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ctDNA Could Improve Monitoring of Response to Chemo in ALL
The current protocol for monitoring the response to chemotherapy in patients with acute lymphoblastic leukemia (ALL) is a bone marrow biopsy, according to a study presented at the NCCN Virtual Annual Conference 2021 (online: March 2021; doi: 10.6004/jnccn.2020.7764).
All cancer types produce circulating tumor DNA (ctDNA) and the concentration of ctDNA in patient plasma has been shown to correlate with tumor burden, the study said, marking it as an important biomarker of tumor spread and recurrence.
The study, led by Thomas Lee Amburn, BA, University of Kentucky College of Medicine and colleagues, sought to develop a new assay to quantify ctDNA in patients with ALL undergoing treatment.
“Bone marrow biopsy is the current protocol to monitoring ALL response to chemotherapy, however, ctDNA (circulating tumor DNA) could be a better way to monitor ALL response to chemotherapy since its less invasive and likely could be more specific,” Amburn said.
To optimize ctDNA isolation, Qiagen, Zymo and Takara kits were analyzed on the efficacy of detecting ctDNA concentrations using human plasma spiked with DNA ladder. Kit optimization with a spike of 3000ng of 100pb ctDNA ladder into human ladder provided the following mean values of ctDNA: Qiagen, 47.7 ng/uL; Zymo, 22.4 ng/uL; and Takara, 16.89 ng/uL. Control plasma, without spike, had 0.56 ng/uL (Qiagen); 0.47 ng/uL (Zymo); and not detected (Takara).
Next, to identify potential B-ALL cell line ctDNA sequences, researchers created ctDNA using iScript from cell line RNA primers known to amplify VDJ in B-cells, with results showing 452 bases.
Finally, changes in DNA methylation between ALL and normal DNA were detected using the Qiagen kit with an ELISA-based methylation array. Hypermethylated patterns were detected for ALL if greater than 0.05% 5-mC, which were the following alleles: U-13-1223, U-13-2297, U-17-0563, U-18-0404, and PBMC1.
Researchers concluded that the Qiagen kit had the best resolution for ctDNA isolation. Also, an ‘off-the-shelf’ type assay for ctDNA in ALL may be possible to develop, researchers said. However, developing a clinical assay of ALL monitoring is still in progress, but may provide a more sensitive diagnostic assay for ALL.—Emily Bader
Amburn TL, Haney M, Moore H, et el. Isolation and Characterization of Circulating Tumor DNA to Monitor Acute Lymphoblastic Leukemia. Presented at: the NCCN 2021 Virtual Annual Conference; March 18-20,2021; Virtual. Abstract CLO21-021.
