Abstract 257: Dual targeting of PI3K/AKT and AR pathway by combination therapy with phloretin in pre-clinical and patient derived xenografts of enzalutamide-resistant prostate cancer
Authors: Saraswati Sarita , Alhaider Abdulqader A. , Abdelgadir Abdelgalil M. 
Published: August 2018

Background:

With the emergence of resistance to FDA-approved inhibitors of androgen receptor (AR) signaling in prostate cancer, AR remains a viable target, engaged in the regulation of processes of pathological importance. CRPC tumors adapt the PI3K/AKT survival pathway to escape ADT. Thus, co-targeting AR and PI3K/AKT signaling is more effective therapeutic means for CRPC patients. Phloretin (PH), is a polyphenolic compound, found in apples, cider etc. It is known to possess anticancer and anti-angiogenetic activity. However, it`s effect against CRPC cells and the underlying mechanism are still unknown.

Experimental procedure:

Ten human PCa cell lines were tested in vitro for sensitivity to the PI3K/AKT inhibitor LY294002; enzalutamide (ENZ); PH; LY294002 + PH; ENZ + PH and LY294002 + ENZ + PH. In vivo studies were conducted using VCaP, 22Rv1, MR49F xenografts and LuCaP and 136CR PCa PDX tumors. Molecular docking was done with AutoDock Vina program. CSF Chimera and Ligplot programs were used for analysis of ligand and proteins interactions.

Results:

LY294002; ENZ; PH; LY294002 + PH; ENZ + PH and LY294002 + ENZ + PH inhibited in vitro growth of 7 of 10; 9 of 10; 9 of 10; 9 of 10; 9 of 10; 10 of 10 PCa cell lines, respectively, with increased sensitivity under androgen depletion. PH inhibited tumor growth in VCaP, 22Rv1, MR49F, MR49C xenografts and LuCaP and 13CR PCa PDX in a dose-dependent manner. Further, dual combination of ENZ + PH was more effective than LY294002 + PH in inhibiting tumor growth, whereas LY294002 + ENZ + PH diminished the tumor growth (P&lt;0.005) and demonstrated a longer disease specific survival. PH alone inhibited the AR-DNA interaction directly or by interfering with AR dimerization and inhibited AR-V7 expression and transcriptional activity. Further, it blocked the R1881 induced expression of AR-target genes kallikrein-related peptidase 3 (KLK3, also known as PSA); transmembrane protease, serine 2 (TMPRSS2); and FK506 binding protein 5 (FKBP5), glucocorticoid receptor (GR). In LuCaP PCa PDX tumors, PH administration decreased TV (P=0.021), proliferation (p=0.0024), PSA (p&lt;0.005) and decreased AR signaling and nuclear glucocorticoid receptor (nGR) localization. Computer aided molecular docking data shows the binding affinity and ligand efficiency scores of PH in following chronological order: AR &gt; AKT1 &gt; GR &gt; PI3K.

Conclusion:

Our studies suggested triple combination improved the efficacy of ENZ and PH. PH could be promising candidates for prevention of CRPC. This pre-clinical synergy provides a strong rationale for clinical evaluation of this combination.

Citation Format: Sarita Saraswati, Abdulqader A. Alhaider, Abdelgalil M. Abdelgadir. Dual targeting of PI3K/AKT and AR pathway by combination therapy with phloretin in pre-clinical and patient derived xenografts of enzalutamide-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 257.