the therapeutic effect of our combination therapy in the ED-B positive F9 teratocarcinoma model, lacking MHCI expression and known to be dependent on NK immune responses.

MATERIAL AND METHODS

In syngeneic F9 tumour bearing 129/FvHsd mice tumour growth delay was evaluated after local tumour irradiation (10Gy) combined with systemic administration of L19-IL2. Immunological responses were investigated using flow cytometry.

RESULTS

Tumour growth delay of L19-IL2 can be further improved by a single dose of RT administered before immunotherapy, but not during immunotherapy. Furthermore, treatment of L19-IL2 favours a NK response and lacks cytotoxic T cell tumour infiltrating immune cells, which may be explained by the absence of MHCI expression.

CONCLUSION

An additive effect can be detected when the NK dependent F9 tumour model is treated with radiotherapy and L19-IL2 and therefore this combination could be useful in the absence of tumoural MHCI expression.

Radiotherapy combined with the immunocytokine L19-IL2 provides long-lasting antitumor effects

PURPOSE

Radiotherapy modifies the tumor microenvironment and causes the release of tumor antigens, which can enhance the effect of immunotherapy. L19 targets the extra domain B (ED-B) of fibronectin, a marker for tumor neoangiogenesis, and can be used as immunocytokine when coupled to IL2. We hypothesize that radiotherapy in combination with L19-IL2 provides an enhanced antitumor effect, which is dependent on ED-B expression.

EXPERIMENTAL DESIGN

Mice were injected with syngeneic C51 colon carcinoma, Lewis lung carcinoma (LLC), or 4T1 mammary carcinoma cells. Tumor growth delay, underlying immunologic parameters, and treatment toxicity were evaluated after single-dose local tumor irradiation and systemic administration of L19-IL2 or equimolar controls.

RESULTS

ED-B expression was high, intermediate, and low for C51, LLC, and 4T1, respectively. The combination therapy showed (i) a long-lasting synergistic effect for the C51 model with 75% of tumors being cured, (ii) an additive effect for the LLC model, and (iii) no effect for the 4T1 model. The combination treatment resulted in a significantly increased cytotoxic (CD8(+)) T-cell population for both C51 and LLC. Depletion of CD8(+) T cells abolished the benefit of the combination therapy.

CONCLUSIONS

These data provide the first evidence for an increased therapeutic potential by combining radiotherapy with L19-IL2 in ED-B-positive tumors. This new opportunity in cancer treatment will be investigated in a phase I clinical study for patients with an oligometastatic solid tumor (NCT02086721). An animation summarizing our results is available at https://www.youtube.com/watch?v=xHbwQuCTkRc.

A longitudinal evaluation of partial lung irradiation in mice by using a dedicated image-guided small animal irradiator

PURPOSE

In lung cancer radiation therapy, the dose constraints are determined mostly by healthy lung toxicity. Preclinical microirradiators are a new tool to evaluate treatment strategies closer to clinical irradiation devices. In this study, we quantified local changes in lung density symptomatic of radiation-induced lung fibrosis (RILF) after partial lung irradiation in mice by using a precision image-guided small animal irradiator integrated with micro-computed tomography (CT) imaging.

METHODS AND MATERIALS

C57BL/6 adult male mice (n=76) were divided into 6 groups: a control group (0 Gy) and groups irradiated with a single fraction of 4, 8, 12, 16, or 20 Gy using 5-mm circular parallel-opposed fields targeting the upper right lung. A Monte Carlo model of the small animal irradiator was used for dose calculations. Following irradiation, all mice were imaged at regular intervals over 39 weeks (10 time points total). Nonrigid deformation was used to register the initial micro-CT scan to all subsequent scans.

RESULTS

Significant differences could be observed between the 3 highest (>10 Gy) and 3 lowest irradiation (<10 Gy) dose levels. A mean difference of 120 ± 10 HU between the 0- and 20-Gy groups was observed at week 39. RILF was found to be spatially limited to the irradiated portion of the lung.

CONCLUSIONS

The data suggest that the severity of RILF in partial lung irradiation compared to large field irradiation in mice for the same dose is reduced, and therefore higher doses can be tolerated.

miR-210 as a marker of chronic hypoxia, but not a therapeutic target in prostate cancer

INTRODUCTION

Radiotherapy in combination with medical castration is the standard treatment for high-risk prostate cancer. Some relapses may be explained by the presence of radioresistant clones arising from hypoxic microenvironment. Since microRNAs (miR) are increased upon hypoxia, the aim of this study was to see whether miR-210 is a potential marker for hypoxia and/or a therapeutic target in prostate cancer.

METHODS

Human LNCaP, DU145 or PC3 prostate cancer cells were exposed to normoxia or hypoxia for several hours. Gene expression of miR-210, miR-373 and several hypoxia markers were analyzed by Taqman and SYBR green qRT-PCR, respectively. Clonogenic survival after LNA miR-210 inhibitor (78 nM) and concomitant irradiation were evaluated.

RESULTS

During anoxia, CAIX and VEGF expressions were dramatically increased. miR-210 expression increased during anoxia exposure, while basal miR-373 expression was low and remained stable upon anoxia. LNA miR-210 inhibitor decreased anoxic miR-210 expression by 90% and clonogenic survival under anoxia (p=0.01). However, no enhanced effect was observed when miR-210 inhibitor was combined with irradiation.

CONCLUSION

miR-210 could be an interesting marker of chronic hypoxia irrespective of the androgen dependency and should, therefore, be tested as a prognostic marker in high risk prostate cancer patients.

Specific inhibition of carbonic anhydrase IX activity enhances the in vivo therapeutic effect of tumor irradiation

BACKGROUND AND PURPOSE

Carbonic anhydrase (CA) IX expression is increased upon hypoxia and has been proposed as a therapeutic target since it has been associated with poor prognosis, tumor progression and pH regulation. The aim of this study was to evaluate the antitumor activity of a high CAIX-affinity indanesulfonamide (11c) combined with irradiation, compared with the general CA inhibitor acetazolamide (AZA).

MATERIAL AND METHODS

HT-29 carcinoma cells with or without (genetic knockdown, KD) CAIX expression were incubated with 11c/AZA under different oxygen levels and proliferation, apoptosis and radiosensitivity were evaluated. 11c/AZA was administered intravenously (1×/day; 5 days) to tumor-bearing mice and tumor irradiation (10 Gy) was performed at day 3 of the injection period. Tumor growth and potential treatment toxicity were monitored (3×/week).

RESULTS

Treatment with 11c/AZA alone resulted in tumor regression, which was further increased in CAIX expressing cells by combining 11c with irradiation. AZA demonstrated also an additional effect in the KD tumors when combined with irradiation. CAIX inhibition in vitro significantly reduced proliferation and increased apoptosis upon hypoxia exposure without affecting intrinsic radiosensitivity.

CONCLUSIONS

Specific inhibition of CAIX activity enhanced the effect of tumor irradiation and might, therefore, be an attractive strategy to improve overall cancer treatment.

Imaging of CA IX with fluorescent labelled sulfonamides distinguishes hypoxic and (re)-oxygenated cells in a xenograft tumour model

BACKGROUND AND PURPOSE

Carbonic anhydrase (CA) IX is suggested to be an endogenous marker of hypoxia. Fluorescent sulfonamides with a high affinity for CA IX (CAI) have been developed and shown to bind to cells only when CA IX protein was expressed and while cells were hypoxic. The aim of this study was to investigate the in vivo CAI binding properties in a xenograft tumour model using fluorescent imaging.

MATERIALS AND METHODS

NMRI-nu mice subcutaneously transplanted with HT-29 colorectal tumours were treated with 7% oxygen or with nicotinamide and carbogen and were compared with control animals. CAI accumulation was monitored by non-invasive fluorescent imaging.

RESULTS

Specific CAI accumulation could be observed in delineated tumour areas as compared with a non-sulfonamide analogue (P<0.01). Administration of nicotinamide and carbogen, decreasing acute and chronic hypoxia, respectively, prevented CAI accumulation (P<0.05). When treated with 7% oxygen breathing, a 3-fold higher CAI accumulation (P<0.01) was observed. Furthermore, the bound CAI fraction was rapidly reduced upon tumour reoxygenation (P<0.01).

CONCLUSIONS

Our in vivo imaging results confirm previous in vitro data demonstrating that CAI binding and retention require exposure to hypoxia. Fluorescent labelled sulfonamides provide a powerful tool to visualize hypoxia response. An important step is made towards clinical applicability, indicating the potential of patient selection for CA IX-directed therapies.

Development and evaluation of a cetuximab-based imaging probe to target EGFR and EGFRvIII

BACKGROUND AND PURPOSE

The epidermal growth factor receptor (EGFR) is overexpressed in a significant percentage of human malignancies and its expression is associated with tumour aggressiveness and treatment resistance. The monoclonal antibody cetuximab (IMC-C225) blocks the ligand-binding domain of EGFR with high affinity, preventing downstream signalling resulting in tumour growth inhibition. We developed and characterized a novel imaging probe using Oregon Green 488 labelled cetuximab to evaluate its usage as an imaging agent to target EGFR.

MATERIALS AND METHODS

Cells with varying expression levels of EGFR or a mutant form of EGFR, called EGFRvIII, were used for in vitro validation. The in vivo binding of labelled cetuximab to EGFR was also assessed ex vivo on tumour material.

RESULTS

The development of Oregon Green 488 labelled cetuximab was successful, demonstrating binding to both EGFR and EGFRvIII in vitro. Accumulation was also found in vivo, which was confirmed by histopathology using anti-EGFR antibodies. However, significant mismatch highlights differences between drug delivery in vivo, and cell expression levels of EGFR.

CONCLUSIONS

The monoclonal antibody cetuximab represents a promising probe to evaluate the biologic and pharmacokinetic effects of in vivo cetuximab binding to EGFR. It not only visualizes the presence of the wild type EGFR, but also the presence of the mutant EGFRvIII.