Magnetic resonance imaging guidance for laser photothermal therapy

Synergistic interventional photothermal therapy and immunotherapy using an iron oxide nanoplatform for the treatment of pancreatic cancer

Pancreatic cancer (PC) is the most lethal malignancy due to its high metastatic ability and poor drug permeability. Here, a synergized interventional photothermal-immunotherapy strategy was developed with imaging guidance and temperature monitoring by magnetic resonance imaging (MRI) technique, for the local treatment of metastatic PC. A tumor microenvironment (TME)-responsive nanoplatform was fabricated via coating of DSPE-PEG and indocyanine green (ICG) onto imiquimod (IMQ) loaded amorphous iron oxide nanoparticles (IONs). This unique nanoplatform, IMQ@IONs/ICG, served as a contrast agent for MRI, a drug delivery vehicle for IMQ and ICG, and a catalyst for TME modulation. The biodegradable IMQ@IONs/ICG was also non-toxic, and improved the penetration of the loaded drugs in PC to maximize thermal ablation of the tumor and minimize damage to the surrounding healthy tissue. For the treatment of aggressive, metastatic Panc02-H7 pancreatic tumors in mice, ION-assisted MRI was employed to guide the administration of interventional photothermal therapy (IPTT) and monitor the temperature distribution in target tumor and surrounding tissue during treatment. The local IPTT treatment induced in situ immunogenic cell death (ICD), and, in combination with released IMQ, triggered a strong antitumor immunity, leading to decreased metastases and increased CD8+ in spleen and tumors. With precise local treatment and monitoring, treated primary tumors were completely eradicated, mesentery metastases were dramatically reduced, and the survival time was significantly prolonged, without damage to normal tissue and systemic autoimmunity. Overall, this synergistic strategy represents a promising approach to treat PC with significant potential for clinical applications. STATEMENT OF SIGNIFICANCE: Pancreatic cancer (PC) is one of the most lethal malignancies because it is non-permeable to drugs and highly metastatic. In this study, we designed a tumor microenvironment-responsive amorphous iron oxide nanoplatform (ION) to co-deliver photothermal agent (ICG) and toll-like-receptor-7 agonist (IMQ). This biodegradable nanoplatform IMQ@IONs/ICG improved the penetration of the loaded drugs in pancreatic tumor. With MR imaging guidance and temperature monitoring, the precise interventional photothermal therapy on mouse Panc02-H7 orthotopic tumors releases tumor antigens to initiate tumor-special immune responses, amplified by the released IMQ. Our results demonstrate that IMQ@IONs/ICG overcomes the obstacle of drug delivery to pancreatic tumors, and when combined with photothermal therapy, induces a systemic antitumor immunity to control metastatic tumors.

Multi-Wavelength Photo-Magnetic Imaging System for Photothermal Therapy Guidance

BACKGROUND AND OBJECTIVES

In photothermal therapy, cancerous tissue is treated by the heat generated from absorbed light energy. For effective photothermal therapy, the parameters affecting the induced temperature should be determined before the treatment by modeling the increase in temperature via numerical simulations. However, accurate simulations can only be achieved when utilizing the accurate optical, thermal, and physiological properties of the treated tissue. Here, we propose a multi-wavelength photo-magnetic imaging (PMI) technique that provides quantitative and spatially resolved tissue optical absorption maps at any wavelength within the near-infrared (NIR) window to assist accurate photothermal therapy planning.

STUDY DESIGN/MATERIALS AND METHODS

The study was conducted using our recently developed multi-wavelength PMI system, which operates at four laser wavelengths (760, 808, 860, and 980 nm). An agar tissue-simulating phantom containing water, lipid, and ink was illuminated using these wavelengths, and the slight internal laser-induced temperature rise was measured using magnetic resonance thermometry (MRT). The phantom optical absorption was recovered at the used wavelengths using our dedicated PMI image reconstruction algorithm. These absorption maps were then used to resolve the concentration of the tissue chromophores, and thus deduce its optical absorption spectrum in the NIR region based on the Beer-Lambert law.

RESULTS

The optical absorption of the phantom was successfully recovered at the used four wavelengths with an average error of ~1.9%. The recovered absorption coefficient was then used to simulate temperature variations inside the phantom. A comparison between the modeled temperature maps and the MRT measured ones showed that these maps are in a good agreement with an average pseudo R2 statistic of 0.992. These absorption values were used to successfully recover the concentration of the used chromophores. Finally, these concentrations are used to accurately calculate the total absorption spectrum of the phantom in the NIR spectral window with an average error as low as ~2.3%.

CONCLUSIONS

Multi-wavelength PMI demonstrated a great ability to assess the distribution of tissue chromophores, thus providing its total absorption at any wavelength within the NIR spectral range. Therefore, applications of photothermal therapy applied at NIR wavelengths can benefit from the absorption spectrum recovered by PMI to determine important parameters such as laser power as well as the laser exposure time needed to attain a specific increase in temperature prior to treatment. Lasers Surg. Med. 00:00-00, 2020. © 2020 Wiley Periodicals LLC.

Determination of temperature distribution in tissue for interstitial cancer photothermal therapy

BACKGROUND

Temperature increase in tumour tissue during photothermal therapy (PTT) is a significant factor in determining the outcomes of the treatment. Therefore, controlling and optimising temperature distribution in target tissue is crucial for PTT. In this study, we developed a unique ex vivo device to study the temperature distribution during PTT to be used as a guide for the desired photothermal effects for cancer treatment.

METHODS

Bovine liver tissue buried inside agarose gel served as a phantom tumour surrounded by normal tissue. A thermostatic incubator was used to simulate tissue environment in live animals. The temperature distributions were measured by thermocouples with needle probes at different locations inside the target tissue, during laser irradiation using an 805-nm laser.

RESULTS

The results obtained using the ex vivo device were verified by comparing the tissue temperature directly measured in animal tumours irradiated under the same conditions. With this model, the spatial distribution of temperature in target tissue can be monitored in real time. A two-dimensional temperature distribution in target tissue allows us to establish the correlations among laser parameters, temperature distribution and tumour size. In addition, the optimal temperature range for tumour destruction and immunological stimulation was determined using metastatic rat mammary tumour model.

CONCLUSION

The device and method developed in this study can provide guidance for choosing the appropriate treatment parameters for optimal photothermal effects, particularly when combined with immunotherapy, for cancer treatment.

Shape-based reconstruction for transrectal diffuse optical tomography monitoring of photothermal focal therapy of prostate cancer: simulation studies

We develop and demonstrate a simple shape-based approach for diffuse optical tomographic reconstruction of coagulative lesions generated during interstitial photothermal therapy (PTT) of the prostate. The shape-based reconstruction assumes a simple ellipsoid shape, matching the general dimensions of a cylindrical diffusing fiber used for light delivery in current clinical studies of PTT in focal prostate cancer. The specific requirement is to accurately define the border between the photothermal lesion and native tissue as the photothermal lesion grows, with an accuracy of ? 1 ?? mm , so treatment can be terminated before there is damage to the rectal wall. To demonstrate the feasibility of the shape-based diffuse optical tomography reconstruction, simulated data were generated based on forward calculations in known geometries that include the prostate, rectum, and lesions of varying dimensions. The only source of optical contrast between the lesion and prostate was increased scattering in the lesion, as is typically observed with coagulation. With noise added to these forward calculations, lesion dimensions were reconstructed using the shape-based method. This approach for reconstruction is shown to be feasible and sufficiently accurate for lesions that are within 4 mm from the rectal wall. The method was also robust for irregularly shaped lesions.

Interstitial photoacoustic sensor for the measurement of tissue temperature during interstitial laser phototherapy

Photothermal therapy is an effective means to induce tumor cell death, since tumor tissue is more sensitive to temperature increases than normal tissue. Biological responses depend on tissue temperature; target tissue temperature needs to be precisely measured and controlled to achieve desired thermal effects. In this work, a unique photoacoustic (PA) sensor is proposed for temperature measurement during interstitial laser phototherapy. A continuous-wave laser light and a pulsed laser light, for photothermal irradiation and photoacoustic temperature measurement, respectively, were delivered to the target tissue through a fiber coupler. During laser irradiation, the PA amplitude was measured. The Grüneisen parameter and the bioheat equation were used to determine the temperature in strategic positions in the target tissue. Our results demonstrate that the interstitial PA amplitude is a linear function of temperature in the range of 22 to 55 °C, as confirmed by thermocouple measurement. Furthermore, by choosing appropriate laser parameters, the maximum temperature surrounding the active diffuse fiber tip in tissue can be controlled in the range of 41 to 55 °C. Thus, this sensor could potentially be used for fast, accurate, and convenient three-dimensional temperature measurement, and for real-time feedback and control of interstitial laser phototherapy in cancer treatment.

InCVAX--a novel strategy for treatment of late-stage, metastatic cancers through photoimmunotherapy induced tumor-specific immunity

A novel, promising potential cancer vaccine strategy was proposed to use a two-injection procedure for solid tumors to prompt the immune system to identify and systemically eliminate primary and metastatic cancers. The two-injection procedure consists of local photothermal application on a selected tumor intended to liberate whole cell tumor antigens, followed by a local injection of an immunoadjuvant that consists of a semi-synthetic functionalized glucosamine polymer, N-dihydro-galacto-chitosan (GC), which is intended to activate antigen presenting cells and facilitate an increased uptake of tumor antigens. This strategy is thus proposed as an in situ autologous cancer vaccine (inCVAX) that may activate antigen presenting cells and expose them to tumor antigens in situ, with the intention of inducing a systemic tumor specific T-cell response. Here, the development of inCVAX for the treatment of metastatic cancers in the past decades is systematically reviewed. The antitumor immune responses of local photothermal treatment and immunological stimulation with GC are also discussed. This treatment approach is also commonly referred to as laser immunotherapy (LIT).

Magnetic Prussian blue nanoparticles for targeted photothermal therapy under magnetic resonance imaging guidance

This paper reported a core-shell nanotheranostic agent by growing Prussian blue (PB) nanoshells of 3-6 nm around superparamagnetic Fe3O4 nanocores for targeted photothermal therapy of cancer under magnetic resonance imaging (MRI) guidance. Both in vitro and in vivo experiments proved that the Fe3O4@PB core-shell nanoparticles showed significant contrast enhancement for T2-weighted MRI with the relaxivity value of 58.9 mM(-1)·s(-1). Simultaneously, the composite nanoparticles exhibited a high photothermal effect under irradiation of a near-infrared laser due to the strong absorption of PB nanoshells, which led to more than 80% death of HeLa cells with only 0.016 mg·mL(-1) of the nanoparticles with the aid of the magnetic targeting effect. Using tumor-bearing nude mice as the model, the near-infrared laser light ablated the tumor effectively in the presence of the Fe3O4@PB nanoparticles and the tumor growth inhibition was evaluated to be 87.2%. Capabilities of MRI, magnetic targeting, and photothermal therapy were thus integrated into a single agent to allow efficient MRI-guided targeted photothermal therapy. Most importantly, both PB and Fe3O4 nanoparticles were already clinically approved drugs, so the Fe3O4@PB nanoparticles as a theranostic nanomedicine would be particularly promising for clinical applications in the human body due to the reliable biosafety.

MRI-guided monitoring of thermal dose and targeted drug delivery for cancer therapy

Application of localized hyperthermia treatment for solid tumor therapy is under active clinical investigation. The success of this treatment methodology, whether for tumor ablation or drug delivery, requires accurate target localization and real-time temperature mapping of the targeted region. Magnetic Resonance Imaging (MRI) can monitor temperature elevations in tissues in real-time during tumor therapy. MRI can also be applied in concert with methods such as High Intensity Focused Ultrasound (HIFU) to enable image-guided drug delivery (IGDD) from temperature sensitive nanocarriers, by exploiting not only its anatomic resolution, but its ability to detect and measure drug release using markers co-loaded with drugs within the nanocarriers. We review this rapidly emerging technology, providing an overview of MRI-guided tissue thermal dose monitoring for HIFU and Laser therapy, its role in targeted drug delivery and its future potential for clinical translation.

Assessment of thermal effects of interstitial laser phototherapy on mammary tumors using proton resonance frequency method

Laser immunotherapy (LIT) uses a synergistic approach to treat cancer systemically through local laser irradiation and immunological stimulation. Currently, LIT utilizes dye-assisted noninvasive laser irradiation to achieve selective photothermal interaction. However, LIT faces difficulties treating deeper tumors or tumors with heavily pigmented overlying skin. To circumvent these barriers, we use interstitial laser irradiation to induce the desired photothermal effects. The purpose of this study is to analyze the thermal effects of interstitial irradiation using proton resonance frequency (PRF). An 805-nm near-infrared laser with an interstitial cylindrical diffuser was used to treat rat mammary tumors. Different power settings (1.0, 1.25, and 1.5 W) were applied with an irradiation duration of 10 min. The temperature distributions of the treated tumors were measured by a 7 T magnetic resonance imager using PRF. We found that temperature distributions in tissue depended on both laser power and time settings, and that variance in tissue composition has a major influence in temperature elevation. The temperature elevations measured during interstitial laser irradiation by PRF and thermocouple were consistent, with some variations due to tissue composition and the positioning of the thermocouple's needle probes. Our results indicated that, for a tissue irradiation of 10 min, the elevation of rat tumor temperature ranged from 8 to 11°C for 1 W and 8 to 15°C for 1.5 W. This is the first time a 7 T magnetic resonance imager has been used to monitor interstitial laser irradiation via PRF. Our work provides a basic understanding of the photothermal interaction needed to control the thermal damage inside a tumor using interstitial laser treatment. Our work may lead to an optimal protocol for future cancer treatment using interstitial phototherapy in conjunction with immunotherapy.