Resistance development to one chemotherapeutic reagent leads frequently to acquired tolerance to other compounds, limiting the therapeutic options for cancer treatment. Herein, we find that overexpression of Rac1 is associated with multi-drug resistance to the neoadjuvant chemotherapy (NAC). Mechanistically, Rac1 activates aldolase A and ERK signaling which up-regulates glycolysis and especially the non-oxidative pentose phosphate pathway (PPP). This leads to increased nucleotides metabolism which protects breast cancer cells from chemotherapeutic-induced DNA damage. To translate this finding, we develop endosomal pH-responsive nanoparticles (NPs) which deliver Rac1-targeting siRNA together with cisplatin and effectively reverses NAC-chemoresistance in PDXs from NAC-resistant breast cancer patients. Altogether, our findings demonstrate that targeting Rac1 is a potential strategy to overcome acquired chemoresistance in breast cancer.

Resistance to radiotherapy is frequently encountered in clinic, leading to poor prognosis of cancer patients. Long noncoding RNAs (lncRNAs) play important roles in the development of radioresistance due to their functions in regulating the expression of target genes at both transcriptional and posttranscriptional levels. Exploring key lncRNAs and elucidating the mechanisms contributing to radioresistance are crucial for the development of effective strategies to reverse radioresistance, which however remains challenging. Here, actin filament‐associated protein 1 antisense RNA1 (lncAFAP1‐AS1) is identified as a key factor in inducing radioresistance of triple‐negative breast cancer (TNBC) via activating the Wnt/β‐catenin signaling pathway. Considering the generation of a high concentration of reduction agent glutathione (GSH) under radiation, a reduction‐responsive nanoparticle (NP) platform is engineered for effective lncAFAP1‐AS1 siRNA (siAFAP1‐AS1) delivery. Systemic delivery of siAFAP1‐AS1 with the reduction‐responsive NPs can synergistically reverse radioresistance by silencing lncAFAP1‐AS1 expression and scavenging intracellular GSH, leading to a dramatically enhanced radiotherapy effect in both xenograft and metastatic TNBC tumor models. The findings indicate that lncAFAP1‐AS1 can be used to predict the outcome of TNBC radiotherapy and combination of systemic siAFAP1‐AS1 delivery with radiotherapy can be applied for the treatment of recurrent TNBC patients.

Highlights d BDNF-AS induces tamoxifen resistance and malignant progression of breast cancers d BDNF-AS driven by MEF2A-regulated enhancer acts as scaffold of RNH1/TRIM21 d BDNF-AS activates mTOR pathway by abolishing RNH1regulated mTOR mRNA decay