Letters in Drug Design & Discovery - Volume 3, Issue 6, 2006

To therapeutically target disseminated tumor cells, while sparing the surrounding tissues, it is necessary to develop agents that interact with structures exposed selectively on the tumor cell surface. Members of the epidermal growth factor receptor family are commonly overexpressed in several tumor types and may serve as targeting structures. In this review we discuss the effects of EGFR and HER2 targeting agents that can deliver radioactive nuclides, i.e. antibodies and affibody molecules, on intracellular signaling. If the targeting agent, in addition to deliver radioactivity to the tumor, can sensitize the tumor for its effects by influencing signal pathways that regulate cell survival and proliferation this will probably be advantageous. We discuss the changes in intracellular signaling that occurs after treatment of cancer cells with the clinically approved monoclonal antibodies cetuximab (anti-EGFR), trastuzumab (anti-HER2) as well as HER2 targeted affibody molecules which are under preclinical development. An important defence mechanism for cells against radiation is to activate DNA repair systems and we also address how DNA repair proteins are regulated in response to radiation or EGFR activation.

The MDR chemosensitising activity of several analogues of the ardeemins, including five derivatives of the ABCD fragment, nine derivatives of the complete hexacyclic framework and one seco analogue lacking the B ring was studied. The results obtained confirm that the pharmacophoric moiety of the ardeemins as MDR reversers is located at their DEF fragment, and suggest that the epimer of the ardeemins at the alanine stereocenter should be more active than the natural stereoisomer.

Coenzyme Q10 (CoQ10) is a vitamin-like substance used in the treatment of several disorders including mitochondrial and neurodegenerative diseases. CoQ10 is a safe supplement with minimal side effects and low drug interaction potential. Here we review the clinical data on safety and efficacy of CoQ10 in neurological diseases.

Nelfinavir (Viracept®, Pfizer), and Amprenavir (Ageneraze®, GlaxoSmithKline) are potent bioavailable inhibitors of the enzyme Protease (PR) of the Human Immunodeficiency Vírus-1 (HIV-1), which have been developed by consistent structure-based drug design projects, and have been approved worldwide for the treatment of HIV infected patients. They act as competitive inhibitors, and tightly bind the active site of PR with high shape and electrostatic potential complementarity. However, the virus has shown the ability of fixating mutations which decrease the affinity of the antiretrovirals for the binding pocket of PR, although at the cost of decreasing (but to a minor extent) the affinity for the substrate. The consequent appearance of drug resistance compromised the long term efficacy of the drug. In this work we have extended such structure based drug design effort with computational methodologies, by performing very small substitutions in the inhibitors, directed at interacting with the most conserved amino acids. It is not possible to mutate the latter, at the cost of making the enzyme catalytically inactive. We show with a set of examples that significant increases in affinity can still be achieved without changing the overall structure, molecular mass and hydrophobicity of the inhibitors, thus preserving their very favourable ADME properties.

Ribozymes are involved in strategies to block gene expression and have been used as agents against viral infections and cancer. Emphasis has been on studies using hairpin and hammerhead ribozymes. The uniqueness of ribozymes is that they posses multiple turnover allowing high efficiency as antiviral agents. Ribozymes have been directed to human immunodeficiency virus (HIV), hepatitis (B, C and E) and human papillomavirus (HPV), the cause of cervical cancer. The mode of action of antiviral ribozymes, their structure and their in vitro effectiveness as inhibitors of HIV, HBV, HCV, HEV and HPV is reviewed. Although ribozymes have been demonstrated as effective antivirals in cell culture and some animal models, clinical studies have been limited. Nevertheless, ribozymes remain as a viable alternative to antisense and RNA interference

Phenylalanine 4-monooxygenase is a hepatic enzyme that controls the rate of catabolism of Lphenylalanine in man. Genetic defects in the phenylalanine 4-monooxygenase gene are known to be the cause of the majority of cases of phenylketonuria and these defects are now well characterized at the DNA and proteomic levels. However, the role of the phenylalanine 4-monooxygenase in xenobiotic metabolism is poorly understood. This Fe containing non-haem cytosolic monoxygenase is responsible for the S-oxidation of the thioether moiety of the mucoactive drugs, S-carboxymethyl-L-cysteine and S-methyl-L-cysteine, the major route of metabolism of these compounds. This S-oxidation biotransformation is regulated at both the genetic and hormonal level and results in both qualitative and quantitative differences in the metabolic profiles seen in individuals. To date the molecular genetic defects associated with the S-oxidation polymorphism are unknown and remain to be identified. Phenylalanine 4-monooxygenase appears to be like xanthine oxidase, aldehyde oxidase, prostaglandin H synthase, lipooxygenase and dopamine β-hydroxylase. Enzymes of intermediary metabolism are certainly involved in drug metabolism and their role will become more important and widespread in the future.

In the last five years we prepared and studied some dialkylaminoalkylnaphthalenes and cycloaminoalkylnaphthalenes with interesting opioid-like analgesic activity. In this paper we report on their lipophilicity evaluation combining computational and RP-HPLC experiments. A suitable computational method for the high-throughput log P screening was identified.

The in vitro evaluation of a series of (hetero)aromatic-substituted 4-hydroxycyclohexa-2,5-dienones (quinols) and analogues against M. tuberculosis is reported. The most active compound in the series was found to be 4-(benzothiazol-2-yl)-4-hydroxycyclohexa-2,5-dienone 1a with a minimum inhibitory concentration of 0.78 μg/mL. Biochemical evidence for involvement of the small redox protein thioredoxin C - a novel drug target - is also presented.

A series of eight N'-(disubstitutedbenzoyl)isoniazid derivatives have been synthesized and evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv using the alamar blue susceptibility test and the activity expressed as the minimum inhibitory concentration (MIC) in μg/mL. Compounds 15 and 16 exhibited a significant activity (0.5 μg/mL) when compared with first line drugs such as isoniazid (INH) and rifampicin (RIP) and could be a good starting point to develop new lead compounds in the fight against multi-drug resistant tuberculosis.

Interactions between cyclosporin A and three silymarin flavonoids (silybin, silydianin, and silychristin) were studied on the rat hepatocyte plasma membrane using the replacement of [3H]cyclosporin A by silymarin flavonoids. It was found that flavonoids significantly replaced CsA from its binding to the rat hepatocyte plasma membrane. It seems that these two types of compounds are competitors at the same binding site of the plasma membrane receptor.