Treatment Patterns, Healthcare Resource Utilization, and Costs of Patients With Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma in the US

BACKGROUND

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia among US adults and has experienced a rapidly evolving treatment landscape; yet current data on treatment patterns in clinical practice and economic burden are limited. This study aimed to provide an up-to-date description of real-world characteristics, treatments, and costs of patients with CLL or small lymphocytic lymphoma (SLL).

MATERIALS AND METHODS

Using retrospective data from the Optum Clinformatics DataMart database (January 2013 to December 2021), adults with diagnosis codes for CLL/SLL on two different dates were selected. An adapted algorithm identified lines of therapy (LOT). Treatment patterns were stratified by the index year pre- and post-2018. Healthcare resource utilization and costs were evaluated per patient-years.

RESULTS

A total of 18 418 patients with CLL/SLL were identified, 5226 patients (28%) were treated with ≥1 LOT and 1728 (9%) with ≥2 LOT. Among patients diagnosed with CLL in 2014-2017 and ≥1 LOT (N = 2585), 42% used targeted therapy and 30% used chemoimmunotherapy in first line (1L). The corresponding proportions of patients diagnosed with CLL in 2018-2021 (N = 2641) were 54% and 16%, respectively. Total costs were numerically 3.5 times higher and 4.9 times higher compared with baseline costs among patients treated with 1L+ and 3L+, respectively.

CONCLUSION

This study documented the real-world change in CLL treatment landscape and the substantial economic burden of patients with CLL/SLL. Specifically, targeted therapies were increasingly used as 1L treatments and they were part of more than half of 1L regimens in recent years (2018-2021).

Real-world analysis of adverse event rates after initiation of ibrutinib among Medicare beneficiaries with chronic lymphocytic leukemia

BACKGROUND

The first-generation BTK inhibitor ibrutinib is a standard-of-care therapy in the treatment of chronic lymphocytic leukemia (CLL) despite potential side effects that often lead to discontinuation.

METHODS

This study used 2013-2019 claims data to describe the incidence rate of adverse events (AEs) among elderly Medicare beneficiaries newly initiating ibrutinib for CLL.

RESULTS

The final sample contained 11,870 Medicare beneficiaries with CLL (mean age 77.2) newly initiating ibrutinib, of whom 65.2% discontinued over mean follow-up of 2.3 years. The overall incidence rate of AEs was 62.5 per 1000 patient-months for all discontinuers and 32.9 per 1000 patient-months for non-discontinuers. Discontinuers had a higher incidence rate of AEs per 1000 patient-months compared with non-discontinuers for all AEs examined, including infection (22.8 vs. 14.5), atrial fibrillation (15.1 vs. 7.0), anemia (21.9 vs. 14.5), and arthralgia/myalgia (19.5 vs. 13.6).

CONCLUSION

In this first real-world study of a national sample of elderly US patients treated with ibrutinib, we found a clear unmet need for improved management of ibrutinib-related AEs and/or new treatments to improve real-world outcomes in patients with CLL.

Ibrutinib discontinuation and associated factors in a real-world national sample of elderly Medicare beneficiaries with chronic lymphocytic leukemia

Prior studies evaluating ibrutinib discontinuation are limited to clinical trials and selected medical centers and hence may not reflect real-world practice. This study used Medicare claims (2013-2019) to examine ibrutinib discontinuation and associated factors among elderly patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Over a median follow-up of 2.1 years, two-thirds (65.2%) of the 11,870 new ibrutinib initiators were discontinued, with half (45.1%) of patients discontinuing within 12 months of initiation. Factors such as advanced age, lack of Part D low-income subsidy, evidence of prior CLL/SLL treatment, and cardiovascular comorbidities (e.g. atrial fibrillation) were associated with higher risk of discontinuation. Over a median of 1.2 years from discontinuation, 40% of discontinuers initiated another CLL/SLL treatment after ibrutinib discontinuation; 25% of patients restarted ibrutinib treatment at some point over follow-up. Our findings point to a large unmet need with the widely used BTKi ibrutinib and underscore the importance of ongoing development of efficacious and well-tolerated CLL/SLL therapies.

Use of the Woven EndoBridge Device for Sidewall Aneurysms: Systematic Review and Meta-analysis

BACKGROUND

The Woven EndoBridge device was originally approved to treat intracranial wide-neck saccular bifurcation aneurysms. Recent studies have suggested its use for the treatment of sidewall intracranial aneurysms with variable success.

PURPOSE

Our aim was to evaluate the safety and efficacy of the Woven EndoBridge device for sidewall aneurysms using a meta-analysis of the literature.

DATA SOURCES

We performed a systematic review of all studies including patients treated with the Woven EndoBridge device for sidewall aneurysms from inception until May 2022 on Scopus, EMBASE, MEDLINE, the Web of Science, and the Cochrane Central Register of Controlled Trials.

STUDY SELECTION

Ten studies were selected, and 285 patients with 288 sidewall aneurysms were included.

DATA ANALYSIS

A random-effects meta-analysis of proportions using a generalized linear mixed model was performed as appropriate. Statistical heterogeneity across studies was assessed with I2 statistics.

DATA SYNTHESIS

The adequate occlusion rate at last follow-up was 89% (95% CI, 81%-94%; I2, = 0%), the composite safety outcome was 8% (95% CI, 3%-17%; I2 = 34%), and the mortality rate was 2% (95% CI, 1%-7%; I2 = 0%). Aneurysm width (OR = 0.5; P = .03) was the only significant predictor of complete occlusion.

LIMITATIONS

Given the level of evidence, our results should be interpreted cautiously until confirmation from larger prospective studies is obtained.

CONCLUSIONS

The initial evidence evaluating the use of the Woven EndoBridge device for the treatment of wide-neck sidewall intracranial aneurysms has demonstrated high rates of adequate occlusion with low procedural complications. Our findings favor the consideration of the Woven EndoBridge device as an option for the treatment of sidewall aneurysms.

Pembrolizumab for patients with non-Hodgkin lymphoma: phase 1b KEYNOTE-013 study

The multicohort phase 1b KEYNOTE-013 study (NCT01953692) evaluated the safety and efficacy of pembrolizumab in patients with relapsed or refractory NHL who were ineligible for or failed hematopoietic cell transplantation (HCT). Patients received pembrolizumab (cohort 4) or pembrolizumab plus lenalidomide (cohort 5). Primary end points were safety and objective response rate (ORR) per IWG 2007 criteria. Cohort 4 included 89 patients. ORR was 22% (19/86; 90% CI 15-31; 10 CR, nine PR); ORRs by disease type were 48% (10/21), 10% (2/20), 12% (5/41), and 50% (2/4), for PMBCL, FL, DLBCL, and 'other' NHL, respectively. Toxicity was as predicted. Cohort 5 included 19 patients. ORR was 39% (90% CI 20-61; four CR, three PR). Hematologic toxicities were the most common treatment-related AEs. In conclusion, pembrolizumab following HCT ineligibility/failure confirms prior experience in PMBCL but not with NHL subtypes in this study. Additional analyses in DLBCL may not be warranted.

Pembrolizumab for myelodysplastic syndromes after failure of hypomethylating agents in the phase 1b KEYNOTE-013 study

The phase 1b multicohort KEYNOTE-013 study assessed the safety and antitumor activity of pembrolizumab given at 10 mg/kg/day every 2 weeks for up to 2 years in hematologic malignancies, including myelodysplastic syndromes (MDS) refractory to a hypomethylating agent (HMA). Primary outcomes were safety and objective response rate per International Working Group 2006 criteria. By June 26, 2020, 28 patients were enrolled; median duration of follow-up was 5.6 months (range, 1-78), and 25 patients (89%) had died. Treatment-related adverse events occurred in 10 patients (36%), including 2 (7%) treatment-related discontinuations. No patient achieved complete or partial response. Five patients (19%) had bone marrow complete response, 12 (44%) stable disease, 10 (37%) progressive disease, 6 (22%) cytogenetic response, and 5 (19%) hematologic improvement. Median overall survival (OS) was 6.0 months (95% CI, 4-12); the overall 2-year OS rate was 17%. Pembrolizumab had manageable safety and clinical activity in patients with HMA-refractory MDS.This trial was registered at www.clinicaltrials.gov as #NCT01953692.

Health-related quality of life in patients with microsatellite instability-high or mismatch repair deficient metastatic colorectal cancer treated with first-line pembrolizumab versus chemotherapy (KEYNOTE-177): an open-label, randomised, phase 3 trial

BACKGROUND

In the KEYNOTE-177 study, pembrolizumab monotherapy provided statistically significant and clinically meaningful improvements in progression-free survival versus chemotherapy as first-line treatment in patients with microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer. To further support the efficacy and safety findings of the KEYNOTE-177 study, results of the health-related quality of life (HRQOL) analyses are reported here.

METHODS

KEYNOTE-177 is an open-label, randomised, phase 3 trial being done at 192 cancer centres in 23 countries, in patients aged 18 years and older with microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer, with an Eastern Cooperative Oncology Group performance status of 0 or 1, and who had not received previous systemic therapy for metastatic disease. Eligible patients were randomly assigned (1:1) centrally by use of interactive voice response or integrated web response technology to receive pembrolizumab 200 mg intravenously every 3 weeks or investigator's choice chemotherapy (mFOLFOX6 [leucovorin, fluorouracil, and oxaliplatin] or FOLFIRI [leucovorin, fluorouracil, and irinotecan] intravenously every 2 weeks with or without intravenous bevacizumab or cetuximab). Patients and investigators were not masked to treatment assignment. The primary endpoints were progression-free survival (previously reported) and overall survival (data to be reported at the time of the final analysis). HRQOL outcomes were evaluated as prespecified exploratory endpoints. The analysis population comprised all randomly assigned patients who received at least one dose of study treatment and completed at least one HRQOL assessment. HRQOL outcomes were mean change from baseline to prespecified week 18 in European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-C30) and EORTC Quality of Life Questionnaire-Colorectal 29 (EORTC QLQ-CR29) scale and item scores, and in the EuroQoL 5 Dimensions 3 Levels (EQ-5D-3L) visual analogue scale and health utility scores; the proportion of patients with improved, stable, or deteriorated scores from baseline to prespecified week 18 in EORTC QLQ-C30 scales and items; and time to deterioration in EORTC QLQ-C30 global health status/quality of life (GHS/QOL), physical functioning, social functioning, and fatigue scores and EORTC QLQ-CR29 urinary incontinence scores. The threshold for a small and clinically meaningful mean difference in EORTC QLQ-C30 score was 5-8 points. This study is registered with ClinicalTrials.gov, NCT02563002 and is ongoing; recruitment is closed.

FINDINGS

Between Feb 11, 2016, and Feb 19, 2018, 307 patients were enrolled and randomly assigned to receive pembrolizumab (n=153) or chemotherapy (n=154). The HRQOL analysis population comprised 294 patients (152 receiving pembrolizumab and 142 receiving chemotherapy). As of Feb 19, 2020, median time from randomisation to data cutoff was 32·4 months (IQR 27·7-37·8). Least squares mean (LSM) change from baseline to prespecified week 18 showed a clinically meaningful improvement in EORTC QLQ-C30 GHS/QOL scores with pembrolizumab versus chemotherapy (between-group LSM difference 8·96 [95% CI 4·24-13·69]; two-sided nominal p=0·0002). Median time to deterioration was longer with pembrolizumab versus chemotherapy for GHS/QOL (hazard ratio 0·61 [95% CI 0·38-0·98]; one-sided nominal p=0·019), physical functioning (0·50 [95% CI 0·32-0·81]; one-sided nominal p=0·0016), social functioning (0·53 [95% CI 0·32-0·87]; one-sided nominal p=0·0050), and fatigue scores (0·48 [95% CI 0·33-0·69]; one-sided nominal p<0·0001).

INTERPRETATION

Pembrolizumab monotherapy led to clinically meaningful improvements in HRQOL compared with chemotherapy in patients with previously untreated microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer. These data, along with the previously reported clinical benefits, support pembrolizumab as a first-line treatment option for this population.

FUNDING

Merck Sharp & Dohme, a subsidiary of Merck & Co, Kenilworth, NJ, USA.

Pembrolizumab plus lenalidomide and dexamethasone in treatment-naive multiple myeloma (KEYNOTE-185): subgroup analysis in Japanese patients

The global, randomized, open-label KEYNOTE-185 study closed early after an interim analysis showed an unfavorable benefit-risk profile with pembrolizumab plus lenalidomide and low-dose dexamethasone (Rd) versus Rd alone in treatment-naive, transplant-ineligible multiple myeloma. This subgroup analysis reported outcomes in the Japanese population. Patients were randomly assigned (1:1) to pembrolizumab plus Rd or Rd alone, stratified by age and International Staging System. The primary end point was progression-free survival (PFS). Fifty-two Japanese patients were randomly assigned to pembrolizumab plus Rd (n = 27) or Rd (n = 25). The median follow-up was 7.2 months (range, 0.4-13.8). The median PFS was not reached (NR); 6-month PFS was 91.2% versus 86.2% with pembrolizumab plus Rd versus Rd [hazard ratio (HR), 0.31; 95% CI, 0.06-1.63]. The median overall survival (OS) was NR; 6-month OS was 96.2% versus 95.7% with pembrolizumab plus Rd versus Rd (HR, 0.33; 95% CI, 0.03-3.72). With pembrolizumab plus Rd versus Rd, grade 3-5 adverse events occurred in 70.4% versus 69.6% of patients; serious adverse events occurred in 40.7% versus 52.5%. Although in the Japanese subgroup of KEYNOTE-185 adding pembrolizumab to Rd did not show an unfavorable risk-benefit, the analysis is limited by short follow-up and small sample size, affecting generalizability of the results.

The C-terminal tails of the mitochondrial transcription factors Mtf1 and TFB2M are part of an autoinhibitory mechanism that regulates DNA binding

The structurally homologous Mtf1 and TFB2M proteins serve as transcription initiation factors of mitochondrial RNA polymerases in Saccharomyces cerevisiae and humans, respectively. These transcription factors directly interact with the nontemplate strand of the transcription bubble to drive promoter melting. Given the key roles of Mtf1 and TFB2M in promoter-specific transcription initiation, it can be expected that the DNA binding activity of the mitochondrial transcription factors is regulated to prevent DNA binding at inappropriate times. However, little information is available on how mitochondrial DNA transcription is regulated. While studying C-terminal (C-tail) deletion mutants of Mtf1 and TFB2M, we stumbled upon a finding that suggested that the flexible C-tail region of these factors autoregulates their DNA binding activity. Quantitative DNA binding studies with fluorescence anisotropy-based titrations revealed that Mtf1 with an intact C-tail has no affinity for DNA but deletion of the C-tail greatly increases Mtf1's DNA binding affinity. Similar observations were made with TFB2M, although autoinhibition by the C-tail of TFB2M was not as complete as in Mtf1. Analysis of available TFB2M structures disclosed that the C-tail engages in intramolecular interactions with the DNA binding groove in the free factor, which, we propose, inhibits its DNA binding activity. Further experiments showed that RNA polymerase relieves this autoinhibition by interacting with the C-tail and engaging it in complex formation. In conclusion, our biochemical and structural analyses reveal autoinhibitory and activation mechanisms of mitochondrial transcription factors that regulate their DNA binding activities and aid in specific assembly of transcription initiation complexes.

Pembrolizumab plus pomalidomide and dexamethasone for patients with relapsed or refractory multiple myeloma (KEYNOTE-183): a randomised, open-label, phase 3 trial

BACKGROUND

Pomalidomide and dexamethasone is a standard of care for patients with multiple myeloma in whom bortezomib and lenalidomide treatment has failed. KEYNOTE-183 assessed efficacy and safety of pomalidomide and dexamethasone with or without pembrolizumab in patients with relapsed or refractory multiple myeloma. Here, we present the findings of an unplanned, ad-hoc interim analysis at the request of the US Food and Drug Administration (FDA).

METHODS

KEYNOTE-183 was a randomised, open-label, phase 3 trial done at 97 medical centres across 11 countries (Australia, Canada, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Spain, and USA). Patients aged at least 18 years with multiple myeloma, an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1, previously treated with at least two lines of therapy (excluding pomalidomide) and refractory to the last line were randomly assigned 1:1 to the pembrolizumab plus pomalidomide and dexamethasone group or the pomalidomide and dexamethasone group via an interactive voice response or integrated web response system. Patients received oral pomalidomide 4 mg daily on days 1-21 and oral low-dose dexamethasone 40 mg on days 1, 8, 15, and 22 in 28-day cycles, with or without intravenous pembrolizumab 200 mg every 3 weeks. The dual primary endpoints were progression-free survival and overall survival. Efficacy was assessed in all randomly assigned patients and safety was assessed in patients who received at least one dose of study treatment. The trial is registered at ClinicalTrials.gov, number NCT02576977, and it is closed for accrual.

FINDINGS

Between Jan 18, 2016, and June 7, 2017, 249 patients were randomly assigned to either the pembrolizumab plus pomalidomide and dexamethasone group (n=125) or the pomalidomide and dexamethasone group (n=124). On July 3, 2017, the FDA established that risks associated with the triple combination outweighed benefits and halted the study. Median follow-up was 8·1 months (IQR 4·5-10·9). Median progression-free survival was 5·6 months (95% CI 3·7-7·5) in the pembrolizumab plus pomalidomide and dexamethasone group versus 8·4 months (5·9-not reached) in the pomalidomide and dexamethasone group; progression-free survival estimates at 6 months were 48% (95% CI 37-58) versus 60% (49-69) at 6 months (hazard ratio [HR] 1·53; 95% CI 1·05-2·22; p=0·98). Median overall survival was not reached (95% CI 12·9-not reached) versus 15·2 months (12·7-not reached; HR 1·61; 95% CI 0·91-2·85; p=0·95); overall survival estimates at 6 months were 82% (95% CI 74-88) versus 90% (82-95). Serious adverse events occurred in 75 (63%) of 120 patients in the pembrolizumab plus pomalidomide and dexamethasone group versus 56 (46%) of 121 patients in the pomalidomide and dexamethasone group. Four (3%) treatment-related deaths occurred in the pembrolizumab plus pomalidomide and dexamethasone group (one each of unknown cause, neutropenic sepsis, myocarditis, and Stevens-Johnson syndrome); myocarditis and Stevens-Johnson syndrome were considered related to pembrolizumab. No treatment-related deaths were reported in the pomalidomide and dexamethasone group.

INTERPRETATION

The results from this unplanned, FDA-requested, interim analysis showed that the benefit-risk profile of pembrolizumab plus pomalidomide and dexamethasone is unfavourable for patients with relapsed or refractory multiple myeloma.

FUNDING

Merck Sharp & Dohme, a subsidiary of Merck & Co (Kenilworth, NJ, USA).

Targeting the paracrine hormone-dependent guanylate cyclase/cGMP/phosphodiesterases signaling pathway for colorectal cancer prevention

Colorectal cancer (CRC) is one of the leading causes of cancer related-deaths. The risk of development of CRC is complex and multifactorial, and includes disruption of homeostasis of the intestinal epithelial layer mediated though dysregulations of tumor suppressing/promoting signaling pathways. Guanylate cyclase 2C (GUCY2C), a membrane-bound guanylate cyclase receptor, is present in the apical membranes of intestinal epithelial cells and maintains homeostasis. GUCY2C is activated upon binding of paracrine hormones (guanylin and uroguanylin) that lead to formation of cyclic GMP from GTP and activation of downstream signaling pathways that are associated with normal homeostasis. Dysregulation/suppression of the GUCY2C-mediated signaling promotes CRC tumorigenesis. High-calorie diet-induced obesity is associated with deficiency of guanylin expression and silencing of GUCY2C-signaling in colon epithelial cells, leading to tumorigenesis. Thus, GUCY2C agonists, such as linaclotide, exhibit considerable role in preventing CRC tumorigenesis. However, phosphodiesterases (PDEs) are elevated in intestinal epithelial cells during CRC tumorigenesis and block GUCY2C-mediated signaling by degrading cyclic GMP to 5`-GMP. PDE5-specific inhibitors, such as sildenafil, show considerable anti-tumorigenic potential against CRC by amplifying the GUCY2C/cGMP signaling pathway, but cannot achieve complete anti-tumorigenic effects. Hence, dual targeting the elevation of cGMP by providing paracrine hormone stimuli to GUCY2C and by inhibition of PDEs may be a better strategy for CRC prevention than alone. This review delineates the involvement of the GUCY2C/cGMP/PDEs signaling pathway in the homeostasis of intestinal epithelial cells. Further, the events are associated with dysregulation of this pathway during CRC tumorigenesis are also discussed. In addition, current updates on targeting the GUCY2C/cGMP/PDEs pathway with GUCY2C agonists and PDEs inhibitors for CRC prevention and treatment are described in detail.

Using high-sensitivity sequencing for the detection of mutations in BTK and PLCγ2 genes in cellular and cell-free DNA and correlation with progression in patients treated with BTK inhibitors

Patients with chronic lymphocytic leukemia (CLL) that develop resistance to Bruton tyrosine kinase (BTK) inhibitors are typically positive for mutations in BTK or phospholipase c gamma 2 (PLCγ2). We developed a high sensitivity (HS) assay utilizing wild-type blocking polymerase chain reaction achieved via bridged and locked nucleic acids. We used this high sensitivity assay in combination with Sanger sequencing and next generation sequencing (NGS) and tested cellular DNA and cell-free DNA (cfDNA) from patients with CLL treated with the BTK inhibitor, ibrutinib. We also tested ibrutinib-naïve patients with CLL. HS testing achieved 100x greater sensitivity than Sanger. HS Sanger sequencing was capable of detecting < 1 mutant allele in background of 1000 wild-type alleles (1:1000). Similar sensitivity was achieved with HS NGS. No BTK or PLCγ2 mutations were detected in any of the 44 ibrutinib-naïve CLL patients. We demonstrate that without the HS testing 56% of positive samples would have been missed for BTK and 85% of PLCγ2 would have been missed. With the use of HS, we were able to detect multiple mutant clones in the same sample in 37.5% of patients; most would have been missed without HS testing. We also demonstrate that with HS sequencing, plasma cfDNA is more reliable than cellular DNA in detecting mutations. Our studies indicate that wild-type blocking and HS sequencing is necessary for proper and early detection of BTK or PLCγ2 mutations in monitoring patients treated with BTK inhibitors. Furthermore, cfDNA from plasma is very reliable sample-type for testing.

Abstract 1490: Potentiating immunotherapy by targeting complement deposited on cancer cell surfaces

Treatment of lymphoid malignancies with anti-CD20 antibodies (mAbs) can be frustrated by the loss of cell surface CD20 through trogocytosis, creating “escape variants” that are no longer sensitive to the anti-CD20 mAb. In patients with chronic lymphocytic leukemia (CLL) treated with the anti-CD20 mAb ofatumumab, we observed that these CD20 escape variants carried covalently bound C3d complement fragments and that these C3d opsonized CLL cells persisted for weeks in circulation. Therefore, we hypothesized that C3d is a neoantigen that could be exploited to re-target cells that have escaped from anti-CD20 mAb therapy.

To target complement opsonized cells we generated a human IgG1 mouse chimera mAb specific to C3d that is not competed by full length C3 in serum. To test whether targeting C3d can eliminate escape variants after anti-CD20 therapy, we collected blood samples from CLL patients before (day 1) and 24 hours after administration of ofatumumab (day 2). As expected, CLL cells on day 2 had lost CD20 expression and could neither bind, nor be killed by ofatumumab. In contrast, the anti-C3d mAb did not bind CLL cells obtained pre-treatment but bound cells obtained on day 2 with high affinity (kD = 6.7nM) and were effectively killed through CDC, NK cell mediated ADCC, and phagocytosis. Importantly, non B lymphocytes were neither bound nor killed by the anti-C3d mAb, consistent with the highly targeted and selective deposition of C3d on CD20+ cells by ofatumumab. Interestingly, when C3d opsonized CLL was exposed repetitively to anti-C3d mAb ex vivo, the amount of cell bound C3d and the fraction of cells killed increased with successive rounds of treatment consistent with an auto-amplification of C3d targeting.

We tested the efficacy of a chimerized anti-C3d mAb in two mouse models. First, we transferred PBMCs obtained from CLL patients on day 2 of ofatumumab treatment (containing the C3d opsonized CD20 escape variants) into NSG mice and three days later injected either isotype control mAb (trastuzumab) or anti-C3d mAb. One injection of anti-C3d mAb effectively reduced tumor burden in both peripheral blood (from 42.5 to 0.59 CLL cells/ul of blood; p&lt;0.01) and spleen (from 574 to 2.19 CLL cells/100,000 splenocytes; p&lt;0.01). Second, we subcutaneously xenografted HBL2 cells, a CD20+ mantle cell lymphoma line, into SCID mice. Mice were treated three days after cell injection with ofatumumab alone, ofatumumab and anti-C3d mAb or isotype control (trastuzumab). Caliper measurements of the tumor dimensions and survival were recorded. The combination of the anti-C3d mAb with ofatumumab extended time to tumor development and prolonged overall survival compared to ofatumumab alone (median survival 88 days vs 22 days, respectively, p&lt;0.02).

We conclude that targeting C3d deposited on cancer cells can eliminate antigen escape variants and potentiate complement fixing antibodies.

Citation Format: Elizabeth J. Carstens, Martin Skarzynski, Vicent Butera, Margaret Lindorfer, Berengere Vire, Mohammed Farooqui, Christoph Rader, Ronald Taylor, Adrian Wiestner. Potentiating immunotherapy by targeting complement deposited on cancer cell surfaces. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1490.

Treatment-resistant recurrent membranoproliferative glomerulonephritis in renal allograft responding to rituximab: case report

We report a case of idiopathic membranoproliferative glomerulonephritis (MPGN) recurring 2 years after a living-unrelated kidney transplantation. The disease was refractory to intravenous immunoglobulin and plasmapheresis. Treatment with 2 doses of rituximab resulted in remission of the disease. The disease relapsed 18 months later after an episode of cytomegalovirus pneumonitis. After treatment of the pneumonitis, a lung biopsy was performed owing to persistent chest symptoms, which revealed bronchiolitis obliterans with organizing pneumonia. Bone marrow examination and culture revealed presence of acid-fast bacilli, and culture grew Mycobacterium tuberculosis. A repeated course of rituximab was withheld because of infection with tuberculosis, the patient's chest symptoms, and rare reports of noninfectious lung disease after the use of rituximab. The patient continues to have proteinuria with impaired kidney function.

Utility of indium-111 octreotide to identify a cardiac metastasis of a carcinoid neoplasm

Carcinoid heart disease is classically described as right-sided valvular pathology. Solid cardiac metastases from carcinoid tumors are seldom reported. A multimodality imaging approach is needed to diagnose and localize this disease. Biopsy remains the gold standard to confirm the diagnosis of carcinoid. Octreotide uptake is characteristic of carcinoid tumor but not myxoma; thus, an indium-111 octreotide scan is very specific for the diagnosis of carcinoid tumor and helps in assessing the extent of carcinoid disease. We present a case in which an indium-111 octreotide scan revealed uptake in three distinct masses in the colon, liver, and right ventricle. The results of the scan were contradictory to the biopsy results, which were diagnostic for hepatic carcinoid and cardiac myxoma.

Treatment with Ibrutinib Inhibits BTK- and VLA-4-Dependent Adhesion of Chronic Lymphocytic Leukemia Cells In Vivo

PURPOSE

Ibrutinib leads to a transient lymphocytosis in patients with chronic lymphocytic leukemia (CLL) that develops within hours of starting drug and is due to the efflux of cells from lymphoid tissues into the blood. We therefore sought to investigate the in vivo effect of ibrutinib on migration and adhesion of CLL cells.

EXPERIMENTAL DESIGN

Patients received single-agent ibrutinib (420 mg daily) on an investigator-initiated phase II trial. Serial blood samples were collected pretreatment and during treatment for ex vivo functional assays.

RESULTS

Adhesion of CLL cells to fibronectin was rapidly (within hours) and almost completely inhibited (median reduction 98% on day 28, P < 0.001), while the effect on migration to chemokines was more moderate (median reduction 64%, P = 0.008) and less uniform. Although cell surface expression of key adhesion molecules such as CD49d, CD29, and CD44 were modestly reduced, this was only apparent after weeks of treatment. Stimulation of CLL cells from patients on ibrutinib with PMA, which activates PKC independent of BTK, restored the ability of the cells to adhere to fibronectin in a VLA-4-dependent manner. Finally, the addition of ibrutinib to CLL cells adhered to fibronectin in vitro caused the detachment of 17% of the cells, on average; consisten t with in vivo observations of an increasing lymphocytosis within 4 hours of starting ibrutinib.

CONCLUSIONS

Inhibition of BTK and VLA-4-dependent adhesion of CLL cells to stroma and stromal components provides a mechanistic explanation for the treatment-induced lymphocytosis and may reduce CD49d-dependent prosurvival signals in the tissue microenvironment.

Targeting deposited complement component C3d to potentiate monoclonal antibody cancer therapy (VAC3P.1057)

Treatment-induced loss of targeted cell surface antigens through trogocytosis or internalization reduces efficacy of monoclonal antibody (mAb) therapy of cancer. However, cells that escape therapy mediated by complement-fixing mAbs carry covalently deposited complement activation fragments on their cell surfaces, in particular C3d. We hypothesized that cell-associated C3d constitutes a neoantigen that could be exploited to selectively retarget cells escaping from therapeutic mAbs. We generated an anti-C3d IgG1 human/mouse chimeric mAb specific for human C3d that is not competed by C3 in human serum. For proof of concept, we used cells from chronic lymphocytic leukemia (CLL) patients that had substantially reduced CD20 levels due to treatment with the anti-CD20 mAb ofatumumab (OFA). The chimeric anti-C3d mAb bound cell surface C3d on these CLL cells ex vivo (KD = 6.7nM), and mediated complement-dependent, and antibody-dependent cellular cytotoxicity and phagocytosis in vitro. CLL cells opsonized by C3d in vivo and reacted with the anti-C3d mAb in vitro were further C3d opsonized, resulting in an amplification loop that enhanced anti-C3d mAb binding capacity and killing of target cells. In vivo, the anti-C3d mAb was effective in reducing tumor burden in blood and spleens of NSG mice xenografted with human CLL cells. Our results identify anti-C3d mAbs as a means to specifically and potently augment the therapeutic efficacy of complement-fixing mAbs.

Effects of the Bruton’s tyrosine kinase inhibitor ibrutinib on humoral immunity in patients with chronic lymphocytic leukemia (HUM1P.258)

Chronic lymphocytic leukemia (CLL) is characterized by immune dysregulation, often including hypogammaglobulinemia. Ibrutinib, a covalent inhibitor of Bruton’s tyrosine kinase (BTK), is highly active in B cell malignancies, including CLL. Inactivating mutations in BTK cause X-linked agammaglobulinemia. We evaluated the impact of ibrutinib on immunoglobulin (Ig) levels in CLL patients (pts) treated at NIH. Consistent with previous reports, IgG remained stable during the first 6 months, but decreased from a median of 707 mg/dL at baseline to 611 mg/dL at 24 months (17% reduction, n=25, p&lt;0.0001). In contrast, there was a sustained increase in IgA and a transient increase in IgM. Next, we assessed serum free light chains (FLCs) to distinguish the effects on clonal from non-clonal B cells. In κ-clonal CLL cases, the clonal (κ) FLC decreased from a median of 6.71 to 1.42 mg/dL after 6 months (n=39, p&lt;0.0001). Interestingly, the non-clonal (λ) FLC increased, suggesting the recovery of normal B cell function. Consistently, we found an increase in normal B cells in blood and bone marrow, including early B cell precursors. In comparison, CLL pts (n=16) treated with anti-CD20-based chemoimmunotherapy also showed a decrease in IgG at 24 months (12% reduction, p=0.0052), and surprisingly, an improvement in IgA levels, suggesting that the latter effect is not drug-specific but due to tumor reduction. The consequences of long-term BTK inhibition on immune function require further study.

Ibrutinib-induced lymphocytosis in patients with chronic lymphocytic leukemia: correlative analyses from a phase II study

Ibrutinib and other targeted inhibitors of B-cell receptor signaling achieve impressive clinical results for patients with chronic lymphocytic leukemia (CLL). A treatment-induced rise in absolute lymphocyte count (ALC) has emerged as a class effect of kinase inhibitors in CLL and warrants further investigation. We here report correlative studies in 64 patients with CLL treated with ibrutinib. We quantified tumor burden in blood, lymph nodes, spleen, and bone marrow, assessed phenotypic changes of circulating cells, and measured whole blood viscosity. With just one dose of ibrutinib the average increase in ALC was 66%, and in over 40% of patients the ALC peaked within 24 hours of initiating treatment. Circulating CLL cells on day 2 showed increased Ki67 and CD38 expression, indicating an efflux of tumor cells from the tissue compartments into the blood. The kinetics and degree of the treatment-induced lymphocytosis was highly variable; interestingly in patients with a high baseline ALC the relative increase was mild and resolution rapid. After two cycles of treatment the disease burden in lymph node, bone marrow, and spleen decreased irrespective of the relative change in ALC. Whole blood viscosity was dependent on both ALC and hemoglobin. No adverse events were attributed to the lymphocytosis.

Quantification of expression of antigens targeted by antibody-based therapy in chronic lymphocytic leukemia

OBJECTIVES

Anti-CD20 (rituximab), anti-CD52 (alemtuzumab), anti-CD22 (BL22, HA22), and anti-CD25 (Oncotac) are therapeutic options that are the mainstay or in preclinical development for the treatment of chronic lymphocytic leukemia (CLL). Studies suggest that levels of surface antigen expression may affect response to monoclonal antibody-based therapy.

METHODS

Using the flow cytometric Quantibrite method (BD Biosciences, San Jose, CA) to determine antibodies bound per cell, we quantified the levels of surface expression of CD20, CD22, CD25, and CD52 in CLL cells from 28 untreated patients.

RESULTS

The CLL cells in all cases expressed CD20, CD22, and CD52 but 4 (14%) cases were negative for CD25. Although the ranking of levels of expression from highest to lowest was CD52, CD20, CD22, and CD25, the level of antigen expression on any specific case could not be accurately predicted.

CONCLUSIONS

Quantification of antigens might be useful in evaluating new antigens to target for therapy and may provide a systematic approach to selecting individualized therapy in CLL.

Morphine stimulates platelet-derived growth factor receptor-β signalling in mesangial cells in vitro and transgenic sickle mouse kidney in vivo

BACKGROUND

Pain and renal dysfunction occur in sickle cell disease. Morphine used to treat pain also co-activates platelet-derived growth factor receptor-β (PDGFR-β), which can adversely affect renal disease. We examined the influence of morphine in mesangial cells in vitro and in mouse kidneys in vivo.

METHODS

> Mouse mesangial cells treated with 1 μM morphine in vitro or kidneys of transgenic homozygous or hemizygous sickle or control mice (n=3 for each), treated with morphine (0.75, 1.4, 2.14, 2.8, 3.6, and 4.3 mg kg(-1) day(-1) in two divided doses during the first, second, third, fourth, fifth, and sixth weeks, respectively), were used. Western blotting, bromylated deoxy uridine incorporation-based cell proliferation assay, reverse transcriptase-polymerase chain reaction, immunofluorescent microscopy, and blood/urine chemistry were used to analyse signalling, cell proliferation, opioid receptor (OP) expression, and renal function.

RESULTS

Morphine stimulated phosphorylation of PDGFR-β and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) to the same extent as induced by platelet-derived growth factor-BB (PDGF-BB) and promoted a two-fold increase in mesangial cell proliferation. The PDGFR-β inhibitor, AG1296, OP antagonists, and silencing of μ- and κ-OP abrogated morphine-induced MAPK/ERK phosphorylation and proliferation by ~100%. Morphine treatment of transgenic mice resulted in phosphorylation of PDGFR-β, MAPK/ERK, and signal transducer and activator of transcription 3 (Stat3) in the kidneys. Morphine inhibited micturition and blood urea nitrogen (BUN) clearance and increased BUN and urinary protein in sickle mice.

CONCLUSION

Morphine stimulates mitogenic signalling leading to mesangial cell proliferation and promotes renal dysfunction in sickle mice.

Exhaustion of cytotoxic effector systems may limit monoclonal antibody-based immunotherapy in cancer patients

The CD20 mAb ofatumumab (OFA) induces complement-mediated lysis of B cells. In an investigator-initiated phase II trial of OFA plus chemotherapy for chronic lymphocytic leukemia (CLL), OFA treatment promoted partial CLL B cell depletion that coincided with reduced complement titers. Remaining CLL B cells circulated with bound OFA and covalently bound complement breakdown product C3d, indicative of ongoing complement activation. Presumably, neither complement- nor effector cell-based mechanisms were sufficiently robust to clear these remaining B cells. Instead, almost all of the bound OFA and CD20 was removed from the cells, in accordance with previous clinical studies that demonstrated comparable loss of CD20 from B cells after treatment of CLL patients with rituximab. In vitro experiments with OFA and rituximab addressing these observations suggest that host effector mechanisms that support mAb-mediated lysis and tumor cell clearance are finite, and they can be saturated or exhausted at high B cell burdens, particularly at high mAb concentrations. Interestingly, only a fraction of available complement was required to kill cells with CD20 mAbs, and killing could be tuned by titrating the mAb concentration. Consequently, maximal B cell killing of an initial and secondary B cell challenge was achieved with intermediate mAb concentrations, whereas high concentrations promoted lower overall killing. Therefore, mAb therapies that rely substantially on effector mechanisms subject to exhaustion, including complement, may benefit from lower, more frequent dosing schemes optimized to sustain and maximize killing by cytotoxic immune effector systems.

Glomerulonephritis with crescents among adult Saudi patients outcome and its predictors

The aim of this study is to investigate the clinical and pathological features and outcome of glomerulonephritis with crescents among adult patients. This is a retrospective study of all cases of crescentic GN seen over a 9-year period (2001-2010). Histological features were assessed, and renal function at baseline and end of follow-up period was recorded. Results among different etiological groups at baseline and end of follow-up period were compared. The mean age in the whole group was 35.6 years (16.2), with the lowest mean in the lupus nephritis (LN) group [27.7 years (9.9)] and the highest in the pauciimmune glomerulonephritis (PIGN) group (P = 0.001). There were 72 cases enrolled in the study. LN accounted for 49.3% of the cases, PIGN for 26.5%, other immune complex glomerulonephritis (ICGN) for 19% and post-infectious GN accounted for 6.3% The majority (85.7%) of the patients had renal impairment at presentation (mean serum creatinine levels were 247 (85) μmol/l, 412 (75) μmol/l and 230 (141) μmol/l in LN, PICN and ICGN, respectively (P = 0.05). Women accounted for 85.3, 76.5 and 36.2% of the patients in LN, PICN and ICGN, respectively (P = 0.025). By the end of the follow-up period of 26 (22.9) months, 25.8% of the patients were requiring dialysis (16.70% in the LN group, 50% in PIGN and 25% in ICGN (P = 0.05) and 21.7% had nephrotic range proteinuria (16.7, 1 and 33.3%, respectively (P = 0.4). Using logistic multivariate analysis, the only independent factors found to predict need for dialysis of prognosis were percent of sclerosed glomeruli (P = 0.05) and presence of ATN (P = 0.028). Baseline proteinuria or SCr, gender and number of glomeruli with crescents, on the other hand, did not impact prognosis. Using linear regression multivariate analysis, SCr, protein excretion and activity score at biopsy did not influence change in SCr or final SCr during the follow-up period. Using ANOVA to compare the groups of LN, PIGN and ICGN), we found significant differences only in gender between LN and ICGN (P = 0.035), in percent glomerular global sclerosis (between LN and PIGN (P = 0.007) and between LN and ICGN (P = 0.012) and in age (between LN and PIGN (P = 0.006). Almost half of our patients with CrGN were due to LN which is higher than that reported by others where PIGN was the more prevalent etiology. Patients with PICN were older and had worse prognosis. This could be explained by the higher number of globally sclerosed glomeruli in the PIGN group.

Activation of CD44, a receptor for extracellular matrix components, protects chronic lymphocytic leukemia cells from spontaneous and drug induced apoptosis through MCL-1

Survival of chronic lymphocytic leukemia (CLL) cells in vivo is supported by the tissue microenvironment, which includes components of the extracellular matrix. Interactions between tumor cells and the extracellular matrix are in part mediated by CD44, whose principal ligand is hyaluronic acid. Here, we show that CD44 is more highly expressed on CLL cells of the clinically more progressive immunglobulin heavy chain variable gene (IGHV)-unmutated subtype than on cells of the IGHV-mutated type. Engagement of CD44 activated the phosphatidylinositol 3-kinase (PI3K)/AKT and mitogen activated protein kinase (MAPK)/ERK pathways and increased myeloid cell leukemia sequence 1 (MCL-1) protein expression. Consistent with the induction of these anti-apoptotic mechanisms, CD44 protected CLL cells from spontaneous and fludarabine-induced apoptosis. Obatoclax, an antagonist of MCL-1, blocked the pro-survival effect of CD44. In addition, obatoclax synergized with fludarabine to induce apoptosis of CLL cells. In conclusion, components of the extracellular matrix may provide survival signals to CLL cells through engagement of CD44. Inhibition of MCL-1 is a promising strategy to reduce the anti-apoptotic effect of the microenvironment on CLL cells.

Abstract 5080: Improved ZAP-70 assay using two clones: Multiple methods of analysis, and a scoring system

Background. ZAP-70 expression is a stage independent prognostic marker in CLL. However, inter-laboratory variation is large and there is neither a consensus nor method that has been approved by regulatory authorities.

Methods. Multicolor flow-cytometric expression of ZAP-70 was tested in 45 untreated-CLL patients. Two anti-ZAP70 clones (1E7.2 and SBZAP) were compared. Nine different methods were evaluated: M1 using the isotype control; M2 internal residual T-cell to determine positive; M3, normal donor (ND) T-cell to determine positive; M4 internal T-cell/clone ratio; M5, ND residual T-cell/clone ratio; M6 clone/normal remaining B-cell ratio; M7 clone/ND B- cell ratio; M8 CLL- Z score; M9 modified CLL-Z score. Four methods were selected for designation of a scoring system integrating both clones for ZAP-70 assignment. For a given specimen, each method of analysis was given a score of 1 point if it was positive, and 0 point if it was negative. We considered the cases that show no or one positive method (score 0 or 1) as negative, the cases that showed positivity by two method (score 2) as equivocal, and those with three or four positive methods (score 3 or 4) as positive. This score was calculated for each clone separately and then integrating both clones together. A correlation analysis between IGHV mutational status, FISH, and ZAP-70 score was undertaken.

Results. The correlation coefficients between clones for the four selected statistically significant methods were as follows: M1 0.71, M3 0.72, M7 0.67 and M9 0.64. The two reagents showed agreement using the designed scoring system for 37/45 samples (82%) while 8/45 (18%) showed an equivocal result with one of the two clones. Seven of the eight equivocal samples were resolved using the combined scoring system. For both clones, ZAP-70 expression was significantly correlated with IGHV mutational status with all four methods selected for analysis. The scoring system for a single reagent favored the use of multiple methods of analysis. Furthermore, the combined score indicated a substantial enhancement over the use of a single reagent (p value of 0.0003). Regarding FISH cytogenetics, the absence of ZAP-70 expression correlated with del13q14 (p=0.0049), while the presence of ZAP-70 expression correlated with trisomy 12 (p=0.011) using our designated ZAP-70 score. Conclusions: The use of two independent ZAP-70 reagents increases analytical certitude and the scoring method aids in the resolution of equivocal results. The combined use of two reagents, four methods of analysis, and a scoring system allowed for assignment of ZAP-70 expression in 44/45 samples tested and improved performance of this important prognostic assay. ZAP-70 expression was a good predictor of the IGHV mutational status and 13q14 del/trisomy 12. The correlation analysis confirms that the use of four methods of analysis with a single reagent or both reagents is superior to the use of a single method of analysis

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5080. doi:10.1158/1538-7445.AM2011-5080

Standard clinical practice underestimates the role and significance of erythropoietin deficiency in sickle cell disease

In sickle cell disease (SCD), vigorous reticulocytosis is required to partially compensate for chronic hemolytic anaemia. Consequently, early renal damage, insufficient to cause azotemia but sufficient to cause erythropoietin deficiency and chronic relative reticulocytopenia (chRR), could have severe clinical consequences. chRR was defined as reticulocytes <250×10(9) /l despite haemoglobin <9 g/dl on ≥ two occasions ≥4 weeks apart. The influence of multiple variables including chRR on time from first clinic visit to death was evaluated in 306 SCD patients. In univariate analyses, fetal haemoglobin, indices of renal damage (serum creatinine, proteinuria), chRR and age, were associated with rate of death. In multivariate analysis, only age and chRR (Hazard ratio 3·6, 95% CI 2·049-6·327, P<0·0001) were significant, underlining that chRR could be an early and important clinical consequence of renal damage. Even in chRR patients with normal serum creatinine levels, low haemoglobin and low reticulocyte counts were associated with low erythropoietin levels. In the general population, evaluation of erythropoietin levels is prompted by the combination of anaemia and abnormal serum creatinine. In SCD patients, this standard approach can miss a substantial risk factor for early death. chRR could be a practical and important criterion for diagnosis of erythropoietin deficiency in SCD.

The orphan nuclear receptor TR2 interacts directly with both class I and class II histone deacetylases

A combination of in vivo and in vitro assays was employed to describe the ligand-independent interaction of the orphan nuclear receptor TR2 and histone deacetylase proteins. The repressive effect of TR2 on transcription of a luciferase reporter driven by a promoter containing a direct repeat-5 (DR5) derived from the human RARbeta gene was suppressed by the addition of the histone deacetylase inhibitor trichostatin A. Immunoprecipitation with FLAG-epitope (MDYKDDDDK)-tagged histone deacetylase proteins was used to demonstrate that TR2 and histone deacetylases 3 or 4 are present in the same immunoprecipitated complex. Deacetylase activity was demonstrated for these coimmunoprecipitates, further confirming the in vivo interaction of TR2 and histone deacetylases. Immunoprecipitation with anti-TR2 antibody was used to demonstrate interaction of TR2 with endogenously expressed histone deacetylases 3 and 4 in COS-1 cells. Dissection of TR2 domains showed that the DNA binding domain of the receptor was responsible for interaction with both histone deacetylases 3 and 4 in glutathione-S-transferase pull-down assays, while the ligand binding domain did not interact. The pull-down data were confirmed with far Western blots that also showed a direct interaction between labeled histone deacetylase proteins and TR2. It is suggested that repression mediated by unliganded TR2 is mediated, in part, by a direct interaction of this receptor with histone deacetylase proteins.

Increased levels of serum hepatocyte growth factor in patients with end-stage renal disease

Blood levels of hepatocyte growth factor (HGF) have been found to be elevated in patients with chronic renal failure. The cause of the increase in this mitogen is unclear. We determined serum HGF levels in 34 patients on maintenance dialysis and ten healthy volunteers. Predialysis serum HGF levels were elevated in patients with end-stage renal disease as compared to control subjects (1.65 +/- 0.2 ng/mL vs 0.46 +/- 0.04 ng/mL, p<0.01). In addition, serum HGF levels were significantly higher in African-American dialysis patients compared to Caucasian patients (2.18 +/- 0.36ng/mL vs 1.18 +/- 0.12ng/mL, p<0.01). The observed differences could not be accounted for by variations in serum creatinine, serumalbumin, or blood pressure between the African-American and Caucasian patients. Serum HGF levels were elevated in patients with end-stage renal disease, and were higher in African-American than Caucasian patients, but the pathophysiology and significance of this finding remain unclear.

Ligand-dependent formation of retinoid receptors, receptor-interacting protein 140 (RIP140), and histone deacetylase complex is mediated by a novel receptor-interacting motif of RIP140

Receptor-interacting protein 140 (RIP140) interacts with retinoic acid receptor and retinoid X receptor in a ligand-dependent manner and suppresses retinoic acid (RA) induction of its target genes. The receptor-interacting motif is mapped to a C-terminal peptide sequence (LTKTNPILYYMLQK) of RIP140. The functional role of this motif in mediating the suppressive effects of RIP140 on RA induction is demonstrated in mutation studies. RA induces coimmunoprecipitation of histone deacetylase 3 with retinoic acid receptor/retinoid X receptor in the presence of wild type RIP140, but not in the presence of the C-terminal motif-deleted RIP140. A decrease in histone acetylation on the promoter region that carries a RA response element is associated with the expression of wild type RIP140, but not with expression of the mutant RIP140, in a dose-dependent manner. These data provide a molecular explanation for RIP140 acting as a novel ligand-dependent, negative modulator of RA-regulated gene expression.

Receptor-interacting protein 140 directly recruits histone deacetylases for gene silencing

Receptor-interacting protein 140 (RIP140) encodes a histone deacetylase (HDAC) inhibitor-sensitive repressive activity. Direct interaction of RIP140 with HDAC1 and HDAC3 occurs in vitro and in vivo as demonstrated in co-immunoprecipitation and glutathione S-transferase pull-down experiments. The HDAC-interacting domain of RIP140 is mapped to its N-terminal domain, between amino acids 78 and 303 based upon glutathione S-transferase pull-down experiments. In chromatin immunoprecipitation assays, it is demonstrated that histone deacetylation occurs at the chromatin region of the Gal4 binding sites as a result of Gal4 DNA binding domain-tethered RIP expression. The immunocomplexes of RIP140 from cells transfected with RIP140 and HDAC are able to deacetylate histone proteins in vitro. This study presents the first evidence for RIP140 as a negative coregulator for nuclear receptor actions by directly recruiting histone deacetylases and categorizes RIP140 as a novel negative coregulator that is able to directly interact with HDACs.