Novel Androgen Receptor Antagonists for the Treatment of Prostate Cancer - Accounts in Drug Discovery Case Studies in Medicinal Chemistry - page 123

expressing either endogenous wt (MDA-MB-453) or mutant (CWR-22rv1 or
LNCaP) forms of AR that were transiently transfected with constructs con-
sisting of secreted alkaline phosphatase or luciferase reporter genes driven by
both the immediate promoter and enhancer of the human PSA gene. Effects of
human prostate cell proliferation were assessed in LNCaP cells, or LNCaP cells
engineered to overexpress wt AR. Pharmacodynamic (PD) effects on the
growth of ventral prostate and seminal vesicles induced by exogenous testos-
terone propionate supplementation were evaluated in sexually immature male
rats in a 3-day assay (immature rat prostate weight or IRPW assay). Weights of
the prostates and seminal vesicles, expressed as percent control of the full body
weight, were obtained to gauge the extent of PD effects. Anti-tumor activity
was measured in prostate tumor xenograft mouse models derived from patients
with advanced prostate carcinoma. The CWR-22-BMSLD1 (H874Y mutant
AR) human tumors are derived from prostate and retain sensitivity to endo-
genous circulating levels of androgens, but are only marginally responsive to
bicalutamide. Thus, this model was appropriate to investigate anti-tumor
activity in a bicalutamide-refractory setting. MDA PCa 2b is a tumor line
derived from bone metastasis of a prostate cancer patient and harbors two AR
mutations (L701H and T877A) which confer decreased AR sensitivity and
increased susceptibility to AR agonist activity of hormones, such as cortisol
and cortisone. LuCaP 23.1 and LuCaP 35 are human tumor xenografts derived
from lymph node metastases which express wt AR with gene amplification and
are expected to provide a good measure of activity against HRPC.
6.2.3 Screening Hits and Early Structure-Activity Relationships
An in silico pharmacophore-driven screening approach based upon clinical
anti-androgens, such as bicalutamide 2 and 2-hydroxyflutamide, 2 led to the
identification of novel bicyclic imides 9 and hydantoins 10 (e.g., 1 and 2,
Figure 6.1) that demonstrated potent binding anity to and functional
antagonism of the endogenous wt AR in MDA-MB-453 cells (Table 6.1).
Attempts to co-crystallize ligands in an antagonist conformation with the AR
LBD were unsuccessful due to aggregation of the protein. Compound 3 pro-
vided a unique opportunity since it was an antagonist of wt AR, but exhibited
an agonist profile toward the T877A mutant AR in LNCaP cells. 11 Co-crystal
structures of the T877A AR LBD with 3 provided significant insight into
binding of the lead series to AR at the molecular level. Several key structural
features were elucidated upon comparison of this structure to the available
crystal structure of DHT with T877A AR LBD. 11 The 4-nitro group on the
naphthalene ring occupies the same space as the C3 carbonyl of DHT, making
contacts with R752 and Q711. F764 forms an edge-face interaction with the
first aromatic ring of the naphthalene. The lipophilic bicyclic portion of 3
occupies the same position in the LBD as the C and D rings of DHT, but does
not carry substituents to form hydrogen bonds similar to those forged by the
C17 hydroxyl of DHT. Neither the carbonyls nor the nitrogen atom of the