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About 20% of breast cancer patients are positive for HER2. The efficacy of current treatments is limited by primary and secondary resistance to trastuzumab. tRNA-derived fragments (tRFs) have shown crucial regulatory roles in various cancers. This study aimed to evaluate the role of tRF-27 in regulating the resistance of HER2-positive breast cancer against trastuzumab. tRF-27 was highly expressed in trastuzumab-resistant cells, and its expression level could predict the resistance to trastuzumab. High expression of tRF-27 promoted the growth and proliferation of trastuzumab-exposed cells. RNA-pulldown assay and mass spectrometry were performed to identify Ras GTPase-activating protein-binding proteins 1 and 2 (G3BPs) (two proteins targeted by tRF-27 ); RNA-immunoprecipitation (RIP) to confirm their bindings; co-immunoprecipitation (co-IP) and RNA-pulldown assay to determine the binding domains between G3BPs and tRF-27 . tRF-27 bound to the nuclear transport factor 2 like domain(NTF2 domain) of G3BPs through a specific sequence. tRF-27 relied on G3BPs and NTF2 domain to increase trastuzumab tolerance. tRF-27 competed with lysosomal associated membrane protein 1(LAMP1) for NTF2 domain, thereby inhibiting lysosomal localization of G3BPs and tuberous sclerosis complex (TSC). Overexpression of tRF-27 inhibited phosphorylation of TSCs and promoted the activation of mechanistic target of rapamycin complex 1(MTORC1) to enhance cell proliferation and entice the resistance of HER2-positive breast cancer against trastuzumab., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Background/aims: Resistance to trastuzumab remains a common challenge to HER-2 positive breast cancer. Up until now, the underlying mechanism of trastuzumab resistance is still unclear. tRNA-derived small non-coding RNAs, a new class of small non-coding RNA (sncRNAs), have been observed to play an important role in cancer progression. However, the relationship between tRNA-derived fragments and trastuzumab resistance is still unknown., Methods: We detected the levels of tRNA-derived fragments expression in normal breast epithelial cell lines, trastuzumab-sensitive and -resistant breast cancer cell lines using high-throughput sequencing. qRT-PCR was conducted to validate the differentially expressed fragments in serums from trastuzumab-sensitive and -resistant patients. A receiver operating characteristic (ROC) curve analysis was performed to evaluate the power of specific tRNA-derived fragments. Progression-free survival (PFS) was analyzed using Cox-regression., Results: Our sequence results showed that tRNA-derived fragments were differentially expressed in the HBL-100, SKBR3, and JIMT-1 cell lines. tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN were found significantly upregulated in trastuzumab-resistant patients compared to sensitive individuals, and the ROC analysis showed that tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN were correlated with trastuzumab resistance. In a multivariate analysis, higher levels of tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN expression were associated with significantly shorter PFS in patients with metastatic HER-2 positive breast cancer., Conclusion: Our results suggest that tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN play important roles in trastuzumab resistance. Patients with high levels of tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN expression benefitted less from trastuzumab-based therapy than those that express lower-levels of these molecules. tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN may be potential biomarkers and intervention targets in the clinical treatment of trastuzumab-resistant breast cancer., (© 2018 The Author(s). Published by S. Karger AG, Basel.)

The use of trastuzumab emtansine (T‐DM1) has revealed significant efficacy in HER2‐positive metastatic breast cancer (MBC). However, optimal therapeutic strategies following T‐DM1 failure remain a subject of debate in clinical practice. In this multicenter, retrospective, real‐world study, we sought to examine the effectiveness and safety of tyrosine kinase inhibitors (TKIs) as a therapeutic strategy in HER2‐positive MBC who developed T‐DM1 resistance. Between September 2018 and December 2022, 66 patients were enrolled. The median progression‐free survival of TKIs‐based therapy was 10.1 months (95% CI, 4.7–15.6). Objective response rate and clinical benefit rate were 18.2 and 66.7%, respectively. TKIs‐based therapy demonstrated better effectiveness in patients who had previously derived benefit from T‐DM1 and featured acquired resistance to trastuzumab. The most common adverse events were diarrhea (36, 54.5%), hand‐foot syndrome (31, 47.0%), and leucopenia (30, 45.5%). In conclusion, TKIs‐based therapy showed promising effectiveness and safety in HER2‐positive MBC patients after T‐DM1 failure. [ABSTRACT FROM AUTHOR]