Glycoprotein nonmetastatic melanoma protein B overexpression—a marker of resistance to cyclin-dependent kinase 4 and 6 inhibitors

BACKGROUND: Resistance to cyclin-dependent kinase 4 and 6 inhibitors remains a major clinical challenge in treating estrogen receptor-positive breast cancer, with no reliable predictive biomarkers currently available for patient selection. METHODS: To investigate resistance mechanisms, we generated drug-tolerant persisters to abemaciclib and palbociclib in a panel of estrogen receptor-positive breast cancer cell lines. Clariom D human transcriptomic profiling was performed to identify differentially expressed genes, and the data were compared with published data from the PEARL (Phase III study of palbociclib plus endocrine therapy versus capecitabine in patients with HR-positive/HER2-negative metastatic breast cancer resistant to aromatase inhibitors) clinical trial to verify the clinical relevance. The impact of stable glycoprotein nonmetastatic melanoma protein B overexpression in sensitive cells was studied in in vitro and in vivo xenograft models. RESULTS: Cyclin-dependent kinase (CDK) 4 and 6 inhibitor-resistant drug-tolerant persisters exhibited G1 arrest and demonstrated increased senescence. Transcriptomic profiling of drug-tolerant persister models identified 154 genes consistently associated with resistance across cell lines. In the comparison with published resistance-associated genes from the phase III PEARL trial, glycoprotein nonmetastatic melanoma protein B was a strongly upregulated candidate in both datasets. Glycoprotein nonmetastatic melanoma protein B overexpression in sensitive cells conferred resistance to CDK 4 and 6 inhibition, enhanced migratory capacity, and accelerated tumor progression, abrogating the growth-inhibitory effects of abemaciclib observed in control tumors. Across all treatment arms, glycoprotein nonmetastatic melanoma protein B overexpression tumors failed to respond to CDK 4 and 6 blockade. Glycoprotein nonmetastatic melanoma protein B overexpression increased the expression of integrins, including integrin beta 1 (ITGB1) and integrin alpha 5 (ITGA5), and activated protein kinase B (AKT) and extracellular signal-regulated kinase (ERK) signaling, as evidenced by elevated phospho-AKT (Ser473) and phospho-ERK 1 and 2 (Thr202/204). Treatment of glycoprotein nonmetastatic melanoma protein B overexpression cells with the antibody-drug conjugate glembatumumab vedotin, as a single agent, potently decreased cell viability. Additionally, strong synergy with abemaciclib was observed. CONCLUSIONS: Glycoprotein nonmetastatic melanoma protein B is a potential biomarker and therapeutic target that may help identify patients unlikely to benefit from CDK 4 and 6 inhibition.