Mechanism Of MPPa-PDT On Prostate Carcinoma

Tumors are very complicated disease and increase year by year in the world.The etiopathogenesis is still not clear and,thus,cancer is always an intense focus in medical science.Photodynamic therapy(PDT) was a new technique that arose in the 1970's last century and has shown its effectiveness in the treatment of a variety of tumors.PDT involves the administration of a tumorlocalizing photosensitizing agent followed by the activation of a specific wavelength.A photosensitizer is taken up by malignant or dysplastic tissues with some selectivity.Light delivery can be targeted to the appropriate tissue when the photosensitizer is illuminated with the light of an appropriate wavelength,and the molecule is excited.The energy of the activated photosensitizer is subsequently transferred to molecular oxygen with a series of energy transfers,and the highly reactive oxygen species are produced,resulting in cell death.The distinct characteristic of photosensitizers is the selective uptake,and,as a result,PDT can kill tumor cells definitely and can be used to clean up the remaining tumor cells after surgery to promote an effective cure.In fact,as early as 1900,Raab,a medical student in Germany,discovered a photodynamic reaction,but it was not applied to the clinic until recent years.The emergence of lasers in 1960 affected medical science effectively and it provided a new direction for tumor treatment.The laser became the preferred choice for photodynamic therapy because of its high monochromaticity.The use of photodynamic therapy in the treatment of malignant lesions has increased dramatically.Photosensitizer is often applied intravenously or topically prior to light irradiation and taken up by malignant or dysplastic tissues with some selectivity.The selective uptake of photosensitizer may also rely on the upregulation of low density lipoprotein receptor-mediated endocytosis of photosensitizer.And so there is less photosensitizer in the adjacent normal tissue and less reaction occurs to it.In contrast to radiation therapy and chemotherapy,PDT has few adverse effects,except for skin phototoxicity.It can be used repeatedly and consociates with other tumour treatments. The first health agency approval for PDT was granted for Photofrin in Canada in 1993 for use in bladder cancer.Although Photofrin is the most commonly used photosensitizer it has significant side effects.Therefore,major effort has been invested in the development of new sensitizers.However,so far,only a handful of photosensitizers have received regulatory approval and for a small number of diseases. Researchers continue their studies to improve the effectiveness of PDT and expand its use.Numerous new photosensitizers are in various stages of trials demonstrating the broad applicability.Emphasis is placed on those photosensitizers that can easily be prepared from the abundant natural precursors,protoheme and chlorophylls. Chlorophylls and their derivatives have shown themselves to be good potent photosensitizers.MPPa,one of the derivatives,is evidenced to be a potent photosensitizer.Apoptosis is recognised as an important cellular event during both normal development and disease progression.When cells undergo apoptosis,intracellular contents are wrapped in small bubbles of membrane and swallowed by phagocytes in the end.PDT can induce tumour cell apoptotic or necrosis.Mode of death induced by PDT mainly depends on types of cells and photosensitizers,and dosages of photodynamic therapy.Some studies show cells given a low photodynamic dose will engage with apoptotic;and with a high dose cells may undergo necrosis as cellular metabolism is catastrophically overwhelmed and this prevents apoptosis from occurring.The subcellular location of photosensitizer is also an important factor, mitochondria,lysosomes,plasma membranes,and nuclei of tumour cells have been evaluated as potential PDT targets.In our previous studies,we found MPPa-PDT induced apoptosis mainly via the mitochondrial/Caspase-9/Caspase-3 pathway.In vivo,histopathological examinations demonstrated apoptotic PC-3M cells with intact karyotheca,condensed nuclear chromatin,wide perinuclear spaces,and cellular shrinkage.Swollen mitochondria and their disappeared cristae were also observed.Mitochondrion plays an important role in apoptosis. Based on the previous results,we infer that MPPa-PDT probably affects mitochondrion firstly by increasing its membrane permeability,which results in swollen mitochondrion,and then cytochrome C is released followed by caspase cascade.ROS,GSH,NO,Ca²⁺,mitochondrial membrane potential,and cytochrome C were measured to elucidate the whole event.ROS played a very important role in apoptosis under both physiological and pathological conditions.Mitochondria were the target of ROS.PDT-triggered cancer destruction is thought to be primarily mediated by the cytotoxic action of ROS.GSH can scavenge molecules induced by oxidative stress.In mitochondria,ROS generated with MPPa-PDT stimuli.ROS can oxidize almost every compound in the cell and hence cause severe damage.The oxidative stress may lead to the free radical attack of membrane phospholipids, destroy of mitochondrion membrane,opening of permeability transition(PT) pores, and so improves membrane permeability.PT pores participate in the regulation of Ca²⁺,pH and MMP.All in all,ROS generated with MPPa-PDT stimuli,then the permeability of mitochondria was increased and finally cytochrome C was released. The latter may activate caspase cascade,which cleaved a variety of target proteins and eventually caused cell apoptosis.The above results showed MPPa to be a good photosensitizer candidature.We continued to examine the relationship between HIF-1αand MPPa-PDT.The Hypoxia Inducible Factors(HIFs) are key molecules in the hypoxic response and play critical roles during tumor cell expansion by regulating energy metabolism.The primary transcriptional response factor for hypoxic adaptation is HIF-1α,which can affect the regulation and expression of a series of genes in response to low levels of tissue oxygenation.The hypoxic signaling pathway is known to activate cell survival genes involved in glycolysis,angiogenesis and erythropoiesis.Therefore,adaptive mechanisms operate during hypoxia to achieve maintenance of cellular and tissue function,so that tumor cells can adapt to the adverse external environment.In some cases,the increment of HIF-1αwill cause tumor resistance to gammaradiation and anticancer drugs.Here,whether it'll cause tumor resistance to MPPa-PDT or not is to be studied.CoCl₂ might lead to various levels of hypoxia in cells,and result in HIF-1αexpression.The sequence specific siRNA can effectively block the expression of HIF- 1α.The results supported our previous hypothesis that HIF-1αwas a resistant effector towards PDT.