Improved therapeutic targeting of the androgen receptor: rational drug design improves survival in castration-resistant prostate cancer.

The growth and dependence of Prostate Cancer (PCa) on androgen stimulation led to the use of castration to reduce circulating levels of androgens and anti-androgens to directly target the androgen receptor (AR) ligand-binding domain (LBD). However, castration-resistant prostate cancer (CRPC) resistant to anti-androgens invariably develops and can be associated with AR genomic aberrations (mutations, amplification) and/or an increase in AR mRNA expression. Efforts to more effectively target the AR in CRPC led to the rational design of CYP17A1 inhibitors and more potent antiandrogens. The front-runner 2nd generation rationally-designed therapeutics targeting the AR, abiraterone and enzalutamide have been shown to improve survival and clinical outcome for CRPC patients. Several other CYP17A1 inhibitors and anti-androgens are in clinical and preclinical development. However, patients ultimately progress and current evidence suggests that this can occur through reactivation of AR signaling. Several ongoing programs aim to develop LBD independent therapeutic strategies that for example target the N terminus domain (NTD) of the AR or chaperone proteins. Rationally-designed approaches combining different strategies for targeting the AR or associated pathways also warrant clinical evaluation.

Interactions of abiraterone, eplerenone, and prednisolone with wild-type and mutant androgen receptor: a rationale for increasing abiraterone exposure or combining with MDV3100.

Prostate cancer progression can be associated with androgen receptor (AR) mutations acquired following treatment with castration and/or an antiandrogen. Abiraterone, a rationally designed inhibitor of CYP17A1 recently approved for the treatment of docetaxel-treated castration-resistant prostate cancer (CRPC), is often effective, but requires coadministration with glucocorticoids to curtail side effects. Here, we hypothesized that progressive disease on abiraterone may occur secondary to glucocorticoid-induced activation of mutated AR. We found that prednisolone plasma levels in patients with CRPC were sufficiently high to activate mutant AR. Mineralocorticoid receptor antagonists, such as spironolactone and eplerenone that are used to treat side effects related to mineralocorticoid excess, can also bind to and activate signaling through wild-type or mutant AR. Abiraterone inhibited in vitro proliferation and AR-regulated gene expression of AR-positive prostate cancer cells, which could be explained by AR antagonism in addition to inhibition of steroidogenesis. In fact, activation of mutant AR by eplerenone was inhibited by MDV3100, bicalutamide, or greater concentrations of abiraterone. Therefore, an increase in abiraterone exposure could reverse resistance secondary to activation of AR by residual ligands or coadministered drugs. Together, our findings provide a strong rationale for clinical evaluation of combined CYP17A1 inhibition and AR antagonism.

BCR-ABL1 kinase domain mutations: methodology and clinical evaluation.

The introduction of tyrosine kinase inhibitors (TKIs), starting with imatinib and followed by second and third generation TKIs, has significantly changed the clinical management of patients with chronic myeloid leukemia (CML). Despite their unprecedented clinical success, a proportion of patients fail to achieve complete cytogenetic remission by 12 months of treatment (primary resistance) while others experience progressive resistance after an initial response (secondary resistance). BCR-ABL1 kinase domain (KD) mutations have been detected in a proportion of patients at the time of treatment failure, and therefore their identification and monitoring plays an important role in therapeutic decisions particularly when switching TKIs. When monitoring KD mutations in a clinical laboratory, the choice of method should take into account turnaround time, cost, sensitivity, specificity, and ability to accurately quantify the size of the mutant clone. In this article, we describe in a "manual" style the methods most widely used in our laboratory to monitor KD mutations in patients with CML including direct sequencing, D-HPLC, and pyrosequencing. Advantages, disadvantages, interpretation of results, and their clinical applications are reviewed for each method.