Inhibition of a new AXL isoform, AXL3, induces apoptosis of mantle cell lymphoma cells.

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma having a poor overall survival that is in need for the development of new therapeutics. In this study, we report the identification and expression of a new isoform splice variant of the tyrosine kinase receptor AXL in MCL cells. This new AXL isoform, called AXL3, lacks the ligand-binding domain of the commonly described AXL splice variants and is constitutively activated in MCL cells. Interestingly, functional characterization of AXL3, using CRISPR inhibition, revealed that only the knock down of this isoform leads to apoptosis of MCL cells. Importantly, pharmacological inhibition of AXL activity resulted in a significant decrease in the activation of well-known proproliferative and survival pathways activated in MCL cells (ie, ß-catenin, Ak strain transforming, and NF-κB). Therapeutically, preclinical studies using a xenograft mouse model of MCL indicated that bemcentinib is more effective than ibrutinib in reducing the tumor burden and to increase the overall survival. Our study highlights the importance of a previously unidentified AXL splice variant in cancer and the potential of bemcentinib as a targeted therapy for MCL.

Dihydroorotate dehydrogenase inhibition acts synergistically with tyrosine kinase inhibitors to induce apoptosis of mantle cell lymphoma cells.

Mantle cell lymphoma (MCL) is a non-Hodgkin lymphoma that remains incurable with the treatment options available today. In the present study, we have identified the dihydroorotate dehydrogenase (DHODH), an essential enzyme for the de novo biosynthesis of pyrimidine-based nucleotides, to be overexpressed in MCL in comparison to healthy peripheral blood mononuclear cells (PBMC). In vitro inhibition of the DHODH activity using a newly developed DHODH inhibitor, namely (R)-HZ05, can induce MCL cell death in the nanomolar range independently than the P53 status of the investigated cell lines. Moreover, the combination of (R)-HZ05 with tyrosine kinase inhibitor shows the synergistic activity on cell death. Pre-clinical investigation on the efficacy of (R)-HZ05 shows that it can be prolonged animal lifespan similar to ibrutinib. (R)-HZ05 use in combination with tyrosine kinase inhibitor demonstrated a superior efficacy on tumor burden reduction and survival than either drug alone. We have demonstrated that the depletion of the pyrimidine nucleotide pool, using DHODH inhibitor, represents a new therapeutic strategy that may benefit MCL patients.

Publisher Correction: A DHODH inhibitor increases p53 synthesis and enhances tumor cell killing by p53 degradation blockage.

The original PDF version of this Article listed the authors as "Marcus J.G.W. Ladds," where it should have read "Marcus J. G. W. Ladds, Ingeborg M. M. van Leeuwen, Catherine J. Drummond et al.#".Also in the PDF version, it was incorrectly stated that "Correspondence and requests for materials should be addressed to S. Lín.", instead of the correct "Correspondence and requests for materials should be addressed to S. Laín."This has been corrected in the PDF version of the Article. The HTML version was correct from the time of publication.

A DHODH inhibitor increases p53 synthesis and enhances tumor cell killing by p53 degradation blockage.

The development of non-genotoxic therapies that activate wild-type p53 in tumors is of great interest since the discovery of p53 as a tumor suppressor. Here we report the identification of over 100 small-molecules activating p53 in cells. We elucidate the mechanism of action of a chiral tetrahydroindazole (HZ00), and through target deconvolution, we deduce that its active enantiomer (R)-HZ00, inhibits dihydroorotate dehydrogenase (DHODH). The chiral specificity of HZ05, a more potent analog, is revealed by the crystal structure of the (R)-HZ05/DHODH complex. Twelve other DHODH inhibitor chemotypes are detailed among the p53 activators, which identifies DHODH as a frequent target for structurally diverse compounds. We observe that HZ compounds accumulate cancer cells in S-phase, increase p53 synthesis, and synergize with an inhibitor of p53 degradation to reduce tumor growth in vivo. We, therefore, propose a strategy to promote cancer cell killing by p53 instead of its reversible cell cycle arresting effect.

COL6A3 expression in adipocytes associates with insulin resistance and depends on PPARγ and adipocyte size.

OBJECTIVE: COL6A3 may modulate adipose tissue function in obesity and insulin resistance. A role for human adipocytes linking COL6A3 with insulin resistance warrants exploration. METHODS: COL6A3 mRNA in abdominal subcutaneous adipose samples was compared between (1) BMI-matched obese subjects resistant or sensitive to insulin (surgical whole tissue biopsies, n = 30/group), (2) lean/overweight and obese subjects (isolated adipocytes from collagenase-treated surgical biopsies, n = 11/group), (3) developing primary human adipocytes with/without knockdown of the insulin-sensitizing adipogenic gene PPARG (collagenase-treated lipoaspirate, n = 5), and (4) small and large adipocytes from lean/overweight subjects (collagenase-treated surgical biopsies or lipoaspirate, n = 10). Insulin resistance and sensitivity were assessed by euglycemic-hyperinsulinemic clamp (glucose infusion rate <60 and >70 µmol kg(-1) min(-1) , respectively) (1), or by HOMA-IR and TG/HDL ratio (2). RESULTS: Whole tissue COL6A3 mRNA was 2.6-fold higher in insulin resistant compared to sensitive subjects (P < 0.001). In isolated adipocytes, COL6A3 mRNA correlated positively with BMI (P = 0.007), HOMA-IR (P = 0.039), and TG/HDL (P = 0.004). PPARG knockdown in developing adipocytes increased COL6A3 mRNA 1.5-fold (P = 0.043). The inverse relationship with adipocyte development was further supported by 2.8-fold higher COL6A3 mRNA in small compared to large adipocytes (P = 0.004). CONCLUSION: Increased adipocyte COL6A3 expression associates with insulin resistance in humans, which may involve impaired PPARγ-mediated adipocyte development.