Abemaciclib in Combination With Endocrine Therapy for Patients With Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: A Phase 1b Study

Background Cyclin-dependent kinases (CDK) 4 and 6 regulate G1 to S cell cycle progression and are often altered in cancers. Abemaciclib is a selective inhibitor of CDK4 and CDK6 approved for administration on a continuous dosing schedule as monotherapy or as combination therapy with an aromatase inhibitor or fulvestrant in patients with advanced or metastatic breast cancer. This Phase 1b study evaluated the safety and tolerability, pharmacokinetics, and antitumor activity of abemaciclib in combination with endocrine therapy for metastatic breast cancer (MBC), including aromatase inhibitors (letrozole, anastrozole, or exemestane) or tamoxifen. Patients and Methods Women ≥18 years old with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) MBC were eligible for enrollment. Eligibility included measurable disease or non-measurable but evaluable bone disease by Response Evaluation Criteria in Solid Tumours (RECIST) v1.1, Eastern Cooperative Oncology Group performance status 0–1, and no prior chemotherapy for metastatic disease. Adverse events were graded by the National Cancer Institute Common Terminology Criteria for Adverse Events v4.0 and tumor response were assessed by RECIST v1.1. Results Sixty-seven patients were enrolled and received abemaciclib 200 mg every 12 hours in combination with letrozole (Part A, n=20), anastrozole (Part B, n=16), tamoxifen (Part C, n=16), or exemestane (Part D, n=15). The most common treatment-emergent adverse events (TEAE) were diarrhea, fatigue, nausea, and abdominal pain. Grade 4 TEAEs were reported in five patients (one each with hyperglycemia, hypertension, neutropenia, procedural hemorrhage, and sepsis). There was no effect of abemaciclib or endocrine therapy on the pharmacokinetics of any combination study drug. Across all treated patients, the median progression-free survival was 25.4 months (95% confidence interval: 18.0, 35.8). The objective response rate was 38.9% in 36 patients with measurable disease. Conclusions Abemaciclib in combination with multiple endocrine therapy options exhibited manageable safety and promising antitumor activity in patients with HR+, HER2- MBC. Clinical Trial Registration https://clinicaltrials.gov/, identifier NCT0205713

Mutation site and context dependent effects of ESR1 mutation in genome-edited breast cancer cell models

Abstract Background Mutations in the estrogen receptor alpha (ERα) 1 gene (ESR1) are frequently detected in ER+ metastatic breast cancer, and there is increasing evidence that these mutations confer endocrine resistance in breast cancer patients with advanced disease. However, their functional role is not well-understood, at least in part due to a lack of ESR1 mutant models. Here, we describe the generation and characterization of genome-edited T47D and MCF7 breast cancer cell lines with the two most common ESR1 mutations, Y537S and D538G. Methods Genome editing was performed using CRISPR and adeno-associated virus (AAV) technologies to knock-in ESR1 mutations into T47D and MCF7 cell lines, respectively. Various techniques were utilized to assess the activity of mutant ER, including transactivation, growth and chromatin-immunoprecipitation (ChIP) assays. The level of endocrine resistance was tested in mutant cells using a number of selective estrogen receptor modulators (SERMs) and degraders (SERDs). RNA sequencing (RNA-seq) was employed to study gene targets of mutant ER. Results Cells with ESR1 mutations displayed ligand-independent ER activity, and were resistant to several SERMs and SERDs, with cell line and mutation-specific differences with respect to magnitude of effect. The SERD AZ9496 showed increased efficacy compared to other drugs tested. Wild-type and mutant cell co-cultures demonstrated a unique evolution of mutant cells under estrogen deprivation and tamoxifen treatment. Transcriptome analysis confirmed ligand-independent regulation of ERα target genes by mutant ERα, but also identified novel target genes, some of which are involved in metastasis-associated phenotypes. Despite significant overlap in the ligand-independent genes between Y537S and D538G, the number of mutant ERα-target genes shared between the two cell lines was limited, suggesting context-dependent activity of the mutant receptor. Some genes and phenotypes were unique to one mutation within a given cell line, suggesting a mutation-specific effect. Conclusions Taken together, ESR1 mutations in genome-edited breast cancer cell lines confer ligand-independent growth and endocrine resistance. These biologically relevant models can be used for further mechanistic and translational studies, including context-specific and mutation site-specific analysis of the ESR1 mutations

Efficacy and safety of talazoparib (TALA) or physician's choice of therapy (PCT) in United States patients (pts) with HER2- germline BRCA1/2-mutated (gBRCAm) locally advanced/metastatic breast cancer (LA/MBC) in the EMBRACA study

1044 Background: TALA is a poly(ADP-ribose) polymerase (PARP) inhibitor approved in the US for HER2- g BRCAm LA/MBC. Approval was based on results from the Phase 3 EMBRACA trial comparing efficacy/safety of TALA (1 mg/d) to PCT (capecitabine, eribulin, gemcitabine, vinorelbine) in HER2- g BRCAm LA/MBC pts. This analysis describes outcomes in US pts included in the pivotal study. Methods: Clinical findings from US pts enrolled in EMBRACA were analyzed. Pt characteristics, progression-free survival (PFS), objective response rate (ORR), clinical benefit rate (CBR), and safety/adverse events (AEs) were among the parameters assessed. Results: Of 431 randomized pts, 156 pts (36%) were from the US (TALA: 99; PCT: 57). Pt characteristics were balanced, although a higher percentage in the TALA arm had more poor prognostic features (eg, triple-negative breast cancer, disease-free interval < 12 mo, and more disease sites). TALA improved PFS, ORR, CBR, and duration of response (DOR) vs PCT (Table). 22% of pts in the TALA arm had a continued objective response at month 12 vs 0 pts in the PCT arm. The most common AEs in the TALA arm included anemia, neutropenia, thrombocytopenia, fatigue, nausea, alopecia, and headache; hematologic grade 3/4 AEs occurred more often than nonhematologic AEs. Conclusions: In US pts with HER2- g BRCAm LA/MBC, TALA demonstrated significant improvements in outcomes vs PCT with a manageable safety profile. Clinical trial information: NCT01945775. [Table: see text

ANG1005, a brain penetrating peptide-drug conjugate, shows activity in patients with breast cancer with leptomeningeal carcinomatosis and recurrent brain metastases.

PURPOSE: ANG1005, a novel taxane derivative, consists of 3 paclitaxel molecules covalently linked to Angiopep-2, designed to cross the blood-brain and blood-cerebrospinal barriers and to penetrate malignant cells via LRP1 transport system. Preclinical and clinical evidence of efficacy with ANG1005 has been previously shown. EXPERIMENTAL DESIGN: A multi-center, open-label phase 2 study in adult patients with measurable recurrent brain metastases from breast cancer (BCBM), with or without leptomeningeal carcinomatosis (LC) was conducted (n=72 BCBM; n=28 LC subset). ANG1005 was administered IV at 600 mg/m RESULTS: Median age was 47.5 years. Safety profile was similar to that of paclitaxel with myelosuppression as the predominating toxicity. Average number of prior CNS directed therapies was 2.6 and 94% of the patients had prior taxane treatment. Patient benefit (stable disease or better) was seen in 77% (intracranial) and 86% (extracranial) of the evaluable patients, with iORR of 15% (investigator) or 8% (independent radiology review). In the LC subset, 79% of the patients had intracranial disease control and estimated median overall survival of 8.0 months (95% CI 5.4 - 9.4). CONCLUSIONS: Even though the study pre-set rule for iORR per IRF was not met in this heavily pretreated population, a notable CNS and systemic treatment effect was seen in all patients, particularly in LC patients, including symptom improvement and prolonged overall survival compared to historical control