👤 Bruno André

Approximately 40% of patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), advanced breast cancer (ABC) have PIK3CA alterations, which contributes to endocrine therapy resistance. Alpelisib, an α-selective phosphatidylinositol 3-kinase inhibitor and degrader, given in combination with fulvestrant, is approved for the treatment of PIK3CA-mutated, HR+, HER2- ABC, based on the SOLAR-1 trial. Aside from PIK3CA, other gene alterations are associated with poor prognosis and limited response to treatment in this patient population. In this retrospective analysis, we performed tissue-based next-generation sequencing of 398 patients (237 PIK3CA-altered, 161 PIK3CA-wild type) from SOLAR-1. Progression-free survival (PFS) correlative analysis was performed in the PIK3CA-altered cohort. PIK3CA-altered and PIK3CA-wild type tumors had distinct genomic profiles. In the PIK3CA-altered cohort, patients who received alpelisib plus fulvestrant had a median PFS (mPFS) of 11.01 months versus 5.55 months for those receiving placebo plus fulvestrant (P=0.0004). Patients in the lowest tumor mutational burden quartile as well as those with FGFR1 or FGFR2 alterations derived greater PFS benefit from alpelisib plus fulvestrant versus placebo plus fulvestrant (18.5 versus 3.22 months; HR 0.38; 95% CI 0.21-0.68. FGFR1 12.71 versus 3.75 months; HR 0.38; 95% CI 0.17-0.81; P=0.32. FGFR2: 9.63 versus 2.78 months; HR 0.31; 95% CI 0.1-0.94; P=0.29); patients with MYC or RAD21 alterations derived limited PFS benefit. Cox and multi-task machine learning models identified lower Eastern Cooperative Oncology Group performance status, prior cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) treatment, and PTEN or TP53 alterations among the most deleterious factors for PFS in the PIK3CA-altered cohort. Alpelisib plus fulvestrant provides clinical benefit for patients with PIK3CA-altered, HR+, HER2- ABC across a range of concomitant alterations, including those previously implicated in endocrine therapy or CDK4/6i resistance. Machine learning models identified factors including gene mutations that influenced PFS. Show less

Degradation of various membrane proteins in the lumen of the vacuole/lysosome requires their prior sorting into the multivesicular body (MVB) pathway. In this process, ubiquitin serves as a sorting signal for most cargoes. The yeast ubiquitin hydrolase Doa4 acts late in the MVB pathway. It's role is to catalyze deubiquitination of cargo proteins prior to their sorting into the endosomal vesicles. This step rescues ubiquitin from degradation in the vacuole/lysosome, enabling it to be recycled. Accordingly, the level of monomeric ubiquitin is typically reduced in doa4 mutants. Although MVB sorting of cargo proteins is also impaired in doa4 mutants, the question of whether this defect is due solely to Doa4's role in maintaining a normal pool of ubiquitin in the cell remains open. We here show that the requirement of Doa4 for correct MVB sorting of the endocytic cargo general amino acid permease and of the biosynthetic cargo carboxypeptidase S are not because of the role of Doa4 in ubiquitin recycling. This suggests a direct role of Doa4 in MVB sorting and we show that this role depends on Doa4's catalytic activity. We propose that deubiquitination by Doa4 of cargo proteins and/or some components of the MVB sorting machinery is essential to correct sorting of cargoes into the MVB pathway. Show less