Review identifies DNA methylation as a potential factor behind treatment resistance, highlighting three molecular components that could help guide future breast cancer therapies.
SRINAGAR: Researchers from the University of Kashmir and other institutions have examined how changes in DNA methylation may help breast cancer cells evade programmed cell death, potentially contributing to tumour progression and resistance to treatment.
The review, published in the journal Molecular Biology Reports, explores how epigenetic modifications influence three important components of the tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) signalling pathway: DR5, DcR2 and caspase-3.
The researchers argue that abnormal DNA methylation can disrupt the molecular mechanisms responsible for eliminating damaged or cancerous cells, allowing malignant cells to survive despite the body’s natural defence mechanisms and certain cancer treatments.
Breast cancer remains the most commonly diagnosed cancer among women worldwide. Although advances in screening and treatment have improved survival, disease progression, recurrence and resistance to chemotherapy continue to pose significant challenges, particularly in more aggressive forms of the disease.
One of the mechanisms that enables cancer cells to survive is their ability to evade apoptosis, a naturally occurring process through which the body eliminates damaged, unnecessary or potentially harmful cells.
Under normal circumstances, apoptosis helps maintain tissue balance by removing cells that could otherwise develop into malignancies. However, cancer cells can develop mechanisms to interfere with this process, allowing them to continue growing and multiplying.
The review examines how epigenetic changes, particularly DNA methylation, can interfere with this process.
How cancer cells evade death?
The TRAIL pathway has attracted scientific interest because of its ability to trigger programmed cell death selectively in cancer cells while largely sparing normal cells.
The process begins when TRAIL binds to death receptors on the surface of a cell, particularly DR5. This activates a chain of molecular events involving proteins such as caspase-8 and caspase-3, ultimately leading to apoptosis.
However, breast cancer cells can develop resistance to this mechanism by reducing the expression of death receptors, increasing the activity of decoy receptors or interfering with downstream proteins responsible for carrying out cell death.
The paper, DNA methylation-mediated regulation of TRAIL pathway components (DR5, DcR2, and CASP3) in breast cancer: molecular mechanisms and therapeutic implications, was authored by Nuzhat Khursheed, Suhail Ashraf, Qurat-ul-Quadir, Allah-u-deen Khursheed, Asia Asiaf and Showkat Ahmad Ganie.
Nuzhat Khursheed, Qurat-ul-Quadir and Showkat Ahmad Ganie are affiliated with the Department of Clinical Biochemistry at the University of Kashmir, Srinagar. Suhail Ashraf is from the Department of Clinical Biochemistry at Lovely Professional University, Phagwara, Punjab, while Allah-u-deen Khursheed is affiliated with Government Medical College, Baramulla. Asia Asiaf is from the Department of Biotechnology at the Central University of Kashmir, Ganderbal.
The researchers focus on three components of this pathway.
DR5, also known as TRAIL receptor-2, plays a central role in initiating apoptosis. When its expression is reduced, cancer cells may become less responsive to TRAIL-induced cell death.
DcR2, or decoy receptor-2, can bind to TRAIL but lacks the functional death domain required to initiate apoptosis. It can therefore interfere with the interaction between TRAIL and the death receptors DR4 and DR5.
The third component, caspase-3, acts further downstream as an executioner protein. Once activated, it breaks down essential cellular components, completing the process of programmed cell death.
According to the review, alterations affecting these three components can disrupt the balance between cell survival and cell death, potentially contributing to treatment resistance.
DNA methylation and treatment resistance
A central focus of the review is DNA methylation, an epigenetic process through which chemical groups are added to DNA, influencing whether particular genes are switched on or off without changing the underlying genetic sequence.
The researchers explain that abnormal methylation, particularly hypermethylation in gene promoter regions, can suppress the expression of genes involved in tumour suppression and apoptosis.
In the case of DR5, promoter hypermethylation may silence the gene, reducing the availability of death receptors needed to initiate the TRAIL signalling pathway.
This can weaken the cell’s ability to respond to apoptosis-inducing signals and contribute to resistance against treatment.
The review also highlights the complex role of DcR2. Although hypermethylation of its promoter has been associated with reduced gene expression in breast cancer, the relationship between its methylation status and its biological function is not straightforward.
The authors note that DcR2 regulation can vary depending on the cancer subtype, methylation density, promoter region and activity of other proteins involved in apoptosis.
Caspase-3 presents another layer of complexity. Reduced expression or impaired activation of this protein can interfere with the execution of apoptosis, allowing damaged cancer cells to survive treatment.
The researchers also caution that higher levels of caspase-3 expression do not necessarily indicate increased cell death because the protein must first be activated to perform its function.
Together, these findings suggest that examining DNA methylation alongside gene and protein expression could provide a more comprehensive understanding of why some breast cancer cells resist treatment.
Potential for new therapeutic approaches
An important aspect of epigenetic changes is that, unlike permanent genetic mutations, some of them can potentially be reversed.
The review discusses the possibility of using drugs that inhibit DNA methyltransferases, enzymes responsible for adding methyl groups to DNA, to restore the expression of genes involved in apoptosis.
Among the compounds discussed are 5-azacytidine and 5-aza-2’-deoxycytidine, also known as decitabine.
Experimental studies in breast cancer models suggest that these compounds can reactivate silenced genes and alter apoptotic signalling pathways, potentially making cancer cells more responsive to treatments designed to induce cell death.
The authors also examine the possibility of combining epigenetic drugs with TRAIL-based therapies.
Several TRAIL receptor-targeting agents, including tigatuzumab, have been investigated as potential cancer treatments. However, clinical results have been limited.
In one study involving patients with metastatic triple-negative breast cancer, tigatuzumab was evaluated in combination with nab-paclitaxel. Although complete responses were observed in a small number of patients, the overall clinical benefit was not significantly different among the patients studied.
The review suggests that activating TRAIL receptors alone may not be sufficient to overcome the multiple resistance mechanisms present in breast tumours.
Combining epigenetic therapies with existing treatments could therefore offer a potential research direction, although the authors emphasise that this approach requires further investigation.
Implications for personalised medicine
The researchers suggest that DNA methylation patterns involving DR5, DcR2 and CASP3 could eventually help identify molecular characteristics associated with treatment resistance and disease progression.
Such markers could potentially contribute to diagnostic, prognostic and predictive assessments, helping researchers understand which patients may respond to particular therapies.
However, the effects of epigenetic changes are not uniform across all breast cancers.
The review points out that tumour subtype, disease stage, receptor status and the surrounding tumour microenvironment can influence how the TRAIL pathway responds to treatment.
For instance, luminal breast cancers, HER2-positive tumours and triple-negative breast cancers have different molecular characteristics that may affect their response to apoptosis-targeting therapies.
The authors therefore recommend that future clinical trials consider molecular subtype, DNA methylation status, receptor expression and the functional capacity of downstream apoptotic proteins when evaluating TRAIL-directed and epigenetic treatments.
Researchers call for further clinical validation
Despite the potential therapeutic implications, the researchers acknowledge that evidence directly connecting DNA methylation of DR5, DcR2 or CASP3 with patients’ responses to TRAIL receptor-targeting treatments remains limited.
Much of the available evidence is based on experimental models and early translational research rather than established clinical applications.
The authors also highlight the risk that drugs designed to reverse DNA methylation may produce widespread epigenetic changes rather than targeting only specific genes involved in apoptosis. Such changes could have unintended effects on gene expression.
They call for further studies integrating promoter methylation, messenger RNA levels, protein expression and functional apoptosis measurements across different breast cancer subtypes.
The review concludes that understanding how epigenetic modifications regulate the TRAIL pathway could help identify potential biomarkers and inform the development of more personalized approaches to breast cancer treatment.
While the findings do not establish a new treatment, they highlight DNA methylation as an important area for further research into the molecular mechanisms underlying treatment resistance.
