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Targeting conditioned media dependencies and FLT-3 in chronic lymphocytic leukemia
Salma Parvin1, Aditi Aryal1, Shanye Yin1,2
1Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA.
Abstract:
The importance of the stromal microenvironment in chronic lymphocytic leukemia (CLL) pathogenesis and drug resistance is well established. Despite recent advances in CLL therapy, identifying novel ways to disrupt interactions between CLL and its microenvironment may identify new combination partners for the drugs currently in use. To understand the role of microenvironmental factors on primary CLL cells, we took advantage of an observation that conditioned media (CM) collected from stroma was protective of CLL cells from spontaneous cell death ex vivo. The cytokine in the CM-dependent cells that most supports CLL survival in short-term ex vivo culture was CCL2. Pretreatment of CLL cells with anti-CCL2 antibody enhanced venetoclax-mediated killing. Surprisingly, we found a group of CLL samples (9/23 cases) that are less likely to undergo cell death in the absence of CM support. Functional studies revealed that CM-independent (CMI) CLL cells are less sensitive to apoptosis than conventional stroma-dependent CLL. In addition, a majority of the CMI CLL samples (80%) harbored unmutated immunoglobulin heavy-chain variable (IGHV) region. Bulk-RNA sequence analysis revealed upregulation of the focal adhesion and RAS signaling pathways in this group, along with expression of fms-like tyrosine kinase 3 (FLT3) and CD135. Treatment with FLT3 inhibitors caused a significant reduction in cell viability among CMI samples. In summary, we were able to discriminate and target 2 biologically distinct subgroups of CLL based on CM dependence with distinct microenvironmental vulnerabilities.
Insights
Stromal microenvironment supports chronic lymphocytic leukemia (CLL) cell survival via CCL2. Targeting this interaction and identifying distinct CLL subgroups, like CM-independent (CMI) CLL, offers new therapeutic strategies.
Area of Science:
- Hematology
- Cancer Biology
- Immunology
Background:
- The stromal microenvironment significantly influences chronic lymphocytic leukemia (CLL) pathogenesis and treatment resistance.
- Novel therapeutic strategies are needed to overcome drug resistance by targeting CLL-microenvironment interactions.
Purpose of the Study:
- To investigate the role of microenvironmental factors in CLL cell survival and drug resistance.
- To identify distinct CLL subgroups based on their dependence on the microenvironment for survival.
- To explore novel therapeutic targets for CLL.
Main Methods:
- Utilized conditioned media (CM) from stroma to culture primary CLL cells ex vivo.
- Measured CLL cell survival and apoptosis in response to CM and specific cytokines like CCL2.
- Analyzed gene expression (Bulk-RNA sequencing) and functional responses to targeted inhibitors in different CLL subgroups.
Main Results:
- Stromal CM protects CLL cells from spontaneous death, primarily mediated by the cytokine CCL2.
- A subset of CLL samples (CM-independent, CMI) exhibited inherent resistance to apoptosis.
- CMI CLL samples, often associated with unmutated IGHV, showed upregulated focal adhesion and RAS signaling pathways, including FLT3/CD135 expression.
- FLT3 inhibitors effectively reduced viability in CMI CLL samples.
Conclusions:
- Stromal microenvironment, particularly CCL2, plays a crucial role in CLL cell survival.
- Two distinct CLL subgroups exist: stroma-dependent and CMI, with differing apoptotic sensitivities and molecular profiles.
- Targeting microenvironmental vulnerabilities, such as FLT3 in CMI CLL, presents a promising therapeutic avenue for distinct CLL patient subgroups.
