Potential Biomarkers for Treatment Response to the BCL-2 Inhibitor Venetoclax: State of the Art and Future Directions

Single-cell systems pharmacology identifies development-driven drug response and combination therapy in B cell acute lymphoblastic leukemia

Leukemia can arise at various stages of the hematopoietic differentiation hierarchy, but the impact of developmental arrest on drug sensitivity is unclear. Applying network-based analyses to single-cell transcriptomes of human B cells, we define genome-wide signaling circuitry for each B cell differentiation stage. Using this reference, we comprehensively map the developmental states of B cell acute lymphoblastic leukemia (B-ALL), revealing its strong correlation with sensitivity to asparaginase, a commonly used chemotherapeutic agent. Single-cell multi-omics analyses of primary B-ALL blasts reveal marked intra-leukemia heterogeneity in asparaginase response: resistance is linked to pre-pro-B-like cells, with sensitivity associated with the pro-B-like population. By targeting BCL2, a driver within the pre-pro-B-like cell signaling network, we find that venetoclax significantly potentiates asparaginase efficacy in vitro and in vivo. These findings demonstrate a single-cell systems pharmacology framework to predict effective combination therapies based on intra-leukemia heterogeneity in developmental state, with potentially broad applications beyond B-ALL.

B-cell lymphoma 2 family members and sarcomas: a promising target in a heterogeneous disease

Targeting the B-cell lymphoma 2 (Bcl-2) family proteins has been the backbone for hematological malignancies with overall survival improvements. The Bcl-2 family is a major player in apoptosis regulation and, has captured the researcher's interest in the treatment of solid tumors. Sarcomas are a heterogeneous group of diseases, comprising several entities, with high morbidity and mortality and with few specific therapies available. The treatment for sarcomas is based on platinum regimens, with variable results and poor outcomes, especially in advanced lesions. The high number of different sarcoma entities makes treatment standardization as well as the performance of clinical trials difficult. The use of Bcl-2 family members modifiers has revealed promising results in in vitro and in vivo models and may be a valid option, especially when used in combination with chemotherapy. In this article, a revision of these results and possibilities for the use of Bcl-2 family members inhibitors in sarcomas was performed.

The Role of Venetoclax in Relapsed/Refractory Acute Myeloid Leukemia: Past, Present, and Future Directions

Relapsed and/or refractory (R/R) acute myeloid leukemia (AML) is hallmarked by dramatic prognosis. Treatment remains challenging, with allogeneic hematopoietic stem cell transplantation (HSCT) as the only curative option. The BCL-2 inhibitor venetoclax (VEN) has proven to be a promising therapy for AML and is currently the standard of care in combination with hypomethylating agents (HMAs) for newly diagnosed AML patients ineligible for induction chemotherapy. Given its satisfactory safety profile, VEN-based combinations are increasingly being investigated as a part of the therapeutic strategy for R/R AML. The current paper aims to provide a comprehensive review of the main evidence regarding VEN in the setting of R/R AML, with a specific focus on combinational strategies, including HMAs and cytotoxic chemotherapy, as well as different clinical settings, especially in view of the crucial role of HSCT. A discussion of what is known about drug resistance mechanisms and future combinational strategies is also provided. Overall, VEN-based regimes (mainly VEN + HMA) have provided unprecedented salvage treatment opportunities in patients with R/R AML, with low extra-hematological toxicity. On the other hand, the issue of overcoming resistance is one of the most important fields to be addressed in upcoming clinical research.

Augmenting Venetoclax Activity Through Signal Transduction in AML

Venetoclax, a small-molecule B-cell lymphoma 2 (BCL-2) inhibitor, selectively eradicates leukemic stem cells (LSCs). While venetoclax has revolutionized the treatment of acute myeloid leukemia (AML), treatment failure and disease relapse are common. Mechanisms underlying venetoclax resistance are surprisingly heterogeneous. Venetoclax resistance encompasses a spectrum of genetic and epigenetic changes, with numerous pathways contributing to the upregulation of additional anti-apoptotic proteins. In this review, we address the mechanisms of venetoclax resistance in the context of signal transduction. We emphasize how aberrant cell signaling impairs apoptosis and predisposes to venetoclax failure. Commonly activated pathways, such as FLT3, PI3K/AKT/mTOR, and RAS, contribute to upregulated anti-apoptotic mediators and are frequently responsible for refractory disease or disease relapse. We highlight novel combination strategies aimed at disabling constitutively active signal transduction to augment response and overcome venetoclax resistance.

Rationale for Combining the BCL2 Inhibitor Venetoclax with the PI3K Inhibitor Bimiralisib in the Treatment of IDH2- and FLT3-Mutated Acute Myeloid Leukemia

In October 2020, the FDA granted regular approval to venetoclax (ABT-199) in combination with hypomethylating agents for newly-diagnosed acute myeloid leukemia (AML) in adults 75 years or older, or in patients with comorbidities precluding intensive chemotherapy. The treatment response to venetoclax combination treatment, however, may be short-lived, and leukemia relapse is the major cause of treatment failure. Multiple studies have confirmed the upregulation of the anti-apoptotic proteins of the B-cell lymphoma 2 (BCL2) family and the activation of intracellular signaling pathways associated with resistance to venetoclax. To improve treatment outcome, compounds targeting anti-apoptotic proteins and signaling pathways have been evaluated in combination with venetoclax. In this study, the BCL-XL inhibitor A1331852, MCL1-inhibitor S63845, dual PI3K-mTOR inhibitor bimiralisib (PQR309), BMI-1 inhibitor unesbulin (PTC596), MEK-inhibitor trametinib (GSK1120212), and STAT3 inhibitor C-188-9 were assessed as single agents and in combination with venetoclax, for their ability to induce apoptosis and cell death in leukemic cells grown in the absence or presence of bone marrow stroma. Enhanced cytotoxic effects were present in all combination treatments with venetoclax in AML cell lines and AML patient samples. Elevated in vitro efficacies were observed for the combination treatment of venetoclax with A1331852, S63845 and bimiralisib, with differing response markers for each combination. For the venetoclax and bimiralisib combination treatment, responders were enriched for IDH2 and FLT3 mutations, whereas non-responders were associated with PTPN11 mutations. The combination of PI3K/mTOR dual pathway inhibition with bimiralisib and BCL2 inhibition with venetoclax has emerged as a candidate treatment in IDH2- and FLT3-mutated AML.

No time to die? Intrinsic apoptosis signaling in hematopoietic stem and progenitor cells and therapeutic implications

PURPOSE OF REVIEW

Dysregulated apoptosis contributes to the pathogenesis of many hematologic malignancies. BH3-mimetics, antagonists of antiapoptotic BCL-2 proteins, represent novel, and promising cancer drugs. While the acute myelosuppressive effects of Venetoclax, the first Food and Drug Administration approved BCL-2 inhibitor, are fairly well described, little is known about side effects of novel BH3-mimetics and effects of chronic Venetoclax treatment.

RECENT FINDINGS

Highly relevant publications focused on the effects of acute and chronic Venetoclax therapy, with focus on cell-type specific adaptive mechanisms, the emergence of clonal hematopoiesis, and the selection of BAX-mutated hematopoietic cells in patients treated with Venetoclax for a long period. Important advances were made in understanding primary and secondary Venetoclax resistance and prediction of Venetoclax response. Combination therapies of BH3-mimetics targeting different BCL-2 proteins are highly anticipated. However, human stem and progenitors require both MCL-1 and BCL-XL for survival, and serious myelosuppressive effects of combined MCL-1/BCL-XL inhibition can be expected.

SUMMARY

Long-term studies are indispensable to profile the chronic side effects of Venetoclax and novel BH3-mimetics and better balance their risk vs. benefit in cancer therapy. Combination therapies will be powerful, but potentially limited by severe myelosuppression. For precision medicine, a better knowledge of BCL-2 proteins in the healthy and diseased hematopoietic system is required.

Making Sense of Antisense Oligonucleotide Therapeutics Targeting Bcl-2

The B-cell lymphoma 2 (Bcl-2) family, comprised of pro- and anti-apoptotic proteins, regulates the delicate balance between programmed cell death and cell survival. The Bcl-2 family is essential in the maintenance of tissue homeostasis, but also a key culprit in tumorigenesis. Anti-apoptotic Bcl-2, the founding member of this family, was discovered due to its dysregulated expression in non-Hodgkin’s lymphoma. Bcl-2 is a central protagonist in a wide range of human cancers, promoting cell survival, angiogenesis and chemotherapy resistance; this has prompted the development of Bcl-2-targeting drugs. Antisense oligonucleotides (ASO) are highly specific nucleic acid polymers used to modulate target gene expression. Over the past 25 years several Bcl-2 ASO have been developed in preclinical studies and explored in clinical trials. This review will describe the history and development of Bcl-2-targeted ASO; from initial attempts, optimizations, clinical trials undertaken and the promising candidates at hand.