Monitoring antivascular therapy in head and neck cancer xenografts using contrast-enhanced MR and US imaging

Pattern recognition of microcirculation with super-resolution ultrasound imaging provides markers for early tumor response to anti-angiogenic therapy

Rationale: Cancer treatment outcome is traditionally evaluated by tumor volume change in clinics, while tumor microvascular heterogeneity reflecting tumor response has not been fully explored due to technical limitations. Methods: We introduce a new paradigm in super-resolution ultrasound imaging, termed pattern recognition of microcirculation (PARM), which identifies both hemodynamic and morphological patterns of tumor microcirculation hidden in spatio-temporal space trajectories of microbubbles. Results: PARM demonstrates the ability to distinguish different local blood flow velocities separated by a distance of 24 μm. Compared with traditional vascular parameters, PARM-derived heterogeneity parameters prove to be more sensitive to microvascular changes following anti-angiogenic therapy. Particularly, PARM-identified "sentinel" microvasculature, exhibiting evident structural changes as early as 24 hours after treatment initiation, correlates significantly with subsequent tumor volume changes (|r| > 0.9, P < 0.05). This provides prognostic insight into tumor response much earlier than clinical criteria. Conclusions: The ability of PARM to noninvasively quantify tumor vascular heterogeneity at the microvascular level may shed new light on early-stage assessment of cancer therapy.

In vivo noninvasive preclinical tumor hypoxia imaging methods: a review

Tumors exhibit areas of decreased oxygenation due to malformed blood vessels. This low oxygen concentration decreases the effectiveness of radiation therapy, and the resulting poor perfusion can prevent drugs from reaching areas of the tumor. Tumor hypoxia is associated with poorer prognosis and disease progression, and is therefore of interest to preclinical researchers. Although there are multiple different ways to measure tumor hypoxia and related factors, there is no standard for quantifying spatial and temporal tumor hypoxia distributions in preclinical research or in the clinic. This review compares imaging methods utilized for the purpose of assessing spatio-temporal patterns of hypoxia in the preclinical setting. Imaging methods provide varying levels of spatial and temporal resolution regarding different aspects of hypoxia, and with varying advantages and disadvantages. The choice of modality requires consideration of the specific experimental model, the nature of the required characterization and the availability of complementary modalities as well as immunohistochemistry.

Photoacoustic and Magnetic Resonance Imaging of Hybrid Manganese Dioxide-Coated Ultra-small NaGdF4 Nanoparticles for Spatiotemporal Modulation of Hypoxia in Head and Neck Cancer

Simple Summary

Tumor hypoxia is a documented negative prognostic factor that contributes to treatment resistance in head and neck cancer. In the present study, we use non-invasive magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) to evaluate the ability of ultra-small manganese dioxide coated nanoparticles to modulate tumor oxygenation in vitro and in vivo. Our results highlight the utility of MRI and PAI in mapping tumor hypoxia and nanoparticle delivery and demonstrate the potential of image-guided nanodelivery in alleviating tumor hypoxia in head and neck cancer.

Abstract

There is widespread interest in developing agents to modify tumor hypoxia in head and neck squamous cell carcinomas (HNSCC). Here, we report on the synthesis, characterization, and potential utility of ultra-small NaYF₄:Nd³⁺/NaGdF₄ nanocrystals coated with manganese dioxide (usNP-MnO₂) for spatiotemporal modulation of hypoxia in HNSCC. Using a dual modality imaging approach, we first visualized the release of Mn²⁺ using T1-weighted magnetic resonance imaging (MRI) and modulation of oxygen saturation (%sO₂) using photoacoustic imaging (PAI) in vascular channel phantoms. Combined MRI and PAI performed in patient-derived HNSCC xenografts following local and systemic delivery of the hybrid nanoparticles enabled mapping of intratumoral nanoparticle accumulation (based on T1 contrast enhancement) and improvement in tumor oxygenation (increased %sO₂) within the tumor microenvironment. Our results demonstrate the potential of hybrid nanoparticles for the modulation of tumor hypoxia in head and neck cancer. Our findings also highlight the potential of combined MRI-PAI for simultaneous mapping nanoparticle delivery and oxygenation changes in tumors. Such imaging methods could be valuable in the precise selection of patients that are likely to benefit from hypoxia-modifying nanotherapies.

Power Doppler ultrasound and contrast-enhanced ultrasound demonstrate non-invasive tumour vascular response to anti-vascular therapy in canine cancer patients

Combretastatin A4-phosphate (CA4P) is an anti-vascular agent which selectively shuts down blood supply in tumours, resulting in extensive tumour necrosis. The aim of this study was to assess in vivo, non-invasive ultrasound techniques for the early evaluation of tumour perfusion following CA4P treatment of spontaneous tumours. Eight dogs that bore spontaneous tumours were enrolled and were subsequently treated with a single dose of intravenous CA4P. Perfusion of tumours was evaluated by power Doppler ultrasound (PDUS) pre-treatment (0 h), during the injection (10 min, 20 min, 30 min) and after CA4P infusion (24 and 72 h). Vascularity index (VI) of the tumour tissue was quantitatively analysed and accuracy was verified by correlation analysis with the results of immunohistochemical evaluation of microvessel density (MVD). Central and peripheral perfusion was evaluated by contrast-enhanced ultrasound (CEUS) pre-treatment and at 72 h post-treatment. Post-treatment, PDUS demonstrated a significant decrease in VI within 10 min of CA4P infusion. CEUS parameters demonstrated a significant decrease in blood velocity and volume in the central aspect of the tumour. Histology revealed a 4.4-fold reduction (p < 0.001, 95% CI [2.2,9.4]) in MVD and a 4.1-fold increase (p = 0.003, 95% CI [1.4,11.8]) in necrotic tumour tissue. A strong correlation between PDUS results and immunohistochemical results was found (Pearson R² = 0.957, p < 0.001). Furthermore, the findings of PDUS were supported by the objective results of the CEUS analyses. These data suggest a role for ultrasound in real-time, non-invasive monitoring of tumour vascular response as an early indicator of CA4P treatment efficacy.

Multimodal imaging guided preclinical trials of vascular targeting in prostate cancer

The high mortality rate associated with castration-resistant prostate cancer (CRPC) underscores the need for improving therapeutic options for this patient population. The purpose of this study was to examine the potential of vascular targeting in prostate cancer. Experimental studies were carried out in subcutaneous and orthotopic Myc-CaP prostate tumors implanted into male FVB mice to examine the efficacy of a novel microtubule targeted vascular disrupting agent (VDA), EPC2407 (Crolibulin™). A non-invasive multimodality imaging approach based on magnetic resonance imaging (MRI), bioluminescence imaging (BLI), and ultrasound (US) was utilized to guide preclinical trial design and monitor tumor response to therapy. Imaging results were correlated with histopathologic assessment, tumor growth and survival analysis. Contrast-enhanced MRI revealed potent antivascular activity of EPC2407 against subcutaneous and orthotopic Myc-CaP tumors. Longitudinal BLI of Myc-CaP tumors expressing luciferase under the androgen response element (Myc-CaP/ARE-luc) revealed changes in AR signaling and reduction in intratumoral delivery of luciferin substrate following castration suggestive of reduced blood flow. This reduction in blood flow was validated by US and MRI. Combination treatment resulted in sustained vascular suppression, inhibition of tumor regrowth and conferred a survival benefit in both models. These results demonstrate the therapeutic potential of vascular targeting in combination with androgen deprivation against prostate cancer.

Nanotherapy silencing the interleukin-8 gene produces regression of prostate cancer by inhibition of angiogenesis

Interleukin-8 (IL-8) is a pro-angiogenic cytokine associated with aggressive prostate cancer (CaP). We detected high levels of IL-8 in sera from patients with CaP compared with healthy controls and patients with benign prostatic hypertrophy. This study examines the role of IL-8 in the pathogenesis of metastatic prostate cancer. We developed a biocompatible, cationic polylactide (CPLA) nanocarrier to complex with and efficiently deliver IL-8 small interfering RNA (siRNA) to CaP cells in vitro and in vivo. CPLA IL-8 siRNA nanocomplexes (nanoplexes) protect siRNA from rapid degradation, are non-toxic, have a prolonged lifetime in circulation, and their net positive charge facilitates penetration of cell membranes and subsequent intracellular trafficking. Administration of CPLA IL-8 siRNA nanoplexes to immunodeficient mice bearing human CaP tumours produced significant antitumour activities with no adverse effects. Systemic (intravenous) or local intra-tumour administration of IL-8 siRNA nanoplexes resulted in significant inhibition of CaP growth. Magnetic resonance imaging and ultrasonography of experimental animals demonstrated reduction of tumour perfusion in vivo following nanoplex treatment. Staining of tumour sections for CD31 confirmed significant damage to tumour neovasculature after nanoplex therapy. These studies demonstrate the efficacy of IL-8 siRNA nanotherapy for advanced, treatment-resistant human CaP.

Photoacoustic monitoring of tumor and normal tissue response to radiation

Hypoxia is a recognized characteristic of tumors that influences efficacy of radiotherapy (RT). Photoacoustic imaging (PAI) is a relatively new imaging technique that exploits the optical characteristics of hemoglobin to provide information on tissue oxygenation. In the present study, PAI based measures of tumor oxygen saturation (%sO2) were compared to oxygen-enhanced magnetic resonance imaging (MRI) measurements of longitudinal relaxation rate (R1 = 1/T1) and ex-vivo histology in patient derived xenograft (PDX) models of head and neck cancer. PAI was utilized to assess early changes (24 h) in %sO2 following RT and chemoRT (CRT) and to assess changes in salivary gland hemodynamics following radiation. A significant increase in tumor %sO2 and R1 was observed following oxygen inhalation. Good spatial correlation was observed between PAI, MRI and histology. An early increase in %sO2 after RT and CRT detected by PAI was associated with significant tumor growth inhibition. Twenty four hours after RT, PAI also detected loss of hemodynamic response to gustatory stimulation in murine salivary gland tissue suggestive of radiation-induced vascular damage. Our observations illustrate the utility of PAI in detecting tumor and normal tissue hemodynamic response to radiation in head and neck cancers.

A FAK scaffold inhibitor disrupts FAK and VEGFR-3 signaling and blocks melanoma growth by targeting both tumor and endothelial cells

Melanoma has the highest mortality rate of all skin cancers and a major cause of treatment failure is drug resistance. Tumors heterogeneity requires novel therapeutic strategies and new drugs targeting multiple pathways. One of the new approaches is targeting the scaffolding function of tumor related proteins such as focal adhesion kinase (FAK). FAK is overexpressed in most solid tumors and is involved in multiple protein-protein interactions critical for tumor cell survival, tumor neovascularization, progression and metastasis. In this study, we investigated the anticancer activity of the FAK scaffold inhibitor C4, targeted to the FAK-VEGFR-3 complex, against melanomas. We compared C4 inhibitory effects in BRAF mutant vs BRAF wild type melanomas. C4 effectively caused melanoma tumor regression in vivo, when administered alone and sensitized tumors to chemotherapy. The most dramatic effect of C4 was related to reduction of vasculature of both BRAF wild type and V600E mutant xenograft tumors. The in vivo effects of C4 were assessed in xenograft models using non-invasive multimodality imaging in conjunction with histologic and molecular biology methods. C4 inhibited cell viability, adhesion and motility of melanoma and endothelial cells, specifically blocked phosphorylation of VEGFR-3 and FAK and disrupted their complexes. Specificity of in vivo effects for C4 were confirmed by a decrease in tumor FAK and VEGFR-3 phosphorylation, reduction of vasculogenesis and reduced blood flow. Our collective observations provide evidence that a small molecule inhibitor targeted to the FAK protein-protein interaction site successfully inhibits melanoma growth through dual targeting of tumor and endothelial cells and is effective against both BRAF wild type and mutant melanomas.

Early detection of antiangiogenic treatment responses in a mouse xenograft tumor model using quantitative perfusion MRI

Angiogenesis plays a major role in tumor growth and metastasis, with tumor perfusion regarded as a marker for angiogenesis. To evaluate antiangiogenic treatment response in vivo, we investigated arterial spin labeling (ASL) magnetic resonance imaging (MRI) to measure tumor perfusion quantitatively. Chronic and 24-h acute treatment responses to bevacizumab were assessed by ASL and dynamic-contrast-enhanced (DCE) MRI in the A498 xenograft mouse model. After the MRI, tumor vasculature was assessed by CD34 staining. After 39 days of chronic treatment, tumor perfusion decreased to 44.8 ± 16.1 mL/100 g/min (P < 0.05), compared to 92.6 ± 42.9 mL/100 g/min in the control group. In the acute treatment study, tumor perfusion in the treated group decreased from 107.2 ± 32.7 to 73.7 ± 27.8 mL/100 g/min (P < 0.01; two-way analysis of variance), as well as compared with control group post dosing. A significant reduction in vessel density and vessel size was observed after the chronic treatment, while only vessel size was reduced 24 h after acute treatment. The tumor perfusion correlated with vessel size (r = 0.66; P < 0.005) after chronic, but not after acute treatment. The results from DCE-MRI also detected a significant change between treated and control groups in both chronic and acute treatment studies, but not between 0 and 24 h in the acute treatment group. These results indicate that tumor perfusion measured by MRI can detect early vascular responses to antiangiogenic treatment. With its noninvasive and quantitative nature, ASL MRI would be valuable for longitudinal assessment of tumor perfusion and in translation from animal models to human.

Early quantification of the therapeutic efficacy of the vascular disrupting agent, CKD-516, using dynamic contrast-enhanced ultrasonography in rabbit VX2 liver tumors

Purpose:

To evaluate the usefulness of dynamic contrast-enhanced ultrasonography (DCE-US) in the early quantification of hemodynamic change following administration of the vascular disrupting agent (VDA) CKD-516 using a rabbit VX2 liver tumor model.

Methods:

This study was approved by our institutional animal care and use committee. Eight VX2 liver-tumor-bearing rabbits were treated with intravenous CKD-516, and all underwent DCE-US using SonoVue before and again 2, 4, 6, and 24 hours following their treatment. The tumor perfusion parameters were obtained from the time-intensity curve of the DCE-US data. Repeated measures analysis of variance was performed to assess any significant change in tumor perfusion over time. Relative changes in the DCE-US parameters between the baseline and follow-up assessments were correlated with the relative changes in tumor size over the course of seven days using Pearson correlation.

Results:

CKD-516 treatment resulted in significant changes in the DCE-US parameters, including the peak intensity, total area under the time-intensity curve (AUC_total), and AUC during wash-out (AUC_out) over time (P<0.05). Pairwise comparison tests revealed that the AUC_total and AUC during wash-in (AUC_in) seen on the two-hour follow-up were significantly lower than the baseline values (P<0.05). However, none of early changes in the DCE-US parameters until 24-hour follow-up showed a significant correlation with the relative changes in tumor size during seven days after CKD-516 treatment.

Conclusion:

Our results suggest that a novel VDA (CKD-516) can cause disruption of tumor perfusion as early as two hours after treatment and that the therapeutic effect of CKD-516 treatment can be effectively quantified using DCE-US.

Vascular priming enhances chemotherapeutic efficacy against head and neck cancer

PURPOSE

The need to improve chemotherapeutic efficacy against head and neck squamous cell carcinomas (HNSCC) is well recognized. In this study, we investigated the potential of targeting the established tumor vasculature in combination with chemotherapy in head and neck cancer.

METHODS

Experimental studies were carried out in multiple human HNSCC xenograft models to examine the activity of the vascular disrupting agent (VDA) 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in combination with chemotherapy. Multimodality imaging (magnetic resonance imaging, bioluminescence) in conjunction with drug delivery assessment (fluorescence microscopy), histopathology and microarray analysis was performed to characterize tumor response to therapy. Long-term treatment outcome was assessed using clinically-relevant end points of efficacy.

RESULTS

Pretreatment of tumors with VDA prior to administration of chemotherapy increased intratumoral drug delivery and treatment efficacy. Enhancement of therapeutic efficacy was dependent on the dose and duration of VDA treatment but was independent of the chemotherapeutic agent evaluated. Combination treatment resulted in increased tumor cell kill and improvement in progression-free survival and overall survival in both ectopic and orthotopic HNSCC models.

CONCLUSION

Our results show that preconditioning of the tumor microenvironment with an antivascular agent primes the tumor vasculature and results in enhancement of chemotherapeutic delivery and efficacy in vivo. Further investigation into the activity of antivascular agents in combination with chemotherapy against HNSCC is warranted.

Lysyl oxidase-like-2 promotes tumour angiogenesis and is a potential therapeutic target in angiogenic tumours

Lysyl oxidase-like 2 (LOXL2), a secreted enzyme that catalyzes the cross-linking of collagen, plays an essential role in developmental angiogenesis. We found that administration of the LOXL2-neutralizing antibody AB0023 inhibited bFGF-induced angiogenesis in Matrigel plug assays and suppressed recruitment of angiogenesis promoting bone marrow cells. Small hairpin RNA-mediated inhibition of LOXL2 expression or inhibition of LOXL2 using AB0023 reduced the migration and network-forming ability of endothelial cells, suggesting that the inhibition of angiogenesis results from a direct effect on endothelial cells. To examine the effects of AB0023 on tumour angiogenesis, AB0023 was administered to mice bearing tumours derived from SKOV-3 ovarian carcinoma or Lewis lung carcinoma (LLC) cells. AB0023 treatment significantly reduced the microvascular density in these tumours but did not inhibit tumour growth. However, treatment of mice bearing SKOV-3-derived tumours with AB0023 also promoted increased coverage of tumour vessels with pericytes and reduced tumour hypoxia, providing evidence that anti-LOXL2 therapy results in the normalization of tumour blood vessels. In agreement with these data, treatment of mice bearing LLC-derived tumours with AB0023 improved the perfusion of the tumour-associated vessels as determined by ultrasonography. Improved perfusion and normalization of tumour vessels after treatment with anti-angiogenic agents were previously found to improve the delivery of chemotherapeutic agents into tumours and to result in an enhancement of chemotherapeutic efficiency. Indeed, treatment with AB0023 significantly enhanced the anti-tumourigenic effects of taxol. Our results suggest that inhibition of LOXL2 may prove beneficial for the treatment of angiogenic tumours.

Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) in Preclinical Studies of Antivascular Treatments

Antivascular treatments can either be antiangiogenic or targeting established tumour vasculature. These treatments affect the tumour microvasculature and microenvironment but may not change clinical measures like tumour volume and growth. In research on antivascular treatments, information on the tumour vasculature is therefore essential. Preclinical research is often used for optimization of antivascular drugs alone or in combined treatments. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is an in vivo imaging method providing vascular information, which has become an important tool in both preclinical and clinical research. This review discusses common DCE-MRI imaging protocols and analysis methods and provides an overview of preclinical research on antivascular treatments utilizing DCE-MRI.