Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy




Li, Shawn


Chronic Myeloid Leukemia (CML) accounts for 15% of new leukemia cases in adults. In the United States alone, CML cases have increased steadily from 30,000 in 2000 to 150,000-180,000 in 2020. CML is characterized by a fusion protein called BCR-ABL, resulting from chromosomes 9 and 22 translocating. Imatinib, a BCR-ABL kinase inhibitor, was approved in 2001 and has improved CML patients' survival and quality of life. However, over 25% of patients will have to switch to other tyrosine kinase inhibitors (TKIs) after imatinib due to resistance or intolerance.

To better understand the resistance mechanism in CML, we used proteomics and phosphoproteomics to study parental and imatinib-resistant cell lines with and without imatinib treatment. We observed an enrichment of pathways involved in oxidative phosphorylation, fatty acid metabolism, and translation in the resistance clones. Kinase-substrate prediction analysis showed increased activity for the kinase AKT1. Furthermore, we found that LIN28A, an mRNA-binding protein that regulates the AKT signalling, was upregulated in imatinib-resistant cells and had increased phosphorylation at S200. Previous studies have shown that LIN28A/B increases in later and more resistant stages of CML. Additionally, LIN28A is involved in the resistance of breast, ovarian and pancreatic cancers to multiple therapies. To confirm the activity of LIN28A in our resistant cells, we measured the expression of let-7 family miRNAs and found significantly lower levels for the majority of the family in the resistant cells. LIN28A knockdowns resensitized the resistant clone to imatinib, and overexpression of LIN28A promoted resistance to imatinib. Using phosphoproteomics, we identified AKT, RPS6K, and PKC drivers of LIN28A resistance. With the use of midostaurin, a PKC inhibitor and AKTi-1/2, an AKT inhibitor, we were able to overcome the resistance.

The recent development of LIN28 inhibitors has been used to overcome resistance in other cancers. Therefore, we screened three commercially available LIN28 inhibitors, identifying LIN28i-1632 to be synergistic with imatinib. The synergistic combination led to changes in G2M checkpoint apoptosis and AKT signalling. These results show that targeting LIN28A both pharmacologically and genetically overcomes resistance to imatinib in CML.

Summary for Lay Audience

Leukemias are cancers that develop in blood-forming adult stem cells in the bone marrow of patients. There are many different types of leukemias, and they are differentiated and defined by which stem cells they develop from and how quickly they progress. These stem cells can develop into two lineages called myeloid (red blood cells, platelets or granulocytes) or lymphoid (T and B cells). Chronic myeloid leukemia (CML) results from an overproduction of abnormal and immature myeloid blood cells. CML develops from a single genetic event, creating the BCR-ABL fusion protein. In 2001, the approval of imatinib, the commercial name Gleevec, specifically targets this BCR-ABL protein.

Multiple mechanisms led to resistance to imatinib, either through the mutation of the BCR-ABL protein, or the overexpression of the BCR-ABL protein, or through the activation of different survival, growth and transporter pathways. As CML progresses to a later stage of the disease, the likelihood of one of these events occurring increases and patients with later stages of CML often become resistant to BCR-ABL inhibitors. Since imatinib was discovered, more inhibitors targeting BCR-ABL have been developed. These overcome mutations on the BCR-ABL protein but are not always effective against the other ways in which resistance occurs. Early interventions in CML patients prevent the development to later stages of the disease, where resistance is more likely.

My thesis explores a new mechanism of CML resistance to imatinib. First, I found that CML with a higher expression of LIN28A led to the resistance of imatinib. Decreasing LIN28A in cells made them respond to imatinib treatment again while increasing LIN28A in sensitive cells led to a greater resistance to imatinib. Next, I found that LIN28A altered the signalling of key survival and growth pathways including, AKT, PKC and RPS6K. Lastly, I investigated the potential of LIN28 inhibitors for treating CML resistance, in which we identified the commercially available LIN28i-1632 having a combined effect with imatinib. Altogether, my work sheds light on a novel mechanism of imatinib resistance and a potential way of targeting imatinib resistance in CML.

Available for download on Wednesday, April 01, 2026

Included in

Biochemistry Commons