In vitro and In vivo Molecular Evidence for Better Therapeutic Efficacy of ABT-627 and Taxotere Combination in Prostate Cancer

Abstract

Bone is the key metastatic site for prostate cancer. Endothelin 1 (ET-1) produced abundantly by prostate cancer cells binds to its receptor present on bone marrow stromal cells and favors osteoblastic response during bone metastases of prostate cancer. This suggests that interrupting ET-1 interaction with its endothelin A (ET A ) receptor could be useful for inhibiting prostate cancer bone metastasis and, as such, may enhance the therapeutic activity of docetaxel (Taxotere), the most commonly used drug for the treatment of metastatic prostate cancer. Therefore, the goal of our study was to obtain preclinical data supporting our hypothesis that the combined use of ET A receptor antagonist (ABT-627; Atrasentan) with Taxotere will be superior in inducing apoptosis in vitro and inhibiting tumor growth in vivo in a SCID-hu model of experimental bone metastasis induced by C4-2b prostate cancer cells. In vitro studies were done on a panel of prostate cancer cell lines to understand the molecular basis of combination therapy, and we found that the combination was more effective in the inhibition of cell viability and induction of apoptosis in LNCaP and C4-2b cells (androgen receptor positive) but not in PC-3 cells. These results were correlated with inactivation of Akt/nuclear factor-KB and its target genes. For in vivo studies, the therapeutic regimen was initiated when the tumor began showing signs of growth and treatment was continued for 5 weeks. Tumor volume and serum prostate-specific antigen were used as terminal index to evaluate the therapeutic advantage of combination therapy relative to a single regimen and untreated control. At termination, we found a 90% reduction in tumor volume by combination treatment relative to the untreated control group. Most importantly, the antitumor activity was associated with the down-regulation of molecular markers in tumor tissues that were similar to those observed in vitro. [Cancer Res 2007;67(8):3818-26]

Bone-specific growth inhibition of prostate cancer metastasis by Atrasentan

“…18 However, in the Scid-hu model, where prostate cancer cells are injected directly into human fetal bone explants, atrasentan alone was ineffective at blocking C4-2b prostate tumor growth; though it did enhance the antitumor efficacy of docetaxel. 19 Other studies indicate that ET-1 may also play a role in cancer beyond bone metastasis. ET-1 has been repeatedly shown to mediate survival and/or proliferation in cell-based assays, including prostate cancer cells.…”

A Phase I-II Study of Docetaxel and Atrasentan in Men with Castration-Resistant Metastatic Prostate Cancer

“…Recent evidence suggests that endothelin-1 may reduce the rates of apoptosis in prostate cancer cell lines exposed to docetaxel, and endothelin-A blockade with atrasentan reduces the rate of tumor growth in preclinical models compared with docetaxel alone (13,14). Single agent phase III studies have not shown convincing evidence of clinical benefit in castration-resistant prostate cancer; however, given the complexity of the pathogenesis of tumor progression and bone microenvironment interactions, it is likely that combination therapy is needed in this disease (12,15,16).…”

3,3′-Diindolylmethane Enhances Taxotere-Induced Apoptosis in Hormone-Refractory Prostate Cancer Cells through Survivin Down-regulation

“…The severe combined immunodeficiency (SCID)-human prostate cancer and breast cancer model of experimental bone metastasis was used for our study as described earlier (37)(38)(39). Briefly, suspensions of C4-2B cells were injected intraosseously by insertion of a 27-gauge needle through the mouse (Taconic Farms) skin directly into the marrow surface of the previously implanted bone (38,39).…”

“…11,[26][27][28]. In addition, the mice from group III received three doses of Taxotere (5 mg/kg body weight given intravenously) every 72 h after 24 h DIM gavaging (39,40). Group IV was exposed to DIM and treated with Taxotere as shown for groups II and III.…”

“…Tissue collection, fixation, and H&E and immunohistochemical staining were done according to the methods as described earlier (26,38,39 Increased apoptotic response was evident in the combination treatment group relative to untreated control or single-agent-treated group as measured by ELISA (A ). Western blot analysis showed that DIM in combination with Taxotere (Tax) significantly decreased the expression of survivin, poly(ADP-ribose) polymerase (PARP ), AR, prostate-specific antigen (PSA ), FoxM1, caspase-3, and NF-nB p65 (B ).…”