Jason M. D'Antonio

Adaptive Auto-Regulation of Androgen Receptor Provides a Paradigm Shifting Rationale for Bipolar Androgen Therapy (BAT) for Castrate Resistant Human Prostate Cancer

Cell culture/xenograft and gene arrays of clinical material document that development of castration resistant prostate cancer (CRPC) cells involves acquisition of adaptive auto‐regulation resulting in >25‐fold increase in Androgen Receptor (AR) protein expression in a low androgen environment. Such adaptive AR increase paradoxically is a liability in castrated hosts, however, when supraphysiologic androgen is acutely replaced. Cell synchronization/anti‐androgen response is due to AR binding to replication complexes (RC) at origin of replication sites (ORS) in early G1 associated with licensing/restricting DNA for single round of duplication during S‐phase. When CRPC cells are acutely exposed to supraphysiologic androgen, adaptively increased nuclear AR is over‐stabilized, preventing sufficient degradation in mitosis, inhibiting DNA re‐licensing, and thus death in the subsequent cell cycle. These mechanistic results and the fact that AR/RC binding occurs in metastatic CRPCs directly from patients provides a paradigm shifting rationale for bipolar androgen therapy (BAT) in patient progressing on chronic androgen ablation. BAT involves giving sequential cycles alternating between periods of acute supraphysiologic androgen followed by acute ablation to take advantage of vulnerability produced by adaptive auto‐regulation and binding of AR to RC in CRPC cells. BAT therapy is effective in xenografts and based upon positive results has entered clinical testing. Prostate 72:1491–1505, 2012.

Longitudinal analysis of androgen deprivation of prostate cancer cells identifies pathways to androgen independence.

Following androgen ablation therapy, the majority of prostate cancer patients develop treatment resistance with a median time of 18–24 months to disease progression.

Cell‐autonomous intracellular androgen receptor signaling drives the growth of human prostate cancer initiating cells

The lethality of prostate cancer is due to the continuous growth of cancer initiating cells (CICs) which are often stimulated by androgen receptor (AR) signaling. However, the underlying molecular mechanism(s) for such AR‐mediated growth stimulation are not fully understood. Such mechanisms may involve cancer cell‐dependent induction of tumor stromal cells to produce paracrine growth factors or could involve cancer cell autonomous autocrine and/or intracellular AR signaling pathways.

Loss of Androgen Receptor-Dependent Growth Suppression by Prostate Cancer Cells Can Occur Independently from Acquiring Oncogenic Addiction to Androgen Receptor Signaling

The conversion of androgen receptor (AR) signaling as a mechanism of growth suppression of normal prostate epithelial cells to that of growth stimulation in prostate cancer cells is often associated with AR mutation, amplification and over-expression. Thus, down-regulation of AR signaling is commonly therapeutic for prostate cancer. The E006AA cell line was established from a hormone naïve, localized prostate cancer. E006AA cells are genetically aneuploid and grow equally well when xenografted into either intact or castrated male NOG but not nude mice. These cells exhibit: 1) X chromosome duplication and AR gene amplification, although paradoxically not coupled with increased AR expression, and 2) somatic, dominant-negative Serine-599-Glycine loss-of-function mutation within the dimerization surface of the DNA binding domain of the AR gene. No effect on the growth of E006AA cells is observed using targeted knockdown of endogenous mutant AR, ectopic expression of wild-type AR, or treatment with androgens or anti-androgens. E006AA cells represent a prototype for a newly identified subtype of prostate cancer cells that exhibit a dominant-negative AR loss-of-function in a hormonally naïve patient. Such loss-of-function eliminates AR-mediated growth suppression normally induced by normal physiological levels of androgens, thus producing a selective growth advantage for these malignant cells in hormonally naïve patients. These data highlight that loss of AR-mediated growth suppression is an independent process, and that, without additional changes, is insufficient for acquiring oncogene addiction to AR signaling. Thus, patients with prostate cancer cells harboring such AR loss-of-function mutations will not benefit from aggressive hormone or anti-AR therapies even though they express AR protein.

DNA licensing as a novel androgen receptor mediated therapeutic target for prostate cancer.

During middle G(1) of the cell cycle origins of replication orchestrate the ordered assembly of the pre-replication complex (pre-RC), allowing licensing of DNA required for DNA replication. Cyclin-dependent kinase activation of the pre-RC facilitates the recruitment of additional signaling factors, which triggers DNA unwinding and replication, while limiting such DNA replication to once and only once per cell cycle. For both the normal and malignant prostate, androgen is the major stimulator of cell proliferation and thus DNA replication. In both cases, the binding of androgen to the androgen receptor (AR) is required. However, the biochemical cascade involved in such AR-stimulated cell proliferation and DNA synthesis is dramatically different in normal versus malignant prostate cells. In normal prostate, AR-stimulated stromal cell paracrine secretion of andromedins stimulates DNA replication within prostatic epithelial cells, in which AR functions as a tumor suppressor gene by inducing proliferative quiescence and terminal differentiation. By direct contrast, nuclear AR in prostate cancer cells autonomously stimulates continuous growth via incorporation of AR into the pre-RC. Such a gain of function by AR-expressing prostate cancer cells requires that AR be efficiently degraded during mitosis since lack of such degradation leads to re-licensing problems, resulting in S-phase arrest during the subsequent cell cycle. Thus, acquisition of AR as part of the licensing complex for DNA replication represents a paradigm shift in how we view the role of AR in prostate cancer biology, and introduces a novel vulnerability in AR-expressing prostate cancer cells apt for therapeutic intervention.

AR (androgen receptor (dihydrotestosterone receptor; testicular feminization; spinal and bulbar muscular atrophy; Kennedy disease))

Review on AR (androgen receptor (dihydrotestosterone receptor; testicular feminization; spinal and bulbar muscular atrophy; Kennedy disease)), with data on DNA, on the protein encoded, and where the gene is implicated.