Idelalisib (PI3Kδ inhibitor) therapy for patients with relapsed/refractory chronic lymphocytic leukemia: A Swedish nation-wide real-world report on consecutively identified patients

OBJECTIVES

We examined the efficacy and toxicity of the PI3Kδ inhibitor idelalisib in combination with rituximab salvage therapy in consecutively identified Swedish patients with chronic lymphocytic leukemia (CLL).

METHODS AND RESULTS

Thirty-seven patients with relapsed/refractory disease were included. The median number of prior lines of therapy was 3 (range 1-11); the median age was 69 years (range 50-89); 22% had Cumulative Illness Rating Scale (CIRS) >6 and 51% had del(17p)/TP53 mutation. The overall response rate was 65% (all but one was partial response [PR]). The median duration of therapy was 9.8 months (range 0.9-44.8). The median progression-free survival was 16.4 months (95% CI: 10.4-26.3) and median overall survival had not been reached (75% remained alive at 24 months of follow-up). The most common reason for cessation of therapy was colitis (n = 8, of which seven patients experienced grade ≥3 colitis). The most common serious adverse event was grade ≥3 infection, which occurred in 24 patients (65%).

CONCLUSIONS

Our real-world results suggest that idelalisib is an effective and relatively safe treatment for patients with advanced-stage CLL when no other therapies exist. Alternative dosing regimens and new PI3K inhibitors should be explored, particularly in patients who are double-refractory to inhibitors of BTK and Bcl-2.

Progression in patients with low- and intermediate-1-risk del(5q) myelodysplastic syndromes is predicted by a limited subset of mutations

A high proportion of patients with lower-risk del(5q) myelodysplastic syndromes will respond to treatment with lenalidomide. The median duration of transfusion-independence is 2 years with some long-lasting responses, but almost 40% of patients progress to acute leukemia by 5 years after starting treatment. The mechanisms underlying disease progression other than the well-established finding of small TP53-mutated subclones at diagnosis remain unclear. We studied a longitudinal cohort of 35 low- and intermediate-1-risk del(5q) patients treated with lenalidomide (n=22) or not (n=13) by flow cytometric surveillance of hematopoietic stem and progenitor cell subsets, targeted sequencing of mutational patterns, and changes in the bone marrow microenvironment. All 13 patients with disease progression were identified by a limited number of mutations in TP53, RUNX1, and TET2, respectively, with PTPN11 and SF3B1 occurring in one patient each. TP53 mutations were found in seven of nine patients who developed acute leukemia, and were documented to be present in the earliest sample (n=1) and acquired during lenalidomide treatment (n=6). By contrast, analysis of the microenvironment, and of hematopoietic stem and progenitor cells by flow cytometry was of limited prognostic value. Based on our data, we advocate conducting a prospective study aimed at investigating, in a larger number of cases of del(5q) myelodysplastic syndromes, whether the detection of such mutations before and after lenalidomide treatment can guide clinical decision-making.

Myelodysplastic syndromes are propagated by rare and distinct human cancer stem cells in vivo

Evidence for distinct human cancer stem cells (CSCs) remains contentious and the degree to which different cancer cells contribute to propagating malignancies in patients remains unexplored. In low- to intermediate-risk myelodysplastic syndromes (MDS), we establish the existence of rare multipotent MDS stem cells (MDS-SCs), and their hierarchical relationship to lineage-restricted MDS progenitors. All identified somatically acquired genetic lesions were backtracked to distinct MDS-SCs, establishing their distinct MDS-propagating function in vivo. In isolated del(5q)-MDS, acquisition of del(5q) preceded diverse recurrent driver mutations. Sequential analysis in del(5q)-MDS revealed genetic evolution in MDS-SCs and MDS-progenitors prior to leukemic transformation. These findings provide definitive evidence for rare human MDS-SCs in vivo, with extensive implications for the targeting of the cells required and sufficient for MDS-propagation.

The transporter ABCB7 is a mediator of the phenotype of acquired refractory anemia with ring sideroblasts

Refractory anemia with ring sideroblasts (RARS) is characterized by mitochondrial ferritin (FTMT) accumulation and markedly suppressed expression of the iron transporter ABCB7. To test the hypothesis that ABCB7 is a key mediator of ineffective erythropoiesis of RARS, we modulated its expression in hematopoietic cells. ABCB7 up and downregulation did not influence growth and survival of K562 cells. In normal bone marrow, ABCB7 downregulation reduced erythroid differentiation, growth and colony formation, and resulted in a gene expression pattern similar to that observed in intermediate RARS erythroblasts, and in the accumulation of FTMT. Importantly, forced ABCB7 expression restored erythroid colony growth and decreased FTMT expression level in RARS CD34+ marrow cells. Mutations in the SF3B1 gene, a core component of the RNA splicing machinery, were recently identified in a high proportion of patients with RARS and 11 of the 13 RARS patients in this study carried this mutation. Interestingly, ABCB7 exon usage differed between normal bone marrow and RARS, as well as within the RARS cohort. In addition, SF3B1 silencing resulted in downregulation of ABCB7 in K562 cells undergoing erythroid differentiation. Our findings support that ABCB7 is implicated in the phenotype of acquired RARS and suggest a relation between SF3B1 mutations and ABCB7 downregulation.

Comparison of ATP-binding cassette transporter interactions with the tyrosine kinase inhibitors imatinib, nilotinib, and dasatinib

Although the development of tyrosine kinase inhibitors (TKIs) to control the unregulated activity of BCR-ABL revolutionized the therapy of chronic myeloid leukemia, resistance to TKIs is a clinical reality. Among the postulated mechanisms of resistance is the overexpression of ATP-binding cassette (ABC) transporters, such as P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2), which mediate reduced intracellular drug accumulation. We compared the interactions of the TKIs imatinib, nilotinib, and dasatinib with ABCB1 and ABCG2 in ex vivo and in vitro systems. The TKIs inhibited rhodamine 123 and Hoechst 33342 efflux mediated by endogenous expression of the transporters in murine and human hematopoietic stem cells with potency order nilotinib >> imatinib >> dasatinib. Studies with ABCB1-, ABCG2-, and ABCC1-transfected human embryonic kidney 293 cells verified that nilotinib was the most potent inhibitor of ABCB1 and ABCG2. Cytotoxicity assays in stably transduced K562-ABCG2 and K562-ABCB1 cells confirmed that the TKIs were also substrates for the two transporters. Like imatinib, both nilotinib and dasatinib decreased ABCG2 surface expression in K562-ABCG2 cells. Finally, we found that all TKIs were able to compete labeling of ABCB1 and ABCG2 by the photo-cross-linkable prazosin analog [(125)I]iodoarylazidoprazosin, suggesting interaction at the prazosin-binding site of both proteins. Our experiments support the hypothesis that all three TKIs are substrates of ABC transporters and that, at higher concentrations, TKIs overcome transporter function. Taken together, the results suggest that therapeutic doses of imatinib and nilotinib may diminish the potential of ABCB1 and ABCG2 to limit oral absorption or confer resistance. Clinical data are required to definitively answer the latter question.

Imatinib mesylate and nilotinib (AMN107) exhibit high-affinity interaction with ABCG2 on primitive hematopoietic stem cells

The majority of chronic phase chronic myeloid leukemia (CML) patients treated with the tyrosine kinase inhibitor (TKI) imatinib mesylate maintain durable responses to the drug. However, most patients relapse after withdrawal of imatinib and advanced stage patients often develop drug resistance. As CML is considered a hematopoietic stem cell cancer, it has been postulated that inherent protective mechanisms lead to relapse in patients. The ATP binding-cassette transporters ABCB1 (MDR-1; P-glycoprotein) and ABCG2 are highly expressed on primitive hematopoietic stem cells (HSCs) and have been shown to interact with TKIs. Herein we demonstrate a dose-dependent, reversible inhibition of ABCG2-mediated Hoechst 33342 dye efflux in primary human and murine HSC by both imatinib and nilotinib (AMN107), a novel aminopyrimidine inhibitor of BCR-ABL. ABCG2-transduced K562 cells were protected from imatinib and nilotinib-mediated cell death and from downregulation of P-CRKL. Moreover, photoaffinity labeling revealed interaction of both TKIs with ABCG2 at the substrate binding sites as they compete with the binding of [(125)I] IAAP and also stimulate the transporter's ATPase activity. Therefore, our evidence suggests for the role of ABC transporters in resistance to TKI on primitive HSCs and CML stem cells and provides a rationale how TKI resistance can be overcome in vivo.

Thrombotic pulmonary arteriopathy in polycythemia vera

Pulmonary infarction and hemorrhage are important differential diagnoses in pulmonary coin lesions, especially in patients with underlying hematologic malignancies. We report a 58-year-old female patient suffering from polycythemia vera presenting with multiple pulmonary coin lesions. Open lung biopsy and subsequent histologic investigations showed organized pulmonary infarction and primary pulmonary thrombotic arteriopathy. Although histologic features are non-contributory in distinguishing organized thrombosis from organized thromboembolism, the clinical setting and localization of the lesions suggest that in the present case the vascular lesions are due to organized thrombosis.

[Increase of prilocaine-induced methemoglobinemia following anesthesia induction]

Although the local anaesthetic prilocaine is less cardio- and neurotoxic than lidocaine, it bears the disadvantage of the formation of methaemoglobin by the metabolite o-toluidine. Prilocaine is often successfully used, especially for the blockade of the brachial plexus, but one problem of this technique is the failure rate of 3-10%, with the consequence that general anaesthesia after administration of prilocaine is frequently necessary. Methaemoglobin formation after prilocaine administration has been thoroughly investigated. Nothing is known, however, about the interactions of prilocaine and the induction of general anaesthesia relative to methaemoglobinaemia. CASE REPORT. Two patients (47 and 52 years old) each received 500 mg prilocaine for the axillary blockade of the brachial plexus. After 100 and 120 min respectively, it was necessary to induce general anaesthesia, for which 350 mg thiopental, 1 mg alfentanil and 45 mg atracurium were used. At 15 min after induction, methaemoglobin levels had increased by 70% and 25%, respectively, from baseline before general anaesthesia. CONCLUSION. It is not possible to explain these findings conclusively with the present method. To check whether displacement of o-toluidine from the plasma protein binding might have been responsible, we provoked methaemoglobinaemia in vitro by adding o-toluidine to heparinised blood. Thiopental was then added to half the specimens. Subsequently, methaemoglobin levels were lower in the samples with thiopental. Three explanations seem plausible: (1) Thiopental blocks the hydroxylase of the endoplasmic reticulum, with the result that o-toluidine cannot be further metabolised, leading to higher o-toluidine and methaemoglobin levels. (2) Isoflurane improves the blood supply of the liver. This results in increased metabolism of prilocaine to o-toluidine. (3) The results were accidental. To clarify which of these explanations is correct, further investigation is necessary.