Current Medicinal Chemistry - Volume 12, Issue 14, 2005

The mitotic cell cycle is a tightly regulated process that ensures the correct division of one cell into two daughter cells. Progress along the different phases of the cell cycle is positively regulated by the sequential activation of a family of serine-threonine kinases called CDKs (Cyclin Dependent Kinases). Their activity is counteracted by small proteins known as CDK inhibitors (CKI) that ensure the correct timing of CDK activation in the different phases of the cell cycle. The present review will deal with the role of one of this CKI, p27kip1, in human cancer, focusing in particular on the mechanisms underlying its functional inactivation in tumor cells. p27kip1 protein downregulation is usually achieved by proteasomal degradation and is often correlated to a worse prognosis in several types of human cancers, resulting in the reduction of disease free and overall survival. More recently, it has been proposed that p27kip1 protein, rather than degraded, can be functionally inactivated. The mechanisms and the implications of these two types of p27kip1 deregulation will be discussed and some potential therapeutic approaches targeting p27kip1 functions will be proposed.

Peptide deformylase (PDF) is a prokaryotic metalloenzyme that is essential for bacterial growth but is not required by mammalian cells. Thus, it represents a selective and promising target for the development of new antibacterial agents. Since deformylase inhibitors have yet to be used clinically as antibacterial drugs, compounds targeting this enzyme should avoid cross-resistance with currently used antibacterial agents. The PDF enzyme is a ferrous ion-containing metallohydrolase, but a nickel-containing surrogate is routinely used in the laboratory for testing inhibitors due to its better stability. Enzymes from several bacterial species have been cloned and both their three-dimensional structures and co-crystal structures with bound inhibitor have been determined. As a metallo enzyme, PDF lends itself to the well-precedented mechanism-based rational drug design approach. Using structural and mechanistic information together with high throughput screening, several types of potent PDF inhibitors have been identified. PDF inhibitors identified to date share a common structural feature of a “chelator + peptidomimetic” scaffold. Although compounds with many different chelators inhibit the cell free enzyme, only compounds containing hydroxamic acid or N-formyl hydroxylamine exhibit appreciable antibacterial activity. Several lead inhibitors have demonstrated in vivo efficacy and an excellent safety profile. Two PDF inhibitors, VIC-104959 (LBM415) and BB-83698, have progressed to Phase I clinical trials. In this review, different PDF inhibitors are compared and their biological activities are discussed. Structureactivity relationships have been established and the implications of this work in the design of future PDF inhibitors are considered.

The cytochrome P450 monooxygenase enzyme system is involved in the synthesis and/or degradation of a large number of endogenous compounds and in the biotransformation of drugs and other xenobiotics. 17α-Hydroxylase-C17,20-lyase (P450 17, CYP 17) is the key enzyme of the androgen biosynthesis. As androgens have been implicated in the development and progression of prostate cancer, this enzyme has become a promising therapeutic target. This paper will review the possible approaches dealing with P450 17 inhibition as a chemotherapeutic strategy in the struggle against prostate cancer.

Hyperphosphatemia is a common serious complication of chronic renal diseases, which needs appropriate continuous treatment in order to avoid ominous side effects. Therefore, oral chelating agents able to avoid phosphate absorption by the gut are mandatory. In the past, Aluminium salts, and more recently Calcium and Magnesium salts, and a synthetic resin polyallylamine hydrochloride have been employed, but Aluminium was later abandoned, because it has been a silent killer of many uremic patients, due to subtle absorption eventually leading to toxicity on Central Nervous System and bone, with allucinations, seizures, dementia, and osteomalacia, bone pain, fracturing osteodystrophy, and death. Recently, a new chelating agent able to bind dietary phosphate, namely Lanthanum carbonate has been introduced, with a proven efficacy profile for short-term treatment. However, after careful examination of the very few scientific papers available to date, we strongly advise caution before adopting, at present, lanthanum carbonate as a phosphate binder in uremic patients. In fact, notwithstanding minimized, some data are worrying: first, Lanthanum ions are absorbed, though at a minimal extent, by human gut; 2) pharmacokinetic evaluations show a greater exposure to Lanthanum in uremic patients;3) Lanthanum concentration is increased tenfold in blood and fivefold in bone after short-term supplementation in uremic patients; 4) there is no proofs that Lanthanum cannot cross the blood brain barrier in uremic patients; 5)Lanthanum has many biological effects and is potentially highly toxic. The Aluminum story should serve as cautionary tale when considering the use of new metal ions.

The irreversible spread of new resistance mechanisms against existing therapeutical antibiotics has led to the development of technologies and strategies for the glycosylation engineering of novel antibiotics. Amino-, C-branched and O-methylated 6-deoxyhexoses play a favourite role in the biosynthesis of clinically important antibiotics like tylosin, erythromycin or oleandomycin and are essential for the antibiotic activity. They are transferred onto the aglycon by glycosyltransferases using dTDP-activated deoxyhexoses. The in vitro biochemical characterization of the biosynthetic enzymes and the glycosyltransferases are, however, hampered due to the poor synthetic access to dTDP-activated deoxysugars and their biosynthetic intermediates. The overcoming of the poor availability of dTDP-activated sugars was the target of several researchers to fulfil their distinct aims with these sugars which were mostly involved in the synthesis of different biological active compounds. Several completely different strategies were used in the past years to improve the availability of dTDP-activated deoxysugars, varying from complete enzymatic synthesis via syntheses using reaction technology for yield optimization to full organic synthesis or shortcuts like the decomposition of commercially available antibiotics and later chemical activation of the sugar moieties. This review gives a survey of the synthesis of dTDP-activated sugars by chemical and chemoenzymatic approaches and discusses the promiscuity of glycosyltransferases to evaluate the chances for applying them for the production of new bioactive compounds. It summarizes the most important enzymes in the field of synthesis using biosynthetic pathway enzymes and describes solutions for occurring challenges during application. Finally, this review will give a survey about the availability of dTDP-activated sugars in sufficient scale and will also point at important sugars which are still bottlenecks and difficult to synthesize and therefore should become a target for enhanced research efforts.

The exact cause of Alzheimer's disease is still unknown; despite the dramatic progress in understanding. Most gene mutations associated with Alzheimer's disease point to the amyloid precursor protein and amyloid β. The α-, β- and γ-secretases are the three executioners of amyloid precursor protein processing. Significant progress has been made in the selective inhibition of these proteases, regardless of the availability of structural information. Several peptidic and non-peptidic leads were identified and first drug candidates are in clinical trials. Cholesterol lowering drugs and metal chelators are also in advanced clinical stages as disease modifiers. Successful trials demand either large cohorts or reliable markers for Alzheimer's disease. Therefore, several radiomarkers are under investigation to support such clinical trials.

Streptomyces is a genus of soil dwelling bacteria with the ability to produce natural products that have found widespread use in medicine. Annotation of Streptomyces genome sequences has revealed far more biosynthetic gene clusters than previously imagined, offering exciting possibilities for future combinatorial biosynthesis. Experiments to manipulate modular biosynthetic clusters to create novel chemistries often result in no detectable product or product yield is extremely low. Understanding the coupling between components in these hybrid enzymes will be crucial for efficient synthesis of new compounds. We are using new algebraic approaches to predict protein properties, and homologous recombination to exploit natural evolutionary constraints to generate novel functional enzymes. The methods and techniques developed could easily be adapted to study modular, multi-interacting complex systems where appreciable biochemical and comparative sequence data are available, for example, clinically significant non-ribosomally synthesised peptides and polyketides.