Chromosomal change during 6-mercaptopurine (6-MP) therapy in juvenile myelomonocytic leukemia: the growth of a 6-MP-refractory clone that already exists at onset

Abstract

Among 11 JMML children, two had an abnormal karyotype, and nine had a normal karyotype at onset. In one patient with trisomy 8 and four patients with a normal karyotype, a new clone with an aberrant karyotype emerged 1-14 months after 6-mercaptopurine (6-MP) therapy as shown by G-banding analyses. Fluorescence in situ hybridization disclosed that an abnormal clone existed in approximately 3-6% of bone marrow cells at onset or before 6-MP therapy in all the four cases examined, and increased to approximately 12-90% during the treatment. In culture with granulocyte-macrophage colonystimulating factor, cytogenetically abnormal clones that proliferated during 6-MP therapy possessed significantly less sensitivity to the antimetabolite, compared with cells that decreased in numbers after the therapy. A PTPN11 mutation was detected in all of granulocyte-macrophage colonies irrespective of karyotypic aberration in one patient, whereas approximately 80% of erythroid colonies and 20% of mixed colonies possessed neither a PTPN11 mutation nor chromosomal abnormalities. The appearance of chromosomal aberrations shown by G-banding during 6-MP therapy in some JMML cases may result, in part, from the growth of a 6-MP-refractory clone that already exists at onset. It is possible that treatment with 6-MP promotes progression of the disease.

Myeloid progenitors with PTPN11 and nonRAS pathway gene mutations are refractory to treatment with 6-mercaptopurine in juvenile myelomonocytic leukemia

“…[4][5][6][7][8][9] We have previously reported seven cases of patients (five with PTPN11 mutation; one with NRAS mutation) with significant chromosomal changes after chemotherapy or allogeneic hematopoietic stem cell transplantation (HSCT). 10 In addition, we observed a loss of wild-type NRAS locus and monosomy 7 after blastic crisis in a patient with JMML and a heterozygous NRAS mutation. 11 The present study aimed to evaluate whether JMML clones with the RAS pathway-associated gene mutation coexist at the onset with those harboring both the RAS pathway-associated and nonRAS pathway gene mutations, and examine 6-mercaptopurine (6-MP)-susceptibility of these two clone types.…”

“…Sequence analyses were then performed on individual GM colony-constituent cells, as described previously. 10 As presented in Figure 1, 16 of 34 GM colonies derived from PBMNCs obtained at diagnosis of case no. 1 had both JAK3 mutation and PTPN11 mutations.…”

“…10 The study was approved by the Institutional Review Board of Shinshu University. Informed consent was obtained from the guardians of the patients in accordance with the institutional guidelines.…”

In vitro expansion of CD34+CD38− cells under stimulation with hematopoietic growth factors on AGM-S3 cells in juvenile myelomonocytic leukemia

“…Exons 3, 8 and 11 of PTPN11, and exon 1 (codons 12 and 13) and exon 2 (codon 61) of NRAS and KRAS genes were amplified by PCR, using primer pairs described previously. 8,14,15 The PCR products were subjected to direct sequencing from both directions on an automatic DNA sequencer.…”

Genetic analysis of TP53 in childhood myelodysplastic syndrome and juvenile myelomonocytic leukemia

“…Dishes were incubated at 37℃ in a humidified atmosphere with 5% CO 2 . On day 14, GM colonies and erythroid colonies were individually lifted and prepared as single-cell suspensions, as described previously [12]. Then, sequence and FISH analyses were performed on GM or erythroid colony-constituent cells.…”