Novel Agents in Chronic Lymphocytic Leukemia: New Combination Therapies and Strategies to Overcome Resistance

Knowledge, skills, and confidence gaps impacting treatment decision making in relapsed/refractory chronic lymphocytic leukemia and mantle cell lymphoma: a quantitative survey study in France, Germany, and the United States

BACKGROUND

With recent advancements in the treatment of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), healthcare specialists may face challenges making treatment and management decisions based on latest evidence for the optimal care of patients with these conditions. This study aimed to identify specific knowledge, skills, and confidence gaps impacting the treatment of CLL and MCL, to inform future educational activities.

METHODS

Hematologists and hemato-oncologists (HCPs, n = 224) from France (academic settings), Germany, and the United States (academic and community settings) responded to a 15-minute quantitative needs assessment survey that measured perceived knowledge, skills, and confidence levels regarding different aspects of treatment and management of CLL and MCL patients, as well as clinical case questions. Descriptive statistics (cross tabulations) and Chi-square tests were conducted.

RESULTS

Four areas of educational need were identified: (1) sub-optimal knowledge of treatment guidelines; (2) sub-optimal knowledge of molecular testing to inform CLL/MCL treatment decisions; (3) sub-optimal skills when making treatment decisions according to patient profile (co-morbidities, molecular testing results); and (4) challenges balancing the risk of toxicities with benefits of treatment. Over one-third of the respondents reported skill gaps when selecting suitable treatment options and prescribing therapies and reported a lack in confidence to initiate and manage treatment. Larger gaps in knowledge of guidelines and skills in patient assessment were identified in MCL, compared to CLL.

CONCLUSIONS

This study suggests the need for continuing medical education specifically to improve knowledge of treatment guidelines, and to assist clinicians in developing skills and confidence when faced with clinical decision-making scenarios of patients with specific comorbidities and/or molecular test results, for example, through case-based learning activities.

Lysosome-Disrupting Agents in Combination with Venetoclax Increase Apoptotic Response in Primary Chronic Lymphocytic Leukemia (CLL) Cells Mediated by Lysosomal Cathepsin D Release and Inhibition of Autophagy

Venetoclax and obinutuzumab are becoming frontline therapies for chronic lymphocytic leukemia (CLL) patients. Unfortunately, drug resistance still occurs, and the combination could be immunosuppressive. Lysosomes have previously been identified as a target for obinutuzumab cytotoxicity in CLL cells, but the mechanism remains unclear. In addition, studies have shown that lysosomotropic agents can cause synergistic cell death in vitro when combined with the BTK inhibitor, ibrutinib, in primary CLL cells. This indicates that targeting lysosomes could be a treatment strategy for CLL. In this study, we have shown that obinutuzumab induces lysosome membrane permeabilization (LMP) and cathepsin D release in CLL cells. Inhibition of cathepsins reduced obinutuzumab-induced cell death in CLL cells. We further determined that the lysosomotropic agent siramesine in combination with venetoclax increased cell death in primary CLL cells through an increase in reactive oxygen species (ROS) and cathepsin release. Siramesine treatment also induced synergistic cytotoxicity when combined with venetoclax. Microenvironmental factors IL4 and CD40L or incubation with HS-5 stromal cells failed to significantly protect CLL cells from siramesine- and venetoclax-induced apoptosis. We also found that siramesine treatment inhibited autophagy through reduced autolysosomes. Finally, the autophagy inhibitor chloroquine failed to further increase siramesine-induced cell death. Taken together, lysosome-targeting drugs could be an effective strategy in combination with venetoclax to overcome drug resistance in CLL.

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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Resisting the Resistance: Navigating BTK Mutations in Chronic Lymphocytic Leukemia (CLL)

Bruton's tyrosine kinase (BTK) plays a key role in the B-cell receptor (BCR) signaling pathway and confers anti-apoptotic and proliferative properties to malignant B-cells in chronic lymphocytic leukemia (CLL). Small molecule BTK inhibitors were designed to bind BTK's active site and block downstream signaling. These drugs have now been used in the treatment of thousands of patients with CLL, the most common form of leukemia in the western hemisphere. However, adverse effects of early generations of BTK inhibitors and resistance to treatment have led to the development of newer, more selective and non-covalent BTK inhibitors. As the use of these newer generation BTK inhibitors has increased, novel BTK resistance mutations have come to light. This review aims to discuss previously known and novel BTK mutations, their mechanisms of resistance, and their relationship with patient treatment. Also discussed here are future studies that are needed to investigate the underlying cause allowing these mutations to occur and how they incite resistance. New treatments on the horizon that attempt to maneuver around these resistance mutations can be met with new resistance mutations, creating an unmet need for patients with CLL. Novel therapies and combinations that address all forms of resistance are discussed.

Characterization of Three Somatic Mutations in the 3'UTR of RRAS2 and Their Inverse Correlation with Lymphocytosis in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by progressive accumulation of a rare population of CD5+ B-lymphocytes in peripheral blood, bone marrow, and lymphoid tissues. CLL exhibits remarkable clinical heterogeneity, with some patients presenting with indolent disease and others progressing rapidly to aggressive CLL. The significant heterogeneity of CLL underscores the importance of identifying novel prognostic markers. Recently, the RAS-related gene RRAS2 has emerged as both a driver oncogene and a potential marker for CLL progression, with higher RRAS2 expression associated with poorer disease prognosis. Although missense somatic mutations in the coding sequence of RRAS2 have not been described in CLL, this study reports the frequent detection of three somatic mutations in the 3' untranslated region (3'UTR) affecting positions +26, +53, and +180 downstream of the stop codon in the mRNA. An inverse relationship was observed between these three somatic mutations and RRAS2 mRNA expression, which correlated with lower blood lymphocytosis. These findings highlight the importance of RRAS2 overexpression in CLL development and prognosis and point to somatic mutations in its 3'UTR as novel mechanistic clues. Our results may contribute to the development of targeted therapeutic strategies and improved risk stratification for CLL patients.

Expression and Activity of the NF-κB Subunits in Chronic Lymphocytic Leukaemia: A Role for RelB and Non-Canonical Signalling

BACKGROUND

Canonical NF-κB signalling by p65 (RelA) confers chemo-resistance and poor survival in chronic lymphocytic leukaemia (CLL). The role of non-canonical NF-κB signalling (leading to RelB and p52 subunit activation) in CLL is less understood, but given its importance in other B-cell tumour types, we theorised that RelB and p52 may also contribute to the pathology of CLL.

METHODS

DNA binding activity of all five NF-kB subunits, p65, p50, RelB, p52, and c-Rel, was quantified using ELISA and correlated to ex vivo chemoresistance, CD40L-stimulated signalling (to mimic the lymph node microenvironment), and clinical data.

RESULTS

Importantly, we show for the first time that high basal levels of RelB DNA binding correlate with nuclear RelB protein expression and are associated with del(11q), ATM dysfunction, unmutated IGHV genes, and shorter survival. High levels of nuclear p65 are prevalent in del(17p) cases (including treatment-naïve patients) and also correlate with the outcome. CD40L-stimulation resulted in rapid RelB activation, phosphorylation and processing of p100, and subsequent CLL cell proliferation.

CONCLUSIONS

These data highlight a role for RelB in driving CLL cell tumour growth in a subset of patients and therefore strategies designed to inhibit non-canonical NF-κB signalling represent a novel approach that will have therapeutic benefit in CLL.

The preclinical discovery and development of orelabrutinib as a novel treatment option for B-cell lymphoid malignancies

INTRODUCTION

Bruton's tyrosine kinase (BTK) inhibitors have recently been approved for clinical use against several B-cell indolent lymphoid malignancies, both as single agents or in combination. One second-generation BTK inhibitor that is being developed for the treatment of B-cell hematological malignancies, as well as for autoimmune disorders, is orelabrutinib.

AREAS COVERED

This paper reviews recent developments in the use of orelabrutinib against B-cell indolent lymphoid malignancies such as chronic lymphocytic leukemia, mantle cell lymphoma, diffuse large B-cell lymphoma, Waldenstrom macroglobulinemia and central nervous system lymphoma. Google Scholar and PubMed were initially searched for articles, and the corpus of articles was broadened by reviewing the references of the identified papers. All were in English. The corpus comprised papers from 2016 to April 2023. In addition, a manual search was performed of conference proceedings from the last five years of The American Society of Hematology, American Society of Clinical Oncology and the European Hematology Association.

EXPERT OPINION

Orelabrutinib is an active drug in indolent and aggressive B-cell lymphoid malignancies. It demonstrates high selectivity, good efficacy and an excellent safety profile. Nevertheless, further clinical trials are required to optimize its use. In addition, several other highly selective BTK inhibitors are being examined in early-phase studies.

Treatment Refractoriness in Chronic Lymphocytic Leukemia: Old and New Molecular Biomarkers

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. Despite its indolent clinical course, therapy refractoriness and disease progression still represent an unmet clinical need. Before the advent of pathway inhibitors, chemoimmunotherapy (CIT) was the commonest option for CLL treatment and is still widely used in areas with limited access to pathway inhibitors. Several biomarkers of refractoriness to CIT have been highlighted, including the unmutated status of immunoglobulin heavy chain variable genes and genetic lesions of TP53, BIRC3 and NOTCH1. In order to overcome resistance to CIT, targeted pathway inhibitors have become the standard of care for the treatment of CLL, with practice-changing results obtained through the inhibitors of Bruton tyrosine kinase (BTK) and BCL2. However, several acquired genetic lesions causing resistance to covalent and noncovalent BTK inhibitors have been reported, including point mutations of both BTK (e.g., C481S and L528W) and PLCG2 (e.g., R665W). Multiple mechanisms are involved in resistance to the BCL2 inhibitor venetoclax, including point mutations that impair drug binding, the upregulation of BCL2-related anti-apoptotic family members, and microenvironmental alterations. Recently, immune checkpoint inhibitors and CAR-T cells have been tested for CLL treatment, obtaining conflicting results. Potential refractoriness biomarkers to immunotherapy were identified, including abnormal levels of circulating IL-10 and IL-6 and the reduced presence of CD27⁺CD45RO^- CD8⁺ T cells.

Treatment Discontinuation Patterns for Patients With Chronic Lymphocytic Leukemia in Real-World Settings: Results From a Multi-Center International Study

INTRODUCTION

This study assessed treatment discontinuation patterns and reasons among chronic lymphocytic leukemia (CLL) patients initiating first-line (1L) and second-line (2L) treatments in real-world settings.

MATERIALS AND METHODS

Using deidentified electronic medical records from the CLL Collaborative Study of Real-World Evidence, premature treatment discontinuation was assessed among FCR, BR, BTKi-based, and BCL-2-based regimen cohorts.

RESULTS

Of 1364 1L patients (initiated in 1997-2021), 190/13.9% received FCR (23.7% discontinued prematurely); 255/18.7% received BR (34.5% discontinued prematurely); 473/34.7% received BTKi-based regimens, of whom 28.1% discontinued prematurely; and 43/3.2% received venetoclax-based regimens, of whom 16.3% discontinued prematurely (venetoclax monotherapy: 7/0.5%, of whom 42.9% discontinued; VG/VR: 36/2.6%, of whom 11.1% discontinued). The most common reasons for treatment discontinuation were adverse events (FCR: 25/13.2%; BR: 36/14.1%; BTKi-based regimens: 75/15.9%) and disease progression (venetoclax-based: 3/7.0%). Of 626 2L patients, 20/3.2% received FCR (50.0% discontinued); 62/9.9% received BR (35.5% discontinued); 303/48.4% received BTKi-based regimens, of whom 38.0% discontinued; and 73/11.7% received venetoclax-based regimens, of whom 30.1% discontinued (venetoclax monotherapy: 27/4.3%, of whom 29.6% discontinued; VG/VR: 43/6.9%, of whom 27.9% discontinued). The most common reasons for treatment discontinuation were adverse events (FCR: 6/30.0%; BR: 11/17.7%; BTKi-based regimens: 60/19.8%; venetoclax-based: 6/8.2%).

CONCLUSION

The findings of this study highlight the continued need for tolerable therapies in CLL, with finite therapy offering a better tolerated option for patients who are newly diagnosed or relapsed/refractory to prior treatments.

Learning from TCR Signaling and Immunological Synapse Assembly to Build New Chimeric Antigen Receptors (CARs)

Chimeric antigen receptor (CAR) T cell immunotherapy is a revolutionary pillar in cancer treatment. Clinical experience has shown remarkable successes in the treatment of certain hematological malignancies but only limited efficacy against B cell chronic lymphocytic leukemia (CLL) and other cancer types, especially solid tumors. A wide range of engineering strategies have been employed to overcome the limitations of CAR T cell therapy. However, it has become increasingly clear that CARs have unique, unexpected features; hence, a deep understanding of how CARs signal and trigger the formation of a non-conventional immunological synapse (IS), the signaling platform required for T cell activation and execution of effector functions, would lead a shift from empirical testing to the rational design of new CAR constructs. Here, we review current knowledge of CARs, focusing on their structure, signaling and role in CAR T cell IS assembly. We, moreover, discuss the molecular features accounting for poor responses in CLL patients treated with anti-CD19 CAR T cells and propose CLL as a paradigm for diseases connected to IS dysfunctions that could significantly benefit from the development of novel CARs to generate a productive anti-tumor response.

HIF-PH Encoded by EGLN1 Is a Potential Therapeutic Target for Chronic Lymphocytic Leukemia

Owing to the recent emergence of drug resistance to Bruton's tyrosine kinase inhibitors (BTK) in chronic lymphocytic leukemia (CLL) treatment, it is crucial to identify alternative therapeutic targets. Therefore, we aimed to identify therapeutic options for CLL besides BTK. We identified that HIF1A expression was higher in CLL patients than in controls, which may suggest good prognosis. We used a lentiviral knockdown of EGLN1 (encoding hypoxia-inducible factor prolyl hydroxylase [HIF-PH]) and found that the growth of MEC-1 cells slowed in the knockdown group. Treatment of CLL cell lines MEC-1 and HG3 with the HIF-PH inhibitor molidustat showed that molidustat could induce apoptosis in a concentration-dependent manner in CLL cells and had low cytotoxicity at this concentration. CXCR4, HIF1A, SLC2AI, and VEGF, the downstream molecules of the HIF pathway, were upregulated after molidustat treatment. Western blotting results indicated that molidustat increased HIF1A expression in CLL cell lines and cells from CLL patients, and sequencing/quantitative PCR analysis demonstrated that the ribosome biogenesis pathway was inhibited in MEC-1 cells after molidustat treatment. We further identified synergistic cytotoxicity of molidustat in combination with ibrutinib on the MEC-1 and HG3 cell lines at certain concentrations. Therefore, molidustat is a potential therapeutic option for CLL.

Combining BTK inhibitors with BCL2 inhibitors for treating chronic lymphocytic leukemia and mantle cell lymphoma

The advent of BTK inhibitors has changed the treatment of patients with chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). The first-in-class BTK inhibitor ibrutinib has shown remarkable therapeutic effects and manageable toxicities in multiple clinical trials. The second-generation BTK inhibitors, including acalabrutinib and zanubrutinib, also show remarkable efficacies. However, using BTK inhibitors as monotherapies requires continuous treatment. Resistance to BTK inhibitors and severe side effects unavoidably occur during BTK inhibitor monotherapy, frequently resulting in treatment failure. The addition of the BCL2 inhibitor venetoclax to BTK inhibitor may improve the therapeutic effects and result in deeper responses, providing a potential fixed-duration treatment, especially for patients with CLL. In this review, by focusing on CLL and MCL, we discussed the rationale for the combinational use and summarized the current data on the combinations of BTK inhibitors and venetoclax in patients with CLL and MCL.

New Treatment Options for Newly-Diagnosed and Relapsed Chronic Lymphocytic Leukemia

OPINION STATEMENT

The better understanding of the biology of chronic lymphocytic leukemia (CLL) gained over the past decade has led to the development and introduction of several targeted drugs, with an demonstrable improvement in the prognosis for this currently incurable condition. Currently, Bruton's tyrosine kinase (BTK) inhibitors, phosphoinositide 3-kinase (PI3K) inhibitors, venetoclax, and CD20 monoclonal antibodies are the key elements in the treatment of both previously untreated and relapsed/refractory CLL patients. Ibrutinib was the first BTK inhibitor approved for clinical use, and showed excellent efficacy and an acceptable safety profile. Following this, the better-tolerated second-generation irreversible BTK inhibitors acalabrutinib and zanubrutinib have been introduced for the treatment of lymphoid malignancies, and acalabrutinib was approved for CLL. When used as single drugs, BTK inhibitors are given continuously until unacceptable toxicity or disease progression; however, when combined with venetoclax and/or CD20 antibodies, they induce deeper response and can be given for a limited time. Recently, promising new reversible BTK inhibitors pirtobrutinib and nemtabrutinib were discovered, and these seem to be more active and better tolerated than their irreversible predecessors. However, they are in an early phase of development and are not currently approved for CLL. The phosphatidylinositol 3-kinase (PI3K) inhibitors idelalisib and duvelisib are highly effective in patients with relapsed CLL, including high-risk disease. The major limitations for their use are adverse events, mostly of autoimmune origin (hepatitis, enteritis/colitis, and pneumonitis). Otherwise, cellular therapies like allogeneic hematopoietic stem cell transplantation and chimeric antigen receptor (CAR) T cells and bispecific monoclonal antibodies offer promise for patients who have failed BTK inhibitors and venetoclax treatment. In the coming years, it is likely that novel targeted therapies will replace immunochemotherapy regimens in most patients.

Glycerophosphoinositol Promotes Apoptosis of Chronic Lymphocytic Leukemia Cells by Enhancing Bax Expression and Activation

An imbalance in the expression of pro- and anti-apoptotic members of the Bcl-2 family of apoptosis-regulating proteins is one of the main biological features of CLL, highlighting these proteins as therapeutic targets for treatment of this malignancy. Indeed, the Bcl-2 inhibitor Venetoclax is currently used for both first-line treatment and treatment of relapsed or refractory CLL. An alternative avenue is the transcriptional modulation of Bcl-2 family members to tilt their balance towards apoptosis. Glycerophosphoinositol (GroPIns) is a biomolecule generated from membrane phosphoinositides by the enzymes phospholipase A2 and lysolipase that pleiotropically affects key cellular functions. Mass-spectrometry analysis of GroPIns interactors recently highlighted the ability of GroPIns to bind to the non-receptor tyrosine phosphatase SHP-1, a known promoter of Bax expression, suggesting that GroPIns might correct the Bax expression defect in CLL cells, thereby promoting their apoptotic demise. To test this hypothesis, we cultured CLL cells in the presence of GroPIns, alone or in combination with drugs commonly used for treatment of CLL. We found that GroPIns alone increases Bax expression and apoptosis in CLL cells and enhances the pro-apoptotic activity of drugs used for CLL treatment in a SHP-1 dependent manner. Interestingly, among GroPIns interactors we found Bax itself. Short-term treatments of CLL cells with GroPIns induce Bax activation and translocation to the mitochondria. Moreover, GroPIns enhances the pro-apoptotic activity of Venetoclax and Fludarabine in CLL cells. These data provide evidence that GroPIns exploits two different pathways converging on Bax to promote apoptosis of leukemic cells and pave the way to new studies aimed at testing GroPIns in combination therapies for the treatment of CLL.

Immunoproteasome Activity in Chronic Lymphocytic Leukemia as a Target of the Immunoproteasome-Selective Inhibitors

Targeting proteasome with proteasome inhibitors (PIs) is an approved treatment strategy in multiple myeloma that has also been explored pre-clinically and clinically in other hematological malignancies. The approved PIs target both the constitutive and the immunoproteasome, the latter being present predominantly in cells of lymphoid origin. Therapeutic targeting of the immunoproteasome in cells with sole immunoproteasome activity may be selectively cytotoxic in malignant cells, while sparing the non-lymphoid tissues from the on-target PIs toxicity. Using activity-based probes to assess the proteasome activity profile and correlating it with the cytotoxicity assays, we identified B-cell chronic lymphocytic leukemia (B-CLL) to express predominantly immunoproteasome activity, which is associated with high sensitivity to approved proteasome inhibitors and, more importantly, to the immunoproteasome selective inhibitors LU005i and LU035i, targeting all immunoproteasome active subunits or only the immunoproteasome β5i, respectively. At the same time, LU102, a proteasome β2 inhibitor, sensitized B-CLL or immunoproteasome inhibitor-inherently resistant primary cells of acute myeloid leukemia, B-cell acute lymphoblastic leukemia, multiple myeloma and plasma cell leukemia to low doses of LU035i. The immunoproteasome thus represents a novel therapeutic target, which warrants further testing with clinical stage immunoproteasome inhibitors in monotherapy or in combinations.

Pharmacological modulation of Kv1.3 potassium channel selectively triggers pathological B lymphocyte apoptosis in vivo in a genetic CLL model

BACKGROUND

Ion channels are emerging as promising oncological targets. The potassium channels Kv1.3 and IKCa are highly expressed in the plasma membrane and mitochondria of human chronic lymphocytic leukemia (CLL) cells, compared to healthy lymphocytes. In vitro, inhibition of mitoKv1.3 by PAPTP was shown to kill ex vivo primary human CLL cells, while targeting IKCa with TRAM-34 decreased CLL cell proliferation.

METHODS

Here we evaluated the effect of the above drugs in CLL cells from ibrutinib-resistant patients and in combination with Venetoclax, two drugs used in the clinical practice. The effects of the drugs were tested also in the Eμ-TCL1 genetic CLL murine model, characterized by a lympho-proliferative disease reminiscent of aggressive human CLL. Eμ-TCL1 mice showing overt disease state were treated with intraperitoneal injections of non-toxic 5 nmol/g PAPTP or 10 nmol/g TRAM-34 once a day and the number and percentage of pathological B cells (CD19⁺CD5⁺) in different, pathologically relevant body districts were determined.

RESULTS

We show that Kv1.3 expression correlates with sensitivity of the human and mouse neoplastic cells to PAPTP. Primary CLL cells from ibrutinib-resistant patients could be killed with PAPTP and this drug enhanced the effect of Venetoclax, by acting on mitoKv1.3 of the inner mitochondrial membrane and triggering rapid mitochondrial changes and cytochrome c release. In vivo, after 2 week- therapy of Eμ-TCL1 mice harboring distinct CLL clones, leukemia burden was reduced by more than 85%: the number and percentage of CLL B cells fall in the spleen and peritoneal cavity and in the peripheral blood, without signs of toxicity. Notably, CLL infiltration into liver and spleen and splenomegaly were also drastically reduced upon PAPTP treatment. In contrast, TRAM-34 did not exert any beneficial effect when administered in vivo to Eμ-TCL1 mice at non-toxic concentration.

CONCLUSION

Altogether, by comparing vehicle versus compound effect in different Eμ-TCL1 animals bearing unique clones similarly to CLL patients, we conclude that PAPTP significantly reduced leukemia burden in CLL-relevant districts, even in animals with advanced stage of the disease. Our results thus identify PAPTP as a very promising drug for CLL treatment, even for the chemoresistant forms of the disease.

The Role of Bruton's Kinase Inhibitors in Chronic Lymphocytic Leukemia: Current Status and Future Directions

The use of Bruton's tyrosine kinase (BTK) inhibitors has changed the management and clinical history of patients with chronic lymphocytic leukemia (CLL). BTK is a critical molecule that interconnects B-cell antigen receptor (BCR) signaling. BTKis are classified into two categories: irreversible (covalent) inhibitors and reversible (non-covalent) inhibitors. Ibrutinib was the first irreversible BTK inhibitor approved by the U.S. Food and Drug Administration in 2013 as a breakthrough therapy in CLL patients. Subsequently, several studies have evaluated the efficacy and safety of new agents with reduced toxicity when compared with ibrutinib. Two other irreversible, second-generation BTK inhibitors, acalabrutinib and zanubrutinib, were developed to reduce ibrutinib-mediated adverse effects. Additionally, new reversible BTK inhibitors are currently under development in early-phase studies to improve their activity and to diminish adverse effects. This review summarizes the pharmacology, clinical efficacy, safety, dosing, and drug-drug interactions associated with the treatment of CLL with BTK inhibitors and examines their further implications.

Bruton Tyrosine Kinase Inhibitors in B-Cell Malignancies: Their Use and Differential Features

Starting with the first-in-class agent ibrutinib, the development of Bruton tyrosine kinase (BTK) inhibitors has led to dramatic improvements in the management of B-cell malignancies. Subsequently, more-highly selective second-generation BTK inhibitors (including acalabrutinib, zanubrutinib, tirabrutinib and orelabrutinib) have been developed, primarily with an aim to reduce off-target toxicities. More recently, third-generation agents including the non-covalent BTK inhibitors pirtobrutinib and nemtabrutinib have entered later-stage clinical development. BTK inhibitors have shown strong activity in a range of B-cell malignancies, including chronic lymphocytic leukaemia/small lymphocytic lymphoma, mantle cell lymphoma, Waldenström's macroglobulinaemia and marginal zone lymphoma. The agents have acceptable tolerability, with adverse events generally being manageable with dosage modification. This review article summarises the evidence supporting the role of BTK inhibitors in the management of B-cell malignancies, including highlighting some differential features between agents.

Progestins as Anticancer Drugs and Chemosensitizers, New Targets and Applications

Progesterone and its synthetic analogues, progestins, participate in the regulation of cell differentiation, proliferation and cell cycle progression. Progestins are usually applied for contraception, maintenance of pregnancy, and hormone replacement therapy. Recently, their effectiveness in the treatment of hormone-sensitive tumors was revealed. According to current data, the anticancer activity of progestins is mainly mediated by their cytotoxic and chemosensitizing influence on different cancer cells. In connection with the detection of previously unknown targets of the progestin action, which include the membrane-associated progesterone receptor (PR), non-specific transporters related to the multidrug resistance (MDR) and mitochondrial permeability transition pore (MPTP), and checkpoints of different signaling pathways, new aspects of their application have emerged. It is likely that the favorable influence of progestins is predominantly associated with the modulation of expression and activity of MDR-related proteins, the inhibition of survival signaling pathways, especially TGF-β and Wnt/β-catenin pathways, which activate the proliferation and promote MDR in cancer cells, and the facilitation of mitochondrial-dependent apoptosis. Biological effects of progestins are mediated by the inhibition of these signaling pathways, as well as the direct interaction with the nucleotide-binding domain of ABC-transporters and mitochondrial adenylate translocase as an MPTP component. In these ways, progestins can restore the proliferative balance, the ability for apoptosis, and chemosensitivity to drugs, which is especially important for hormone-dependent tumors associated with estrogen stress, epithelial-to-mesenchymal transition, and drug resistance.

Challenges with Approved Targeted Therapies against Recurrent Mutations in CLL: A Place for New Actionable Targets

Chronic lymphocytic leukemia (CLL) is characterized by a high degree of genetic variability and interpatient heterogeneity. In the last decade, novel alterations have been described. Some of them impact on the prognosis and evolution of patients. The approval of BTK inhibitors, PI3K inhibitors and Bcl-2 inhibitors has drastically changed the treatment of patients with CLL. The effect of these new targeted therapies has been widely analyzed in TP53-mutated cases, but few data exist about the response of patients carrying other recurrent mutations. In this review, we describe the biological pathways recurrently altered in CLL that might have an impact on the response to these new therapies together with the possibility to use new actionable targets to optimize treatment responses.

Current and emerging investigational venetoclax-based therapies in chronic lymphocytic leukemia

Introduction: Venetoclax has emerged as a breakthrough treatment which has revolutionized the therapeutic paradigm of chronic lymphocytic leukemia (CLL). This is primarily attributed to the efficacy of venetoclax as a time-limited, chemo-free, therapy in a field dominated by targeted agents given on a continuous schedule. Furthermore, compelling clinical data support the use of venetoclax in combination with other targeted agents in the hope of preventing drug resistance due to the emergence of acquired mutations.Areas covered: This paper provides an overview of clinical results of newly approved or investigational venetoclax-based therapies for CLL. In view of current and potential roles in CLL care, the strengths and disadvantages of venetoclax-combinations are discussed. The MEDLINE database, ClinicalTrials.gov and conference proceedings were all reviewed to select the relevant literature.Expert opinion: While the advent of venetoclax-based combinations has significantly expanded the therapeutic options for patients with CLL, further research with longer follow-up is required to address remaining open questions such as (I) the role of venetoclax as fixed duration therapy(II) timing and threshold of minimal residual disease (MRD) assessment for therapy discontinuation, (III) the efficacy of novel triplet combinations with venetoclax as backbone therapy, (IV) indications for the re-initiation of therapy with venetoclax.