Targeting NPEPPS to Enhance Cisplatin Efficacy: A Pathway to Overcome Chemotherapy Resistance

Significance 

Cisplatin, a cornerstone of modern chemotherapy, has been instrumental in treating various cancers, including lung, ovarian, testicular, and bladder cancers. Its effectiveness hinges on its ability to penetrate cancer cells, bind to DNA, and disrupt vital cellular processes, ultimately leading to cell death. However, despite its widespread use and initial success, the long-term efficacy of cisplatin is severely hampered by the development of drug resistance. Tumors that were once responsive often become refractory to treatment, a phenomenon that represents a significant challenge in oncology. This resistance not only limits the therapeutic options for patients but also contributes to poor clinical outcomes and increased cancer-related mortality. A major factor underlying cisplatin resistance is the reduced accumulation of the drug within cancer cells. This can occur through multiple mechanisms, such as altered drug uptake, enhanced efflux, or cellular adaptations that mitigate its cytotoxic effects. Although considerable research has been devoted to understanding these resistance mechanisms, the precise molecular players that regulate cisplatin entry into cells remain incompletely understood. This gap in knowledge is particularly pressing, as overcoming resistance requires pinpointing druggable targets that can restore the drug’s intracellular concentration and re-sensitize tumors to therapy.

To this account, New research paper published in Science Advances Journal and led by Professor James Costello from the University of Colorado Denver and professor Dan Theodorescu from the Cedars-Sinai Medical Center, investigated the molecular determinants of cisplatin uptake and resistance. They focused on volume-regulated anion channels (VRACs), a class of cellular channels known to facilitate the transport of small molecules, including chemotherapeutics. While VRACs have been implicated in mediating cisplatin entry, the factors that regulate their activity and influence their interaction with the drug have remained elusive. The researchers began their investigation by exploring the molecular interactions between NPEPPS and VRACs to understand their potential role in cisplatin resistance. Using advanced proteomics, they identified that NPEPPS, a puromycin-sensitive aminopeptidase, binds to the VRAC subunit LRRC8A. This interaction was intriguing, as VRACs are known to facilitate the transport of small molecules, including cisplatin, across the cellular membrane. By binding to LRRC8A, NPEPPS appeared to interfere with the channel’s function, thereby reducing the ability of cells to accumulate cisplatin. To validate these findings, the team performed genetic silencing experiments where they knocked down NPEPPS expression in cancer cells. This reduction in NPEPPS levels led to a marked increase in intracellular cisplatin accumulation, confirming the protein’s role in hindering drug uptake. Furthermore, these cells exhibited heightened sensitivity to cisplatin, evidenced by increased DNA damage and cell death. Conversely, when NPEPPS expression was elevated, the opposite effect was observed: cisplatin accumulation decreased, and the cells became more resistant to the chemotherapy.

The authors then tested whether disrupting the interaction between NPEPPS and VRACs could restore the channel’s functionality and improve cisplatin efficacy. They used pharmacological inhibitors designed to target NPEPPS and observed a significant reversal of resistance in cisplatin-refractory cancer cells. Cells treated with these inhibitors displayed increased VRAC activity, greater cisplatin uptake, and enhanced sensitivity to the drug. These results underscored the therapeutic potential of targeting the NPEPPS-VRAC pathway to overcome drug resistance. In an in vivo context, the team extended their experiments to mouse models of cisplatin-resistant tumors. They found that tumors with high NPEPPS expression were more resistant to cisplatin treatment, consistent with their in vitro findings. However, when NPEPPS activity was inhibited pharmacologically or genetically, the tumors showed a significant response to cisplatin, with reduced growth and increased markers of apoptosis. These results confirmed the translational relevance of their discovery, suggesting that interventions targeting NPEPPS could improve the effectiveness of cisplatin in clinical settings. Additionally, the researchers examined patient datasets to understand the clinical significance of their findings. Analysis revealed that high NPEPPS expression correlated with poorer outcomes in patients receiving cisplatin-based chemotherapy, further supporting the role of this protein in mediating resistance. Together, these experiments and findings illuminate a previously unrecognized mechanism of cisplatin resistance and offer a promising new target for therapeutic intervention.

In conclusion, the new study is significant advancement in understanding and addressing cisplatin resistance, a persistent challenge in oncology that limits the efficacy of one of the most widely used chemotherapy drugs. By identifying NPEPPS as a key regulator of VRACs and uncovering its role in mediating resistance, the research provides new insights into the molecular mechanisms that reduce cisplatin uptake in cancer cells. This discovery not only expands the fundamental understanding of cellular drug transport but also paves the way for targeted strategies to overcome chemotherapy resistance. Moreover, the finding that NPEPPS directly interacts with VRAC subunits to hinder cisplatin transport highlights a previously unknown mechanism of resistance. This mechanistic insight is crucial for designing interventions that restore the functionality of these channels, thereby increasing intracellular cisplatin levels and enhancing its cytotoxic effects on cancer cells. The study demonstrates that silencing or inhibiting NPEPPS can significantly increase cisplatin sensitivity, offering a targeted approach to improve the outcomes of patients who currently face poor prognoses due to drug-resistant tumors. We believe one of the most important implications of the research is its potential to guide the development of combination therapies. By pairing cisplatin with pharmacological inhibitors of NPEPPS, it may be possible to resensitize resistant tumors, making them more susceptible to treatment. This strategy could reduce the need for higher doses of chemotherapy, minimizing toxicity and improving the quality of life for patients. Moreover, the study suggests that NPEPPS expression levels could serve as a biomarker to predict patient response to cisplatin-based therapies, enabling more personalized treatment plans. Beyond oncology, the findings have broader implications for understanding VRAC regulation in physiological and pathological contexts. VRACs are involved in processes such as cell volume regulation, apoptosis, and the transport of small molecules, making this study relevant to fields beyond cancer biology. The discovery of NPEPPS as a regulator of these channels opens the door to exploring its role in other diseases where VRAC function is critical, such as neurodegenerative conditions or metabolic disorders.

Targeting NPEPPS to Enhance Cisplatin Efficacy: A Pathway to Overcome Chemotherapy Resistance - Medicine Innovates

About the author

James Costello, PhD

Associate Professor
Department of Pharmacology
University of Colorado Denver

my lab focuses on 3 research areas: 1) Network inference for identifying drug targets, 2) Predicting drug sensitivity from -omics datasets, and 3) Modeling temporal effects of drug combinations. The reason we are able to study these topics is from the generous work of thousands of scientists across the world that help generate, annotate, and manage invaluable datasets. These projects include, but are not limited to, the Cancer Genome Atlas (TCGA)Cancer Cell Line Encylopedia (CCLE)Genomics of Drug Sensitivity in Cancer (GDSC), and the Connectivity map.

Network inference for identifying drug targets: Network inference tools aim to identify the most relevant dependencies that exist between any two elements given a large set of data. In particular, we explore the relationship between transcriptional regulatory genes and the biological pathways they regulate. Genes that control dysregulated pathways in disease become potential targets for therapeutic intervention. We develop tools that effectively identify these target genes.

Predicting drug sensitivity from –omics datasets: A central goal of personalized medicine is to determine treatment for patients given their genomic backgrounds. We are far from systematically accomplishing this goal with patients, thus we use human cell lines as a proxy to study the interactions between cells and drugs. We focus on understanding the genomic factors that contribute to drug response or resistance.

Modeling temporal effects of drug combinations: The study of drugs and drug combinations often involves measuring dead versus live or growing cells, yet there are many other endpoints that can be measured, for example, the activation of disease-related signaling pathway. Additionally, drug combinations can have synergistic or antagonistic results depending on which drug is administered first. We focus on integrating experimental and computational approaches to model the effects of drug treatment as a function of different endpoint measurements and the order and timing of administration.

About the author

Distinguished university professor Dan Theodorescu, MD, PhD,

Director for the Samuel Oschin Comprehensive Cancer Institute
Cedars-Sinai Medical Center

Dr. Theodorescu is known for his work on the molecular mechanisms underlying bladder cancer and tools that determine drug response as well as the discovery of new drugs for cancer. Examples include the discovery of genes that regulate tumor growth and metastasis (RhoGDI2, AGL, GON4L) and novel biomarkers (DNA/NGS, RNA, and proteomic), and concepts for precision therapeutic approaches such as the COXEN principle that was tested in national (SWOG) clinical trials. He also conceptualized the approach and then led the discovery and development of a “first in class” RalGTPase inhibitor as a new therapeutic in cancer. This drug was awarded a U.S. patent and is in commercial development. Most recently he investigated the significance of loss of the Y chromosome (LOY) in cancer which had been commonly observed in multiple cancer types. Results of this groundbreaking study showed that cancer cells with LOY alter T cell function, promote T cell exhaustion, and sensitize them to checkpoint (PD-1-targeted) inhibitor immunotherapy. This work also provided insights into the basic biology of LOY and potential biomarkers for improving cancer immunotherapy. Dr. Theodorescu has published over 300 articles including articles in Nature, Science, Cancer Cell, PNAS, and JCI. His laboratory is funded by grants from the NIH-NCI. He is an elected member of the American Society for Clinical Investigation (ASCI), Association of American Physicians (AAP), the American Association of Genitourinary Surgeons (AAGUS), the American Surgical Association (ASA), and the National Academy of Medicine (NAM), and a Fellow of the American Association for the Advancement of Science (AAAS).

Reference 

Feldman LER, Mohapatra S, Jones RT, Scholtes M, Tilton CB, Orman MV, Joshi M, Deiter CS, Broneske TP, Qu F, Gutierrez C, Ye H, Clambey ET, Parker S, Mahmoudi T, Zuiverloon T, Costello JC, Theodorescu D. Regulation of volume-regulated anion channels alters sensitivity to platinum chemotherapy. Sci Adv. 2024 Dec 13;10(50):eadr9364. doi: 10.1126/sciadv.adr9364

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