Sequencing of Novel Therapies for Mantle Cell Lymphoma

Retinoic acid and proteotoxic stress induce AML cell death overcoming stromal cell protection

BACKGROUND

Acute myeloid leukemia (AML) patients bearing the ITD mutation in the tyrosine kinase receptor FLT3 (FLT3-ITD) present a poor prognosis and a high risk of relapse. FLT3-ITD is retained in the endoplasmic reticulum (ER) and generates intrinsic proteotoxic stress. We devised a strategy based on proteotoxic stress, generated by the combination of low doses of the differentiating agent retinoic acid (R), the proteasome inhibitor bortezomib (B), and the oxidative stress inducer arsenic trioxide (A).

METHODS

We treated FLT3-ITD+ AML cells with low doses of the aforementioned drugs, used alone or in combinations and we investigated the induction of ER and oxidative stress. We then performed the same experiments in an in vitro co-culture system of FLT3-ITD+ AML cells and bone marrow stromal cells (BMSCs) to assess the protective role of the niche on AML blasts. Eventually, we tested the combination of drugs in an orthotopic murine model of human AML.

RESULTS

The combination RBA exerts strong cytotoxic activity on FLT3-ITD+ AML cell lines and primary blasts isolated from patients, due to ER homeostasis imbalance and generation of oxidative stress. AML cells become completely resistant to the combination RBA when treated in co-culture with BMSCs. Nonetheless, we could overcome such protective effects by using high doses of ascorbic acid (Vitamin C) as an adjuvant. Importantly, the combination RBA plus ascorbic acid significantly prolongs the life span of a murine model of human FLT3-ITD+ AML without toxic effects. Furthermore, we show for the first time that the cross-talk between AML and BMSCs upon treatment involves disruption of the actin cytoskeleton and the actin cap, increased thickness of the nuclei, and relocalization of the transcriptional co-regulator YAP in the cytosol of the BMSCs.

CONCLUSIONS

Our findings strengthen our previous work indicating induction of proteotoxic stress as a possible strategy in FLT3-ITD+ AML therapy and open to the possibility of identifying new therapeutic targets in the crosstalk between AML and BMSCs, involving mechanotransduction and YAP signaling.

BTK Inhibitors and CAR T-Cell Therapy in Treating Mantle Cell Lymphoma-Finding a Dancing Partner

PURPOSE OF REVIEW

This review focuses on the feasibility of combining Bruton's tyrosine kinase (BTK) inhibitors (BTKis) with chimeric antigen receptor (CAR) T-cell therapy in patients with relapsed or refractory (R/R) mantle cell lymphoma (MCL). Potential scenarios for combination treatment with these agents are presented.

RECENT FINDINGS

BTKis and CAR T-cell therapy have revolutionized the treatment paradigm for R/R MCL. Ibrutinib, acalabrutinib, and zanubrutinib are covalent irreversible BTKis approved for R/R MCL. Brexucabtagene autoleucel was the first CAR T-cell therapy approved for R/R MCL based on findings from the ZUMA-2 trial. There is evidence to suggest that combination treatment with BTKis and CAR T-cell therapy may improve CAR T-cell efficacy. As BTKis and CAR T-cell therapy become mainstays in R/R MCL therapy, combination treatment strategies should be evaluated for their potential benefit in R/R MCL.