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.

Internal comorbidities and complications of multiple sclerosis therapy - don't be caught off guard!

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system, mainly affecting young adults. Factors positively influencing its course include early antiinflammatory treatment and the influencing of other comorbidities. The most common comorbidities occurring in MS patients with a higher frequency than in the general population are neurological, psychiatric, cardiovascular, metabolic and autoimmune. Just as comorbidity compensation affects the course of MS, in some cases, MS decompensation is associated with a worse course of associated diseases. Due to common risk factors and partially shared immunopathogenesis, treatment covering multiple conditions can be used, especially for some autoimmune diseases. On the other hand, some drugs may potentiate the development of other autoimmunity or disorder. A special topic is the side effects and complications of treatment (especially infections and malignancies) of disease-modifying therapies used in patients with MS. However, the potential treatment discontinuation carries significant risks and should always be discussed with the MS specialist. Therefore, close interdisciplinary collaboration is crucial.