Acid Ceramidase Upregulation in Prostate Cancer Cells Confers Resistance to Radiation: AC Inhibition, a Potential Radiosensitizer

Abstract

Radiation resistance in a subset of prostate tumors remains a challenge to prostate cancer radiotherapy. The current study on the effects of radiation on prostate cancer cells reveals that radiation programs an unpredicted resistance mechanism by upregulating acid ceramidase (AC). Irradiated cells demonstrated limited changes of ceramide levels while elevating levels of sphingosine and sphingosine-1-phosphate. By genetically downregulating AC with small interfering RNA (siRNA), we observed radiosensitization of cells using clonogenic and cytotoxicity assays. Conversely, AC overexpression further decreased sensitivity to radiation. We also observed that radiation-induced AC upregulation was sufficient to create cross-resistance to chemotherapy as demonstrated by decreased sensitivity to Taxol and C(6) ceramide compared to controls. Lower levels of caspase 3/7 activity were detected in cells pretreated with radiation, also indicating increased resistance. Finally, utilization of the small molecule AC inhibitor, LCL385, sensitized PPC-1 cells to radiation and significantly decreased tumor xenograft growth. These data suggest a new mechanism of cancer cell resistance to radiation, through upregulation of AC that is, in part, mediated by application of the therapy itself. An improved understanding of radiotherapy and the application of combination therapy achieved in this study offer new opportunities for the modulation of radiation effects in the treatment of cancer.

Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse

“…Moreover, shASAH1 transduction into PPC-1, 22Rv1, DU 145, and LNCaP cell lines significantly enhanced susceptibility in each case to IR-mediated clonogenic cell death ( Figure 7D and Supplemental Figure 9). These results recapitulate our previous observations using transient transfection of siRNA against ASAH1 to sensitize PCa cells to IR (49). Moreover, we transduced another shRNA construct, targeted toward the ASAH1 ORF, and found similarly effective radiosensitization ( Figure 7D).…”

“…While the characterization of aberrant, cancer-associated gene expression in tissues obtained for diagnosis versus noncancerous tissues is a prominent arena of research (39), the response of tumors to therapy also represents a critical avenue of investigation (22). Work by this group and others has demonstrated that the ceramide-metabolizing enzyme, acid ceramidase (AC), can play an important role in resistance to anticancer therapies (40)(41)(42)(43)(44)(45)(46)(47), including IR (26,36,48,49). In this report, we evaluated transcriptional activation of AC in PCa cells treated with radiation.…”

Hepatosellüler Karsi̇nom Hücreleri̇nde Karmofurun Si̇totoksi̇k Ve Apoptoti̇k Etki̇leri̇

“…Kanserli prostat hücrelerinde (DU145, LnCaP ve PC3), baş ve boyun ile melanoma hücrelerinde seramidaz enzim düzeylerinin kontrol gruplarına göre yüksek olduğu gösterilmiştir (6,17,18). Kanserli prostat hücrelerinde radyasyon terapisi sırasında seramidaz enzim düzeyinin arttığı ve bu artışın ilaç-la tedaviye ve radyasyon terapisine karşı direnç oluşturduğu tespit edilmiştir (12,18). Seramidaz enziminin baskılanmasının kanserli prostat hücrelerinde apoptozu uyardığı ve kanser büyümesini engellediği gösterilmiştir (19,20).…”

“…Bu nedenle, hücre içi seramidaz enzim düzeyi seramid, sfingozin ve S1P dengesinin korunmasında oldukça önemli bir yer tutmaktadır. Bu denge bir hücrenin ölüme direncini, ölümünü veya çoğalmasını düzenlemektedir (11,12). Birçok kanser hücresinde normal hücrelere göre seramidaz düzeyinin yüksek olduğu bulunmuş-tur.…”

Effects of ceranib-2 on cell survival and TNF-alpha in colon cancer cell line

“…Therefore, defects in ceramide synthesis and signaling have been implicated in cancer pathophysiology (3,4). It has been suggested that over-expression of ceramidases is associated with an increased resistance to apoptosis, which results in poor prognosis in several types of cancer including melanoma, prostate cancer, head and neck cancers (5,6). Entirely, these fi ndings indicate that ceramidases are potential targets in cancer therapy.…”