Improved Efficacy of Acylfulvene in Colon Cancer Cells When Combined with a Nuclear Excision Repair Inhibitor

Abstract

The efficacy of DNA-damaging anticancer drugs is highly influenced by cellular DNA repair capacity, and by inhibiting the relevant DNA repair pathway, efficacy of alkylating agents may be increased. Therefore, combining DNA repair inhibitors with anticancer agents that selectively target tumour tissue should improve cancer treatment. The objective of this study was to test the hypothesis that co-treatment of cancer cells with acylfulvene (AF, alkylating agent) and UCN-01 (DNA repair inhibitor) would improve drug efficacy and promote the persistence of DNA adducts. Previous data regarding the relative susceptibility of repair proficient versus deficient cells toward an AF analog suggests that corresponding adducts are repaired by nuclear excision repair (NER), a cellular process that has been shown to be prevented with UCN-01. In this study, cells were co-treated with non-toxic levels of UCN-01 together with increasing doses of AF. The efficacy of AF was assessed by measuring cytotoxicity and DNA adducts. In addition, cells were co-treated with non-toxic levels of methoxyamine, a known base excision repair (BER) inhibitor, to determine if inhibiting BER also promotes cytotoxicity of AF. DNA-adducts were measured in a sensitive and precise manner by using stable isotope-labeled mass spectrometry analysis. The data obtained in this study demonstrate for the first time that pharmacological inhibition of the NER pathway of DNA repair leads to the persistence of AF-specific adducts and promotes AF cytotoxicity.

Minor Groove 3‐Deaza‐Adenosine Analogues: Synthesis and Bypass in Translesion DNA Synthesis

“…Similarly, the 3‐AF‐A adduct has a half‐life of 8.5 h in naked DNA . In nucleotide excision repair (NER)‐deficient cells this value increased to 12 days, whereas in NER‐proficient cells it was one day . The use of stable deaza‐adenosine analogues as models for N‐alkylation has been used as an approach to avoid depurination and enable biochemical studies.…”

Nucleotide excision repair in humans

“…Ironically, some agents that induce these lesions are regularly used in chemotherapeutic regimens to combat cancer; a problem often found is that the highly mutable tumor cells develop resistance to the drug. Synthetic lethality, originally defined as the combination of mutations in two or more separate genes leading to cell death, has been adopted as a strategy for overcoming drug resistance; it consists of combining two or more drugs, for example cisplatin to damage DNA and the NER inhibitor UCN-01 [62]. …”

DNA Adducts from Anticancer Drugs as Candidate Predictive Markers for Precision Medicine

“…147 Impairing NER function, but not BER, led to the persistence of AF-induced DNA adducts and promoted AF cytotoxicity by reducing the concentration required to kill HT-29 colon cancer cells by 2-fold. 147 This study also measured the formation and repair of AF-induced adducts versus time by exposing the cells to 500 nM AF for 24 h and then to fresh medium lacking the drug for 48 h. During the first 24 h, AF-induced adduct levels increased with increasing time of AF exposure, whereas a decrease in adduct levels was observed for the 48 h that followed medium replacement. 147 Studies addressing the kinetic of formation and repair of DNA adducts may be useful for identifying the appropriate timing of sample collection for diagnostics tests.…”