Absence of BTK, BCL2, and PLCG2 Mutations in Chronic Lymphocytic Leukemia Relapsing after First-Line Treatment with Fixed-Duration Ibrutinib plus Venetoclax

PURPOSE

Mutations in BTK, PLCG2, and BCL2 have been reported in patients with progressive disease (PD) on continuous single-agent BTK or BCL2 inhibitor treatment. We tested for these mutations in samples from patients with PD after completion of first-line treatment with fixed-duration ibrutinib plus venetoclax for chronic lymphocytic leukemia (CLL) in the phase II CAPTIVATE study.

PATIENTS AND METHODS

A total of 191 patients completed fixed-duration ibrutinib plus venetoclax (three cycles of ibrutinib then 12-13 cycles of ibrutinib plus venetoclax). Genomic risk features [del(11q), del(13q), del(17p), trisomy 12, complex karyotype, unmutated IGHV, TP53 mutated] and mutations in genes recurrently mutated in CLL (ATM, BIRC3, BRAF, CHD2, EZH2, FBXW7, MYD88, NOTCH1, POT1, RPS15, SF3B1, XPO1) were assessed at baseline in patients with and without PD at data cutoff; gene variants and resistance-associated mutations in BTK, PLCG2, or BCL2 were evaluated at PD.

RESULTS

Of 191 patients completing fixed-duration ibrutinib plus venetoclax, with median follow-up of 38.9 months, 29 (15%) developed PD. No baseline risk feature or gene mutation was significantly associated with development of PD. No previously reported resistance-associated mutations in BTK, PLCG2, or BCL2 were detected at PD in 25 patients with available samples. Of the 29 patients with PD, 19 have required retreatment (single-agent ibrutinib, n = 16, or ibrutinib plus venetoclax, n = 3); 17 achieved partial response or better, 1 achieved stable disease, and 1 is pending response assessment.

CONCLUSIONS

First-line fixed-duration combination treatment with ibrutinib plus venetoclax may mitigate development of resistance mechanisms associated with continuous single-agent targeted therapies, allowing for effective retreatment. See related commentary by Al-Sawaf and Davids, p. 471.

Immune restoration with ibrutinib plus venetoclax in first-line chronic lymphocytic leukemia: the phase 2 CAPTIVATE study

We evaluated immune cell subsets in patients with chronic lymphocytic leukemia (CLL) who received first-line therapy with 3 cycles of ibrutinib then 13 cycles of ibrutinib plus venetoclax in the minimal residual disease (MRD) cohort of the CAPTIVATE study (NCT02910583). Patients with Confirmed undetectable MRD (uMRD) were randomly assigned to placebo or ibrutinib groups; patients without Confirmed uMRD were randomly assigned to ibrutinib or ibrutinib plus venetoclax groups. We compared immune cell subsets in samples collected at 7 time points with age-matched healthy donors. CLL cells decreased within 3 cycles after venetoclax initiation; from cycle 16 onward, levels were similar to healthy donor levels (HDL; ≤0.8 cells per μL) in patients with Confirmed uMRD and slightly above HDL in patients without Confirmed uMRD. By 4 months after cycle 16, normal B cells had recovered to HDL in patients randomly assigned to placebo. Regardless of randomized treatment, abnormal counts of T cells, classical monocytes, and conventional dendritic cells recovered to HDL within 6 months (median change from baseline -49%, +101%, and +91%, respectively); plasmacytoid dendritic cells recovered by cycle 20 (+598%). Infections generally decreased over time regardless of randomized treatment and were numerically lowest in patients randomly assigned to placebo within 12 months after cycle 16. Sustained elimination of CLL cells and recovery of normal B cells were confirmed in samples from patients treated with fixed-duration ibrutinib plus venetoclax in the GLOW study (NCT03462719). These results demonstrate promising evidence of restoration of normal blood immune composition with ibrutinib plus venetoclax.

Abstract 3248: Pharmacodynamic activity of epcoritamab (GEN3013; CD3xCD20) as monotherapy is maintained in combination with standard of care therapies in patients with diffuse large B-cell lymphoma

Introduction: B-cell lymphoma is a heterogeneous disease with an unmet medical need for efficacious, well tolerated, off-the-shelf therapies that can combine with standard of care (SOC) regimens. Epcoritamab is an IgG1 bispecific antibody that simultaneously binds to CD3 on T cells and CD20 on malignant B cells, inducing activation and cytotoxic activity of T cells and enabling killing of target lymphoma cells. Epcoritamab is well suited for combination therapy due to its distinct mechanism of action from that of many SOC regimens that may lead to improved clinical responses. Herein we evaluated the longitudinal pharmacodynamic (PD) effects of epcoritamab in clinical trial patients with diffuse large B-cell lymphoma (DLBCL) treated as monotherapy (EPCORE NHL-1: NCT03625037) and in combination with SOC therapies (EPCORE NHL-2: NCT04663347).

Methods: Patients with relapsed/refractory (R/R) DLBCL from EPCORE NHL-1 expansion phase received subcutaneous epcoritamab administered in 28-d cycles. Patients with newly diagnosed or R/R DLBCL from EPCORE NHL-2 received epcoritamab administered with a dosing schedule similar to that in EPCORE NHL-1, in combination with SOC therapies: R-CHOP, R-DHAX/C and GemOx. Biomarkers in fresh whole blood were assessed using validated flow cytometry assays. Cytokine levels in plasma were tested using a validated multiplex immunoassay.

Results: Epcoritamab monotherapy induced rapid (within the first cycle), sustained depletion of circulating peripheral B cells (CD19+) in patients with detectable peripheral B cells at baseline. A similar pattern of peripheral B-cell depletion was observed for epcoritamab in combination with SOC. Approximately 24 h following the first full dose, epcoritamab monotherapy induced a moderate but transient elevation of circulating cytokines IFNγ, IL-6 and IL-10. These cytokine patterns were similar for epcoritamab in combination with SOC. Within the first 8 wk of dosing, both epcoritamab monotherapy and in combination with SOC induced a transient elevation of percentages of peripheral CD8+ T cells expressing proliferation (Ki67) and activation (HLA-DR) markers. Expansion of peripheral CD8+ T cells and their effector memory subsets was observed with epcoritamab monotherapy, as well as in combination with SOC in later cycles. Peripheral CD4+ T cells demonstrated patterns similar to most of the biomarker observations in CD8+ T cells with epcoritamab as monotherapy and in combination.

Conclusion: These biomarker analyses show that the PD characteristics of epcoritamab monotherapy are maintained overall in combination with SOC therapies containing chemotherapeutic agents with or without rituximab and support the ongoing clinical studies investigating the combination of epcoritamab with SOC therapies in patients with DLBCL.

Citation Format: Jimin Zhang, Han Si, Monica Wielgos-Bonvallet, David Soong, Edith Szafer-Glusman, Herve Ghesquieres, Chan Y. Cheah, Lorenzo Falchi, Joshua Brody, Mariana Sacchi, Ali Rana, Brandon Higgs, Brian Elliot, Maria Jure-Kunkel, Christopher W. Chiu. Pharmacodynamic activity of epcoritamab (GEN3013; CD3xCD20) as monotherapy is maintained in combination with standard of care therapies in patients with diffuse large B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3248.

The iR2 regimen (ibrutinib plus lenalidomide and rituximab) for relapsed/refractory DLBCL: A multicentre, non-randomised, open-label phase 2 study

BACKGROUND

This phase 1b/2 PCYC-1123-CA study evaluated efficacy and safety of the combination of ibrutinib, lenalidomide, and rituximab (iR² regimen) in patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL) ineligible for stem cell transplantation.

METHODS

In phase 2, patients with relapsed/refractory non-germinal centre B-cell-like DLBCL received oral ibrutinib 560 mg once daily and oral lenalidomide 20 mg or 25 mg once daily on Days 1-21 of each 28-day cycle until disease progression or unacceptable toxicity and intravenous rituximab 375 mg/m² on Day 1 of Cycles 1-6. The primary endpoint was overall response rate (ORR) in the response-evaluable population (received any study treatment and had ≥1 post-baseline disease assessment). The study was done at 24 academic and community hospitals in Belgium, Germany, United Kingdom, and USA. This study was registered with ClinicalTrials.gov, NCT02077166.

FINDINGS

Between March 13, 2014 and October 2, 2018, 89 patients were enrolled with a median time on study of 35.0 months. Best ORR in the response-evaluable population (n = 85) was 49% (95% confidence interval [CI], 38-61) across dose cohorts and 53% (95% CI, 39-67) and 44% (95% CI, 26-62) in the 20 mg and 25 mg lenalidomide cohorts, respectively, with complete responses in 24/85 (28%), 17/53 (32%), and 7/32 (22%) patients, respectively. Grade 3/4 adverse events (AEs) occurred in 81/89 patients (91%), most frequently neutropenia (36/89; 40%), maculopapular rash (16/89; 18%), anaemia (12/89; 13%), and diarrhoea (9/89; 10%). Serious adverse events occurred in 57/89 patients (64%). Fatal AEs occurred in 12/89 patients (13%); causes of death were worsening of DLBCL (n = 7), pneumonia (n = 3), sepsis (n = 1), and cardiac arrest (n = 1).

INTERPRETATION

The most frequent AEs (diarrhoea, neutropenia, fatigue, cough, anaemia, peripheral oedema, and maculopapular rash) were consistent with known safety profiles of the individual drugs. The iR² regimen demonstrated antitumour activity with durable responses in patients with relapsed/refractory DLBCL.

FUNDING

Pharmacyclics LLC, an AbbVie Company.

Fixed-duration ibrutinib plus venetoclax for first-line treatment of CLL: primary analysis of the CAPTIVATE FD cohort

CAPTIVATE (NCT02910583) is an international phase 2 study in patients aged ≤70 years with previously untreated chronic lymphocytic leukemia (CLL). Results from the cohort investigating fixed-duration (FD) treatment with ibrutinib plus venetoclax are reported. Patients received 3 cycles of ibrutinib lead-in then 12 cycles of ibrutinib plus venetoclax (oral ibrutinib [420 mg/d]; oral venetoclax [5-week ramp-up to 400 mg/d]). The primary endpoint was complete response (CR) rate. Hypothesis testing was performed for patients without del(17p) with prespecified analyses in all treated patients. Secondary endpoints included undetectable minimal residual disease (uMRD) rates, progression-free survival (PFS), overall survival (OS), and safety. Of the 159 patients enrolled and treated, 136 were without del(17p). The median time on study was 27.9 months, and 92% of patients completed all planned treatment. The primary endpoint was met, with a CR rate of 56% (95% confidence interval [CI], 48-64) in patients without del(17p), significantly higher than the prespecified 37% minimum rate (P < .0001). In the all-treated population, CR rate was 55% (95% CI, 48-63); best uMRD rates were 77% (peripheral blood [PB]) and 60% (bone marrow [BM]); 24-month PFS and OS rates were 95% and 98%, respectively. At baseline, 21% of patients were in the high tumor burden category for tumor lysis syndrome (TLS) risk; after ibrutinib lead-in, only 1% remained in this category. The most common grade ≥3 adverse events (AEs) were neutropenia (33%) and hypertension (6%). First-line ibrutinib plus venetoclax represents the first all-oral, once-daily, chemotherapy-free FD regimen for patients with CLL. FD ibrutinib plus venetoclax achieved deep, durable responses and promising PFS, including in patients with high-risk features.

Fixed-duration (FD) ibrutinib (I) + venetoclax (V) for first-line (1L) treatment (tx) of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL): Three-year follow-up from the FD cohort of the phase 2 CAPTIVATE study

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Background: CAPTIVATE (PCYC-1142) is a multicenter phase 2 study of 1L I+V in CLL. The primary analysis (PA) evaluating FD tx with I+V was previously presented (Ghia et al., ASCO 2021). Here we present 3-y follow-up results from the FD cohort. Methods: Patients (pts) aged ≤70 y with previously untreated CLL/SLL received 3 cycles of I then 12 cycles of I+V (I 420 mg/d orally; V ramp-up to 400 mg/d orally). Responses were investigator assessed per iwCLL 2008 criteria. Undetectable minimal residual disease (uMRD; <10-4) was measured by 8-color flow cytometry. Serious AEs (SAEs) deemed related to I reported >30 d after last dose of study drug were collected. Results: 159 pts were enrolled (median age 60 y), including pts with high-risk features of del(17p)/ TP53 mutation (17%), unmutated IGHV (uIGHV; 56%), and complex karyotype (19%). 147 (92%) and 149 (94%) pts completed tx with I and V, respectively. With 1 y of additional follow-up since PA, median time on study was 39 mo (range 1-41). ORR was 96% and was consistent (96%-97%) in pts with high-risk features (Table).The primary endpoint of complete response (CR) including CR with incomplete bone marrow recovery (CRi) rate in pts without del(17p) (n=136) increased nominally from 56% (95% CI, 48-64) to 58% (95% CI 50-66); in all pts, CR rate increased from 55% (95% CI 48-63) to 57% (95% CI 50-65). In pts achieving CR, 93% had durable responses lasting ≥12 mo post-tx. Of pts with uMRD in peripheral blood at 3 mo post-tx, 66/85 (78%) evaluable pts maintained uMRD through 12-mo post-tx. At 36 mo, PFS was 88% (95% CI 82‒92) and OS was 98% (95% CI 94‒99); similar rates were seen in pts with high-risk features (Table). All pts are off tx; no new SAEs of any kind have occurred since the PA. Available data on relevant mutations in BTK, PLCɣ2, or BCL-2 at time of PD will be presented. As of January 2022, 12 pts were retreated with single-agent I after PD (tx duration range 3-29 mo); of evaluated pts, 7/9 had partial responses and 2/9 had stable disease. Conclusions: Fixed duration I+V continues to provide deep, durable responses and clinically meaningful PFS, including in pts with high-risk disease features, representing an all-oral, once-daily, chemotherapy-free FD regimen for previously untreated pts with CLL/SLL. With an additional 1 y of follow-up, no OS events or SAEs occurred. Manageable safety profile is unchanged as previously reported. To date, successful single-agent I retreatment responses are observed. Clinical trial information: NCT02910583. [Table: see text]

Ibrutinib Plus Venetoclax for First-Line Treatment of Chronic Lymphocytic Leukemia: Primary Analysis Results From the Minimal Residual Disease Cohort of the Randomized Phase II CAPTIVATE Study

PURPOSE

CAPTIVATE (NCT02910583), a randomized phase II study, evaluates minimal residual disease (MRD)-guided treatment discontinuation following completion of first-line ibrutinib plus venetoclax treatment in patients with chronic lymphocytic leukemia (CLL).

METHODS

Previously untreated CLL patients age < 70 years received three cycles of ibrutinib and then 12 cycles of combined ibrutinib plus venetoclax. Patients in the MRD cohort who met the stringent random assignment criteria for confirmed undetectable MRD (Confirmed uMRD) were randomly assigned 1:1 to double-blind placebo or ibrutinib; patients without Confirmed uMRD (uMRD Not Confirmed) were randomly assigned 1:1 to open-label ibrutinib or ibrutinib plus venetoclax. Primary end point was 1-year disease-free survival (DFS) rate with placebo versus ibrutinib in the Confirmed uMRD population. Secondary end points included response rates, uMRD, and safety.

RESULTS

One hundred sixty-four patients initiated three cycles of ibrutinib lead-in. After 12 cycles of ibrutinib plus venetoclax, best uMRD response rates were 75% (peripheral blood) and 68% (bone marrow). Patients with Confirmed uMRD were randomly assigned to receive placebo (n = 43) or ibrutinib (n = 43); patients with uMRD Not Confirmed were randomly assigned to ibrutinib (n = 31) or ibrutinib plus venetoclax (n = 32). Median follow-up was 31.3 months. One-year DFS rate was not significantly different between placebo (95%) and ibrutinib (100%; arm difference: 4.7% [95% CI, -1.6 to 10.9]; P = .15) in the Confirmed uMRD population. After ibrutinib lead-in tumor debulking, 36 of 40 patients (90%) with high tumor lysis syndrome risk at baseline shifted to medium or low tumor lysis syndrome risk categories. Adverse events were most frequent during the first 6 months of ibrutinib plus venetoclax and generally decreased over time.

CONCLUSION

The 1-year DFS rate of 95% in placebo-randomly assigned patients with Confirmed uMRD suggests the potential for fixed-duration treatment with this all-oral, once-daily, chemotherapy-free regimen in first-line CLL.

Abstract 1574: Preclinical evaluation of epcoritamab combined with standard of care therapies for the treatment of B-cell lymphomas

B-cell non-Hodgkin lymphoma (B-NHL) is a heterogeneous disease with an unmet medical need for new efficacious, well tolerated, off-the-shelf therapies that can combine with standard of care (SOC) regimens. Epcoritamab (GEN3013; DuoBody®-CD3×CD20) is a novel subcutaneously administered bispecific antibody with a manageable safety profile and promising preliminary anti-tumor activity in both aggressive and indolent B-NHL. Epcoritamab simultaneously binds to CD3 on T cells and to CD20-expressing tumor cells to induce potent T-cell-mediated killing. SOC treatments for B-NHL include rituximab in combination with chemotherapy regimens such as CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone), bendamustine, or immunomodulatory agents such as lenalidomide. These therapies have mechanisms of action distinct from that of epcoritamab, and mostly non-overlapping adverse event profiles. Previous preclinical studies demonstrated that epcoritamab can induce effective anti-tumor activity in the presence of a rituximab analog, supporting the combination of the two in clinical trials. Here, we present in vitro studies conducted to evaluate whether epcoritamab can be used in combination with current SOC therapies for B-NHL.

Healthy donor T cells as effector cells and/or CD20-expressing B-NHL tumor cell lines were pre-treated with each individual SOC component (lenalidomide, cyclophosphamide, doxorubicin, vincristine, prednisone) to evaluate the impact on T cells and target cell lines. Next, co-cultures of pre-treated T and B-NHL cells were incubated with the same SOC component in the presence of epcoritamab, and T-cell mediated cytotoxicity and associated T-cell activation were assessed by flow cytometry. Bendamustine was added together with epcoritamab during the T-cell activation and cytotoxicity assay to assess potential antagonizing effect.

Lenalidomide enhanced T-cell activation induced by CD3 crosslinking with immobilized anti-CD3 or epcoritamab, resulting in higher potency of these T cells to exert epcoritamab-induced cytotoxicity of CD20-expressing tumor cells. T cells pre-treated with individual CHOP components were capable of mediating epcoritamab-induced cytotoxicity. Finally, bendamustine did not antagonize T-cell activation and had an additive effect on T-cell-mediated cytotoxicity by epcoritamab. These preclinical data indicate that epcoritamab-can be combined with these SOC agents.

In conclusion, these data warrant clinical evaluation of epcoritamab combinations with multiple SOC therapies. Given the promising single-agent activity of epcoritamab, these combinations may lead to deep and durable responses that can translate into improved long-term outcomes for B-NHL patients. Epcoritamab combination therapies are planned to be evaluated in a clinical trial sponsored by Genmab and Abbvie.

Citation Format: Christopher W. Chiu, Ida H. Hiemstra, Wessel ten Hagen, Rajaa Snijdewint-Nkairi, Bart de Jong, Roberto S. Oliveri, Brian Elliot, Edith Szafer-Glusman, Danita Schuurhuis, Julie Blaedel, Tahamatan Ahmadi, Esther Breij, A. Kate Sasser, Maria Jure-Kunkel. Preclinical evaluation of epcoritamab combined with standard of care therapies for the treatment of B-cell lymphomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1574.

Fixed-duration (FD) first-line treatment (tx) with ibrutinib (I) plus venetoclax (V) for chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL): Primary analysis of the FD cohort of the phase 2 captivate study

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Background: CAPTIVATE (PCYC-1142) is a multicenter phase 2 study of first-line I+V in CLL. We previously reported results from the Minimal Residual Disease (MRD) cohort wherein undetectable MRD (uMRD) was achieved in over two-thirds of patients (pts) with 12 cycles of I+V, and 30-mo PFS rates were ≥95% irrespective of subsequent randomized treatment (Wierda, ASH 2020). We now present results from the FD cohort, evaluating fixed-duration tx with I+V. Methods: Pts aged ≤70 y with previously untreated CLL/SLL received 3 cycles of I then 12 cycles of I+V (I 420 mg/d orally; V ramp-up to 400 mg/d orally). Primary endpoint was CR rate, including CR with incomplete recovery (CRi); secondary endpoints were ORR, duration of response, uMRD rate (<10-4 by 8-color flow cytometry), PFS, OS, tumor lysis syndrome (TLS) risk reduction, and adverse events (AEs). Results: 159 pts were enrolled (median age 60 y). High-risk features included del(17p)/ TP53 mutation, 17%; del(11q), 18%; complex karyotype, 19%; and unmutated IGHV, 56%. 147 (92%) and 149 (94%) pts completed planned tx with I and V, respectively. Median time on study was 27.9 mo (range, 0.8–33.2). With fixed-duration I+V, CR rate was 55% (95% CI 48–63) in the overall population and was consistent across high-risk subgroups. Of the 88 pts who achieved CR, 78 (89%) had durable CR (duration ≥1 y); 1 died 7 mo after CR, and 9 with <1 y follow-up were not evaluable. ORR was 96%. Best uMRD response was achieved in 77% of pts in peripheral blood (PB) and 60% of pts in bone marrow (BM). 24-mo PFS was 95%; 24-mo OS was 98%. Results were similar in pts without del(17p) (n=136) (Table). In pts with del(17p)/ TP53 mutation (n=27), CR rate was 56%, uMRD rate was 81% (PB) and 41% (BM), and 24-mo PFS was 84% (95% CI 63–94). Of 34 pts with high baseline TLS risk based on tumor burden, 32 (94%) shifted to medium or low risk after I lead-in; no TLS occurred. AEs were primarily grade 1/2. Most common grade 3/4 AEs were neutropenia (33%), hypertension (6%), and neutrophil count decreased (5%). AEs led to discontinuation of I in 4% and V in 2%. Conclusions: First-line I+V is an all-oral, once-daily, chemotherapy-free, fixed-duration regimen that provides deep, durable responses in pts with CLL/SLL, including those with genomic high-risk features. CR, uMRD rates, PFS, and OS appear favorable. The safety profile of I+V was consistent with known AEs for each agent; no new safety signals were identified. Clinical trial information: NCT02910583. [Table: see text]

BCL2 Expression in First-Line Diffuse Large B-Cell Lymphoma Identifies a Patient Population With Poor Prognosis

INTRODUCTION

The prognostic value of B-cell lymphoma 2 (BCL2) expression in de novo diffuse large B-cell lymphoma (DLBCL) treated with immunochemotherapy is of interest to define a target patient population for clinical development of BCL2 inhibitors. We aimed to develop a reproducible immunohistochemistry algorithm and assay to determine BCL2 protein expression and assess the prognostic value of BCL2 in newly diagnosed DLBCL cohorts.

PATIENTS AND METHODS

The prospectively defined algorithm incorporated BCL2 staining intensity and percentage of BCL2-positive cells. Functionally relevant cutoffs were based on the sensitivity of lymphoma cell lines to venetoclax. This assay was highly reproducible across laboratories. The prognostic impact of BCL2 expression was assessed in DLBCL patients from the phase 3 MAIN (n = 230) and GOYA (n = 366) trials, and a population-based registry (n = 310).

RESULTS

Approximately 50% of tumors were BCL2 positive, with a higher frequency in high International Prognostic Index (IPI) and activated B-cell-like DLBCL subgroups. BCL2 expression was associated with poorer progression-free survival in the MAIN study (hazard ratio [HR], 1.66; 95% confidence interval [CI], 0.81-3.40; multivariate Cox regression adjusted for IPI and cell of origin). This trend was confirmed in the GOYA and registry cohorts in adjusted multivariate analyses (GOYA: HR, 1.72; 95% CI, 1.05-2.82; registry: HR, 1.89; 95% CI, 1.29-2.78). Patients with BCL2 immunohistochemistry-positive and IPI-high disease had the poorest prognosis: 3-year progression-free survival rates were 51% (GOYA) and 37% (registry).

CONCLUSION

Findings support use of our BCL2 immunohistochemistry scoring system and assay to select patients with BCL2-positive tumors for future studies.

Genomic Analysis of Circulating Tumor Cells at the Single-Cell Level

Circulating tumor cells (CTCs) have a great potential for noninvasive diagnosis and real-time monitoring of cancer. A comprehensive evaluation of four whole genome amplification (WGA)/next-generation sequencing workflows for genomic analysis of single CTCs, including PCR-based (GenomePlex and Ampli1), multiple displacement amplification (Repli-g), and hybrid PCR- and multiple displacement amplification–based [multiple annealing and loop-based amplification cycling (MALBAC)] is reported herein. To demonstrate clinical utilities, copy number variations (CNVs) in single CTCs isolated from four patients with squamous non–small-cell lung cancer were profiled. Results indicate that MALBAC and Repli-g WGA have significantly broader genomic coverage compared with GenomePlex and Ampli1. Furthermore, MALBAC coupled with low-pass whole genome sequencing has better coverage breadth, uniformity, and reproducibility and is superior to Repli-g for genome-wide CNV profiling and detecting focal oncogenic amplifications. For mutation analysis, none of the WGA methods were found to achieve sufficient sensitivity and specificity by whole exome sequencing. Finally, profiling of single CTCs from patients with non–small-cell lung cancer revealed potentially clinically relevant CNVs. In conclusion, MALBAC WGA coupled with low-pass whole genome sequencing is a robust workflow for genome-wide CNV profiling at single-cell level and has great potential to be applied in clinical investigations. Nevertheless, data suggest that none of the evaluated single-cell sequencing workflows can reach sufficient sensitivity or specificity for mutation detection required for clinical applications.

Drosophila Doublefault protein coordinates multiple events during male meiosis by controlling mRNA translation

During the extended prophase of Drosophila gametogenesis, spermatocytes undergo robust gene transcription and store many transcripts in the cytoplasm in a repressed state, until translational activation of select mRNAs in later steps of spermatogenesis. Here, we characterize the Drosophila Doublefault (Dbf) protein as a C2H2 zinc-finger protein, primarily expressed in testes, that is required for normal meiotic division and spermiogenesis. Loss of Dbf causes premature centriole disengagement and affects spindle structure, chromosome segregation and cytokinesis. We show that Dbf interacts with the RNA-binding protein Syncrip/hnRNPQ, a key regulator of localized translation in Drosophila We propose that the pleiotropic effects of dbf loss-of-function mutants are associated with the requirement of dbf function for translation of specific transcripts in spermatocytes. In agreement with this hypothesis, Dbf protein binds cyclin B mRNA and is essential for translation of cyclin B in mature spermatocytes.

Changes in circulating tumor DNA levels are associated with treatment response and progression-free survival in relapse/refractory DLBCL subjects

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Background: Detection of an initial molecular response to therapy in DLBCL could help differentiate patients who will relapse (30-40% of frontline subjects) from those who will not. Recent studies in DLBCL showed ability to detect residual disease and molecular response to therapy from analysis of circulating tumor DNA (ctDNA). Here we performed targeted next generation sequencing (NGS) of baseline ctDNA vs. tumor tissue, and on-treatment ctDNA samples in 32 relapse/refractory DLBCL subjects from the ROMULUS study to assess correlation of outcome with molecular response. Methods: We sequenced plasma, plasma depleted whole blood (PDWB), and tumor DNA from 32 subjects (range 2-6 samples / subject). Library preparation and NGS were performed using hybrid capture-based workflows, with a panel of ~300 kb targeting regions relevant for disease detection in DLBCL. Variants were called from tissue and plasma data, and PDWB data were used to filter out non-tumor specific variants. Results: 83% of variants detected in tissue (1441/1745) were found in the corresponding plasma samples, and 78% of variants detected in plasma (1441/1846) were found in corresponding tissue samples, in line with previous reports. To follow ctDNA changes with treatment, tumor-specific variants were determined from tissue or cycle 1 day 1 (C1D1) plasma samples. These variants were then monitored in C1D1 and later timepoints, with similar ctDNA levels based on variants determined from C1D1 plasma or tissue (R2=0.99). Change in ctDNA levels from C1D1 to C2D1 separated subjects that responded from subjects that progressed (Wilcoxon p-value: 9.39×10-4). Subjects that showed a 10-fold or higher drop in ctDNA levels between C1D1 and C2D1 had significantly longer PFS than those with a smaller ctDNA fold change (HR: 8.06; p=0.0008). Conclusions: This study showed that tumor-specific variants can be identified in baseline plasma with similar performance as from tumor tissue, and that monitoring molecular response as an early change in ctDNA levels after one cycle of treatment correlated with outcomes in this DLBCL study. Clinical trial information: NCT01691898.

Detection of PD-L1 in circulating tumor cells and white blood cells from patients with advanced non-small-cell lung cancer

Background

Expression of PD-L1 in tumor cells and tumor-infiltrating immune cells has been associated with improved efficacy to anti-PD-1/PD-L1 inhibitors in patients with advanced-stage non-small-cell lung cancer (NSCLC) and emerged as a potential biomarker for the selection of patients to cancer immunotherapies. We investigated the utility of circulating tumor cells (CTCs) and circulating white blood cells (WBCs) as a noninvasive method to evaluate PD-L1 status in advanced NSCLC patients.

Patients and methods

CTCs and circulating WBCs were enriched from peripheral blood samples (ISET® platform; Rarecells) from 106 NSCLC patients. PD-L1 expression on ISET filters and matched-tumor tissue was evaluated by automated immunostaining (SP142 antibody; Ventana), and quantified in tumor cells and WBCs.

Results

CTCs were detected in 80 (75%) patients, with levels ranging from 2 to 256 CTCs/4 ml, and median of 60 CTCs/4 ml. Among 71 evaluable samples with matched-tissue and CTCs, 6 patients (8%) showed ≥1 PD-L1-positive CTCs and 11 patients (15%) showed ≥1% PD-L1-positive tumor cells in tumor tissue with 93% concordance between tissue and CTCs (sensitivity = 55%; specificity = 100%). From 74 samples with matched-tissue and circulating WBCs, 40 patients (54%) showed ≥1% PD-L1-positive immune infiltrates in tumor tissue and 39 patients (53%) showed ≥1% PD-L1 positive in circulating WBCs, with 80% concordance between blood and tissue (sensitivity = 82%; specificity = 79%). We found a trend for worse survival in patients receiving first-line cisplatin-based chemotherapy treatments, whose tumors express PD-L1 in CTCs or immune cells (progression-free and overall survival), similar to the effects of PD-L1 expression in matched-patient tumors.

Conclusions

These results demonstrated that PD-L1 status in CTCs and circulating WBCs correlate with PD-L1 status in tumor tissue, revealing the potential of CTCs assessment as a noninvasive real-time biopsy to evaluate PD-L1 expression in patients with advanced-stage NSCLC.

Immune Characteristics of Chinese Diffuse Large B-Cell Lymphoma Patients: Implications for Cancer Immunotherapies

Immunotherapeutic agents have demonstrated encouraging signs of clinical utility in non-Hodgkin lymphoma. The goal of this study is to analyze the immune characteristics of Chinese patients with diffuse large B-cell lymphoma (DLBCL) to inform the development of immunotherapies in this patient population. Tumor samples from 211 DLBCL patients were analyzed for cell of origin (COO) and immune characteristics using the NanoString platform as well as MYC protein expression through immunohistochemistry. Lower incidence of the germinal center B-cell (GCB) subtype (93/211, 44.1%) was observed in this cohort. Compared to the GCB subtype, the activated B-cell (ABC) subtype was associated with significantly increased expression of multiple pro-inflammatory gene signatures and decreased expression of anti-inflammatory gene signatures. Instead of affecting the pro-inflammatory genes, MYC protein overexpression showed a negative correlation with the expression of T-cell receptor (TCR) and T regulatory genes as well as the OX40 gene. Regardless of COO, higher PD-L1 or IDO1 gene expression correlated with increased expression of T effector and Interferon-γ gene signatures while the expression of multiple oncogenes including ACTR3B, ERBB2, AKT2 and SMARCD1 was down-regulated. Our findings may thus be helpful in guiding further development of immunotherapies for the different subsets of Chinese DLBCL patients.

Expression of MET in circulating tumor cells correlates with expression in tumor tissue from advanced-stage lung cancer patients

Given the difficulty in obtaining adequate tissue in NSCLC, we investigated the utility of circulating tumor cells (CTCs) for MET status assessment in NSCLC patients. We used two platforms for CTC capture, and assessed MET expression in CTCs and matched-bronchial biopsies in patients with advanced-stage III/IV lung adenocarcinoma. Baseline peripheral blood was collected from 256 advanced-stage III/IV NSCLC patients from Genentech clinical trials, and from 106 patients with advanced-stage III/IV lung adenocarcinoma treated at the Department of Pneumology, Pasteur Hospital, Nice. CTCs were enriched using CellSearch (Genentech), or ISET technologies (Pasteur Hospital). MET expression was evaluated by immunofluorescence on CellSearch, and by immunocytochemistry on ISET-enriched CTCs and on matched FFPE tissue sections (Pasteur Hospital). CTCs were detected in 83 of 256 (32%) patients evaluated on CellSearch, with 30 samples (12%) exhibiting ≥ 5 CTCs/7.5 ml blood. On ISET, CTC were observed in 80 of 106 patients (75%), and 79 patients (75%) exhibited ≥ 5 CTCs/4 ml blood. MET expression on ISET CTCs was positive in 72% of cases, and the MET expression on matched-patient tissue was positive in 65% patients using the Onartuzumab IHC scoring algorithm (93% concordance). Quantification of MET expression using H-scores showed strong correlation between MET expression in tissue and CTCs (Spearman correlation, 0.93). MET status in CTCs isolated on ISET filters from blood samples of advanced-stage NSCLC patients correlated strongly with MET status in tumor tissue, illustrating the potential for using CTCs as a non-invasive, real-time biopsy to determine MET status of patients entering clinical trials.

BCL2 mutations do not confer adverse prognosis in follicular lymphoma patients treated with rituximab

BCL2 mutations have been suggested to confer an adverse prognosis to follicular lymphoma (FL) patients, but their prognostic value has not been assessed in patients treated with a rituximab-containing regimen. Here we evaluated the prognostic value of BCL2 mutations in a large prospective cohort of 252 patients with FL treated with immunochemotherapy in the PRIMA randomized trial. Using a DNA-targeted sequencing approach, we detected amino acid altering mutations in 135 patients (54%) and showed that these mutations were probably mediated by the over-activation of AICDA (activation-induced cytidine deaminase) in the context of the t(14;18) translocation. The BCL2 variants identified in PRIMA patients affected the BH1, BH2, and BH3 functional motifs at a lower frequency than the N-terminus and flexible loop domain, with mostly conservative aminoacid changes. With a median follow-up of 6.7 years, we did not observe any impact of BCL2 mutations either on overall survival or progression-free survival.

Rituximab treatment circumvents the prognostic impact of tumor-infiltrating T-cells in follicular lymphoma patients

Previous immunohistochemical (IHC) studies showed controversial data about the prognostic value of tumor-infiltrating lymphocytes (TILs) in follicular lymphoma (FL). To clarify this issue, a large series of FL samples from rituximab-treated patients enrolled in the randomized PRIMA trial was examined. IHC was quantified using automated image analysis in 417, 287, 418, 406, 379, and 369 patients for CD3, CD4, CD8, PD1, ICOS, and FOXP3, respectively. RNAseq analysis was used to quantify TIL-related mRNA transcripts from 148 patients. When each IHC marker was used as a continuous variable in the whole cohort, high CD3 counts were associated with better progression-free survival (PFS) (P = .025). When an optimal IHC cut point was applied to the whole patient population, high CD3 counts and high PD1 counts were associated with better PFS (P = .011 and P = .044, respectively), whereas none of the other TIL markers had any significant correlation with outcome. When a stringent analysis was performed by dividing the whole cohort into a training set and a validation set, none of the TIL markers showed a prognostic significance in both groups. RNAseq analysis showed a significant correlation between high levels of CD3 and CD8 transcripts and better PFS (P = .001 and P = .037, respectively). No prognostic correlation was found as to the level of other immune gene transcripts. These results suggest that the IHC prognostic value of TILs is circumvented by rituximab treatment, although there is a trend for high numbers of CD3+ TILs to correlate with better PFS.

Abstract 1580: MET expression in circulating tumor cells (CTCs) isolated on the ISET platform correlates with MET expression in matched tumor tissue in advanced NSCLC patients

Background: Overexpression of the MET receptor tyrosine kinase is frequent in lung cancers and is associated with poor prognosis. Recent clinical studies of MET targeted therapies have used immunohistochemistry (IHC) in tissue biopsies to evaluate MET protein expression. Due to the difficulty in obtaining adequate tissue in diseases such as NSCLC, we investigated the utility of circulating tumor cells (CTCs) as a non-invasive method to evaluate MET status in NSCLC patients. We compared two platforms for CTC capture, CellSearch and ISET, and assessed MET expression in CTCs vs. matched bronchial biopsies in patients with advanced-stage III/IV lung adenocarcinoma

Design: CTC capture and MET expression in CTCs was evaluated in 358 MET positive NSCLC patients (Phase III OAM4971 trial) using the CellSearch platform. CTC capture and MET expression was evaluated in a cohort of 80 CTC-positive NSCLC patients using the ISET platform (filtration). MET was detected in CellSearch-captured CTCs by immunofluorescence using the 15A5 mouse monoclonal antibody (Genentech), and in ISET-captured CTCs and FFPE tissue sections by immunohistochemistry using the SP44 c-MET antibody from Ventana Medical Systems, Tucson, USA. Both reagents performed equally on the CellSearch platform.

Results: CTCs were detected in 108 of 358 (30%) patients evaluated on CellSearch, with CTC enumeration ranging from 0 to 193 CTCs/7.5 ml blood, and median 0 CTCs/7.5ml blood. Although OAM4971 patients were selected for positive MET expression in tissue, we failed to detect MET expression in most CTCs isolated by CellSearch, with 75% patients showing CTC H-score &lt; 15. On the ISET platform, CTCs enumeration ranged from 2 to 268 CTCs/ml, with median 65 CTCs/ml. Clusters of CTCs were observed in 93% of patients, exhibiting between 1 to 23-clusters/ml blood. The MET assay on CTCs was positive in 54 of 75 (72%) patients, and the MET assay on tissue was positive in 46 of 75 (62%) patients using the onartuzumab IHC scoring algorithm*, with MET status in CTCs concordant with status in patient-matched tumor tissue.

Conclusion: Based on our data, CTCs enumeration and MET status on CTCs from NSCLC patients captured and evaluated on the ISET system were more successful than on the CellSearch platform. On ISET, MET status in CTCs correlated strongly with MET status in tumor tissue biopsies, illustrating the potential for using CTCs as a non-invasive, real-time biopsy to determine MET status of patients entering clinical trials. We are now expanding the CTC analysis on ISET to other biomarkers with relevance for lung therapeutics.

* Koeppen H et al. Clin Cancer Res. 2014 Sep 1;20(17):4488-98

Citation Format: Marius Ilie, Edith Szafer-Glusman, Veronique Hofman, Rebecca Suttman, Walter Darbonne, Charles-Hugo Marquette, David S. Shames, Elizabeth Punnoose, Paul Hofman. MET expression in circulating tumor cells (CTCs) isolated on the ISET platform correlates with MET expression in matched tumor tissue in advanced NSCLC patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1580. doi:10.1158/1538-7445.AM2015-1580

Abstract 4310: Predictive biomarkers of tumor sensitivity to STEAP1 antibody-drug conjugate (ADC) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

ADCs hold promise for enhancing the therapeutic index of cytotoxics. STEAP1 is overexpressed in mCRPC and is the target of an ADC currently under clinical development. To identify pts most likely to benefit from the ADC, we explored STEAP1 expression as a predictive biomarker in tumor tissue using a CLIA-certified IHC assay, and on circulating tumor cells (CTCs) in blood using the CellSearch and EPIC platforms. Sixty pts with progressive mCRPC received doses ranging from 0.3 to 2.8 mg/kg once every three weeks. Response was defined as a ≥50% decline in PSA from baseline, and time on study for &gt;6 months was consistent with continued clinical benefit. At doses of ≥2 mg/kg, the response rate (RR) was 10/45 (22%, 95% CI 9.9-34.1) and was highest in the STEAP1 IHC 3+ group, as was the fraction of patients who remained on study for &gt;6 months. At ≥2 mg/kg, 20/45 pts (44%, 95% CI 29.5-58.5) had unfavorable CTC counts of ≥5/7.5mL at baseline and were considered evaluable. After treatment, conversions from unfavorable to favorable CTC counts of &lt;5/7.5mL were seen in 11/20 patients (55%, 95% CI 33.2-76.8) and were significantly correlated with PSA declines (Spearman rank r = 0.74). STEAP1 expression in tissues and on CTCs as it related to clinical activity is presented in the following table:

STEAP1 IHC Score and Treatment ResponseSTEAP1 IHC ScorePts Observed/TotalPSA decline by ≥50% from baseline&gt;6 months on treatment(%, 95% CI)(%, 95% CI)(%, 95% CI)1+5/45 (11%, 1.9-20.1)1/5 (20%, -15.1-55.1)0/5 (0%)2+27/454/276/27(60%, 45.7-74.3)(15%, 1.5-28.5)(22%, 6.4-37.6)3+13/455/136/13(29%, 15.7-42.2)(39%, 12.5-65.5)(46%, 18.9-73.1)CTC Analysis and Treatment ResponseCTC endpointTime Point & CTC Conversion vs. baselinePts Observed/TotalPSA decline by ≥50% from baseline&gt;6 months on treatment(%, 95% CI)(%, 95% CI)(%, 95% CI)CTC countsBaseline ≥5/7.5mL20/456/206/20(at ≥2 mg/kg)(44%, 29.5-58.5)(30%, 9.9-50.1)(30%, 9.9-50.1)Baseline &lt;5/7.5mL25/453/257/25(56%, 41.5-70.5)(12%, -0.7-24.7)(28%, 10.4-45.6)CTC conversion11/206/115/11(55%, 33.1-76.8)(55%, 25.6-84.4)(45%, 15.6-74.4)STEAP Expression Status on CTCsBaseline STEAP +ve9/131/91/9(most at &lt;2mg/kg)(69%, 43.9-94.1)(11%, -9.4-31.4)(11%, -9.4-31.4)Baseline STEAP -ve4/13 (31%, 5.9-56.1)0/4 (0%)0/4 (0%)After treatment STEAP +ve4/14 (29%, 5.2-52.8)0/4 (0%)0/4 (0%)After treatment STEAP -ve10/14 (71%, 47.2-94.8)1/10 (10%, -8.6-28.6)1/10 (10%, -8.6-28.6)

An immuno-fluorescence-based assay developed to measure STEAP1 expression levels on CTCs showed readily detectable signal in 18/42 samples (43%, 95% CI 28-58), with a range from 1-56% of STEAP1-positive CTCs per case. After treatment, a decrease in the fraction of patients with STEAP1-positive and an increase in the STEAP1-negative CTCs was observed compared to baseline (see Table). We are prospectively selecting pts with STEAP1 IHC 2+/3+ tumors and assessing STEAP1 levels on CTCs in an ongoing Ph1 expansion study with the goal of developing a companion diagnostic to enrich for mCRPC pts most likely to benefit from treatment with the STEAP1 ADC.

Citation Format: Daniel C. Danila, Howard I. Scher, Edith Szafer-Glusman, Amrita Herkal, Rebecca Suttmann, Martin Fleisher, Nicole A. Schreiber, Kristen Curtis, Houston Gilbert, Daniel Maslyar, Bernard Fine, Ron Firestein, Michael Mamounas, Mark R. Lackner, Omar Kabbarah. Predictive biomarkers of tumor sensitivity to STEAP1 antibody-drug conjugate (ADC) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4310. doi:10.1158/1538-7445.AM2015-4310

Abstract 4819: Evaluation of PTEN status in circulating tumor cells (CTCs) and matched tumor tissue from castrate-resistant prostate cancer (CRPC) patients

Background:

PTEN loss occurs frequently in prostate cancer and may trigger progression to CRPC through activation of the PI3K/AKT pathway. A blood-based assay that determines PTEN status in CRPC patients could enable informed treatment decisions such as the use of a PI3K-targeted therapy. Here we examined the relationship between PTEN status in CTCs and matched archival and fresh tumor biopsies in 43 CRPC patients.

Methods:

Nucleated cells from CRPC patient blood were plated onto glass slides and subjected to IF staining and CTC identification by high-speed fluorescent scanners at Epic Sciences. CTCs were identified as CK+/CD45- cells with intact DAPI nuclei, and samples with ≥4 CTCs per 2 slides (74%) were then tested for PTEN by FISH. Heterozygous loss was defined as a decrease in PTEN copies (PTEN &lt; CEP10 and &lt; 2 copies) and homozygous loss as zero PTEN copies. PTEN IHC in tissue was stained using CST clone 138G6 and H-scores ≤ 200 counted as loss.

Results:

Heterozygous or homozygous loss of PTEN by FISH was observed in 16 of 43 patients (37%) by CTC analysis. In addition to loss of PTEN, changes in ploidy were frequently observed and broad heterogeneity seen both within and between patients. The PTEN status in CTCs correlated strongly with the PTEN status in metastatic tissue: All 10 patients that exhibited homozygous PTEN loss in CTCs showed concordant homozygous PTEN loss in fresh biopsies. This correlation extended to three patients that showed correlated mixed homozygous and hemizygous PTEN loss populations in CTCs and tissue. “Drift or change” in PTEN status from archival to fresh biopsies occurred in 15 patients, In 12 of these patients, PTEN status in CTCs was reflective of the status in fresh tissue. Together with PTEN evaluation, the analysis of androgen receptor expression by immunofluorescence and ERG rearrangements by FISH proved feasibility of multiplex biomarker assessment in CTCs. This analysis demonstrated heterogeneity of AR phenotypes and a positive association of ERG rearrangements and PTEN loss in CTCs, consistent with literature reports.

Conclusion:

Our results illustrate the potential for using CTCs as a non-invasive, real-time biopsy to determine a patient's current PTEN status. PTEN status will be determined using these assays in an ongoing AKT inhibitor Phase II trial.

Citation Format: Elizabeth Punnoose, Eric Tucker, Edith Szafer-Glusman, Jin Zhu, Dena Marrinucci, Jessica Louw, Florence Lee, Mikel Kitchen, Natalee Bales, Lukas Amler, Hartmut Koeppen, Premal Patel, Yibing Yan, Ruth Riisnaes, Gerhardt Attard, Johann de Bono. Evaluation of PTEN status in circulating tumor cells (CTCs) and matched tumor tissue from castrate-resistant prostate cancer (CRPC) patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4819. doi:10.1158/1538-7445.AM2014-4819

Role of Survivin in cytokinesis revealed by a separation-of-function allele

A mutation in Drosophila Survivin that enables metaphase functions but impairs cytokinesis demonstrates a role for Survivin and CPC in Rho activation and contractile ring assembly and highlights striking differences in regulation of cytokinesis in different cell systems.

The chromosomal passenger complex (CPC), containing Aurora B kinase, Inner Centromere Protein, Survivin, and Borealin, regulates chromosome condensation and interaction between kinetochores and microtubules at metaphase, then relocalizes to midzone microtubules at anaphase and regulates central spindle organization and cytokinesis. However, the precise role(s) played by the CPC in anaphase have been obscured by its prior functions in metaphase. Here we identify a missense allele of Drosophila Survivin that allows CPC localization and function during metaphase but not cytokinesis. Analysis of mutant cells showed that Survivin is essential to target the CPC and the mitotic kinesin-like protein 1 orthologue Pavarotti (Pav) to the central spindle and equatorial cell cortex during anaphase in both larval neuroblasts and spermatocytes. Survivin also enabled localization of Polo kinase and Rho at the equatorial cortex in spermatocytes, critical for contractile ring assembly. In neuroblasts, in contrast, Survivin function was not required for localization of Rho, Polo, or Myosin II to a broad equatorial cortical band but was required for Myosin II to transition to a compact, fully constricted ring. Analysis of this “separation-of-function” allele demonstrates the direct role of Survivin and the CPC in cytokinesis and highlights striking differences in regulation of cytokinesis in different cell systems.

ArfGAP1 interacts with coat proteins through tryptophan-based motifs

The Arf1 GTPase-activating protein ArfGAP1 regulates vesicular traffic through the COPI system. This protein consists of N-terminal catalytic domain, lipid packing sensors (the ALPS motifs) in the central region, and a carboxy part of unknown function. The carboxy part contains several diaromatic sequences that are reminiscent of motifs known to interact with clathrin adaptors. In pull-down experiments using GST-fused peptides from rat ArfGAP1, a peptide containing a (329)WETF sequence interacted strongly with clathrin adaptors AP1 and AP2, whereas a major coatomer-binding determinant was identified within the extreme carboxy terminal peptide ((405)AADEGWDNQNW). Mutagenesis and peptide competition experiments revealed that this determinant is required for coatomer binding to full-length ArfGAP1, and that interaction is mediated through the delta-subunit of the coatomer adaptor-like subcomplex. Evidence for a role of the carboxy motif in ArfGAP1-coatomer interaction in vivo is provided by means of a reporter fusion assay. Our findings point to mechanistic differences between ArfGAP1 and the other ArfGAPs known to function in the COPI system.

A role for very-long-chain fatty acids in furrow ingression during cytokinesis in Drosophila spermatocytes

Cell shape and membrane remodeling rely on regulated interactions between the lipid bilayer and cytoskeletal arrays at the cell cortex. During cytokinesis, animal cells build an actomyosin ring anchored to the plasma membrane at the equatorial cortex. Ring constriction coupled to plasma-membrane ingression separates the two daughter cells. Plasma-membrane lipids influence membrane biophysical properties such as membrane curvature and elasticity and play an active role in cell function, and specialized membrane domains are emerging as important factors in regulating assembly and rearrangement of the cytoskeleton. Here, we show that mutations in the gene bond, which encodes a Drosophila member of the family of Elovl proteins that mediate elongation of very-long-chain fatty acids, block or dramatically slow cleavage-furrow ingression during early telophase in dividing spermatocytes. In bond mutant cells at late stages of division, the contractile ring frequently detaches from the cortex and constricts or collapses to one side of the cell, and the cleavage furrow regresses. Our findings implicate very-long-chain fatty acids or their derivative complex lipids in allowing supple membrane deformation and the stable connection of cortical contractile components to the plasma membrane during cell division.