Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma, Version 2.2024

Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are essentially different manifestations of the same disease that are similarly managed. A number of molecular and cytogenetic variables with prognostic implications have been identified. Undetectable minimal residual disease at the end of treatment with chemoimmunotherapy or venetoclax-based combination regimens is an independent predictor of improved survival among patients with previously untreated or relapsed/refractory CLL/SLL. The selection of treatment is based on the disease stage, presence or absence of del(17p) or TP53 mutation, immunoglobulin heavy chain variable region mutation status, patient age, performance status, comorbid conditions, and the agent's toxicity profile. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with CLL/SLL.

A phase 1b study of zilovertamab in combination with paclitaxel for locally advanced/unresectable or metastatic Her2-negative breast cancer

BACKGROUND

Zilovertamab is a humanized monoclonal antibody targeting ROR1, an onco-embryonic antigen expressed by malignant cells of a variety of solid tumors, including breast cancer. A prior phase 1 study showed that zilovertamab was well tolerated and effective in inhibiting ROR1-signaling, which leads to activation of ERK1/2, NF-κB, and NRF2 target genes. This phase 1b study evaluated the safety and tolerability of zilovertamab with paclitaxel in patients with advanced breast cancer.

PATIENTS AND METHODS

Eligible patients had locally advanced, unresectable, or metastatic HER2- breast cancer with Eastern Cooperative Group performance status of 0-2 and without prior taxane therapy in the advanced setting. Study treatment included 600 mg of zilovertamab administered intravenously (IV) on Days 1 and 15 of Cycle 1 and then Day 1 of each 28-day cycle along with paclitaxel weekly at 80 mg/m2 IV.

RESULTS

Study patients had received a median of 4 prior therapies (endocrine therapy + chemotherapy) for locally advanced, unresectable, or metastatic disease. No patient discontinued therapy due to toxicity ascribed to zilovertamab. Adverse events were consistent with the known safety profile of paclitaxel. Of 16 patients, 6 (38%) had a partial response, and 6/16 (38%) patients had stable disease as best tumor response.

CONCLUSION

The combination of zilovertamab and paclitaxel was safe and well tolerated in heavily pre-treated advanced breast cancer patients. Further evaluation of ROR1 targeting in breast cancer patients with zilovertamab is warranted.

TRIAL REGISTRATION

NCT02776917. Registered on ClinicalTrials.gov on 05/17/2016.

A + AVD for Treatment of Hodgkin Lymphoma Variant of Richter's Transformation

Hodgkin lymphoma variant of Richter's transformation (HvRT) is a rare complication for patients with chronic lymphocytic leukemia (CLL), with an overall poor prognosis. We present the first known case series of patients with HvRT treated with the combination of brentuximab vedotin, doxorubicin, vinblastine, and dacarbazine (A + AVD). In our series of 4 patients, two patients treated with A + AVD for HvRT had durable remissions of 40 and 42 months, while two patients had disease progression and ultimately died. Continued investigation into the optimal management for patients with HvRT is still needed.

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.

Outcomes in Patients with High-Risk Features after Fixed-Duration Ibrutinib plus Venetoclax: Phase II CAPTIVATE Study in First-Line Chronic Lymphocytic Leukemia

PURPOSE

The CAPTIVATE study investigated first-line ibrutinib plus venetoclax for chronic lymphocytic leukemia in 2 cohorts: minimal residual disease (MRD)-guided randomized discontinuation (MRD cohort) and Fixed Duration (FD cohort). We report outcomes of fixed-duration ibrutinib plus venetoclax in patients with high-risk genomic features [del(17p), TP53 mutation, and/or unmutated immunoglobulin heavy chain (IGHV)] in CAPTIVATE.

PATIENTS AND METHODS

Patients received three cycles of ibrutinib 420 mg/day then 12 cycles of ibrutinib plus venetoclax (5-week ramp-up to 400 mg/day). FD cohort patients (n = 159) received no further treatment. Forty-three MRD cohort patients with confirmed undetectable MRD (uMRD) after 12 cycles of ibrutinib plus venetoclax received randomized placebo treatment.

RESULTS

Of 195 patients with known status of genomic risk features at baseline, 129 (66%) had ≥1 high-risk feature. Overall response rates were >95% regardless of high-risk features. In patients with and without high-risk features, respectively, complete response (CR) rates were 61% and 53%; best uMRD rates: 88% and 70% (peripheral blood) and 72% and 61% (bone marrow); 36-month progression-free survival (PFS) rates: 88% and 92%. In subsets with del(17p)/TP53 mutation (n = 29) and unmutated IGHV without del(17p)/TP53 mutation (n = 100), respectively, CR rates were 52% and 64%; uMRD rates: 83% and 90% (peripheral blood) and 45% and 80% (bone marrow); 36-month PFS rates: 81% and 90%. Thirty-six-month overall survival (OS) rates were >95% regardless of high-risk features.

CONCLUSIONS

Deep, durable responses and sustained PFS seen with fixed-duration ibrutinib plus venetoclax are maintained in patients with high-risk genomic features, with similar PFS and OS to those without high-risk features. See related commentary by Rogers, p. 2561.

Association of baseline ROR1 and ROR2 gene expression with clinical outcomes in the I-SPY2 neoadjuvant breast cancer trial

PURPOSE

ROR1 and ROR2 are Type 1 tyrosine kinase-like orphan receptors for Wnt5a that are associated with breast cancer progression. Experimental agents targeting ROR1 and ROR2 are in clinical trials. This study evaluated whether expression levels of ROR1 or ROR2 correlated with one another or with clinical outcomes.

METHODS

We interrogated the clinical significance of high-level gene expression of ROR1 and/or ROR2 in the annotated transcriptome dataset from 989 patients with high-risk early breast cancer enrolled in one of nine completed/graduated/experimental and control arms in the neoadjuvant I-SPY2 clinical trial (NCT01042379).

RESULTS

High ROR1 or high ROR2 was associated with breast cancer subtypes. High ROR1 was more prevalent among hormone receptor-negative and human epidermal growth factor receptor 2-negative (HR-HER2-) tumors and high ROR2 was less prevalent in this subtype. Although not associated with pathologic complete response, high ROR1 or high ROR2 each was associated with event-free survival (EFS) in distinct subtypes. High ROR1 associated with a worse EFS in HR + HER2- patients with high post-treatment residual cancer burden (RCB-II/III) (HR 1.41, 95% CI = 1.11-1.80) but not in patients with minimal post-treatment disease (RCB-0/I) (HR 1.85, 95% CI = 0.74-4.61). High ROR2 associated with an increased risk of relapse in patients with HER2 + disease and RCB-0/I (HR 3.46, 95% CI = 1.33-9.020) but not RCB-II/III (HR 1.07, 95% CI = 0.69-1.64).

CONCLUSION

High ROR1 or high ROR2 distinctly identified subsets of breast cancer patients with adverse outcomes. Further studies are warranted to determine if high ROR1 or high ROR2 may identify high-risk populations for studies of targeted therapies.

Abstract 1789: Pre-clinical studies to advance anti-ROR1 CAR-T cell therapy for metastatic prostate cancer

Background: Alterations in WNT signaling are frequently associated with tumorigenesis and metastasis in many cancers including prostate cancer (PCa). The Wnt ligand, WNT5A, is required for normal prostate gland development and is increased in bone metastatic, castration resistant PCa (CRPC) patients. WNT5A signaling is mediated in part through ROR1, a non-canonical Wnt receptor and fetal oncoprotein for which the therapeutic inhibitory antibody, Zilovertamab, has been developed. Its safety has been clinically proven in trials for chronic lymphocytic leukemia (CLL) and metastatic breast cancer. We sought to investigate Zilovertamab-based anti-ROR1 therapies for metastatic prostate cancer.Our Hypothesis is that WNT5A may activate a stem-cell-like program via ROR1 which leads to therapy resistance in metastatic prostate cancer. The anti-ROR1 biologic, Zilovertamab, may inhibit this mechanism of resistance. The expression of ROR1 on CRPC and NEPC tumors and its lack of expression on normal adult tissues makes it a promising CART cell target.

Methods: We used the patient-derived xenograft (PDX), PCSD13, small cell bone metastatic prostate cancer model and the neuroendocrine PCa cell lines, PC3 and DU145, to test the effect of Zilovertamab and Zilovertamab-CART cells in vitro using the real time cell viability, proliferation, and cell cycle tracking assays in an Incucyte S3. We used in vivo bioluminescence and tumor caliper measurements to monitor effects in vivo.

Results: Studies using RNASeq, qRT-PCR, FACS and Westerns showed high expression of ROR1 in PC3, DU145, and in PCSD13. CRISPR-Cas9 Knock out of ROR1 in PC3 and DU145 cells showed increased inhibition of proliferation at lower docetaxel concentrations. Treatment of PCSD13 PDX in vivo with Zilovertamab increased docetaxel-mediated tumor growth inhibition. Mice bearing PC3 xenografts injected intravenously with Zilovertamab anti-ROR1 CAR-T cells showed durable, tumor ablation in 67% of mice compared to 22% of mice injected with activated T cells from the same donor and 0% of untreated mice. Survival of mice at Day 70 injected with CART was 78% compared to 0% of mice injected with control donor T cells and 0% of untreated mice. Zilovertamab antibody could inhibit Zilovertamab CART cell tumor cell killing.

Conclusions: ROR1 was expressed at high levels on castration resistant small cell PCa and neuroendocrine PCa cell lines and PDX models. Zilovertamab synergized with docetaxel to inhibit tumor growth in patient derived xenograft in vivo and in organoid cultures. Zilovertamab-based CART cells durably eradicated ROR1+ prostate cancer xenograft tumors. These studies supported the recently launched Phase 1b clinical trial of Zilovertamab plus docetaxel in metastatic CRPC patients. Clinical development of GMP Zilovertamab CART cells for a clinical trial in CLL is in progress and may lead to rapid progression to a clinical trial for metastatic CRPC and NEPC.

Citation Format: Christina A.M. Jamieson, Jamillah Murtadha, Christopher S. Oh, Michelle Muldong, Evodie Koutouan, JOngwook Kim, Niloofar Etemadfard, Hae Soo Choo, Navyaa Sinha, Sanghee Lee, Christina Wu, Gabriel Pineda, Kathleen Lennon, Karl Willert, Catriona H. Jamieson, Terry Gaasterland, Rana Mckay, Christopher J. Kane, Thomas J. Kipps, Anna A. Kulidjian, Nicholas A. Cacalano, Charles Prussak. Pre-clinical studies to advance anti-ROR1 CAR-T cell therapy for metastatic prostate cancer [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 1789.

Many People With Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma Benefit From Ibrutinib Treatment Up To 8 Years: A Plain Language Summary

WHAT IS THIS SUMMARY ABOUT?

This is a plain language summary of a publication describing long-term results from the RESONATE-2 study with up to 8 years of follow-up. The original paper was published in Blood Advances in June 2022.

WHAT WERE THE RESULTS?

Researchers looked at 269 adults with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) who had not received any treatment for their CLL/SLL. Study participants were randomly divided into two groups: 136 participants received treatment with a drug called ibrutinib, and 133 participants received treatment with a drug called chlorambucil. Participants in the study were treated and followed for up to 8 years, with results showing that more participants who took ibrutinib (59%) were alive without worsening of their disease at 7 years after starting treatment than participants who took chlorambucil (9%). Almost half of the participants (42%) were able to stay on ibrutinib treatment for up to 8 years.

WHAT DO THE RESULTS OF THE STUDY MEAN?

In people with CLL or SLL, more participants who were taking ibrutinib were alive without worsening of their disease after 7 years compared with participants who took chlorambucil. Clinical Trial Registration: NCT01722487 (ClinicalTrials.gov) Clinical Trial Registration: NCT01724346 (ClinicalTrials.gov).

Evolutionary history of transformation from chronic lymphocytic leukemia to Richter syndrome

Richter syndrome (RS) arising from chronic lymphocytic leukemia (CLL) exemplifies an aggressive malignancy that develops from an indolent neoplasm. To decipher the genetics underlying this transformation, we computationally deconvoluted admixtures of CLL and RS cells from 52 patients with RS, evaluating paired CLL-RS whole-exome sequencing data. We discovered RS-specific somatic driver mutations (including IRF2BP2, SRSF1, B2M, DNMT3A and CCND3), recurrent copy-number alterations beyond del(9p21)(CDKN2A/B), whole-genome duplication and chromothripsis, which were confirmed in 45 independent RS cases and in an external set of RS whole genomes. Through unsupervised clustering, clonally related RS was largely distinct from diffuse large B cell lymphoma. We distinguished pathways that were dysregulated in RS versus CLL, and detected clonal evolution of transformation at single-cell resolution, identifying intermediate cell states. Our study defines distinct molecular subtypes of RS and highlights cell-free DNA analysis as a potential tool for early diagnosis and monitoring.

Utility of measurable residual disease for predicting treatment outcomes with BCR- and BCL2-Targeted therapies in patients with CLL

Inhibitors targeting B-cell receptor (BCR) signaling pathway proteins and B-cell lymphoma-2 (BCL2) in chronic lymphocytic leukemia (CLL) are recommended in the first-line and relapsed/refractory disease settings. Measurable residual disease (MRD) is an important prognostic tool in patients treated with the BCL2-targeted agent, venetoclax. We explored the relationship between MRD status and progression-free (PFS)/overall survival (OS) in patients with CLL, following treatment with novel BCR- and BCL2-targeted agents. Compared with chemoimmunotherapy, higher rates of undetectable (u)MRD were achieved with BCL2-targeted therapies; achieving uMRD status was associated with longer PFS and OS than MRD-positivity. Continuous treatment with BCR-targeted agents did not achieve uMRD status in many patients, and outcomes were not correlated with uMRD status. Future clinical trials of targeted treatment combinations could be designed to demonstrate uMRD as a treatment objective, and allow a response-driven, personalized strategy to optimize treatment and improve OS outcomes.

Molecular map of chronic lymphocytic leukemia and its impact on outcome

Recent advances in cancer characterization have consistently revealed marked heterogeneity, impeding the completion of integrated molecular and clinical maps for each malignancy. Here, we focus on chronic lymphocytic leukemia (CLL), a B cell neoplasm with variable natural history that is conventionally categorized into two subtypes distinguished by extent of somatic mutations in the heavy-chain variable region of immunoglobulin genes (IGHV). To build the 'CLL map,' we integrated genomic, transcriptomic and epigenomic data from 1,148 patients. We identified 202 candidate genetic drivers of CLL (109 new) and refined the characterization of IGHV subtypes, which revealed distinct genomic landscapes and leukemogenic trajectories. Discovery of new gene expression subtypes further subcategorized this neoplasm and proved to be independent prognostic factors. Clinical outcomes were associated with a combination of genetic, epigenetic and gene expression features, further advancing our prognostic paradigm. Overall, this work reveals fresh insights into CLL oncogenesis and prognostication.

ROR1: an orphan becomes apparent

Since its initial identification in 1992 as a possible class 1 cell-surface receptor without a known parent ligand, receptor tyrosine kinase-like orphan receptor 1 (ROR1) has stimulated research, which has made apparent its significance in embryonic development and cancer. Chronic lymphocytic leukemia (CLL) was the first malignancy found to have distinctive expression of ROR1, which can help distinguish leukemia cells from most noncancer cells. Aside from its potential utility as a diagnostic marker or target for therapy, ROR1 also factors in the pathophysiology of CLL. This review is a report of the studies that have elucidated the expression, biology, and evolving strategies for targeting ROR1 that hold promise for improving the therapy of patients with CLL or other ROR1-expressing malignancies.

Abstract A13: Evolutionary history of transformation from chronic lymphocytic leukemia to Richter syndrome

Richter syndrome (RS), an aggressive lymphoma that develops in patients with chronic lymphocytic leukemia (CLL), is a striking example of histologic transformation. While recent therapeutic advances have transformed the treatment landscape of CLL and lymphoma, RS remains associated with dismal overall survival. Despite an advanced genomic and molecular characterization of CLL over the past decade, the current understanding of the genetic factors driving evolution of CLL to RS is limited. To decipher the genetics underlying this transformation, we have performed an integrative analysis of exome, genome and transcriptome data generated from matched RS and CLL samples from a discovery cohort of 53 patients with newly diagnosed RS of DLBCL histology. Through computational deconvolution of CLL and RS clones, we constructed phylogenetic relationships and traced evolution of CLL to RS, confirming both clonal related (87%) and unrelated cases (13%). In addition to identifying recognized RS-risk genetic lesions, we discovered novel RS-specific alterations, including 5 putative somatic driver genes (IRF2BP2, SRSF1, B2M, DNMT3A and EZH2), frequent copy number alterations beyond del(9p21)(CDKN2A/B), (including amp(7q21.2) (CDK6), amp(9p24) (PDL1/L2), and amp(1q23)(MCL1)), and recurrent whole genome duplication and chromothripsis. Integration of exome and genome sequencing data led to the identification of distinct molecular subtypes of RS with prognostic importance. To confirm these molecular subtypes, a validation cohort of 47 RS cases has been assembled with paired exome and transcriptome data. To further investigate the stepwise clonal evolution of CLL to RS, we performed single-cell RNA-sequencing on biopsy samples obtained at diagnosis from 5 individuals with clonally related transformation. Using a novel tool, CNVSingle, we inferred allele specific single-cell copy number alterations that enabled identification of the single-cell clusters representing distinct CLL and RS genetic subclones as well as intermediate, or transitional, evolutionary states. RS cells displayed gene expression enriched in pathways of MYC targets and cell cycle, in line with similar analysis on bulk transcriptomes. Finally, by ultra-low pass (ULP)-WGS sequencing of plasma samples from RS patients, we demonstrate detection of RS tumor DNA in plasma months prior to initial clinical diagnosis (n=3 of 6) or post-allogeneic stem cell transplant relapse (n=2 of 2). cfDNA is thus a promising tool for early detection of emerging RS and RS relapse as well as for non-invasive detection surrounding diagnosis. Altogether, our study defines RS-specific alterations and provides a molecular definition of RS, identifies distinct genetic subtypes of RS with prognostic significance, traces the evolutionary path to RS and suggests future strategies for improved detection.

Citation Format: Erin M Parry, Ignaty Leshchiner, Romain Guieze, Connor Johnson, Eugen Tausch, Sameer A Parikh, Camilla K Lemvigh, Conor Messer, Filippo Utro, Chaya Levovitz, Kahn Rhrissorrakrai, Matthew S Davids, Julien Broseus, Shuqiang Li, Ziao Lin, Binyamin A Knisbacher, Christof Schneider, Laura Z Rassenti, Thomas J Kipps, Nitin Jain, William Wierda, Florence Cymbalista, Neil E Kay, Kenneth J Livak, Brian P Danysh, Chip Stewart, Donna Neuberg, Jennifer R Brown, Laxmi Paridi, Stephan Stilgenbauer, Gaddy Getz, Catherine Wu. Evolutionary history of transformation from chronic lymphocytic leukemia to Richter syndrome [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A13.

Enduring undetectable MRD and updated outcomes in relapsed/refractory CLL after fixed-duration venetoclax-rituximab

The MURANO trial (A Study to Evaluate the Benefit of Venetoclax Plus Rituximab Compared With Bendamustine Plus Rituximab in Participants With Relapsed or Refractory Chronic Lymphocytic Leukemia [CLL]; ClinicalTrials.gov identifier #NCT02005471) reported superior progression-free survival (PFS) and overall survival (OS) with venetoclax-rituximab (VenR) vs bendamustine-rituximab (BR) in relapsed/refractory (R/R) CLL. Patients were randomized to 2 years of VenR (n = 194; rituximab for the first 6 months) or 6 months of BR (n = 195). Although undetectable minimal residual disease (uMRD) was achieved more often with VenR, the long-term implications of uMRD with this fixed-duration, chemotherapy-free regimen have not been explored. We report MRD kinetics and updated outcomes with 5 years' follow-up. Survival benefits with VenR vs BR were sustained (median PFS [95% confidence interval]: 53.6 [48.4, 57.0] vs 17.0 [15.5, 21.7] months, respectively, P < .0001; 5-year OS [95% confidence interval]: 82.1% [76.4, 87.8] vs 62.2% [54.8, 69.6], P < .0001). VenR was superior to BR, regardless of cytogenetic category. VenR-treated patients with uMRD at end of treatment (EOT; n = 83) had superior OS vs those with high-MRD+ (n = 12): 3-year post-EOT survival rates were 95.3% vs 72.9% (P = .039). In those with uMRD at EOT, median time to MRD conversion was 19.4 months. Of 47 patients with documented MRD conversion, 19 developed progressive disease (PD); median time from conversion to PD was 25.2 months. A population-based logistic growth model indicated slower MRD median doubling time post-EOT with VenR (93 days) vs BR (53 days; P = 1.2 × 10-7). No new safety signals were identified. Sustained survival, uMRD benefits, and durable responses support 2-year fixed-duration VenR treatment in R/R CLL.

Impact of the Types and Relative Quantities of IGHV Gene Mutations in Predicting Prognosis of Patients With Chronic Lymphocytic Leukemia

Patients with CLL with mutated IGHV genes (M-CLL) have better outcomes than patients with unmutated IGHVs (U-CLL). Since U-CLL usually express immunoglobulins (IGs) that are more autoreactive and more effectively transduce signals to leukemic B cells, B-cell receptor (BCR) signaling is likely at the heart of the worse outcomes of CLL cases without/few IGHV mutations. A corollary of this conclusion is that M-CLL follow less aggressive clinical courses because somatic IGHV mutations have altered BCR structures and no longer bind stimulatory (auto)antigens and so cannot deliver trophic signals to leukemic B cells. However, the latter assumption has not been confirmed in a large patient cohort. We tried to address the latter by measuring the relative numbers of replacement (R) mutations that lead to non-conservative amino acid changes (Rnc) to the combined numbers of conservative (Rc) and silent (S) amino acid R mutations that likely do not or cannot change amino acids, "(S+Rc) to Rnc IGHV mutation ratio". When comparing time-to-first-treatment (TTFT) of patients with (S+Rc)/Rnc ≤ 1 and >1, TTFTs were similar, even after matching groups for equal numbers of samples and identical numbers of mutations per sample. Thus, BCR structural change might not be the main reason for better outcomes for M-CLL. Since the total number of IGHV mutations associated better with longer TTFT, better clinical courses appear due to the biologic state of a B cell having undergone many stimulatory events leading to IGHV mutations. Analyses of larger patient cohorts will be needed to definitively answer this question.

Abstract CT028: Fixed-duration (FD) ibrutinib (Ibr) + venetoclax (Ven) for first-line treatment of chronic lymphocytic leukemia (CLL) in patients (pts) with high-risk features: phase 2 CAPTIVATE study

Background: CAPTIVATE (PCYC-1142; NCT02910583) is an international, multicenter phase 2 study of first-line Ibr + Ven in CLL with 2 cohorts: the Minimal Residual Disease (MRD) and FD cohorts. FD Ibr + Ven provides deep, durable responses (Ghia, ASCO 2021; Wierda, J Clin Oncol 2021). Here, we report efficacy and safety of FD Ibr + Ven in pts with high-risk features.

Methods: Pts aged ≤70 y with previously untreated CLL received 3 cycles of Ibr then 12 cycles of Ibr + Ven (Ibr 420 mg/d orally; Ven ramp-up to 400 mg/d orally). Pts in the FD cohort received no further treatment. Pts in the MRD cohort were randomized to subsequent treatment according to MRD status, including a placebo arm for pts who achieved confirmed undetectable MRD (uMRD) with 12 cycles of Ibr + Ven. Data from the FD cohort and MRD cohort placebo arm were pooled for pts with high-risk features (del(17p), TP53 mutated, or unmutated IGHV) treated with FD Ibr + Ven.

Results: Of 202 pts treated with FD Ibr + Ven in the FD cohort (n=159) or MRD cohort placebo arm (n=43), 129 pts had high-risk features (Table). Median time on study for these pts was 28.7 mo (range 0.8-45.1). 94% of pts completed planned treatment with Ibr and Ven. Median treatment duration was 13.8 mo (range 0.7-24.9) for Ibr and 11.1 mo (range 9.9-22.1) for Ven. Best response rates of CR and uMRD in peripheral blood and bone marrow were high (Table). The 18-mo landmark estimate for duration of CR was 95%. 24-mo PFS rate was 94%, which was similar to pts without high-risk features (97%). Only 3% of pts discontinued Ibr or Ven due to AEs. The AE profile of Ibr + Ven in pts with high-risk features showed no new safety findings for this FD regimen (Table).

Conclusion: First-line Ibr + Ven for a fixed duration provides durable treatment-free remissions and sustained PFS in pts with CLL. These clinical outcomes are maintained in pts with high-risk features, with PFS rates that were similar to pts without high-risk features.

Table. Baseline characteristics, efficacy outcomes, and safety Pts with high-risk features (n=129) BASELINE CHARACTERISTICS Median age, y (range) 60 (33-70) Rai stage III/IV, n (%) 36 (28) Bulky disease ≥5 cm, n (%) 47 (36) Genomic risk features, n (%) del(17p) and/or TP53 mutated 29 (22) Unmutated IGHV 119 (92) Complex karyotypea 27 (21) EFFICACY OUTCOMES Overall response rate, n (%) 126 (98) CR, n (%) 76 (59) 18-mo DOCR, % (95% CI) 95 (85-98) uMRD &lt;10-4 by flow, n (%) Peripheral blood 114 (88) Bone marrow 93 (72) 24-mo PFS rate, % (95% CI) 94 (88-97) 24-mo OS rate, % (95% CI) 98 (93-99) SAFETY OUTCOMES Grade 3/4 AEs in ≥5% of pts, n (%) Neutropenia 38 (29) Hypertension 12 (9) Neutrophil count decreased 9 (7) aDefined as ≥3 abnormalities by CpG-stimulated cytogenetics.

Citation Format: John N. Allan, Ian W. Flinn, Tanya Siddiqi, Paolo Ghia, Constantine S. Tam, Thomas J. Kipps, Paul M. Barr, Anna Elinder Camburn, Alessandra Tedeschi, Xavier C. Badoux, Ryan Jacobs, Bryone J. Kuss, Livio Trentin, Cathy Zhou, Anita Szoke, Maoko Naganuma, William G. Wierda. Fixed-duration (FD) ibrutinib (Ibr) + venetoclax (Ven) for first-line treatment of chronic lymphocytic leukemia (CLL) in patients (pts) with high-risk features: phase 2 CAPTIVATE study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT028.

Abstract 4007: Evolutionary history of transformation from chronic lymphocytic leukemia to Richter’s syndrome

Richter’s syndrome (RS) arising from chronic lymphocytic leukemia (CLL) is a striking example of an aggressive malignant histology that emerges from indolent cancer. RS is a major barrier to disease control in CLL and is associated with poor clinical outcomes and limited survival. The genetic basis of RS is poorly understood, and its relationship to the antecedent CLL remains incompletely characterized.

To study RS, we performed whole-exome sequencing (WES) on samples collected from 52 patients with RS of diffuse large B cell lymphoma (DLBCL) histology. For this genomic characterization, samples from 42 patients were analyzed as ‘trios’ (matched germline, CLL and RS tissue DNA) and those from 10 as ‘duos’ (matched CLL and RS DNA). Beyond addressing contamination of CLL DNA in the germline sample, we developed methods for discriminating between the RS and CLL clones which often coexist in the same samples.

The discovery cohort revealed that RS and CLL were clonally-related in 45/52 (87%) cases based on WES analysis, with a distinct RS clone emerging from a CLL subclone. The remaining 13% were determined to be clonally unrelated. RS clones presented ~3x higher rates of additional mutations than the ancestral CLL clones from which they developed. We identified novel RS somatic driver mutations (in IRF2BP2, SRSF1, B2M, DNMT3A and others), a high rate of copy number variations with recurrent deletions (e.g., del(17p) [TP53], del(13q14.3), del(7q36), and del(15q13.11) [MGA], del(9p21.3) [CDKN2A/B], del(16q12.2)), focal amplifications (amp(7q21.2) [CDK6], amp(8q24.2) [RECQL4, MYC], amp(13q31.2) [ERCC5], and frequent whole genome duplication.

To further investigate RS and CLL clonal evolution, we performed single-cell RNA-sequencing on biopsies at the time of RS diagnosis in 5 individuals with clonally related transformation. Using our novel tool, CNVSingle, we inferred allele specific single-cell copy number alterations, yielding cluster-specific copy number profiles that matched the WES results of individual subclones of the RS and CLL populations. This enabled mapping genetic clones to specific expression patterns. Finally, we devised and tested a methodology that uses cfDNA for early detection of emerging Richter’s disease and have successfully identified Richter‘s tumor DNA in the blood several months prior to the clinical diagnosis. Our study thus defines drivers, distinct molecular subtypes and evolutionary path to RS and suggests strategies for its improved detection.

Citation Format: Erin M. Parry, Ignaty Leshchiner, Romain Guièze, Connor Johnson, Eugen Tausch, Sameer Parikh, Camilla Lemvigh, Conor Messer, Daniel Rosebrock, Filippo Utro, Chaya Levovitz, Kahn Rhrissorrakrai, Matthew Davids, Raquel A. Jacobs, Kara Slowik, Julien Broseus, Shanye Yin, Shuqiang Li, Geoff Fell, Ziao Lin, Binyamin A. Knisbacher, Neil Ruthen, Dimitri Livitz, Christof Schneider, Jialin Ma, Julian Hess, Laura Z. Rassenti, Thomas J. Kipps, Nitin Jain, William Wierda, Florence Cymbalista, Neil E. Kay, Kenneth J. Livak, Brian P. Danysh, Chip Stewart, Donna Neuberg, Jennifer R. Brown, Laxmi Parida, Stephan Stilgenbauer, Gad Getz, Catherine J. Wu. Evolutionary history of transformation from chronic lymphocytic leukemia to Richter’s syndrome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4007.

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.

Phase 1/2 study of zilovertamab and ibrutinib in mantle cell lymphoma (MCL) or chronic lymphocytic leukemia (CLL)

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Background: Zilovertamab (Zilo) is a humanized monoclonal antibody that inhibits the tumor promoting activity of ROR1 and has demonstrated additive/synergistic activity with many anti-cancer agents, including ibrutinib (Ibr). Methods: Patients (Pts) with relapsed or refractory (RR) MCL or treatment-naïve (TN) or RR CLL were enrolled. In Part 1 (Dose Escalation), multiple doses were examined. Zilo 600 mg IV starting q2wks x3 then q4wks + Ibr qD was selected as the recommended dosing regimen for use in Part 2 (Expansion) and Part 3 (CLL only, Zilo+Ibr vs. Ibr alone). Results: As of 18Jan2022 data cutoff, 26 evaluable RR MCL pts, including pts who received prior Ibr (5) or auto-SCT (7), and 34 evaluable CLL pts (12 TN and 22 RR) were enrolled into Parts 1&2. In Part 3, 22 evaluable pts were randomized (2:1) to receive either Zilo+Ibr (15) or Ibr (7). Safety: Treatment-emergent adverse events (TEAEs) (≥30%, N = 84), regardless of relationship, included fatigue (41.7%), contusion (39.3%), and diarrhea (38.1%). Most common (≥5%) Grade ≥3 TEAEs included hypertension (10.7%), pneumonia (7.1%), atrial fibrillation, fatigue, and neutropenia (all 6.0%). Grade ≥3 neutrophil decrease observed in 9.4% or 17.6%, platelet decrease in 12.5% or 2.9%, or hemoglobin decrease in 9.4% or 0% of pts with MCL or CLL, respectively in Parts 1&2. Investigators scored TEAEs as due to Ibr in 78.1% or 85.3%, or to Zilo in 15.6% or 23.5% of pts with MCL or CLL, respectively. Efficacy (MCL): Objective response rate (ORR) was 80.8% (34.6% CR, 46.2% PR). ORR for pts with prior Ibr was 80% (2CR, 2PR) and median duration of response (mDOR) was 13.7 months (M) (95%CI: 11.93, NE). ORR was 100% in pts who had prior SCT+/- CAR-T (5CR, 2PR), and mDOR was 34.1 M (95% CI 13.84, NE). Overall median PFS (mPFS) was 35.9 M (95% CI: 17.3, NE) at median follow-up of 15.0 M. For MCL pts with TP 53 aberrancy (6), Ki67 > 30% (13), ≥ 3 prior lines of therapies (4), blastoid histology (3), bulky disease ≥5 cm (4), intermediate MIPIb (6), or high MIPIb (11), the mPFS (in M) was 17.3 (95% CI: 2.85, NE), Not Reached (NR) (95% CI: 2.85, NE), 35.9 (95% CI: 16.52, NE), NR (min 9.18, max 27.87), 26.6 (95% CI: 0.03, NE), 35.9 (min 8.30, max 35.9) or 16.5 (95% CI: 2.72, NE). Efficacy (CLL): In Parts 1&2 ORR was 91.2% (8.8% CR, 82.3% PR/PR-L), and 8.8% had stable disease (SD). At median follow-up of 31.4 M, mDOR was 33.5 M and mPFS was NR (95% CI: 36.3, NE); the mPFS (in M) for pts with 1, 2, or ≥ 3 prior therapies was NR (min 19.3, max 41.3), NR (min 31.3, max 36.8) or 36.3 (95% CI: 15.7, NE). At median follow-up of 21.1 M in Part 3, mPFS was NR for TN or RR in both Zilo+Ibr and Ibr arms. Conclusions: Zilo+Ibr is well-tolerated. Striking responses were observed in MCL pts, with mPFS of 35.9 M (95% CI: 17.3, NE) and CR of 34.6%, which compares favorably to mPFS of 12.8 M (95% CI 8.5, 16.6) and CR of 20% reported for single agent Ibr (Rule 2017). For CLL, ORR and PFS compare very favorably to Ibr monotherapy data (Byrd 2019). Clinical trial information: NCT03088878.

NCCN Guidelines® Insights: Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma, Version 3.2022

The treatment landscape of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) has significantly evolved in recent years. Targeted therapy with Bruton's tyrosine kinase (BTK) inhibitors and BCL-2 inhibitors has emerged as an effective chemotherapy-free option for patients with previously untreated or relapsed/refractory CLL/SLL. Undetectable minimal residual disease after the end of treatment is emerging as an important predictor of progression-free and overall survival for patients treated with fixed-duration BCL-2 inhibitor-based treatment. These NCCN Guidelines Insights discuss the updates to the NCCN Guidelines for CLL/SLL specific to the use of chemotherapy-free treatment options for patients with treatment-naïve and relapsed/refractory disease.

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]

cyCombine allows for robust integration of single-cell cytometry datasets within and across technologies

Combining single-cell cytometry datasets increases the analytical flexibility and the statistical power of data analyses. However, in many cases the full potential of co-analyses is not reached due to technical variance between data from different experimental batches. Here, we present cyCombine, a method to robustly integrate cytometry data from different batches, experiments, or even different experimental techniques, such as CITE-seq, flow cytometry, and mass cytometry. We demonstrate that cyCombine maintains the biological variance and the structure of the data, while minimizing the technical variance between datasets. cyCombine does not require technical replicates across datasets, and computation time scales linearly with the number of cells, allowing for integration of massive datasets. Robust, accurate, and scalable integration of cytometry data enables integration of multiple datasets for primary data analyses and the validation of results using public datasets.

Phase 1 TRANSCEND CLL 004 study of lisocabtagene maraleucel in patients with relapsed/refractory CLL or SLL

Bruton tyrosine kinase inhibitors (BTKi) and venetoclax are currently used to treat newly diagnosed and relapsed/refractory chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). However, most patients eventually develop resistance to these therapies, underscoring the need for effective new therapies. We report results of the phase 1 dose-escalation portion of the multicenter, open-label, phase 1/2 TRANSCEND CLL 004 (NCT03331198) study of lisocabtagene maraleucel (liso-cel), an autologous CD19-directed chimeric antigen receptor (CAR) T-cell therapy, in patients with relapsed/refractory CLL/SLL. Patients with standard- or high-risk features treated with ≥3 or ≥2 prior therapies, respectively, including a BTKi, received liso-cel at 1 of 2 dose levels (50 × 106 or 100 × 106 CAR+ T cells). Primary objectives included safety and determining recommended dose; antitumor activity by 2018 International Workshop on CLL guidelines was exploratory. Minimal residual disease (MRD) was assessed in blood and marrow. Twenty-three of 25 enrolled patients received liso-cel and were evaluable for safety. Patients had a median of 4 (range, 2-11) prior therapies (100% had ibrutinib; 65% had venetoclax) and 83% had high-risk features including mutated TP53 and del(17p). Seventy-four percent of patients had cytokine release syndrome (9% grade 3) and 39% had neurological events (22% grade 3/4). Of 22 efficacy-evaluable patients, 82% and 45% achieved overall and complete responses, respectively. Of 20 MRD-evaluable patients, 75% and 65% achieved undetectable MRD in blood and marrow, respectively. Safety and efficacy were similar between dose levels. The phase 2 portion of the study is ongoing at 100 × 106 CAR+ T cells. This trial was registered at clinicaltrials.gov as NCT03331198.

Modulation of RNA splicing associated with Wnt signaling pathway using FD-895 and pladienolide B

Alterations in RNA splicing are associated with different malignancies, including leukemia, lymphoma, and solid tumors. The RNA splicing modulators such as FD-895 and pladienolide B have been investigated in different malignancies to target/modulate spliceosome for therapeutic purpose. Different cell lines were screened using an RNA splicing modulator to test in vitro cytotoxicity and the ability to modulate RNA splicing capability via induction of intron retention (using RT-PCR and qPCR). The Cignal Finder Reporter Array evaluated [pathways affected by the splice modulators in HeLa cells. Further, the candidates associated with the pathways were validated at protein level using western blot assay, and gene-gene interaction studies were carried out using GeneMANIA. We show that FD-895 and pladienolide B induces higher apoptosis levels than conventional chemotherapy in different solid tumors. In addition, both agents modulate Wnt signaling pathways and mRNA splicing. Specifically, FD-895 and pladienolide B significantly downregulates Wnt signaling pathway-associated transcripts (GSK3β and LRP5) and both transcript and proteins including LEF1, CCND1, LRP6, and pLRP6 at the transcript, total protein, and protein phosphorylation's levels. These results indicate FD-895 and pladienolide B inhibit Wnt signaling by decreasing LRP6 phosphorylation and modulating mRNA splicing through induction of intron retention in solid tumors.

Up to 6.5 years (median 4 years) of follow-up of first-line ibrutinib in patients with chronic lymphocytic leukemia/small lymphocytic lymphoma and high-risk genomic features: integrated analysis of two phase 3 studies

Genomic abnormalities, including del(17p)/TP53 mutation, del(11q), unmutated IGHV, and mutations in BIRC3, NOTCH1, SF3B1, and XPO1 predict poor outcomes with chemoimmunotherapy in chronic lymphocytic leukemia. To better understand the impact of these high-risk genomic features on outcomes with first-line ibrutinib-based therapy, we performed pooled analysis of two phase 3 studies with 498 patients randomized to receive ibrutinib- or chlorambucil-based therapy with median follow-up of 49.1 months. Ibrutinib-based therapy improved overall response rates (ORRs), complete response rates, and progression-free survival (PFS) versus chlorambucil-based therapy across all subgroups. In ibrutinib-randomized patients with versus without specified genomic features, ORR and PFS were comparable across subgroups. PFS hazard ratio (95% CI) for del(17p)/TP53 mutated/BIRC3 mutated: 1.05 (0.54-2.04); del(17p)/TP53 mutation, del(11q), and/or unmutated IGHV: 1.11 (0.69-1.77); unmutated IGHV: 1.79 (0.99-3.24); and NOTCH1 mutated 1.05 (0.65-1.69). This integrated analysis demonstrated efficacy of first-line ibrutinib-based treatment irrespective of cytogenetic and mutational risk features.Registered at ClinicalTrials.gov (NCT01722487 and NCT02264574).

Zilovertamab Vedotin Targeting of ROR1 as Therapy for Lymphoid Cancers

Zilovertamab Vedotin Targeting of ROR1 as Therapy for Lymphoid Cancers In a Phase 1 trial, patients with refractory lymphoid cancers, an antibody-drug complex directed against ROR1 had no unexpected toxicities. About half of the patients with mantle cell lymphoma and diffuse large B-cell lymphoma had clinically meaningful responses.

Activation of Notch and Myc Signaling via B-cell-Restricted Depletion of Dnmt3a Generates a Consistent Murine Model of Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is characterized by disordered DNA methylation, suggesting these epigenetic changes might play a critical role in disease onset and progression. The methyltransferase DNMT3A is a key regulator of DNA methylation. Although DNMT3A somatic mutations in CLL are rare, we found that low DNMT3A expression is associated with more aggressive disease. A conditional knockout mouse model showed that homozygous depletion of Dnmt3a from B cells results in the development of CLL with 100% penetrance at a median age of onset of 5.3 months, and heterozygous Dnmt3a depletion yields a disease penetrance of 89% with a median onset at 18.5 months, confirming its role as a haploinsufficient tumor suppressor. B1a cells were confirmed as the cell of origin of disease in this model, and Dnmt3a depletion resulted in focal hypomethylation and activation of Notch and Myc signaling. Amplification of chromosome 15 containing the Myc gene was detected in all CLL mice tested, and infiltration of high-Myc-expressing CLL cells in the spleen was observed. Notably, hyperactivation of Notch and Myc signaling was exclusively observed in the Dnmt3a CLL mice, but not in three other CLL mouse models tested (Sf3b1-Atm, Ikzf3, and MDR), and Dnmt3a-depleted CLL were sensitive to pharmacologic inhibition of Notch signaling in vitro and in vivo. Consistent with these findings, human CLL samples with lower DNMT3A expression were more sensitive to Notch inhibition than those with higher DNMT3A expression. Altogether, these results suggest that Dnmt3a depletion induces CLL that is highly dependent on activation of Notch and Myc signaling. SIGNIFICANCE: Loss of DNMT3A expression is a driving event in CLL and is associated with aggressive disease, activation of Notch and Myc signaling, and enhanced sensitivity to Notch inhibition.

Longitudinal Single-Cell Dynamics of Chromatin Accessibility and Mitochondrial Mutations in Chronic Lymphocytic Leukemia Mirror Disease History

While cancers evolve during disease progression and in response to therapy, temporal dynamics remain difficult to study in humans due to the lack of consistent barcodes marking individual clones in vivo. We employ mitochondrial single-cell assay for transposase-accessible chromatin with sequencing to profile 163,279 cells from 9 patients with chronic lymphocytic leukemia (CLL) collected across disease course and utilize mitochondrial DNA (mtDNA) mutations as natural genetic markers of cancer clones. We observe stable propagation of mtDNA mutations over years in the absence of strong selective pressure, indicating clonal persistence, but dramatic changes following tight bottlenecks, including disease transformation and relapse posttherapy, paralleled by acquisition of copy-number variants and changes in chromatin accessibility and gene expression. Furthermore, we link CLL subclones to distinct chromatin states, providing insight into nongenetic sources of relapse. mtDNA mutations thus mirror disease history and provide naturally occurring genetic barcodes to enable patient-specific study of cancer subclonal dynamics.

SIGNIFICANCE

Single-cell multi-omic profiling of CLL reveals the utility of somatic mtDNA mutations as in vivo barcodes, which mark subclones that can evolve over time along with changes in accessible chromatin and gene expression profiles to capture dynamics of disease evolution. See related commentary by Hilton and Scott, p. 2965. This article is highlighted in the In This Issue feature, p. 2945.

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.

Exploring the pathways to chronic lymphocytic leukemia

In chronic lymphocytic leukemia (CLL), increasing knowledge of the biology of the tumor cells has led to transformative improvements in our capacity to assess and treat patients. The dependence of tumor cells on surface immunoglobulin receptor signaling, survival pathways, and accessory cells within the microenvironment has led to a successful double-barreled attack with designer drugs. Studies have revealed that CLL should be classified based on the mutational status of the expressed IGHV sequences into 2 diseases, either unmutated (U) or mutated (M) CLL, each with a distinctive cellular origin, biology, epigenetics/genetics, and clinical behavior. The origin of U-CLL lies among the natural antibody repertoire, and dominance of IGHV1-69 reveals a superantigenic driver. In both U-CLL and M-CLL, a calibrated stimulation of tumor cells by self-antigens apparently generates a dynamic reiterative cycle as cells, protected from apoptosis, transit between blood and tissue sites. But there are differences in outcome, with the balance between proliferation and anergy favoring anergy in M-CLL. Responses are modulated by an array of microenvironmental interactions. Availability of T-cell help is a likely determinant of cell fate, the dependency on which varies between U-CLL and M-CLL, reflecting the different cells of origin, and affecting clinical behavior. Despite such advances, cell-escape strategies, Richter transformation, and immunosuppression remain as challenges, which only may be met by continued research into the biology of CLL.

Phase II study of acalabrutinib in ibrutinib-intolerant patients with relapsed/refractory chronic lymphocytic leukemia

B-cell receptor signaling inhibition by targeting Bruton tyrosine kinase (BTK) is effective in treating chronic lymphocytic leukemia. The BTK inhibitor ibrutinib may be intolerable for some patients. Acalabrutinib is a more selective BTK inhibitor that may be better tolerated by patients who are intolerant to ibrutinib. A phase II study of acalabrutinib was conducted in patients with relapsed/refractory chronic lymphocytic leukemia who were ibrutinib-intolerant and had continued disease activity. Intolerance was defined as having discontinued ibrutinib due to persistent grade 3/4 adverse events or persistent/recurrent grade 2 adverse events despite dose modification/interruption. Patients received oral acalabrutinib 100 mg twice daily until disease progression or intolerance. Sixty patients were treated. The overall response rate to acalabrutinib was 73% and three patients (5%) achieved complete remission. At a median follow-up of 35 months, the median progression-free and overall survival were not reached; 24-month estimates were 72% and 81%, respectively. The most frequent adverse events with acalabrutinib were diarrhea (53%), headache (42%), contusion (40%), dizziness (33%), upper respiratory tract infection (33%), and cough (30%). The most common reasons for acalabrutinib discontinuation were progressive disease (23%) and adverse events (17%). Most patients with baseline samples (49/52; 94%) and all with on-treatment samples (3/3; 100%) had no detectable BTK and/or PLCG2 mutations. Acalabrutinib is effective and tolerable in most patients with relapsed/refractory chronic lymphocytic leukemia who are intolerant of ibrutinib. Acalabrutinib may be useful for patients who may benefit from BTK inhibitor therapy but are ibrutinib intolerant. ClinicalTrials.gov identifier: NCT02717611.

Long-term Follow-up of Patients with Relapsed or Refractory Non-Hodgkin Lymphoma Treated with Venetoclax in a Phase I, First-in-Human Study

PURPOSE

We previously reported a 44% overall response rate (ORR) with the oral BCL-2 inhibitor venetoclax in a phase I study of relapsed/refractory non-Hodgkin lymphoma (NHL). Complete response (CR) was observed in patients with mantle cell lymphoma [(MCL), 21%, n = 6/28] and follicular lymphoma [(FL), 17%, n = 5/29], and partial response (PR) noted in several patients with Waldenström macroglobulinemia (WM), and marginal zone lymphoma (MZL). Here, we report the long-term outcomes of these four cohorts.

PATIENTS AND METHODS

All patients (n = 106) received venetoclax monotherapy in dose cohorts of 200 to 1,200 mg daily until disease progression or unacceptable toxicity. ORR, progression-free survival (PFS), duration of response (DoR), and adverse events (AEs) were evaluated.

RESULTS

At a median follow-up of 38.5 months (range, 30.0-46.5), the median PFS for all 106 patients was 5.4 [95% confidence interval (CI), 3.5-8.4] months (FL, 10.8; MCL, 11.3; MZL, 21.2; and WM, 30.4). The median DoR was 14.9 (95% CI, 9.7-27.6) months (FL, 26.6; MCL, 15.7; MZL, 20.1; and WM, 25.3). Achievement of CR versus PR predicted longer DoR in both MCL (31.5 vs. 10.1 months) and FL (37.6 vs. 9.7 months). All grade hematologic AEs were infrequent: neutropenia (19%), anemia (19%), and thrombocytopenia (17%), with no new cytopenias after 2 years on therapy. Nonhematologic AEs included nausea (49%), diarrhea (46%), fatigue (44%), with decreased incidence after 1 year.

CONCLUSIONS

Venetoclax monotherapy has a manageable safety profile and achieves durable responses in a subset of patients with FL, MCL, WM, and MZL, particularly in those who achieve CR. Further research is warranted on combination strategies to enhance the durability of response to venetoclax.

Abstract 3102: Venetoclax resistance associates with high-level expression of ROR1 and cancer stemness in chronic lymphocytic leukemia

The BH3-mimetic venetoclax is highly cytotoxic for chronic lymphocytic leukemia (CLL) cells. Nonetheless, some patients (pts) fail to clear minimal residual disease (MRD) and develop progressive disease (PD) on venetoclax-based therapy (V-Rx). Acquisition of de novo BCL2 mutations that reduce venetoclax-binding to BCL2 has been observed in CLL cells of pts who develop PD on V-Rx (Blombery et al., 2019; Blombery et al., 2020; Tausch et al., 2019). However, such BCL2 mutations generally are either subclonal or not invariably detected in CLL cells of pts who develop resistance to venetoclax (Blombery et al., 2019; Guieze et al., 2019). Moreover, CLL cells of pts with PD on V-Rx appear even more resistant to the cytotoxic effects of venetoclax when cultured under conditions mimicking stroma (Blombery et al., 2019; Thijssen et al., 2015), arguing that factors other than BCL2 mutations account for venetoclax resistance. We find that high-level expression of ROR1 and Wnt5a-induced ROR1-signaling causes enrichment in cancer-stemness gene expression in CLL. We examined whether this was associated with resistance to V-Rx. We performed flow cytometry and transcriptome analyses on CLL cells of pts prior to V-Rx (pre-Rx) and on CLL cells of the same pts after they developed PD on V-Rx after a median of 2 years of therapy. At PD, we identified de novo BCL2 mutations that were subclonal in 66% of these cases. Pre-Rx CLL cells of all 6 pts expressed high levels of ROR1, which became even higher on the CLL cells of the same pts after they developed PD on V-Rx. We found that that transcriptomes of CLL cells of pts with PD had even greater enrichment in cancer-stemness gene expression than pre-Rx CLL cells of these same pts. To examine whether expression of ROR1 could influence cancer stemness and resistance to venetoclax, we transfected the CLL-cell line MEC1 with ROR1 to generate MEC1-ROR1 cells. We found that MEC1-ROR1 had greater enrichment in cancer-stemness gene expression than MEC1 cells and had increased resistance to venetoclax in vitro. Moreover, mutant forms of BCL2 identified in CLL cells of pts with PD on V-Rx, and reducing venetoclax-binding to BCL2, were significantly more effective in protecting MEC1-ROR1 cells than MEC1 cells from the cytotoxic effects of venetoclax in vitro. We find that treatment of primary CLL cells with Wnt5a to induce ROR1-signaling could enhance their resistance to the cytotoxic effects of venetoclax in vitro; such induced-resistance could be inhibited by an anti-ROR1 mAb (cirmtuzumab), which can block Wnt5a-induced ROR1-signaling. Collectively these studies demonstrate that Wnt5a-induced ROR1-signaling in CLL promotes cancer dedifferentiation/stemness and increases resistance to Ven. Strategies that inhibit ROR1-signaling with agents such as cirmtuzumab may enhance the cytotoxic activity of venetoclax and/or mitigate risk of developing resistance to venetoclax therapy.

Citation Format: Emanuela M. Ghia, Laura Z. Rassenti, Michael Y. Choi, Miguel Quijada-Alamo, Elvin Chu, George F. Widhopf, II, Thomas J. Kipps. Venetoclax resistance associates with high-level expression of ROR1 and cancer stemness in chronic lymphocytic leukemia [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 3102.

Distinct evolutionary paths in chronic lymphocytic leukemia during resistance to the graft-versus-leukemia effect

Leukemic relapse remains a major barrier to successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) for aggressive hematologic malignancies. The basis for relapse of advanced lymphoid malignancies remains incompletely understood and may involve escape from the graft-versus-leukemia (GvL) effect. We hypothesized that for patients with chronic lymphocytic leukemia (CLL) treated with allo-HSCT, leukemic cell-intrinsic features influence transplant outcomes by directing the evolutionary trajectories of CLL cells. Integrated genetic, transcriptomic, and epigenetic analyses of CLL cells from 10 patients revealed that the clinical kinetics of post-HSCT relapse are shaped by distinct molecular dynamics. Early relapses after allo-HSCT exhibited notable genetic stability; single CLL cell transcriptional analysis demonstrated a cellular heterogeneity that was static over time. In contrast, CLL cells relapsing late after allo-HSCT displayed notable genetic evolution and evidence of neoantigen depletion, consistent with marked single-cell transcriptional shifts that were unique to each patient. We observed a greater rate of epigenetic change for late relapses not seen in early relapses or relapses after chemotherapy alone, suggesting that the selection pressures of the GvL bottleneck are unlike those imposed by chemotherapy. No selective advantage for human leukocyte antigen (HLA) loss was observed, even when present in pretransplant subpopulations. Gain of stem cell modules was a common signature associated with leukemia relapse regardless of posttransplant relapse kinetics. These data elucidate the biological pathways that underlie GvL resistance and posttransplant relapse.

Phase 1/2 study of cirmtuzumab and ibrutinib in mantle cell lymphoma (MCL) or chronic lymphocytic leukemia (CLL)

7556

Background: Cirmtuzumab (Cirm) is a humanized monoclonal antibody that inhibits the tumor promoting activity of ROR1 and had demonstrated additive/synergistic activity with many anti-cancer agents including ibrutinib (Ibr). Methods: Patients (Pts) with relapsed or refractory (RR) MCL or treatment naïve (TN) or RR CLL were enrolled. In Part 1 (Dose Escalation), doses of Cirm IV q2wks x5 then q4wks of 2-16 mg/kg and 300 or 600 mg were examined. Safety of Cirm alone was assessed during the first 28 days, then Ibr was started at approved doses for each indication. Cirm 600 mg IV q2wks x3 then q4wks in combination with Ibr starting day 0 was chosen as the recommended dosing regimen for use in Part 2 (Expansion) and Part 3 (CLL only, Cirm/Ibr vs. Ibr alone). Results: Twelve evaluable MCL pts were enrolled into Part 1, and 5 into Part 2. Median number of prior regimens was 2 (1-5), including pts relapsing after Ibr (4), auto-SCT (3), auto-SCT/ allo-SCT (1), auto-SCT/CAR-T (1). In CLL, 34 evaluable pts (12 TN and 22 RR) enrolled into Part 1 (18) or Part 2 (16). At least 74% of CLL pts in Parts 1 and 2 were high risk as determined by unmutated IGHV, del17p, and/or del11q. In Part 3, 22 evaluable pts received Cirm/Ibr (15) or Ibr (7). As of the 30OCT2020 safety cut-off for MCL and CLL, common TEAEs (all grades) included diarrhea (41%), contusion (39%), fatigue (39%), URI (31%), hypertension (25%) arthralgia (23%). Grade ≥3 neutropenia was 13% and thrombocytopenia 1%. There were no Cirm dose reductions or discontinuations for toxicity. Overall, Cirm did not appear to negatively impact the safety of Ibr. Efficacy (MCL): As of the 02FEB2021 efficacy cutoff, the best response of 17 evaluable pts in Parts 1 and 2 included an objective response rate (ORR) of 82%, 41% CR/CMR, 41% PR, 12% SD, and 6% PD. CR/CMR remain durable from 8-28+ mos. Most responses occurred rapidly after ̃3 mos of Cirm/Ibr. Notably, responses were achieved in all pts who received prior SCT+/- CAR-T (4CR, 1PR) or prior Ibr (2CR, 2PR). At a median follow-up of 14.6 mos, the median PFS (mPFS) had not been reached (NR) (95% CI: 17.5, NA). Efficacy (CLL): The best response of 34 evaluable pts in Parts 1 and 2 included 91% ORR, 3% CR, 88% PR/PR-L, 9% SD, 0% PD. In Part 3, both arms achieved 100% ORR (all PRs). At a median follow-up of 20.2 mos, the mPFS was NR (95% CI: NA, NA), and the PFS estimate at 24 months was 95% for R/R, and 87% for TN, respectively, for evaluable CLL pts receiving Cirm/Ibr. Conclusions: Cirm/Ibr is a well-tolerated, active regimen in both MCL and CLL. For MCL, the mPFS of NR (95% CI: 17.5, NA) and CRR (41%), with all CRs remaining without PD, compare favorably to mPFS of 12.8 mos (95% CI 8.5-16.6) and CRR (20%) reported for single agent Ibr (Rule 2017). For CLL, the high ORR and PFS are encouraging, particularly for RR CLL. The study is ongoing, with MCL enrollment expanded to study Cirm + Ibr in pts who have had a suboptimal response to an Ibr regimen, or who have failed other approved BTKi agents. Clinical trial information: NCT03088878.

Up to seven years of follow-up in the RESONATE-2 study of first-line ibrutinib treatment for patients with chronic lymphocytic leukemia

7523

Background: Ibrutinib, a once-daily Bruton’s tyrosine kinase inhibitor, is the only targeted therapy with significant progression-free survival (PFS) and overall survival (OS) benefit in multiple randomized phase 3 studies versus established therapies in patients (pts) with previously untreated chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). Extended long-term follow-up data for the RESONATE-2 study of first-line ibrutinib vs chlorambucil in older pts with CLL/SLL are reported. Methods: In the phase 3 RESONATE-2 study, older pts (≥65 years [y]) with previously untreated CLL/SLL and without del(17p) (N=269) were randomly assigned 1:1 to once-daily single-agent ibrutinib 420 mg until disease progression (PD) or unacceptable toxicity (n=136) or chlorambucil 0.5–0.8 mg/kg up to 12 cycles (n=133). Outcomes included PFS, OS, overall response rate (ORR), and safety. Long-term responses were investigator-assessed per 2008 iwCLL criteria. Results: With up to 7y of follow-up (median, 74.9 months; range, 0.1–86.8), significant PFS benefit was sustained for pts treated with ibrutinib vs chlorambucil (hazard ratio [HR] 0.160 [95% confidence interval (CI): 0.111–0.230]). At 6.5y, PFS was 61% in pts treated with ibrutinib vs 9% in pts treated with chlorambucil. This PFS benefit was observed across all subgroups, including in ibrutinib-treated pts with high-risk genomic features of unmutated IGHV (HR 0.109 [95% CI: 0.063–0.189]) or del(11q) (HR 0.033 [95% CI: 0.010–0.107]). OS at 6.5y was 78% with ibrutinib treatment. ORR was 92% for ibrutinib-treated pts with complete response (CR/CRi) rate increasing to 34% with this follow-up. Ongoing rates of grade ≥3 adverse events (AEs) of interest remained low for hypertension (5–6y interval: 5%, n=4; 6–7y: 4%, n=3) and atrial fibrillation (5–6y: 1%, n=1; 6–7y: 1%, n=1); no grade ≥3 major hemorrhage occurred in 5–7y. Dose reductions due to grade ≥3 AEs occurred in 1% (n=1) of pts during the 5–6y and 6–7y intervals. Across full follow-up, 31 pts had dose reductions due to any-grade AEs of whom 22/31 (71%) had resolution or improvement the AE. Primary reason for discontinuations in 5–7y was PD (5–6y: 5%, n=4; 6–7y: 6%, n=4). Any-grade AEs leading to discontinuations were seen in 3% (n=2) of pts from 5–6y and none in 6–7y. With over 7y of follow-up, 47% of pts remain on single-agent ibrutinib. Conclusions: Extended long-term data from RESONATE-2 demonstrate the sustained PFS and OS benefit of first-line ibrutinib treatment for pts with CLL, including for pts with high-risk genomic features. Responses continue to deepen over time. Rates of grade ≥3 AEs of interest continued to be low at up to 7y follow-up and further discontinuations and dose reductions due to AEs were rare; most AEs leading to dose reduction resolved or improved. Ibrutinib remains well tolerated with no new safety signals observed. Clinical trial information: NCT01722487, NCT01724346.

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

7501

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]

A hotspot mutation in transcription factor IKZF3 drives B cell neoplasia via transcriptional dysregulation

Hotspot mutation of IKZF3 (IKZF3-L162R) has been identified as a putative driver of chronic lymphocytic leukemia (CLL), but its function remains unknown. Here, we demonstrate its driving role in CLL through a B cell-restricted conditional knockin mouse model. Mutant Ikzf3 alters DNA binding specificity and target selection, leading to hyperactivation of B cell receptor (BCR) signaling, overexpression of nuclear factor κB (NF-κB) target genes, and development of CLL-like disease in elderly mice with a penetrance of ~40%. Human CLL carrying either IKZF3 mutation or high IKZF3 expression was associated with overexpression of BCR/NF-κB pathway members and reduced sensitivity to BCR signaling inhibition by ibrutinib. Our results thus highlight IKZF3 oncogenic function in CLL via transcriptional dysregulation and demonstrate that this pro-survival function can be achieved by either somatic mutation or overexpression of this CLL driver. This emphasizes the need for combinatorial approaches to overcome IKZF3-mediated BCR inhibitor resistance.

Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma, Version 4.2020, NCCN Clinical Practice Guidelines in Oncology

Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are characterized by a progressive accumulation of leukemic cells in the peripheral blood, bone marrow, and lymphoid tissues. Treatment of CLL/SLL has evolved significantly in recent years because of the improved understanding of the disease biology and the development of novel targeted therapies. In patients with indications for initiating treatment, the selection of treatment should be based on the disease stage, patient's age and overall fitness (performance status and comorbid conditions), and cytogenetic abnormalities. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with CLL/SLL.

Impact of long-term ibrutinib treatment on circulating immune cells in previously untreated chronic lymphocytic leukemia

This study evaluated long-term immunophenotypic changes in circulating levels of 24 immune cell subsets through 4 years of continuous treatment with first-line ibrutinib (420 mg once daily) in 31 patients with chronic lymphocytic leukemia (CLL) from the RESONATE-2 study, and compared them with untreated age-matched healthy donors (n = 20). Ibrutinib progressively decreased total B-cell counts and preferentially targeted malignant CLL B cells over normal B cells. Elevated counts of chronically activated, exhausted, and effector memory T cells were normalized within 6-16 months, while naive T cells remained mostly within healthy donor range (HDR). Immunosuppressive regulatory T cells and myeloid-derived suppressor cells were normalized within the first 1-2 years and then plateaued. Additionally, ibrutinib restored low counts of innate cell populations associated with antitumor immunity: plasmacytoid dendritic cells were restored to HDR after 2 years, and classical monocyte counts progressively and continuously increased toward HDR. Ibrutinib also consistently preserved circulating mature natural killer cell counts. The data indicate that ibrutinib continuously exerted positive effects on immune cell populations throughout 4 years of treatment, consistent with improved clinical outcomes observed in patients. The normalization of adaptive and innate immune cell populations suggests that long-term ibrutinib treatment mediates restoration of immunity.

Recurrent XPO1 mutations alter pathogenesis of chronic lymphocytic leukemia

BACKGROUND

Exportin 1 (XPO1/CRM1) is a key mediator of nuclear export with relevance to multiple cancers, including chronic lymphocytic leukemia (CLL). Whole exome sequencing has identified hot-spot somatic XPO1 point mutations which we found to disrupt highly conserved biophysical interactions in the NES-binding groove, conferring novel cargo-binding abilities and forcing cellular mis-localization of critical regulators. However, the pathogenic role played by change-in-function XPO1 mutations in CLL is not fully understood.

METHODS

We performed a large, multi-center retrospective analysis of CLL cases (N = 1286) to correlate nonsynonymous mutations in XPO1 (predominantly E571K or E571G; n = 72) with genetic and epigenetic features contributing to the overall outcomes in these patients. We then established a mouse model with over-expression of wildtype (wt) or mutant (E571K or E571G) XPO1 restricted to the B cell compartment (Eµ-XPO1). Eµ-XPO1 mice were then crossed with the Eµ-TCL1 CLL mouse model. Lastly, we determined crystal structures of XPO1 (wt or E571K) bound to several selective inhibitors of nuclear export (SINE) molecules (KPT-185, KPT-330/Selinexor, and KPT-8602/Eltanexor).

RESULTS

We report that nonsynonymous mutations in XPO1 associate with high risk genetic and epigenetic features and accelerated CLL progression. Using the newly-generated Eµ-XPO1 mouse model, we found that constitutive B-cell over-expression of wt or mutant XPO1 could affect development of a CLL-like disease in aged mice. Furthermore, concurrent B-cell expression of XPO1 with E571K or E571G mutations and TCL1 accelerated the rate of leukemogenesis relative to that of Eµ-TCL1 mice. Lastly, crystal structures of E571 or E571K-XPO1 bound to SINEs, including Selinexor, are highly similar, suggesting that the activity of this class of compounds will not be affected by XPO1 mutations at E571 in patients with CLL.

CONCLUSIONS

These findings indicate that mutations in XPO1 at E571 can drive leukemogenesis by priming the pre-neoplastic lymphocytes for acquisition of additional genetic and epigenetic abnormalities that collectively result in neoplastic transformation.

Preneoplastic Alterations Define CLL DNA Methylome and Persist through Disease Progression and Therapy

Most human cancers converge to a deregulated methylome with reduced global levels and elevated methylation at select CpG islands. To investigate the emergence and dynamics of the cancer methylome, we characterized genome-wide DNA methylation in pre-neoplastic monoclonal B cell lymphocytosis (MBL) and chronic lymphocytic leukemia (CLL), including serial samples collected across disease course. We detected the aberrant tumor-associated methylation landscape at CLL diagnosis and found no significantly differentially methylated regions in the high-count MBL-to-CLL transition. Patient methylomes showed remarkable stability with natural disease and post-therapy progression. Single CLL cells were consistently aberrantly methylated, indicating a homogeneous transition to the altered epigenetic state, and a distinct expression profile together with MBL cells compared to normal B cells. Our longitudinal analysis reveals the cancer methylome to emerge early, which may provide a platform for subsequent genetically-driven growth dynamics and together with its persistent presence suggests a central role in the normal-to-cancer transition.

Venetoclax plus obinutuzumab versus chlorambucil plus obinutuzumab for previously untreated chronic lymphocytic leukaemia (CLL14): follow-up results from a multicentre, open-label, randomised, phase 3 trial

BACKGROUND

Venetoclax plus obinutuzumab has been established as a fixed-duration treatment regimen for patients with chronic lymphocytic leukaemia. We compared the long-term efficacy after treatment cessation of the combination of venetoclax plus obinutuzumab with chlorambucil plus obinutuzumab in patients with previously untreated chronic lymphocytic leukaemia.

METHODS

CLL14 is a multicentre, randomised, open-label, phase 3 trial done at 196 sites in 21 countries. Eligible patients were aged 18 years or older, had untreated chronic lymphocytic leukaemia, and coexisting conditions with a cumulative illness rating scale greater than 6, a creatinine clearance of 30-69 mL/min, or both. Patients were randomly assigned (1:1) via a web and voicemail system with allocation concealment and based on a computer-generated randomisation schedule with a block size of six and stratified by Binet stage and geographical region. Patients received either venetoclax plus obinutuzumab (oral venetoclax initiated on day 22 of cycle 1 [28-day cycles], with a 5-week dose ramp-up [20 mg, 50 mg, 100 mg, and 200 mg, then 400 mg daily for 1 week], thereafter continuing at 400 mg daily until completion of cycle 12; combined with intravenous obinutuzumab for six cycles starting with 100 mg on day 1 and 900 mg on day 2 [or 1000 mg on day 1], 1000 mg on days 8 and day 15 of cycle 1, and subsequently 1000 mg on day 1 of cycles 2 through 6) or chlorambucil plus obinutuzumab (oral chlorambucil at 0·5 mg/kg bodyweight on days 1 and 15 of each cycle for 12 cycles combined with the same obinutuzumab regimen). The primary endpoint was investigator-assessed progression-free survival in the intention-to-treat population. Safety was assessed in all patients who received at least one dose of study treatment. Patient enrolment is complete, and the study is registered with ClinicalTrails.gov, NCT02242942.

FINDINGS

Between Aug 7, 2015, and Aug 4, 2016, 432 patients were enrolled and randomly assigned to receive either venetoclax plus obinutuzumab (n=216) or chlorambucil plus obinutuzumab (n=216). All patients had been off treatment for at least 24 months at data collection. At a median follow-up of 39·6 months (IQR 36·8-43·0), patients given venetoclax plus obinutuzumab had a significantly longer progression-free survival than did patients given chlorambucil plus obinutuzumab (HR 0·31, 95% CI 0·22-0·44; p<0·0001). Median progression-free survival was not reached (95% CI not estimable to not estimable) in the venetoclax plus obinutuzumab group vs 35·6 months (33·7-40·7) in the chlorambucil plus obinutuzumab group. The most common grade 3 or 4 adverse event in both groups was neutropenia (112 [53%] of 212 patients in the venetoclax plus obinutuzumab group versus 102 [48%] of 214 patients in the chlorambucil plus obinutuzumab group). Serious adverse events occurred in 115 (54%) of 212 patients in the venetoclax plus obinutuzumab group and 95 (44%) of 214 patients in the chlorambucil plus obinutuzumab group. Venetoclax or chlorambucil treatment-related deaths were reported in one (1%) of 212 patients in the venetoclax plus obinutuzumab group (n=1 sepsis) and two (1%) of 214 patients in the chlorambucil plus obinutuzumab group (n=1 septic shock, n=1 metastatic skin squamous carcinoma).

INTERPRETATION

2 years after treatment cessation, venetoclax plus obinutuzumab continues to significantly improve progression-survival compared with chlorambucil plus obinutuzumab, thereby providing a limited duration treatment option for patients with previously untreated chronic lymphocytic leukaemia.

FUNDING

F Hoffmann-La Roche and AbbVie.

Abstract 3687: Wnt5a induces DOCK1 to complex with ROR1 and activate Rac1 leading to enhanced growth of breast cancer cells

ROR1 (Receptor tyrosine kinase-like orphan receptor 1) is an evolutionarily conserved, oncoembryonic surface antigen that is expressed on breast cancer, but not on normal postpartum tissues. We found ROR1 was a receptor for Wnt5a, and high-level expression of ROR1 in tumors of breast cancer patients associated with enhanced cell growth, aggressive disease, and shorter overall survival (Zhang S., et al., PLOS ONE, 7(3): e31127, 2012). More recently, ROR1 could activate RhoGTPases and enhance tumor growth in breast cancer (Zhang S., et al., PNAS, 116(4), 2019). Such effects of Wnt5a on breast cancer patient-derived-xenograft (PDX) tumors could be blocked by cirmtuzumab, a humanized anti-ROR1 mAb, which is undergoing clinical evaluation in patients with cancer. However, the molecular mechanism(s) for how ROR1 contributes such functions remained elusive. We performed mass spectrometry-based proteomic analysis on anti-ROR1 immune precipitates from breast cancer PDX tumors and detected DOCK1 in addition to ROR1, implying that ROR1 associates with DOCK1. DOCK1 (Dedicator of cytokinesis 1, also known as DOCK180) that expressed in breast cancer PDXs and cell lines, is a cytoplasmic protein, and a member of the DOCK-A subfamily of guanine exchange factors (GEFs) specific for Rac1. Moreover, DOCK1 consists SH3 domain, which allows it to bind characteristic motifs (-P-X-X-P-), which often are found in the proline rich domains (PRD) of other proteins. Immunoblot analysis confirmed that ROR1 associated with DOCK1 in breast cancer PDX tumors or MCF7 cells transfected to express ROR1 (MCF7-ROR1) in response to Wnt5a, leading to enhanced activation of Rac1. To explore functional role, we performed a 2-week colony-formation assay using MCF7-ROR1 cells, and found that treatment of Wnt5a could enhance number of colonies of MCF7-ROR1 cells and that such colony formation capability could be inhibited by reducing expression of DOCK1 with specific siRNA, but not by control siRNA, suggesting a dependency on DOCK1 for Wnt5a-enhanced MCF7-ROR1 cells colony formation capability. Moreover, such effects of Wnt5a to enhance colony formation ability of MCF7-ROR1 cells could be inhibit by cirmtuzumab. We also introduced single amino-acid substitutions of proline (P) to alanine (A) in the ROR1 proline-rich-domain (PRD) at positions 784, 808, 826, or 841 in potential SH3-binding sites. In contrast to wild-type ROR1, or other ROR1P⇒A mutants, ROR1P(808)A was unable to recruit DOCK1 to ROR1, or activate Rac1 in response to Wnt5a. Next we examined the tumor-growth potential of MCF7-Ctrl, MCF7-ROR1, or MCF7-P808A cells. The cells (5 × 104 cells/inoculate in RPMI 1640 together with an equal volume of Matrigel) were injected subcutaneously into the second right mammary pad of 4-to 6-week-old Rag2−/−γc−/- mice pretreated with estrogen pellets (17β-estradiol), which were placed subcutaneously in the intrascapular region one week before the cells inoculation. We found that MCF7-ROR1 cells (n=6) had significantly higher tumor growth relative to MCF7 cells (n=8), which had the same tumor growth as that of MCF7-P808A cells (n=6). Moreover, MCF7-ROR1P808A tumors had less activation of Rac1 compared to MCF7-ROR1 cells expressing wild-type ROR1. This study reveals that the recruitment of DOCK1 to ROR1 may be critical for the capacity of Wnt5a to enhance breast cancer tumor growth.

Citation Format: Md Kamrul Hasan, George F. Widhopf II, Suping Zhang, Sharon M. Lam, Barbara A. Parker, Thomas J. Kipps. Wnt5a induces DOCK1 to complex with ROR1 and activate Rac1 leading to enhanced growth of breast cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3687.

Ibrutinib restores immune cell numbers and function in first-line and relapsed/refractory chronic lymphocytic leukemia

Ibrutinib positively modulates many T-cell subsets in chronic lymphocytic leukemia (CLL). To understand ibrutinib's effects on the broader landscape of immune cell populations, we comprehensively characterized changes in circulating counts of 21 immune blood cell subsets throughout the first year of treatment in patients with relapsed/refractory (R/R) CLL (n = 55, RESONATE) and previously untreated CLL (n = 50, RESONATE-2) compared with untreated age-matched healthy donors (n = 20). Ibrutinib normalized abnormal immune cell counts to levels similar to those of age-matched healthy donors. Ibrutinib significantly decreased pathologically high circulating B cells, regulatory T cells, effector/memory CD4⁺ and CD8⁺ T cells (including exhausted and chronically activated T cells), natural killer (NK) T cells, and myeloid-derived suppressor cells; preserved naive T cells and NK cells; and increased circulating classical monocytes. T-cell function was assessed in response to T-cell receptor stimulation in patients with R/R CLL (n = 21) compared with age-matched healthy donors (n = 18). Ibrutinib significantly restored T-cell proliferative ability, degranulation, and cytokine secretion. Over the same period, ofatumumab or chlorambucil did not confer the same spectrum of normalization as ibrutinib in multiple immune subsets. These results establish that ibrutinib has a significant and likely positive impact on circulating malignant and nonmalignant immune cells and restores healthy T-cell function.

NCCN Guidelines Insights: Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma, Version 2.2019

Chronic lymphocytic leukemia (CLL) is generally characterized by an indolent disease course. Histologic transformation (also known as Richter's transformation) to more aggressive lymphomas, such as diffuse large B-cell lymphoma or Hodgkin lymphoma, occurs in approximately 2% to 10% of patients and is associated with a poor prognosis. These NCCN Guidelines Insights discuss the recommendations for the diagnosis and management of patients with histologic transformation.