4001 - Chronic lymphocytic leukemia patient-derived xenografts recapitulate clonal evolution to Richter transformation

Abstract Text: Chronic lymphocytic leukemia (CLL) is a B-cell neoplasm with a very heterogeneous biological and clinical behavior. In 5-10% of patients, CLL transforms into diffuse large B-cell lymphoma (DLBCL) through a process called Richter transformation (RT). This transformation has been associated with poor prognosis (Condoluci & Rossi, 2022; Delgado et al., 2020). Patient-derived xenograft (PDX) models are dynamic systems that mimic inter-tumoral and inter-patient diversity, providing a basis to assess tumor evolution through serial propagation in mice (Zanella et al., 2022). Establishing PDXs from primary CLL tumors can improve the understanding of the disease's pathogenesis and help to evaluate effective new therapies.

In this study we have generated two new RT-PDXs (PDX12 and PDX19) by co-xenotransplanting CLL or RT tumoral B cells with autologous activated T cells into immunocompromised NOD-scid IL2rγnull (NSG) mice (Chen, 2019). Both PDXs had a clonal relationship with their original tumors. The study's most notable finding was the generation of a RT-PDX (PDX12) from a primary CLL sample collected before ibrutinib treatment. Whole-genome sequencing analysis revealed that PDX samples showed a genomic landscape similar to RT tumors from both patients, but also uncovered an unprecedented RT subclonal heterogeneity and clonal evolution during PDX generation. In PDX12, a small clinically silent RT subclone that was already present at the CLL stage expanded in the mice, recapitulating the disease transformation observed in the patient five months after the RT was diagnosed. Transcriptomic analysis revealed that the generated PDXs had a gene expression signature associated with RT, characterized by high oxidative phosphorylation (OXPHOS) and low B-cell receptor (BCR) signaling. Furthermore, pathways such as mTOR and glycolysis, among others, were also found to be upregulated. The results indicate that ibrutinib treatment is not responsible for the OXPHOShigh–BCRlow axis in RT, as PDX12 originated from a sample collected prior to ibrutinib treatment.
Both PDXs were treated in vitro with ibrutinib and venetoclax. All RT patient’s samples and PDX cells were resistant to both drugs, while cells from CLL samples were sensitive at the doses tested. Since we detected high levels of OXPHOS in both PDXs, we analyzed the biological impact of inhibiting OXPHOS activity using IACS-010759 (Molina et al., 2018). Our findings demonstrated that IACS-010759 led to an in vitro reduction in cell proliferation in all cases with high OXPHOS activity. Consistent with these observations, in vivo studies revealed reduced tumor infiltration in the spleen of mice following treatment with IACS-010759. Based on these results, we postulated that IACS-010759 could serve as a potential therapeutic approach to overcome venetoclax resistance, similar to its use in acute myeloid leukemia (Bosc et al., 2021; Farge et al., 2017). Combining venetoclax with IACS-010759 demonstrated a synergistic effect in vitro, and in vivo studies indicated a reduced tumor burden when both drugs were combined. Targeting the mTOR or glycolysis pathways was insufficient in counteracting venetoclax resistance.

Overall, PDX models will aid in studying the clonal evolution of CLL to RT and could offer new therapeutic options for RT patients with limited treatment possibilities and a poor prognosis. The research remarks a subclonal heterogeneity and confirms the presence of multiple RT subclones in early stages of the disease. The combination of OXPHOS inhibitor with BH3-mimetic inhibitors could be a promising therapeutic approach for RT patients.

Keywords : Chronic lymphocytic leukemia, Richter transformation, patient-derived xenografts.

Please indicate how this research was funded. : This study was supported by the Spanish Ministry of Science and Innovation (RTI2018-094584-B-I00 and PID2021-123165OB-I00 to D.C.) and was cofounded by the European Regional Development Fund (ERDF) and the CERCA program from Generalitat de Catalunya, CIBER -Consorcio Centro de Investigación Biomédica en Red- (CB16/12/00334), Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación, and Generalitat de Catalunya [2017 SGR 1009]. Also Heribert Playa-Albinyana is a recipient of a predoctoral fellowship from the Spanish Ministry of Universities (grant number FPU19/03110).

Please indicate the name of the funding organization.: Spanish Ministry of Science and Innovation, European Regional Development Fund (ERDF), Generalitat de Catalunya, Consorcio Centro de Investigación Biomédica en Red and Spanish Ministry of Universities.