1107 - Mechanisms of differential response to BTKi targeted therapy in patients with chronic lymphocytic leukemia

Introduction
Clinical findings have shown that the response of patients with chronic lymphocytic leukemia (CLL) to treatment with BTKi is either fast or slow. The peripheral blood clonal B cells of patients sensitive to BTKi increase rapidly in the early stage of treatment, and these patients easily obtain a complete response (CR). Patients insensitive to BTKi therapy do not respond until several months of BTKi treatment, and the reason for the difference is unknown. According to the therapeutic response to BTKi, the patients with CLL can be divided into two groups, early responders (ER) and late responders (LR), who may have different characteristics and underlying molecular mechanisms for responding to BTKi. In this study, we begin exploring the differences between ER and LR patients and the underlying molecular mechanisms affecting the difference. When we understand molecular mechanisms, will be able to improve our future clinical treatment, and further optimize the strategy for treatment of patients with CLL.
Materials and methods
The clinical characteristics and treatment response of 32 newly diagnosed patients with CLL treated with single-agent BTKi (zanubrutinib 19, ibrutinib 11 and orelabrutinib 2) were analyzed. Early Responders (ER) refers to a 50% increase in lymphocytes at 3-months of BTKi treatment and/or a complete response at 12 months of treatment, otherwise patients were categorized as LR. Microchips and principal component analysis (PCA) were used to analyze differentially expressed genes in both groups. Immunohistochemistry, PCR, Western Blotting, and other methods were used to analyze the expression of the related molecules of the leukemia cells. Mass spectrometry and CHiP were used to analyze the phosphorylation level of key regulatory molecules.
Results
1. There were 14 patients in the ER group and 18 in the LR group. The mean age of the patients in the two groups was 63.6 and 69.6 years, respectively. In the ER group 57% of patients were high risk of CLL-IPI, while 72% were high risk in the LR group. The proportion of ER between different BTKi treatments is roughly the same. All 14 patients with ER showed a rapid rise of early lymphocytes, and eight of them achieved complete remission after 12 months of treatment.
2. Compared with the LR group, the expression of IL-2, IL-6, CCL3, CCL4, and CCL17 in the ER group decreased significantly after BTKi treatment. Gene expression profile (GEP) showed that there were significantly different molecular expression patterns in the two groups, and the phosphorylation level of the transcription factor Ikaros in the ER group was significantly higher than that in the LR group.
3. The nuclear localization and transcriptional activity of Ikaros depends on BTK-mediated phosphorylation of pSer442 residues, and the function of BTKi in the regulation of Ikaros was significantly different in the ER group than in the LR group. After the treatment with BTKi, the gene and protein expression of MYC (Ikaros activator) in the ER group was significantly down-regulated, while the expression of the YES1 (Ikaros inhibitor) gene and protein was significantly upregulated. Changes of MYC and YES1 in the LR group were not significant.
Discussion and conclusions
The difference in the treatment response to BTKi in patients with treatment naïve CLL was related to the level of Ikaros phosphorylation. For those with an ER the immune response of the tumor microenvironment is enhanced, and inflammatory factors are inhibited, which is conducive to immune reconstruction after BTKi treatment. On the other hand, BTKi can inhibit the proliferation of cloned cells by reducing the ikaros function through upregulating YES1 expression and downregulating MYC expression. The research conclusions reveal the key molecules affecting the response of CLL cells to BTKi therapy and provide a basis for formulating precise treatment strategies for patients with treatment naïve CLL. Of course, because the number of cases included in this study is small and the observation time is not long, it is difficult to infer that ER patients have a better and longer survival advantage. These are subjects of follow-up experiments and observations.
References
1, Marcelo LR, Diana RG, Meritxell V. et al. Antitumor Activity of the Novel BTK Inhibitor TG-1701 Is Associated with Disruption of Ikaros Signaling in Patients with B-cell Non-Hodgkin Lymphoma. Clin Cancer Res. 2021 Dec 1;27(23):6591-6601.