Tumor Suppressor PLK2 May Serve as a Biomarker in Triple-Negative Breast Cancer for Improved Response to PLK1 Therapeutics

Polo-like kinase (PLK) family members play important roles in cell-cycle regulation. The founding member PLK1 is oncogenic and preclinically validated as a cancer therapeutic target. Paradoxically, frequent loss of chromosome 5q11–35, which includes PLK2, is observed in basal-like breast cancer. In this study, we found that PLK2 was tumor suppressive in breast cancer, preferentially in basal-like and triple-negative breast cancer (TNBC) subtypes. Knockdown of PLK1 rescued phenotypes induced by PLK2 loss both in vitro and in vivo. We also demonstrated that PLK2 directly interacted with PLK1 at prometaphase through the kinase but not the polo-box domains of PLK2, suggesting PLK2 functioned at least partially through the interaction with PLK1. Furthermore, an improved treatment response was seen in both Plk2-deleted/low mouse preclinical and patient-derived xenograft (PDX) TNBC models using the PLK1 inhibitor volasertib alone or in combination with carboplatin. Reexpression of PLK2 in an inducible PLK2-null mouse model reduced the therapeutic efficacy of volasertib. In summary, this study delineates the effects of chromosome 5q loss in TNBC that includes PLK2, the relationship between PLK2 and PLK1, and how this may render PLK2-deleted/low tumors more sensitive to PLK1 inhibition in combination with chemotherapy. Significance: The tumor-suppressive role of PLK2, and its relationship with oncogene PLK1, provide a mechanistic rationalization to use PLK1 inhibitors in combination with chemotherapy to treat PLK2-low/deleted tumors. TNBC, and other cancers with low PLK2 expression, are such candidates to leverage precision medicine to identify patients who might benefit from treatment with these inhibitors.

TIRAP Drives Marrow Failure through an Ifnγ-Hmgb1 Axis That Disrupts the Endothelial Niche

The myelodysplastic syndrome (MDS) are a group of hematological malignancies with the propensity to develop into either acute myeloid leukemia (AML) or bone marrow failure (BMF). Dysregulation of immune and inflammatory responses has been implicated in MDS and other BMF disorders. There is significant evidence for IFNγ playing a key role in MDS and BMF syndromes. However, there are conflicting theories regarding the mechanism by which IFNγ promotes BMF. There is also very little information on the triggers that underlie upregulation of IFNγ in these BMF syndromes. Interstitial deletion of chromosome 5q is the most common cytogenetic abnormality observed in MDS, accounting for approximately 10% of all cases. Our lab has previously shown that miR-145, which is located on the minimally deleted region of chromosome 5q, targets Toll/Interleukin-1 receptor domain containing adaptor protein (TIRAP) - an innate immune adaptor protein. However, the role of TIRAP in marrow failure has not been well elucidated. In this study, we identify a novel role for TIRAP in dysregulating normal hematopoiesis through activation of Ifnγ. Using bone marrow transplants in wild-type mice, we showed that constitutive expression of TIRAP in wild-type hematopoietic stem and progenitor cells (HSPC) caused peripheral blood cytopenia, suppressed the bone marrow endothelial niche and significantly reduced overall survival of the mice (median survival 9 weeks post-transplant) compared to controls (p < 0.0001). RNA-seq analysis of TIRAP expressing HSPC identified several proinflammatory cytokines to be significantly overrepresented. Geneset enrichment analysis (GSEA) identified the Ifnγ response as the single most significantly enriched pathway of the Hallmark genesets. To test the functional role of Ifnγ in TIRAP-mediated BMF, wild-type recipient mice were transplanted with TIRAP- HSPC from Ifnγ-/- donor mice. Mice that received TIRAP-transduced Ifnγ-/- HSPC were rescued from BMF, as evidenced by normalized blood cell counts and improved median survival (median survival 48.6 weeks) (Ifnγ-/- TIRAP vs. wild-type TIRAP: p = 0.0004). Interestingly, in our model of TIRAP induced BMF, myeloid rather than the conventional T and NK cells were the cells most responsible for the increased production of Ifnγ. Further, when we transplanted TIRAP expressing wild-type HSPC into NSG recipient mice, which are deficient in functional B, T and NK cells, the NSG mice developed BMF with pancytopenia in a similar time-frame as wild-type mice. This suggested that T and NK cells are not central for the development of TIRAP induced BMF. Delving deeper into the mechanism by which the TIRAP-Ifnγ axis causes BMF, we saw that while Ifnγ played a direct role in suppressing erythropoiesis and megakaryopoiesis, it played an indirect, Ifnγ receptor independent role on myelopoiesis. TIRAP-induced activation of Ifnγ released the alarmin, Hmgb1, which suppressed the marrow endothelial niche, which in turn promoted myeloid suppression. Overexpression of TIRAP in Ifnγ -/- background blocked Hmgb1 release. Further, blocking Hmgb1 in presence of TIRAP expression was sufficient to reverse the marrow endothelial defect and restore myelopoiesis in vivo. Our findings highlight a novel, non-canonical effect of aberrant TIRAP expression via the Ifnγ-Hmgb1 axis on the endothelial cell component of the marrow microenvironment and hematopoiesis. Further understanding of this pathway would open up avenues for developing new therapies for BMF. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Decitabine Combined with Minimally Myelosuppressive Therapy for Induction of Remission of Pediatric High-Risk Acute Myeloid Leukemia with Chromosome 5q Deletion. a Report of Three Cases

Cases of pediatric acute myeloid leukemia (AML) with complex karyotypes including chromosome 5 abnormalities are rare and have a dismal prognosis. Management of AML with monosomy 5/del(5q) has not been uniform. We treated three adolescents with this AML subtype with combined low-dose cytarabine and mitoxantrone, concurrent with decitabine and G-CSF, for remission induction. Decitabine was also included in the conditioning regimen before hematopoietic cell transplantation (HCT). All three patients attained complete remission after treatment with this combination. The treatment was well tolerated, and the patients are alive and free of disease at 3.6, 3.2, and 3.0 years after HCT, respectively. Our experience suggests that HCT is required for the eradication of pediatric AML, and possibly MDS, with complex karyotypes including del(5q). Decitabine combined with regimens of low myelotoxicity for remission induction represents an alternative approach to decrease the risk of complications associated with post-remission chemotherapy before HCT. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Novel Molecular Mechanism of Lenalidomide in Myeloid Malignancies Independent of Deletion of Chromosome 5q

Lenalidomide as well as other immunomodulatory drugs (IMiDs) have achieved clinical efficacies in certain sub-types of hematologic malignancies, such as multiple myeloma, lower-risk myelodysplastic syndromes (MDS) with a single deletion of chromosome 5q (del(5q)) and others. Despite superior clinical response to lenalidomide in hematologic malignancies, relapse and resistance remains a problem in IMiD-based therapy. The last ten years have witnessed the discovery of novel molecular mechanism of IMiD-based anti-tumor therapy. IMiDs bind human cereblon (CRBN), the substrate receptor of the CRL4 E3 ubiquitin ligase complex. Binding of CRBN with IMiDs leads to degradation of the Ikaros family zinc finger proteins 1 and 3 (IKZF1 and IKZF3) and casein kinase 1 alpha. We have found that lenalidomide-mediated degradation of IKZF1 leads to activation of the G protein-coupled receptor 68 (GPR68)/calcium/calpain pro-apoptotic pathway and inhibition of the regulator of calcineurin 1 (RCAN1)/calcineurin pro-survival pathway in MDS and acute myeloid leukemia (AML). Calcineurin inhibitor Cyclosporin-A potentiates the anti-leukemia activity of lenalidomide in MDS/AML with or without del(5q). These findings broaden the therapeutic potential of IMiDs. This review summarizes novel molecular mechanism of lenalidomide in myeloid malignancies, especially without del(5q), in the hope to highlight novel therapeutic targets.

Amyotrophie spinale: une mise à jour

proximale liée au chromosome 5q ») est une maladie neuromusculaire progressive touchant les motoneurones inférieurs et causant une faiblesse musculaire croissante. Longtemps considérée comme une des principales causes génétiques de mortalité infantile, les avancées scientifiques des 2 dernières décennies ont permis le développement des premiers traitements spécifiques, marquant une révolution dans la prise en charge. Nous allons ainsi passer en revue la maladie, son mécanisme pathogénique, ses présentations cliniques, et les options thérapeutiques actuellement disponibles.

The CRBN, CUL4A and DDB1 Expression Predicts the Response to Immunomodulatory Drugs and Survival of Multiple Myeloma Patients

Immunomodulatory drugs (IMiDs) are effective in the treatment of multiple myeloma (MM), myelodysplastic syndrome with deletion of chromosome 5q and other haematological malignancies. Recent studies showed that IMiDs bind to cereblon (CRBN), a substrate receptor of the CRL4–CRBN complex, to induce the ubiquitination and degradation of IKZF1 and IKZF3 in MM cells, contributing to their anti-myeloma activity. We aimed to determine whether the CRL4–CRBN complex proteins’ expression predicts the prognosis of MM patients treated with IMiDs. Here, we evaluated the expression of CRL4–CRBN complex proteins and their downstream targets with immunohistochemistry (IHC) staining in 130 bone marrow samples from MM patients treated with thalidomide or lenalidomide-based regimens. We found that the expression of CRBN and CUL4A was associated with the superior IMiD-based treatment response (p = 0.007 and p = 0.007, respectively). Moreover, the CUL4A expression was associated with improved PFS (HR = 0.66, 95% CI 0.44–0.99; p = 0.046) and DDB1 expression showed a negative impact on OS both in the univariate (HR = 2.75, 95% CI 1.65–4.61; p = 0.001) and the multivariate (HR 3.67; 95% CI 1.79–7.49; p < 0.001) analysis. Overall, our data suggest that the expression of DDB1, CUL4A and CRBN assessed by IHC predicts the clinical course of MM patients and identifies patients with a high probability of responding to IMiD-based therapy.

Key regulators of sensitivity to immunomodulatory drugs in cancer treatment

Immunomodulatory drugs (IMiDs) include thalidomide, lenalidomide, and pomalidomide, which have shown significant efficacy in the treatment of multiple myeloma (MM), myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)) and other hematological malignancies. IMiDs hijack the CRL4CRBN ubiquitin ligase to target cellular proteins for ubiquitination and degradation, which is responsible for their clinical activity in MM and MDS with del(5q). However, intrinsic and acquired resistance frequently limit the efficacy of IMiDs. Recently, many efforts have been made to explore key regulators of IMiD sensitivity, resulting in great advances in the understanding of the regulatory networks related to this class of drugs. In this review, we describe the mechanism of IMiDs in cancer treatment and summarize the key regulators of IMiD sensitivity. Furthermore, we introduce genome-wide CRISPR-Cas9 screenings, through which the regulatory networks of IMiD sensitivity could be identified.

Cytogenetic and Genetic Advances in Myelodysplasia Syndromes

Myelodysplasia syndromes (MDS) are defined by a heterogeneous group of myeloid malignancies characterized by peripheral blood cytopenia and dishematopoiesis and frequently progress to acute myeloid leukemia. Conventional karyotype has a crucial role in myelodysplastic syndrome (MDS) and is one of items of the International Prognostic Scoring System (IPSS) for patient risk stratification and treatment selection. Approximately 50–60% of cases of MDS present chromosomal abnormalities, like the deletions of chromosome 5q and 7q, trisomy 8, and complex karyotypes. New genomic technologies have been developted, like single-nucleotide polymorphism array and next-generation sequencing. They can identify the heterozygous deletions wich result in haplo-insufficient gene expression (e.g., CSNK1A1, DDX41 on chromosome 5, CUX1, LUC7L2, EZH2 on chromosome 7) involved in the pathogenesis of myelodysplasia syndromes. Genetic abnormalities are multiple, the most recurrent one are involved in the RNA splicing like SF3B1, SRSF2, U2AF1, ZRSR2, LUC7L2, and DDX41. Epigenetic modifications are also identified, such as histone modification as ASXL1, EZH2. Finally, it can be DNA methylation (e.g., TET2, DNMT3A, IDH1/IDH2). On this review we will summarize the most recent progress in molecular pathogenesis of MDS, and try to better understand the pathogenesis of the specific subgroups of MDS patients and applications of discovery of new genetic mutation in the development of new therapeutic.

Concomitant chromosome 5q-deletion and JAK2V617F mutation present with myelodysplastic and myeloproliferative overlap features

Myelodysplastic Syndrome (MDS) with an isolated deletion of chromosome 5q [del(5q)] is a relatively rare MDS variant (5%) characterized by a moderate to severe anemia and normal or elevated platelet count with modest neutropenia [1-3]. These latter features, in addition to its excellent response to lenalidomide, are likely what contribute for its favorable prognosis [3-5]. The somatic gain of function mutation in JAK2 V617F is a driving mutation in Myeloproliferative Neoplasms (MPN), occurring in 97% of polycythemia vera (PV), 50-60% of essential thrombocytosis (ET) and primary myelofibrosis (PMF) [6]. This mutation results in constitutive activation of the JAK-STAT signaling pathway leading to increased proliferation and hypersensitivity to cytokines erythropoietin, IL-3, thrombopoietin, and GCSF. An allelic burden of JAK2 V617F mutation correlates with an increased risk of thrombosis and hemorrhage, as well as secondary fibrosis in MPN patients [7].