Extended Porphyrins

Photoacoustic lifetime oxygen imaging of radiotherapy-induced tumor reoxygenation In Vivo

Purpose

Early detection and diagnosis of cancer is critical for achieving positive therapeutic outcomes. Biomarkers that can provide clinicians with clues to the outcome of a given therapeutic course are highly desired. Oxygen is a small molecule that is nearly universally present in biological tissues and plays a critical role in the effectiveness of radiotherapies by reacting with DNA radicals and subsequently impairing cellular repair of double strand breaks.Techniques for measuring oxygen in biological tissues often use blood oxygen saturation to approximate the oxygen partial pressure in surrounding tissues despite the complex, nonlinear, and dynamic relationship between these two separate oxygen populations.

Methods and materials

We combined a directly oxygen-sensitive, tumor-targeted, chemical contrast nanoelement with the photoacoustic lifetime-based (PALT) oxygen imaging technique to obtain image maps of oxygen in breast cancer tumors in vivo. The oxygen levels of patient-derived xenografts in a mouse model were characterized before and after a course of radiotherapy.

Results

We show that, independent of tumor size, radiotherapy induced an increase in the overall oxygenation levels of the tumor. Further, this increase in the oxygenation of the tumor significantly correlated with a positive response to radiotherapy, as demonstrated by a reduction in tumor volume over the twenty-day monitoring period following therapy and histological staining.

Conclusion

Our PALT imaging presented here is simple, fast, and non-invasive. Facilized by the PALT approach, imaging of tumor reoxygenation may be utilized as a simple, early indicator for evaluating cancer response to radiotherapy. Further characterization of the reoxygenation degree, temporal onset, and possible theragnostic implications are warranted.

Multidomain-Based Responsive Materials with Dual-Mode Optical Readouts

Responsive materials designed to generate signals for both surface-enhanced Raman spectroscopy (SERS) and phosphorescence lifetime-"dual-mode"-measurements are described. To demonstrate this concept, we incorporated pH-sensitive and oxygen-sensitive microdomains into a single hydrogel that could be interrogated via SERS and phosphorescence lifetime, respectively. Microdomains consisted two populations of discrete microcapsules containing either (1) gold nanoparticles capped with pH-sensitive Raman molecules or (2) oxygen-sensitive benzoporphyrin phosphors. While the microdomain-embedded hydrogels presented an expected background luminescence, the pH-sensitive SERS signal was distinguishable for all tested conditions. Response characteristics of the dual sensor showed no significant difference when compared to standalone single-mode pH and oxygen sensors. In addition, the feasibility of redundant multimode sensing was proven by observing the reaction produced by glucose oxidase chemically cross-linked within the corresponding alginate matrix. Each optical mode showed a signal change proportional to glucose concentration with an opposite signal directionality. These results support the promise of micro-/nanocomposite materials to improve measurement accuracy using intrinsic multimode responses and built-in redundancy, concepts that have broad appeal in the chemical sensing and biosensing fields.

Synthesis of lutetium(iii)–porphyrin complexes: old problems and new excellent conditions found

A convenient high-yielding method for the preparation of very attractive lutetium(iii)–porphyrin complexes was developed (in sulfolane at reflux temperature, 0.5 h, up to 88%).

POTENTIAL USAGE OF LIPOSOME-ENCAPSULATED PHOSPHOR FOR IN VIVO IMAGING OF TISSUE OXYGENATION

Oxygen-dependent quenching of phosphorescence can provide a quantitative measurement with high temporal resolution of tissue oxygenation in vivo. It is a real-time optical means for prognosis of diseases where the oxygen concentration is essential. Phosphorescence quenching is a noninvasive methodology, otherwise no more than minimally invasive as the phosphor is necessarily introduced into vasculature prior to the measurement. Oxyphor R2, a dendritic phosphor with twolayer of glutamates, is a suitable phosphor for oxygen measurements owing to its high water solubility. We used a frequency-domain, phase modulation based instrument to calibrate Oxyphor R2. The acquired quenching constant (kQ) and lifetime at zero oxygen (τ°) were consistent with those calibrated from conventional time-domain instrument. Administered with Oxygen R2, the rat hepatic oxygen distributions were imaged throughout the course of ischemia and reperfusion. After 5 min ischemia and subsequent 20 min reperfusion, distinct ischemic areas on the hepatic tissue were observed. In order to extend the application of in vivo oxygen imaging using phosphorescence quenching by minimizing the possible immunoresponse induced by phosphor, we are the first to co-synthesize the dipalmitoylphosphatidylglycerol (DPPG)-rich liposome with Oxyphor R2 to generate the liposome-encapsulated Oxyphor R2. Its calibration using the frequency domain measurement displayed higher quenching constant and shorter lifetime at zero oxygen (kQ= 1186 mmHg−1sec−1; τ° = 150 μsec) comparing to original Oxyphor R2 (kQ= 438 mmHg−1sec−1; τ° = 630 μsec). It implicated that the liposome-encapsulated Oxyphor R2 designed to neutralize the immunoresponse could be further applied to measure the tissue oxygenation in vivo, especially those with low oxygen concentration such as tumor.

Effects of structural deformations on optical properties of tetrabenzoporphyrins: free-bases and Pd complexes

A recently developed method of synthesis of pi-extended porphyrins made it possible to prepare a series of tetrabenzoporphyrins (TBP) with different numbers of meso-aryl substituents. The photophysical parameters of free-bases and Pd complexes of meso-unsubstituted TBP's, 5,15-diaryl-TBP's (Ar2TBP's) and 5,10,15,20-tetraaryl-TBP's (Ar4TBP's) were measured. For comparison, similarly meso-arylsubstituted porphyrins fused with nonaromatic cyclohexeno-rings, i.e. Ar(n)-tetracyclohexenoporphyrins (Ar(n)TCHP's, n = 0, 2, 4), were also synthesized and studied. Structural information was obtained by ab initio (DFT) calculations and X-ray crystallography. It was found that: 1) Free-base Ar4TBP's are strongly distorted out-of-plane (saddled), possess broadened, red-shifted spectra, short excited-state lifetimes and low fluorescence quantum yields (tau(fl) = 2-3 ns, phi(fl) = 0.02-0.03). These features are characteristic of other nonplanar free-base porphyrins, including Ar4TCHP's. 2) Ar2TBP free-bases possess completely planar geometries, although with significant in-plane deformations. These deformations have practically no effect on the singlet excited-state properties of Ar2TBP's as compared to planar meso-unsubstituted TBP's. Both types of porphyrins retain strong fluorescence (tau(fl) = 10-12 ns, phi(fl) = 0.3-0.4), and their radiative rate constants (k(r)) are 3-4 times higher than those of planar H2TCHP's. 3) Nonplanar deformations dramatically enhance nonradiative decay of triplet states of regular Pd porphyrins. For example, planar PdTCHP phosphoresces with high quantum yield (phi(phos) = 0.45, tau(phos) = 1118 micros), while saddled PdPh4TCHP is practically nonemissive. In contrast, both ruffled and saddled PdAr(n)TBP's retain strong phosphorescence at ambient temperatures (PdPh2TBP: tau(phos) = 496 micros, phi(phos) = 0.15; PdPh4TBP: tau(phos) = 258 micros, phi(phos) = 0.08). It appears that pi-extension is capable of counterbalancing deleterious effects of nonplanar deformations on triplet emissivity of Pd porphyrins.

Regional temperature changes in the brain during somatosensory stimulation

Time-dependent variations in the brain temperature (Tt) are likely to be caused by fluctuations of cerebral blood flow (CBF) and cerebral metabolic rate of oxidative consumption (CMRO2) both of which are seemingly coupled to alterations in neuronal activity. We combined magnetic resonance, optical imaging, temperature sensing, and electrophysiologic methods in alpha-chloralose anesthetized rats to obtain multimodal measurements during forepaw stimulation. Localized changes in neuronal activity were colocalized with regional increases in Tt (by approximately 0.2%), CBF (by approximately 95%), and CMRO2 (by approximately 73%). The time-to-peak for Tt (42+/-11 secs) was significantly longer than those for CBF and CMRO2 (5+/-2 and 18+/-4 secs, respectively) with a 2-min stimulation. Net heat in the region of interest (ROI) was modeled as being dependent on the sum of heats attributed to changes in CMRO2 (Qm) and CBF (Qf) as well as conductive heat loss from the ROI to neighboring regions (Qc) and to the environment (Qe). Although tissue cooling because of Qf and Qc can occur and are enhanced during activation, the net increase in Tt corresponded to a large rise in Qm, whereas effects of Qe can be ignored. The results show that Tt increases slowly (by approximately 0.1 degrees C) during physiologic stimulation in alpha-chloralose anesthetized rats. Because the potential cooling effect of CBF depends on the temperature of blood entering the brain, Tt is mainly affected by CMRO2 during functional challenges. Implications of these findings for functional studies in awake humans and temperature regulation are discussed.

Synthesis and luminescence of soluble meso-unsubstituted tetrabenzo- and tetranaphtho[2,3]porphyrins

[Structure: see text]. Syntheses of soluble tetrabenzoporphyrins (TBP) and tetranaphtho[2,3]porphyrins (TNP), with multiple substituents in the conjugated aromatic rings but bearing no substituents in the meso-positions, is reported. Both types of porphyrins were obtained by direct aromatization of precursor porphyrins, annealed with either cyclohexene or dihydronaphthalene fragments. TBPs and TNPs possess powerful absorption bands in the near-infrared (lambda = 610-710 nm, epsilon = 100,000-300,000 M(-1) cm(-1)) and exhibit strong luminescence. Free bases and Zn complexes fluoresce with quantum yields of up to 50%, whereas Pd and Pt complexes phosphoresce in solutions at ambient temperatures. Remarkably, the phosphorescence quantum yields of Pd and Pt TBPs reach as high as 20-50%, which places them among the brightest near-infrared phosphors known to date.

Synthesis of symmetrical tetraaryltetranaphtho[2,3]porphyrins

A new method of synthesis of meso-tetraaryltetranaphtho[2,3]porphyrins (Ar4TNP) has been developed. Ar4TNPs with peripheral functional groups are obtained by oxidative aromatization of meso-tetraarylporphyrins in which pyrrole units are fused with either octahydro- or dihydronaphthalene moieties. These precursor porphyrins are synthesized in four to five steps from readily available starting materials, such as naphthalene or 1,4-benzoquinone. The pathway originating in dihydronaphthalene, i.e., the "dialine" route, was found to be superior to the alternative "octaline"route in that it (1) enables the shortening of the overall reaction sequence, (2) has a broader scope in terms of the peripheral substitution in Ar4TNPs, and (3) affords higher yields of the target porphyrins. Pd complexes of the synthesized Ar4TNPs exhibit remarkably strong absorption bands at 710-720 nm (epsilon approximately 200,000 M(-1) cm(-1)) and phosphoresce at room temperature with moderate quantum yields (phi = 2-3%, lambda(max) = 900-1000 nm). The absorption maxima of naphthoporphyrins substituted with eight methoxy groups (Ar4TNP(OMe)8) were found to be about 15-20 nm red shifted compared to the corresponding maxima of unsubstituted Ar4TNPs. The X-ray crystallographic data suggest that these spectral shifts are caused not by the differences in nonplanar distortions of the macrocycles but by the purely electronic effects of the substituents.

Emerging Applications of Phosphorescent Metalloporphyrins

The subject of phosphorescent metalloporphyrins is reviewed, focusing mainly on the development and application of Pt- and Pd-porphyrins. A summary of their general chemical and photophysical properties, and guidelines for rational design of the phosphorescent labels, bioconjugates and probes is given. Examples of different detection formats and particular bio-analytical applications developed in recent years are presented. The potential of phosphorescent porphyrin label methodology is discussed and compared to that of the long-decay fluorescent lanthanide chelates and other common fluorophores.

Phosphorescence lifetime imaging in turbid media: the inverse problem and experimental image reconstruction

Three-dimensional phosphorescence lifetime imaging is a novel method for the mapping of oxygen concentration in biological tissues. We present reconstruction techniques for recovering phosphorescent objects in highly scattering media based on the telegraph equation and two regularization methods, i.e., the Tikhonov-Phillips regularization and the maximum entropy method. Theoretical results are experimentally validated, and the reconstructed images of phosphorescent objects rendering oxygen maps in a layer are presented.

Novel Versatile Synthesis of Substituted Tetrabenzoporphyrins

A novel general synthetic route to tetraaryltetrabenzoporphyrins (Ar(4)TBP) with various peripheral functional groups is developed. The procedure includes (i) Barton-Zard condensation of 1-nitro- or 1-phenylsulfonylcyclohexenes with isocyanoacetic acid esters, (ii) condensation of the resulting 4,5,6,7-tetrahydroisoindoles with aromatic aldehydes to give fused tetraaryltetracylohexenoporphyrins (Ar(4)TCHP), and (iii) aromatization of the metal complexes of Ar(4)TCHP's into the corresponding Ar(4)TBP's. Cu and Zn complexes of Ar(4)TBP's are further demetalated to give the corresponding Ar(4)TBP free bases. The overall yields for the sequence range from 15% to 40%, making the method suitable for the preparation of gram quantities of Ar(4)TBP's in a single run. The scope of the method, the selection of the peripheral substituents, the choice of the metal ions, and their influence on the yields of aromatization are discussed. The basic spectroscopic properties of newly synthesized Ar(4)TBP's and Ar(4)TCHP's are reported together with the first X-ray crystallographic structure of the NiAr(4)TBP complex.

Phosphorescence lifetime imaging in turbid media: the forward problem

An adequate description of the propagation of near-infrared light in highly scattering media is important for imaging hidden luminescent inhomogeneities in tissues. We present an improved approach to modeling of the forward problem based on a telegraph equation. The asymptotic solutions of the telegraph equation are derived and analyzed. The expression for the mean photon path length is also obtained.

A method for measuring oxygen distributions in tissue using frequency domain phosphorometry

Phosphorescence lifetime of phosphors dissolved in biological fluids is dependent on the local oxygen concentration. When phosphor is added to the blood in vivo there is a distribution of lifetimes due to the distribution of oxygen concentrations in the blood of the sampled tissue volume. The distribution of oxygen can be assessed non-invasively and in practically real-time using frequency domain time-resolved phosphorometry. Here we describe a multi-frequency system for measurements of oxygen distributions in tissue in vivo.