Mechanisms of growth inhibition of primary prostate epithelial cells following gamma irradiation or photodynamic therapy include senescence, necrosis, and autophagy, but not apoptosis

Abstract

In comparison to more differentiated cells, prostate cancer stem‐like cells are radioresistant, which could explain radio‐recurrent prostate cancer. Improvement of radiotherapeutic efficacy may therefore require combination therapy. We have investigated the consequences of treating primary prostate epithelial cells with gamma irradiation and photodynamic therapy (PDT), both of which act through production of reactive oxygen species (ROS). Primary prostate epithelial cells were cultured from patient samples of benign prostatic hyperplasia and prostate cancer prior to treatment with PDT or gamma irradiation. Cell viability was measured using MTT and alamar blue assay, and cell recovery by colony‐forming assays. Immunofluorescence of gamma‐H2AX foci was used to quantify DNA damage, and autophagy and apoptosis were assessed using Western blots. Necrosis and senescence were measured by propidium iodide staining and beta‐galactosidase staining, respectively. Both PDT and gamma irradiation reduced the colony‐forming ability of primary prostate epithelial cells. PDT reduced the viability of all types of cells in the cultures, including stem‐like cells and more differentiated cells. PDT induced necrosis and autophagy, whereas gamma irradiation induced senescence, but neither treatment induced apoptosis. PDT and gamma irradiation therefore inhibit cell growth by different mechanisms. We suggest these treatments would be suitable for use in combination as sequential treatments against prostate cancer.

Duramycin-porphyrin conjugates for targeting of tumour cells using photodynamic therapy

“…An increased uptake and localisation of the "capped" porphyrin could potentially explain this increased sensitivity. However DNA damage in the prostate cells (suggesting localisation occurred in the nucleus) was induced after 1 hour incubation with the porphyrin [40]. This movement into the cell and localisation of the "capped" control porphyrin is unlike-ly to have occurred in the A2780 cells in the relatively short incubation of 5 min used in this study.…”

“…In a recent study [40] this "capped" control porphyrin was used in PDT experiments against benign and malignant prostate cells to assess its cytotoxic potential. "Capped" porphyrin N8.75 μM was seen to induce necrosis and prevent colony forming in irradiated prostate cells.…”

“…A porphyrin PS (5-[Aminobutyl-Noxycarbonyl)phenyl]phenyl]-10,15,20-tris(N-methyl-4-pyridinium) porphyrin trichloride) plus light irradiation was able to reduce cell survival and prevent colony forming in prostate epithelial cells at concentrations of N8.75 μM [40]. The porphyrins TTP (5,10,15,20-tetra-p-tolyl porphyrin) and THNP (5,10,15,20-tetra-p-naphthyl-porphyrin) after a light irradiation dose of 4.5 J/cm 2 were able to cause cell death in a human melanoma cell line in a concentration dependent manner [37].…”

“…Recovery of 4.8 mg of conjugate was achieved equating to 34.4% yield. An unconjugated, "capped" porphyrin was used as a control in which the NHS ester group used for conjugation was reacted with butylamine to eliminate any non-specific conjugation [40]. All photosensitiser containing compounds were kept, protected from light, at −20 °C.…”

Tumor heterogeneity and therapy resistance - implications for future treatments of prostate cancer

“…There was a significant reduction in viability with the combination treatment in normal and cancer cells, however the cancer cells showed less of a reduction in viability. We have previously shown that radiation can cause senescence of primary prostate epithelial cells rather than cell death, and so the small reduction in viability as measured by alamar blue could be because the cells are senescing rather than dying [20] . Therefore, we tested the effect of three drug doses with and without 2 Gy of radiation on colony formation [ Figure 2F].…”