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.

Metal-based photosensitizers are of interest as their absorption and chemical binding properties can be modified via the use of different ligands. Ru(2+) based photosensitizers are known to be effective photodynamic therapy (PDT) agents against bacteria, whereas use for oncological indications in vivo has not been demonstrated with the same level of evidence. We present data showing that premixing the Ru(2+)-complex TLD1433 with transferrin increases the molar extinction coefficient, including longer activation wavelengths, reduces photobleaching rates, and reduces the toxicity of the complex improving overall PDT efficacy. As the transferrin receptor is upregulated in most malignancies, premixing the Ru(2+) complex with transferrin converts the active pharmaceutical ingredient TLD1433 into a drug of potentially considerable clinical utility.

Cancer remains a major global malaise requiring the advent of new, efficient and low-cost treatments. Photodynamic therapy, which combines a photosensitizer and photons to produce cytotoxic reactive oxygen species, has been established as an effective cancer treatment but has yet to become mainstream. One of the main limitations has been the paucity of photosensitizers that are effective over a wide range of wavelengths, can exert their cytotoxic effects in hypoxia, are easily synthesized and produce few if any side effects. To address these shortfalls, three new osmium-based photosensitizers (TLD1822, TLD1824 and TLD1829) were synthesized and their photophysical and photobiological attributes determined. These photosensitizers are panchromatic (i.e. black absorbers), activatable from 200 to 900 nm and have strong resistance to photobleaching. In vitro studies show photodynamic therapy efficacy with both red and near-infrared light in normoxic and hypoxic conditions, which translated to good in vivo efficacy of TLD1829 in a subcutaneous murine colon cancer model.

Accurate biodosimetry is needed to estimate radiation doses received in vivo from accidental or unwarranted radiation exposures. We investigated the use of DNA repair foci (e.g. gamma-H2AX) at late times after irradiation in vivo as a biodosimeter of initial ionizing radiation dose. Two radiosensitive strains (SCID and BALB/c) and two radioresistant strains (C57BL/6 and C3H/HeJ) were used to quantify gamma-H2AX foci in a skin tissue microarray after doses of 1 to 10 Gy at early and late times after irradiation (1 and 7 days). Using a 3D quantitative immunofluorescence microscopy analysis, we observed a dose response for gamma-H2AX foci for all strains at 30 min, 24 h and 7 days after irradiation. The numbers of residual foci were significantly different between each of the four strains and reflected the relative radiosensitivity in vivo. In comparing gamma-H2AX focus and micronucleus formation after irradiation, we also observed association between the number of micronuclei and number of foci after 1 and 7 days between radiosensitive and radioresistant strains. We conclude that 3D image analysis of gamma-H2AX in skin can be used to detect relative radiosensitivity based on late residual gamma-H2AX foci. This technique may be a useful biodosimeter to determine dose at times up to 1 week after accidental or catastrophic radiation exposure in vivo.