Cancer-associated fibroblasts in acute leukemia

Lactate accumulation promotes immunosuppression and fibrotic transformation of bone marrow microenvironment in myelofibrosis

BACKGROUND

Clonal myeloproliferation and fibrotic transformation of the bone marrow (BM) are the pathogenetic events most commonly occurring in myelofibrosis (MF). There is great evidence indicating that tumor microenvironment is characterized by high lactate levels, acting not only as an energetic source, but also as a signaling molecule.

METHODS

To test the involvement of lactate in MF milieu transformation, we measured its levels in MF patients' sera, eventually finding a massive accumulation of this metabolite, which we showed to promote the expansion of immunosuppressive subsets. Therefore, to assess the significance of its trafficking, we inhibited monocarboxylate transporter 1 (MCT1) by its selective antagonist, AZD3965, eventually finding a mitigation of lactate-mediated immunosuppressive subsets expansion. To further dig into the impact of lactate in tumor microenvironment, we evaluated the effect of this metabolite on mesenchymal stromal cells (MSCs) reprogramming.

RESULTS

Our results show an activation of a cancer-associated phenotype (CAF) related to mineralized matrix formation and early fibrosis development. Strikingly, MF serum, enriched in lactate, causes a strong deposition of collagen in healthy stromal cells, which was restrained by AZD3965. To corroborate these outcomes, we therefore generated for the first time a TPOhigh zebrafish model for the establishment of experimental fibrosis. By adopting this model, we were able to unveil a remarkable increase in lactate concentration and monocarboxylate transporter 1 (MCT1) expression in the site of hematopoiesis, associated with a strong downregulation of lactate export channel MCT4. Notably, exploiting MCTs expression in biopsy specimens from patients with myeloproliferative neoplasms, we found a loss of MCT4 expression in PMF, corroborating changes in MCT expression during BM fibrosis establishment.

CONCLUSIONS

In conclusion, our results unveil lactate as a key regulator of immune escape and BM fibrotic transformation in MF patients, suggesting MCT1 blocking as a novel antifibrotic strategy.

The critical role of the bone marrow stromal microenvironment for the development of drug screening platforms in leukemia

Extensive research over the past 50 years has resulted in significant improvements in survival for patients diagnosed with leukemia. Despite this, a subgroup of patients harboring high-risk genetic alterations still suffer from poor outcomes. There is a desperate need for new treatments to improve survival, yet consistent failure exists in the translation of in vitro drug development to clinical application. Preclinical screening conventionally utilizes tumor cell monocultures to assess drug activity; however, emerging research has acknowledged the vital role of the tumor microenvironment in treatment resistance and disease relapse. Current co-culture drug screening methods frequently employ fibroblasts as the designated stromal cell component. Alternative stromal cell types that are known to contribute to chemoresistance are often absent in preclinical evaluations of drug efficacy. This review highlights mechanisms of chemoresistance by a range of different stromal constituents present in the bone marrow microenvironment. Utilizing an array of stromal cell types at the early stages of drug screening may enhance the translation of in vitro drug development to clinical use. Ultimately, we highlight the need to consider the bone marrow microenvironment in drug screening platforms for leukemia to develop superior therapies for the treatment of high-risk patients with poor prognostic outcomes.

Cancer-associated fibroblasts in hematologic malignancies: elucidating roles and spotlighting therapeutic targets

Hematologic malignancies comprise a diverse range of blood, bone marrow, and organ-related disorders that present significant challenges due to drug resistance, relapse, and treatment failure. Cancer-associated fibroblasts (CAFs) represent a critical component of the tumor microenvironment (TME) and have recently emerged as potential therapeutic targets. In this comprehensive review, we summarize the latest findings on the roles of CAFs in various hematologic malignancies, including acute leukemia, multiple myeloma, chronic lymphocytic leukemia, myeloproliferative neoplasms, and lymphoma. We also explore their involvement in tumor progression, drug resistance, and the various signaling pathways implicated in their activation and function. While the underlying mechanisms and the existence of multiple CAF subtypes pose challenges, targeting CAFs and their associated pathways offers a promising avenue for the development of innovative treatments to improve patient outcomes in hematologic malignancies.