Tumour vessel damage resulting from laser-induced hyperthermia alone and in combination with photodynamic therapy

Synthesis of a versatile mitochondria-targeting small molecule for cancer near-infrared fluorescent imaging and radio/photodynamic/photothermal synergistic therapies

Although as a mainstay modal for cancer treatment, the clinical effect of radiotherapy (RT) does not yet meet the need of cancer patients. Developing tumour-preferential radiosensitizers or combining RT with other treatments has been acknowledged highly necessary to enhance the efficacy of RT. The present study reported a multifunctional bioactive small-molecule (designated as IR-83) simultaneously exhibiting tumour-preferential accumulation, near-infrared imaging and radio/photodynamic/photothermal therapeutic effects. IR-83 was designed and synthesized by introducing 2-nitroimidazole as a radiosensitizer into the framework of heptamethine cyanine dyes inherently with tumour-targeting and photosensitizing effects. As results, IR-83 preferentially accumulated in tumours, suppressed tumour growth and metastasis by integrating radio/photodynamic/photothermal multimodal therapies. Mechanism studies showed that IR-83 accumulated in cancer cell mitochondria, induced excessive reactive oxygen species (ROS), and generated high heat after laser irradiation. On one hand, these phenomena led to mitochondrial dysfunction and a sharp decline in oxidative phosphorylation to lessen tissue oxygen consumption. On the other hand, excessive ROS in mitochondria destroyed the balance of antioxidants and oxidative stress balance by down-regulating the intracellular antioxidant system, and subsequently sensitized ionizing radiation-generated irreversible DNA double-strand breaks. Therefore, this study presented a promising radiosensitizer and a new alternative strategy to enhance RT efficacy via mitochondria-targeting multimodal synergistic treatment.

•

IR-83 is chemically synthesized via introduction of a radiosensitizing moiety into a cancer-targeting heptamethine cyanine framework..

•

IR-83 exhibits multifunctional bioactivities of cancer-preferential accumulation, near infrared imaging-guided multimodal treatment.

•

IR-83 exerts a synergistic therapeutic effect of RT/PDT/PTT by targeting cancer cell mitochondria.

•

Cancer radiotherapy is significantly sensitized by mitochondria-targeting delivery of a radiosensitizing moiety, PTT-triggered increase of O₂ level and PDT-induced irreversible DNA double-strand breaks.

Combinatorial Therapeutic Approaches with Nanomaterial-Based Photodynamic Cancer Therapy

Photodynamic therapy (PDT), in which a light source is used in combination with a photosensitizer to induce local cell death, has shown great promise in therapeutically targeting primary tumors with negligible toxicity and minimal invasiveness. However, numerous studies have shown that noninvasive PDT alone is not sufficient to completely ablate tumors in deep tissues, due to its inherent shortcomings. Therefore, depending on the characteristics and type of tumor, PDT can be combined with surgery, radiotherapy, immunomodulators, chemotherapy, and/or targeted therapy, preferably in a patient-tailored manner. Nanoparticles are attractive delivery vehicles that can overcome the shortcomings of traditional photosensitizers, as well as enable the codelivery of multiple therapeutic drugs in a spatiotemporally controlled manner. Nanotechnology-based combination strategies have provided inspiration to improve the anticancer effects of PDT. Here, we briefly introduce the mechanism of PDT and summarize the photosensitizers that have been tested preclinically for various cancer types and clinically approved for cancer treatment. Moreover, we discuss the current challenges facing the combination of PDT and multiple cancer treatment options, and we highlight the opportunities of nanoparticle-based PDT in cancer therapies.

Hyperthermia enhances the antitumor effect of photodynamic therapy with ALA hexyl ester in a squamous cell carcinoma tumor model

BACKGROUND

Photodynamic therapy (PDT) using 5-aminolevulinic acid is considered to be ineffective in the treatment of tumors with progression to the deep layer. Therefore, for such tumors, a method is required which can enhance the effectiveness of this therapy. We examined the anti tumor effect of the combination of PDT with 5-aminolevulinic acid hexyl ester (hALA) and hyperthermia (HT) in a squamous cell carcinoma (SCC) tumor model.

METHODS

A tumor model was prepared by subcutaneously implanting SCC into nude mice, and treated with HT, PDT with hALA (hALA-PDT), or hALA-PDT combined with HT (PDT+HT). The treatment was performed by remodeled near infra-red irradiator which allows the generation of two types of rays for PDT and HT. With HT, the tumor was irradiated for raising the temperature with a light dose of 437.5 J/cm(2). With hALA-PDT, the tumor treated with 250 mg/kg hALA was irradiated with a light dose of 50 J/cm(2). With PDT+HT, the tumor was treated as for hALA-PDT except that the temperature was raised during irradiation with a light dose of 437.5 J/cm(2) (including light dose of 50 J/cm(2) for PDT).

RESULTS

The tumor growth rates on Day 12 were 97.10% in HT, 67.55% in hALA-PDT and 33.90% in PDT+HT, and PDT+HT showed significant inhibitory effects on tumor growth, although the anti-tumoral effects of HT and hALA-PDT were not seen.

CONCLUSION

hALA-PDT combined with HT demonstrated a significant inhibitory effect on the tumor growth of squamous cell carcinoma showing a progression in the deep layer. This suggests that this therapy is useful for tumors showing progression to the deep layer, which hALA-PDT alone is generally ineffective in treating.

Fluorescein and indocyanine green angiography after transpupillary thermotherapy of choroidal neovascularization. Early vascular changes

Transpupillary thermotherapy (TTT) is currently being evaluated in clinical trials for the treatment of choroidal neovascularization (CNV). Preliminary results show that TTT achieves closure of CNV and reduction in subretinal exudation while preserving visual acuity. Fluorescein and indocyanine green angiography reveal increased leakage activity from CNV and collateral choroid within 1 hour after TTT and absence of dye leakage from CNV at 1 week after treatment. Optical coherence tomography confirms the angiographic findings. The early vascular changes after TTT of CNV are similar to those observed after PDT of CNV. Transpupillary thermotherapy and PDT might share common mechanisms of action. A placebo-controlled, multi-center trial (TTT4CNV) evaluating the long-term efficacy and visual implications of TTT in occult CNV is underway.

Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity

The time-resolved fluorescence of photosensitizers (PSs) of varying hydrophobicities, di-and tetrasulfonated Al phthalocyanines (Al-2 and Al-4), and Photochlor (HPPH), was investigated in liposomes used as cell-mimetic models. Using frequency-and time-domain apparatus, the fluorescence lifetime, tau(fluo), was compared for PSs free in aqueous solution and in a liposome-associated state at varied temperatures (25 to 78 degrees C) and oxygen concentrations (0-190 microM). The analysis of tau(fluo) revealed different decay behaviors for the free-solution and liposome-confined PSs, most significantly for the lipophilic HPPH. Hydrophilic PS drugs (Al-4, Al-2) were less affected by the liposomal confinement, depending on the relative hydrophilicity of the compound and the consequent localization in liposomes. Changes in the emission decay due to confinement were detected as differences in the lifetime between the bulk solution and the liposome-localized PS in response to heating and deoxygenation. Specifically, hydrophilic Al-4 produced an identical lifetime trend as a function of temperature both in solu and in a liposome-confined state. Hydrophobic HPPH exhibited a fundamental transformation in its fluorescence decay kinetics, transitioning from a multiexponential (in free solution) to single-exponential (in liposome) decay. Deoxygenation resulted in a ubiquitous tau(fluo) increase for all PSs in free solution, while the opposite, a tau(fluo) decrease, occurred in all liposomal PSs.

Enhanced cytotoxic effects of 5-aminolevulinic acid-mediated photodynamic therapy by concurrent hyperthermia in glioma spheroids

During photodynamic therapy (PDT) both normal and pathological brain tissue, in close proximity to the light source, can experience significant temperature increases. The purpose of this study was to investigate the anti-tumor effects of concurrent 5-aminolevulinic acid (ALA)-mediated PDT and hyperthermia (HT) in human and rat glioma spheroids. Human or rat glioma spheroids were subjected to PDT, HT, or a combination of the two treatments. Therapies were given concurrently to simulate the conditions that will occur during patient PDT. Predictions of diffusion theory suggest that brain tissue immediately adjacent to a spherical light applicator may experience temperature increases approaching 8 degrees C for laser input powers of 2 W. In the in vitro model employed here, HT had no effect on spheroid survival at temperatures below 49 degrees C, while sub-threshold fluence PDT results in only modest decrease in survival. HT (40-46 degrees C) and PDT interact in a synergistic manner if the two treatments are given concurrently. The degree of synergism increases with increasing temperature and light fluence. Apoptosis is the primary mode of cell death following both low-fluence rate PDT and combined HT + PDT.

Enhancing the antitumoral effect of hypericin-mediated photodynamic therapy by hyperthermia

BACKGROUND AND OBJECTIVES

In the previous study, we have found a synergistic effect on the RIF-1 tumor cell killing when hypericin-mediated photodynamic therapy (PDT) was combined with hyperthermia. The purpose of the present study was to investigate the antitumoral effect of hypericin-PDT in combination with hyperthermia in the RIF-1 mouse tumor model.

STUDY DESIGN/MATERIALS AND METHODS

Tumor response to PDT in combination with hyperthermia was compared to the response to PDT or hyperthermia alone. To explore the possible mechanism involved in the interaction of PDT and hyperthermia, we determined the tumor cell survival by in vivo/in vitro cell survival assay and analyzed the functional blood vessels by Hoechst 33342 staining. The mode of cell death was examined by TUNEL assay.

RESULTS

Enhanced tumor response was obtained by PDT immediately followed by hyperthermia. Tumor cell survival assay revealed that indirect vascular effect contributed greatly to the overall tumor cell death induced by PDT with hypericin, whereas direct tumor cytotoxicity played a major role in hyperthermia-induced tumor cell killing. Combining PDT with hyperthermia brought about a synergistic interaction on direct tumor cell killing. Even though PDT or hyperthermia alone induced severe blood vessel shutdown and the combined treatments led to significant potentiation of the vascular damage as examined by Hoechst staining, the gain in tumor cell death as a result of this secondary vascular effect was limited after the combined treatments. Following the cellular damage by PDT in combination with hyperthermia, tumor cells were triggered to undergo apoptosis.

CONCLUSIONS

Our study demonstrated the possibility of using hyperthermia to potentiate the antitumoral effect of hypericin-mediated PDT.

Indocyanine green-mediated photothrombosis as a new technique of treatment for persistent central serous chorioretinopathy

PURPOSE

To evaluate the potential benefit and complications of indocyanine green-mediated photothrombosis (IMP) in the management of patients with persistent central serous chorioretinopathy (CSC).

METHODS

Interventional noncomparative case series. Eleven patients with CSC presenting with persistent subretinal fluid in optical coherence tomography (OCT) four months after presentation and decrease in visual acuity (VA) were submitted to a single IMP session with 2 mg/kg body weight ICG and application of 5.6 W/cm(2) light at 810 nm. A continuous follow-up was provided with best-corrected ETDRS VA assessment, and angiographic and OCT documentation 72 hours before and at 2 days, 1 and 2 weeks, 1, 3, 6, and 12 months after treatment.

RESULTS

Pretreatment VA levels ranged from 20/32 - 1 to 20/100 (mean, 20/63 + 2 [logMAR equivalent, 0.460 +/- 0.155]); post treatment levels ranged from 20/25 - 2 to 20/20 (mean, 20/20 - 2 [logMAR equivalent, 0.038 +/- 0.048]). Ten out of eleven patients presented with VA levels of >/=20/25 2 weeks after treatment; the mean logMAR VA change of 0.345 at that time was statistically significant (p < 0.05, Friedman test). OCT disclosed resolution of persistent subretinal fluid in all eyes. No recurrence was observed after 12 months of follow-up. Complications included transient retinal whitening in two patients, and associated occlusion of retinal capillaries in one.

CONCLUSIONS

Photothrombosis using low-intensity 810 nm light to direct laser energy continuously at the active leakage sites after intravenous ICG infusion induced rapid VA recovery in patients with persistent CSC; accordingly, restoration of the macular architecture was evidenced on OCT, and no recurrence was noted 12 months after IMP.

Early vascular changes induced by transpupillary thermotherapy of choroidal neovascularization

OBJECTIVE

To study early direct effects of transpupillary thermotherapy (TTT) on choroidal neovascularization (CNV) and choroid.

DESIGN

Retrospective, noncomparative interventional case series.

PARTICIPANTS

Sixty-four eyes with subfoveal CNV.

INTERVENTION

TTT was delivered using a diode laser at 810 nm through a contact lens. Exposure time was 60 seconds with a power/diameter ratio of 247 mW/mm. The end point was an invisible treatment with no color change at the retina level.

MAIN OUTCOME MEASURES

Fluorescein and indocyanine green angiographic findings within 1 hour, and at 1, 2, and 4 weeks after TTT.

RESULTS

Fluorescein angiography (FA) and indocyanine green angiography (ICGA) performed within 1 hour after TTT showed increased leakage of CNV and choroidal vessels. Follow-up at 1 and 2 weeks demonstrated a hypofluorescent area corresponding to the laser spot and absence of angiographic leakage seen on FA and ICGA. At 4 weeks after TTT, FA showed mottled hypofluorescence-hyperfluorescence of the TTT-treated area and absence of angiographic leakage.

CONCLUSIONS

TTT induces a characteristic dynamic sequence of vascular changes. Treatment with TTT can lead to absence of angiographic (FA and ICGA) leakage for 4 weeks. Determination of the long-term efficacy and visual implications awaits the results of clinical trials.

Tumor vessel destruction resulting from high-intensity focused ultrasound in patients with solid malignancies

The purpose of this study was to explore the sequential imaging and histologic alterations of tumor blood vessels in the patient with solid malignancies after extracorporeal treatment of high-intensity focused ultrasound (HIFU). A total of 164 patients underwent extracorporeal HIFU ablation of malignant solid tumors. After HIFU treatment, enhanced magnetic resonance imaging (MRI), color Doppler ultrasound (US) imaging, dynamic radionuclide scanning, digital subtraction angiography, and histologic study were performed to monitor the response of tumor vessels to HIFU ablation. Compared with tumor images in the patients before HIFU, clinical images showed an abrupt interruption, followed by the cessation of blood flow within the tumor vessels after HIFU treatment. The histologic examination indicated that not only the treated tumor cells showed coagulative necrosis, but also small tumor vessels were severely damaged by the HIFU treatment. The results strongly imply that the damaged tumor vessels might play a critical role in secondary tumor cell death, and then indirectly strengthen the destructive force of focused US beams on tumor tissue. It is concluded that tumor vessel damage can be induced by HIFU, which may be a promising strategy in the treatment of patients with solid malignancies.

PpIX fluorescence kinetics and increased skin damage after intracutaneous injection of 5-aminolevulinic acid and repeated illumination

Photodynamic therapy with topically applied 5-aminolevulinic acid is used successfully for superficial skin lesions. The results for thicker, nodular lesions are less favorable. The method of aminolevulinic acid administration, the concentrations of aminolevulinic acid, and the irradiation schemes used so far have not been investigated thoroughly. As aminolevulinic acid photodynamic therapy has high potential for the increasing problem of skin cancer, we investigated both visually and histopathologically the photodynamic-therapy-induced skin damage after intracutaneous administration of aminolevulinic acid in normal porcine skin. We also investigated the kinetics of the aminolevulinic-acid-induced photosensitizer protoporphyrin IX fluorescence after irradiation in relation to fluence and irradiance. Finally we investigated the effect on photodynamic-therapy-induced damage of a fractionated irradiation. This study demonstrates that intracutaneous administration of aminolevulinic acid leads to higher fluorescence levels and thus to formation of higher protoporphyrin IX concentrations than topical application of aminolevulinic acid cream. The peak level of protoporphyrin IX after intracutaneous administration of aminolevulinic acid is reached earlier than after topical administration. The comeback of fluorescence, indicating re-synthesis of protoporphyrin IX after irradiation, is inhibited with increasing fluence. Photodynamic-therapy-induced damage increases with increasing fluence, but is independent of the irradiance. Finally, the photodynamic-therapy-induced skin damage seems to be greater after fractionated irradiations with two equal light fractions of 15 J per cm2 separated by a dark interval of 2 h.

Noninvasive monitoring of hemodynamic stress using quantitative near-infrared frequency-domain photon migration spectroscopy

Hemorrhagic hypovolemia and inotropic agent administration were used to manipulate cardiac output (CO) and oxygen delivery in rabbits to investigate the correlation between noninvasive frequency domain photon migration (FDPM) spectroscopy and invasive hemodynamic monitoring parameters. Frequency-domain photon migration provides quantitative measurements of light absorption and reduced scattering (mu(a) and mu(s)(prime prime or minute), respectively) in tissue. Wavelength dependent mu(a) values were used to calculate in vivo tissue concentration of deoxyhemoglobin [Hb], oxyhemoglobin [HbO(2)], total hemoglobin [TotHb], and water [H(2)O] as well as mixed arterial-venous oxygen saturation (S(t)O(2)) in tissue. FDPM-derived physiologic properties were correlated with invasive measurements of CO and mean pulmonary artery pressure (mPAP), FDPM-derived [TotHb] and S(t) O(2) correlated significantly with hemorrhaged volume (HV), mPAP, and CO. Correlation coefficients for [TotHb] vs HV, mPAP, and CO were -0.77, 0.86, and 0.70, respectively. Correlation coefficients of S(t)O( 2) vs HV, mPAP, and CO were -0.71, 0.55, and 0.61, respectively. Dobutamine induced changes resulted in correlation coefficients between FDPM-derived and invasively measured physiologic parameters that are comparable to those induced by hypovolemia. FDPM spectroscopy is sensitive to changes in mPAP and CO of as little as 15%. These results suggest that FDPM spectroscopy may be used in clinical settings to noninvasively monitor central hemodynamic parameters and to directly assess oxygenation of tissues.

Interstitial laser-induced thermotherapy: influence of carbonization on lesion size

BACKGROUND AND OBJECTIVE

The size of laser-induced coagulated lesions produced in porcine muscle in vitro using a cylindrical diffusing fiber tip and a conductive heat source, made by covering the diffuser with a hollow steel needle, were compared to investigate the influence of charring.

MATERIALS AND METHODS

Light from a Nd:YAG laser was utilized for thermotherapy. A theoretical model for calculating tissue temperature was used to predict the experimental results and to simulate in vivo treatments.

RESULTS

The metal-covered tip produced carbonization and tissue vaporization that was not found with the diffuser. After 20 min of irradiation at a laser power of 7 W, the coagulated volumes with and without carbonization were found to be 13.1 cm3 (range 12.4-14.1 cm3, n = 4) and 12.2 cm3 (range 11.5-13.4 cm3, n = 4), respectively. Mathematical simulations showed that in unperfused tissue, a diffusing laser heat source produces smaller lesions than does a conductive heat source at the same power, the difference in coagulated volume becoming smaller with increased treatment time and increased power.

CONCLUSION

Using cylindrical diffusers, interstitial laser-induced thermotherapy without carbonization at the fiber tip can be as efficient as treatment with carbonization.

Photodynamic parameters in the chick chorioallantoic membrane (CAM) bioassay for topically applied photosensitizers

The relative efficacy of Photofrin-based photodynamic therapy (PDT) has been compared with that of the second-generation photosensitizers 5-aminolevulinic acid (ALA), sulfonated chloro-aluminum phthalocyanine (AlPcSn), benzoporphyrin derivative monoacid ring A (BPD-MA), and lutetium texaphyrin (Lutex). PDT-induced vascular damage in the chick chorioallantoic membrane (CAM) is measured following topical application of the photosensitizers. In order to make meaningful comparisons, care is taken to keep treatment variables the same. These include light dose (5 and 10 J/cm2), power density (33 and 100 mW/cm2), and drug uptake time (30 and 90 min). The drug dose ranges from 0.1 microgram/cm2 for BPD to 5000 micrograms/cm2 for ALA. Results are also analyzed statistically according to CAM vessel type (arterioles versus venules), vessel diameter, and vessel development (embryonic age). For each photosensitizer, the order of importance for the various PDT parameters is found to be unique. The differences between the sensitizers are most likely due to variation in biophysical and biochemical characteristics, biodistribution, and uptake kinetics.