Synthesis and Evaluation of Small Molecule Inhibitors of the Androgen Receptor N-Terminal Domain.

The androgen receptor (AR) is central to prostate cancer pathogenesis and has been extensively validated as a drug target. However, small-molecule anti-androgen therapies remain limited due to resistance and will eventually fail to suppress tumor growth, resulting in progression to castration-resistant prostate cancer (CRPC). The intrinsically disordered N-terminal domain (NTD) is crucial for AR transactivation and has been investigated as a suitable target in the presence of ligand binding domain mutations. A screening campaign identified biaryl isoxazole compound 7 as a weak inhibitor of the AR NTD. A library of biaryl analogues were synthesized, and their biological activities were assessed in a VCaP cell-based luciferase reporter gene assay. A structure-activity relationship (SAR) study revealed that indazole analogue 16 exhibited increased potency and favorable physicochemical properties with a benchmarked pharmacokinetic profile, providing a suitable starting point for further optimization of 16 as a CRPC therapeutic in the presence of AR mutations.

Current and emerging approaches to noncompetitive AR inhibition.

The androgen receptor (AR) has been shown to be a key determinant in the pathogenesis of castration-resistant prostate cancer (CRPC). The current standard of care therapies targets the ligand-binding domain of the receptor and can afford improvements to life expectancy often only in the order of months before resistance occurs. Emerging preclinical and clinical compounds that inhibit receptor activity via differentiated mechanisms of action which are orthogonal to current antiandrogens show promise for overcoming treatment resistance. In this review, we present an authoritative summary of molecules that noncompetitively target the AR. Emerging small molecule strategies for targeting alternative domains of the AR represent a promising area of research that shows significant potential for future therapies. The overall quality of lead candidates in the area of noncompetitive AR inhibition is discussed, and it identifies the key chemotypes and associated properties which are likely to be, or are currently, positioned to be first in human applications.

A rationale for determining, testing, and controlling specific impurities in pharmaceuticals that possess potential for genotoxicity.

The synthesis of pharmaceutical products frequently involves the use of reactive reagents and the formation of intermediates and by-products. Low levels of some of these may be present in the final drug substance and drug product as impurities. Such chemically reactive impurities may have at the same time the potential for unwanted toxicities including genotoxicity and carcinogenicity and hence can have an impact on product risk assessment. This paper outlines a procedure for testing, classification, qualification, toxicological risk assessment, and control of impurities possessing genotoxic potential in pharmaceutical products. Referencing accepted principles of cancer risk assessment, this document proposes a staged threshold of toxicological concern (TTC) approach for the intake of genotoxic impurities over various periods of exposure. This staged TTC is based on knowledge about tumorigenic potency of a wide range of genotoxic carcinogens and can be used for genotoxic compounds, for which cancer data are limited or not available. The delineated acceptable daily intake values of between approximately 1.5 microg/day for approximately lifetime intake and approximately 120 microg/day for < or = 1 month are virtually safe doses. Based on sound scientific reasoning, these virtually safe intake values do not pose an unacceptable risk to either human volunteers or patients at any stage of clinical development and marketing of a pharmaceutical product. The intake levels are estimated to give an excess cancer risk of 1 in 100,000 to 1 in a million over a lifetime, and are extremely conservative given the current lifetime cancer risk in the population of over 1 in 4 (http://seer.cancer.gov/statfacts/html.all.html). The proposals in this document apply to all clinical routes of administration and to compounds at all stages of clinical development. It is important to note that certain types of products, such as those for life-threatening indications for which there are no safer alternatives, allow for special considerations using adaptations of the principles outlined in this paper.

BIS repetita non placent -- a statistical analysis of the number of sample preparations and number of injections required for chromatographic analyses.

This article attempts to answer the question of how many replicate sample preparations and replicate chromatographic injections must be done to provide accurate results in chromatographic analyses of pharmaceuticals. Using a random selection of chromatographic runs obtained with 1-3 replicate preparations and duplicate injections, the variance associated with preparation-to-preparation and injection-to-injection variability were estimated by a mixed-model statistical analysis. The analysis also predicted the probability that two injections of the same sample preparation are not in agreement with each other. Results indicated that, with modern chromatographic equipment, duplicate injections do not improve the precision. The number of replicate preparations needed to provide accurate results for various types of analysis depends on the type of sample and the desired tightness of the specification limits.

Analysis of non-covalent aggregation of synthetic hPTH (1-34) by size-exclusion chromatography and the importance of suppression of non-specific interactions for a precise quantitation.

There are few methods available for the rapid and precise quantitation of non-covalent aggregation. Size-exclusion chromatography (SEC), a traditional approach, used to measure the non-covalent aggregation can easily disrupt the weak forces holding an aggregate together. Under the conditions described in this paper the disaggregation of non-covalent aggregate of the synthetic human parathyroid hormone hPTH (1-34) due to hydrophobic/electrostatic interactions with the size-exclusion chromatography column packing was completely suppressed. This report details the effectiveness of adding salts and organic solvents in the mobile phase to overcome non-specific interactions that disrupt the aggregate during the SEC process and may aid in the understanding precise quantitation of non-covalent aggregation.

A validated, sensitive HPLC method for the determination of trace impurities in acetaminophen drug substance.

A high-performance liquid chromatography (HPLC) method has been developed and validated for the simultaneous determination of n-propionyl-p-aminophenol, 3-chloro-4-hydroxyacetanilide, 4'-hydroxyacetophenone, 4-hydroxyacetophenone oxime, 4-acetoxyacetanilide and 4'-chloroacetanilide, the main impurities in acetaminophen drug substance. The chromatographic separation was achieved on an Eclipse XDB-18 reversed-phase column using a gradient elution, being solvent A: 0.01 M phosphate buffer at pH 3.0 and solvent B: methanol. The limit of quantitation (S/N=10:1) was 0.1 microg/ml for each impurity. The coefficients of variation were less than 4% for intra-day and inter-day analyses. The individual recovery of acetaminophen spiked samples ranged from 94 to 104% and the mean recovery for each level from 99 to 103% in the 1-150 microg/ml range for all impurities. The proposed method was successfully applied to the analyses of different lots and different manufactures of acetaminophen drug substance. The proposed method can be used for the routine quality control of acetaminophen.