Relapsed CLL: sequencing, combinations, and novel agents

First-Line Treatment of Older Patients with CLL: A New Approach in the Chemo-Free Era

Bruton tyrosine kinase inhibitors (BTKi) and the BCL2 inhibitor venetoclax, with or without the anti-CD20 monoclonal antibody Obinutuzumab, represent the preferred options for the first-line therapy of CLL because they are more effective and may improve quality of life. However, patient inclusion criteria are heterogeneous across trials designed for older patients, and the identification of CLL-specific parameters identifying unfit patients at risk of developing drug-specific adverse events is required to guide treatment choice. Due to inclusion/exclusion criteria in trials, higher discontinuation rates with BTKi were reported in real-world studies, and registry analyses provided useful information on factors predicting earlier discontinuation in a real-world setting. Though targeted agents were shown to be cost-effective treatments in high-income countries, the out-of-pocket expenses may limit accessibility to these drugs, and the overall expenditure for new drugs in CLL is projected to increase substantially, posing an issue for sustainability. This being said, the choice of a finite-duration treatment based on venetoclax-containing regimens or treatment until progression with BTKi is today possible in high-income countries, and the therapy choice drivers are represented by coexisting medical conditions rather than age, patient expectations, logistics, and sustainability.

Sequencing and combination of current small-molecule inhibitors for chronic lymphocytic leukemia: Where is the evidence?

Small-molecule inhibitors have revolutionized the treatment of chronic lymphocytic leukemia (CLL), a landscape once dominated by chemoimmunotherapy (i.e., an anti-CD20 monoclonal antibody in combination with systemic chemotherapy) in fit and unfit individuals. Key challenges include the management of refractory disease as well as the optimization of the therapy sequence. Decreased responsiveness has been observed with prolonged treatment, especially with Bruton tyrosine kinase (BTK) and phosphatidylinositol 3-kinase (PI3K) inhibitors which are given continuously, while venetoclax, an agent that targets dysregulations in intrinsic apoptosis signaling, has a fixed duration when combined with anti-CD20 monoclonal antibodies or BTK inhibitors. Combination therapy aims to synergistically target different oncogenic signaling pathways to abrogate the proliferation of resistant clones and thereby allows for fixed-duration treatments. An advantage of fixed-duration therapy is the potential to decrease financial and drug-induced toxicities. Sequencing of therapies is important to individualize treatment decisions based on factors such as age, comorbidities, tolerability, and patient preferences. However, to date, there are limited data to guide the rational sequencing or combination of these therapies, since conventional chemoimmunotherapy or chemotherapy regimens were used as comparators against these small-molecule inhibitors in trials that led to their regulatory approvals. In this article, we examined and evaluated the current evidence for sequencing versus the combination of small-molecule inhibitors for CLL by conducting comprehensive searches of the United States National Library of Medicine PubMed database, key meeting abstracts, and clinical practice guidelines. We also summarized findings from expert opinions to elucidate best practices for clinical scenarios with limited evidence to guide treatment selection.

Ibrutinib Does Not Impact CCR7-Mediated Homeostatic Migration in T-Cells from Chronic Lymphocytic Leukemia Patients

Bruton's tyrosine kinase inhibitor ibrutinib has significantly changed treatment landscape in chronic lymphocytic leukemia (CLL). Growing evidence supports ibrutinib to work beyond the effect on tumor cells by means of, for example, restoring functionality of the T-cell compartment and increasing circulating T-cell numbers. Recent evidence suggests T-cell enhanced expansion, rather than increased egress from secondary lymphoid organs (SLO), as a root cause for ibrutinib-induced lymphocytosis. However, whether the latter physiological change is also a consequence of a forced retention in blood remains undisclosed. Since CCR7 is the main chemokine receptor taking over the homing of T-cells from peripheral compartments to lymph nodes and other SLO, we aimed to investigate the impact of ibrutinib on CCR7 functionality in T-cells. To this end, we documented receptor expression in T-cells from a large cohort of ibrutinib-treated CLL patients, and performed different in vivo and in vitro migration models. Overall, our data confirm that CCR7 expression or receptor-mediated migration in CLL T-cells is not affected by ibrutinib. Furthermore, it does not modulate CCR7-driven homing nor nodal interstitial migration. Together, our results support that ibrutinib-induced CLL T-cell accumulation in the blood stream is not derived from an impairment of CCR7-driven recirculation between the SLO and bloodstream, and therefore T-cell expansion is the most plausible cause.

Effect of ibrutinib on CCR7 expression and functionality in chronic lymphocytic leukemia and its implication for the activity of CAP-100, a novel therapeutic anti-CCR7 antibody

CAP-100 is a novel therapeutic antibody directed against the ligand binding site of human CCR7. This chemokine receptor is overexpressed in chronic lymphocytic leukemia (CLL) and orchestrates the homing of CLL cells into the lymph node. Previous studies, on a very limited number of samples, hypothesized that the Bruton's tyrosine kinase inhibitor (BTKi) ibrutinib might induce loss of surface CCR7 levels in CLL cells. CAP-100 will be evaluated in clinical trials as a therapy for relapse/refractory CLL patients, who have received at least two systemic therapies (NCT04704323). As nowadays many relapse/refractory CLL patients will have received ibrutinib as a prior therapy, we aimed to investigate in a large cohort of CLL patients the impact of this BTKi on CCR7 expression and functionality as well as on the therapeutic activity of CAP-100. Our data confirm that ibrutinib moderately down-regulates the very high expression of CCR7 in CLL cells but has no apparent effect on CCR7-induced chemotaxis. Moreover, CLL cells are perfectly targetable by CAP-100 which led to a complete inhibition of CCR7-mediated migration and induced strong target cell killing through antibody-dependent cell-mediated cytotoxicity, irrespective of previous or contemporary ibrutinib administration. Together, these results validate the therapeutic utility of CAP-100 as a next-line single-agent therapy for CLL patients who failed to ibrutinib and confirm that CAP-100 and ibrutinib have complementary non-overlapping mechanisms of action, potentially allowing for combination therapy.

Targeting cancer homing into the lymph node with a novel anti-CCR7 therapeutic antibody: the paradigm of CLL

Lymph node (LN) is a key tissue in the pathophysiology of mature blood cancers, especially for chronic lymphocytic leukemia (CLL). Within the multiple de-regulated pathways affecting CLL homeostasis, the CC-chemokine receptor 7 (CCR7) grants homing of CLL cells into the LN where protective environments foster tumor progression. To cover the lack of specific therapies targeting the CCR7-dependence of CLL to enter into the LN, and aiming to displace the disease from LN, we generated CAP-100, an antibody that specifically binds to hCCR7 and neutralizes its ligand-binding site and signaling. In various in vitro and in vivo preclinical models CAP-100 strongly inhibited CCR7-induced migration, extravasation, homing, and survival in CLL samples. Moreover, it triggered potent tumor cell killing, mediated by host immune mechanisms, and was effective in xenograft models of high-risk disease. Additionally, CAP-100 showed a favorable toxicity profile on relevant hematopoietic subsets. Our results validated CAP-100 as a novel therapeutic tool to prevent the access of CLL cells, and other neoplasia with nodal-dependence, into the LN niches, thus hitting a central hub in the pathogenesis of cancer. The first-in-human clinical trial (NCT04704323), which will evaluate this novel therapeutic approach in CLL patients, is pending.

Of Lymph Nodes and CLL Cells: Deciphering the Role of CCR7 in the Pathogenesis of CLL and Understanding Its Potential as Therapeutic Target

The lymph node (LN) is an essential tissue for achieving effective immune responses but it is also critical in the pathogenesis of chronic lymphocytic leukemia (CLL). Within the multitude of signaling pathways aberrantly regulated in CLL the homeostatic axis composed by the chemokine receptor CCR7 and its ligands is the main driver for directing immune cells to home into the LN. In this literature review, we address the roles of CCR7 in the pathophysiology of CLL, and how this chemokine receptor is of critical importance to develop more rational and effective therapies for this malignancy.

Bidirectional linkage between the B-cell receptor and NOTCH1 in chronic lymphocytic leukemia and in Richter's syndrome: therapeutic implications

NOTCH1 mutations in chronic lymphocytic leukemia (CLL) lead to accumulation of NOTCH1 intracellular domain (NICD) and prolong signaling. These mutations associate with a more aggressive disease compared to wild-type (WT) CLL. In this work we demonstrate a bidirectional functional relationship between NOTCH1 and the B cell receptor (BCR) pathways. By using highly homogeneous cohorts of primary CLL cells, activation of NOTCH1 is shown to increase expression of surface IgM, as well as LYN, BTK, and BLNK, ultimately enhancing BCR signaling responses, including global mRNA translation. Upon BCR cross-linking, NOTCH1 itself is actively translated and increased on cell surface. Furthermore, BCR ligation induces calcium mobilization that can facilitate ligand-independent NOTCH1 activation. These data suggest that the two pathways are functionally linked, providing a rationale for dual inhibition strategies. Consistently, addition of the γ-secretase inhibitor DAPT to ibrutinib significantly potentiates its effects, both in vitro and in a short-term patient-derived xenograft model. While this observation may find limited applications in the CLL field, it is more relevant for Richter's Syndrome (RS) management, where very few successful therapeutic options exist. Treatment of RS-patient-derived xenografts (RS-PDX) with the combination of ibrutinib and DAPT decreases disease burden and increases overall survival.

Relapsed/Refractory Chronic Lymphocytic Leukemia: Chemoimmunotherapy, Treatment until Progression with Mechanism-Driven Agents or Finite-Duration Therapy?

Treatment of relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL) has dramatically improved thanks to the development of mechanism-driven agents including drugs that inhibit kinases in the BCR pathway or BCL2. The treating physician has now the opportunity to decide i) which patient can be still offered chemoimmunotherapy as salvage treatment, ii) which patient at relapse is a candidate to receiving, continuous treatment with ibrutinib, idelalisib and rituximab or venetoclax and iii) which patient may benefit from a fixed-duration treatment using the BCL2 antagonist venetoclax in association with rituximab.

Ibrutinib is the most actively investigated drug in R/R CLL and data at a 7-year follow-up were reported, showing durable efficacy and favorable efficacy profile. The patients with cardiac disease, hypertension, and anticoagulant therapy are not ideal candidates for continuous therapy with this agent. Idelalisib and rituximab were tested in patients with unfavorable characteristics including cytopenias. The short follow-up and treatment-emergent adverse events limit its role to patients unlikely to get a benefit with other agents. Venetoclax and rituximab is the only effective chemo-free approach for the treatment of R/R with a fixed duration (up to 24 months) schedule capable of inducing deep responses in the majority of cases with a reassuring safety profile.

While a deep knowledge of the growing body of scientific evidence is required to inform and guide the appropriate treatment choice and management, physicians cannot disregard the growing problem of sustainability.