Furthermore, blocking of either CXCR2 or NF kB activa tion down regulates BCL 2. Our results extend this obser vation to both anti apoptotic proteins and pro apoptotic proteins, BAX and BAD, with one difference. We did not use external IL 8 stimulation, but decreased the endog enous level that resulted in both transcriptional inhibi tion of BCL 2 and BCL 2 protein stability. Collectively, these finding suggest that IL 8 is the major regulator of chemoresistance in aggressive, AIPC Bortezomib cells and likely in patients with metastatic CaP. Indeed, IL 8 is prog nostic marker for aggressive disease and elevated levels of IL 8 in the plasma of patients with advanced disease have been reported. Targeted therapy offers a unique opportunity to inhibit the activity of specific gene that is critical for growth and metastasis. It is significant to note that knockdown of IL 8 expression in PC 3 and DU145 cells with IL 8 siRNA sig nificantly enhanced the chemotherapy responses as increased cytotoxicity. These observations might open a new opportunity to enhance the therapeutic efficacy of antitumor drugs docetaxel, Staurosporine and rapamy cin, in refractory tumors or in metastatic stage of AIPC. The combination of anti IL8 and approved chemotherapy protocols may allow, not only reduction in the dose of the drugs, but also increased efficacy. Conclusion We provide extensive evidence to demonstrate IL 8 medi ated regulation of complex intracellular molecular signal ing that leads to aggressive tumor cell behavior and increased survival during response to chemotherapy drug toxicity. We provide direct evidence for the control of anti apoptotic protein expression by IL 8, both at the tran scription and protein stability. The suppression of IL 8 using RNAi or specific cell permeable inhibitors of IL 8 or its receptors, may help sensitize AIPC to a wide variety of chemotherapeutic agents and might increase the survival of patients with end stage disease. Materials and methods Reagents Characterized fetal bovine serum was from Atlanta Bio logicals, Cell culture grade gentamicin, cul ture media, and transfection reagents were all from Gibco Invitrogen. Both non targeted, random sequence small interfering RNA and On Target anti IL 8siRNA were purchased from Dharmacon. The Smartpool On Target siRNA were an equal mix of 4 siRNA species designed to hybridize and destroy human IL 8 mRNA . These siRNAs were sequence verified to be specific to IL 8, thus eliminating the off target effects. Dual Glo luciferase assay kit was from Promega Corpora tion. All reagents, other than primer sets, for real time, quantitative RT PCR were from BioRad labs. All DNA primer sets for PCR and Q RTPCR were custom designed and synthesized from Sigma Genosys. Various primary and secondary antibodies were purchased from Cell signaling or Sigma Aldrich, unless otherwise indicated.