Population pharmacokinetics of trastuzumab emtansine (T-DM1), a HER2-targeted antibody–drug conjugate, in patients with HER2-positive metastatic breast cancer: clinical implications of the effect of covariates

PURPOSE: Trastuzumab emtansine (T-DM1) is an antibody–drug conjugate comprising the humanized monoclonal antibody trastuzumab linked to DM1, a highly potent cytotoxic agent. A population pharmacokinetic (PK) analysis was performed to estimate typical values and interindividual variability of T-DM1 PK parameters and the effects of clinically relevant covariates. METHODS: Serum samples were collected from 671 patients with human epidermal growth factor receptor 2-positive locally advanced or metastatic breast cancer (MBC) who received single-agent T-DM1 in five phase I to phase III studies. Nonlinear mixed-effects modeling with the first-order conditional estimation method was used. RESULTS: A linear two-compartment model with first-order elimination from the central compartment described T-DM1 PKs in the clinical dose range. T-DM1 elimination clearance was 0.676 L/day, volume of distribution in the central compartment (V(c)) was 3.127 L, and terminal elimination half-life was 3.94 days. Age, race, region, and renal function did not influence T-DM1 PK. Given the low-to-moderate effect of all statistically significant covariates on T-DM1 exposure, none of these covariates is expected to result in a clinically meaningful change in T-DM1 exposure. CONCLUSIONS: T-DM1 PK properties are consistent and predictable in patients. A further refinement of dose based on baseline covariates other than body weight for the current 3.6 mg/kg regimen would not yield clinically meaningful reductions in interindividual PK variability in patients with MBC. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00280-014-2500-2) contains supplementary material, which is available to authorized users

Loss of STAT6 leads to anchorage-independent growth and trastuzumab resistance in HER2+ breast cancer cells.

Approximately 20% of breast cancers are HER2-positive. Trastuzumab has improved patient outcomes significantly for these cancers. However, acquired resistance remains a major hurdle in the clinical management of these patients. Therefore, identifying molecular changes that cause trastuzumab resistance is worthwhile. STAT6 is a transcription factor that regulates a variety of genes involved in cell cycle regulation, growth inhibition, and apoptosis. STAT6 expression is lost in approximately 3% of breast cancers, but little work has been done in the context of trastuzumab resistance in breast cancer. In isogenic cell line pairs, we observed that trastuzumab-resistant cells expressed significantly lower levels of STAT6 compared to trastuzumab-sensitive cells. Therefore, in order to study the consequences of STAT6 loss in HER2+ breast cancer, we knocked out both alleles of the STAT6 gene using somatic cell gene targeting. Interestingly, loss of STAT6 resulted in anchorage-independent growth and changes in several genes involved in epithelial to mesenchymal transition. This study suggests that STAT6 may play a role in the pathophysiology of HER2+ human breast cancer

Somatic loss of PIK3R1 may sensitize breast cancer to inhibitors of the MAPK pathway

Purpose: The PI3K pathway, which includes the PI3K catalytic subunits p110α (PIK3CA) and the PI3K regulatory subunit p85α (PIK3R1), is the most frequently altered pathway in cancer. We encountered a breast cancer patient whose tumor contained a somatic alteration in PIK3R1. Some commercial sequencing platforms suggest that somatic mutations in PIK3R1 may sensitize cancers to drugs that inhibit the mammalian target of rapamycin (mTOR). However, a review of the preclinical and clinical literature did not find evidence substantiating that hypothesis. The purpose of this study was to knock out PIK3R1 in order to determine the optimal therapeutic approach for breast cancers lacking p85α. Methods: We created an isogenic cellular system by knocking out both alleles of the PIK3R1 gene in the non-tumorigenic human breast cell line MCF-10A. Knockout cells were compared with wild-type cells by measuring growth, cellular signaling, and response to drugs. Results: We observed hyperphosphorylation of MEK in these knockouts, which sensitized PIK3R1-null cells to a MEK inhibitor, trametinib. However, they were not sensitized to the mTOR inhibitor, everolimus. Conclusions: Our findings suggest that breast cancers with loss of p85α may not respond to mTOR inhibition, but may be sensitive to MEK inhibition

<i>BRCA</i> phenocopy hypothesis.

<p>A. Maternal-fetal microchimerism. B. Tetragametic chimerism. C. A woman with <i>BRCA</i>-mutant chimeric cells.</p

Patient 3 pedigree.

<p>This pedigree represents the family history of cancer in patient number 3. The proband, or original patient, is denoted by the arrow. The type of cancer each relative has a history of is denoted below their pedigree symbol. If a relative had genetic testing and was found to carry the known familial <i>BRCA1</i> mutation, this is also denoted below their pedigree symbol. If a relative tested negative for the known familial <i>BRCA1</i>mutation, this is also denoted below their pedigree symbol. The proband had full gene sequencing and deletion/duplication analysis of the <i>BRCA1/2</i> genes; therefore, ‘<i>BRCA1/2-</i>‘ is listed below their pedigree symbol. The proband was also found to carry a variant of uncertain significance in <i>MSH2</i>.</p

Mutation primer sequences.

<p>Primers used to detect point mutations by sequence specific PCR, Inner primers end on the indicated variant bases. The size of the resulting product of the extended inner primer and its opposite outer primer will indicate the mutation status.</p

Patient clinical characteristics and family history.

<p>Patient clinical characteristics and family history.</p

Molecular testing in tumor tissue.

<p><b>A.</b> The <i>BRCA1</i> 187del AG deletion heterozygote (families 1 and 5) is detected as an n-2 product by capillary electrophoresis (left) and by an indicative peak pattern by pyrosequencing (top right). Neither the deletion product nor the mutant peak pattern was detected in the patient tumors (bottom panels). <b>B.</b> The heterozygote detected as a 163 bp product by gel electrophoresis. The synthetic oligomer carrying the mutation confirmed the detection of the mutation by mutation sequence specific primers. This band is not present in the negative control nor family 8 DNA (left four lanes). The 137 bp band specific to the normal A allele was detected by primers specific to that allele in the patient sample. Tumor DNA tested for the familial mutation 5215G>A gave similar results (not shown). <b>C.</b> The <i>BRCA2</i> 8107 A→T mutation was tested by sequence-specific PCR. The 92 bp product (T allele, positive) is not present in the patient’s tissue where only the A allele (80bp) is observed. Reagent blanks for the A and T allele primer sets (Bl A, Bl T) are shown. <b>D.</b> <i>BRCA1</i> 3109 insAA (left), and <i>BRCA2</i> 6794 insA (patients 10 and 11, respectively; right) mutation analysis by PCR-capillary electrophoresis. Amplified products from DNA without (negative control, top) and with (positive control, middle panels) demonstrate the expected right shift in migration for the <i>BRCA1</i> 3109 insAA n+2 product (76 bp) and the <i>BRCA2</i> 6794 insA n+1 product (82 bp)(bottom panels). Patient samples show an unexpected left shift (n-1) product.</p