Targeting IKKε in Androgen-Independent Prostate Cancer Causes Phenotypic Senescence and Genomic Instability

Abstract

Advanced prostate cancer (PC) will often progress to a lethal, castration-resistant state. We previously demonstrated that IKKε expression correlated with the aggressiveness of PC disease.Here, we address the potential of IKKε as a therapeutic target in PC. We examined cell fate decisions (proliferation, cell death and senescence) in IKKε-depleted PC-3 cells, which exhibited delayed cell proliferation and a senescent phenotype, but did not undergo cell death. Using IKKε/TBK1 inhibitors, BX795 and Amlexanox, we measured their effects on cell fate decisions in androgen-sensitive-PC and androgen-independent-PC cell lines. Cell cycle analyses revealed a G2/M cell cycle arrest and a higher proportion of cells with 8N DNA content in androgenindependent-PC cells only. Androgen-independent-PC cells also displayed increased senescenceassociated (SA)--galactosidase activity; increased H2AX foci; genomic instability; and altered p15, p16 and p21 expression. In our mouse model, IKK inhibitors also decreased tumor growth of androgen-independent-PC xenografts but not 22Rv1 androgen-sensitive-PC xenografts. Our study suggests that targeting IKK with BX795 or Amlexanox in androgen-independent-PC cells induces a senescence phenotype and demonstrates in vivo anti-tumor activity. These results strengthen the potential of exploiting IKKε as a therapeutic target.

IKKε Inhibitor Amlexanox Promotes Olaparib Sensitivity through the C/EBP-β-Mediated Transcription of Rad51 in Castrate-Resistant Prostate Cancer

“…We have previously shown that IKKε inhibitors BX795 and Amlexanox decrease CRPC proliferation through the induction of a senescence phenotype accompanied with DNA damage and genomic instability [ 17 ]. To characterize the role of IKKε in the HR-mediated DNA damage repair induced by Olaparib, we evaluated the Amlexanox-Olaparib combination in the CRPC cell lines PC-3, DU145 and C4-2B.…”

“…The Amlexanox-Olaparib combination was also tested in hormone-sensitive PC (HSPC) cell lines ( Figure S2 ). Previously, we have shown that HSPC cells do not overexpress IKKε, and IKKε inhibitors have no effect on HSPC proliferation and DNA damage induction [ 17 ]. Similarly, the Amlexanox-Olaparib combination did not affect cell proliferation of LNCaP and 22Rv1 cells ( Figure S2 ).…”

“…The therapeutic potential of IKKε has been demonstrated through IKKε depletion, which decreased cell proliferation and tumor growth for breast, gastric, colorectal and prostate cancers [ 13 , 31 , 33 , 34 ]. Moreover, IKKε inhibitors, such as Amlexanox, BX795 or CYT387, show anti-proliferative activity in vitro and in vivo in breast cancer as well as CRPC cells [ 17 , 35 ]. Amlexanox is the only IKKε inhibitor approved by the FDA and is clinically used for the treatment of buccal ulcers and asthma.…”

“…IKKε-depleted PC-3 cells were produced in previous study [ 17 ]. The lentiviral short hairpin RNAs (shRNAs) against IKKε and RFP were purchased from Dharmacon (Chicago, IL, USA).…”

“…We have previously shown that IKKε inhibitors, BX795 and Amlexanox (an FDA-approved drug), also decreased CRPC cell proliferation and induced a senescence phenotype accompanied with DNA damage and genomic instability. Moreover, we demonstrated that BX795 and Amlexanox delay tumor growth in CRPC xenografts [ 17 ]. Taken together, these observations suggest that IKKε represents a promising target for the development of new treatments against CRPC.…”