Philadelphia chromosome-positive leukemia stem cells in acute lymphoblastic leukemia and tyrosine kinase inhibitor therapy

Effects of different types of allogeneic hematopoietic stem cell transplantation donors on Philadelphia chromosome-positive acute lymphoblastic leukemia during the tyrosine kinase inhibitor era: A systematic review and meta-analysis

BACKGROUND

Matched donor (MD) allogeneic hematopoietic stem cell transplantation (allo-HSCT) is currently the preferred choice of treatment for Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) patients who have achieved complete remission. This systematic review and meta-analysis was conducted to investigate the effects of allo-HSCTs from different donor types for Ph+ ALL patients who received tyrosine kinase inhibitors (TKIs).

METHODS

Studies in EMBASE and MEDLINE between inception and December 2020 were identified using search terms related to "Ph+ ALL" and "HSCT." Eligible studies were studies with Ph+ ALL patients who received a TKI and allo-HSCT. The primary outcomes of interest-the overall survival (OS) or relapse-free survival (RFS)-needed to be reported. The Mantel-Haenszel method was used to combine the effect estimates and associated 95% confidence intervals (CIs) of each donor type.

RESULTS

Fourteen cohort studies were identified for the meta-analysis. Haploidentical (HID)-HSCT for Ph+ ALL patients resulted in a superior RFS to MD-HSCT, with a pooled odds ratio (OR) of 1.57 (95% CI, 1.05-2.32; I2 = 0%). However, HID-HSCT and MD-HSCT had comparable OS. Furthermore, HID-HSCT group had a significantly lower relapse rate than MD-HSCT group. On the other hand, the risks of graft-versus-host disease (GvHD) were higher for HID-HSCT and pooled OR of chronic GvHD rate. The OS and RFS of matched sibling-HSCT, matched unrelated-HSCT, and cord blood-HSCT were comparable with those of HID-HSCT.

CONCLUSION

This systematic review and meta-analysis showed that HID-HSCT is as effective as MD-HSCT in Ph+ ALL patients.

Desmoplastic small round cell tumor cancer stem cell-like cells resist chemotherapy but remain dependent on the EWSR1-WT1 oncoprotein

Desmoplastic Small Round Cell Tumor (DSRCT) is a rare and aggressive pediatric cancer driven by the EWSR1-WT1 fusion oncogene. Combinations of chemotherapy, radiation and surgery are not curative, and the 5-years survival rate is less than 25%. One potential explanation for refractoriness is the existence of a cancer stem cell (CSC) subpopulation able escape current treatment modalities. However, no study to-date has examined the role of CSCs in DSRCT or established in vitro culture conditions to model this subpopulation. In this study, we investigated the role of stemness markers in DSRCT survival and metastasis, finding that elevated levels of SOX2 and NANOG are associated with worse survival in sarcoma patients and are elevated in metastatic DSRCT tumors. We further develop the first in vitro DSRCT CSC model which forms tumorspheres, expresses increased levels of stemness markers (SOX2, NANOG, KLF4, and OCT4), and resists doxorubicin chemotherapy treatment. This model is an important addition to the DSRCT tool kit and will enable investigation of this critical DSRCT subpopulation. Despite lower sensitivity to chemotherapy, the DSRCT CSC model remained sensitive to knockdown of the EWSR1-WT1 fusion protein, suggesting that future therapies directed against this oncogenic driver have the potential to treat both DSRCT bulk tumor and CSCs.

Ruxolitinib/nilotinib cotreatment inhibits leukemia-propagating cells in Philadelphia chromosome-positive ALL

Background

As one of the major treatment obstacles in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ALL), relapse of Ph⁺ALL may result from the persistence of leukemia-propagating cells (LPCs). Research using a xenograft mouse assay recently determined that LPCs were enriched in the CD34⁺CD38⁻CD58⁻ fraction in human Ph⁺ALL. Additionally, a cohort study demonstrated that Ph⁺ALL patients with a LPCs phenotype at diagnosis exhibited a significantly higher cumulative incidence of relapse than those with the other cell phenotypes even with uniform front-line imatinib-based therapy pre- and post-allotransplant, thus highlighting the need for novel LPCs-based therapeutic strategies.

Methods

RNA sequencing (RNA-Seq) and real-time quantitative polymerase chain reaction (qRT-PCR) were performed to analyze the gene expression profiles of the sorted LPCs and other cell fractions from patients with de novo Ph⁺ALL. In order to assess the effects of the selective BCR–ABL and/or Janus kinase (JAK)2 inhibition therapy by the treatment with single agents or a combination of ruxolitinib and imatinib or nilotinib on Ph⁺ALL LPCs, drug-induced apoptosis of LPCs was investigated in vitro, as well as in vivo using sublethally irradiated and anti-CD122-conditioned NOD/SCID xenograft mouse assay. Moreover, western blot analyses were performed on the bone marrow cells harvested from the different groups of recipient mice.

Results

RNA-Seq and qRT-PCR demonstrated that JAK2 was more highly expressed in the sorted LPCs than in the other cell fractions in de novo Ph⁺ALL patients. Combination treatment with a selective JAK1/JAK2 inhibitor (ruxolitinib) and nilotinib more effectively eliminated LPCs than either therapy alone or both in vitro and in humanized Ph⁺ALL mice by reducing phospho-CrKL and phospho-JAK2 activities at the molecular level.

Conclusions

In summary, this pre-clinical study provides a scientific rationale for simultaneously targeting BCR–ABL and JAK2 activities as a promising anti-LPCs therapeutic approach for patients with de novo Ph⁺ALL.

A sequential approach with imatinib, chemotherapy and transplant for adult Ph+ acute lymphoblastic leukemia: final results of the GIMEMA LAL 0904 study

In the GIMEMA LAL 0904 protocol, adult Philadelphia positive acute lymphoblastic leukemia patients were treated with chemotherapy for induction and consolidation, followed by maintenance with imatinib. The protocol was subsequently amended and imatinib was incorporated in the induction and post-remission phase together with chemotherapy. Due to the toxicity of this combined approach, the protocol was further amended to a sequential scheme based on imatinib plus steroids as induction, followed by consolidation with chemotherapy plus imatinib and, when applicable, by a hematopoietic stem cell transplant. Fifty-one patients (median age 45.9 years) were enrolled in the final sequential protocol. At the end of induction (day +50), 96% of evaluable patients (n=49) achieved a complete hematologic remission; after consolidation, all were in complete hematologic remission. No deaths in induction were recorded. Overall survival and disease-free survival at 60 months are 48.8% and 45.8%, respectively. At day +50 (end of imatinib induction), a more than 1.3 log-reduction of BCR-ABL1 levels was associated with a significantly longer disease-free survival (55.6%, 95%CI: 39.0-79.3 vs. 20%, 95%CI: 5.8-69.1; P=0.03), overall survival (59.1%, 95%CI: 42.3-82.6 vs. 20%, 95%CI: 5.8-69.1; P=0.02) and lower incidence of relapse (20.5%, 95%CI: 7.2-38.6 vs. 60.0%, 95%CI: 21.6-84.3; P=0.01). Mean BCR-ABL1 levels remained significantly higher in patients who subsequently relapsed. Finally, BCR-ABL1^p190 patients showed a significantly faster molecular response than BCR-ABL1^p210 patients (P=0.023). Though the study was not powered to evaluate the role of allogeneic stem cell transplant, allografting positively impacted on both overall and disease-free survival. In conclusion, a sequential approach with imatinib alone in induction, consolidated by chemotherapy plus imatinib followed by a stem cell transplant is a feasible, well-tolerated and effective strategy for adult Philadelphia positive acute lymphoblastic leukemia, leading to the best long-term survival rates so far reported. (clinicaltrials.gov identifier: 00458848).

Quantitative phenotyping-based in vivo chemical screening in a zebrafish model of leukemia stem cell xenotransplantation

Zebrafish-based chemical screening has recently emerged as a rapid and efficient method to identify important compounds that modulate specific biological processes and to test the therapeutic efficacy in disease models, including cancer. In leukemia, the ablation of leukemia stem cells (LSCs) is necessary to permanently eradicate the leukemia cell population. However, because of the very small number of LSCs in leukemia cell populations, their use in xenotransplantation studies (in vivo) and the difficulties in functionally and pathophysiologically replicating clinical conditions in cell culture experiments (in vitro), the progress of drug discovery for LSC inhibitors has been painfully slow. In this study, we developed a novel phenotype-based in vivo screening method using LSCs xenotransplanted into zebrafish. Aldehyde dehydrogenase-positive (ALDH+) cells were purified from chronic myelogenous leukemia K562 cells tagged with a fluorescent protein (Kusabira-orange) and then implanted in young zebrafish at 48 hours post-fertilization. Twenty-four hours after transplantation, the animals were treated with one of eight different therapeutic agents (imatinib, dasatinib, parthenolide, TDZD-8, arsenic trioxide, niclosamide, salinomycin, and thioridazine). Cancer cell proliferation, and cell migration were determined by high-content imaging. Of the eight compounds that were tested, all except imatinib and dasatinib selectively inhibited ALDH+ cell proliferation in zebrafish. In addition, these anti-LSC agents suppressed tumor cell migration in LSC-xenotransplants. Our approach offers a simple, rapid, and reliable in vivo screening system that facilitates the phenotype-driven discovery of drugs effective in suppressing LSCs.