Synergy of 5-aza-2′-deoxycytidine (DAC) and paclitaxel in both androgen-dependent and -independent prostate cancer cell lines
Introduction
Prostate carcinoma (PC) is the most common malignancy among American males and is the second-leading cause of cancer-related mortality. Although radical prostatectomy and radiation therapy offer hope for a cure for the majority of patients with localized tumors, undetectable residual tumor cells at local or distant sites eventually become clinically evident and lead to recurrence [1]. Most patients that responded initially to ablation of androgen through orchiectomy, luteinizing hormone-releasing hormone agonists and non-steroidal anti-androgens will eventually develop progressive disease [2]. Once androgen-independent PC occurs, prognosis is poor, with a median survival from 7 to 12 months [3], [4]. Although chemotherapy has an established role in the treatment of PC and various strategies have been pursued to improve the outcome of PC, more effective combined treatment should be developed to overcome this malignancy [5].
Recently, there has been much emphasis on the critical role of DNA methylation in carcinogenesis, and hypermethylation of cancer-associated genes is prevalent in malignant tumors. 5-aza-2′-deoxycytidine (DAC), a DNA methyltransferase inhibitor, has been used to reverse methylation and reactivate the expression of silenced genes. DAC could suppress the growth of various tumors in vitro, and showed clinical utility against hematopoietic malignancies [6], studies indicated that DAC had clinical activity against metastatic lung carcinoma [7] and is a well tolerated regimen against androgen-independent PC [8]. Several studies have been carried out to examine the synergistic effects of DAC and chemotherapeutic agents against tumor cells, DAC was reported to increase the cytotoxicity of cisplatin (CDDP) and sensitize lung cancer cells to CDDP treatment [9], moreover, a combination of DAC and CDDP showed synergy in triggering apoptotic death of PC cells [10].
In the present study, we demonstrated the synergistic growth suppression of DAC and paclitaxel (PTX) in PC cell lines by isobolographic analysis. The increased susceptibility of PC cells to PTX induced by DAC suggested that combination chemotherapy with PTX and DAC may be a new therapeutic option for both androgen-dependent and -independent PC.
Section snippets
Cell lines and agents
PC cell lines: LNCap (androgen-dependent PC cell line), Du145 and PC3 (androgen-independent PC cell lines) cells were used. AILNCap is an androgen-independent PC cell line that was established as described in reference [11], LNCap cells were maintained in phenol-red-free RPMI supplemented with 10% charcoal-stripped fetal bovine serum, with a change of this steroid-free medium every 3–4 days over 3 months. All PC cell lines were cultured in complete medium and maintained as monolayers and
Synergistic growth suppression by DAC and PTX
DAC (Fig. 1A) and PTX (Fig. 1B and C, results for LNCap and AILNCap are shown) each caused dosage-dependent cell growth suppression of PC cells. DAC could increase the susceptibility of PC cells to PTX (Fig. 1B and C, results for LNCap and AILNCap are shown), and combined treatment with DAC and PTX caused synergistic growth suppression in all PC cell lines examined, as shown by isobolographic analysis (Fig. 1D).
Induction of apoptosis and cell cycle arrest by DAC and/or PTX
To clarify the mechanism of the synergy of DAC and PTX, we analyzed the induction of
Discussions
Although patients with PC initially respond to androgen-deprivation, this response is temporary, and most patients develop androgen-independent disease that results in progressive clinical deterioration and ultimately death. At present, treatment options for hormone-refractory disease include radiotherapy, chemotherapy and hormonal manipulations.
Promising new antitumor agents usually appear as our understanding of oncogenesis advances. Although decitabine, a pharmacological form of DAC, has
Conclusions
We observed synergistic growth suppression by DAC and PTX in PC cell lines, and the synergy of the combined treatments was observed in both androgen-dependent and -independent lines. This suggests that combination chemotherapy with DAC and PTX might become a new clinical therapeutic strategy to overcome advanced PC.
Conflict of interest
None of the authors has any direct or indirect commercial financial incentive associated with publishing the article. Neither the manuscript nor any portions thereof are under consideration by any other journal and the data have not been previously published.
Acknowledgement
Our research is supported by a Grant from the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
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