Noncanonical EZH2 drives retinoic acid resistance of variant acute promyelocytic leukemias

Cancer cell heterogeneity is a major driver of therapy resistance. To characterize resistant cells and their vulnerabilities, we studied the PLZF-RARA variant of acute promyelocytic leukemia, resistant to retinoic acid (RA), using single-cell multiomics. We uncovered transcriptional and chromatin heterogeneity in leukemia cells. We identified a subset of cells resistant to RA with proliferation, DNA replication, and repair signatures that depend on a fine-tuned E2F transcriptional network targeting the epigenetic regulator enhancer of zeste homolog 2 (EZH2). Epigenomic and functional analyses validated the driver role of EZH2 in RA resistance. Targeting pan-EZH2 activities (canonical/noncanonical) was necessary to eliminate leukemia relapse-initiating cells, which underlies a dependency of resistant cells on an EZH2 noncanonical activity and the necessity to degrade EZH2 to overcome resistance. Our study provides critical insights into the mechanisms of RA resistance that allow us to eliminate treatment-resistant leukemia cells by targeting EZH2, thus highlighting a potential targeted therapy approach. Beyond RA resistance and acute promyelocytic leukemia context, our study also demonstrates the power of single-cell multiomics to identify, characterize, and clear therapy-resistant cells.

Whole-genome/exome analysis of circulating tumor DNA and comparison to tumor genomics from patients with heavily pre-treated ovarian cancer: subset analysis of the PERMED-01 trial

Introduction

The poor prognosis of ovarian carcinoma (OvC) is due to the advanced stage at diagnosis, a high risk of relapse after first-line therapies, and the lack of efficient treatments in the recurrence setting. Circulating tumor DNA (ctDNA) analysis is a promising tool to assess treatment-resistant OvC and may avoid iterative tissue biopsies. We aimed to evaluate the genomic profile of recurrent heavily pre-treated OvC.

Methods

We performed tumor panel-based sequencing as well as low-coverage whole-genome sequencing (LC-WGS) of tumor and plasma collected in patients with ovarian cancer included in the PERMED-01 trial. Whole-exome sequencing (WES) data of plasma samples were also analyzed and compared to mutation and copy number alteration (CNA) tumor profiles. The prognostic value [progression-free survival (PFS)] of these alterations was assessed in an exploratory analysis.

Results

Tumor and plasma genomic analyses were done for 24 patients with heavily pretreated OvC [67% high-grade serous carcinoma (HGSC)]. Tumor mutation burden was low (median 2.04 mutations/Mb) and the most frequent mutated gene was TP53 (94% of HGSC). Tumor CNAs were frequent with a median of 50% of genome altered fraction. Plasma LC-WGS and WES detected ctDNA in 21/24 cases (88%) with a median tumor fraction of 12.7%. We observed a low correlation between plasma and tumor CNA profiles. However, this correlation was significant in cases with the highest circulating tumor fraction. Plasma genome altered fraction and plasma mutation burden (p = 0.011 and p = 0.041, respectively, log-rank tests) were associated with PFS.

Conclusions

Combination of LC-WGS and WES can detect ctDNA in most pre-treated OvCs. Some ctDNA characteristics, such as genome altered fraction and plasma mutation burden, showed prognostic value. ctDNA assessment with LC-WGS may be a promising and non-expansive tool to evaluate disease evolution in this disease with high genomic instability.

Clinical Trial Registration

https://clinicaltrials.gov/ct2/show/NCT02342158, identifier NCT02342158.

Overcoming Resistance to Anti-nectin-4 Antibody-Drug Conjugate

Antibody-drug conjugates (ADCs) represent a fast-growing drug class in oncology. However, ADCs are associated with resistance, and therapies able to overcome it are of utmost importance. Recently, enfortumab vedotin-ejfv (EV) was approved in nectin-4+ metastatic urothelial cancer. We previously described PVRL4/nectin-4, as a new therapeutic target in breast cancer (BC), and produced an efficient EV-like ADC comprising a human anti-nectin-4 monoclonal antibody conjugated to monomethyl auristatin-E (MMAE) named N41mab-vcMMAE. To study the consequence of the long-term treatment with this ADC, we developed a preclinical BC model in mice, and report a mechanism of resistance to N41mab-vcMMAE after a 9- months treatment and a way to reverse it. RNA-sequencing pointed to an upregulation in resistant tumors of ABCB1 expression, encoding the multidrug resistance protein MDR-1/P-glycoprotein (P-gp), associated with focal gene amplification and high protein expression. Sensitivity to N41mab-vcMMAE of the resistant model was restored in vitro by P-gp pharmacological inhibitors, like tariquidar. P-gp is expressed in a variety of normal tissues. By delivering the drug to the tumor more specifically than does classical chemotherapy, we hypothesized that the combined use of ADC with P-gp inhibitors might reverse resistance in vivo without toxicity. Indeed, we showed that the tariquidar/N41mab-vcMMAE combination was well tolerated and induced a rapid regression of ADC-resistant tumors in mice. By contrast, the tariquidar/docetaxel combination was toxic and poorly efficient. These results show that ABC transporter inhibitors can be safely used with ADC to reverse ADC-induced resistance and open new opportunities in the fight against multidrug resistance.

Circulating tumor DNA predicts efficacy of a dual AKT/p70S6K inhibitor (LY2780301) plus paclitaxel in metastatic breast cancer: plasma analysis of the TAKTIC phase IB/II study

The phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway is frequently activated in HER2-negative breast cancer and may play a role in taxane resistance. The phase IB/II TAKTIC trial (NCT01980277) has shown that combining a dual AKT and p70 ribosomal protein S6 kinase (p70S6K) inhibitor (LY2780301) taken orally with weekly paclitaxel in HER2-negative advanced breast cancer is feasible, with preliminary evidence of efficacy. We wanted to explore whether circulating tumor DNA (ctDNA) may be a surrogate marker of treatment efficacy in this setting. Serial plasma samples were collected and cell-free DNA was sequenced using low-coverage whole-genome sequencing, and analysis was completed with droplet digital PCR for some patients with driver mutations. Baseline tumor fraction (TF) and TF after 7 weeks on treatment were compared to progression-free survival (PFS) and overall response rate. We also explored circulating copy number alterations associated with treatment failure. Of the 51 patients enrolled in the TAKTIC trial, at least one plasma sample was available for 44 cases (96 time points). All patients with tumor TP53, PI3KCA or AKT1 mutations harbored at least one of these alterations in plasma. TF at inclusion was correlated to PFS (6m-PFS was 92% for ctDNAneg patients vs 68% for ctDNApos cases; HR=3.45, 95%CI [1.34-8.90], p=0.007). ctDNA status at week 7 was not correlated to prognosis. Even though most circulating copy number alterations were conserved at disease progression, some genomic regions of interest were altered in post-progression samples. In conclusions, ctDNA detection at baseline was associated with shorter PFS in patients included in the TAKTIC trial. Plasma-based copy number analysis may help to identify alterations involved in resistance to treatment.

Menin inhibition suppresses castration-resistant prostate cancer and enhances chemosensitivity

Disease progression and therapeutic resistance of prostate cancer (PC) are linked to multiple molecular events that promote survival and plasticity. We previously showed that heat shock protein 27 (HSP27) acted as a driver of castration-resistant phenotype (CRPC) and developed an oligonucleotides antisense (ASO) against HSP27 with evidence of anti-cancer activity in men with CRPC. Here, we show that the tumor suppressor Menin (MEN1) is highly regulated by HSP27. Menin is overexpressed in high-grade PC and CRPC. High MEN1 mRNA expression is associated with decreased biochemical relapse-free and overall survival. Silencing Menin with ASO technology inhibits CRPC cell proliferation, tumor growth, and restores chemotherapeutic sensitivity. ChIP-seq analysis revealed differential DNA binding sites of Menin in various prostatic cells, suggesting a switch from tumor suppressor to oncogenic functions in CRPC. These data support the evaluation of ASO against Menin for CRPC.

Circulating tumor DNA as a noninvasive marker of resectability in ovarian carcinomas

5548

Background: Ovarian cancer is the leading cause of death by gynecological cancer. Complete surgery remains one of the main prognostic factors. Laparoscopic exploration is mandatory to assess surgical resectability at diagnosis or after neoadjuvant chemotherapy. However, there is no clinical or biological marker that can correctly predict resectability and may be able to avoid a second laparoscopic exploration for initially unresectable diseases. Our aim was to assess circulating tumor DNA (ctDNA) value as a predictive non-invasive marker of evolution towards resectability for patients with epithelial ovarian cancer receiving first-line chemotherapy. Methods: We explored in this work one of the secondary objectives of the CIDOC study (NCT03302884). CIDOC is a multicenter prospective study aiming to explore ctDNA value as early marker of disease relapse after first-line treatment for epithelial ovarian cancer. Patients with mucinous histology or early stages not requiring chemotherapy are excluded. Plasma samples are collected at diagnosis, during neoadjuvant chemotherapy, and during follow-up. After DNA extraction, panel-based next generation sequencing is performed on both tumor samples and germline DNA, and somatic mutations of interest are selected for ctDNA monitoring. ctDNA analyses are conducted using droplet digital PCR (BioRad QX200) by measuring the variant allele fraction (VAF) of previously identified mutations. Results: This intermediary analysis has included 47 patients diagnosed between March 2017 and December 2019. Median age was 69 years old (48 – 84). Most of the patients had advanced disease (89.4% stage FIGO III or IV), serous histology (94.8%), and high grade tumor (92.3%). Most of the patients underwent complete interval cytoreductive surgery (76.3% vs 17.4% complete upfront surgery). Most of the tumors had TP53 mutations (85.1%), following by alterations involving DNA repair genes (38.3%). Median cell-free DNA concentration at baseline was 0.38 ng/µL (0 – 12.8). ctDNA was identified in 92.1% of patients at baseline with a median VAF of 1.84% (0 – 42.52%). ctDNA VAF was correlated to the peritoneal dissemination ( p= 0.039) assessed with the peritoneal cancer index. ctDNA clearance after preoperative chemotherapy tended to be correlated to achievement of complete interval surgery for patients receiving neoadjuvant chemotherapy ( p= 0.108). Conclusions: ctDNA may be a promising non-invasive marker to assess peritoneal cancer spreading and to predict surgical resectability after neoadjuvant chemotherapy. If confirmed in larger populations, this may enable to avoid additional surgical explorations for patients who remain ctDNA positive after chemotherapy. Clinical trial information: NCT03302884.

Prospective high-throughput genome profiling of advanced cancers: results of the PERMED-01 clinical trial

BACKGROUND

The benefit of precision medicine based on relatively limited gene sets and often-archived samples remains unproven. PERMED-01 (NCT02342158) was a prospective monocentric clinical trial assessing, in adults with advanced solid cancer, the feasibility and impact of extensive molecular profiling applied to newly biopsied tumor sample and based on targeted NGS (t-NGS) of the largest gene panel to date and whole-genome array-comparative genomic hybridization (aCGH) with assessment of single-gene alterations and clinically relevant genomic scores.

METHODS

Eligible patients with refractory cancer had one tumor lesion accessible to biopsy. Extracted tumor DNA was profiled by t-NGS and aCGH. We assessed alterations of 802 "candidate cancer" genes and global genomic scores, such as homologous recombination deficiency (HRD) score and tumor mutational burden. The primary endpoint was the number of patients with actionable genetic alterations (AGAs). Secondary endpoints herein reported included a description of patients with AGA who received a "matched therapy" and their clinical outcome, and a comparison of AGA identification with t-NGS and aCGH versus whole-exome sequencing (WES).

RESULTS

Between November 2014 and September 2019, we enrolled 550 patients heavily pretreated. An exploitable complete molecular profile was obtained in 441/550 patients (80%). At least one AGA, defined in real time by our molecular tumor board, was found in 393/550 patients (71%, two-sided 90%CI 68-75%). Only 94/550 patients (17%, 95%CI 14-21) received an "AGA-matched therapy" on progression. The most frequent AGAs leading to "matched therapy" included PIK3CA mutations, KRAS mutations/amplifications, PTEN deletions/mutations, ERBB2 amplifications/mutations, and BRCA1/2 mutations. Such "matched therapy" improved by at least 1.3-fold the progression-free survival on matched therapy (PFS2) compared to PFS on prior therapy (PFS1) in 36% of cases, representing 6% of the enrolled patients. Within patients with AGA treated on progression, the use of "matched therapy" was the sole variable associated with an improved PFS2/PFS1 ratio. Objective responses were observed in 19% of patients treated with "matched therapy," and 6-month overall survival (OS) was 62% (95%CI 52-73). In a subset of 112 metastatic breast cancers, WES did not provide benefit in term of AGA identification when compared with t-NGS/aCGH.

CONCLUSIONS

Extensive molecular profiling of a newly biopsied tumor sample identified AGA in most of cases, leading to delivery of a "matched therapy" in 17% of screened patients, of which 36% derived clinical benefit. WES did not seem to improve these results.

TRIAL REGISTRATION

ID-RCB identifier: 2014-A00966-41; ClinicalTrials.gov identifier: NCT02342158 .

A chemogenomic approach to identify personalized therapy for patients with relapse or refractory acute myeloid leukemia: results of a prospective feasibility study

Targeted next-generation sequencing (tNGS) and ex vivo drug sensitivity/resistance profiling (DSRP) have laid foundations defining the functional genomic landscape of acute myeloid leukemia (AML) and premises of personalized medicine to guide treatment options for patients with aggressive and/or chemorefractory hematological malignancies. Here, we have assessed the feasibility of a tailored treatment strategy (TTS) guided by systematic parallel ex vivo DSRP and tNGS for patients with relapsed/refractory AML (number NCT02619071). A TTS issued by an institutional personalized committee could be achieved for 47/55 included patients (85%), 5 based on tNGS only, 6 on DSRP only, while 36 could be proposed on the basis of both, yielding more options and a better rationale. The TSS was available in <21 days for 28 patients (58.3%). On average, 3 to 4 potentially active drugs were selected per patient with only five patient samples being resistant to the entire drug panel. Seventeen patients received a TTS-guided treatment, resulting in four complete remissions, one partial remission, and five decreased peripheral blast counts. Our results show that chemogenomic combining tNGS with DSRP to determine a TTS is a promising approach to propose patient-specific treatment options within 21 days.

NOTCH and DNA repair pathways are more frequently targeted by genomic alterations in inflammatory than in non-inflammatory breast cancers

Inflammatory breast cancer (IBC) is the most pro‐metastatic form of breast cancer. Better understanding of its pathophysiology and identification of actionable genetic alterations (AGAs) are crucial to improve systemic treatment. We aimed to define the DNA profiles of IBC vs noninflammatory breast cancer (non‐IBC) clinical samples in terms of copy number alterations (CNAs), mutations, and AGAs. We applied targeted next‐generation sequencing (tNGS) and array‐comparative genomic hybridization (aCGH) to 57 IBC and 50 non‐IBC samples and pooled these data with four public datasets profiled using NGS and aCGH, leading to a total of 101 IBC and 2351 non‐IBC untreated primary tumors. The respective percentages of each molecular subtype [hormone receptor‐positive (HR+)/HER2−, HER2+, and triple‐negative] were 68%, 15%, and 17% in non‐IBC vs 25%, 35%, and 40% in IBC. The comparisons were adjusted for both the molecular subtypes and the American Joint Committee on Cancer (AJCC) stage. The 10 most frequently altered genes in IBCs were TP53 (63%), HER2/ERBB2 (30%), MYC (27%), PIK3CA (21%), BRCA2 (14%), CCND1 (13%), GATA3 (13%), NOTCH1 (12%), FGFR1 (11%), and ARID1A (10%). The tumor mutational burden was higher in IBC than in non‐IBC. We identified 96 genes with an alteration frequency (p < 5% and q < 20%) different between IBC and non‐IBC, independently from the molecular subtypes and AJCC stage; 95 were more frequently altered in IBC, including TP53, genes involved in the DNA repair (BRCA2) and NOTCH pathways, and one (PIK3CA) was more frequently altered in non‐IBC. Ninety‐seven percent of IBCs displayed at least one AGA. This percentage was higher than in non‐IBC (87%), notably for drugs targeting DNA repair, NOTCH signaling, and CDK4/6, whose pathways were more frequently altered (DNA repair) or activated (NOTCH and CDK4/6) in IBC than in non‐IBC. The genomic landscape of IBC is different from that of non‐IBC. Enriched AGAs in IBC may explain its aggressiveness and provide clinically relevant targets.

Targeted molecular characterization shows differences between primary and secondary myelofibrosis

INTRODUCTION

In BCR-ABL1-negative myeloproliferative neoplasms, myelofibrosis (MF) is either primary (PMF) or secondary (SMF) to polycythemia vera or essential thrombocythemia. MF is characterized by an increased risk of transformation to acute myeloid leukemia (AML) and a shortened life expectancy.

METHODS

Because natural histories of PMF and SMF are different, we studied by targeted next generation sequencing the differences in the molecular landscape of 86 PMF and 59 SMF and compared their prognosis impact.

RESULTS

PMF had more ASXL1 (47.7%) and SRSF2 (14%) gene mutations than SMF (respectively 27.1% and 3.4%, P = .04). Poorer survival was associated with RNA splicing mutations (especially SRSF2) and TP53 in PMF (P = .0003), and with ASXL1 and TP53 mutations in SMF (P < .0001). These mutations of poor prognosis were associated with biological features of scoring systems (DIPSS and MYSEC-PM score). Mutations in TP53/SRSF2 in PMF or TP53/ASXL1 in SMF were more frequent as the risk of these scores increased. This allowed for a better stratification of MF patients, especially within the DIPSS intermediate-1 risk group (DIPSS) or the MYSEC-PM high risk group. AML transformation occurred faster in SMF than in PMF and patients who transformed to AML were more SRSF2-mutated and less CALR-mutated at MF sampling.

CONCLUSIONS

PMF and SMF have different but not specific molecular profiles and different prognosis depending on the molecular profile. This may be due to differences in disease history. Combining mutations and existing scores should improve prognosis assessment.

A Comparison of DNA Mutation and Copy Number Profiles of Primary Breast Cancers and Paired Brain Metastases for Identifying Clinically Relevant Genetic Alterations in Brain Metastases

Improving the systemic treatment of brain metastases (BM) in primary breast cancer (PBC) is impaired by the lack of genomic characterization of BM. To estimate the concordance of DNA copy-number-alterations (CNAs), mutations, and actionable genetic alterations (AGAs) between paired samples, we performed whole-genome array-comparative-genomic-hybridization, and targeted-next-generation-sequencing on 14 clinical PBC–BM pairs. We found more CNAs, more mutations, and higher tumor mutational burden, and more AGAs in BM than in PBC; 92% of the pairs harbored at least one AGA in the BM not observed in the paired PBC. This concerned various therapeutic classes, including tyrosine-kinase-receptor-inhibitors, phosphatidylinositol 3-kinase/AKT/ mammalian Target of Rapamycin (PI3K/AKT/MTOR)-inhibitors, poly ADP ribose polymerase (PARP)-inhibitors, or cyclin-dependent kinase (CDK)-inhibitors. With regards to the PARP-inhibitors, the homologous recombination defect score was positive in 79% of BM, compared to 43% of PBC, discordant in 7 out of 14 pairs, and positive in the BM in 5 out of 14 cases. CDK-inhibitors were associated with the largest percentage of discordant AGA appearing in the BM. When considering the AGA with the highest clinical-evidence level, for each sample, 50% of the pairs harbored an AGA in the BM not detected or not retained from the analysis of the paired PBC. Thus, the profiling of BM provided a more reliable opportunity, than that of PBC, for diagnostic decision-making based on genomic analysis. Patients with BM deserve an investigation of several targeted therapies.

Targeted NGS, array-CGH, and patient-derived tumor xenografts for precision medicine in advanced breast cancer: a single-center prospective study

Background

Routine feasibility and clinical impact of genomics-based tumor profiling in advanced breast cancer (aBC) remains to be determined. We conducted a pilot study to evaluate whether precision medicine could be prospectively implemented for aBC patients in a single center and to examine whether patient-derived tumor xenografts (PDX) could be obtained in this population.

Results

Thirty-four aBC patients were included. Actionable targets were found in 28 patients (82%). A targeted therapy could be proposed to 22 patients (64%), either through a clinical trial (n=15) and/or using already registered drugs (n=21). Ten patients (29%) eventually received targeted treatment, 2 of them deriving clinical benefit. Of 22 patients subjected to mouse implantation, 10 had successful xenografting (45%), mostly in triple-negative aBC.

Methods

aBC patients accessible to tumor biopsy were prospectively enrolled at the Institut Paoli-Calmettes in the BC-BIO study (ClinicalTrials.gov, NCT01521676). Genomic profiling was established by whole-genome array comparative genomic hybridization (aCGH) and targeted next-generation sequencing (NGS) of 365 candidate cancer genes. For a subset of patients, a sample of fresh tumor was orthotopically implanted in humanized cleared fat pads of NSG mice for establishing PDX.

Conclusions

Precision medicine can be implemented in a single center in the context of clinical practice and may allow genomic-driven treatment in approximately 30% of aBC patients. PDX may be obtained in a significant fraction of cases.

Abstract P4-13-23: Next-generation sequencing (NGS), array comparative genomic hybridization (aCGH) and patient-derived tumor xenograft (PDX) for precision medicine in advanced breast cancer: A single-center prospective study

Background

Genomic-based approaches in advanced breast cancer (ABC) were recently demonstrated as feasible in the clinical practice, but only a limited number of patients were actually treated with targeted therapies matching genomic alterations, with low antitumor activity. We conducted a pilot study to evaluate whether precision medicine using NGS and aCGH could be implemented prospectively at a single center in ABC patients. In addition, we examined whether PDX could be derived from ABC and thus could help inform therapeutic decision.

Methods

ABC patients accessible to tumor biopsy were prospectively enrolled at the Institut Paoli-Calmettes in the BC-BIO study (ClinicalTrials.gov, NCT01521676). Tumor tissue from locally recurrent or metastatic disease was immediately frozen after dedicated biopsy. Genomic profiling included high-resolution 4x180K aCGH (Agilent Technologies, Massy, France) and DNA sequencing, using a library of 365 cancer candidate genes (HaloPlex target enrichment kit, Agilent technologies, Santa Clara, CA, USA) and MiSeq analyzer (Illumina, San Diego, CA, USA) with 2x150-bp, paired-end at about 300x coverage. In a subset of patients, fresh tumor was implanted orthotopically in humanized cleared fat pads of NSG mice for establishing xenotransplants.

Results

A total of 34 ABC patients were included, with the following characteristics: median age 54 years (35-77); molecular subtypes: 11 triple-negative (32%), 12 luminal non-HER2 (35%), 4 luminal HER2 (12%), 3 HER2 non-luminal (9%), and 4 unknown (12%); 33 with previous chemotherapy (97%); 22 with previous endocrine treatment (35%); 7 with previous anti-HER2 (21%). Tumor biopsies were obtained from liver (15), skin (6), peritoneum (4), breast (3), node (3), lung (1), pleura (1), and ascitis (1), with a median tumor cellularity of 70% (range 10-90%). aCGH and NGS were available from 34 and 33 patients, respectively. An actionable target was found in 28 patients (82%), corresponding to 66 targets, including 37 mutations (8 in PIK3CA, 7 TP53, 4 ESR1, 2 AKT1, 2 BRCA2, 2 HER2), 22 amplifications (7 for CCND1, 2 CCNE1, 2 FGFR1, 2 IGF1R) and 7 homozygous deletions (3 for PTEN, 2 CDKN2A/B,1 BRCA2, 1 STK11). A targeted therapeutic proposal was possible, either in a clinical trial (N=18, 52%) or using already registered drugs (N=17, 50%). Ten patients actually received a targeted treatment, 1 of them experienced objective response and 1 showed stable disease for more than 6 months. Of 26 patients subjected to mouse implantation, 10 had successful xenografting (6 triple-negative, 2 HER2, 1 luminal non-HER2, 1 subtype non-attributed), with a median time to reach 10 mm of 148 days. These PDX will be used as models to understand the patient's therapeutic response.

Conclusion

Precision medicine using high-throughput DNA sequencing and aCGH can be implemented at a single center in the context of clinical practice and may allow direct therapeutic proposal in 1/3 of patients, but antitumor activity was minimal. PDX may be obtained in a significant fraction of patients, especially in triple-negative and HER2 subtypes, and could phenotypically complement genomic data.

Citation Format: Gonçalves A, Bertucci F, Chaffanet M, Guille A, Garnier S, Adelaide J, Carbuccia N, Brunelle S, Piana G, Cabaud O, Thomassin-Piana J, Paciencia-Gros M, Chereau-Ewald E, Lambaudie E, Sabatier R, Tarpin C, Provansal M, Jalaguier-Coudray A, Extra J-M, Sarran A, Pakradouni J, Viens P, Lopez M, Ginestier C, Charafe-Jauffret E, Birnbaum D. Next-generation sequencing (NGS), array comparative genomic hybridization (aCGH) and patient-derived tumor xenograft (PDX) for precision medicine in advanced breast cancer: A single-center prospective study. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-13-23.

Acute myeloid leukemia with myelodysplasia-related changes are characterized by a specific molecular pattern with high frequency of ASXL1 mutations

To determine whether the distinct and heterogeneous WHO category called "AML with myelodysplasia-related changes" (MRC-AML), presents specific molecular alterations we searched for mutations in genes known to be mutated in malignant myeloid diseases. In 48 MRC-AML patients analyzed, we found 17 mutations in ASXL1 (35%), eight in RUNX1 (17%), seven in TET2 (15%), 12 in IDH (n = 2) or IDH2 (n = 10) (25%), four in DNMT3A (8%), four in NPM1 (8%), and one in FLT3 (2%). Mutations were more frequent in the intermediate cytogenetic (IC) subgroup of 36 patients than in the unfavorable karyotype subgroup, with an average ratio mutations/patients of 1.36 [0-3] vs. 0.33 [0-2] (P < 0.001). Then, we compared these 36 patients with IC MRC-AML with a control panel of 37 no-MRC-AML patients, who had both IC and no dysplasia. IC MRC-AMLs were associated with higher incidence of ASXL1 mutations (47% vs. 0%, P < 0.001) and lower incidence of DNMT3A (6% vs. 38%, P = 0.001), NPM1 (11% vs. 62%, P < 0.001) and FLT3 (3% vs. 49%, P < 0.001) mutations. No difference was found in the incidence of IDH1/2 or TET2 mutations according to the presence of dysplasia. Complete remission rate after intensive treatment was lower in the MRC-AML group than in the no-MRC-AML group (48% vs. 78%, P = 0.023) and in wild type NPM1 patients (50% vs. 84%, P = 0.009). Our study showed that MRC-AML as defined in the WHO 2008 classification presents a specific mutation pattern characterized by a high frequency of ASXL1 mutations and a low rate of NPM1, FLT3, and DNMT3A mutations.

Mutation analysis of ASXL1, CBL, DNMT3A, IDH1, IDH2, JAK2, MPL, NF1, SF3B1, SUZ12, and TET2 in myeloproliferative neoplasms

Since the discovery of the JAK2V617F tyrosine kinase-activating mutation several genes have been found mutated in nonchronic myeloid leukemia (CML) myeloproliferative neoplasms (MPNs), which mainly comprise three subtypes of "classic" MPNs; polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). We searched for mutations in ASXL1, CBL, DNMT3A, IDH1, IDH2, JAK2, MPL, NF1, SF3B1, SUZ12, and TET2 genes in 149 non-CML MPNs, including 127 "classic" MPNs cases. JAK2 was mutated in 100% PV, 66% ET and 68% MF. We found a high incidence of ASXL1 mutation in MF patients (20%) and a low incidence in PV (7%) and ET (4%) patients. Mutations in the other genes were rare (CBL, DNMT3A, IDH2, MPL, SF3B1, SUZ12, NF1) or absent (IDH1).

ASXL1 mutation is associated with poor prognosis and acute transformation in chronic myelomonocytic leukaemia

Chronic myelomonocytic leukaemia (CMML) is a haematological disease currently classified in the category of myelodysplastic syndromes/myeloproliferative neoplasm (MDS/MPN) because of its dual clinical and biological presentation. The molecular biology of CMML is poorly characterized. We studied a series of 53 CMML samples including 31 cases of myeloproliferative form (MP-CMML) and 22 cases of myelodysplastic forms (MD-CMML) using array-comparative genomic hybridisation (aCGH) and sequencing of 13 candidate genes including ASXL1, CBL, FLT3, IDH1, IDH2, JAK2, KRAS, NPM1, NRAS, PTPN11, RUNX1, TET2 and WT1. Mutations in ASXL1 and in the genes associated with proliferation (CBL, FLT3, PTPN11, NRAS) were mainly found in MP-CMML cases. Mutations of ASXL1 correlated with an evolution toward an acutely transformed state: all CMMLs that progressed to acute phase were mutated and none of the unmutated patients had evolved to acute leukaemia. The overall survival of ASXL1 mutated patients was lower than that of unmutated patients.

Absence of R140Q mutation of isocitrate dehydrogenase 2 in gliomas and breast cancers

Somatic mutations of isocitrate dehydrogenase (IDH)-1 and IDH2 proteins have been described in gliomas. The mutations target the R132 amino acid residue and the R172 residue in IDH1 and IDH2, respectively. The same mutations were observed in acute myeloid leukemias with normal karyotype, but a new mutation in IDH2 (R140Q substitution) was detected in malignant myeloid diseases and appears to be the most frequent IDH mutation in these pathologies. To the best of our knowledge, no study thus far has reported the presence of this R140Q mutation in IDH2 in tumors of the nervous system and breast cancers. We evaluated IDH1 and IDH2 exon 4 in 48 low-grade gliomas, 58 primary glioblastomas and 94 breast cancers to evaluate the frequency of mutation and investigated the R140Q substitution in IDH2. The results were compared to our recently obtained results in hematopoietic diseases. The frequency of IDH1 and IDH2 mutations in our panel of gliomas was similar to previously reported mutations. No IDH2 R140 mutation was observed. Compared to hematopoietic diseases, the IDH2 R172 mutation was also more rare and IDH1 mutations more prominent in tumors of the nervous system. No IDH1 or IDH2 mutation was detected in the 94 breast cancer samples. Thus, the IDH2 R140 mutation appears to be restricted to hematopoietic diseases.

Alteration of cohesin genes in myeloid diseases

New genes involved in leukemogenesis, such as ASXL1 and TET2, have been identified recently using genomic analyses of DNA from patient samples. We have studied by array-comparative genomic hybridization (aCGH) a series of 167 samples including myelodysplastic syndromes, chronic myelomonocytic leukemias, and acute myeloid leukemias. We found a deletion of the RAD21 and STAG2 genes, which encode two components of the cohesin complex. We propose that these alterations may compromise the cohesin complex and its regulation of the transcription of genes.

Combined mutations of ASXL1, CBL, FLT3, IDH1, IDH2, JAK2, KRAS, NPM1, NRAS, RUNX1, TET2 and WT1 genes in myelodysplastic syndromes and acute myeloid leukemias

Background

Gene mutation is an important mechanism of myeloid leukemogenesis. However, the number and combination of gene mutated in myeloid malignancies is still a matter of investigation.

Methods

We searched for mutations in the ASXL1, CBL, FLT3, IDH1, IDH2, JAK2, KRAS, NPM1, NRAS, RUNX1, TET2 and WT1 genes in 65 myelodysplastic syndromes (MDSs) and 64 acute myeloid leukemias (AMLs) without balanced translocation or complex karyotype.

Results

Mutations in ASXL1 and CBL were frequent in refractory anemia with excess of blasts. Mutations in TET2 occurred with similar frequency in MDSs and AMLs and associated equally with either ASXL1 or NPM1 mutations. Mutations of RUNX1 were mutually exclusive with TET2 and combined with ASXL1 but not with NPM1. Mutations in FLT3 (mutation and internal tandem duplication), IDH1, IDH2, NPM1 and WT1 occurred primarily in AMLs.

Conclusion

Only 14% MDSs but half AMLs had at least two mutations in the genes studied. Based on the observed combinations and exclusions we classified the 12 genes into four classes and propose a highly speculative model that at least a mutation in one of each class is necessary for developing AML with simple or normal karyotype.

A gene expression signature of primary resistance to imatinib in chronic myeloid leukemia

Using gene expression profiling we show that the expression of 105-probe sets in mononuclear cells collected from chronic myeloid leukemia (CML) chronic phase (CP) patients with raised leukocyte counts who subsequently achieved complete cytogenetic response after 12 months on imatinib, differed substantially from that of patients who failed to achieve any degree of cytogenetic response. In the non-responder cohort, 9 of the 50 overexpressed genes were involved in DNA repair by homologous recombination, whereas 36 genes, including PTEN, were downregulated. This pattern of altered gene expression in responders and non-responders was validated in another independent dataset. These findings may prove useful for identifying at the time of diagnosis a subset of CP-CML patients who are likely to be resistant to imatinib and require an alternative treatment.

Mutations of polycomb-associated gene ASXL1 in myelodysplastic syndromes and chronic myelomonocytic leukaemia

The myelodysplastic syndromes (MDSs) are a heterogeneous group of clonal haematological diseases characterized by ineffective haematopoiesis and predisposition to acute myeloid leukaemia (AML). The pathophysiology of MDSs remains unclear. A definition of the molecular biology of MDSs may lead to a better classification, new prognosis indicators and new treatments. We studied a series of 40 MDS/AML samples by high-density array-comparative genome hybridization (aCGH). The genome of MDSs displayed a few alterations that can point to candidate genes, which potentially regulate histone modifications and WNT pathways (e.g. ASXL1, ASXL2, UTX, CXXC4, CXXC5, TET2, TET3). To validate some of these candidates we studied the sequence of ASXL1. We found mutations in the ASXL1 gene in four out of 35 MDS patients (11%). To extend these results we searched for mutations of ASXL1 in a series of chronic myelomonocytic leukaemias, a disease classified as MDS/Myeloproliferative disorder, and found mutations in 17 out of 39 patients (43%). These results show that ASXL1 might play the role of a tumour suppressor in myeloid malignancies.

Common features of myeloproliferative disorders with t(8;9)(p12;q33) and CEP110-FGFR1 fusion: report of a new case and review of the literature

The 8p12 myeloproliferative syndrome is a rare, generally aggressive chronic myeloproliferative disorder (MPD). The hallmark of this MPD is the disruption of the FGFR1 gene, which encodes a tyrosine kinase receptor for members of the fibroblast growth factor family. In MPD cells FGFR1 is fused to several partners. The most frequent partner genes are BCR, CEP110, FOP, and ZNF198, localized on 22q11, 9q33, 6q27, and 13q12, respectively. We report here the tenth case of translocation (8;9)(p12;q33) in an acute myelomonocytic leukemia and provide a review of the literature that points to common syndrome features: the t(8;9)(p11;q33) MPD transforms rapidly, and always in myelomonocytic leukemia, with a possible B- or T-lymphoid involvement, which may include tonsil invasion. The FGFR1-MPD seems refractory to current chemotherapies and is not sensitive to imatinib. Currently, only the patients with bone marrow transplantation stand a chance of survival.

Rearrangements involving 12q in myeloproliferative disorders: possible role of HMGA2 and SOCS2 genes

We report two cases of translocation associated with deletion on derivative chromosomes in atypical myeloproliferative disorder (MPD). In a MPD with t(3;12)(q29;q14), the rearrangement targeted the HMGA2 locus at 12q14 and deleted a region of about 1.5 megabases (Mb) at 3q29. In an MPD with t(9;12)(q13 approximately q21;q22) and JAK2 V617F mutation, array comparative genomic hybridization delineated a deletion of about 3 Mb at 9q13 approximately q21 and a deletion of about 2 Mb at 12q22 containing SOCS2. These results show that close examination of translocations in hematopoietic diseases may reveal associated microdeletions. The role of these deletions is discussed.

Combined translocation with ZNF198-FGFR1 gene fusion and deletion of potential tumor suppressors in a myeloproliferative disorder

Tyrosine kinases activated by mutation or translocation are involved in the chronic phase of myeloproliferative disorders. Complementary or alternative events are not so well characterized. We report here a case of t(8;13) generating a ZNF198-FGFR1 fusion kinase gene on the derivative chromosome 13. ZNF198-FGFR1 mRNA, but not FGFR1-ZNF198, was detected by polymerase chain reaction amplification. By using fluorescence in situ hybridization with BAC clones, we mapped a deletion of about 2 megabases on the derivative chromosome 8, including the reciprocal FGFR1-ZNF198 fusion gene and the surrounding genes from 8p11 and 13q12. Potential tumor suppressor genes affected by the deletion by loss (IFT88, CRYL1, TACC1) or break (LATS2) may participate in the malignant process.

Gene expression profiling identifies molecular subgroups among nodal peripheral T-cell lymphomas

The classification of peripheral T-cell lymphomas (PTCL) is still a matter of debate. To establish a molecular classification of PTCL, we analysed 59 primary nodal T-cell lymphomas using cDNA microarrays, including 56 PTCL and three T-lymphoblastic lymphoma (T-LBL). The expression profiles could discriminate angioimmunoblastic lymphoma, anaplastic large-cell lymphoma and T-LBL. In contrast, cases belonging to the broad category of 'PTCL, unspecified' (PTCL-U) did not share a single molecular profile. Using a multiclass predictor, we could separate PTCL-U into three molecular subgroups called U1, U2 and U3. The U1 gene expression signature included genes known to be associated with poor outcome in other tumors, such as CCND2. The U2 subgroup was associated with overexpression of genes involved in T-cell activation and apoptosis, including NFKB1 and BCL-2. The U3 subgroup was mainly defined by overexpression of genes involved in the IFN/JAK/STAT pathway. It comprised a majority of histiocyte-rich PTCL samples. Gene Ontology annotations revealed different functional profile for each subgroup. These results suggest the existence of distinct subtypes of PTCL-U with specific molecular profiles, and thus provide a basis to improve their classification and to develop new therapeutic targets.

Identification of new classes among acute myelogenous leukaemias with normal karyotype using gene expression profiling

Conventional cytogenetic analysis currently stratifies acute myelogenous leukaemia (AML) into prognostically relevant groups. However, approximately 50% of adult AMLs have normal cytogenetics (NC-AMLs), and represent a heterogeneous and poorly understood group. We analysed gene expression in 55 AML samples including 53 cases from adult patients with NC-AML (n = 36), trisomy 8, t(15;17), t(8;21), t(11;19), 7q deletion, and two cell lines using 9000-gene DNA microarrays. Global hierarchical clustering showed that NC-AMLs are a heterogeneous group. Supervised analysis distinguished two subgroups of NC-AML: one subgroup constituted a homogeneous NC cluster ('pure NC-AML'), and the other NC-AMLs were close to the AML cases with translocations ('translocation like'). Gene expression signatures were also derived for patients with trisomy 8, as well as FLT3 and MLL gene duplications. Importantly, samples from 24 NC-AML patients who could be evaluated for clinical outcome were analysed. In all, 43 genes that discriminated two classes of patients with significantly different prognosis were identified. The poor prognosis class contained a majority of 'pure NC-AMLs', whereas the 'translocation-like' AMLs were in the good prognosis class. Discriminator genes included genes involved in drug resistance (TOP2B), protein transport (MTX2, SLC35A2), and cell signalling (MAPK1, PRKAB2). Our results demonstrate the transcriptional heterogeneity of NC-AMLs, and suggest the existence of 'translocation-like' NC-AMLs and of a gene expression signature that may predict response to chemotherapy.

Variant MYST4-CBP gene fusion in a t(10;16) acute myeloid leukaemia

We report a novel fusion of the MYST4 and CBP genes in an acute myeloid leukaemia (AML)-M4 patient exhibiting t(10;16)(q22;p13) and t(11;17)(q23;q21). The t(10;16)(q22;p13) resulted in a rearrangement, where MYST4-CBP and CBP-MYST4 chimaeric transcripts were products of in-frame fusions of MYST4 exon 17 to CBP exon 6 and CBP exon 4 to MYST4 exon 18 respectively. The potential resulting chimaeric proteins showed similarities with MYST3-CBP, MYST3-P300 and MYST3-NCOA2 putative fusion proteins found in other cases of AML.

Simple variant t(8;21) acute myeloid leukemias harbor insertions of the AML1 or ETO genes

We report on the molecular characterization of two acute myeloid leukemias (AML), one AML-M1 (patient 1) and one AML-M2 (patient 2) with t(8;21)(p21;q22) and t(8;20)(q22;p13), respectively, at diagnosis. The locations of the breakpoints, 21q22 in patient 1 and 8q22 in patient 2, prompted us to search for a cryptic t(8;21)(q22;q22) and involvement of the AML1 and ETO genes. Dual-color fluorescence in situ hybridization (FISH) using whole chromosome painting probes for chromosomes 8, 20, and 21 confirmed the conventional cytogenetic karyotypes. However, dual-color FISH using appropriate ETO and AML1 probes disclosed an insertion of AML1 into 8q22 on the derivative chromosome 8 in patient 1 and of ETO into 21q22 on one chromosome 21 in patient 2, leading to AML1-ETO fusion signals. Both cases expressed an AML1-ETO transcript, shown by reverse transcriptase polymerase chain reaction and cDNA sequencing. Creation of functional AML1-ETO fusion genes in these two simple variant t(8;21) probably occurred through complex mechanisms, combining translocation and insertion of chromosomal segments.

A defective retroviral vector encoding human interferon-alpha2 can transduce human leukemic cell lines

Using the LXSN backbone, a defective retroviral vector (LISN) was constructed that encodes the human interferon (IFN)-alpha2 (hIFN-alpha2) gene and the neomycin resistance gene; the hIFN-alpha2 gene was cloned from human placental genomic DNA. High titers of the LISN retrovirus were produced by the amphotropic packaging cell line GP+envAM12. LISN is able to infect three human hematopoietic and leukemic cell lines: K562, LAMA-84, and TF-1. G418-resistant cells were detected in a similar proportion after infection with either the LISN retroviral vector or the LnLSN retroviral vector (encoding the nlsLacZ gene instead of hIFN-alpha2), suggesting that hIFN-alpha2 does not inhibit (or only partially inhibits) the production of retroviral particles by the packaging cell line and the infection of human cells. LISN-infected cells express and secrete hIFN-alpha2 as demonstrated by Northern blot analysis of poly(A)+ RNA, detection of the intracellular protein by fluorescence-activated cell sorter analysis, and detection of secreted hIFN-alpha in cell supernatants using an enzyme-linked immunosorbent assay. Retrovirally produced hIFN-alpha2 is biologically active, as demonstrated by the partial inhibition of the growth of K562 and TF-1, the modulation of the expression of cell surface antigens, the induction of the (2'-5') oligoadenylate synthetase, and, for LAMA-84, the down-modulation of the BCR-ABL protein. We conclude that the infection of human leukemic cell lines with a retroviral vector encoding hIFN-alpha2 is feasible and induces the expected biological effects. This experimental model will be useful in investigating the possibility of transducing normal and leukemic cells and hematopoietic progenitors and in determining the consequences of the autocrine production of hIFN-alpha2 on the behavior of these cells.

Unbalanced translocation t(5;17) in an typical acute promyelocytic leukemia

Acute promyelocytic leukemia (APL; M3 in the FAB classification) is specifically associated with the t(15;17)(q23;q12) and the consequent formation of a PML/RARA fusion gene. A few cases of APL with a t(11;17)(q23;q12) and a PLZF/RARA fusion gene have recently been reported. In addition, a new variant, t(5;17)(q32;q12), with a RARA rearrangement was described in a child with atypical APL. We report an unbalanced der(5)t(5;17) in an atypical APL case showing unusual dysgranulopoiesis and some M2 features. The breakpoints were difficult to localize precisely on chromosome 5, because the translocation may have occurred on a previous del(5q). The karyotype also showed del(8q) and multiple double-minutes (dmin). Molecular studies evidenced RARA rearrangement but showed neither PML rearrangement nor PML/RARA fusion. Fluorescence in situ hybridization revealed that the dmin were of chromosome 8 origin and that they accounted for the MYC amplification observed in Southern blots. The patient did very poorly despite chemotherapy and all-trans retinoic acid (ATRA) treatment. Thus, the t(5;17) could represent a second type of variant translocation in APL that, like the disease associated with t(11;17), does not seem to respond to ATRA therapy. Whereas RARA rearrangement appears sufficient for an APL-like phenotype, it seems that the presence of a classical PML/RARA is required for typical APL with response to ATRA.

Search for rearrangements and/or allelic loss of the fas/APO-1 gene in 101 human lymphomas

The authors analyzed the possible occurrence of rearrangements and/or allelic loss of the fas/APO-1 gene in a representative series of human lymphomas, including 101 cases of Hodgkin's disease (HD) and non-Hodgkin's lymphomas (NHL). The rationale for this study was double. Chromosome 10 alterations, frequently observed in lymphoma subtypes, encompass the chromosomal localization of fas/APO-1. In addition, Ipr mouse mutants, which present with a generalized lymphoproliferative disease, were shown to exhibit alterations of fas/APO-1 structure and expression. In this retrospective study, the authors performed gene dosage of fas/APO-1 by Southern blots. No fas/APO-1 alterations were observed in the 31 HD cases. Among 70 T-cell and B-cell NHL, allelic loss of fas/APO-1 was observed in three cases. Two cases with different clinical, phenotypic, and histologic presentations showed a rearrangement of fas/APO-1. A third case showed amplification. Thus fas/APO-1 alterations do occur in human lymphomas, although at a relatively low frequency.

Frequent expression of FAS/APO-1 in Hodgkin's disease and anaplastic large cell lymphomas

FAS/APO-1 (CD95) is a membrane glycoprotein belonging to the tumour necrosis factor/nerve growth factor receptor family, and which can trigger apoptosis in some lymphoid cell lines. Immunohistochemistry combined with Northern blotting allowed determination of the pattern of FAS/APO-1 expression in a series of Ki-1 [CD30] positive lymphoid malignancies, including 27 Hodgkin's disease and eight anaplastic large cell lymphomas. CD30 negative tumours used as controls included 27 B-cell non-Hodgkin's lymphomas. 14 T-cell non-Hodgkin's lymphomas, four reactive lymphadenitis, and non-lymphoid tissues. Immunohistochemistry, performed on frozen sections, revealed a strong FAS/APO-1 expression in 25 out of 27 (92%) Hodgkin's disease cases, predominantly in Reed Sternberg cells; 50 to 100% of the neoplastic cells in eight out of (100%) anaplastic large cell lymphoma cases were positive. In contrast, positive FAS/APO-1 immunostaining was observed only in 22 out of 41 (53%) CD30 negative non-Hodgkin's lymphomas. Northern blot analysis detected variable amounts of the FAS/APO-1 transcript in the immunohistochemistry-positive samples. These results suggest possible hyper-expression of FAS/APO-1 (CD95) in Hodgkin's disease and anaplastic large cell lymphomas.

The expression of FMS, KIT and FLT3 in hematopoietic malignancies

Three receptor molecules, belonging to the class III of receptor tyrosine kinases, namely the receptors for colony-stimulating factor 1, CSF1R (product of the FMS proto-oncogene) and Steel factor, SLFR (product of the KIT proto-oncogene), as well as the recently identified FLT3/FLK2 gene product, appear to play distinct roles in normal hematopoietic differentiation. Their potential role in leukemic hematopoiesis has been approached by expression studies in hematopoietic malignancies, especially in acute leukemias of the myeloid and lymphoid lineages. We present here a review of available data, and discuss the possible significance and potential applications of these results.

Monensin action on the Golgi complex in perfused rat liver: evidence against bile salt vesicular transport

Several studies suggest that bile salts are transported from the basolateral to the canalicular membrane of hepatocytes by a vesicular pathway, possibly in part via the Golgi complex. To test this hypothesis, the present study examined, in the perfused rat liver, the influence of the Na+ ionophore monensin on the biliary secretion of taurocholate and biliary lipids. The effects of the drug have been checked by the study of the ultrastructural modifications of the Golgi complex, secretion of horseradish peroxidase, and bile salt uptake. An infusion of monensin (1, 3, or 5 mumol/L) into the liver induced considerable swelling of the Golgi complex within 5 minutes. After a bolus injection of horseradish peroxidase during monensin infusion, the biliary secretion of the protein was delayed (1 mumol/L monensin) and markedly reduced (5 mumol/L monensin). Bile salt uptake was virtually unchanged except with 5 mumol/L monensin. This suggests that monensin has the same effects on the subcellular traffic in the perfused liver as in cultured cells. After a bolus injection of taurocholate (0.25, 5.0, or 8.5 mumol/100 g body wt) during monensin infusion, the pattern of biliary secretion of the bile salt was identical to that of controls. During continuous infusion of taurocholate, a 10-minute monensin infusion (1 or 3 mumol/L) had no effect on the biliary secretion of taurocholate and on the secretion of lecithin and cholesterol induced by taurocholate. High concentrations (5 mumol/L) or prolonged infusions (20 minutes) of monensin decreased the biliary secretion of bile salts but corresponded to a marked decrease of taurocholate uptake. In summary, the Na+ ionophore monensin altered the Golgi complex and the vesicular transport of horseradish peroxidase, whereas taurocholate biliary secretion was not influenced unless taurocholate biliary secretion was not influenced unless taurocholate uptake by the liver was markedly decreased. It may be concluded that taurocholate and biliary lipid secretion, under these conditions, does not depend essentially on pathways involving acidic transporting vesicles and particularly the trans-Golgi complex.