Synergistic targeting of PI3K/AKT pathway and androgen receptor axis significantly delays castration-resistant prostate cancer progression in vivo.

The progression to castration-resistant prostate cancer (CRPC) correlates with gain-of-function of the androgen receptor (AR) and activation of AKT. However, as single agents, AR or AKT inhibitors result in a reciprocal feedback loop. Therefore, we hypothesized that combination of an AKT inhibitor with an antiandrogen might result in a more profound, long-lasting remission of CRPC. Here, we report that the AKT inhibitor AZD5363 potently inhibits proliferation and induces apoptosis in prostate cancer cell lines expressing the AR and has anticancer activity in vivo in androgen-sensitive and castration-resistant phases of the LNCaP xenograft model. However, we found that the effect of castration-resistant tumor growth inhibition and prostate-specific antigen (PSA) stabilization is transient and resistance occurs with increasing PSA after approximately 30 days of treatment. Mechanistically, we found that single agent AZD5363 induces increase of AR binding to androgen response element, AR transcriptional activity, and AR-dependent genes such as PSA and NKX3.1 expression. These effects were overcome by the combination of AZD5363 with the antiandrogen bicalutamide, resulting in synergistic inhibition of cell proliferation and induction of apoptosis in vitro, and prolongation of tumor growth inhibition and PSA stabilization in CRPC in vivo. This study provides a preclinical proof-of-concept that combination of an AKT inhibitor with antiandrogen results in prolonged disease stabilization in a model of CRPC.

Thomas C ，Lamoureux F ，Crafter C ，Davies BR ，Beraldi E ，Fazli L ，Kim S ，Thaper D ，Gleave ME ，Zoubeidi A ... -  《-》

Reciprocal feedback inhibition of the androgen receptor and PI3K as a novel therapy for castrate-sensitive and -resistant prostate cancer.

Qi W ，Morales C ，Cooke LS ，Johnson B ，Somer B ，Mahadevan D ... -  《Oncotarget》

Combination AZD5363 with Enzalutamide Significantly Delays Enzalutamide-resistant Prostate Cancer in Preclinical Models.

The phosphatidylinositol-4,5-bisphosphate 3-kinase/Akt (PI3K/Akt) pathway is a key pathway activated in castrate-resistant prostate cancer (CRPC). This preclinical study evaluates targeting of Akt with AZD5363 alone and in combination with enzalutamide (ENZ) to prevent and delay resistance. Our results demonstrate AZD5363 has significant proapoptotic, antiproliferative activity as monotherapy in ENZ-resistant cell lines in vitro and significantly decreased tumour growth in ENZ-resistant xenograft. The combination of AZD5363 and ENZ showed synergistic decreases in cell proliferation and induced cell-cycle arrest and apoptosis in prostate cancer cell lines LNCaP and C4-2. Notably, the combination of AZD5363 and ENZ resulted in an impressive regression of castrate-resistant LNCaP xenograft tumours without any recurrence demonstrated, whereas progression occurred with both monotherapies. Serum prostate-specific antigen (PSA) levels were also continuously suppressed, and nadir PSA levels were lower in the combination arm compared to ENZ alone. Combination AZD5363 and ENZ at time of castration similarly resulted in significant regression of tumours, with greater relative suppression of PSA compared to when administered to castrate-resistant xenografts. In summary, combination AZD5363 and ENZ significantly delays the development of ENZ resistance in preclinical models through synergistic increases in apoptosis and cell cycle arrest. Our results also suggest greater efficacy may be seen with earlier combination treatment. This study provides preclinical data to support evaluation of combination targeting of the PI3K/Akt pathway and the androgen-receptor axis in the clinic using AZD5363 and ENZ, respectively. Targeting of the Akt and androgen receptor pathways with AZD5363 and enzalutamide, respectively, significantly delayed the development of enzalutamide-resistant prostate cancer through increased apoptosis and cell cycle arrest. This preclinical synergy provides a strong rationale for clinical evaluation of this combination.

Toren P ，Kim S ，Cordonnier T ，Crafter C ，Davies BR ，Fazli L ，Gleave ME ，Zoubeidi A ... -  《-》

Carbidopa enhances antitumoral activity of bicalutamide on the androgen receptor-axis in castration-resistant prostate tumors.

Response to bicalutamide after castration failure is not durable and treatment options at this stage are limited. Carbidopa, an L-dopa decarboxylase (AR-coactivator) inhibitor, has been shown to retard prostate tumor growth/PSA production in xenografts. Here, we hypothesize that pharmacological targeting of the AR-axis by combination treatment with bicalutamide plus carbidopa significantly enhances antitumoral activity in vitro and in vivo compared to monotherapy with either drug. Carbidopa was tested for its ability to enhance the effects of bicalutamide on cell viability, apoptosis and PSA transactivation in LNCaP and C4-2 cells. The castration-resistant prostate cancer (CRPC) LNCaP xenograft tumor model was used in vivo. After CRPC progression, mice were treated with carbidopa (50 mg/kg) and bicalutamide (50 mg/kg) as monotherapy or in combination. Tumor volume and serum PSA were evaluated weekly. Combination treatment of carbidopa plus bicalutamide significantly inhibited cell viability in both cell lines and induced apoptosis. The combination treatment also decreased androgen-induced PSA transactivation by 62.6% in LNCaP cells and by 55.6% in C4-2 cells compared to control, while bicalutamide monotherapy reduced PSA levels by 27.5% and 29.1% in LNCaP and C4-2 cells. In vivo, bicalutamide monotherapy delayed LNCaP CRPC tumor growth rate by 72.2%, while combination treatment reduced tumor growth by 84.4% compared to control. Serum PSA was also reduced 70.6% with bicalutamide monotherapy, while combination therapy reduced PSA levels by 76.7% compared to control. This study demonstrates preclinical proof-of-principle that pharmacological targeting of prostate tumors by combination treatment of bicalutamide plus carbidopa significantly reduces AR activity, and thereby delays CRPC tumor progression in vivo.

Thomas C ，Wafa LA ，Lamoureux F ，Cheng H ，Fazli L ，Gleave ME ，Rennie PS ... -  《-》

Combination of carmustine and selenite effectively inhibits tumor growth by targeting androgen receptor, androgen receptor-variants, and Akt in preclinical models: New hope for patients with castration resistant prostate cancer.

Despite established androgen receptor (AR) antagonists, AR/AR-variants signaling remain a major obstacle for the successful treatment of castration resistant prostate cancer (CRPC). In addition, CRPC cells adapt to survive via AR-independent pathways to escape next generation therapies. Therefore, there is an urgent need for drugs that can target these signaling pathways in CRPC. In this study, we sought to determine whether carmustine and selenite in combination could induce apoptosis and inhibit growth of CRPC in-vitro and in-vivo. CRPC (22Rv1, VCaP, and PC-3) cell lines in culture and xenograft mouse were used. Combination of carmustine and selenite treatment significantly increased reactive oxygen species, apoptosis and growth inhibition in CRPC cells with down regulation of anti-apoptotic (Bcl-2 and Mcl-1) and proliferative proteins (c-Myc and cyclin-D1). This effect was associated with complete reduction of AR/AR-variants, AR-V7, PSA and significant induction of p27Kip1. Combination treatment substantially abolished phospho-Akt, phospho-GSK-3β, and anchorage-independent growth in AR-positive and AR-negative cells. Consistent with in-vitro results, combination treatment effectively induced apoptosis and completely inhibited xenograft tumor growth and markedly reduced AR/AR-variants, AR-V7, PSA, and Bcl-2 in xenograft tumors without causing genotoxicity in host mice. Individual agent treatment showed only partial effect. The combination treatment showed a significant synergistic effect. The present study is the first to demonstrate that the combination of carmustine and selenite treatment completely suppressed CRPC tumor growth by reducing AR/AR-variants and Akt signaling. Our findings suggest that the combination of carmustine and selenite could constitute a promising next-generation therapy for successful treatment of patients with CRPC.

Thamilselvan V ，Menon M ，Thamilselvan S 《-》