Role of Lenalidomide in the Treatment of Myelodysplastic Syndromes

Exploiting the ubiquitin system in myeloid malignancies. From basic research to drug discovery in MDS and AML

The ubiquitin-proteasome system is the crucial homeostatic mechanism responsible for the degradation and turnover of proteins. As such, alterations at this level are often associated with oncogenic processes, either through accumulation of undegraded pathway effectors or, conversely, excessive degradation of tumor-suppressing factors. Therefore, investigation of the ubiquitin- proteasome system has gained much attraction in recent years, especially in the context of hematological malignancies, giving rise to efficient therapeutics such as bortezomib for multiple myeloma. Current investigations are now focused on manipulating protein degradation via fine-tuning of the ubiquitination process through inhibition of deubiquitinating enzymes or development of PROTAC systems for stimulation of ubiquitination and protein degradation. On the other hand, the efficiency of Thalidomide derivates in myelodysplastic syndromes (MDS), such as Lenalidomide, acted as the starting point for the development of targeted leukemia-associated protein degradation molecules. These novel molecules display high efficiency in overcoming the limitations of current therapeutic regimens, such as refractory diseases. Therefore, in this manuscript we will address the therapeutic opportunities and strategies based on the ubiquitin-proteasome system, ranging from the modulation of deubiquitinating enzymes and, conversely, describing the potential of modern targeted protein degrading molecules and their progress into clinical implementation.

Recent Advances in the 5q- Syndrome

The 5q- syndrome is the most distinct of the myelodysplastic syndromes (MDS) and patients with this disorder have a deletion of chromosome 5q [del(5q)] as the sole karyotypic abnormality. Several genes mapping to the commonly deleted region of the 5q- syndrome have been implicated in disease pathogenesis in recent years. Haploinsufficiency of the ribosomal gene RPS14 has been shown to cause the erythroid defect in the 5q- syndrome. Loss of the microRNA genes miR-145 and miR-146a has been associated with the thrombocytosis observed in 5q- syndrome patients. Haploinsufficiency of CSNK1A1 leads to hematopoietic stem cell expansion in mice and may play a role in the initial clonal expansion in patients with 5q- syndrome. Moreover, a subset of patients harbor mutation of the remaining CSNK1A1 allele. Mouse models of the 5q- syndrome, which recapitulate the key features of the human disease, indicate that a p53-dependent mechanism underlies the pathophysiology of this disorder. Importantly, activation of p53 has been demonstrated in the human 5q- syndrome. Recurrent TP53 mutations have been associated with an increased risk of disease evolution and with decreased response to the drug lenalidomide in del(5q) MDS patients. Potential new therapeutic agents for del(5q) MDS include the translation enhancer L-leucine.

The relationship of TP53 R72P polymorphism to disease outcome and TP53 mutation in myelodysplastic syndromes

Nonsynonymous TP53 exon 4 single-nucleotide polymorphism (SNP), R72P, is linked to cancer and mutagen susceptibility. R72P associations with specific cancer risk, particularly hematological malignancies, have been conflicting. Myelodysplastic syndrome (MDS) with chromosome 5q deletion is characterized by erythroid hypoplasia arising from lineage-specific p53 accumulation resulting from ribosomal insufficiency. We hypothesized that apoptotically diminished R72P C-allele may influence predisposition to del(5q) MDS. Bone marrow and blood DNA was sequenced from 705 MDS cases (333 del(5q), 372 non-del(5q)) and 157 controls. Genotype distribution did not significantly differ between del(5q) cases (12.6% CC, 38.1% CG, 49.2% GG), non-del(5q) cases (9.7% CC, 44.6% CG, 45.7% GG) and controls (7.6% CC, 37.6% CG, 54.8% GG) (P=0.13). Allele frequency did not differ between non-del(5q) and del(5q) cases (P=0.91) but trended towards increased C-allele frequency comparing non-del(5q) (P=0.08) and del(5q) (P=0.10) cases with controls. Median lenalidomide response duration increased proportionate to C-allele dosage in del(5q) patients (2.2 (CC), 1.3 (CG) and 0.89 years (GG)). Furthermore, C-allele homozygosity in del(5q) was associated with prolonged overall and progression-free survival and non-terminal interstitial deletions that excluded 5q34, whereas G-allele homozygozity was associated with inferior outcome and terminal deletions involving 5q34 (P=0.05). These findings comprise the largest MDS R72P SNP analysis.

Clinical utility of lenalidomide in the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a heterogeneous group of acquired clonal hematopoietic disorders characterized by peripheral blood cytopenias, paradoxical BM hypercellularity, ineffective hematopoiesis, and increased risk of leukemic transformation. Risk stratification, using different prognostic scores and markers, is at the core of MDS management. Deletion 5q [del(5q)] MDS is a distinct class of MDS characterized by the haploinsufficiency of specific genes, microRNAs, and proteins, which has been linked to increased sensitivity to the drug lenalidomide. Phase II and III clinical trials have demonstrated the efficacy of lenalidomide in improving clinical outcomes of patients with del(5q) MDS, including reduction in red blood cell transfusion requirements and improvements in quality of life. Lenalidomide has also demonstrated some activity in non-del(5q) lower-risk MDS as well as higher-risk MDS, especially in combination with other agents. In this paper, we review the pathogenesis of del(5q) MDS, the proposed mechanisms of action of lenalidomide, the major clinical trials that documented the activity of lenalidomide in different MDS populations, potential predictors of benefit from the drug and suggested mechanisms of resistance, and the use of combination strategies to expand the clinical utility of lenalidomide in MDS.

Myelodysplastic syndromes with 5q deletion: pathophysiology and role of lenalidomide

Myelodysplastic syndrome (MDS) is a hematopoietic stem cell disorder primarily affecting CD34+ cells, characterized by ineffective hematopoiesis, often transforming into acute myelogenous leukemia (AML). A subset of patients has 5q deletion (del(5q)) as the culprit pathogenetic trigger. Del(5q) affects critical regions 5q31 and 5q33, leading to gene haplodeficiency with subsequent RPS14 haplodeficiency and P53 activation. Subsequent to P53 activation, erythroid cell apoptosis and ineffective erythropoiesis occur. Other pathogenetic elements include protein phosphatase 2a and CDC25C haplodeficiency and decreased miR-145 and miR-146a expression. Lenalidomide is an immunomodulatory agent that selectively suppresses the del(5q) clone. While the mechanism is not fully understood, it is associated with diverse molecular changes including stabilization of MDM2 with subsequent enhanced P53 degradation. Lenalidomide showed success in low- and intermediate-1-risk MDS as reported in the 002, 003, and 004 trials. However, in higher-risk MDS, the results of lenalidomide monotherapy were modest, mandating the use of combination therapy. The role and priority of lenalidomide varies between different guidelines, and accordingly, future efforts are necessary to reach a unified therapeutic algorithm. TP53 mutations are important predictors of AML progression and possible resistance to lenalidomide. It is recommended to identify TP53 mutation early in the disease since it may change the decision regarding choice of therapy. Challenges with lenalidomide therapy remain the long-term effects and timing of its discontinuation.

Higher-risk myelodysplastic syndromes with del(5q): is sequential azacitidine-lenalidomide combination the way to go?

High-risk myelodysplastic syndromes (HR-MDS) and acute myeloid leukemia (AML) with deletions of long arm of chromosome 5 (del[5q]) are characterized by rapid progression and poor survival. The majority of these patients are elderly with comorbidities, therefore limiting the use of intensive therapies which, even if used, unfortunately yield low responses. While azacitidine prolongs survival in patients with HR-MDS by a median of 9.5 months, responses only occur in less than half of the patients, and azacitidine therapy is not curative, with most patients relapsing within 2 years. Therefore, strategies to improve outcomes in these patients are needed. Azacitidine and lenalidomide both have meaningful single-agent clinical activity in HR-MDS and AML with del(5q). Early-phase trials in HR-MDS without del(5q) suggest increased activity with a concurrent azacitidine-lenalidomide combination. In this article, we review the results of a Phase I trial of a sequential azacitidine-lenalidomide combination approach in patients with HR-MDS and AML with del(5q) abnormality.

Analysis of the efficacy of lenalidomide in patients with intermediate-1 risk myelodysplastic syndrome without 5q deletion

The aim of this study was to evaluate the efficacy and adverse effects of lenalidomide in the treatment of intermediate-1 risk non-5q deletion [non-del (5q)] myelodysplastic syndrome (MDS). A total of 30 patients with MDS were classified through G-banding chromosome karyotype analysis and fluorescence in situ hybridization (FISH). According to the International Prognostic Scoring System scores, among the 30 patients, 23 and seven cases had scores of 0.5 and 1.0, respectively. Lenalidomide (Revlimid^®), 10 mg/day) was administered for 21 days every 28 days. All 30 cases were treated with lenalidomide for at least three cycles, including 20 cases with four cycles. The patients did not require erythropoietin, cyclosporine or iron chelation treatments. Statistical analysis was performed using SPSS statistical software version 13.0, and comparisons among groups were conducted using a t-test. The efficacy of lenalidomide was demonstrated in patients with intermediate-1 risk non-del (5q) MDS. Peripheral blood cell counts were improved following treatment, and absolute neutrophil, haemoglobin and platelet counts increased following 2–4 cycles of treatment. All patients became stable having undergone three cycles of treatment; however, 17 patients with chromosomal abnormalities had no cytogenetic response to the treatment, as confirmed through the FISH test. Patients with intermediate-1 risk non-del (5q) MDS treated with lenalidomide did not achieve complete haematological remission, although they demonstrated haematological improvement.

Complete Remission of del(5q) Myelodysplastic Syndrome after 7 Days of Lenalidomide Therapy Gives an Alert!

Myelodysplastic syndrome (MDS) refers to a group of haematological, monoclonal disorders. A 50-year-old woman was diagnosed with MDS 5q deletion syndrome [del(5q)], becoming dependent on blood transfusion after long-term treatment with cytotoxic drugs for chronic scleritis. Lenalidomide therapy (10 mg/day) led to profound pancytopaenia, followed by recovery of her blood cell counts. A cytogenetic study, repeated 4 months after lenalidomide treatment, revealed complete remission after only 1 week of lenalidomide therapy. Lenalidomide was approved for low- and intermediate-1-risk MDS, where it normalises platelet counts and induces haematological and cytogenetic remission. This patient has remained transfusion independent for 3 years by continuing on a minimal maintenance dose of lenalidomide. Starting MDS patients on lenalidomide has to be done cautiously or with only 5 mg/day because of the potentially high sensitivity of the stem cells to this immunomodulatory agent in MDS patients.

Serial assessment of suspected myelodysplastic syndromes: significance of flow cytometric findings validated by cytomorphology, cytogenetics, and molecular genetics

The significance of flow cytometry indicating myelodysplasia without proof of myelodysplasia by cytomorphology remains to be clarified. We evaluated follow-up analyses in 142 patients analyzed in parallel by flow cytometry, cytomorphology and cytogenetics for suspected myelodysplasia without proof of myelodysplasia by cytomorphology. At initial assessment, flow cytometry indicated myelodysplasia in 64 of 142 (45.1%) patients. In 9 of 142 (6.3%) patients, cytogenetics revealed aberrant karyotypes at first evaluation that were found in 5 of 64 (7.8%) patients rated with myelodysplasia by flow cytometry. The remaining 133 patients without proof of myelodysplasia by cytomorphology and with normal karyotype underwent follow-up analyses that confirmed myelodysplasia by cytomorphology, cytogenetics or molecular genetics in 47 (35.3%) after a median interval of nine months (range 1-53 months). As far as initial flow cytometry results are concerned, this applied to 30 of 59 (50.1%) with myelodysplasia, 10 of 42 (23.8%) with "possible myelodysplasia" (minor antigen aberrancies only) and 7 of 32 (21.9%) without myelodysplasia (P=0.004). Notably, in these latter 7 patients, flow cytometry results changed at follow up to "possible myelodysplasia" (n=4) and "myelodysplasia" (n=2). These data argue in favor of including flow cytometry along with cytomorphology, cytogenetics and molecular genetics to diagnose myelodysplasia, and suggest a closer monitoring of patients with myelodysplasia-typical aberrant antigen expression found by flow cytometry.