DNA polymerase θ protects leukemia cells from metabolically induced DNA damage.

Leukemia cells accumulate DNA damage, but altered DNA repair mechanisms protect them from apoptosis. We showed here that formaldehyde generated by serine/1-carbon cycle metabolism contributed to the accumulation of toxic DNA-protein crosslinks (DPCs) in leukemia cells, especially in driver clones harboring oncogenic tyrosine kinases (OTKs: FLT3(internal tandem duplication [ITD]), JAK2(V617F), BCR-ABL1). To counteract this effect, OTKs enhanced the expression of DNA polymerase theta (POLθ) via ERK1/2 serine/threonine kinase-dependent inhibition of c-CBL E3 ligase-mediated ubiquitination of POLθ and its proteasomal degradation. Overexpression of POLθ in OTK-positive cells resulted in the efficient repair of DPC-containing DNA double-strand breaks by POLθ-mediated end-joining. The transforming activities of OTKs and other leukemia-inducing oncogenes, especially of those causing the inhibition of BRCA1/2-mediated homologous recombination with and without concomitant inhibition of DNA-PK-dependent nonhomologous end-joining, was abrogated in Polq-/- murine bone marrow cells. Genetic and pharmacological targeting of POLθ polymerase and helicase activities revealed that both activities are promising targets in leukemia cells. Moreover, OTK inhibitors or DPC-inducing drug etoposide enhanced the antileukemia effect of POLθ inhibitor in vitro and in vivo. In conclusion, we demonstrated that POLθ plays an essential role in protecting leukemia cells from metabolically induced toxic DNA lesions triggered by formaldehyde, and it can be targeted to achieve a therapeutic effect.

High dose melphalan is an adequate preparative regimen for autologous hematopoietic stem cell transplantation in relapsed/refractory lymphoma.

INTRODUCTION: High-dose melphalan (HD-Mel) has been successfully employed in autografting patients with multiple myeloma. An advantage of this regimen is that the total dose of Mel can be delivered in a single day, being particularly useful when non-frozen hematopoietic stem cells are employed in the autograft. MATERIAL AND METHODS: All consecutive patients with R/R lymphomas, both HL and NHL studied and treated at two different centers were prospectively included in a study of ASCT employing a single dose of HD-Mel (200 mg/m2). A group of R/R HL or NHL autografted employing BEAM-like preparative regimens was constructed matched by diagnosis and age. The primary endpoint of the study was overall survival (OS), the secondary endpoint was event-free survival (EFS). RESULTS: Twenty-five R/R HL/NHL patients were prospectively accrued in the study. There were 8 (32%) females, 13 (52%) patients had at least 1 adverse effect: 7 (28%) developed mucositis, 5 (20%) neutropenic fever, and 6 (24%) grade IV nausea. In the HD-Mel group, median overall survival (OS) was not achieved and OS at 36 months was 71%, the transplant-related mortality being 0%. In the control group, median OS was not achieved and the 36-month OS was 76%, results not statistically significant (p 0.5). The EFS was also similar in both groups (p 0.5). CONCLUSION: HD-Mel alone is non-inferior to a BEAM-like regimen as a preparative regimen for autografting patients with R/R HL and NHL. The regimen is adequate to graft persons with non-frozen stem cells.

Etiologies of Extreme Thrombocytosis: A Contemporary Series.

OBJECTIVE: To describe the multifactorial etiologies of extreme thrombocytosis (EXT) in different care settings and the frequency of finding an occult malignancy. PATIENTS AND METHODS: We conducted a retrospective chart review at Mayo Clinic from January 1, 2011, through December 31, 2016. Adult patients who had at least 2 readings of platelet counts greater than 1000×109/L within 30 days of each other were included. We determined the causes of EXT on the basis of preset definitions of precipitating factors and identified the dominant causes on the basis of the trend of platelet counts. RESULTS: A total of 44,490 patients had thrombocytosis, and 305 patients (0.7%) had EXT. In 242 patients (79.3%), EXT was multifactorial. Surgical complications (54.1%) and hematologic malignancies (27.9%) were the 2 most dominant causes. Thirty-eight patients (12.5%) had new diagnoses of malignancies, mostly myeloproliferative neoplasms. In inpatients, surgical complications (71.9%), concurrent/previous splenectomy (50.5%), and infections (44.9%) were the most common causes, whereas hematologic malignancies (56.9%), iron deficiency (36.7%), and previous splenectomy (28.4%) were the most common causes in outpatients. Hematologic malignancy was 3.4 times more likely to be the cause of EXT in outpatients than in inpatients (56.9% vs 16.8%), and a new diagnosis of hematologic malignancy was 1.9 times more likely to be made in outpatients (15.6% vs 8.2%). Eighty-four percent of patients had resolution of EXT within 30 days. One patient died during the period of EXT. Nonsurgical patients with hematologic malignancies had the most prolonged period of EXT. CONCLUSION: Extreme thrombocytosis is a multifactorial hematologic condition, and its etiology differs substantially between inpatients and outpatients. Occult hematologic malignancies are uncommon in EXT when other major causes are present.