Venetoclax (ABT-199) Might Act as a Perpetrator in Pharmacokinetic Drug-Drug Interactions

Identification of Bromophenols' glucuronidation and its induction on UDP- glucuronosyltransferases isoforms

Bromophenols (BPs) are prominent environmental pollutants extensively utilized in aquaculture, pharmaceuticals, and chemical manufacturing. This study aims to identify UDP- glucuronosyltransferases (UGTs) isoforms involved in the metabolic elimination of BPs. Mono-glucuronides of BPs were detected in human liver microsomes (HLMs) incubated with the co-factor uridine-diphosphate glucuronic acid (UDPGA). The glucuronidation metabolism reactions catalyzed by HLMs followed Michaelis-Menten or substrate inhibition kinetics. Recombinant enzymes and inhibition experiments with chemical reagents were employed to phenotype the principal UGT isoforms participating in BP glucuronidation. UGT1A6 emerged as the major enzyme in the glucuronidation of 4-Bromophenol (4-BP), while UGT1A1, UGT1A6, and UGT1A8 were identified as the most essential isoforms for metabolizing 2,4-dibromophenol (2,4-DBP). UGT1A1, UGT1A8, and UGT2B4 were deemed the most critical isoforms in the catalysis of 2,4,6-tribromophenol (2,4,6-TBP) glucuronidation. Species differences were investigated using the liver microsomes of pig (PLM), rat (RLM), monkey (MyLM), and dog (DLM). Additionally, 2,4,6-TBP effects on the expression of UGT1A1 and UGT2B7 in HepG2 cells were evaluated. The results demonstrated potential induction of UGT1A1 and UGT2B7 upon exposure to 2,4,6-TBP at a concentration of 50 μM. Collectively, these findings contribute to elucidating the metabolic elimination and toxicity of BPs.

BCL2 inhibitor ABT-199 and BCL2L1 inhibitor WEHI-539 coordinately promote NOXA-mediated degradation of MCL1 in human leukemia cells

Human leukemia U937 cells that were continuously treated with hydroquinone (HQ) were transformed into U937/HQ cells with increased MCL1 and BCL2L1 expression. Compared with their parental cells, U937/HQ cells were less sensitive to ABT-263 (BCL2/BCL2L1 inhibitor)/ABT-199 (BCL2 inhibitor) cytotoxicity. The combination of WEHI-539 (BCL2L1 inhibitor) with either ABT-199 or ABT-263 showed synergistic cytotoxicity to U937 and U937/HQ cells. Therefore, we further investigated the cytotoxic mechanism induced by the combination of WEHI-539 and ABT-199. The combined treatment of WEHI-539 and ABT-199 induced NOX4/ROS/p38 MAPK axis-mediated autophagy, which in turn accelerated β-TrCP mRNA turnover. Downregulation of β-TrCP increased Sp1 expression, thereby promoting Sp1-mediated NOXA transcription, which in turn induced NOXA-dependent MCL1 degradation. Enforced expression of MCL1 alleviated the cytotoxicity of WEHI-539 plus ABT-199 to induce the loss of mitochondrial membrane potential and cell viability. WEHI-539 alone induced Sp1/NOXA axis-mediated MCL1 downregulation, while ABT-199 significantly decreased the dose of WEHI-539 by approximately 350- and 50-fold to induce MCL1 suppression in parental and HQ-selected cells, respectively. Furthermore, WEHI-539 sensitized ABT-199-resistant U937 cells to ABT-199 cytotoxicity by inducing NOXA-mediated degradation of MCL1. Collectively, the data in this study indicate that ABT-199 and WEHI-539 cooperatively induce NOXA-dependent MCL1 degradation, and the inhibition of MCL1 mainly explains their combined cytotoxicity in parental, HQ-selected, and ABT-199-resistant U937 cells.

Lipase-triggered drug release from BCL2 inhibitor ABT-199-loaded nanoparticles to elevate anti-leukemic activity through enhanced drug targeting on the mitochondrial membrane

Selective BCL2 inhibitor ABT-199 has been approved to treat hematological malignancies including acute myeloid leukemia (AML). However, acquired drug resistance and severe side effects occur after extended treatment limiting the clinical usage of ABT-199. Here, we successfully encapsulated pure ABT-199 in amphiphilic mPEG-b-PTMC₁₆₉ block copolymer, forming mPEG-b-PTMC₁₆₉@ABT-199 nanoparticles (abbreviated as PEG-ABT-199), which presented better aqueous dispersion and higher efficiency of loading and encapsulation than pure ABT-199. We then compared the anti-leukemic ability of pure ABT-199 and PEG-ABT-199 in vitro and in vivo. PEG-ABT-199 had a lower IC50 value compared with pure ABT-199 in MV4-11 and MOLM-13 cell lines. In addition, PEG-ABT-199 significantly induced apoptosis and decreased colony number than pure ABT-199. Most importantly, PEG-ABT-199 markedly reduced leukemic burden, inhibited the infiltration of leukemic blasts in the spleen, and extended the overall survival (OS) in MLL-AF9-transduced murine AML compared with free ABT-199. Meanwhile, the blank PEG169 NP was non-toxic to normal hematopoiesis in vitro and in vivo, suggesting that PEG169 NP is a safe carrier. Mechanistically, PEG-ABT-199 enhanced mitochondria-targeted delivery of ABT-199 to trigger the collapse of mitochondrial membrane potential (MMP), the release of cytochrome c (cyt-c), and mitochondria-based apoptosis. In conclusion, our results suggest that PEG-ABT-199 has more vital anti-leukemic ability than pure ABT-199. PEG-ABT-199 has potential application in clinical trials to alleviate side effects and improve anti-leukemia ability. STATEMENT OF SIGNIFICANCE: ATB-199, an orally selective inhibitor for BCL2 protein, presents marked activity in relapsed or refractory AML, T-ALL, and CLL patients. However, ABT-199 resistance severely limits the further clinical usage because of off-target effects, non-specific toxicities, and low delivery of drugs. To reduce the side-effects and improve the solubility and bioavailability, ABT-199 was encapsulated into the amphiphilic mPEG-b-PTMC block copolymer by co-assembly method to obtain mPEG-b-PTMC@ABT-199 nanoparticles (PEG-ABT-199). PEG-ABT-199 has several advantages compared with pure ABT-199. 1.PEG-ABT-199 presents better aqueous dispersion and higher efficiencies of loading and encapsulation than pure ABT-199. 2. PEG-ABT-199 substantially enhances the anti-leukemic ability in vitro and in vivo compared with pure ABT-199. 3. PEG-ABT-199 has little effects on normal cells. 4. PEG-ABT-199 can reduce treatment cost.

CREB/Sp1-mediated MCL1 expression and NFκB-mediated ABCB1 expression modulate the cytotoxicity of daunorubicin in chronic myeloid leukemia cells

Although some studies have hinted at the therapeutic potential of daunorubicin (DNR) in chronic myeloid leukemia (CML), the mechanism by which DNR induces CML cell death is unclear. Therefore, this study aimed to investigate DNR-induced cell death signaling pathways in CML cell lines K562 and KU812. DNR-triggered apoptosis in K562 cells was characterized by inhibition of MCL1 expression, while restoration of MCL1 expression protected K562 cells from DNR-mediated cytotoxicity. In addition, DNR induced NOX4-dependent ROS production, leading to the activation of p38 MAPK and inactivation of Akt and ERK. Activated p38 MAPK stimulated protein phosphatase 2A-dependent dephosphorylation of CREB. Since Akt-mediated activation of ERK reduced β-TrCP mRNA stability, the inactivation of Akt-ERK axis increased β-TrCP expression, which in turn promoted proteasomal degradation of Sp1. Inhibition of CREB phosphorylation and Sp1 expression simultaneously reduced MCL1 transcription and protein expression. DNR-induced MCL1 suppression was not reliant on its ability to induce DNA damage. In addition, DNR induced the expression of drug exporter ABCB1 in K562 cells through the p38 MAPK/NFκB-mediated pathway, while imatinib or ABT-199 inhibited the DNR-induced effect. The combination of imatinib or ABT-199 with DNR showed synergistic cytotoxicity in K562 cells by increasing intracellular DNR retention. Cumulatively, our data indicate that DNR induces MCL1 downregulation in K562 cells by promoting p38 MAPK-mediated dephosphorylation of CREB and inhibiting the Akt-ERK axis-mediated Sp1 protein stabilization. Furthermore, experimental evidence indicates that DNR-induced death of KU812 cells occurs through a similar pathway.

Chemoimmunotherapy in the First-Line Treatment of Chronic Lymphocytic Leukaemia: Dead Yet, or Alive and Kicking?

The paradigm of first-line treatment of chronic lymphocytic leukaemia (CLL) is currently undergoing a radical change. On the basis of several randomised phase III trials showing prolongation of progression-free survival, chemoimmunotherapy is being replaced by treatment based on novel, orally available targeted inhibitors such as Bruton tyrosine kinase inhibitors ibrutinib and acalabrutinib or bcl-2 inhibitor venetoclax. However, the use of these agents may be associated with other disadvantages. First, with the exception of one trial in younger/fit patients, no studies have so far demonstrated benefit regarding the ultimate endpoint of overall survival. Second, oral inhibitors are extremely expensive and thus currently unavailable due to the absence of reimbursement in some countries. Third, treatment with ibrutinib and acalabrutinib necessitates long-term administration until progression; this may be associated with accumulation of late side effects, problems with patient compliance, and selection of resistant clones. Therefore, the identification of a subset of patients who could benefit from chemoimmunotherapy would be ideal. Current data suggest that patients with the mutated variable region of the immunoglobulin heavy chain (IGHV) achieve fairly durable remissions, especially when treated with fludarabine, cyclophosphamide, and rituximab (FCR) regimen. This review discusses current options for treatment-naïve patients with CLL.

Targeting Chronic Myeloid Leukemia Stem/Progenitor Cells Using Venetoclax-Loaded Immunoliposome

CML is a hematopoietic stem-cell disorder emanating from breakpoint cluster region/Abelson murine leukemia 1 (BCR/ABL) translocation. Introduction of different TKIs revolutionized treatment outcome in CML patients, but CML LSCs seem insensitive to TKIs and are detectable in newly diagnosed and resistant CML patients and in patients who discontinued therapy. It has been reported that CML LSCs aberrantly express some CD markers such as CD26 that can be used for the diagnosis and for targeting. In this study, we confirmed the presence of CD26+ CML LSCs in newly diagnosed and resistant CML patients. To selectively target CML LSCs/progenitor cells that express CD26 and to spare normal HSCs/progenitor cells, we designed a venetoclax-loaded immunoliposome (IL-VX). Our results showed that by using this system we could selectively target CD26+ cells while sparing CD26- cells. The efficiency of venetoclax in targeting CML LSCs has been reported and our system demonstrated a higher potency in cell death induction in comparison to free venetoclax. Meanwhile, treatment of patient samples with IL-VX significantly reduced CD26+ cells in both stem cells and progenitor cells population. In conclusion, this approach showed that selective elimination of CD26+ CML LSCs/progenitor cells can be obtained in vitro, which might allow in vivo reduction of side effects and attainment of treatment-free, long-lasting remission in CML patients.

Venetoclax for the treatment of elderly or chemotherapy-ineligible patients with acute myeloid leukemia: a step in the right direction or a game changer?

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive malignancy with poor prognosis and high rates of relapse, especially in elderly patients who are ineligible to receive intensive chemotherapy. Venetoclax, an oral BCL-2 inhibitor, is approved by the Food and Drug Administration in combination with hypomethylating agents or low-dose cytarabine in newly-diagnosed AML patients who are ineligible to receive intensive chemotherapy. Confirmatory phase III VIALE-A and VIALE-C trials showed a composite complete remission rate of 66.4% and 48%, respectively. Thus, further validating venetoclax as an attractive therapeutic option in the AML treatment landscape.

AREAS COVERED

A review of venetoclax in AML, focusing on preclinical and clinical data, toxicity profile, and mechanisms of resistance; and its strengths and weaknesses in regards to its current and future role in AML treatment is discussed. To find relevant studies, authors searched PubMed/Medline and ClinicalTrials.gov.

EXPERT OPINION

The introduction of venetoclax-based combination therapies has greatly expanded the therapeutic options for elderly and chemotherapy-ineligible AML patients. Additional studies with extended follow-up are necessary to address remaining open questions such as (I) durability of responses, (II) head-to-head comparisons with intensive chemotherapy in selected patients (e.g. TP53 mutations), and (III) novel triplet combinations using an HMA-venetoclax backbone.

Prognostic value of using glucosylceramide synthase and cytochrome P450 family 1 subfamily A1 expression levels for patients with triple-negative breast cancer following neoadjuvant chemotherapy

Neoadjuvant chemotherapy (NACT) has been considered to be the preferred treatment option for early operable triple-negative breast cancer (TNBC). However, resistance to drugs remains to be the barrier to the efficacy of NACT. Glucosylceramide synthase (GCS) and cytochrome P450 family 1 subfamily A1 (CYP1A1) have been previously associated with drug resistance in breast cancer. The present study aimed to explore whether the expression levels of GCS and/or CYP1A1 are associated with the prognosis of TNBC after NACT. Immunohistochemistry was used to detect and measure GCS and CYP1A1 expression. Associations between GCS or CYP1A1 expression and the clinicopathological characteristics, pathological complete response (pCR), clinical complete response (cCR) and disease-free survival (DFS) were analyzed. GCS expression was found to be associated with tumor size (P=0.021) and TNM staging (P=0.042), whilst CYP1A1 expression was associated with lymph node metastasis (P = 0.026) and TNM staging (P=0.034). The expression levels of GCS (P=0.024) and CYP1A1 (P=0.027) were upregulated after NACT. GCS and CYP1A1 expression were positively correlated (P=0.003; r=0.327). No difference was observed between the GCS⁺ (P=0.188) or CYP1A1⁺ group (P=0.073) and the GCS^- or CYP1A1^- group in terms of pCR. However, compared with that in the GCS⁺CYP1A1⁺ group, the pCR was markedly increased in the GCS^-CYP1A1^- group (P=0.031). The cCR was lower in the GCS⁺ (P=0.021) and CYP1A1⁺ groups (P=0.016) compared with in the GCS^- or CYP1A1^- group. The DFS rate (57.9 vs. 65.4%; P=0.049) was lower in the GCS⁺CYP1A1⁺ group compared with that in the GCS^-CYP1A1^- group. However, there was no statistical significance after P-value was adjusted for multiple comparisons using Bonferroni correction. In conclusion, co-expression of GCS and CYP1A1 was associated with pCR and DFS in TNBC, which may serve a role in the prediction of the prognosis of patients with TNBC following treatment with NACT.

Deciphering molecular mechanisms underlying chemoresistance in relapsed AML patients: towards precision medicine overcoming drug resistance

Background

Acute myeloid leukemia (AML) remains a devastating disease with a 5-year survival rate of less than 30%. AML treatment has undergone significant changes in recent years, incorporating novel targeted therapies along with improvements in allogeneic bone marrow transplantation techniques. However, the standard of care remains cytarabine and anthracyclines, and the primary hindrance towards curative treatment is the frequent emergence of intrinsic and acquired anticancer drug resistance. In this respect, patients presenting with chemoresistant AML face dismal prognosis even with most advanced therapies. Herein, we aimed to explore the potential implementation of the characterization of chemoresistance mechanisms in individual AML patients towards efficacious personalized medicine.

Methods

Towards the identification of tailored treatments for individual patients, we herein present the cases of relapsed AML patients, and compare them to patients displaying durable remissions following the same chemotherapeutic induction treatment. We quantified the expression levels of specific genes mediating drug transport and metabolism, nucleotide biosynthesis, and apoptosis, in order to decipher the molecular mechanisms underlying intrinsic and/or acquired chemoresistance modalities in relapsed patients. This was achieved by real-time PCR using patient cDNA, and could be readily implemented in the clinical setting.

Results

This analysis revealed pre-existing differences in gene expression levels between the relapsed patients and patients with lasting remissions, as well as drug-induced alterations at different relapse stages compared to diagnosis. Each of the relapsed patients displayed unique chemoresistance mechanisms following similar treatment protocols, which could have been missed in a large study aimed at identifying common drug resistance determinants.

Conclusions

Our findings emphasize the need for standardized evaluation of key drug transport and metabolism genes as an integral component of routine AML management, thereby allowing for the selection of treatments of choice for individual patients. This approach could facilitate the design of efficacious personalized treatment regimens, thereby reducing relapse rates of therapy refractory disease.

Advances of Nanoparticles for Leukemia Treatment

Leukemia is a liquid tumor caused by a hematopoietic stem cell malignant clone, which seriously affects the normal function of the hematopoietic system. Conventional drugs have poor therapeutic effects due to their poor specificity and stability. With the development of nanotechnology, nonviral nanoparticles bring hope for the efficient treatment of leukemia. Nanoparticles are easily modified. They can be designed to target lesion sites and control drug release. Thereby, nanoparticles can improve the effects of drugs and reduce side effects. This review mainly focuses on and summarizes the current research progress of nanoparticles to deliver different leukemia therapeutic drugs, as to demonstrate the potential of nanoparticles in leukemia treatment.

Implementing Systems Modelling and Molecular Imaging to Predict the Efficacy of BCL-2 Inhibition in Colorectal Cancer Patient-Derived Xenograft Models

Resistance to chemotherapy often results from dysfunctional apoptosis, however multiple proteins with overlapping functions regulate this pathway. We sought to determine whether an extensively validated, deterministic apoptosis systems model, 'DR_MOMP', could be used as a stratification tool for the apoptosis sensitiser and BCL-2 antagonist, ABT-199 in patient-derived xenograft (PDX) models of colorectal cancer (CRC). Through quantitative profiling of BCL-2 family proteins, we identified two PDX models which were predicted by DR_MOMP to be sufficiently sensitive to 5-fluorouracil (5-FU)-based chemotherapy (CRC0344), or less responsive to chemotherapy but sensitised by ABT-199 (CRC0076). Treatment with ABT-199 significantly improved responses of CRC0076 PDXs to 5-FU-based chemotherapy, but showed no sensitisation in CRC0344 PDXs, as predicted from systems modelling. ¹⁸F-Fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT) scans were performed to investigate possible early biomarkers of response. In CRC0076, a significant post-treatment decrease in mean standard uptake value was indeed evident only in the combination treatment group. Radiomic CT feature analysis of pre-treatment images in CRC0076 and CRC0344 PDXs identified features which could phenotypically discriminate between models, but were not predictive of treatment responses. Collectively our data indicate that systems modelling may identify metastatic (m)CRC patients benefitting from ABT-199, and that ¹⁸F-FDG-PET could independently support such predictions.

Allosteric modulation of sigma receptors by BH3 mimetics ABT-737, ABT-263 (Navitoclax) and ABT-199 (Venetoclax)

ABT-737, ABT-263 (Navitoclax) and ABT-199 (Venetoclax) are under intensive preclinical and clinical investigation as treatments for hematologic and other malignancies. These small molecules mimic pro-death B-cell lymphoma-2 (Bcl-2) Homology 3 (BH3) domain-only proteins. They also bear a structural resemblance to certain sigma (σ) receptor ligands. Moreover, the Bcl-2 and σ receptor protein families are both located primarily at the endoplasmic reticulum, mediate cell death and survival through protein-protein interactions, and physically associate. Accordingly, we examined the ability of the ABT series of BH3 mimetics to interact with σ receptors using radioligand-binding techniques. Negative allosteric modulation of [3H](+)-pentazocine, an agonist, binding to σ1 receptors in guinea pig brain membranes was observed for ABT-737, ABT-263 and ABT-199. Findings included reduction of specific binding to distinct plateaus in concentration-dependent fashion, significant slowing of radioligand dissociation kinetics, and decreases in radioligand affinity with no or modest changes in maximal receptor densities. Using a ternary complex model, dissociation constants (KX) for modulator binding to the σ1 receptor ranged from 1 to 2.5 μM, while negative cooperativity factors (α), representing the changes in affinity of ligand and modulator when bound as a ternary complex with the receptor, ranged from 0.15 to 0.42. These observations were extended and reinforced by studies using intact small cell (NCI-H69) and non-small cell (NCI-H23) lung cancer cells, and by using an antagonist σ1 receptor radioligand, E-N-1-(3'-[125I]iodoallyl)-N'-4-(3″,4″-dimethoxyphenethyl)piperazine, in mouse brain membranes. By contrast, exploratory studies indicate marked enhancement of the σ2 receptor binding of [3H]1,3-di-(o-tolyl)guanidine/(+)-pentazocine in NCI-H23 cells and guinea pig brain membranes. These findings raise intriguing questions regarding mechanism and potential functional outcomes.

Venetoclax: Targeting BCL2 in Hematological Cancers

Over the last years, targeted anti-cancer therapy with small-molecule inhibitors and antibodies moved to the forefront as a strategy to treat hematological cancers. These novel agents showed outstanding effects in treatment of patients, often irrespective of their underlying genetic features. However, evolution and selection of subclones with continuous treatment leads to disease relapse and resistance toward these novel drugs. Venetoclax (ABT-199) is a novel, orally bioavailable small-molecule inhibitor for selective targeting of B-cell lymphoma 2 (BCL2). Venetoclax is in clinical development and shows high efficacy and safety in particular in the treatment of chronic lymphocytic leukemia (CLL), but preliminarily also in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). The most important and impressive outcomes of venetoclax treatment include a rapid induction of apoptosis and drastic reduction of the tumor bulk within a few hours after administration. Venetoclax was approved by the FDA and EMA in 2016 for patients with previously treated CLL with del(17p13) and patients failing B cell receptor signaling inhibitors (EMA only), on the basis of a single-arm phase II trial demonstrating a tremendous response rate of 79% with complete remission in 20% of cases and an estimated 1-year progression-free survival of 72%. This review focuses on the mode of action, the preclinical models, and outcomes from various clinical trials with venetoclax in different hematologic cancers as well as future development.

Venetoclax for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Venetoclax, an orally bioavailable inhibitor of BCL-2, was approved in 2016 by the United States Food and Drug Administration (FDA) for the treatment of chronic lymphocytic leukemia (CLL) patients with 17p deletion [del(17p)], who have received at least one prior therapy. Areas covered: We focus on the mechanism of action of venetoclax and on the clinical trial data that led to the approval of venetoclax for CLL patients. We also review the studies in which this drug has being explored in combination with other anti-CLL drugs. Expert opinion: Data from early clinical trials have shown that venetoclax, as a single agent, is highly effective for relapsed/refractory CLL patients, including those cases with high-risk features. Furthermore, venetoclax seems to be an appropriate option for patients who progress on B-cell receptor (BCR) pathway kinase inhibitors. Venetoclax is also safe, with the most common serious adverse events being neutropenia. The risk of tumor lysis syndrome (TLS) can be reduced by a slow dose ramp-up, careful monitoring, and adequate prophylaxis. Ongoing trials will further clarify the safety and efficacy of venetoclax in combination with other drugs in both relapsed/refractory and untreated CLL patients.

Pharmacotherapy of relapsed/refractory chronic lymphocytic leukemia

INTRODUCTION

The treatment of relapsed/refractory (RR) CLL has been revolutionized by the advent of the new oral inhibitors of B-cell receptor (BCR) signaling and the pro-survival protein, B-cell lymphoma 2 (BCL2). Additionally, new and more potent monoclonal antibodies against CD20 have replaced/may replace rituximab in many settings. Areas covered: Herein, we review the entire therapeutic landscape of RR CLL, with particular attention to the new small-molecule kinase inhibitors and BH3-mimetics. We discuss preclinical data with these agents in CLL, cover available efficacy and safety information, and examine potential resistance mechanisms and possible rational combinations to circumvent them. Expert opinion: The availability of potent and selective inhibitors of BCR signaling and of the anti-apoptotic functions of BCL2 has enormously enhanced our therapeutic armamentarium, with unprecedented efficacy now observed in patients who historically had poor outcomes with chemoimmunotherapy (CIT), e.g., those with deletion 17p/11q and/or IGHV-unmutated disease. The next challenge is to optimally sequence these agents and develop rational combinations that will hopefully lead to deeper and more durable remissions than ever seen before. Indeed, long term relapse free survival, already achievable with CIT in patients with genetically favorable-risk disease, now appears to be a realistic possibility for most patients with CLL.

Venetoclax: A First-in-Class Oral BCL-2 Inhibitor for the Management of Lymphoid Malignancies

Objective: To review the pharmacology, efficacy, and safety of venetoclax for treatment of lymphoid malignancies. Data Sources: A literature search was performed of PubMed and MEDLINE databases (2005 to September 2016), abstracts from the American Society of Hematology and the American Society of Clinical Oncology, and ongoing studies from clinicaltrials.gov. Searches were performed utilizing the following key terms: venetoclax, ABT-199, GDC-199, obatoclax, GX15-070, BCL-2 inhibitor, navitoclax, ABT-263, and Venclexta. Study Selection/Data Extraction: Studies of pharmacology, pharmacokinetics, pharmacodynamics, clinical efficacy, and safety of venetoclax in lymphoid malignancies were identified. Data Synthesis: Recently, treatment of B-cell lymphoproliferative disorders has shifted from conventional cytotoxic chemotherapy to novel small-molecule inhibitors. The advent of recently Food and Drug Administration–approved oral agents ibrutinib and idelalisib has shifted the paradigm of chronic lymphocytic leukemia (CLL) treatment; however, complete remission is uncommon, and the outcome for patients progressing on these treatments remains poor. Attention has been focused on a novel target, the B-cell lymphoma-2 protein (BCL-2), which serves an essential role in regulation of apoptosis. Venetoclax has demonstrated efficacy in multiple subtypes of lymphoid malignancies, including patients with relapsed/refractory CLL harboring deletion 17p, with an overall response rate of nearly 80%. Venetoclax is generally well tolerated, with the significant adverse effect being tumor lysis syndrome, for which there are formal management recommendations. Conclusion: Venetoclax has demonstrated promising results in relapsed/refractory lymphoid malignancies, with an acceptable adverse effect profile. As the role of BCL-2 inhibition in various malignancies becomes further elucidated, venetoclax may offer benefit to a myriad other patient populations.

High-content screening identifies kinase inhibitors that overcome venetoclax resistance in activated CLL cells

Novel agents such as the Bcl-2 inhibitor venetoclax (ABT-199) are changing treatment paradigms for chronic lymphocytic leukemia (CLL) but important problems remain. Although some patients exhibit deep and durable responses to venetoclax as a single agent, other patients harbor subpopulations of resistant leukemia cells that mediate disease recurrence. One hypothesis for the origin of resistance to venetoclax is by kinase-mediated survival signals encountered in proliferation centers that may be unique for individual patients. An in vitro microenvironment model was developed with primary CLL cells that could be incorporated into an automated high-content microscopy-based screen of kinase inhibitors (KIs) to identify agents that may improve venetoclax therapy in a personalized manner. Marked interpatient variability was noted for which KIs were effective; nevertheless, sunitinib was identified as the most common clinically available KI effective in overcoming venetoclax resistance. Examination of the underlying mechanisms indicated that venetoclax resistance may be induced by microenvironmental signals that upregulate antiapoptotic Bcl-xl, Mcl-1, and A1, which can be counteracted more efficiently by sunitinib than by ibrutinib or idelalisib. Although patient-specific drug responses are common, for many patients, combination therapy with sunitinib may significantly improve the therapeutic efficacy of venetoclax.