Common structural basis for central nervous system drug design

The main theme of this thesis is that there is a common structural basis for drugs acting on the central nervous system (CNS), and that this concept may be used to design new CNS-active drugs which have greater specificity and hence less side-effects. To develop these ideas, the biological basis of how drugs modify CMS neurotransmission is described, and illustrated using dopaminergic pathways. An account is then given of the use of physicochemical concepts in contemporary drug design. The complete conformational analysis of several antipsychotic drugs is used to illustrate some of these techniques in the development of a model for antipsychotic drug action. After reviewing current structure-activity studies in several classes of CNS drugs (antipsychotics, anti-depressants, stimulants, hal1ucinogens, anticonvulsants and analgesics), a hypothesis for a common structural basis of CNS drug action is proposed- This is based on a topographical comparison of the X-ray structures of eight representative CNS-active drugs, and consists of three parts: 1.there is a common structural basis for the activity of many different CNS-active drug classes; 2. an aromatic ring and a nitrogen atom are the primary binding groups whose topographical arrangement is fundamental to the activity of these drug classes; 3. the nature and placement of secondary binding determines different classes of CNS drug activity. A four-Point model for this common structural basis is then defined using 14- CNS-active drug structures that include the original eight used in proposing the hypothesis. The coordinates of this model are: R1 (0. 3.5, 0), R2 (0, -3.5, O), N (4.8. -0.3, 1.4), and R3 (6.3, 1.3, 0), where R1 and R2 represent the point locations of a hydrophobic interaction of the common aromatic ring with a receptor, and R3 locates the receptor point for a hydrogen bond involving the common nitrogen, N. Extended structures were used to define the receptor points R1, R2 and R3, and the complete conformational space of each of the 14 molecules was considered. It is then shoun that the model may be used to predict whether a given structure is likely to show CNS activity: a search over 1,000 entries in the current Merck Index shows a high probability (82%) of CNS activity in compounds fitting the structural model. Analysis of CNS neurotransmitters and neuropeptides shows that these fit the common model well. Based on the available evidence supporting chemical evolution, protein evolution, and the evolution of neurotransmitter functions, it is surmised that the aromatic ring/nitrogen atom pharmacophore proposed in the common model supports the idea of the evolution of CNS receptors and their neurotransmitters, possibly from an aromatic amine or acety1cho1ine acting as a primaeval communicating molecule. The third point in the hypothesis trilogy is then addressed. The extensive conformation-activity analyses that have resulted in well-defined models for five separate CNS drug classes are used to map out the locations of secondary binding groups relative to the common model for anti-psychotics, antidepressants, analgesics, anticholinergics, and anticonvulsants. With this information, and knowledge derived from receptor-binding data, it is postulated that drugs having specified activity could be designed. In order to generate novel structures having a high probability of CNS-activity, a process of drug design is described in which known CNS structures are superimposed topographically using the common model as a template. Atoms regarded as superfluous may be selectively deleted and the required secondary binding groups added in predicted locations to give novel structures. It is concluded that this process provides the basis for the rational design of new lead compounds which could further be optimized for potent and specific CNS activity.

Evidence for a common role for the serine-type Plasmodium falciparum serine repeat antigen proteases : implications for vaccine and drug design

Serine repeat antigens (SERAs) are a family of secreted “cysteine-like” proteases of Plasmodium parasites. Several SERAs possess an atypical active-site serine residue in place of the canonical cysteine. The human malaria parasite Plasmodium falciparum possesses six “serine-type” (SERA1 to SERA5 and SERA9) and three “cysteine-type” (SERA6 to SERA8) SERAs. Here, we investigate the importance of the serine-type SERAs to blood-stage parasite development and examine the extent of functional redundancy among this group. We attempted to knock out the four P. falciparum serine-type SERA genes that have not been disrupted previously. SERA1, SERA4, and SERA9 knockout lines were generated, while only SERA5, the most strongly expressed member of the SERA family, remained refractory to genetic deletion. Interestingly, we discovered that while SERA4-null parasites completed the blood-stage cycle normally, they exhibited a twofold increase in the level of SERA5 mRNA. The inability to disrupt SERA5 and the apparent compensatory increase in SERA5 expression in response to the deletion of SERA4 provides evidence for an important blood-stage function for the serine-type SERAs and supports the notion of functional redundancy among this group. Such redundancy is consistent with our phylogenetic analysis, which reveals a monophyletic grouping of the serine-type SERAs across the genus Plasmodium and a predominance of postspeciation expansion. While SERA5 is to some extent further validated as a target for vaccine and drug development, our data suggest that the expression level of other serine-type SERAs is the only barrier to escape from anti-SERA5-specific interventions.

Drug-herb interactions: eliminating toxicity with hard drug design.

By searching the literatures, it was found that a total of 32 drugs interacting with herbal medicines in humans. These drugs mainly include anticoagulants (warfarin, aspirin and phenprocoumon), sedatives and antidepressants (midazolam, alprazolam and amitriptyline), oral contraceptives, anti-HIV agents (indinavir, ritonavir and saquinavir), cardiovascular drug (digoxin), immunosuppressants (cyclosporine and tacrolimus) and anticancer drugs (imatinib and irinotecan). Most of them are substrates for cytochrome P450s (CYPs) and/or P-glycoprotein (PgP) and many of which have narrow therapeutic indices. However, several drugs including acetaminophen, carbamazepine, mycophenolic acid, and pravastatin did not interact with herbs. Both pharmacokinetic (e.g. induction of hepatic CYPs and intestinal PgP) and/or pharmacodynamic mechanisms (e.g. synergistic or antagonistic interaction on the same drug target) may be involved in drug-herb interactions, leading of altered drug clearance, response and toxicity. Toxicity arising from drug-herb interactions may be minor, moderate, or even fatal, depending on a number of factors associated with the patients, herbs and drugs. Predicting drug-herb interactions, timely identification of drugs that interact with herbs, and therapeutic drug monitoring may minimize toxic drug-herb interactions. It is likely to predict pharmacokinetic herb-drug interactions by following the pharmacokinetic principles and using proper models that are used for predicting drug-drug interactions. Identification of drugs that interact with herbs can be incorporated into the early stages of drug development. A fourth approach for circumventing toxicity arising from drug-herb interactions is proper design of drugs with minimal potential for herbal interaction. So-called ”hard drugs” that are not metabolized by CYPs and not transported by PgP are believed not to interact with herbs due to their unique pharmacokinetic properties. More studies are needed and new approached are required to minimize toxicity arising from drug-herb interactions.

Evidence based drug therapy : are optimal doses and multiple medication therapies realistic in patients with chronic heart failure

Background: Chronic Heart Failure (CHF) has a high mortality and morbidity. Large scale randomised controlled trials have proven the benefits of beta blockade and ACE inhibitors in reducing mortality in patients with CHF and expert guidelines mandate their use. In spite of these recommendations, important therapies are under-prescribed and under-utilised.

Method: 1015 consecutive patients enrolled in CHF management programs across Australia were surveyed during 2005-2006 to determine prescribing patterns in heart failure medications. These patients were followed-up for a period of 6 months.

Results: The survey revealed that beta blockers were prescribed to 80% of patients (more than 85% were on sub-optimal doses) and 70% were prescribed Angiotensin converting enzyme (ACE) inhibitors (approximately 50% were on sub-optimal dose). 19% of patients were prescribed Angiotensin receptor blockers (ARBs). By 6 months <25% of the patients who were on sub-optimal dose beta blockers or ACE inhibitors at baseline, had been up-titrated to maximum dose (p<0.0001). In CHF programs, were nurses were able to titrate medications, 75% of patients reached optimal dose of beta blockers compared to those programs with no nurse-led medication titration, where only 25% of patients reached optimal dose (p<0.004). When examining optimal dosage for any two of these mandatory medications, less patients were on optimal therapy. Beta blockers and ACE inhibitors, were both prescribed in combination in 60% of patients. While beta blockers and ARBs were prescribed to 15% of patients.

Conclusion: Whilst prescribing rates for a single medication strategy of beta blockers, or ACE inhibitors were greater than 70%, an increase in dosage of these medications and utilisation of proven combination therapy of these medications was poor. It is suggested that clinical outcomes for this cohort of patients could be further improved by adherence to evidence-based practice, ESC guidelines, and optimisation of these medications by heart failure nurses in a CHF program. On the basis of these findings and in the absence of ready access to a polypill, focussing on evidence-based practice to increase utilisation and optimal dosage of combination medication therapy is critical.

pH-sensitive and targeted PLGA-based drug delivery to colorectal cancer

Investigation on targeted PLGA based drug delivery system for the therapy of colorectal cancer. The results from in-vitro cell experiments indicated that prepared systems have potent cytotoxicity and high affinity to HT-29 cancer cells. Results were published on Biomedical Engineering and Informatics and ICONN conference proceeding.

Observer-based controller design of time-delay systems with an interval time-varying delay

This paper considers the problem of designing an observer-based output feedback controller to exponentially stabilize a class of linear systems with an interval time-varying delay in the state vector. The delay is assumed to vary within an interval with known lower and upper bounds. The time-varying delay is not required to be differentiable, nor should its lower bound be zero. By constructing a set of Lyapunov–Krasovskii functionals and utilizing the Newton–Leibniz formula, a delay-dependent stabilizability condition which is expressed in terms of Linear Matrix Inequalities (LMIs) is derived to ensure the closed-loop system is exponentially stable with a prescribed α-convergence rate. The design of an observerbased output feedback controller can be carried out in a systematic and computationally efficient manner via the use of an LMI-based algorithm. A numerical example is given to illustrate the design procedure.

Synthesis and biological evaluation of novel folic acid receptor-targeted, β-cyclodextrin-based drug complexes for cancer treatment

Drug targeting is an active area of research and nano-scaled drug delivery systems hold tremendous potential for the treatment of neoplasms. In this study, a novel cyclodextrin (CD)-based nanoparticle drug delivery system has been assembled and characterized for the therapy of folate receptor-positive [FR(+)] cancer. Water-soluble folic acid (FA)-conjugated CD carriers (FACDs) were successfully synthesized and their structures were confirmed by 1D/2D nuclear magnetic resonance (NMR), matrix-assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF-MS), high performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), and circular dichroism. Drug complexes of adamatane (Ada) and cytotoxic doxorubicin (Dox) with FACD were readily obtained by mixed solvent precipitation. The average size of FACD-Ada-Dox was 1.5-2.5 nm. The host-guest association constant Ka was 1,639 M-1 as determined by induced circular dichroism and the hydrophilicity of the FACDs was greatly enhanced compared to unmodified CD. Cellular uptake and FR binding competitive experiments demonstrated an efficient and preferentially targeted delivery of Dox into FR-positive tumor cells and a sustained drug release profile was seen in vitro. The delivery of Dox into FR(+) cancer cells via endocytosis was observed by confocal microscopy and drug uptake of the targeted nanoparticles was 8-fold greater than that of non-targeted drug complexes. Our docking results suggest that FA, FACD and FACD-Ada-Dox could bind human hedgehog interacting protein that contains a FR domain. Mouse cardiomyocytes as well as fibroblast treated with FACD-Ada-Dox had significantly lower levels of reactive oxygen species, with increased content of glutathione and glutathione peroxidase activity, indicating a reduced potential for Dox-induced cardiotoxicity. These results indicate that the targeted drug complex possesses high drug association and sustained drug release properties with good biocompatibility and physiological stability. The novel FA-conjugated β-CD based drug complex might be promising as an anti-tumor treatment for FR(+) cancer.

A nanoliposome-based drug delivery system for cancer

The current project shows that the sulfatide-containing nanoliposome (SCL) drug delivery system could be an effective and safe nanocarrier for the anticancer agent doxorubicin to target tumours with high expression of tenascin-C. Moreover, SCL encapsulation could be a new strategy for the treatment of diseases in the central nervous system.

Regulation of HIV Gag conformation and complex formation

The results of this research will help in a better understanding of HIV morphogenesis, which will hopefully lead to a structure based drug design towards the virus.

Tailored mesoporous silica nanoparticles for controlled drug delivery: platform fabrication, targeted delivery, and computational design and analysis

Mesoporous silica nanoparticles (MSNs) are exceptionally promising drug carriers for controlled drug delivery systems because their morphology, pore structure, pore volume and pore size can be well tailored to obtain certain drug release profiles. Moreover, they possess the ability to specifically transport and deliver anti-cancer drugs when targeting molecules are properly grafted onto their surface. MSNs based drug delivery systems have the potential to revolutionize cancer therapy. This review provides a comprehensive overview of the fabrication, modification of MSNs and their applications in tumour-targeted delivery. In addition, the characterization and analysis of MSNs with computer aided strategies were described. The existing issues and future prospective concerning the applications of MSNs as drug carriers for controlled drug delivery systems were discussed.

Assessing team learning practices in project/ design based learning approach

Team learning is considered as a constructive way for enhancing students learning in collaborative environment. It involves interaction between students through peer-to-peer learning, which makes students to be problem solver, an excellent communicator, a good reviewer and a manager. The School of Engineering at Xxx University practices project/design based learning as one of its learning and teaching approach. The project/design based learning process helps students to be self directed leaners which enhances the student learning outcomes towards attaining graduate career expected skills. An Overarching goal of this study is assessing the team learning experiences of cohort of students from third year civil undergraduate engineering in a project/design based learning approach at Xxx University. From the students’ experiences and views, this study will investigate and visualize the students choice of a unique team learning practice which enhances their learning outcomes in project/design based curriculum.

A research agenda for design-based learning in engineering education

It is often argued that ‘design’ is an (perhaps the) essential characteristic of engineering practice; that, “Design requires unique knowledge, skills, and attitudes common to all engineering disciplines, and it is these attributes that distinguish engineering as a profession.” Hence, it is not surprising to see engineering design identified as a key element of engineering education. There are a range of pedagogical models described, badged with a range of names, that are suggested as approaches to teaching engineering design, for example: project-based learning, problem-based learning, design-based learning, conceive-design-implement-operate (CDIO), problem-oriented project-based learning, social design based learning and project-oriented, design-based learning. While significant literature on engineering design education generally exists, many authors note open questions regarding optimal pedagogical approaches, and opportunities for further evaluation and research. In this paper we draw on literature about design education and DBL in engineering education, and synthesise themes that present a potential research agenda for those educators involved in DBL in engineering education.A search of the research literature was conducted using terms related to DBL in engineering education, including ‘Engineering Design’, ‘Design Education’, ‘Engineering + Project Based Learning’, ‘Engineering + Problem Based Learning’ and ‘Engineering + Design Based Learning’. The literature thus collected was expanded by inspecting the lists of references in the initially identified literature set for further potentially relevant literature. This process was repeated until no further related literature was identified, and resulted in 124 items. All collected literature was carefully reviewed for explicitly identified suggestions for future research. The authors also considered the literature set as a whole to identify additional research possibilities implied by aspects of DBL practice commonly addressed weakly, or not at all, in the available published research. From the results of this review, a set of themes was synthesised by grouping related research recommendations and possibilities. In the following section the identified research themes are presented and, for each, a summary of the supporting literature is given and a central research question is formulated by the authors.