Relapsed/Refractory Chronic Lymphocytic Leukemia (CLL)

PURPOSE OF REVIEW

There have been significant advances in the treatment of relapsed/refractory chronic lymphocytic leukemia (CLL) over the past two decades. However, the intention of treatment remains control of the disease and delay of progression rather than a cure which remains largely elusive. Considering that CLL is mostly seen in older patients, there are multiple factors that play a role in the selection of CLL beyond the frontline treatment. Here, we review the concept of relapsed CLL, factors that predispose to relapse, and therapeutic options available to this patient population. We also review investigational therapies and provide a framework for selection of therapies in this setting.

RECENT FINDINGS

Targeted therapies with continuous BTK inhibitors (BTKi) or fixed duration venetoclax plus anti-CD20 monoclonal antibody therapy have established superiority over chemoimmunotherapy in relapsed CLL and have become the preferred standard of care treatment. The second-generation more selective BTK inhibitors (acalabrutinib and zanubrutinib) have shown improved safety profile compared to ibrutinib. However, resistance to the covalent BTK inhibitors may emerge and is commonly associated with mutations in BTK or other downstream enzymes. The novel non-covalent BTK inhibitors such as pirtobrutinib (Loxo-305) and nemtabrutinib (ARQ 531) are showing promising activities for relapsed CLL refractory to prior covalent BTKi. Other novel therapies such as chimeric antigen receptor (CAR) T cell therapy have also shown significant activities for relapsed and refractory CLL. Measurable residual disease (MRD) assessment has a growing importance in venetoclax-based limited-duration therapy and there is mounting evidence that MRD negativity improves outcomes. However, it remains to be seen if this will become an established clinically significant endpoint. Further, the optimal sequence of various treatment options remains to be determined. Patients with relapsed CLL now have more options for the treatment of the disease. The choice of therapy is best individualized especially in the absence of direct comparisons of targeted therapies, and the coming years will bring more data on the best sequence of use of the therapeutic agents.

The TKI Era in Chronic Leukemias

Tyrosine kinases are proteins involved in physiological cell functions including proliferation, differentiation, and survival. However, the dysregulation of tyrosine kinase pathways occurs in malignancy, including hematological leukemias such as chronic myeloid leukemia (CML) and chronic lymphocytic leukemia (CLL). Particularly, the fusion oncoprotein BCR-ABL1 in CML and the B-cell receptor (BCR) signaling pathway in CLL are critical for leukemogenesis. Therapeutic management of these two hematological conditions was fundamentally changed in recent years, making the role of conventional chemotherapy nearly obsolete. The first, second, and third generation inhibitors (imatinib, dasatinib, nilotinib, bosutinib, and ponatinib) of BCR-ABL1 and the allosteric inhibitor asciminib showed deep genetic and molecular remission rates in CML, leading to the evaluation of treatment discontinuation in prospective trials. The irreversible BTK inhibitors (ibrutinib, acalabrutinib, zanubrutinib, tirabrutinib, and spebrutinib) covalently bind to the C481 amino acid of BTK. The reversible BTK inhibitor pirtobrutinib has a different binding site, overcoming resistance associated with mutations at C481. The PI3K inhibitors (idelalisib and duvelisib) are also effective in CLL but are currently less used because of their toxicity profiles. These tyrosine kinase inhibitors are well-tolerated, do have some associated in-class side effects that are manageable, and have remarkably improved outcomes for patients with hematologic malignancies.

Identification of Candidate Risk Factor Genes for Human Idelalisib Toxicity Using a Collaborative Cross Approach

Idelalisib is a phosphatidylinositol 3-kinase inhibitor highly selective for the delta isoform that has shown good efficacy in treating chronic lymphocytic leukemia and follicular lymphoma. In clinical trials, however, idelalisib was associated with rare, but potentially serious liver and lung toxicities. In this study, we used the Collaborative Cross (CC) mouse population to identify genetic factors associated with the drug response that may inform risk management strategies for idelalisib in humans. Eight male mice (4 matched pairs) from 50 CC lines were treated once daily for 14 days by oral gavage with either vehicle or idelalisib at a dose selected to achieve clinically relevant peak plasma concentrations (150 mg/kg/day). The drug was well tolerated across all CC lines, and there were no observations of overt liver injury. Differences across CC lines were seen in drug concentration in plasma samples collected at the approximate Tmax on study Days 1, 7, and 14. There were also small but statistically significant treatment-induced alterations in plasma total bile acids and microRNA-122, and these may indicate early hepatocellular stress required for immune-mediated hepatotoxicity in humans. Idelalisib treatment further induced significant elevations in the total cell count of terminal bronchoalveolar lavage fluid, which may be analogous to pneumonitis observed in the clinic. Genetic mapping identified loci associated with interim plasma idelalisib concentration and the other 3 treatment-related endpoints. Thirteen priority candidate quantitative trait genes identified in CC mice may now guide interrogation of risk factors for adverse drug responses associated with idelalisib in humans.

Small Molecule Inhibitors in Chronic Lymphocytic Lymphoma and B Cell Non-Hodgkin Lymphoma

PURPOSE OF REVIEW

The purpose of this review is to summarize the available literature for the use of small molecule inhibitors in chronic lymphocytic leukemia and B cell non-Hodgkin lymphoma.

RECENT FINDINGS

Ibrutinib, idelalisib, and venetoclax are small molecule inhibitors that have revolutionized therapeutic options for patients with CLL, particularly for those with high-risk disease including 17p deletion. These drugs are increasingly finding application in a variety of subtypes of B cell NHL. Intolerance and resistance are concerns for select patients, highlighting the need for continual development of alternate therapies. The treatment armamentarium for CLL and NHL is vastly different than it was just a few years ago. Patients have a much wider range of non-chemotherapy treatment options, some of which produce durable responses and have long-term tolerability. Future research directions will likely focus on identifying the optimal sequences and combination strategies for these new targeted therapies.

Idelalisib: a review of its use in chronic lymphocytic leukaemia and indolent non-Hodgkin's lymphoma

Idelalisib (Zydelig®) is a first-in-class, orally administered, phosphatidylinositol 3-kinase-δ inhibitor that was recently approved for the treatment of relapsed chronic lymphocytic leukaemia (CLL), relapsed follicular B-cell non-Hodgkin's lymphoma (NHL) and relapsed small lymphocytic lymphoma (SLL) in the USA and for the treatment of CLL and refractory follicular lymphoma in the EU. In a pivotal phase III trial in patients with relapsed CLL who were not able to receive cytotoxic agents, recipients of idelalisib plus rituximab had significantly improved progression-free survival, overall survival, overall response and lymph node response, compared with recipients of placebo plus rituximab. In a pivotal phase II trial, idelalisib monotherapy was effective in patients with relapsed indolent NHL who were refractory to rituximab and an alkylating agent, including in the subgroups of patients with follicular lymphoma or SLL. Oral idelalisib had a generally manageable adverse event profile, although episodes of serious/fatal diarrhoea or colitis, hepatotoxicity, pneumonitis and intestinal perforation were reported. In conclusion, idelalisib represents an important advance in the treatment of relapsed CLL and relapsed indolent NHL.

PKC-β as a therapeutic target in CLL: PKC inhibitor AEB071 demonstrates preclinical activity in CLL

Targeting B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL) has been successful with durable remissions observed with several targeted therapeutics. Protein kinase C-β (PKC-β) is immediately downstream of BCR and has been shown to be essential to CLL cell survival and proliferation in vivo. We therefore evaluated sotrastaurin (AEB071), an orally administered potent PKC inhibitor, on CLL cell survival both in vitro and in vivo. AEB071 shows selective cytotoxicity against B-CLL cells in a dose-dependent manner. Additionally, AEB071 attenuates BCR-mediated survival pathways, inhibits CpG-induced survival and proliferation of CLL cells in vitro, and effectively blocks microenvironment-mediated survival signaling pathways in primary CLL cells. Furthermore, AEB071 alters β-catenin expression, resulting in decreased downstream transcriptional genes as c-Myc, Cyclin D1, and CD44. Lastly, our preliminary in vivo studies indicate beneficial antitumor properties of AEB071 in CLL. Taken together, our results indicate that targeting PKC-β has the potential to disrupt signaling from the microenvironment contributing to CLL cell survival and potentially drug resistance. Future efforts targeting PKC with the PKC inhibitor AEB071 as monotherapy in clinical trials of relapsed and refractory CLL patients are warranted.

Emerging therapies for refractory chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) that becomes refractory to chemotherapy is associated with a poor outcome. For these patients, some of the novel substances that are currently in clinical development for CLL seem to offer new hope. These agents include small molecules, new antibodies, immunomodulators, kinase inhibitors, BCL-2 antagonists and chimeric antigen receptor transduced T-cells (CARTs) and combine high efficacy with a good safety profile. To date, allogeneic stem cell transplant remains the only curative treatment option for patients with relapsed, refractory CLL. However, it is possible that new substances will replace allogeneic stem cell transplant in the near future. This review provides an overview of the currently available data and an outlook on future therapies for chemotherapy refractory CLL.

Idelalisib and rituximab in relapsed chronic lymphocytic leukemia

BACKGROUND

Patients with relapsed chronic lymphocytic leukemia (CLL) who have clinically significant coexisting medical conditions are less able to undergo standard chemotherapy. Effective therapies with acceptable side-effect profiles are needed for this patient population.

METHODS

In this multicenter, randomized, double-blind, placebo-controlled, phase 3 study, we assessed the efficacy and safety of idelalisib, an oral inhibitor of the delta isoform of phosphatidylinositol 3-kinase, in combination with rituximab versus rituximab plus placebo. We randomly assigned 220 patients with decreased renal function, previous therapy-induced myelosuppression, or major coexisting illnesses to receive rituximab and either idelalisib (at a dose of 150 mg) or placebo twice daily. The primary end point was progression-free survival. At the first prespecified interim analysis, the study was stopped early on the recommendation of the data and safety monitoring board owing to overwhelming efficacy.

RESULTS

The median progression-free survival was 5.5 months in the placebo group and was not reached in the idelalisib group (hazard ratio for progression or death in the idelalisib group, 0.15; P<0.001). Patients receiving idelalisib versus those receiving placebo had improved rates of overall response (81% vs. 13%; odds ratio, 29.92; P<0.001) and overall survival at 12 months (92% vs. 80%; hazard ratio for death, 0.28; P=0.02). Serious adverse events occurred in 40% of the patients receiving idelalisib and rituximab and in 35% of those receiving placebo and rituximab.

CONCLUSIONS

The combination of idelalisib and rituximab, as compared with placebo and rituximab, significantly improved progression-free survival, response rate, and overall survival among patients with relapsed CLL who were less able to undergo chemotherapy. (Funded by Gilead; ClinicalTrials.gov number, NCT01539512.).

New treatment options for chronic lymphocytic leukemia

INTRODUCTION

Chemoimmunotherapy is the gold standard of therapy for patients with advanced chronic lymphocytic leukemia (CLL), resulting in high and durable complete response rates. However, all patients eventually relapse and CLL remains incurable. Newer and more rationally developed compounds are needed to improve CLL therapy, particularly in cases of refractory disease.

AREAS COVERED

Following a literature search on PubMed using 'chronic', 'lymphocytic', 'treatment' and 'therapy' as keywords, results obtained with novel agents were critically analyzed. Abstracts presented during 2013 at ASH, EHA, ICML, IWCLL and ASCO meetings were also included in the search.

EXPERT OPINION

New monoclonal antibodies, lenalidomide, B-cell receptor-signal transduction inhibitors and pro-apoptotic molecules have shown efficacy in patients with relapsed or refractory disease. Hopefully, the combined use of these molecules in risk-adapted treatment strategies will improve the outcome of patients with CLL and pave the way for their long-term control.