Selective KIT inhibitor KI-328 and HSP90 inhibitor show different potency against the type of KIT mutations recurrently identified in acute myeloid leukemia

Mutated KIT Tyrosine Kinase as a Novel Molecular Target in Acute Myeloid Leukemia

KIT is a type-III receptor tyrosine kinase that contributes to cell signaling in various cells. Since KIT is activated by overexpression or mutation and plays an important role in the development of some cancers, such as gastrointestinal stromal tumors and mast cell disease, molecular therapies targeting KIT mutations are being developed. In acute myeloid leukemia (AML), genome profiling via next-generation sequencing has shown that several genes that are mutated in patients with AML impact patients’ prognosis. Moreover, it was suggested that precision-medicine-based treatment using genomic data will improve treatment outcomes for AML patients. This paper presents (1) previous studies regarding the role of KIT mutations in AML, (2) the data in AML with KIT mutations from the HM-SCREEN-Japan-01 study, a genome profiling study for patients newly diagnosed with AML who are unsuitable for the standard first-line treatment (unfit) or have relapsed/refractory AML, and (3) new therapies targeting KIT mutations, such as tyrosine kinase inhibitors and heat shock protein 90 inhibitors. In this era when genome profiling via next-generation sequencing is becoming more common, KIT mutations are attractive novel molecular targets in AML.

Genotype and phenotype analysis of patients with pediatric cutaneous mastocytosis, especially wild-type KIT patients

Pediatric cutaneous mastocytosis (CM) is mainly attributed to gain-of-function mutations in KIT in mast cells. On the other hand, growing evidence suggests that CM patients exist without KIT mutations. To date, the association between the KIT mutation status and clinical phenotype has not been elucidated in pediatric CM, especially in patients with wild-type KIT. Nevertheless, genetic analysis has yet to be performed with whole KIT sequence of mast cells in Japanese patients with pediatric CM. In the present study, 11 Japanese patients with pediatric CM were analyzed to determine whether they had KIT mutations in their skin, and their clinical phenotypes were observed. The approximate frequency of patients with KIT mutation and that of wild-type KIT was almost consistent with the European analysis. The distribution of overall macules was similar between the patients with and without KIT mutations.

KIT as an Oncogenic Driver in Melanoma: An Update on Clinical Development

Metastatic melanoma is a heterogenous disease that has served as a model for the development of both targeted therapy and immunotherapy. KIT-mutated melanoma represents a rare subset, most commonly arising from acral, mucosal, and chronically sun-damaged skin. Additionally, KIT alterations are enriched in the triple wild-type subtype of cutaneous melanoma. Activating alterations of KIT-a transmembrane receptor tyrosine kinase important for cell development, growth, and differentiation-have been shown to be critical to oncogenesis across many tumor subtypes. Following the successes of BRAF-targeted therapy in melanoma and KIT-targeted therapy in gastrointestinal stromal tumors, small-molecule tyrosine kinase inhibitors targeting KIT have been examined in KIT-mutated melanoma. KIT inhibitors that have been investigated in relevant clinical trials in advanced melanoma include imatinib, sunitinib, dasatinib, and nilotinib. In these studies, selected patients with KIT-mutated melanoma were shown to be responsive to therapy with KIT inhibition, especially patients with L576P and K642E mutations. This has led to the incorporation of KIT-targeted therapy in the National Comprehensive Cancer Network guidelines for systemic therapy for metastatic or unresectable melanoma. Current research and development efforts include novel KIT-targeted therapies and testing KIT inhibitors in combination with immunotherapy.

miR-145 Antagonizes SNAI1-Mediated Stemness and Radiation Resistance in Colorectal Cancer

Epithelial-to-mesenchymal transition (EMT) has been closely linked with therapy resistance and cancer stem cells (CSCs). However, EMT pathways have proven challenging to therapeutically target. MicroRNA 145 (miR-145) targets multiple stem cell transcription factors and its expression is inversely correlated with EMT. Therefore, we hypothesized that miR-145 represents a therapeutic target to reverse snail family transcriptional repressor 1 (SNAI1)-mediated stemness and radiation resistance (RT). Stable expression of SNAI1 in DLD1 and HCT116 cells (DLD1-SNAI1; HCT116-SNAI1) increased expression of Nanog and decreased miR-145 expression compared to control cells. Using a miR-145 luciferase reporter assay, we determined that ectopic SNAI1 expression significantly repressed the miR-145 promoter. DLD1-SNAI1 and HCT116-SNAI1 cells demonstrated decreased RT sensitivity and, conversely, miR-145 replacement significantly enhanced RT sensitivity. Of the five parental colon cancer cell lines, SW620 cells demonstrated relatively high endogenous SNAI1 and low miR-145 levels. In the SW620 cells, miR-145 replacement decreased CSC-related transcription factor expression, spheroid formation, and radiation resistance. In rectal cancer patient-derived xenografts, CSC identified by EpCAM+/aldehyde dehydrogenase (ALDH)+ demonstrated high expression of SNAI1, c-Myc, and Nanog compared with non-CSCs (EpCAM+/ALDH-). Conversely, patient-derived CSCs demonstrated low miR-145 expression levels relative to non-CSCs. These results suggest that the SNAI1:miR-145 pathway represents a novel therapeutic target in colorectal cancer to overcome RT resistance.

Development of Heat Shock Protein (Hsp90) Inhibitors To Combat Resistance to Tyrosine Kinase Inhibitors through Hsp90-Kinase Interactions

Heat shock protein 90 (Hsp90) is a ubiquitous chaperone of all of the oncogenic tyrosine kinases. Many Hsp90 inhibitors, alone or in combination, have shown significant antitumor efficacy against the kinase-positive naïve and mutant models. However, clinical trials of these inhibitors are unsuccessful due to insufficient clinical benefits and nonoptimal safety profiles. Recently, much progress has been reported on the Hsp90-cochaperone-client complex, which will undoubtedly assist in the understanding of the interactions between Hsp90 and its clients. Meanwhile, Hsp90 inhibitors have shown promise against patients' resistance caused by early generation tyrosine kinase inhibitors (TKIs), and at least 13 Hsp90 inhibitors are being reevaluated in the clinic. In this regard, the objectives of the current perspective are to summarize the structure and function of the Hsp90-cochaperone-client complex, to analyze the structural and functional insights into the Hsp90-client interactions to address several existing unresolved problems with Hsp90 inhibitors, and to highlight the preclinical and clinical studies of Hsp90 inhibitors as an effective treatment against resistance to tyrosine kinase inhibitors.

Heat shock proteins in hematopoietic malignancies

Inducible heat shock proteins are molecular chaperones whose expression is increased after many different types of stress. They have a protective function helping the cell to cope with lethal conditions. Their basal expression is low in nonstressed, normal and nontransformed cells. However, in cancer cells and particularly in hematological malignancies, they are surprisingly abundant. Malignant cells have to rewire their metabolic requirements and therefore have a higher need for chaperones. This cancer cell addiction for HSPs is the basis for the use of HSP inhibitors in cancer therapy. HSPs have been shown to interact with different key apoptotic proteins. As a result, HSPs can essentially block the apoptotic pathways at several steps, most of them involving the activation of cystein proteases called caspases. Apoptosis and differentiation are physiological processes that share many common features, for instance, a controlled caspase activation and chromatin condensation are frequently observed. It is, therefore, not surprising that HSPs may be implicated in the differentiation process. HSPs may determine the fate of the cells by orchestrating the decision of apoptosis versus differentiation. This review will focus on the role of HSPs in hematological malignancies and the emerging therapeutic options that are being either proposed or used to target these protective proteins.