Tumor detection and elimination by a targeted gallium corrole

Photophysical properties and singlet oxygen generation of three sets of halogenated corroles

The luminescence, excited-state absorption, and singlet oxygen generation measurements were performed on three kinds of halogenated corroles: monohydroxyl halogenated corroles (Corrole-F, Corrole-Cl, Corrole-I), peripherally fluorine-substituted corroles (F0, F5, F10, F15), and gallium complexes (F10-Ga, F15-Ga). The fluorescence intensities progressively decrease whereas the triplet quantum yields, oxygen quenching rates, and singlet oxygen quantum yields increase with the increasing of the monohydroxyl halogen atomic weight. Replacing hydrogen atoms of meso-phenyl groups with fluorine atoms induces the blue-shifts of the emission spectra, higher triplet quantum yield, and smaller oxygen quenching rates. Of all peripherally fluorine-substituted corroles, F10 exhibited the highest singlet oxygen quantum yield. In comparison with the free base corroles, both gallium corrole complexes display much stronger fluorescence with the large blue-shifts of emission peaks and slightly higher triplet quantum yields but smaller oxygen quenching rates and singlet oxygen quantum yields. The reasons for the different photophysical behaviors of these corroles are discussed.

A multimode optical imaging system for preclinical applications in vivo: technology development, multiscale imaging, and chemotherapy assessment

PURPOSE

Several established optical imaging approaches have been applied, usually in isolation, to preclinical studies; however, truly useful in vivo imaging may require a simultaneous combination of imaging modalities to examine dynamic characteristics of cells and tissues. We developed a new multimode optical imaging system designed to be application-versatile, yielding high sensitivity, and specificity molecular imaging.

PROCEDURES

We integrated several optical imaging technologies, including fluorescence intensity, spectral, lifetime, intravital confocal, two-photon excitation, and bioluminescence, into a single system that enables functional multiscale imaging in animal models.

RESULTS

The approach offers a comprehensive imaging platform for kinetic, quantitative, and environmental analysis of highly relevant information, with micro-to-macroscopic resolution. Applied to small animals in vivo, this provides superior monitoring of processes of interest, represented here by chemo-/nanoconstruct therapy assessment.

CONCLUSIONS

This new system is versatile and can be optimized for various applications, of which cancer detection and targeted treatment are emphasized here.

Molecular redox: revisiting the electronic structures of the group 9 metallocorroles

The electronic structures of monocationic tris[(5,10,15-pentafluorophenyl)-corrolato]iridium compounds, [Ir(tpfc)L2](+), where L = 4-cyanopyridine [1](+), pyridine [2](+), 4-methoxypyridine [3](+), or 4-(N,N'-dimethylamino)pyridine [4](+), have been probed by electron paramagnetic resonance (EPR) spectroscopy, Ir L3,2-edge X-ray absorption spectroscopy (XAS), UV/visible (UV-vis) spectroelectrochemistry, and density functional theoretical (DFT) calculations. The data demonstrate that these complexes, which have been previously formulated as either of the limiting cases [Ir(III)(tpfc(•))L2](+) or [Ir(IV)(tpfc)L2](+), are best described as possessing a singly occupied molecular orbital (SOMO) dominated by tpfc with small but significant Ir admixture. EPR g-values and electronic absorption spectra are reproduced well using a simple DFT approach. These quantities depend profoundly upon Ir orbital contribution to the SOMO. To wit, the calculated Ir spin population ranges from 10.6% for [1](+) to 16.3% for [4](+), reflecting increased Ir d mixing into the SOMO with increasingly electron-rich axial ligation. This gives rise to experimentally measured gz values ranging from 2.335 to 2.533, metal-to-ligand charge transfer (MLCT) bands ranging from 14730 and 14330 cm(-1), and [Ir(tpfc)L2](+/0) reduction potentials ranging from 0.305 to 0.035 V vs Fc(+/0). In addition, the calculated Ir character in the SOMO tracks with estimated Ir L3,2 XAS branching ratios (EBR), reflecting the increasing degree of Ir d orbital character upon proceeding from [1](+) to [4](+).

Photoexcitation of tumor-targeted corroles induces singlet oxygen-mediated augmentation of cytotoxicity

The tumor-targeted corrole particle, HerGa, displays preferential toxicity to tumors in vivo and can be tracked via fluorescence for simultaneous detection, imaging, and treatment. We have recently uncovered an additional feature of HerGa in that its cytotoxicity is enhanced by light irradiation. In the present study, we have elucidated the cellular mechanisms for HerGa photoexcitation-mediated cell damage using fluorescence optical imaging. In particular, we found that light irradiation of HerGa produces singlet oxygen, causing mitochondrial damage and cytochrome c release, thus promoting apoptotic cell death. An understanding of the mechanisms of cell death induced by HerGa, particularly under conditions of light-mediated excitation, may direct future efforts in further customizing this nanoparticle for additional therapeutic applications and enhanced potency.

Chemotherapy targeting by DNA capture in viral protein particles

AIM

This study tests the hypothesis that DNA intercalation and electrophilic interactions can be exploited to noncovalently assemble doxorubicin in a viral protein nanoparticle designed to target and penetrate tumor cells through ligand-directed delivery. We further test whether this new paradigm of doxorubicin targeting shows therapeutic efficacy and safety in vitro and in vivo.

MATERIALS & METHODS

We tested serum stability, tumor targeting and therapeutic efficacy in vitro and in vivo using biochemical, microscopy and cytotoxicity assays.

RESULTS

Self-assembly formed approximately 10-nm diameter serum-stable nanoparticles that can target and ablate HER2+ tumors at >10× lower dose compared with untargeted doxorubicin, while sparing the heart after intravenous delivery. The targeted nanoparticle tested here allows doxorubicin potency to remain unaltered during assembly, transport and release into target cells,while avoiding peripheral tissue damage and enabling lower, and thus safer, drug dose for tumor killing.

CONCLUSION

This nanoparticle may be an improved alternative to chemical conjugates and signal-blocking antibodies for tumor-targeted treatment.

Multimodality imaging in vivo for preclinical assessment of tumor-targeted doxorubicin nanoparticles

This study presents a new multimodal imaging approach that includes high-frequency ultrasound, fluorescence intensity, confocal, and spectral imaging to improve the preclinical evaluation of new therapeutics in vivo. Here we use this approach to assess in vivo the therapeutic efficacy of the novel chemotherapy construct, HerDox during and after treatment. HerDox is comprised of doxorubicin non-covalently assembled in a viral-like particle targeted to HER2+ tumor cells, causing tumor cell death at over 10-fold lower dose compared to the untargeted drug, while sparing the heart. Whereas our initial proof-of-principle studies on HerDox used tumor growth/shrinkage rates as a measure of therapeutic efficacy, here we show that multimodal imaging deployed during and after treatment can supplement traditional modes of tumor monitoring to further characterize the particle in tissues of treated mice. Specifically, we show here that tumor cell apoptosis elicited by HerDox can be monitored in vivo during treatment using high frequency ultrasound imaging, while in situ confocal imaging of excised tumors shows that HerDox indeed penetrated tumor tissue and can be detected at the subcellular level, including in the nucleus, via Dox fluorescence. In addition, ratiometric spectral imaging of the same tumor tissue enables quantitative discrimination of HerDox fluorescence from autofluorescence in situ. In contrast to standard approaches of preclinical assessment, this new method provides multiple/complementary information that may shorten the time required for initial evaluation of in vivo efficacy, thus potentially reducing the time and cost for translating new drug molecules into the clinic.

Differential cytostatic and cytotoxic action of Metallocorroles against human cancer cells: potential platforms for anticancer drug development

A gallium(III)-substituted amphiphilic corrole noncovalently associated with a targeting protein was previously found by us to confer promising cytotoxic and antitumor activities against a breast cancer cell line and a mouse xenograft breast cancer model. To further explore potential anticancer applications, the cytostatic and cytotoxic properties of six nontargeted metallocorroles were evaluated against seven human cancer cell lines. Results indicated that toxicity toward human cancer cells depended on the metal ion as well as corrole functional group substitution. Ga(III)-substituted metallocorrole 1-Ga inhibited proliferation of breast (MDA-MB-231), melanoma (SK-MEL-28), and ovarian (OVCAR-3) cancer cells primarily by arrest of DNA replication, whereas 2-Mn displayed both cytostatic and cytotoxic properties. Confocal microscopy revealed extensive uptake of 1-Ga into the cytoplasm of melanoma and ovarian cancer cells, while prostate cancer cells (DU-145) displayed extensive nuclear localization. The localization of 1-Ga to the nucleus in DU-145 cells was exploited to achieve a 3-fold enhancement in the IC(50) of doxorubicin upon coadministration. Time-course studies showed that over 90% of melanoma cells incubated with 30 μM 1-Ga internalized metallocorrole after 15 min. Cellular uptake of 1-Ga and 1-Al was fastest and most efficient in melanoma, followed by prostate and ovarian cancer cells. Cell cycle analyses revealed that bis-sulfonated corroles containing Al(III), Ga(III), and Mn(III) induced late M phase arrest in several different cancer cell lines, a feature that could be developed for potential therapeutic benefit.

Investigating photoexcitation-induced mitochondrial damage by chemotherapeutic corroles using multimode optical imaging

We recently reported that a targeted, brightly fluorescent gallium corrole (HerGa) is highly effective for breast tumor detection and treatment. Unlike structurally similar porphryins, HerGa exhibits tumor-targeted toxicity without the need for photoexcitation. We have now examined whether photoexcitation further modulates HerGa toxicity, using multimode optical imaging of live cells, including two-photon excited fluorescence, differential interference contrast (DIC), spectral, and lifetime imaging. Using two-photon excited fluorescence imaging, we observed that light at specific wavelengths augments the HerGa-mediated mitochondrial membrane potential disruption of breast cancer cells in situ. In addition, DIC, spectral, and fluorescence lifetime imaging enabled us to both validate cell damage by HerGa photoexcitation and investigate HerGa internalization, thus allowing optimization of light dose and timing. Our demonstration of HerGa phototoxicity opens the way for development of new methods of cancer intervention using tumor-targeted corroles.

A mechanistic study of tumor-targeted corrole toxicity

HerGa is a self-assembled tumor-targeted particle that bears both tumor detection and elimination activities in a single, two-component complex (Agadjanian et al. Proc. Natl. Acad. Sci. U.S.A.2009, 106, 6105-6110). Given its multifunctionality, HerGa (composed of the fluorescent cytotoxic corrole macrocycle, S2Ga, noncovalently bound to the tumor-targeted cell penetration protein, HerPBK10) has the potential for high clinical impact, but its mechanism of cell killing remains to be elucidated, and hence is the focus of the present study. Here we show that HerGa requires HerPBK10-mediated cell entry to induce toxicity. HerGa (but not HerPBK10 or S2Ga alone) induced mitochondrial membrane potential disruption and superoxide elevation, which were both prevented by endosomolytic-deficient mutants, indicating that cytosolic exposure is necessary for corrole-mediated cell death. A novel property discovered here is that corrole fluorescence lifetime acts as a pH indicator, broadcasting the intracellular microenvironmental pH during uptake in live cells. This feature in combination with two-photon imaging shows that HerGa undergoes early endosome escape during uptake, avoiding compartments of pH < 6.5. Cytoskeletal disruption accompanied HerGa-mediated mitochondrial changes whereas oxygen scavenging reduced both events. Paclitaxel treatment indicated that HerGa uptake requires dynamic microtubules. Unexpectedly, low pH is insufficient to induce release of the corrole from HerPBK10. Altogether, these studies identify a mechanistic pathway in which early endosomal escape enables HerGa-induced superoxide generation leading to cytoskeletal and mitochondrial damage, thus triggering downstream cell death.

Ratiometric spectral imaging for fast tumor detection and chemotherapy monitoring in vivo

We report a novel in vivo spectral imaging approach to cancer detection and chemotherapy assessment. We describe and characterize a ratiometric spectral imaging and analysis method and evaluate its performance for tumor detection and delineation by quantitatively monitoring the specific accumulation of targeted gallium corrole (HerGa) into HER2-positive (HER2 +) breast tumors. HerGa temporal accumulation in nude mice bearing HER2 + breast tumors was monitored comparatively by a. this new ratiometric imaging and analysis method; b. established (reflectance and fluorescence) spectral imaging; c. more commonly used fluorescence intensity imaging. We also tested the feasibility of HerGa imaging in vivo using the ratiometric spectral imaging method for tumor detection and delineation. Our results show that the new method not only provides better quantitative information than typical spectral imaging, but also better specificity than standard fluorescence intensity imaging, thus allowing enhanced in vivo outlining of tumors and dynamic, quantitative monitoring of targeted chemotherapy agent accumulation into them.

Functionalization of the corrole ring: the role of isocorrole intermediates

Bromination of 3-nitro-5,10,15-triarylcorrole selectively provides two regioisomers, depending on the reaction pathway. An isocorrole species is the key intermediate to drive the reaction towards the 2-Br-17-nitro regioisomer.

Multimode Optical Imaging for Translational Chemotherapy: In Vivo Tumor Detection and Delineation by Targeted Gallium Corroles

We report the feasibility of tumor detection and delineation in vivo using multimode optical imaging of targeted gallium corrole (HerGa). HerGa is highly effective for targeted HER2+ tumor elimination in vivo, and it emits intense fluorescence. These unique characteristics of HerGa prompted us to investigate the potential of HerGa for tumor detection and delineation, by performing multimode optical imaging ex vivo and in vivo; the imaging modes included fluorescence intensity, spectral (including ratiometric), lifetime, and two-photon excited fluorescence, using our custom-built imaging system. While fluorescence intensity imaging provided information about tumor targeting capacity and tumor retention of HerGa, ratiometric spectral imaging offered more quantitative and specific information about HerGa location and accumulation. Most importantly, the fluorescence lifetime imaging of HerGa allowed us to discriminate between tumor and non-tumor regions by fluorescence lifetime differences. Finally, two-photon excited fluorescence images provided highly resolved and thus topologically detailed information around the tumor regions where HerGa accumulates. Taken together, the results shown in this report suggest the feasibility of tumor detection and delineation by multimode optical imaging of HerGa, and fluorescent chemotherapy agents in general. Specifically, the multimode optical imaging can offer complementary and even synergetic information simultaneously in the tumor detection and delineation by HerGa, thus enhancing contrast.

Investigating the photosensitizer-potential of targeted gallium corrole using multimode optical imaging

We recently developed a novel therapeutic particle, HerGa, for breast cancer treatment and detection. HerGa consists of a tumor-targeted cell penetration protein noncovalently assembled with a gallium-metallated corrole. The corrole is structurally similar to porphyrin, emits intense fluorescence, and has proven highly effective for breast tumor treatment preclinically, without light exposure. Here, we tested HerGa as a photosensitizer for photodynamic therapy and investigated its mechanism of action using multimode optical imaging. Using confocal fluorescence imaging, we observed that HerGa disrupts the mitochondrial membrane potential in situ, and this disruption is substantially augmented by light exposure. In addition, spectral and fluorescence lifetime imaging were utilized to both validate the mitochondrial membrane potential disruption and investigate HerGa internalization, allowing us to optimize the timing for light dosimetry. We observed, using advanced multimode optical imaging, that light at a specific wavelength promotes HerGa cytotoxicity, which is likely to cause disruption of mitochondrial function. Thus, we can identify for the first time the capacity of HerGa as a photosensitizer for photodynamic therapy and reveal its mechanism of action, opening possibilities for therapeutic intervention in human breast cancer management.

Multimodal wide-field two-photon excitation imaging: characterization of the technique for in vivo applications

We report fast, non-scanning, wide-field two-photon fluorescence excitation with spectral and lifetime detection for in vivo biomedical applications. We determined the optical characteristics of the technique, developed a Gaussian flat-field correction method to reduce artifacts resulting from non-uniform excitation such that contrast is enhanced, and showed that it can be used for ex vivo and in vivo cellular-level imaging. Two applications were demonstrated: (i) ex vivo measurements of beta-amyloid plaques in retinas of transgenic mice, and (ii) in vivo imaging of sulfonated gallium(III) corroles injected into tumors. We demonstrate that wide-field two photon fluorescence excitation with flat-field correction provides more penetration depth as well as better contrast and axial resolution than the corresponding one-photon wide field excitation for the same dye. Importantly, when this technique is used together with spectral and fluorescence lifetime detection modules, it offers improved discrimination between fluorescence from molecules of interest and autofluorescence, with higher sensitivity and specificity for in vivo applications.

Near-IR phosphorescence of iridium(III) corroles at ambient temperature

The photophysical properties of Ir(III) corroles differ from those of phosphorescent porphyrin complexes, cyclometalated and polyimine Ir(III) compounds, and other luminescent metallocorroles. Ir(III) corrole phosphorescence is observed at ambient temperature at wavelengths much longer (>800 nm) than those of most Ir(III) phosphors. The solvatochromic behavior of Ir(III)-corrole Soret and Q absorption bands suggests that the lowest singlet excited states (S(2) and S(1)) are substantially more polar than the ground state.

Superoxide dismutase mimics: chemistry, pharmacology, and therapeutic potential

Oxidative stress has become widely viewed as an underlying condition in a number of diseases, such as ischemia-reperfusion disorders, central nervous system disorders, cardiovascular conditions, cancer, and diabetes. Thus, natural and synthetic antioxidants have been actively sought. Superoxide dismutase is a first line of defense against oxidative stress under physiological and pathological conditions. Therefore, the development of therapeutics aimed at mimicking superoxide dismutase was a natural maneuver. Metalloporphyrins, as well as Mn cyclic polyamines, Mn salen derivatives and nitroxides were all originally developed as SOD mimics. The same thermodynamic and electrostatic properties that make them potent SOD mimics may allow them to reduce other reactive species such as peroxynitrite, peroxynitrite-derived CO(3)(*-), peroxyl radical, and less efficiently H(2)O(2). By doing so SOD mimics can decrease both primary and secondary oxidative events, the latter arising from the inhibition of cellular transcriptional activity. To better judge the therapeutic potential and the advantage of one over the other type of compound, comparative studies of different classes of drugs in the same cellular and/or animal models are needed. We here provide a comprehensive overview of the chemical properties and some in vivo effects observed with various classes of compounds with a special emphasis on porphyrin-based compounds.

Highly efficient catalase activity of metallocorroles

The iron(iii) complex of a bipolar and amphiphilic corrole, which binds strongly to proteins and undergoes protein-mediated cellular uptake, catalyzes the decomposition of hydrogen peroxide faster (k(cat) = 6400 M(-1) s(-1)) and more efficiently (turnover frequency >120 s(-1)) than previously reported synthetic compounds with catalase-like activity.

Neuroprotection against superoxide anion radical by metallocorroles in cellular and murine models of optic neuropathy

Corroles are tetrapyrrolic macrocycles that have come under increased attention because of their unique capabilities for oxidation catalysis, reduction catalysis, and biomedical applications. Corrole-metal complexes (metallocorroles) can decompose certain reactive oxygen species (ROS), similar to metalloporphyrins. We investigated whether Fe-, Mn-, and Ga-corroles have neuroprotective effects on neurons and correlated this with superoxide scavenging activity in vitro and in vivo. Apoptosis was induced in retinal ganglion cell-5 neuronal precursor cells by serum deprivation. Cell death was measured with sodium 3'-[1-[(phenylamino)-carbonyl]-3,4-tetrazolium]-bis (4-methoxy-6-nitro) benzene-sulfonic acid hydrate and calcein-AM/propidium iodide assays. Fe- and Mn-corroles, but not the non-redox-active Ga-corrole used as control, reduced RGC-5 cell death after serum deprivation. Serum deprivation caused increased levels of intracellular superoxide, detected by an increase in the fluorescence intensity of 2-hydroxyethidium, and this was blocked by Fe- and Mn-corroles, but not Ga-corrole. In vivo real-time confocal imaging of retinas after optic nerve transection assessed the superoxide production within individual rat retinal ganglion cells. Fe- and Mn-corroles, but not Ga-corrole, scavenged neuronal superoxide in vivo. Given that the neuroprotective activity of metallocorroles correlated with superoxide scavenging activity, Fe- and Mn-corroles could be candidate drugs for delaying neuronal death after axonal injury in optic neuropathies, such as glaucoma.

Manganese corroles prevent intracellular nitration and subsequent death of insulin-producing cells

Reactive oxygen species are heavily involved in the pathogenesis of diabetes mellitus (DM) because the insulin-producing beta cells are particularly vulnerable to free-radical-mediated cytotoxicity. Catalytic anti-oxidants have been successfully applied for attenuation of DM and its consequences, but most recent research revealed that preventing the nitration of vital proteins/enzymes might be an even more powerful strategy. We now report an unprecedented efficiency of manganese(III) corroles regarding the protection of rat pancreatic beta cells against intracellular nitration by peroxynitrite and subsequent cell death. A comparison between analogous corroles and porphyrin metal complexes reveals significant superiority of the former in all examined aspects. This is particularly true for the positively-charged manganese(III) corrole, which decomposes peroxynitrite fast enough and through a unique catalytic mechanism that is devoid of potentially nitrating reaction intermediates.