Receptor tyrosine kinase alterations in AML - biology and therapy

The Research Advances of Aptamers in Hematologic Malignancies

Currently, research for hematological malignancies is very intensive, with many breakthroughs. Among them, aptamer-based targeted therapies could be counted. Aptamer is a targeting tool with many unique advantages (easy synthesis, low toxicity, easy modification, low immunogenicity, nano size, long stability, etc.), therefore many experts screened corresponding aptamers in various hematological malignancies for diagnosis and treatment. In this review, we try to summarize and provide the recent progress of aptamer research in the diagnosis and treatment of hematologic malignancies. Until now, 29 aptamer studies were reported in hematologic malignancies, of which 12 aptamers were tested in vivo and the remaining 17 aptamers were only tested in vitro. In this case, 11 aptamers were combined with chemotherapeutic drugs for the treatment of hematologic malignancies, 4 aptamers were used in combination with nanomaterials for the diagnosis and treatment of hematologic malignancies, and some studies used aptamers for the targeted transportation of siRNA and miRNA for targeted therapeutic effects. Their research provides multiple approaches to achieve more targeted goals. These findings show promising and encouraging future for both hematological malignancies basic and clinical trials research.

Oligonucleotide aptamer-drug conjugates for targeted therapy of acute myeloid leukemia

Oligonucleotide aptamers can specifically bind biomarkers on cancer cells and can be readily chemically modified with different functional molecules for personalized medicine. To target acute myeloid leukemia (AML) cells, we developed a single-strand DNA aptamer specific for the biomarker CD117, which is highly expressed on AML cells. Sequence alignment revealed that the aptamer contained a G-rich core region with a well-conserved functional G-quadruplex structure. Functional assays demonstrated that this synthetic aptamer was able to specifically precipitate CD117 proteins from cell lysates, selectively bound cultured and patient primary AML cells with high affinity (Kd < 5 nM), and was specifically internalized into CD117-expressing cells. For targeted AML treatment, aptamer-drug conjugates were fabricated by chemical synthesis of aptamer (Apt) with methotrexate (MTX), a central drug used in AML chemotherapy regimens. The formed Apt-MTX conjugates specifically inhibited AML cell growth, triggered cell apoptosis, and induced cell cycle arrest in G1 phase. Importantly, Apt-MTX had little effect on CD117-negative cells under the same treatment conditions. Moreover, exposure of patient marrow specimens to Apt-MTX resulted in selective growth inhibition of primary AML cells and had no toxicity to off-target background normal marrow cells within the same specimens. These findings indicate the potential clinical value of Apt-MTX for targeted AML therapy with minimal to no side effects in patients, and also open an avenue to chemical synthesis of new, targeted biotherapeutics.

Phase I clinical, pharmacokinetic, and pharmacodynamic study of the Akt-inhibitor triciribine phosphate monohydrate in patients with advanced hematologic malignancies

Akt, a serine/threonine protein kinase, is constitutively phosphorylated and hyperactivated in multiple cancers, including acute myeloid leukemia. High levels are linked to poor survival and inferior responses to chemotherapy, making Akt inhibition an attractive therapeutic target. In this phase I/II study of TCN-PM, a small-molecule Akt inhibitor, TCN-PM therapy was well tolerated in patients with advanced hematological malignancies, and reduced levels of phosphorylation of Akt and its substrate Bad were shown, consistent with inhibition of this survival pathway and induction of cell death. Further investigation of TCN-PM alone or in combination in patients with high Akt levels is warranted.

Evaluation of tyrosine-kinase receptor c-KIT (c-KIT) mutations, mRNA and protein expression in canine leukemia: might c-KIT represent a therapeutic target?

The tyrosine-kinase receptor c-KIT (c-KIT) plays an important role in proliferation, survival and differentiation of progenitor cells in normal hematopoietic cells. In human hematological malignancies, c-KIT is mostly expressed by progenitor cell neoplasia and seldom by those involving mature cells. Tyrosine kinase inhibitors (TKIs) are actually licensed for the first- and second-line treatment of human hematologic disorders. Aim of the present study was to evaluate c-KIT mRNA and protein expression and complementary DNA (cDNA) mutations in canine leukemia. Eleven acute lymphoblastic leukemia (ALL) and acute undifferentiated leukemia (AUL) and 12 chronic lymphocytic leukemia (CLL) were enrolled in this study. The amounts of c-KIT mRNA and protein were determined, in peripheral blood samples, by using quantitative real time RT-PCR, flow cytometry and immunocytochemistry, respectively. The presence of mutations on c-KIT exons 8-11 and 17 were investigated by cDNA sequencing. Higher amounts of c-KIT mRNA were found in ALL/AUL compared to CLL, and this latter showed a lower pattern of gene expression. Transcriptional data were confirmed at the protein level. No significant gain-of-function mutations were ever observed in both ALL/AUL and CLL. Among canine hematological malignancies, ALL/AUL typically show a very aggressive biological behavior, partly being attributable to the lack of efficacious therapeutic options. The high level of c-KIT expression found in canine ALL/AUL might represent the rationale for using TKIs in future clinical trials.

Prognostic value of miR-29a expression in pediatric acute myeloid leukemia

OBJECTIVES

As a member of miR-29 family, miR-29a can act as either oncogene or tumor suppressor. However, its expression patterns in acute myeloid leukemia (AML) are controversial according to previous studies. Thus, the aim of this study was to determine the expression and clinical significance of miR-29a in pediatric AML.

METHODS

Expression levels of miR-29a in bone marrow mononuclear cells were detected by real-time quantitative PCR in a cohort of 106 patients with newly diagnosed pediatric AML. The prognostic values of miR-29a in pediatric AML were also analyzed.

RESULTS

Compared with normal controls, we demonstrated a significantly decreased expression of miR-29a in the bone marrow of pediatric AML patients (P<0.001). The expression levels of miR-29a were significantly lower in French-American-British classification subtype M7 than in other subtypes (P<0.001) and differed significantly across cytogenetic risk groups (P=0.002) with high miR-29a expression among those with favorable karyotypes. Moreover, low miR-29a expression was significantly associated with shorter relapse-free (P<0.001) and overall (P=0.008) survival in pediatric AML patients. Cox proportional hazards multivariate analysis of the univariate predictors identified cytogenetic risk and miR-29a expression as independent prognostic factors for relapse-free survival and overall survival. More interestingly, the prognostic value of miR-29a expression was more obvious in the subgroup of patients with intermediate-risk cytogenetics.

CONCLUSION

Our data indicate for the first time that the down-regulation of miR-29a was associated with advanced clinical features and poor prognosis of pediatric AML patients, suggesting that miR-29a down-regulation may be used as an unfavorable prognostic marker in pediatric AML.

Heme controls the regulation of protein tyrosine kinases Jak2 and Src

Protein tyrosine kinases play key roles in many molecular and cellular processes in diverse living organisms. Their proper functioning is crucial for the normal growth, development, and health in humans, whereas their dysfunction can cause serious diseases, including various cancers. As such, intense studies have been performed to understand the molecular mechanisms by which the activities of protein tyrosine kinases are regulated in mammalian cells. Particularly, small molecules that can modulate the activity of tyrosine kinases are of great importance for discovering therapeutic drug candidates for numerous diseases. Notably, heme cannot only serve as a prosthetic group for hemoglobins and enzymes, but it also is a small signaling molecule that can control the activity of diverse signaling and regulatory proteins. Using a computational search, we found that a group of non-membrane spanning tyrosine kinases contains one or more CP motifs that can potentially bind to heme and mediate heme regulation. We then used experimental approaches to determine whether heme can affect the activity of any of these tyrosine kinases. We found that heme indeed affects the phosphorylation of key tyrosine residues in Jak2 and Src, and is therefore able to modulate Jak2 and Src activity. Further experiments showed that Jak2 and Src bind to heme and that the presence of heme alters the sensitivity of Jak2 and Src to trypsin digestion. These results suggest that heme actively interacts with Jak2 and Src and alters their conformation.

CD147 and VEGF co-expression predicts prognosis in patients with acute myeloid leukemia

OBJECTIVE

To investigate the possible role of CD147 and vascular endothelial growth factor in progression and prognosis of acute myeloid leukemia.

METHODS

Immunohistochemical staining was performed to detect the expression of CD147 and vascular endothelial growth factor in paraffin-embedded sections from 62 bone marrow biopsies obtained from an equal number of patients with newly diagnosed acute myeloid leukemia.

RESULTS

CD147 and vascular endothelial growth factor expression in the bone marrow of acute myeloid leukemia patients were significantly higher than those in normal controls (both P < 0.001). Expression of them was significantly increased in patients with a high degree of microvessel density compared with those with a low degree (CD147: P = 0.009; vascular endothelial growth factor: P = 0.01) and correlated well with bone marrow microvessel density (CD147: P = 0.01; vascular endothelial growth factor: P = 0.02). In addition, higher levels of CD147 and vascular endothelial growth factor were also found in acute myeloid leukemia patients with an unfavorable karyotype compared with those with intermediate and favorable karyotypes (both P = 0.01). Moreover, the expression of CD147 was significantly correlated with that of vascular endothelial growth factor (P < 0.001). Furthermore, the co-expression of CD147 and vascular endothelial growth factor in the bone marrow indicated a poor prognosis in acute myeloid leukemia and was an independent prognostic factor for overall survival by multivariate analysis.

CONCLUSIONS

Our data show for the first time that the co-expression of CD147 and vascular endothelial growth factor may indicate a poor prognosis in acute myeloid leukemia and may be a highly sensitive marker for predicting the clinical outcome of patients.