In an interview with <em>Targeted Oncology</em>, Lalit Sehgal, PhD, discussed the rationale for investigating how the tumor microenvironment impacts survival in patients with mantle cell lymphoma through various signaling pathways.
Lalit Sehgal, PhD
Patients with mantle cell lymphoma (MCL) have a median overall survival (OS) of 3 to 5 years, which is the poorest survival among patients with B-cell lymphomas. Standard treatment for these patients chemotherapy, however, chemotherapy regimens induces complications in older patients who cannot handle the toxicities associated with these agents.
Lalit Sehgal, PhD, et al, hypothesized that tumor-infiltrating cells could be responsible for relapse in patients with MCL, as well as resistance to chemotherapy. By identifying the factors associated with MCL cell survival and the maintenance of MCL-initiating cells, investigators could identify new treatment strategies for patients with MCL who are older and do not benefit from chemotherapeutic options.
“We found a mechanism could be targeted by various other single therapeutic agents,” said Sehgal. “It would help people who are in later ages and are not able to get benefit from the highly aggressive chemotherapy regimens available right now.”
In an analysis of primary MCL cells where human mesenchymal stem cells (hMSCs) were co-cultured (n = 24), investigators used flow-cytometry to look at the content of MCL-initiating cells, and factors were confirmed by reverse transcription polymerase chain reaction
analysis. Newly-identified factors were blocked in 3 MCL cell lines so that investigators could confirm the role these factors play in the survival of MCL cells, as well as MCL-initiating cells.
Investigators found IL-6 by hMSCs triggered FGF/FGFR autocrine loop in MCL-initiating cells, and the expression of FGFR correlated with expression of SOX11, which is a negative prognostic marker. For over 4 weeks, MCL-initiating cells were present in about 1% of MCL cells.
The FGFR/mir101/EZH2/NF-kB/XIAP axis regulated both survival and growth of MCL cells. The use of FGFR1 inhibitors led to early reduction in XIAP levels, as well as cell death. These findings demonstrated factors that are essential for survival of MCL and MCL-initiating cells. Overall, this presents new targets that can improve targeted treatment for patients with MCL.
In an interview withTargeted Oncology, Sehgal, a translational scientist and assistant professor in the Division of Hematology at The Ohio State University Comprehensive Cancer Center, discussed the rationale for investigating how the tumor microenvironment impacts survival in patients with MCL through various signaling pathways. He highlighted what he found in his study in patients with MCL.
TARGETED ONCOLOGY: What is prognosis like for patients with MCL?
Sehgal:For MCL, I think the first-line of therapy is first-generation Bruton’s kinase inhibitors (BTK), like ibrutinib (Imbruvica). The results are 65% objective response rate, in which 20% of them would be complete remissions. If you have lenalidomide, typically it’s a 30% OS.
One of the major problems in patients with MCL is the patients coming in at a later age over 60 years old. Because of that, there are not many options available for them. In the frontline [setting], salvage therapies cannot help them. We found a mechanism could be targeted by various other single therapeutic agents. It would help people who are in later ages and are not able to get benefit from the highly aggressive chemotherapy regimens available right now.
TARGETED ONCOLOGY: How has understanding of MCL pathogenesis evolved over the years? What do we know now that we didn’t know before?
Sehgal:MCL is rather large. It has remained the same from single-agent targeted therapies like BTK inhibitors over to resistance and a BTK [regimen] involving venetoclax (Venclexta) treatment opportunity. One of the things that is still the same is there is not a single candidate that would decline the MCL lymphomagenesis apart from FDA regulation of Cyclin D1 translocation in all the MCL cases.
A recent discovery, or recent report that finished whole exome sequencing in over 200 patients, actually showed that there are mutations in different genes with TP53 and ATM being prevalent. Along with that, there are a couple of epigenetic markers that are mutated too. It’s important with the advent of all the inventions and evolving technologies. It’s very important to move toward personalized medicine. For example, it’s difficult these days to identify if 1 patient will progress on this drug or not unless we have a complete exome file for that patient from diagnosis until we finish the longitudinal analysis.
Precision medicine and personalized treatment have come along for patients with MCL where you can actually define TP53 mutation versus wild-type and stratify groups of patients where you would know that patient A would feel better by giving them the normal therapeutic agents versus a single targeted agent, such as ibrutinib.
TARGETED ONCOLOGY: How is precision medicine being adopted among oncologists who treat MCL?
Sehgal:For precision, you mean the inclusion of mutations and segregation of mutational burde in particular patients, then segregating them to clinical trials. There are a couple ongoing trials that are taking TP53 mutations and a couple of other parameters into account when enrolling those patients into the clinical trials.
TARGETED ONCOLOGY: What was the rationale for investigating how the tumor microenvironment influences survival of MCL-initiating cells through FGF/FGFR1 signaling?
Sehgal:We were the first ones to identify and actually show what pathways are important in the stem cell population. We defined them as MCL-initiating cells. We found that when these MCL-initiating cells were in the circulating tumor or leukemic phase of blood, we call them circulating tumor cells, if you take the same circulating tumor cells versus from the tumor microenvironment, either lymph nodes or spleen, they have a total different gene expression profile.
One question that comes in is if it is the same cell, how would the expression pattern locations be different? This brings us back to the original seed and soil hypothesis that somehow the tumor microenvironment is providing an environment for the enrichment of these in patients with MCL. Circulating tumor cells are just circulating, and there is not a right directive measure of what signaling pathways could be targeted. One of the reasons for remission or relapse in patients with MCL is because clones often do not get killed in the tumor microenvironment. It’s important to understand how tumor microenvironment can influence these cells so that we can identify these novel pathways that should be targeted for the complete elimination of MCL-initiating cells.
TARGETED ONCOLOGY: What was the design of the study?
Sehgal:We created an ex-vivo bone marrow microenvironment. We do this using various different scaffolds, and you can culture the patient cells with these scaffolds. When you do that, you can actually isolate and regulate these MCL-initiating cells and normal cells and can run gene expression profiles on them to identify the important critical pathway that might be important for survival. [We can do this by] using various panel approaches to see enrichment analysis and other techniques. We can then go ahead and look at if the target that we found in an unbiased way is actually important for the survival of the stem cells or MCL-initiating cells. Then, we do preclinical assessments on patient-derived xenografts that we regenerated for MCL from patients. This is a big way of studying human disease in xenografts.
TARGETED ONCOLOGY: What were the results from this study?
Sehgal:We have found that the FGFR, MiR101-1, EZH2, NF-κB, and XIAP pathways are being upregulated, mainly because of ibrutinib resistance in patients with MCL. This happens where the programming is an influence of the tumor microenvironment. Currently, we are working on generating a specific inhibitor that is going to target these specific pathways, especially for ibrutinib-relapsed patients or those who have second resistance or primary resistance to ibrutinib.
Sehgal L, Tamer K, Wang X, et al. Tumor Microenvironment Regulates Survival of Mantle Cell Lymphoma Cells through Various Signaling Pathways.Blood. (2015) 126 (23): 4775. doi: 10.1182/blood.V126.23.4775.4775.