Understanding DNA Damage Response and DNA Repair in Multiple Myeloma

Bruceine A Inhibits Cell Proliferation by Targeting the USP13/PARP1 Signalling Pathway in Multiple Myeloma

Multiple myeloma (MM) is an incurable hematologic malignancy, driving significant interest in the discovery of novel therapeutic strategies. Bruceine A (BA), a tetracyclic triterpene quassinoid derived from Brucea javanica, has shown anticancer properties by modulating multiple intracellular signalling pathways and exhibiting various biological effects. However, the specific pharmacological mechanisms by which it combats MM remain unclear. In this study, we identified USP13 as a potential target of BA. We observed a significant increase in USP13 expression in patients with MM, which was strongly associated with a poorer prognosis. Furthermore, enhanced USP13 expression can stimulate MM cell proliferation both in vitro and in vivo. Mass spectrometry analysis, combined with co-immunoprecipitation and in vitro ubiquitination experiments, revealed PARP1 as a critical downstream target of USP13. USP13 can stabilize PARP1 protein through deubiquitination, promoting PARP1-mediated DNA damage repair (DDR) and facilitating MM progression. Notably, we utilized MM cell lines, an MM Patient-Derived Tumour Xenograft model, and a 5TMM3VT mouse model to determine the anticancer effects of BA on MM progression, revealing its potential to target USP13/PARP1 signalling and disrupt DDR in MM cells. In conclusion, these findings suggest that BA inhibiting USP13/PARP1-mediated DDR might be a promising therapeutic strategy for MM.

Therapeutic Potential of PRMT1 as a Critical Survival Dependency Target in Multiple Myeloma

Multiple myeloma (MM) is a neoplasm of antibody-producing plasma cells and is the second most prevalent hematological malignancy worldwide. Development of drug resistance and disease relapse significantly impede the success of MM treatment, highlighting the critical need to discover novel therapeutic targets. In a custom CRISPR/Cas9 screen targeting 197 DNA damage response-related genes, Protein Arginine N-Methyltransferase 1 (PRMT1) emerged as a top hit, revealing it as a potential therapeutic vulnerability and survival dependency in MM cells. PRMT1, a major Type I PRMT enzyme, catalyzes the asymmetric transfer of methyl groups to arginine residues, influencing gene transcription and protein function through post-translational modification. Dysregulation or overexpression of PRMT1 has been observed in various malignancies including MM and is linked to chemoresistance. Treatment with the Type I PRMT inhibitor GSK3368715 resulted in a dose-dependent reduction in cell survival across a panel of MM cell lines. This was accompanied by reduced levels of asymmetric dimethylation of arginine (ADMA) and increased arginine monomethylation (MMA) in MM cells. Cell cycle analysis revealed an accumulation of cells in the G0/G1 phase and a reduction in the S phase upon GSK3368715 treatment. Additionally, PRMT1 inhibition led to a significant downregulation of genes involved in cell proliferation, DNA replication, and DNA damage response (DDR), likely inducing genomic instability and impairing tumor growth. This was supported by Reverse Phase Protein Array (RPPA) analyses, which revealed a significant reduction in levels of proteins associated with cell cycle regulation and DDR pathways. Overall, our findings indicate that MM cells critically depend on PRMT1 for survival, highlighting the therapeutic potential of PRMT1 inhibition in treating MM.

Germline predisposition in multiple myeloma

We present a study of rare germline predisposition variants in 954 unrelated individuals with multiple myeloma (MM) and 82 MM families. Using a candidate gene approach, we identified such variants across all age groups in 9.1% of sporadic and 18% of familial cases. Implicated genes included genes suggested in other MM risk studies as potential risk genes (DIS3, EP300, KDM1A, and USP45); genes involved in predisposition to other cancers (ATM, BRCA1/2, CHEK2, PMS2, POT1, PRF1, and TP53); and BRIP1, EP300, and FANCM in individuals of African ancestry. Variants were characterized using loss of heterozygosity (LOH), biallelic events, and gene expression analyses, revealing 31 variants in 3.25% of sporadic cases for which pathogenicity was supported by multiple lines of evidence. Our results suggest that the disruption of DNA damage repair pathways may play a role in MM susceptibility. These results will inform improved surveillance in high-risk groups and potential therapeutic strategies.

Mimicking Retinoblastoma Treatment With Repeated Topotecan or Melphalan Develops Cross-Resistance to Classic Agents But Not to Repurposed Drugs

Purpose

Refractory or recurrent retinoblastoma results from acquired chemoresistance and the management of these eyes often requires surgical removal. Our objective was to develop retinoblastoma models resistant to chemotherapy by exposing cancer cells to repeated chemotherapy mimicking the clinical scenario. These newly resistant cells were used to evaluate potential novel therapies.

Methods

Chemoresistant cells were obtained by exposing two primary retinoblastoma cell cultures to three weekly doses of melphalan or topotecan. The sensitivity of these resistant cells to each chemotherapy was evaluated, and cross-resistance to topotecan, melphalan, and carboplatin was assessed. Genomic alterations and differential expression of efflux/influx transporters between chemoresistant and parental cells were analyzed. Subsequently, sensitivity of both resistant and parental cells to the repurposed agents digoxin, methylene blue, and gemcitabine was assessed.

Results

Four chemoresistant models were successfully established, showing significantly higher half-maximal inhibitory concentration (IC50) values for melphalan and topotecan compared to their corresponding parental cells (P < 0.05). Cross-resistance between melphalan and topotecan was demonstrated, with a 3-fold increase in the IC50. Chemoresistant cells also showed reduced sensitivity to carboplatin (P < 0.05) compared to parental cells, whereas sensitivity to the evaluated repurposed agents remained unchanged. Genomic analysis revealed no selective alterations in the resistant cells, although differential expression of influx/efflux transporters was observed across all chemoresistant models.

Conclusions

In vitro simulation of patient treatment was useful to establish chemoresistant retinoblastomas and to identify strategies to overcome resistance to topotecan or melphalan through drug repurposed. Our results warrant further investigation to support the clinical translation.

Myeloma and DNA damage

ABSTRACT

DNA-damaging agents have represented the first effective treatment for the blood cancer multiple myeloma, and after 65 years since their introduction to the clinic, they remain one of the mainstay therapies for this disease. Myeloma is a cancer of plasma cells. Despite exceedingly slow proliferation, myeloma cells present extended genomic rearrangements and intense genomic instability, starting at the premalignant stage of the disease. Where does such DNA damage stem from? A reliable model argues that the powerful oncogenes activated in myeloma as well the phenotypic peculiarities of cancer plasma cells, including the dependency on the proteasome for survival and the constant presence of oxidative stress, all converge on modulating DNA damage and repair. Beleaguered by these contraposing forces, myeloma cells survive in a precarious balance, in which the robust engagement of DNA repair mechanisms to guarantee cell survival is continuously challenged by rampant genomic instability, essential for cancer cells to withstand hostile selective pressures. Shattering this delicate equilibrium has been the goal of the extensive use of DNA-damaging agents since their introduction in the clinic, now enriched by novel approaches that leverage upon synthetic lethality paradigms. Exploiting the impairment of homologous recombination caused by myeloma genetic lesions or treatments, it is now possible to design therapeutic combinations that could target myeloma cells more effectively. Furthermore, DNA-damaging agents, as demonstrated in solid tumors, may sensitize cells to immune therapies. In all, targeting DNA damage and repair remains as central as ever in myeloma, even for the foreseeable future.

Aluminium phthalocyanine-mediated photodynamic therapy induces ATM-related DNA damage response and apoptosis in human oesophageal cancer cells

Introduction

Photodynamic therapy (PDT) is a light-based technique used in the treatment of malignant and non-malignant tissue. Aluminium-phthalocyanine chloride tetra sulfonate (AlPcS4Cl)-mediated PDT has been well investigated on several cancer types, including oesophageal cancer. However, the effects of (AlPcS4Cl)-mediated PDT on DNA damage response and the mechanism of cell death in oesophageal cancer needs further investigation.

Methods

Here, we examined the in vitro effects of AlPcS4Cl-mediated PDT on cell cycle, DNA damage response, oxidative stress, and intrinsic apoptotic cell death pathway in HKESC-1 oesophageal cancer cells. The HKESC-1 cells were exposed to PDT using a semiconductor laser diode (673.2 nm, 5 J/cm2 fluency). Cell viability and cytotoxicity were determined by the ATP cell viability assay and the lactate dehydrogenase (LDH) release assay, respectively. Cell cycle and DNA damage response (DDR) analyses were conducted using the Muse™ cell cycle kit and the Muse® multi-color DNA damage kit, respectively. The mode of cell death was identified using the Annexin V-FITC/PI detection assay and Muse® Autophagy LC3 antibody-based kit. The intrinsic apoptotic pathway was investigated by measuring the cellular reactive oxygen species (ROS) levels, mitochondrial membrane potential (ΔΨm) function, cytochrome c levels and the activity of caspase 3/7 enzymes.

Results

The results show that AlPcS4Cl-based PDT reduced cell viability, induced cytotoxicity, cell cycle arrest at the G0/G1 phase, and DNA double-strand break (DSB) through the upregulation of the ataxia telangiectasia mutated (ATM), a DNA damage sensor. In addition, the findings showed that AlPcS4Cl-based PDT induced cell death via apoptosis, which is observed through increased ROS production, reduced ΔΨm, increased cytochrome c release, and activation of caspase 3/7 enzyme. Finally, no autophagy was observed in the AlPcS4Cl-mediated PDT-treated cells.

Conclusion

Our findings showed that apoptotic cell death is the main cell death mechanism triggered by AlPcS4Cl-mediated PDT in oesophageal cancer cells.

Understanding DNA Epigenetics by Means of Raman/SERS Analysis for Cancer Detection

This study delves into the intricate interaction between DNA and nanosystems, exploring its potential implications for biomedical applications. The focus lies in understanding the adsorption geometry of DNA when in proximity to plasmonic nanoparticles, utilizing ultrasensitive vibrational spectroscopy techniques. Employing a combined Raman-SERS analysis, we conducted an in-depth examination to clarify the molecular geometry of interactions between DNA and silver nanoparticles. Our findings also reveal distinctive spectral features regarding DNA samples due to their distinctive genome stability. To understand the subtle differences occurring between normal and cancerous DNA, their thermal stability was investigated by means of SERS measurement performed before and after a thermal treatment at 94 °C. It was proved that thermal treatment did not affect DNA integrity in the case of normal cells. On the other hand, due to epimutation pattern that characterizes cancerous DNA, variations between spectra recorded before and after heat treatment were observed, suggesting genome instability. These findings highlight the potential of DNA analysis using SERS for cancer detection. They demonstrate the applicability of this approach to overcoming challenges associated with low DNA concentrations (e.g., circulating tumor DNA) that occur in biofluids. In conclusion, this research contributes significant insights into the nanoscale behavior of DNA in the presence of nanosystems.