Screening LSCs For AML Drug Resistance, Sensitivity

Researchers used high throughput drug screening on leukemic stem cells (LSCs) to determine drug resistance and sensitivity in acute myeloid leukemia (AML) patients, according to an abstract presented by Frances Linzee Mabrey, MDand colleagues at the American Society of Hematology (ASH) 2018 Annual Meeting & Exposition, held December 1–4 in San Diego. Importantly, LSCs play a big role in AML tumor growth and AML relapse, as well as harboring unique gene expression profiles.

“Here we compared the results of in vitro drug sensitivity testing against a custom panel of drugs and drug combinations for blast populations vs leukemia stem cell populations derived from the same patients, as well as mutation analysis for a panel of 194 recurrently mutated genes in AML,” wrote the authors.

In the current study, the team obtained blood samples from 6 AML patients, with one sample being used to compare pre- and post-engraftment subclones. They conducted high throughput screens on LSCs, blasts, and pre- and post-engraftment AML subclones from the xenograft. They formulated dose-response curves to determine drug resistance patterns. Finally, the researchers completed mutation analysis on LSC and blast cell populations via next-generation sequencing for a panel of 194 recurrently mutated genes in AML (MyAML), which included 37 translocations.

The investigators observed that AML blasts and LSCs demonstrated divergent drug susceptibility patterns unique to each patient. Among 11 drugs commonly used to treat AML, 8 were typical chemotherapy drugs, with 5 of these agents effective vs blasts. However, none of the agents were effective vs LSCs (P = .0256). According to Dr. Mabrey and colleagues this finding indicates a potential mechanism for post-treatment relapse or primary refractoriness. Blast specific drugs included romidepsin, dinaciclib, alvocidib, ganetespib, selinexor, dorsomorphin, vinblastine, cladribine, dabrafenib, selumetinib, etoposide, and torkinib.

The engrafted xenograft subclone grew quickly and was resistant to standard chemotherapy. It also harbored three new deleterious mutations. These findings indicate potential genetic contributions to chemotherapy resistance and AML relapse.

“The distinct drug susceptibility patterns of patient-specific LSC and blast populations highlight the potential of an individualized approach to treat AML. LSCs are resistant to S-phase agents used in standard-of-care chemotherapy,” concluded the authors. “Incorporating the results of functional drug screening focused on LSC subclones may allow more individualized treatment of AML patients and identify patient-specific therapies that lead to improved outcomes.”

In an interview with Cancer Network, Aaron T. Gerds, MD, MS, assistant professor of medicine in the hematology and medical oncology department at the Cleveland Clinic Taussig Cancer Institute, considered the clinical implications of the Mabrey et al study.

“By moving away from empiricism, and matching specific treatments to individual patients by way of biomarkers, personalized medicine is touted by many as the future of healthcare,” he said. “This concept is being tested in trials such as NCI-MATCH and BEAT-AML. However, in the absence of both a targetable mutation and a matching treatment, this approach is not always successful and many patients for these studies are screened to find a few actionable biomarkers. This abstract takes a different approach, and takes viable leukemia cells and tests them against several available compounds using a high-throughput process. In addition to identifying which medications were most effective at treating an individual’s leukemia, they were also able to separate out AML blast cells from leukemia stem cell and found that each population tended to respond to different therapeutic strategies. This study demonstrates the feasibility of functional drug screening a methodology that can bring personalized medicine to the clinic.”