Overcoming KRAS Resistance in Pancreatic Cancer by Targeting the SRSF1-AURKA-MYC Axis
Figura 1 – ASOs interaction and efficacy on SRSF1-AURKA-MYC- induced PDAC cells
Abstract
Pancreatic Ductal Adenocarcinoma is one of the deadliest and clinically relevant tumors in humans. While KRAS represents the crucial oncogenic factor driving malignant transformation in pancreatic cells, the SRSF1-AURKA-MYC oncogenic circuit is extremely relevant in cancer progression. KRAS inhibitor therapies are generally impaired by cancer resistance development, raising the need to find alternative targets in the genetic landscape. A recent study by Kral et al (2026) showed how SRSF1 overexpression forces AURKA protein level dysregulation, and how this alteration can be reversed by targeting AURKA mRNA. In this context, repetitive transposable Alu elements act as a natural brake in AURKA regulation, but the increasing levels of SRSF1 protein impedes the normal AURKA protein balance. Antisense Oligonucleotides (ASOs) specific for AURKA 5’ UTR displayed successful reduction in AURKA protein level, disrupting the SRSF1-AURKA-MYC axis. These results showed the ASOs treatment efficacy on tumoral cells where this oncogenic circuit is present. This strategy has the potential to be a starting point also for other therapies on tumors where AURKA overexpression is related to cancer cells progression.
Review
Pancreatic Ductal Adenocarcinoma (PDAC) is a highly lethal cancer type, with a 5 year survival rate of 10-13% [1]. This pathology is primarily driven by the mutation of the oncogenic gene KRAS, but the high pharmacological resistance to KRAS inhibitors is a crucial limitation to this type of therapy [2]. The oncogenic circuit composed by Ser/Arg-rich splicing factor 1 (SRSF1), Aurora kinase A (AURKA) and cellular myelocytomatosis oncogene (MYC) has been found to be a valid alternative to overcome this obstacle [3, 4], due to its role in PDAC progression. This malignant loop is based on the AURKA 5’ untranslated region (UTR) exon 2 inclusion driven by SRSF1 overexpression, impairing Alu-derived dsRNA natural brake hairpin structure that is normally able to downregulate AURKA expression. In this study, Kral et al. have developed Antisense oligonucleotides (ASOs) [5] in order to target AURKA 5’ UTR mRNA, inhibiting SRSF1 binding and disrupting the oncogenic circuit only in PDAC cells.
How PDAC cells Dismantle the Physiological AURKA Translational Brake
In healthy pancreatic tissue, the predominant AURKA 5’ UTR isoform is the exon-skipped variant (-E2). The authors identified within this isoform two primatespecific transposable elements, AluSp and AluSq2, which are inserted in inverted orientations. Due to their high sequence complementarity, these elements readily base-pair; interestingly, the researchers characterized this interaction as a stable double-stranded RNA (dsRNA) hairpin structure of 294 base pairs. According to their hypothesis, this dsRNA stem loop imposes a structural barrier that impedes the scanning of the preinitiation complex and the 43S ribosomal subunit, thereby maintaining low, basal levels of AURKA translation. In order to validate this model, the authors performed a mini-reporter luciferase assay that showed how the presence of this intact intronic dsRNA structure reduces translation efficiency by over 60% relative to control vectors lacking the inverted repeats.
In pancreatic ductal adenocarcinoma (PDAC), the researchers discovered that this translational brake is completely dismantled by a splicing switch. Using computational analysis via Sashimi plots and radioactive RT-qPCR, they demonstrated a drastic increase in the Percent Spliced-In (PSI) of AURKA Exon 2 in tumor samples. The study displayed that this alteration is driven by the splicing factor SRSF1, which is markedly upregulated in PDAC cells. In particular, the authors found that SRSF1 binds directly to specific Exonic Splicing Enhancers (ESEs) within Exon 2. This binding sterically disrupts the downstream Alu complementarity, unfolding the dsRNA hairpin and forcing the spliceosome to include the 117-nucleotide Exon 2 (+E2 isoform).
The Role of Exon Junction Complexes in AURKA Translation
Then, the study pointed out how the excision of the surrounding introns resulted in the deposition of two Exon Junction Complexes (EJCs) on the 5’ UTR, which specifically recruit the core components mago homolog (MAGOH) and Y14. Following dual-luciferase reporter assays, researchers proved that these EJC footprints facilitate the recruitment of eukaryotic translation initiation factors, thereby enhancing ribosomal loading and resulting in a three- to four-fold increase in AURKA protein synthesis. To confirm that this translation enhancement depends on splicing, they performed an intronless Δ1.2.3 cDNA construct that was utilized as a control. This template, which does not undergo splicing, fails to assemble the EJC footprint and exhibits baseline translation levels irrespective of SRSF1 expression.
AURKA-SRSF1-MYC oncogenic loop is dependent by AURKA protein level
At this point, the authors established how in SUIT2 PDAC cells, the SRSF1-AURKA-MYC circuit is dependent by AURKA protein level rather than AURKA kinase activity. Performing time course analysis on PDAC cells treated with AURKA kinase inhibitor VX-68071, they showed that SRSF1 and MYC protein levels unchanged after the treatment.
In the next experiment, they performed a relative protein expression analysis on PDAC cells treated with the PROteolysis targeting chimera (PROTAC) JB170 specific for AURKA protein. It showed a notable decrease of AURKA protein level by 50% after 12 hours, with a proportional reduction of SRSF1 and MYC protein levels.
ASOs based therapies as a strategy against PDAC
Once established that AURKA protein level is the main factor to the oncogenic circuit progression, the authors created an innovative strategy based on 6 different types of ASOs, in order to target 5’ and 3’ UTR of AURKA on SUIT2 PDAC cells. To validate this new approach, they carried out a Radioactive RT-qPCR, which revealed an ASOs based AURKA mRNA reduction, with ASO3 almost completely eliminating AURKA expression. In particular, ASO3.1 was selected over 3 ASOs overlapping ASO3, and it was renamed ASO-A by the authors.
To assess ASO-A efficacy, the researchers executed a Radioactive RT-qPCR on transfected PDAC cells of ASOA, observing an extensive AURKA mRNA depletion and a modest SRSF1 and MYC mRNA reduction. Furthermore, western blot analysis on treated cells after 48 h revealed an almost complete loss of AURKA, SRSF1 and MYC protein, and cell viability assay and apoptosis assay highlighted a significant increase in cell mortality.
The last, and one of the most clinically relevant parts of the study, was to assess ASO-A specificity for PDAC cells, and its efficacy against KRAS inhibitor resistant cells. The authors treated both SUIT2 PDAC cells and human pancreatic ductal epithelial (HPDE) with ASO-A: the experiment showed a reduction of relative cell viability only in PDAC cells, demonstrating the specificity of treatment only in cancer cells. Next, ASO
A was tested on SUIT2 cells chronically exposed to the KRAS inhibitor RMC 980577 that acquired resistance to the KRAS inhibitor through increased phosphatidylinositol 3-kinase (PI3K) signaling. Interestingly, ASO-A depleted AURKA, SRSF1 and MYC without affecting extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and the mitogen-activated protein kinase (MAPK) signaling, also reducing cell viability.
The most compelling and ambitious aspect of the paper is represented by the extension of this strategy also to other cancer forms. Since AURKA overexpression is conserved also in other types of tumor, this strategy was applied also on renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC) lines. RT-qPCR analysis and cell viability assays highlighted a significant reduction of AURKA transcript levels and cell survival across all cell lines, offering a promising basis for future studies.
Conclusions
In Kral et al. work, researchers were able to find a new strategy focused on interrupting cancer progression, rather than impairing KRAS mutation effects.
The introduction of ASOs has established an important therapeutic framework for PDAC that potentially exceeds current treatment approaches, delivering an efficacy that surpasses conventional expectations. This is especially evident with ASO-A, which not only dismantles the core oncogenic axis, but also demonstrates a remarkable capacity to clear tumor cells that have developed resistance to standard KRAS inhibitors. This particular behaviour could represent a starting point for combinatorial therapies, possibly amplifying the efficacy of the current PDAC drugs.
Another relevant perspective of Kral et al study is depicted by the possibility to extend ASOs strategy application on other types of cancer, like renal and hepatocellular carcinoma.
Despite these promising observations on ASOs therapy application, a notable limitation of the study is that the strategy has only been tested in vitro or in organoid models. Consequently, it remains unclear how this strategy will perform in vivo, given the significant differences between simplified laboratory models and the complex human tumor microenvironment, including challenges related to systemic delivery and drug pharmacokinetics.
Furthermore, the researchers pointed out possible offtarget effects due to unwanted binding with other genome regions.
References
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