Transition metal complexes are of increasing interest as photosensitizers in photodynamic therapy (PDT) and, more recently, for photochemotherapy (PCT). In recent years, Ru (II) polypyridyl complexes have emerged as the most widely studied systems for both PDT and PCT. Their rich photochemical and photophysical properties derive from a variety of excited-state electronic configurations accessible with visible and near-infrared light, and these properties can be exploited for both energy-and electron-transfer processes that can yield highly potent oxygen-dependent and/or oxygen-independent photobiological activity. Selected examples highlight the use of rational design in coordination chemistry to control the lowest-energy triplet excited state configurations for eliciting a particular type of photoreactivity for PDT and/or PCT effects. These principles are also discussed in the context of the development of TLD1433, the first Ru(II)-based photosensitizer for PDT to enter a human clinical trial. The design of TLD1433 arose from a tumor-centered approach, as part of a complete PDT package that included the light component and the protocol for treating nonmuscle invasive bladder cancer. Briefly, this review summarizes *

Dosimetry for photodynamic therapy (PDT) is becoming increasingly complex as more factors are identified which may influence the effectiveness of a given treatment. The simple prescription of a PDT treatment in terms of the administered photosensitizer dose, the incident light and the drug-light time interval does not account for patient-to-patient variability in either the photosensitizer uptake, tissue optical properties or tissue oxygenation, nor for the interdependence of the photosensitizer-light-tissue factors. This interdependence is examined and the implications for developing adequate dosimetry for PDT are considered. The traditional dosimetric approach, measuring each dose factor independently, and termed here 'explicit dosimetry', may be contrasted with the recent trend to use photosensitizer photobleaching as an index of the effective delivered dose, termed here 'implicit dosimetry'. The advantages and limitations of each approach are discussed, and the need to understand the degree to which the photobleaching mechanism is linked, or 'coupled', to the photosensitizing mechanism is analysed. Finally, the influence of the tissue-response endpoints on the optimal dosimetry methods is considered.

Purpose: Anticancer drugs gain access to solid tumors via the circulatory system and must penetrate the tissue to kill cancer cells. Here, we study the distribution of doxorubicin in relation to blood vessels and regions of hypoxia in solid tumors of mice. Experimental Design:The distribution of doxorubicin was quantified by immunofluorescence in relation to blood vessels (recognized by CD31) of murine16C and EMT6 tumors and human prostate cancer PC-3 xenografts. Hypoxic regions were identified by injection of EF5. Results: The concentration of doxorubicin decreases exponentially with distance from tumor blood vessels, decreasing to half its perivascular concentration at a distance of about 40 to 50 Am, The mean distance from blood vessels to regions of hypoxia is 90 to 140 Am in these tumors. Many viable tumor cells are not exposed to detectable concentrations of drug following a single injection. Conclusions: Limited distribution of doxorubicin in solid tumors is an important and neglected cause of clinical resistance that is amenable to modification. The technique described here can be adapted to studying the distribution of other drugs within solid tumors and the effect of strategies to modify their distribution.

The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 mm(-1) and absorption coefficients between 0.002 and 0.1 mm(-1) showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle (breast), were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam.

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The photo-physical and photo-biological properties of two small (<2 kDa), novel Ru(ii) photosensitizers (PSs) referred to as TLD1411 and TLD1433 are presented. Both PSs are highly water-soluble, provide only very limited luminescence emission at 580-680 nm following excitation at 530 nm, and demonstrate high photostability with less than 50% photobleaching at radiant exposures H = 275 J cm(-2) (530 nm irradiation). It was previously shown that these two photosensitizers exhibit a large singlet oxygen ((1)O2) quantum yield (Φ (Δ) ∼0.99 in acetonitrile). Their photon-mediated efficacy to cause cell death (λ = 530 nm, H = 45 J cm(-2)) was tested in vitro in colon and glioma cancer cell lines (CT26.WT, CT26.CL25, F98, and U87) and demonstrated a strong photodynamic effect with complete cell death at concentrations as low as 4 and 1 μM for TLD1411 and TLD1433, respectively. Notably, dark toxicity was negligible at concentrations less than 25 and 10 μM for TLD1411 and TLD1433, respectively. The ability of the PSs to initiate Type I photoreactions was tested by exposing PS-treated U87 cells to light under hypoxic conditions (pO2 < 0.5%), which resulted in a complete loss of the PDT effect. In vivo, the maximum tolerated doses 50 (MTD50) were determined to be 36 mg kg(-1) (TLD1411) and 103 mg kg(-1) (TLD1433) using the BALB/c murine model. In vivo growth delay studies in the subcutaneous colon adenocarcinoma CT26.WT murine model were conducted at a photosensitizer dose equal to 0.5 and 0.2 MTD50 for TLD1411 and TLD1433, respectively. 4 hours post PS injection, tumours were irradiated with continuous wave or pulsed light sources (λ = 525-530 nm, H = 192 J cm(-2)). Overall, treatment with continuous wave light demonstrated a higher tumour destruction efficacy when compared to pulsed light. TLD1433 mediated PDT resulted in statistically significant longer animal survival compared to TLD1411. Two-thirds of TLD1433-treated mice survived more than 100 days (p < 0.01) whereas TLD1411-treated mice did not survive longer than 20 days. Here we present evidence that two novel PSs have very potent photo-biological properties and are able to cause PDT-mediated cell death in both in vitro cell culture models and in vivo tumour regression.

Reversible and localized blood-brain barrier disruption (BBBD) using focused ultrasound (FUS) in combination with intravascularly administered microbubbles (MBs) has been established as a non-invasive method for drug delivery to the brain. Using two-photon fluorescence microscopy (2PFM), we imaged the cerebral vasculature during BBBD and observed the extravasation of fluorescent dye in real-time in vivo. We measured the enhanced permeability upon BBBD for both 10kDa and 70kDa dextran conjugated Texas Red (TR) at the acoustic pressure range of 0.2-0.8 MPa and found permeability constants of TR10kDa and TR70kDa vary from 0.0006 to 0.0359 min−1 and 0.0003 to 0.0231 min−1, respectively. For both substances, a linear regression was applied on the permeability constant against the acoustic pressure and the slope from best-fit was found to be 0.039±0.005 min−1/MPa and 0.018±0.005 min−1/MPa, respectively. In addition, the pressure threshold for successfully induced BBBD was confirmed to be 0.4-0.6 MPa. Finally, we identified two types of leakage kinetics (fast and slow) that exhibit distinct permeability constants and temporal disruption onsets, as well as demonstrated their correlations with the applied acoustic pressure and vessel diameter. Direct assessment of vascular permeability and insights on its dependency on acoustic pressure, vessel size and leakage kinetics are important for treatment strategies of BBBD-based drug delivery.

LILT applied to wounds, delivering commonly used wavelengths and radiant exposures in the range of 1-20 J/cm(2), could produce changes in bacterial growth of considerable importance for wound healing. A wavelength of 630 nm appeared to be most commonly associated with bacterial inhibition. The findings of this study might be useful as a basis for selecting LILT for infected wounds.