With the markedly increased cure rate for children with newly diagnosed pediatric B-cell acute lymphoblastic leukemia (B-ALL), relapse and refractory B-ALL (R/R B-ALL) remain the primary cause of death worldwide due to the limitations of multidrug chemotherapy. As we now have a more profound understanding of R/R ALL, including the mechanism of recurrence and drug resistance, prognostic indicators, genotypic changes and so on, we can use newly emerging technologies to identify operational molecular targets and find sensitive drugs for individualized treatment. In addition, more promising and innovative immunotherapies and molecular targeted drugs that are expected to kill leukemic cells more effectively while maintaining low toxicity to achieve minimal residual disease (MRD) negativity and better bridge hematopoietic stem cell transplantation (HSCT) have also been widely developed. To date, the prognosis of pediatric patients with R/R B-ALL has been enhanced markedly thanks to the development of novel drugs. This article reviews the new advancements of several promising strategies for pediatric R/R B-ALL.

The three major Ras members, Kras, Hras, and Nras, are highly homologous and individual Ras genes can have distinct biological functions. Embryonic lethality of Kras-deficient mice precludes study of the biological functions of this Ras family member. In this study, we generated and examined mice with hematopoietic-specific deletion of Kras and bone marrow (BM) chimeric mice with B cell–specific targeted deletion of Kras. Hematopoietic-specific deletion of Kras impaired early B cell development at the pre–B cell stage and late B cell maturation, resulting in the reduction of BM pre–, immature, and mature B cells and peripheral follicular, marginal zone, and B1 mature B cells. In contrast, Kras deficiency did not affect T cell development. Studies of BM chimeric mice with B cell–specific deletion of Kras demonstrated that Kras deficiency intrinsically impaired B cell development. Kras deficiency reduced BCR-induced B cell proliferation and survival. Furthermore, Kras deficiency specifically impaired pre–BCR- and BCR-induced activation of the Raf-1/MEK/ERK pathway in pre–B and mature B cells, respectively. Thus, Kras is the unique Ras family member that plays a critical role in early B cell development and late B cell maturation through controlling the Raf-1/MEK/ERK pathway.

Anthracycline-associated cardiotoxicity is frequently seen in cancer survivors years after treatment, but it is rare in patients on chemotherapy. This study aimed to investigate the clinical characteristics of cardiac disorders in children with acute lymphoblastic leukemia (ALL) during chemotherapy. A retrospective case study was conducted in children with ALL, for whom electrocardiogram (ECG) and echocardiography (Echo) were regularly assessed before each course of chemotherapy. The cardiac disorders were diagnosed according to the Common Terminology Criteria for Adverse Events (CTCAE) Version 5.0. Binary logistic regression analysis was used to identify risk factors associated with cardiac disorders. There were 171 children eligible for the study, and 78 patients (45.61%) were confirmed as having cardiac disorders. The incidence of cardiac disorders was dependent upon the cumulative dose of daunorubicin (DNR) (p = 0.030, OR = 1.553, 95% CI: 1.005–3.108). Four patients (2.34%) presented with palpitation, chest pain, and persistent tachycardia, and they were cured or improved after medical intervention. A total of 74 patients (43.27%) had subclinical cardiac disorders confirmed by ECG or Echo. ECG abnormalities were commonly seen in the induction and continuation treatments, including arrhythmias (26, 15.20%), ST changes (24, 14.04%) and conduction disorders (4, 2.34%). Pericardial effusion (14, 8.19%), left ventricular hypertrophy (11, 6.43%), a widened pulmonary artery (5, 2.92%) and valvular insufficiency (5, 2.92%) suggested by Echo occurred after induction chemotherapy. Therefore, cardiac disorders with clinical manifestations are rare and need early intervention. Subclinical cardiac disorders are common but very hidden in children during ALL chemotherapy. Regular ECG and Echo could help paediatricians to identify and monitor patients with asymptomatic cardiac disorders earlier.

MTHFR is a crucial enzyme in folate metabolism. This study aimed to determine the relationship between MTHFR genetic polymorphism and elimination and toxicities of methotrexate (MTX). To do that, the study enrolled 145 patients diagnosed with acute lymphoblastic leukemia, who received chemotherapy following the Chinese Children’s Cancer Group Acute Lymphoblastic Leukemia (CCCG-ALL)-2015 protocol (clinical trial number: ChiCTR-IPR-14005706). We analyzed the effects of MTHFR C677T and A1298C polymorphisms on MTX elimination and toxicities. Patients with the MTHFR C677T TT genotype could tolerate a significantly higher MTX dose than those with the CC/CT genotype. However, patients with C677T TT genotypes had an increased risk of hypokalemia (1.369 to CC and 1.409 to CT types). The MTX infusion rate in patients with the MTHFR A1298C AC genotype was slightly lower than that in those with CC or AA genotypes. Patients with the A1298C AA genotype had a 1.405-fold higher risk of hepatotoxicity than those with the AC genotype (P > 0.05). There was no significant difference between the prevalence of other toxicities among MTHFR C677T or A1298C genotypes (P > 0.05). Neither MTHFR C677T nor A1298C polymorphisms were significantly associated with delayed MTX clearance. To conclude, MTHFR polymorphisms were not good predictors of MTX-related toxicities.

Ikaros isoform 6 (Ik6) is associated with a poor prognosis for children with acute lymphoblastic leukemia (ALL). Our previous study demonstrated that overexpression of Ik6 enhances proliferation and chemoresistance of leukemia cells, with a possible underlying mechanism that involves antiapoptosis. In the present study, we investigated whether Ik6 protects against apoptosis by regulating the Akt-FoxO1 pathway. Bone marrow samples from children with ALL were collected and evaluated. In Ik6⁺ patients, the Akt-FoxO1 pathway was activated such that expression of phosphorylated Akt and FoxO1 was significantly increased, but that of Bim and p27 decreased. In vitro experiments in this study were performed by using human ALL Nalm-6 cells that were stably transfected with Ik6 (Nalm-6/Ik6) or Sup-B15 and Ik6 shRNA (Sup-B15/Ik6 shRNA). Upon treatment with daunorubicin, Nalm-6/Ik6 cells exhibited a statistically significant reduction in apoptosis, with increased expression of p-Akt and p-FoxO1. In contrast, an increase in apoptosis with decreased expression of p-Akt and p-FoxO1 was observed in Sup-B15/Ik6 shRNA cells. This protection was dependent on activation of caspase-3 cleavage. By using an activator and an inhibitor of Akt or FoxO1, we demonstrated that Akt or FoxO1 activation had no effect on Ik6 expression. In conclusion, Ik6, the upstream factor of Akt-FoxO1 pathway, can protect ALL cells against daunorubicin-induced apoptosis and can potentially be explored as a therapeutic target in the treatment of patients with ALL.

Philadelphia chromosome-positive (Ph⁺) is considered as a high risk of acute lymphoblastic leukemia (ALL). Tyrosine kinase inhibitors (TKIs) are tailored drug for Ph⁺ ALL, but Ik6 is associated with TKI resistance and poor outcome of Ph⁺ ALL. In the present study, we investigated the potential benefit of combination therapy with imatinib and Huaier extract, a traditional Chinese medicine, in Ik6⁺ Ph⁺ ALL. The Ik6⁺ Ph⁺ -ALL cell lines Sup-B15 or BV173 were treated with Huaier extract, imatinib or the combination of the two. Analysis of cell proliferation showed that the combined treatment of imatinib and Huaier extract exhibited a greater effect on cell inhibition. Using flow cytometry and Western blot, enhanced effects on the induction of cell apoptosis were observed. The combination of the two drugs also exhibited a significant effect in decreasing the protein and enzymatic activity levels of BCR-ABL. The molecular mechanisms may be involved in BCR-ABL related pathways, including the inactivation of p-AKT, p-STAT5, p-mTOR and p-Lyn. Consistent with the in vitro results, the combination of Huaier extract and imatinib inhibit the growth and infiltration of xenografted tumors. Taken together, our findings show that Huaier extract enhances the anticancer efficacy of imatinib in Ik6⁺ Ph⁺ ALL Further, it also provides a potential clinical application in the treatment of refractory Ph⁺ ALL.