An in vitro investigation of the antitumour efficacy of novel hybrids containing artemisinin, porphyrin, or naphthalimide derivatives /

Abstract

Novel hybrid drugs have emerged as a promising new anticancer strategy. A hybrid drug is a compound in which two active ‘parent’ drugs are linked to create a single molecular entity with a multimodal action. The main objective of this study was to evaluate the anticancer potential of several novel hybrid drugs which contained a combination of artemisinin (ART) and either a porphyrin or naphthalimide (NAP) derivative. ARTs, NAPs and porphyrins have already shown promising anticancer activity both in vitro and in vivo. Real time cell analysis (RTCA) and cell count analysis were the chosen methods to evaluate cell growth and cell number following hybrid treatment. Another key objective of the current study was to determine if oxygen concentration could affect anticancer drug efficacy in vitro. This hypothesis was investigated in Chapter 2. Hypoxia, which often develops in tumour tissue, has been reported to adversely affect chemotherapy and radiotherapy during cancer treatment. Despite this evidence, standard atmospheric oxygen levels are employed during in vitro analyses of novel anticancer agents. The generated results clearly demonstrate that artesunate anticancer efficacy against HeLa cells was increased when oxygen levels were lowered to 4% (v/v) or 1% (v/v). This highlights the importance of oxygen concentration when evaluating novel anticancer agents. Photodynamic therapy (PDT) was applied to PC-3 cells in Chapter 3. PDT involves the combination of a photosensitiser (drug), light and oxygen to induce cell death. Hypoxia development in tissues during PDT has been shown to induce resistance highlighting the importance of oxygen in PDT outcome. Oxygen concentration was maintained at 4% (v/v) throughout analysis based on the results from Chapter 2. Protoporphyrin IX (PpIX) and hybrid AP433 were investigated in PC-3 cells. A novel light activation procedure was performed using a Q-Sun solar simulator. Light activation of both PpIX and hybrid AP433 could be observed. However, light irradiation procedure alone accounted for a loss in cell numbers. Therefore, PDT treatment will need to be further optimised before this family of hybrids can be effectively evaluated. viii ART-NAP hybrids were then investigated across four cell lines in 4% (v/v) oxygen environment. SG76, SG77 and SG81 were particularly effective against HL60 and PC-3 tumour cell lines. PNT1A prostate non-tumour cells were more tolerant to hybrid drugs than both parent compounds. Furthermore, SG77 was found to be the most selective hybrid with 11 times more activity in PC-3 when compared to PNT1A. The next objective was to investigate the potential mechanisms responsible for SG77 drug action. Gene expression analysis was performed to determine the potential for SG77 to induce oxidative stress, DNA damage and apoptosis. In addition, ROS generation, glutathione levels and apoptosis induction were quantified following SG77 treatment. Based on the data generated, intrinsic apoptosis, DNA damage and glutathione antioxidant response may be important in SG77 drug action. Furthermore, PC-3 were more sensitive to SG77 than non-tumour PNT1A with increased cytotoxicity, ROS generation, glutathione depletion and apoptosis. SG77 should be considered as a promising candidate for animal trials with the potential for a potent and selective cancer therapy which will improve patient outcome.