Rational Design Of Platinum (?) Antitumoral Prodrugs:Synthesis And Functionalization

The therapeutic effect of conventional anticancer drugs is often undermined by their inability to target cancer cells;and the potency of these drugs is far from perfect due to low drug tolerance,acquired drug resistance and undesirable pharmacokinetics.Platinum-based anticancer drugs such as cisplatin,carboplatin and oxaliplatin are the major therapeutic agents clinically used to treat various cancers;however,the prognosis in most cases is gloomy and the side effects are serious.Tremendous efforts have been made in recent years on the development of Pt? complexes because they are more inert in blood plasma but can be activated once enters into the cells by reducing agents to give cytotoxic Pt? species,offering potential advantage over Pt? compounds regarding oral availability,reduced drug resistance and toxicity.Moreover,Due to the octahedral configuration of the Pt? center,the antitumor activity of these Pt?complexes can be finely tuned by tethering biologically active ligands or other chemotherapeutic drugs at the axial positions.The aim of this Ph.D.thesis is to synthesize,characterize and biologically evaluate Pt? analogues of cisplatin with targeted,non-targeted and biologically active ligands to reduce the toxicity and side effects associated with the Pt? parent drugs and to improve their lipophilicity and pharmacokinetics.The thesis contains four chapters which are summarized as follows.In chapter 1,the scope of platinum metal based anticancer drugs and there general mechanism of action has been reviewed.Usually the cytotoxic mechanism of all the Pt? anticancer complexes shared the same faith i.e.First aquation inside the cells and then their subsequent binding to N7 position of guanine bases of DNA strand.We also give some highlight on recent approaches toward designing and synthesis of Pt? anticancer complexes with dual functionalities.Pt? complexes considered as prodrugs because the octahedral configuration makes them inert in the blood plasma compared to their parental Pt? complexes.The cytotoxicity can only be achieved from these complexes once they get reduced intracellularly or extracellulary with biological reductants such as ascorbic acid and glutathione to release the cytotoxic Pt? species.Beside platinum,the recent research trend in the synthesis of ruthenium(Ru? and Ru?),gold(Au? and Au?)and titanium(Ti?)based anticancer complexes have also been discussed in detail.We also highlighted the role of drug delivery systems for safer and targeted delivery of platinum based drugs with emphasizes on the role of PLGA based targeted and non-targeted nano delivery system.PLGA is the only FDA approved block copolymer owing to its biocompatibility,biodegradability and low toxicity.The therapeutic agents can easily be encapsulated in the inner core of PLGA or they can be directly tether with the polymer and get release once inside the carcinoma cells.In chapter 2,a nanosystem composed of poly(lactic-co-glycolic acid)(PLGA),Pt? prodrug(PPD)and a-tocopheryl succinate(a-TOS)was designed to overcome the side effects of platinum based therapeutic agents.Redox-silent vitamin E succinate or a-tocopheryl succinate(a-TOS)can selectively kill cancer cells at concentrations nontoxic to normal cells or tissues,and hence is helpful for preventing systemic toxicity.The antitumor effect of a-TOS may arise from the inhibition of antiapoptotic proteins(Bcl-xL/Bcl-2)or the generation of reactive oxygen species(ROS).PPD and a-TOS self-assembled with PLGA,forming the dual-drug loaded nanoparticle(DDNP).The surface of DDNP was decorated with galactosamine(G),giving rise to G-DDNP that can actively target the liver cancer cells through the overexpressed asialoglycoprotein receptors.DDNP and G-DDNP were in spherical shape with required polydispersity and suitable mean size.The in vitro cytotoxicity against the human SMMC-7721 liver cancer cell line reveals that GDDNP are more potent than the corresponding free drugs and untargeted DDNP.The results demonstrate that dual-drug loaded nanoformulations with tumor-targeting function could be effective anticancer agents for conquering the shortcomings related with single-drug chemotherapy.In chapter 3,we have discussed the synthesis of two targeted Pt? complexes bearing one and two biotin moieties(Pt-Bio-I&Pt-Bio-II)along with their characterization(ESI-MS,HR-MS and multinuclear 1H-,13C-and 195Pt-NMR spectroscopy)and in vitro behavior in different carcinoma cells.Generally,it is believed that Pt? anticancer complexes works as prodrugs that are reduced with endogenous reductants in the tumor cells to form cytotoxic Pt? species.Cancer cells usually have a voracious appetite for cancer cell than that of normal cells.Biotin(vitamin H or B-7)draws special attention in recent years due to its higher uptake for cancer cells than that of the normal cells.The uptake of biotin is mainly done through a sodium-dependent multivitamin transporter(SMVT),which are significantly expressed over lung,kidney,breast and renal carcinoma cells.In vitro data reveals the conjugation of biotin with Pt? center results in lower IC50 values against all the tested tumor cell lines whereas they were particularly more sensitive toward breast cancer cells.When they were evaluated for their toxicity against mammary epithelial cells(MCF-10A/Vector),interestingly they were found to be marginally active or non-cytotoxic compared with their parental compound cisplatin.CD spectra of DNA binding studies of Pt-Bio-? and Pt-Bio-? with CT-DNA reveals that the Pt-Bio-? bind to DNA even without the presence of ascorbic acid while Pt-Bio-? didn't show any interaction under such conditions.In the presence of ascorbic acid both complexes shows similar binding behavior.The study indicate that these newly developed Pt? agents containing biotin at the axial positions appear to be promising lead compounds for targeted therapy to breast tumors.In chapter 4,we describe the synthesis,characterization(ESI-MS and multinuclear(1H,13C and 195Pt)NMR spectroscopy)and in vitro behavior of a Pt? scaffold tethered with cyclooxygenase inhibitor(Naproxen).Cyclooxygenase is a key enzyme involved in generation of inflammatory responses and also been associated with the tumorigenesis,believed to be the main reason for tumor cell resistance against cisplatin based therapy.COX-2 inhibitors such as non-steroidal anti-inflammatory drugs(NSAIDs)are widely used as cancer preventive and adjuvant chemotherapeutic agents.The in vitro data results suggested that conjugation of naproxen with Pt? center in Platin-N resulted in a better therapeutic profile against all the tested cell lines with IC50 values in micromolar to nanomolar range.Interestingly,Platin-N was found to be 14 fold more active than cisplatin against ovarian carcinoma cells(Caov-3 cells)with IC50 values of about 2 ?M.The lower cytotoxicity values compared to cisplatin might link with its higher intracellular uptake due to the lipophilic nature of the complex.Mechanistic studies reveals that Platin-N shows higher ROS production compared to cisplatin which also associated in the lowering of mitochondrial membrane potential as confirmed by JCl assay.Interestingly,when studied for their DNA binding interactions to plasmid(pBR322)DNA using gel electrophoresis,unlike other Pt? complexes the data reveals that the platin-N shows cleavage of DNA without the presence of any reducing agent.This result reveals that Platin-N is not acting as a prodrug but a drug itself.