Circular RNA circLPAR3 blocks ferroptosis to fuel chemotherapy resistance in prostate cancer

Docetaxel has long stood as the backbone of chemotherapy for metastatic castration-resistant prostate cancer, a stage of the disease in which androgen-targeting therapies have failed and treatment options narrow considerably. For many patients, the drug delivers meaningful initial responses, slowing tumor growth and extending survival. Yet the clinical reality is sobering: resistance to docetaxel almost inevitably emerges, transforming a once-effective therapy into an increasingly futile one and leaving oncologists with limited alternatives. Understanding why this resistance develops has become one of the most pressing questions in urologic oncology, and a new study from researchers at Nanjing Medical University offers a compelling piece of the puzzle.

Writing in the journal Genes & Diseases, the research team reports the identification of a circular RNA molecule, circLPAR3, as a previously unrecognized driver of docetaxel resistance in prostate cancer. Circular RNAs are an unusual class of non-coding RNA molecules. Unlike conventional linear RNAs, their ends are covalently joined in a closed loop through a process called back-splicing, which renders them remarkably resistant to degradation by cellular exonucleases. This structural stability has made circular RNAs objects of intense interest in cancer biology, where they can act as molecular sponges, scaffolds, or interaction hubs that rewire gene regulation from within the cell.

The investigators began their search by comparing the circular RNA profiles of docetaxel-sensitive prostate cancer cell lines with variants engineered to resist the drug. Among the differentially expressed candidates, one molecule stood out: circLPAR3, also catalogued as hsa_circ_0004390, produced from the back-splicing of exons 2 and 3 of the LPAR3 gene. Intriguingly, the abundance of the parental LPAR3 gene’s linear transcripts did not differ meaningfully between sensitive and resistant cells, indicating that the resistance phenotype was tied specifically to the circularized form rather than to a general upregulation of the gene itself. Quantitative reverse transcription PCR confirmed that circLPAR3 was substantially elevated in the resistant derivatives of three distinct prostate cancer cell lines, 22Rv1, DU145, and PC3.

Having established the correlation, the team moved to characterize the molecule in detail. Divergent primers spanning the circular junction verified the back-spliced structure, and treatment with RNase R, an enzyme that digests linear RNA but spares circular transcripts, confirmed the looped architecture. Actinomycin D chase experiments demonstrated that circLPAR3 is far more stable than its linear counterpart, consistent with the closed-loop design. Nuclear-cytoplasmic fractionation and fluorescence in situ hybridization then localized the molecule predominantly to the cytoplasm, a positioning that would prove central to its mechanism of action.

One of the study’s most significant contributions lies in explaining how circLPAR3 becomes elevated in resistant cells in the first place. The researchers found that the circular RNA is subject to N6-methyladenosine, or m6A, the most abundant internal chemical modification found on eukaryotic messenger RNAs and increasingly recognized as a master regulator of RNA fate. Specifically, the methyltransferase METTL3 installs the m6A marks on circLPAR3, and these modifications promote recruitment of IGF2BP2, an m6A reader protein that binds the marked transcript and shields it from degradation. In effect, the epitranscriptomic machinery acts as a stabilizing shield, allowing circLPAR3 to accumulate to pathological levels in cells exposed to docetaxel pressure. This finding adds prostate cancer chemoresistance to the growing list of malignancies in which m6A dynamics shape disease behavior.

With the regulatory mechanism upstream clarified, the team turned to what circLPAR3 actually does inside the cell. Biochemical interaction assays revealed that the cytoplasmic circular RNA physically binds Poly(RC) Binding Protein 2, or PCBP2, an RNA-binding protein with a well-documented role in stabilizing specific target messenger RNAs. Among PCBP2’s targets is the messenger RNA of CHAC1, a gene encoding ChaC glutathione-specific gamma-glutamylcyclotransferase 1, a critical component of the cellular machinery that drives ferroptosis. When circLPAR3 sequesters PCBP2, the protein can no longer perform its stabilizing duty on CHAC1 transcripts, and the CHAC1 messenger RNA rapidly degrades.

The consequences of this molecular sabotage are profound. Ferroptosis is a form of regulated cell death defined by iron-dependent accumulation of lipid peroxides, and it has emerged in recent years as a key mechanism through which chemotherapy eliminates tumor cells. Docetaxel-induced ferroptosis depends on a functioning CHAC1 axis. By depleting CHAC1, circLPAR3 effectively disarms this lethal pathway. The researchers documented the expected biochemical signature of suppressed ferroptosis in resistant cells: reduced accumulation of divalent iron, diminished lipid peroxidation, lowered levels of malondialdehyde, a standard marker of oxidative membrane damage, and preserved intracellular glutathione, the cell’s principal antioxidant buffer. In other words, circLPAR3 rewires tumor cell metabolism to withstand the oxidative assault that docetaxel is meant to deliver.

Crucially, the team showed that the process is reversible. Silencing circLPAR3, or alternatively forcing CHAC1 overexpression, restored the cells’ sensitivity to docetaxel by re-enabling ferroptosis. This rescue experiment carries substantial therapeutic implications, because it demonstrates that the resistance phenotype is not a permanent genetic alteration but a regulable state maintained by a single RNA molecule. It also establishes CHAC1 as a potential downstream effector that could be targeted pharmacologically, even in tumors where the upstream circular RNA is difficult to inhibit directly.

The in vivo evidence strengthened the case further. In subcutaneous xenograft mouse models, tumors engineered to overexpress circLPAR3 grew more aggressively under docetaxel treatment than control tumors, and analysis of the excised tumors confirmed reduced intratumoral CHAC1 expression. The animal data thus recapitulated the cell culture findings, demonstrating that the circLPAR3-PCBP2-CHAC1 axis functions as a genuine resistance mechanism in a living biological system rather than an artifact of laboratory conditions.

Taken together, the study weaves together three of the most dynamic themes in contemporary cancer research: circular RNAs, epitranscriptomic regulation, and ferroptosis. By showing that an m6A-stabilized circular RNA can suppress a ferroptosis-executing gene through sequestration of an RNA-binding protein, the Nanjing Medical University team has illuminated a regulatory circuit that connects chemical RNA modification to chemotherapy failure. The findings position circLPAR3 as a candidate biomarker for predicting treatment response in patients with advanced prostate cancer, and they suggest that disrupting the circLPAR3-PCBP2 interaction, restoring CHAC1 activity, or targeting the METTL3-IGF2BP2 stabilization pathway could open new avenues for resensitizing resistant tumors to docetaxel. As ferroptosis-inducing strategies continue to advance toward clinical testing, understanding the molecular brakes that tumors deploy against this form of cell death will be essential, and circLPAR3 now stands as one of the clearest examples of such a brake in prostate cancer.

Subject of Research: m6A-modified circular RNA circLPAR3 promoting docetaxel resistance in prostate cancer by suppressing ferroptosis via the PCBP2/CHAC1 axis

Article Title: circLPAR3 drives chemotherapy resistance in prostate cancer

Article References: circLPAR3 drives chemotherapy resistance in prostate cancer. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: prostate cancer, circLPAR3, docetaxel resistance, ferroptosis, circular RNA, m6A methylation, METTL3, IGF2BP2, PCBP2, CHAC1, chemoresistance, non-coding RNA