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One of the major requirements for a successful and life-lasting organ transplant is the access to safe, least toxic and permanent tolerance-inducing drugs. In this study we wished to evaluate the effects of tolerogenic doses of the immunosuppressive drugs mycophenolic acid (MPA) and tacrolimus (Tac) on clonal β-cell lines, both in vivo and in vitro. Here we demonstrate that combined administration of low-dose MPA and Tac for 23 days induced permanent tolerance in an allogeneic β-cell line transplant in Wistar rat liver through the portal vein. This short-term treatment of tolerogenic doses of the two drugs was deleterious to the survival of the transplanted cells but a small percentage of the cells could resist the effect and become fully active when the drugs were removed. The surviving cells, retrieved from growth in vivo, did not exhibit increased resistance in comparison to the original cells when tested in vitro at two glucose concentrations, 10 and 20 mM. The presence of a small percentage of resistant cells at the two glucose concentrations was also detected in the in vitro study after a continuous 8-day treatment demonstrating that the in vivo resistance was not related to micro-environmental protection but possibly to a phenotypic cell state that is yet to be determined.

Background The aim of this study was to assess the efficiency of photodynamic therapy (PDT) on human pancreatic cancer cells in vitro and in an animal model. Methods Human pancreatic tumour cell lines were submitted to PDT with pheophorbide a (Ph a) a chlorophyll derivative, in culture and after grafting into athymic mice. Ph a was tested in culture (10−10−10–5 mol/l) with a 5-J/cm2 energy treatment and on tumour-bearing Nude mice (30 mg/kg intraperitoneally) with a 100-J/cm2 PDT session. The effect of PDT was assessed in vitro using proliferative, apoptotic and clonogenic tests and in vivo on tumour growth and on the induction of tumour necrosis. Results PDT inhibited tumour cell growth in culture by affecting DNA integrity. This tumour cell photodamage started at low concentration (10−7 mol/l) as corroborated by clonogenic and tumour growth tests. A strong necrosis was achieved in vivo with a single PDT session. Conclusion PDT destroyed human pancreatic carcinoma after low photosensitizer supply and weak energy application. It exerted this tumoricidal effect via apoptosis induction with a gentle protocol, and apoptosis and/or necrosis with a stronger protocol.

Nitric oxide (NO), an endogenous free radical, has been implicated in a wide range of biological functions. NO is generated enzymatically from the terminal guanidinonitrogen of L-arginine by nitric oxide synthase (NOS). Despite intensive investigations, the role of NO--either as the primary product of the L-arginine/NOS pathway or provided from the NO donor sodium nitroprusside (SNP)--in carcinogenesis and tumour cell growth remains unclear and controversial. The objective of this study was to examine the growth effects of NO on a ductal pancreatic adenocarcinoma in the rat and on a human pancreatic tumour cell line (HA-hpc2). In vivo, both SNP and endogenous induction of NO by endotoxins [lipopolysaccharide (LPS)] plus L-arginine significantly reduced the tumour growth. To investigate the mechanisms of NO anti-tumour growth action, the effects of either the SNP or L-arginine/NOS pathway were analysed on the HA-hpc2 cell line. Nitrite/nitrate production, NOS activity and iNOS expression [assessed by reverse transcription-polymerase chain reaction (RT-PCR)] were tested and related to growth (assessed by [3H]thymidine incorporation assay) and apoptosis (assessed by internucleosomal DNA cleavage). SNP exerted a dual effect on tumour cells: stimulation of the proliferation up to 1 mM and inhibition at higher concentrations. These effects were related to NO production. Both proliferative and cytostatic responses were inhibited by NO scavenger 2-phenyl-4,4,5,5-tetramethyl-hemidazoline-1-oxyl3-oxide (carboxy-PTIO). The marked apoptotic DNA fragmentation induced by SNP was also abolished by PTIO association. Unlike macrophages, the human pancreatic tumour cells did not seem to express intrinsically the L-arginine/NOS pathway. Macrophages were activated by HA-hpc2 cells as well as by LPS plus cytokines [interleukin (IL)-1beta plus tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma]. In HA-hpc2/macrophage co-cultures, NOS activity and inducible NOS (iNOS) transcription were stimulated, whereas an antiproliferative response was observed. These effects were related to both macrophage amount and NO production. Addition of LPS plus cytokines to co-cultures doubled iNOS activity, nitrite/nitrate production and tumoricidal effect. These data suggest the involvement of NO in pancreatic tumour growth and support the fact that generation of high levels of NO with potential production of endogenous reactive nitrogen intermediates may contribute to induction of apoptosis and tumour growth inhibition. Images Figure 2 Figure 5 Figure 6 Figure 7