Talazoparib versus chemotherapy in patients with germline BRCA1/2-mutated HER2-negative advanced breast cancer: final overall survival results from the EMBRACA trial.

BACKGROUND: In EMBRACA, talazoparib prolonged progression-free survival versus chemotherapy (hazard ratio [HR] 0.542 [95% confidence interval (CI) 0.413-0.711]; P < 0.0001) and improved patient-reported outcomes (PRO) in germline BRCA1/2 (gBRCA1/2)-mutated advanced breast cancer (ABC). We report final overall survival (OS). PATIENTS AND METHODS: This randomized phase III trial enrolled patients with gBRCA1/2-mutated HER2-negative ABC. Patients received talazoparib or physician's choice of chemotherapy. OS was analyzed using stratified HR and log-rank test and prespecified rank-preserving structural failure time model to account for subsequent treatments. RESULTS: A total of 431 patients were entered in a randomized study (287 talazoparib/144 chemotherapy) with 412 patients treated (286 talazoparib/126 chemotherapy). By 30 September 2019, 216 deaths (75.3%) occurred for talazoparib and 108 (75.0%) chemotherapy; median follow-up was 44.9 and 36.8 months, respectively. HR for OS with talazoparib versus chemotherapy was 0.848 (95% CI 0.670-1.073; P = 0.17); median (95% CI) 19.3 months (16.6-22.5 months) versus 19.5 months (17.4-22.4 months). Kaplan-Meier survival percentages (95% CI) for talazoparib versus chemotherapy: month 12, 71% (66% to 76%)/74% (66% to 81%); month 24, 42% (36% to 47%)/38% (30% to 47%); month 36, 27% (22% to 33%)/21% (14% to 29%). Most patients received subsequent treatments: for talazoparib and chemotherapy, 46.3%/41.7% received platinum and 4.5%/32.6% received a poly(ADP-ribose) polymerase (PARP) inhibitor, respectively. Adjusting for subsequent PARP and/or platinum use, HR for OS was 0.756 (95% bootstrap CI 0.503-1.029). Grade 3-4 adverse events occurred in 69.6% (talazoparib) and 64.3% (chemotherapy) patients, consistent with previous reports. Extended follow-up showed significant overall improvement and delay in time to definitive clinically meaningful deterioration in global health status/quality of life and breast symptoms favoring talazoparib versus chemotherapy (P < 0.01 for all), consistent with initial analyses. CONCLUSIONS: In gBRCA1/2-mutated HER2-negative ABC, talazoparib did not significantly improve OS over chemotherapy; subsequent treatments may have impacted analysis. Safety was consistent with previous observations. PRO continued to favor talazoparib.

Quality of life with talazoparib versus physician's choice of chemotherapy in patients with advanced breast cancer and germline BRCA1/2 mutation: patient-reported outcomes from the EMBRACA phase III trial.

Background: In the EMBRACA phase III trial, talazoparib (1 mg daily, orally) demonstrated a statistically significant improvement in PFS versus physician's choice of chemotherapy (PCT; capecitabine, eribulin, gemcitabine, or vinorelbine) in patients with HER2-negative advanced breast cancer carrying a germline BRCA1/2 mutation; we evaluated patient-reported outcomes (PROs). Patients and methods: Patients were randomized 2 : 1 to receive talazoparib or PCT. PROs were assessed at day 1 (baseline), the start of each treatment cycle (every 3 weeks), and at the end of treatment, using the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-30) and its breast cancer module, QLQ-BR23. Prespecified exploratory analyses included a longitudinal mixed-effect model comparing treatment arms and a time to definitive clinically meaningful deterioration (TTD) analysis carried out in the global health status/quality of life (GHS/QoL), and all functional and symptom scales from the EORTC QLQ-C30 and -BR23 questionnaires. Between-arm TTD comparisons were made using a stratified log-rank test and a Cox proportional hazards model. Results: Baseline scores were similar between arms. Statistically significant estimated overall improvement from baseline in GHS/QoL was seen for talazoparib compared with statistically significant deterioration for PCT {3.0 [95% confidence interval (CI) 1.2, 4.8] versus -5.4 [95% CI -8.8, -2.0]; between arms, P < 0.0001}. A statistically significant greater delay was observed in TTD in GHS/QoL, favoring talazoparib over PCT [hazard ratio, 0.38 (95% CI 0.26, 0.55; median, 24.3 versus 6.3 months, respectively; P < 0.0001)]. A statistically significant overall change and a statistically significant delay in TTD, all favoring talazoparib, were also observed in multiple functions and symptoms. Conclusion: Patients who received talazoparib had significant overall improvements and significant delay in TTD in multiple cancer-related and breast cancer-specific symptoms, functions, and GHS/QoL. ClinicalTrials.gov: NCT01945775.

Activity of trabectedin in germline BRCA1/2-mutated metastatic breast cancer: results of an international first-in-class phase II study.

BACKGROUND: Breast cancer is a heterogeneous disease defined by both germline and somatic abnormalities. In preclinical models, tumors carrying homologous recombination defects are highly sensitive to trabectedin. This phase II trial evaluated the efficacy and safety of trabectedin in BRCA1/2 germline mutation carriers with pretreated metastatic breast cancer (MBC). PATIENTS AND METHODS: Trabectedin 1.3 mg/m(2) as a 3-h i.v. infusion was administered every 3 weeks until progression or intolerance. The primary efficacy end point was the objective response rate (ORR) as per RECIST. Secondary efficacy end points comprised time-to-event end points, and changes in tumor volume and expression of tumor marker CA15.3. Safety was evaluated using the NCI-CTCAE. RESULTS: Forty BRCA1/2 germline mutation carriers with MBC were included. Confirmed partial response (PR) occurred in 6 of 35 assessable patients [ORR = 17%; 95% confidence interval (CI) 7% to 34%] and lasted 1.4-6.8 months. Median PFS was 3.9 months (95% CI 1.6-5.5 months). Eight patients (21%) showed changes in tumor volume, and 14 (40%) a clinical benefit. Trabectedin-related adverse events were generally mild/moderate, the most common being fatigue, nausea, constipation and anorexia. Severe laboratory abnormalities (neutropenia, transaminase increases) were mostly transient and noncumulative, and were managed by dose adjustments. CONCLUSIONS: With the caveat of the limited patient number, trabectedin monotherapy showed activity and was well tolerated in heavily pretreated MBC patients selected for germline BRCA mutation. These results prompt further evaluation of trabectedin alone or combined with other specific drugs in this indication. CLINICALTRIALSGOV: NCT00580112.

Treatment effect of capecitabine and docetaxel or docetaxel alone by oestrogen receptor status in patients with metastatic breast cancer: results of an exploratory analysis.

We investigated treatment effects by oestrogen receptor (ER) status among women with metastatic breast cancer (MBC) receiving capecitabine (C) plus docetaxel (D) or D alone in a randomised phase III trial. Data were retrospectively analysed from patients whose disease had recurred following (neo)adjuvant anthracyclines. ER status was identified in 356/506 patients. In patients with ER-positive tumours, median overall survival from enrolment was 17.7 months with CD versus 12.5 months with D (hazard ratio [HR] 0.65, 95% confidence interval [CI]: 0.47-0.89; P = 0.007) and median time to progression (TTP) was 6.8 and 5.4 months, respectively (HR 0.62, 95% CI: 0.46-0.84; P = 0.002). For patients with ER-negative tumours, significantly longer TTP was seen with CD (5.2 versus 3.5 months; HR 0.73, 95% CI: 0.53-0.98; P = 0.038). Whether there is an additional C to D treatment benefit in ER-positive versus ER-negative MBC requires further evaluation.

Multicenter, Phase II study of capecitabine in taxane-pretreated metastatic breast carcinoma patients.

BACKGROUND: Capecitabine is an oral, tumor-targeted fluoropyrimidine carbamate with high activity in metastatic breast carcinoma and in paclitaxel-pretreated metastatic breast carcinoma. METHODS: The current multicenter, Phase II trial assessed the efficacy and safety of intermittent oral capecitabine, 1255 mg/m(2) twice daily (2 weeks of treatment followed by a 1-week rest period), in patients with metastatic breast carcinoma in whom prior taxane therapy had failed. All patients had failed treatment or had disease that was refractory to two or three previous chemotherapy regimens, one of which contained a taxane. Nearly all patients (96%) also had received prior anthracycline chemotherapy. Seventy-five patients were recruited at 5 centers, 74 of whom received treatment. RESULTS: The overall response rate was 26%, with response rates of 27% and 20%, respectively, in the subgroups of patients previously pretreated with paclitaxel (n = 47) or docetaxel (n = 27). The median survival was 12.2 months, the median duration of response was 8.3 months, and the median time to disease progression was 3.2 months. The most common treatment-related adverse events (all grades) were hand-foot syndrome (62%), diarrhea (58%), nausea (55%), emesis (37%), and stomatitis (34%). However, the majority were mild to moderate in intensity and only three patients experienced Grade 4 (according to the National Cancer Institute of Canada Common Toxicity criteria) adverse events. The only Grade 3 treatment-related adverse events reported in > or = 10% of the patients were hand-foot syndrome (22%), diarrhea (16%), and stomatitis (12%). Myelosuppression and alopecia were rare, and there were no reported treatment-related deaths. CONCLUSIONS: The results of the current study demonstrate that capecitabine is an effective and well tolerated treatment in patients with taxane-refractory or taxane-failing metastatic breast carcinoma. In addition, it is a convenient, orally administered drug, which makes it an attractive agent for use in outpatient treatment.

A phase I and pharmacologic study of capecitabine and paclitaxel in breast cancer patients.

BACKGROUND: Based on preclinical studies demonstrating that treatment with paclitaxel upregulates intratumoral thymidine phosphorylase (dTHdPase), which catalyzes the final step in the conversion of the oral fluoropyrimidine capecitabine to 5-fluorouracil (5-FU), as well as the overlapping spectra of activity for these agents, particularly in metastatic breast cancer, this phase I study evaluated the feasibility of administering capecitabine on an intermittent schedule in combination with paclitaxel in previously-treated patients with locally advanced or metastatic breast cancer. The study also sought to recommend doses for subsequent disease-specific studies, identify clinically significant pharmacokinetic interactions, and detect preliminary antitumor activity. PATIENTS AND METHODS: Nineteen previously treated women with metastatic breast cancer whose prior treatment included neither paclitaxel or capecitabine received one hundred one courses of capecitabine and paclitaxel. Paclitaxel was administered as a three-hour intravenous (i.v.) infusion at a fixed dose of 175 mg/m2 and capecitabine was administered as 2 divided daily doses for 14 days followed by a seven-day rest period every 3 weeks. The dose of capecitabine was increased from a starting dose of 1650 mg/m2/d. The plasma sampling scheme in the first course permitted characterization of the pharmacokinetics of each agent given alone and concurrently to detect major pharmacokinetic interactions. RESULTS: Palmar plantar erythrodysesthesia (hand foot syndrome) and neutropenia were the principal dose-limiting toxicities (DLT). Other toxicities included diarrhea and transient hyperbilirubinemia. Three of eight new patients treated with capecitabine 2000 mg/m2/d and paclitaxel 175 mg/m2 experienced DLT in the first course, whereas none of eleven new patients treated with capecitabine 1650 mg/m2/d and paclitaxel 175 mg/m2 developed DLT. Pharmacokinetic studies indicated that capecitabine did not grossly affect the pharmacokinetics of paclitaxel, and there were no major effects of paclitaxel on the pharmacokinetics of capecitabine and capecitabine metabolites. However, AUC values for the major 5-FU catabolite, fluorobeta-alanine (FBAL), were significantly lower in the presence of paclitaxel. Two complete and seven partial responses (56% response rate) were observed in sixteen patients with measurable disease; four of six patients whose disease was previously treated with high-dose chemotherapy and hematopoietic stem-cell support had major responses. Seven of nineteen patients had stable disease as their best response. CONCLUSIONS: Recommended combination doses of capecitabine on an intermittent schedule and paclitaxel are capecitabine 1650 mg/m2/d orally for 14 days and paclitaxel 175 mg/m2 i.v. every 3 weeks. The favorable preclinical interactions between capecitabine and paclitaxel, as well as the acceptable toxicity profile and antitumor activity in patients with metastatic breast cancer, support further clinical evaluations to determine an optimal role for the combination of capecitabine and paclitaxel in breast cancer and other relevant malignancies.

The role of capecitabine, an oral, enzymatically activated fluoropyrimidine, in the treatment of metastatic breast cancer.

Capecitabine is an oral fluoropyrimidine that mimics continuous infusion 5-fluorouracil and generates 5-fluorouracil preferentially at the tumor site. It is activated via a three-step enzymatic pathway, the final step of which requires thymidine phosphorylase, an enzyme that is significantly more active in tumor than normal tissue. As an oral agent, capecitabine is more convenient for patients and medical personnel, and avoids the complications associated with venous access. This paper reviews the development and clinical experience of capecitabine in breast cancer treatment. Clinical trials have established the efficacy and tolerability of capecitabine in anthracycline- and taxane-pretreated metastatic breast cancer, showing that capecitabine is an effective therapy for patients who have exhausted all established treatment options. Moreover, randomized, phase II studies have demonstrated that capecitabine is effective in anthracycline-pretreated patients and as first-line therapy for metastatic breast cancer. In addition to its confirmed efficacy, the favorable safety profile of capecitabine, particularly the low myelosuppression rate, makes it an attractive agent for incorporation into combination regimens. Therefore numerous trials have assessed the feasibility of capecitabine-containing regimens, and have shown promising results. Capecitabine is an important new treatment option for breast cancer patients, and ongoing clinical trials should further define its role in a range of settings.

Two identical triplet sisters carrying a germline BRCA1 gene mutation acquire very similar breast cancer somatic mutations at multiple other sites throughout the genome.

Monozygotic twins, each of whom has breast cancer, offer a natural study population for gene-environmental interactions as causation of cancer, because they are genetically identical. If heritable factors play a large role in the origin of a neoplasm, disease concordance should be significant in monozygotic twins. Two monozygotic triplet sisters carrying a germline BRCA1 gene mutation (5382insC) who both developed breast cancer at early ages were studied for loss of heterozygosity (LOH) in their microdissected, paraffin-embedded tumors along with control blood and stromal breast tissue at 19 chromosomal arms using 161 microsatellite markers. Microdissected areas of normal lobular and ductal epithelium and ductal in situ carcinoma were also studied for LOH using a subset of microsatellite markers. The mother's DNA (extracted from peripheral blood lymphocytes) was analyzed to determine the parental allele under LOH in each case. Both tumors demonstrated similar histologic features suggestive of a secretory variant of ductal carcinoma. The tumors from both sisters had similar overall LOH frequency expressed by the fractional allelic loss (FAL) indices (0.56 vs. 0.60) and demonstrated concordance for loss or retention at 82 of 97 informative markers (85% correlation). In addition, detailed mapping analysis of several chromosomal arms revealed that identical breakpoints were detected in both tumors at several chromosome regions. Finally, in both sisters' tumors, when a chromosome exhibited allelic loss, all of the markers exhibited LOH of the same parental allele even when there were intervening regions of retention of heterozygosity. In contrast, 17 archival sporadic breast carcinomas demonstrated a wide range of FAL indexes and highly individual patterns of LOH. Our findings support the hypothesis that inherited factors play a role in the development of the multiple somatic deletions occurring in breast carcinomas. Whether one of these factors is the mutant BRCA1 allele or some other gene(s) remains to be determined. Genes Chromosomes Cancer 28:359-369, 2000.

Xeloda in the treatment of metastatic breast cancer.

There are few treatment options available for patients with metastatic breast cancer who have failed anthracycline- and paclitaxel-based chemotherapy. Xeloda (capecitabine) is a novel selectively tumoractivated fluoropyrimidine carbamate producing clinically active levels of 5-fluorouracil (5-FU) at the tumor site. Xeloda is active in breast cancer and is administered orally. It is the only registered treatment for patients in whom anthracycline and taxoid treatment has failed. In a phase II trial of 163 paclitaxel-refractory patients with metastatic breast cancer, the overall response rate with Xeloda was 20%, with three complete responses, and the median survival was 12.8 months. A total of 20% of patients experienced a Clinical Benefit Response (a composite assessment of clinical benefit). Furthermore, Xeloda was well tolerated; the most common treatment-related adverse events were hand-foot syndrome, diarrhea, nausea, vomiting, and fatigue. Two additional studies of Xeloda in patients with metastatic breast cancer have also been completed. In the first study, patients with anthracycline-resistant metastatic breast cancer received either Xeloda or paclitaxel; the response rates were 36 and 26%, respectively. In the second study, women aged >/=55 years received first-line treatment with either Xeloda or cyclophosphamide/methotrexate/5-FU. The response rates were 25 and 16%, respectively. These studies show that Xeloda is an active agent in the treatment of metastatic breast cancer with the additional advantage of oral administration.

Multicenter phase II study of capecitabine in paclitaxel-refractory metastatic breast cancer.

PURPOSE: Capecitabine is a novel, oral, selectively tumor-activated fluoropyrimidine carbamate. This large multicenter phase II trial tested the efficacy and safety of twice-daily oral capecitabine at 2,510 mg/m2/d given for 2 weeks followed by a 1-week rest period and repeated in 3-week cycles, in patients with paclitaxel-refractory metastatic breast cancer. PATIENTS AND METHODS: Patients were to have received at least two but not more than three prior chemotherapeutic regimens, one of which had to have contained paclitaxel given for metastatic disease. One hundred sixty-three patients were entered onto the study at 25 centers, and 162 patients received capecitabine. One hundred thirty-five patients had bidimensionally measurable disease, and 27 patients had assessable disease. RESULTS: The overall response rate was 20% (95% confidence interval, 14% to 28%). All responding patients were resistant to or had failed paclitaxel, and all had received an anthracycline. Three complete responses were seen, with complete response durations of 106, 109, and 194+ days. Median duration of response was 8.1 months, median survival time was 12.8 months, and the median time to disease progression was 93 days. The most common treatment-related adverse events were hand-foot syndrome, diarrhea, nausea, vomiting, and fatigue. Diarrhea (14%) and hand-foot syndrome (10%) were the only treatment-related adverse events that occurred with grade 3 or 4 intensity in more than 10% of patients. CONCLUSION: Capecitabine is an active drug in the treatment of paclitaxel-refractory metastatic breast cancer. It has a favorable toxicity profile with the added advantage of being an oral drug administered at home.

Characterization of a breast cancer cell line derived from a germ-line BRCA1 mutation carrier.

A tumor cell line, HCC1937, was established from a primary breast carcinoma from a 24-year-old patient with a germ-line BRCA1 mutation. A corresponding B-lymphoblastoid cell line was established from the patient's peripheral blood lymphocytes. BRCA1 analysis revealed that the tumor cell line is homozygous for the BRCA1 5382insC mutation, whereas the patient's lymphocyte DNA is heterozygous for the same mutation, as are at least two other family members' lymphocyte DNA. The tumor cell line is marked by multiple additional genetic changes including a high degree of aneuploidy, an acquired mutation of TP53 with wild-type allele loss, an acquired homozygous deletion of the PTEN gene, and loss of heterozygosity at multiple loci known to be involved in the pathogenesis of breast cancer. Comparison of the primary tumor with the cell line revealed the same BRCA1 mutation and an identical pattern of allele loss at multiple loci, indicating that the cell line had maintained many of the properties of the original tumor. This breast tumor-derived cell line may provide a useful model system for the study of familial breast cancer pathogenesis and for elucidating BRCA1 function and localization.

Guidelines for systemic therapy of early stage breast cancer.

Optimal treatment of early stage breast cancer remains an active area of study. An expert multidisciplinary committee reviewed clinical data on systemic therapy for early stage, stage I and II breast cancer. Guidelines for treatment were developed for Texas Oncology. P.A., the largest private practice group of oncologists in the United States. This group of physicians treats approximately 5000 new breast cancer patients each year and has a major impact on oncology care in the state of Texas. These guidelines identify prognostic factors which help the practitioner in choosing treatment for patients. Subsets of patients are identified for whom no systemic therapy is warrented. Standard chemotherapy and hormonal therapy regimens are outlined for patients with early stage disease at increased risk for relapse. Dose intensification for high risk stage II patients is reviewed. Timing of therapy and the sequencing of chemotherapy and radiation therapy is addressed. Strategies for the follow-up of patients with a history of breast cancer are outlined.

Paclitaxel with mitoxantrone, fluorouracil, and high-dose leucovorin in the treatment of metastatic breast cancer: a phase II trial.

PURPOSE: Paclitaxel is a highly active single agent in the treatment of breast cancer. However, its optimal incorporation into combination regimens awaits definition. In this phase II study, we added paclitaxel, administered by 1-hour infusion, to a previously described combination regimen that included mitoxantrone, fluorouracil (5-FU), and high-dose leucovorin (NFL). PATIENTS AND METHODS: Forty-six patients with metastatic breast cancer received the following regimen as first- or second-line treatment: paclitaxel 135 mg/m2 by 1-hour intravenous (i.v.) infusion on day 1, mitoxantrone 10 mg/m2 by i.v. bolus on day 1, 5-FU 350 mg2/m by i.v. bolus on days 1, 2, and 3, and leucovorin 300 mg i.v. over 30 to 60 minutes immediately preceding 5-FU on days 1, 2, and 3. Courses were administered at 3-week intervals for a total of eight courses in responding patients. RESULTS: Twenty-three of 45 assessable patients (51%) had major responses. Previous chemotherapy, and in particular previous treatment with doxorubicin, did not affect response rate. The median response duration was 7.5 months. Myelosuppression was moderately severe, with 76% of courses resulting in grade 3 or 4 leukopenia. Hospitalization for treatment of fever during neutropenia was required in 13% of courses, and two patients died as a result of sepsis. Two patients developed severe congestive heart failure after a large cumulative anthracycline dose. CONCLUSION: This combination regimen was active as first- or second-line therapy for metastatic breast cancer, although its activity compared with other combination regimens or with paclitaxel alone is unclear. Myelosuppression was more severe than anticipated based on previous results with the NFL regimen or with paclitaxel administered at this dose and schedule as a single agent. The infrequent development of cardiotoxicity in these patients suggests that the paclitaxel/mitoxantrone combination may not share the problems previously reported with the paclitaxel/doxorubicin combination.

The modified Mitchell osteotomy-bunionectomy: indications and technical considerations.

A total of 204 modified Mitchell osteotomy-bunionectomy procedures with Steinmann pin fixation were evaluated by radiograph, history, and physical examination with long-term personal follow-up. The specific surgical technique modifications used in this series are discussed. This modified procedure produced 91% good or excellent results in this series. The complications or unsatisfactory results were due to partial avascular necrosis, lateral metatarsalgia, incomplete correction of hallux valgus, or late stress fractures. These unsatisfactory results led to the development of specific preoperative surgical criteria for the procedure in addition to the technical modifications.

Regulation of mammary differentiation by the extracellular matrix.

In multicellular organisms cell growth and differentiation are influenced by soluble factors, cell-cell interactions and cell-extracellular matrix interactions. We have used the rat mammary gland as a model system to study the role of extracellular matrix components in the regulation of milk protein gene expression. Since mammary epithelial cells differentiate on a basement membrane in vivo, we investigated the effects of basement membrane components on the expression of the milk protein genes, alpha-casein, alpha-lactalbumin, and transferrin. We have demonstrated that a basement membrane gel, as well as its major basement membrane component, laminin, induced alpha-casein and alpha-lactalbumin expression as much as 160-fold compared to tissue culture plastic. We demonstrate that laminin affects mRNA stability as well as having an effect on protein stability and secretion. Laminin interacts with mammary epithelial cells via an 68 kD cell surface receptor which is capable of interacting with the cellular cytoskeleton. In order to provide evidence that laminin affects on mammary differentiation are mediated through this receptor via the cytoskeleton, we examined the effects of cytoskeletal disrupting agents on milk protein gene expression. We demonstrate that cytochalasin D or colchicine selectively block laminin-mediated milk protein gene expression by affecting mRNA stability. Based on these experiments, we propose a model in which laminin affects mammary gene expression through interaction with cell surface receptors which interact with the cytoskeleton resulting in stabilization of mRNAs for milk protein genes.

Role of the cytoskeleton in laminin induced mammary gene expression.

The differentiation of rat mammary epithelial cells is characterized both by morphologic changes and by the expression of a group of milk protein genes. We have previously shown that by culturing these cells on the basement membrane glycoprotein laminin, the synthesis of the milk proteins, transferrin, alpha-casein, and alpha-lactalbumin is induced. In order to determine if this effect is mediated through the cytoskeleton, we have treated these cells with cytochalasin D and colchicine. Treatment with cytochalasin D or colchicine for 24 h inhibits the accumulation of alpha-casein, transferrin, and alpha-lactalbumin without significant effect on general protein synthesis. Pulse chase studies show that cytochalasin D does not alter the intracellular turnover of alpha-casein or transferrin. Additionally, treatment with cytochalasin D causes an early (within 1 h) increase in secretion of alpha-casein and transferrin suggesting that the actin cytoskeleton provides a meshwork for secretory vesicles. The disruption of this network enhances the secretion of preformed proteins. However, long term (24 h) treatment with cytochalasin D inhibits synthesis of these milk proteins. Northern blot analysis indicates that treatment with cytochalasin D or colchicine inhibits the laminin induced increase in alpha-casein, alpha-lactalbumin, and transferrin mRNAs. These studies indicate that the major effect of the cytoskeleton on laminin induced milk protein gene expression occurs at the level of accumulation of mRNAs for these proteins. We conclude that the expression of laminin induced milk protein gene expression in primary rat mammary cultures depends on the integrity of the actin and microtubule cytoskeleton.

Regulation of rat mammary gene expression by extracellular matrix components.

In the mammary gland the induction and maintenance of differentiation are dependent on both lactogenic hormones and the extracellular matrix (ECM). Since mammary epithelial cells differentiate on a basement membrane in vivo we have examined the effects of basement membrane components on the expression of milk protein genes in primary rat mammary cultures. We examined the effects of a basement membrane gel derived from the Englebreth-Holm-Swarm tumor as well as its major component, laminin, on the expression of a group of milk protein genes. We demonstrate that the basement membrane gel induces alpha-casein and alpha-lactalbumin (alpha-LA) accumulation up to 160- and 70-fold, respectively, of that on tissue culture plastic. Laminin, a major component of the basement membrane, also caused significant induction of these same proteins. In order to determine whether these ECM effects occurred at a translational or post-translational level, pulse-chase experiments were performed. These experiments demonstrated that a laminin substratum selectively effects milk protein turnover and secretion. In order to demonstrate whether ECM effects occurred at the level of steady state accumulation of mRNA we performed dot blot and Northern analyses using cloned cDNA probes for alpha-, beta-, and gamma-caseins and alpha-LA. These studies demonstrated that ECM components induced alpha- and beta-caseins up to 10-fold, and alpha-LA up to 3-fold, with no significant effect on gamma-casein. These results demonstrate that milk protein genes are not coordinately regulated by ECM components. Furthermore, since the amount of induction of milk proteins exceeds the amount of induction of mRNAs for these proteins, we conclude that in our system a major effect of ECM components is at the translational and/or post-translational levels. Based on these findings we propose a model in which basement membrane components effect mammary gene expression at multiple levels.