Search

Background & aims: In CML, Leukemic Stem Cells (LSCs) that are insensitive to Tyrosine Kinase Inhibitors are responsible for leukemia maintenance and relapses upon TKI treatment arrest. We previously showed that downregulation of the BMI1 polycomb protein that is crucial for stem/progenitor cells self-renewal induced a CCNG2/dependent proliferation arrest leading to elimination of Chronic Myeloid Leukemia (CML) cells. Unfortunately, as of today, pharmacological inhibition of BMI1 has not made its way to the clinic. Methods: We used the Connectivity Map bioinformatic database to identify pharmacological molecules that could mimick BMI1 silencing, to induce CML cell death. We selected the bis-biguanide Alexidin (ALX) that produced a transcriptomic profile positively correlating with the one obtained after BMI silencing in K562 CML cells. We then evaluated the efficiency of ALX in combination with TKI on CML cells. Results: Here we report that cell growth and clonogenic activity of K562 and LAMA-84 CML cell lines were strongly inhibited by ALX. ALX didn’t modify BCR::ABL1 phosphorylation and didn’t affect BMI1 expression but was able to increase CCNG2 expression leading to autophagic processes that preceed cell death. Besides, ALX could enhance the apoptotic response induced by any Tyrosine Kinase Inhibitors (TKI) of the three generations. We also noted a strong synergism between ALX and TKIs to increase expression of caspase-9 and caspase-3 and induce PARP cleavage, Bad expression and significantly decreased Bcl-xL family member expression. We also observed that the blockage of the mitochondrial respiratory chain by ALX can be associated with inhibition of glycolysis by 2-DG to achieve an enhanced inhibition of K562 proliferation and clonogenicity. ALX specifically affected the differentiation of BCR::ABL1-transduced healthy CD34+ cells but not of mock-infected healthy CD34+ control cells. Importantly, ALX strongly synergized with TKIs to inhibit clonogenicity of primary CML CD34+ cells from diagnosed patients. Long Term Culture of Initiating Cell (LTC-IC) and dilution of the fluorescent marker CFSE allowed us to observe that ALX and Imatinib (IM) partially reduced the number of LSCs by themselves but that the ALX/IM combination drastically reduced this cell compartment. Using an in vivo model of NSG mice intravenously injected with K562-Luciferase transduced CML cells, we showed that ALX combined with IM improved mice survival. Conclusions: Collectively, our results validate the use of ALX bis-biguanide to potentiate the action of conventional TKI treatment as a potential new therapeutic solution to eradicate CML LSCs

Simple Summary The tyrosine kinase inhibitor (TKI) imatinib was the first targeted therapy to show clinical efficacy against chronic myeloid leukemia (CML) through inhibition of the breakpoint cluster region–Abelson murine leukemia viral oncogene homolog (BCR-ABL), which is responsible for the disease. Two other generations of TKIs have succeeded imatinib, offering additional therapeutic solutions for a growing number of patients with imatinib-resistant CML. However, these clinical approaches although very effective, generate many unwanted side effects because of their daily administration. Attempts to stop TKI when the disease is no longer detectable at the molecular level, unfortunately result in relapses in more than half of cases. This highlights the presence of undetectable leukemia cells, recognized as leukemic stem cells (LSCs) that are TKI insensitive. It therefore appears necessary to identify new biochemical pathways in LSCs, the targeting of which would make re-sensitization to TKIs possible. The results presented here demonstrate that targeting the protein kinase Cδ (PKCδ) pathway represents a valid alternative for LSC elimination. Abstract Numerous combinations of signaling pathway blockades in association with tyrosine kinase inhibitor (TKI) treatment have been proposed for eradicating leukemic stem cells (LSCs) in chronic myeloid leukemia (CML), but none are currently clinically available. Because targeting protein kinase Cδ (PKCδ) was demonstrated to eliminate cancer stem cells (CSCs) in solid tumors, we evaluated the efficacy of PKCδ inhibition in combination with TKIs for CML cells. We observed that inhibition of PKCδ by a pharmacological inhibitor, by gene silencing, or by using K562 CML cells expressing dominant-negative (DN) or constitutively active (CA) PKCδ isoforms clearly points to PKCδ as a regulator of the expression of the stemness regulator BMI1. As a consequence, inhibition of PKCδ impaired clonogenicity and cell proliferation for leukemic cells. PKCδ targeting in K562 and LAMA-84 CML cell lines clearly enhanced the apoptotic response triggered by any TKI. A strong synergism was observed for apoptosis induction through an increase in caspase-9 and caspase-3 activation and significantly decreased expression of the Bcl-xL Bcl-2 family member. Inhibition of PKCδ did not modify BCR-ABL phosphorylation but acted downstream of the oncogene by downregulating BMI1 expression, decreasing clonogenicity. PKCδ inhibition interfered with the clonogenicity of primary CML CD34+ and BCR-ABL-transduced healthy CD34+ cells as efficiently as any TKI while it did not affect differentiation of healthy CD34+ cells. LTC-IC experiments pinpointed that PKCδ inhibition strongly decreased the progenitors/LSCs frequency. All together, these results demonstrate that targeting of PKCδ in combination with a conventional TKI could be a new therapeutic opportunity to affect for CML cells.

International audience; Iron is an essential nutrient, acting as a catalyst for metabolic reactions that are fundamental to cell survival and proliferation. Iron complexed to transferrin is delivered to the metabolism after endocytosis via the CD71 surface receptor. We found that transformed cells from a murine PTEN-deficient T-cell lymphoma model and from T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/T-LL) cell lines overexpress CD71. As a consequence, the cells developed an addiction toward iron whose chelation by deferoxamine (DFO) dramatically affected their survival to induce apoptosis. Interestingly, DFO displayed synergistic activity with three ALL-specific drugs: dexamethasone, doxorubicin, and L-asparaginase. DFO appeared to act through a reactive oxygen species-dependent DNA damage response and potentiated the action of an inhibitor of the PARP pathway of DNA repair. Our results demonstrate that targeting iron metabolism could be an interesting adjuvant therapy for acute lymphoblastic leukemia.

Many antibiotics in clinical use target the bacterial ribosome by interfering with the protein synthesis machinery. However, targeting the human ribosome in the case of protein synthesis deregulations such as in highly proliferating cancer cells has not been investigated at the molecular level up to now. Here we report the structure of the human 80S ribosome with a eukaryote-specific antibiotic and show its anti-proliferative effect on several cancer cell lines. The structure provides insights into the detailed interactions in a ligand-binding pocket of the human ribosome that are required for structure-assisted drug design. Furthermore, anti-proliferative dose response in leukaemic cells and interference with synthesis of c-myc and mcl-1 short-lived protein markers reveals specificity of a series of eukaryote-specific antibiotics towards cytosolic rather than mitochondrial ribosomes, uncovering the human ribosome as a promising cancer target., The ribosome of bacteria and other unicellular pathogens is a common target for antibiotic drugs. Here the authors determine a structure of the human ribosome bound to the translation inhibitor cycloheximide, and provide evidence that targeting the ribosome is a promising avenue for cancer therapy.

Background Fetal exposure to environmental estrogens may contribute to hypofertility and/or to testicular germ cell cancer. However, many of these xenoestrogens have only a weak affinity for the classical estrogen receptors (ERs,) which is 1,000-fold less potent than the affinity of 17β-estradiol (E2). Thus, several mechanisms have been suggested to explain how they could affect male germ cell proliferation at low environmental relevant concentrations. Objectives In this study we aimed to explore the possible promoting effect of bisphenol A (BPA) on human testicular seminoma cells. BPA is a well-recognized estrogenic endocrine disruptor used as a monomer to manufacture poly carbonate plastic and released from resin-lined food or beverage cans or from dental sealants. Methods and results BPA at very low concentrations (10−9 to 10−12 M) similar to those found in human fluids stimulated JKT-1 cell proliferation in vitro. BPA activated both cAMP-dependent protein kinase and cGMP-dependent protein kinase pathways and triggered a rapid (15 min) phosphorylation of the transcription factor cAMP response-element–binding protein (CREB) and the cell cycle regulator retinoblastoma protein (Rb). This nongenomic activation did not involve classical ERs because it could not be reversed by ICI 182780 (an ER antagonist) or reproduced either by E2 or by diethylstilbestrol (a potent synthetic estrogen), which instead triggered a suppressive effect. This activation was reproduced only by E2 coupled to bovine serum albumin (BSA), which is unable to enter the cell. As with E2-BSA, BPA promoted JKT-1 cell proliferation through a G-protein–coupled nonclassical membrane ER (GPCR) involving a Gαs and a Gαi/Gαq subunit, as shown by the reversible effect observed by the corresponding inhibitors NF449 and pertussis toxin. Conclusion This GPCR-mediated nongenomic action represents—in addition to the classical ER-mediated effect—a new basis for evaluating xenoestrogens such as BPA that, at low doses and with a high affinity for this GPCR, could interfere with the developmental programming of fetal germ cell proliferation and/or differentiation when they cross the placenta.

The membrane-bound carbonic anhydrase isoforms CAIX and CAXII, underpin a pH-regulating system that enables hypoxic tumor cell survival. Here, we observed for the first time an upregulation of CAXII in T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/LL) cells. First we showed that CAXII is overexpressed in thymocytes from tPTEN−/− mice suffering of T lymphoma and that its pharmacological inhibition decreased cell proliferation and induced apoptosis. The same results were observed with the SupT1 human T cell lymphoma line. In addition we observed an upregulation of CAXII in human T-ALL samples supporting the case that CAXII may represent a new therapeutic target for T-ALL/LL.