A comparative study of the cytotoxic and genotoxic effects of ICRF-154 and bimolane, two catalytic inhibitors of topoisomerase II

Genome Instability Induced by Topoisomerase Misfunction

Topoisomerases alter DNA topology by making transient DNA strand breaks (DSBs) in DNA. The DNA cleavage reaction mechanism includes the formation of a reversible protein/DNA complex that allows rapid resealing of the transient break. This mechanism allows changes in DNA topology with minimal risks of persistent DNA damage. Nonetheless, small molecules, alternate DNA structures, or mutations in topoisomerase proteins can impede the resealing of the transient breaks, leading to genome instability and potentially cell death. The consequences of high levels of enzyme/DNA adducts differ for type I and type II topoisomerases. Top1 action on DNA containing ribonucleotides leads to 2-5 nucleotide deletions in repeated sequences, while mutant Top1 enzymes can generate large deletions. By contrast, small molecules that target Top2, or mutant Top2 enzymes with elevated levels of cleavage lead to small de novo duplications. Both Top1 and Top2 have the potential to generate large rearrangements and translocations. Thus, genome instability due to topoisomerase mis-function is a potential pathogenic mechanism especially leading to oncogenic progression. Recent studies support the potential roles of topoisomerases in genetic changes in cancer cells, highlighting the need to understand how cells limit genome instability induced by topoisomerases. This review highlights recent studies that bear on these questions.

Objectives and achievements of the HUMN project on its 26th anniversary

Micronuclei (MN) are a nuclear abnormality that occurs when chromosome fragments or whole chromosomes are not properly segregated during mitosis and consequently are excluded from the main nuclei and wrapped within nuclear membrane to form small nuclei. This maldistribution of genetic material leads to abnormal cellular genomes which may increase risk of developmental defects, cancers, and accelerated aging. Despite the potential importance of MN as biomarkers of genotoxicity, very little was known about the optimal way to measure MN in humans, the normal ranges of values of MN in healthy humans and the prospective association of MN with developmental and degenerative diseases prior to the 1980's. In the early 1980's two important methods to measure MN in humans were developed namely, the cytokinesis-block MN (CBMN) assay using peripheral blood lymphocytes and the Buccal MN assay that measures MN in epithelial cells from the oral mucosa. These discoveries greatly increased interest to use MN assays in human studies. In 1997 the Human Micronucleus (HUMN) project was founded to initiate an international collaboration to (i) harmonise and standardise the techniques used to perform the lymphocyte CBMN assay and the Buccal MN assay; (ii) establish and collate databases of MN frequency in human populations world-wide which also captured demographic, lifestyle and environmental genotoxin exposure data and (iii) use these data to identify the most important variables affecting MN frequency and to also determine whether MN predict disease risk. In this paper we briefly describe the achievements of the HUMN project during the period from the date of its foundation on 9th September 1997 until its 26th Anniversary in 2023, which included more than 200 publications and 23 workshops world-wide.

A Route for Investigating Psoriasis: From the Perspective of the Pathological Mechanisms and Therapeutic Strategies of Cancer

Psoriasis is an incurable skin disease that develops in about two-thirds of patients before the age of 40 and requires lifelong treatment; its pathological mechanisms have not been fully elucidated. The core pathological process of psoriasis is epidermal thickening caused by the excessive proliferation of epidermal keratinocytes, which is similar to the key feature of cancer; the malignant proliferation of cancer cells causes tumor enlargement, suggesting that there is a certain degree of commonality between psoriasis and cancer. This article reviews the pathological mechanisms that are common to psoriasis and cancer, including the interaction between cell proliferation and an abnormal immune microenvironment, metabolic reprogramming, and epigenetic reprogramming. In addition, there are common therapeutic agents and drug targets between psoriasis and cancer. Thus, psoriasis and cancer share a common pathological mechanisms-drug targets-therapeutic agents framework. On this basis, it is proposed that investigating psoriasis from a cancer perspective is beneficial to enriching the research strategies related to psoriasis.

The roles of kinetochore of micronucleus in mitosis of HeLa cells: a live cell imaging study

Background

Micronuclei (MNi) are extensively used to evaluate genotoxic effects and chromosome instability. However, the roles of kinetochore of MN in mitosis have not been completely addressed.

Methods

The HeLa CENP B-GFP H2B-mCherry cells are applied to address these questions via the long-term live-cell imaging. In the cells, the kinetochore-positive micronucleus (K+MN) contained CENP B-GFP, while the kinetochore-negative micronucleus (K-MN) did not.

Results

K-MN-bearing cells produced much more chromosome fragments than did MN-free cells. Most of the chromosome fragments eventually merged into K-MNi. K+MN-bearing cells yielded more kinetochore-positive lagging chromosomes (K+LCs) and K+MNi than MN-free cells did. The results suggested the differences in the fates of K+MNi and K-MNi in mitosis. The cycle of K-MN → Chromosome fragment → K-MN may occur in generations of K-MN-bearing cells, while part of K+MNi might reincorporate into the main nucleus. The K+MN-bearing cells prolonged significantly duration of mitosis compared with MN-free cells. The presence of micronuclei, regardless of K-MN and K+MN, enhanced apoptosis cell death. And K+MN-bearing cells were inclined to apoptosis more than K-MN-bearing cells. The results suggested differences in fates between K-MN-bearing and K+MN-bearing cells.

Conclusions

Kinetochore determined the fates of micronuclei. Kinetochore in micronuclei indirectly prolonged the duration of mitosis. Kinetochore enhanced cytotoxicity of micronuclei. Our data are direct evidences showing the roles of kinetochore of micronucleus in mitosis of HeLa cells.

Concentration-response studies of the chromosome-damaging effects of topoisomerase II inhibitors determined in vitro using human TK6 cells

Topoisomerase II (topo II) inhibitors are commonly used as chemotherapy to treat multiple types of cancer, though their use is also associated with the development of therapy related acute leukemias. While the chromosome-damaging effects of etoposide, a topo II poison, have been proposed to act through a threshold mechanism, little is known about the chromosome damaging effects and dose responses for the catalytic inhibitors of the enzyme. The current study was designed to further investigate the potencies and concentration-response relationships of several topoisomerase II inhibitors, including the topoisomerase II poison etoposide, as well as catalytic inhibitors aclarubicin, merbarone, ICRF-154 and ICRF-187 using both a traditional in vitro micronucleus assay as well as a flow-cytometry based version of the assay. Benchmark dose (BMD) analysis was used to identify models that best fit the data and estimate a BMD, in this case the concentration at which a one standard deviation increase above the control frequency would be expected. All of the agents tested were potent in inducing micronuclei in human lymphoblastoid TK6 cells, with significant increases seen at low micromolar, and in the cases of aclarubicin and etoposide, at low nanomolar concentrations. Use of the anti-kinetochore CREST antibody with the microscopy-based assay demonstrated that the vast majority of the micronuclei originated from chromosome breakage. In comparing the two versions of the micronucleus assay, significant increases in micronucleated cells were observed at similar or lower concentrations using the traditional microscopy-based assay. BMD modeling of the data exhibited several advantages and proved to be a valuable alternative for concentration-response analysis, producing points of departure comparable to those derived using traditional no-observed or lowest-observed genotoxic effect level (NOGEL or LOGEL) approaches.

Differences in the origins of kinetochore-positive and kinetochore-negative micronuclei: A live cell imaging study

Micronuclei (MNi) are extensively used to evaluate genotoxicity and chromosomal instability. Classification of kinetochore-negative (K-MNi) and kinetochore-positive micronuclei (K+MNi) improves the specificity and sensitivity of the micronucleus (MN) test; however, the fundamental differences in the origins of K-MNi and K+MNi have not been addressed due to the limitations of traditional methods. In the current study, HeLa CENP B-GFP H2B-mCherry cells were constructed in which histone 2B (H2B) and centromere protein B (CENP B) were expressed as fusion proteins to monomeric Cherry (mCherry) and EGFP, respectively. MNi were identified using H2B-mCherry; K+MN contained CENP B-GFP, while K-MN did not. Long-term live cell imaging was conducted to examine MN formation in the dual-color fluorescent HeLa cells. The results suggested that K-MNi were derived from kinetochore-negative displaced chromosomes (K-DCs), kinetochore-negative lagging chromosomes (K-LCs) and fragments of broken chromosome bridges (CBs) during late mitotic stages. The results also indicated that K+MNi are derived from kinetochore-positive displaced chromosomes (K+DCs), kinetochore-positive lagging chromosomes (K+LCs), and fragments of broken CBs. Different aberrant chromosomes emerged during mitosis at different frequencies and developed into K-MNi and/or K+MNi in the daughter cells at different rates. K+LCs formed K+MNi at a higher frequency than K+DCs, and K-LCs formed K-MNi at a higher rate than K-DCs; however, broken CBs transformed into K-MNi and/or K+MNi. In summary, these results show that K-MNi and K+MNi have different origins in HeLa cells and that each mechanism of MN formation contributes differently to the overall number of K-MNi and K+MNi.

Arsenic trioxide-based therapy is suitable for patients with psoriasis-associated acute promyelocytic leukemia - A retrospective clinical study

OBJECTIVE

Many patients with psoriasis have developed acute promyelocytic leukemia (APL) whereas few reports on psoriasis-associated APL were found in the published literature. This study was aimed to study the etiology, clinical characteristics, and prognosis of psoriasis-associated APL and to map a suitable treatment regime for this condition.

METHODS

This study retrospectively analyzed the clinical data of 17 patients with psoriasis-associated APL diagnosed and treated in our hospital in the past decade.

RESULTS

The 17 patients accounted for 8.3% of the total patients diagnosed with de novo APL during the same period in our hospital. Their clinical characteristics of APL were similar to those of general APL. Four patients had a definite history of taking bimolane. All patients received arsenic trioxide (ATO)-based remission induction and postremission treatment. After induction, 15 patients (88%) achieved hematologic complete remission. With a median follow-up of 27 months, the 3-year estimates of overall survival were 77.2% ± 12.4% and the 3-year estimates of event-free survival were 70.6% ± 13.5%. In addition, the ATO-based remission induction and postremission treatment significantly improved psoriasis symptoms in 83 and 85.7% of patients, respectively. Through the final follow-up, no chronic arsenicosis or secondary malignancy was observed.

CONCLUSIONS

Psoriasis patients are at high risk for APL. The increased risk is most likely associated with the genetic background and bimolane treatment. The ATO-based therapy is especially suitable for patients with psoriasis-associated APL. Our study also brings a new treatment option for psoriasis.