Effects of gemcitabine on APE/ref-1 endonuclease activity in pancreatic cancer cells, and the therapeutic potential of antisense oligonucleotides

Abstract

Apurinic/apyrimidinic endonuclease (APE) is a key enzyme involved in DNA base excision repair (BER) that is often expressed at elevated levels in human cancers. Pancreatic cancer cells treated with the nucleoside analogue gemcitabine (2 0 , 2 0 -difluoro-2 0 deoxycytidine) showed increases in APE/redox effector factor (ref-1) protein levels (approximately two-fold for Panc-1 and six-fold for MiaPaCa-2), with corresponding increases in endonuclease activity. These results suggested that the activation of APE/ref-1 might be an adaptive response that contributes to gemcitabine resistance by facilitating BER. To test this hypothesis, we examined the effects of disrupting APE/ref-1 using antisense on gemcitabine toxicity. Antisense oligonucleotides decreased protein levels three-fold in MiaPaCa-2 and five-fold in Panc-1 in comparison to controls, associated with reduced endonuclease activity. Combination treatments with antisense oligonucleotides and gemcitabine partially suppressed the increase in APE/ref-1 activity seen in cells exposed to gemcitabine alone. While clonogenic assays showed only slight decreases in colony formation in cells treated with either antisense oligonucleotides or gemcitabine alone, the combination with APE/ref-1 antisense resulted in a 2-log enhancement of gemcitabine toxicity in Panc-1 cells. Overall these findings suggest that APE/ref-1 plays a significant role in gemcitabine resistance in some pancreatic cancer cells, and support the further investigation of novel treatments that target this protein.

Alterations in the expression of the apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE1/Ref-1) in human ovarian cancer and indentification of the therapeutic potential of APE1/Ref-1 inhibitor

“…Our results are supported by those of others in that the suppression of APE1 results in hypersensitivity to chemotherapeutic agents (10,26,27). Additionally, targeted reduction of Ape1/Ref-1 protein by specific anti-sense oligonucleotides renders mammalian cells hypersensitive to methylmethane sulfonate (MMS), H 2 O 2 , bleomycin, temozolomide (TMZ) and gemcitabine (22,28,29). Moreover, Robertson and colleagues found that elevated expression of APE1 in testicular cancer cell lines results in resistance to certain therapeutic agents, such as bleomycin and radiation (21).…”

Single cell trapping and DNA damage analysis using microwell arrays

“…From a clinical perspective, APE1 overexpression has been observed in numerous cancer types (37). Additionally, reduced expression of APE1 using RNA interference has been shown to sensitize cells to treatment by numerous therapeutic agents (38)(39)(40)(41). Small molecules that inhibit the AP endonuclease activity of APE1 could thus be extremely valuable in combination therapies for treating cancer.…”

Combinatorial therapies improve the therapeutic efficacy of nanoliposomal ceramide for pancreatic cancer

“…Multiple labs, including our own, have reported that the PANC-1 cell line is more chemoresistant than other cell lines, often exhibiting higher IC 50 values. [24][25][26][27][28][29] In this study, we also demonstrate that D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a glucosylceramide synthase inhibitor and gemcitabine, a nucleoside analog, enhance the antitumor activity of Lip-C 6 . We show that the biological effect of Lip-C 6 is achieved through inhibition of Akt phosphorylation, and suggest that the distinctive action of the anti-metabolite gemcitabine can be used to prime the PANC-1 cells to the action of Lip-C 6 .…”