Cyclin dependent kinase 4/6 inhibitor palbociclib synergizes with BCL2 inhibitor venetoclax in experimental models of mantle cell lymphoma without RB1 deletion

BACKGROUND

Mantle cell lymphoma (MCL) is a chronically relapsing malignancy with deregulated cell cycle progression. We analyzed efficacy, mode of action, and predictive markers of susceptibility to palbociclib, an approved CDK 4/6 inhibitor, and its combination with venetoclax, a BCL2 inhibitor.

METHODS

A panel of nine MCL cell lines were used for in vitro experiments. Four patient derived xenografts (PDX) obtained from patients with chemotherapy and ibrutinib-refractory MCL were used for in vivo proof-of-concept studies. Changes of the mitochondrial membrane potential, energy-metabolic pathways, AKT activity, and pro-apoptotic priming of MCL cells were evaluated by JC-1 staining, Seahorse XF analyser, genetically encoded fluorescent AKT reporter, and BH3 profiling, respectively. MCL clones with gene knockout or transgenic (over)expression of CDKN2A, MYC, CDK4, and RB1 were used to estimate impact of these aberrations on sensitivity to palbociclib, and venetoclax.

RESULTS

Co-targeting MCL cells with palbociclib and venetoclax induced cytotoxic synergy in vitro and in vivo. Molecular mechanisms responsible for the observed synthetic lethality comprised palbociclib-mediated downregulation of anti-apoptotic MCL1, increased levels of proapoptotic BIM bound on both BCL2, and BCL-XL and increased pro-apoptotic priming of MCL cells mediated by BCL2-independent mechanisms, predominantly palbociclib-triggered metabolic and mitochondrial stress. Loss of RB1 resulted in palbociclib resistance, while deletion of CDKN2A or overexpression of CDK4, and MYC genes did not change sensitivity to palbociclib.

CONCLUSIONS

Our data strongly support investigation of the chemotherapy-free palbociclib and venetoclax combination as an innovative treatment strategy for post-ibrutinib MCL patients without RB1 deletion.

Experimental model of primary intraocular lymphoma based on BALB/CaNn strain and A20 cells is optimal for investigational research

AIM

The purpose of this project was to compare the characteristics of two experimental murine models of primary intraocular lymphoma (PIOL) and determine which experimental model is most suitable for further investigational research to elucidate the pathophysiology of PIOL and to find new therapeutical strategies.

METHODS

In both experimental models PIOL was induced in immunocompetent mice with intravitreal injection of syngeneic B-cell lymphoma cell lines. Murine strain C3H/HeN and cell line 38C13 were used in the first model and BALB/CaNn mice and cell line A20 in the second model. During the experiments, thorough clinical evaluation (using photo documentation, ultrasonography, and MRI) and histological evaluation were performed.

RESULTS

In both models, the percentage of PIOL development was high, reaching nearly 80%. Disease progression was faster in C3H/HeN with exophthalmos occurring on average on day 10. Vitreous involvement was a predominant sign in the clinical presentation of this group. In BALB/CaNn mice exophthalmos occurred on average on day 22. The predominant clinical sign in the BALB/CaNn group was tumorous infiltration of the retina, optic disc, and tumorous retinal detachment.

CONCLUSION

Slower progression of the disease in BALB/CaNn mice, greater possibility to examine the retina due to mild vitreous involvement, and later occurrence of exophthalmos makes this strain more suitable for further investigational research.

Ibrutinib in mantle cell lymphoma: a real-world retrospective multi-center analysis of 77 patients treated in the Czech Republic

Ibrutinib revolutionized therapy for relapsed/refractory (R/R) mantle cell lymphoma (MCL). Real-world data on the outcome of unselected patients are still limited. We analyzed 77 R/R MCL patients receiving ibrutinib with at least one prior systemic anti-lymphoma therapy. After a median follow-up of 14.0 months, 56 patients relapsed/progressed, and 45 died. The overall response rate was 66%, with 31% of complete metabolic remissions on PET/CT. The median progression-free and overall survival (OS) rates were 10.3 and 23.1 months, respectively. The median OS from ibrutinib failure was 3.7 months. High proliferation rate by Ki67 (≥ 30%) and two or more previous therapy lines both negatively correlated with outcome (HR = 2.2, p = 0.04, and HR = 2.06, p = 0.08, respectively). Female gender borderline correlated with better outcome (HR = 0.53, p = 0.08). In multivariate analysis, Ki67 and response to ibrutinib both correlated with OS (p < 0.05). Importantly, ibrutinib appeared to better control nodal and extranodal lymphoma than bone marrow (BM) involvement. From 20 patients with detectable BM infiltration (before ibrutinib initiation) achieving complete (n = 13) or partial (n = 7) metabolic remission, none achieved remission in BM. We confirmed good efficacy of ibrutinib in unselected heavily pre-treated MCL patients. Our findings support the use of a combination of ibrutinib and rituximab in patients with BM involvement.