Role of Chromatin Damage and Chromatin Trapping of FACT in Mediating the Anticancer Cytotoxicity of DNA-Binding Small-Molecule Drugs

Abstract

Precisely how DNA-targeting chemotherapeutic drugs trigger cancer cell death remains unclear, as it is difficult to separate direct DNA damage from other effects in cells. Recent work on curaxins, a class of small-molecule drugs with broad anticancer activity, shows that they interfere with histone-DNA interactions and destabilize nucleosomes without causing detectable DNA damage. Chromatin damage caused by curaxins is sensed by the histone chaperone FACT, which binds unfolded nucleosomes becoming trapped in chromatin. In this study, we investigated whether classical DNA-targeting chemotherapeutic drugs also similarly disturbed chromatin to cause chromatin trapping of FACT (c-trapping). Drugs that directly bound DNA induced both chromatin damage and c-trapping. However, chromatin damage occurred irrespective of direct DNA damage and was dependent on how a drug bound DNA, specifically, in the way it bound chromatinized DNA in cells. FACT was sensitive to a plethora of nucleosome perturbations induced by DNA-binding small molecules, including displacement of the linker histone, eviction of core histones, and accumulation of negative supercoiling. Strikingly, we found that the cytotoxicity of DNA-binding small molecules correlated with their ability to cause chromatin damage, not DNA damage. Our results suggest implications for the development of chromatin-damaging agents as selective anticancer drugs. These provocative results suggest that the anticancer efficacy of traditional DNA-targeting chemotherapeutic drugs may be based in large part on chromatin damage rather than direct DNA damage. .

Potent antileukemic activity of curaxin CBL0137 against MLL‐rearranged leukemia

“…10 Despite many clinical trials, over the past 20 years, no real improvements have been made regarding outcome or prognosis for patients with MLL-r leukemia. 13,[20][21][22] Here, we confirm that CBL0137 induced p53 pathway activation and an IFN response in MLL-r leukemia models in vivo. In our study, we demonstrated that the curaxin CBL0137 has antileukemic effects in preclinical in vitro and in vivo models of MLL-r leukemia at doses that are well tolerated in mice.…”

“…[45][46][47] In addition, as CBL0137 can act through a number of anticancer mechanisms, including inhibition of the NFκB pathway, activation of the p53 pathway, c-trapping of FACT and induction of an IFN response, 13,[20][21][22] it is possible that the CBL0137-induced inhibition of cancer cell growth is mediated by different mechanisms in different cancer cells. It is possible that in vitro, the anticancer action of CBL0137 is predominantly mediated through its FACT-dependent action of NFκB pathway inhibition, and not through induction of an IFN response.…”

“…[13][14][15][16][17][18][19] CBL0137 acts through a novel, nongenotoxic anticancer mechanism that is based on inducing chromatin disassembly in cells without causing DNA damage, thereby triggering several pathways with anticancer effects. 13,21,22 FACT is involved in chromatin remodeling during transcription, replication and DNA damage repair and has been shown to drive in vitro cell transformation. 13,21,22 FACT is involved in chromatin remodeling during transcription, replication and DNA damage repair and has been shown to drive in vitro cell transformation.…”

Recent Considerations in the Application of RAPTA‐C for Cancer Treatment and Perspectives for Its Combination with Immunotherapies

“…[32] A secondary phase II trial evaluating differential treatment scheduling administering two doses of vorinostat in the same combination in pre-treated metastatic colorectal carcinoma patients failed as well. [123] It was found that compounds causing chromatin trapping, that is, preventing the disassembly of chromatin, induce cell death in various cell types. [114,115] Furthermore, patients diagnosed with metastatic colorectal carcinoma and previously treated with other medications were enrolled to the phase II clinical trial evaluating the activity of two drugs applied in combination, namely the chemotherapeutic 5azacitidine administered subcutaneously (day 1-5 and 8-10) and entinostat, which is a HDAC class 1 inhibitor in clinical evaluation specifically deactivating Treg cells, administered orally (day 3 and 10).…”

“…No objective response was observed during and after the treatment. [123] RAPTA-C binding to the nucleosome core could exert its effect similarly by targeting the facilitates chromatin transcription (FACT) complex or by stabilizing and further distorting the nucleosome-DNA structure. This treatment, however, did not show the expected efficacy and did not meet the "primary RECIST (response evaluation criteria in solid tumor) criteria tumor response rate endpoint," although demethylation of histone proteins at distinct DNA sites was observed.…”