Effective targeting of breast cancer stem cells by combined inhibition of Sam68 and Rad51

Alice Turdo,Caterina D’Accardo,Vittoria Poli,Melania Lo Iacono,Luca Fagnocchi,Alessio Zippo,Giuseppe Pistone,Irene Pillitteri,Francesco Verona,Ruggero De Maria,Naida Faldetta,Veronica Veschi,Stefania Stella,Miriam Gaggianesi,Rossana Porcasi,Rossano Lattanzio,Vincenzo Luca Lentini ,Gabriella Militello,Maria Rita Bongiorno,Gaetana Porcelli,Giorgio Stassi,Sven Beyes,Simone Di Franco,Matilde Todaro

doi:10.1038/s41388-022-02239-4

Abstract

Breast cancer (BC) is the second cause of cancer-related deceases in the worldwide female population. Despite the successful treatment advances, 25% of BC develops resistance to current therapeutic regimens, thereby remaining a major hurdle for patient management. Current therapies, targeting the molecular events underpinning the adaptive resistance, still require effort to improve BC treatment. Using BC sphere cells (BCSphCs) as a model, here we showed that BC stem-like cells express high levels of Myc, which requires the presence of the multifunctional DNA/RNA binding protein Sam68 for the DNA-damage repair. Analysis of a cohort of BC patients displayed that Sam68 is an independent negative factor correlated with the progression of the disease. Genetic inhibition of Sam68 caused a defect in PARP-induced PAR chain synthesis upon DNA-damaging insults, resulting in cell death of TNBC cells. In contrast, BC stem-like cells were able to survive due to an upregulation of Rad51. Importantly, the inhibition of Rad51 showed synthetic lethal effect with the silencing of Sam68, hampering the cell viability of patient-derived BCSphCs and stabilizing the growth of tumor xenografts, including those TNBC carrying BRCA mutation. Moreover, the analysis of Myc, Sam68 and Rad51 expression demarcated a signature of a poor outcome in a large cohort of BC patients. Thus, our findings suggest the importance of targeting Sam68-PARP1 axis and Rad51 as potential therapeutic candidates to counteract the expansion of BC cells with an aggressive phenotype.

Highlights

Breast cancer (BC) is the first malignancy in woman worldwide [1, 2]
Using BC sphere cells (BCSphCs) as a model, here we showed that BC stem-like cells express high levels of Myc, which requires the presence of the multifunctional DNA/RNA binding protein substrate during mitosis of 68 kDa (Sam68) for the DNA-damage repair
We previously reported that cancer progression could be attributed to the emergence of a remnant therapy-resistant cancer stemlike population, which is characterized by highly efficient activation of DNA-damage response (DDR) [35,36,37]

Summary

INTRODUCTION

Breast cancer (BC) is the first malignancy in woman worldwide [1, 2]. Early BC is a curable disease in 80% of patients, as opposed to advanced BC that is characterized by a median overall survival of 2–3 years [1]. The use of PARP inhibitors proved to target SAM68 enrichment among DNA-damage genes in Myccells harboring an impaired recovery mechanism from DNA errors, overexpressing stem-like cells PARP inhibitors considerably Myc-transcriptionally regulates the oncoprotein Sam, which is improved the therapeutic response of BRCA-mutant BC, inter- and overexpressed in several human cancers [11, 29], we selected this intra-tumor heterogeneity limits the treatment efficacy and causes gene for further investigation as an unprecedented pivot of BC the selection and expansion of the aggressive CSC pool expressing DNA-damage repair machinery. We demonstrated that the high Myc expression in BC stem-like detectable in adjacent nontumor breast tissue (Supplementary cells promotes Sam transcription, and activation of Rad Fig. S2A–C) and normal tissues (Supplementary Fig. S2C). Multivariate analysis denoted that Sam is an independent negative prognostic factor of DRFS showing the higher statistical significance over the most important clinical parameters

RESULTS

Turdo et al 3

DISCUSSION

MATERIAL AND METHODS

Findings

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