Bystander effects of nitric oxide in cellular models of anti-tumor photodynamic therapy

Tumor cells exposed to stress-inducing radiotherapy or chemotherapy can send signals to non- or minimally exposed bystander cells. Bystander effects of ionizing radiation are well established, but little is known about such effects in non-ionizing photodynamic therapy (PDT). Our previous studies revealed that several cancer cell types upregulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) after a moderate 5-aminolevulinic acid (ALA)-based PDT challenge. The NO signaled for cell resistance to photokilling as well as greater growth, migration and invasion of surviving cells. Based on this work, we hypothesized that diffusible NO produced by PDT-targeted cells in a tumor might elicit pro-growth/migration responses in non-targeted bystander cells. In the present study, we tested this using a novel approach, in which ALA-PDT-targeted human cancer cells on culture dishes (prostate PC3, breast MDA-MB-231, glioma U87, or melanoma BLM) were initially segregated from non-targeted bystanders via impermeable silicone-rimmed rings. Several hours after LED irradiation, rings were removed, and both cell populations analyzed for various post-hν responses. For a moderate and uniform level of targeted cell killing by PDT (~25%), bystander proliferation and migration were both enhanced. Enhancement correlated with iNOS/NO upregulation in surviving targeted cells in the following order: PC3 > MDA-MB-231 > U87 > BLM. If occurring in an actual tumor PDT setting and not suppressed (e.g., by iNOS activity or transcription inhibitors), then such effects could compromise treatment efficacy or even stimulate disease progression if PDT’s anti-tumor potency is not great enough

Protection of Melanized Cryptococcus neoformans from Lethal Dose Gamma Irradiation Involves Changes in Melanin's Chemical Structure and Paramagnetism

Certain fungi thrive in highly radioactive environments including the defunct Chernobyl nuclear reactor. Cryptococcus neoformans (C. neoformans), which uses L-3,4-dihydroxyphenylalanine (L-DOPA) to produce melanin, was used here to investigate how gamma radiation under aqueous aerobic conditions affects the properties of melanin, with the aim of gaining insight into its radioprotective role. Exposure of melanized fungal cell in aqueous suspensions to doses of γ-radiation capable of killing 50 to 80% of the cells did not lead to a detectable loss of melanin integrity according to EPR spectra of melanin radicals. Moreover, upon UV-visible (Xe-lamp) illumination of melanized cells, the increase in radical population was unchanged after γ-irradiation. Gamma-irradiation of frozen cell suspensions and storage of samples for several days at 77 K however, produced melanin modification noted by a reduced radical population and reduced photoresponse. More direct evidence for structural modification of melanin came from the detection of soluble products with absorbance maxima near 260 nm in supernatants collected after γ-irradiation of cells and cell-free melanin. These products, which include thiobarbituric acid (TBA)-reactive aldehydes, were also generated by Fenton reagent treatment of cells and cell-free melanin. In an assay of melanin integrity based on the metal (Bi+3) binding capacity of cells, no detectable loss in binding was detected after γ-irradiation. Our results show that melanin in C. neoformans cells is susceptible to some damage by hydroxyl radical formed in lethal radioactive aqueous environments and serves a protective role in melanized fungi that involves sacrificial breakdown

Upregulation of iNOS/NO in Cancer Cells That Survive a Photodynamic Challenge: Role of No in Accelerated Cell Migration and Invasion

Anti-tumor photodynamic therapy (PDT) is a unique modality that employs a photosensitizer (PS), PS-exciting light, and O2 to generate cytotoxic oxidants. For various reasons, not all malignant cells in any given tumor will succumb to a PDT challenge. Previous studies by the authors revealed that nitric oxide (NO) from inducible NO synthase (iNOS/NOS2) plays a key role in tumor cell resistance and also stimulation of migratory/invasive aggressiveness of surviving cells. iNOS was the only NOS isoform implicated in these effects. Significantly, NO from stress-upregulated iNOS was much more important in this regard than NO from preexisting enzymes. Greater NO-dependent resistance, migration, and invasion was observed with at least three different cancer cell lines, and this was attenuated by iNOS activity inhibitors, NO scavengers, or an iNOS transcriptional inhibitor. NO diffusing from PDT-targeted cells also stimulated migration/invasion potency of non-targeted bystander cells. Unless counteracted by appropriate measures, all these effects could seriously compromise clinical PDT efficacy. Here, we will review specific examples of these negative side effects of PDT and how they might be suppressed by adjuvants such as NO scavengers or inhibitors of iNOS activity or expression

Optimal algorithms for seeking the minimum

.The definition of the optimality of an algorithm is modified so that the optimal algorithm satisfies Bellman's principle. The search for a minimum using this technique is compared with J. Kiefer's algorith