Karla Alvarez-Valadez

L’effet antitumoral de l’inhibition du transport intracellulaire du cholestérol sur les lysosomes et la mort cellulaire immunogénique: Les lysosomes jouent un rôle central dans la régulation des processus anaboliques et cataboliques, la signalisation cellulaire ainsi que dans la mise en œuvre des programmes transcriptionnels au sein des cellules. Ils favorisent l’adaptation des cellules cancéreuses lors des variations du microenvironnement en leur fournissant les métabolites essentiels et l’énergie nécessaire à leur survie et à leur prolifération. Un acteur majeur dans la réponse adaptative des lysosomes est le facteur de transcription EB (TFEB). TFEB coordonne l’expression de gènes associés à la fonction et à la biogenèse des lysosomes, y compris ceux impliqués dans l’autophagie, un processus catabolique majeur des cellules qui dépend des lysosomes. TFEB et l’autophagie fonctionnent comme des mécanismes adaptatifs visant à rétablir l’homéostasie cellulaire en réponse à un stress. Cependant, la biogenèse des lysosomes et l'augmentation de leur taille induite par TFEB peuvent rendre les cellules cancéreuses plus vulnérables aux composés ciblant les lysosomes. Cette vulnérabilité ouvre la porte au développement de nouvelles stratégies pour lutter contre le cancer en ciblant simultanément les lysosomes et en activant TFEB. L’objectif initial de cette étude a été de découvrir de nouveaux agents pharmacologiques agonistes de TFEB, manifestant une cytotoxicité significative contre les cellules cancéreuses. Par un criblage de la bibliothèque Prestwick comprenant 1200 composés approuvés par la « Food and Drug Administration » (FDA), nous avons identifié deux antidépresseurs, la sertraline et l’indatraline, qui agissent en tant que puissants activateurs de la translocation de TFEB vers le noyau. Les deux composés induisent une accumulation de cholestérol au sein des lysosomes, entraînant la perméabilisation de leurs membranes et une perturbation du flux autophagique. L’analyse de modélisation moléculaire a révélé que les deux composés pourraient inhiber le trafic du cholestérol en se liant au site de fixation du cholestérol des transporteurs, Niemann-Pick type C1 (NPC1) et NPC2. Dans les cellules cancéreuses, la sertraline et l’indatraline provoquent une mort cellulaire immunogénique, en transformant les cellules mourantes en vaccins prophylactiques capables de protéger contre la croissance tumorale chez la souris. Dans un contexte thérapeutique, une dose unique de ces composés était suffisante pour ralentir de façon significative la croissance tumorale de manière dépendante des lymphocytes T. Ces résultats caractérisent la sertraline et l’indatraline comme des agents immunostimulants qui agissent à travers un mécanisme novateur connectant l’accumulation du cholestérol lysosomal aux dommages lysosomaux, entraînant ainsi la mort immunogénique des cellules cancéreuses. Ces résultats soutiennent le repositionnement de ces deux molécules en tant qu’agents immunostimulants pour le traitement du cancer et encouragent l’extension de cette étude à d’autres inhibiteurs du transport lysosomal du cholestérol.

In a recent paper published in Cell, Li et al. suggest that selective serotonin reuptake inhibitors (SSRIs) antidepressants act on serotonin transporters on CD8⁺ T cells to enhance antitumor immunity. Beyond this mechanism, SSRIs can act on malignant cells, as well as on other immune cells, to improve cancer immunosurveillance.

Sertraline and indatraline are two antidepressants that function as serotonin reuptake inhibitors and have demonstrated promising anticancer potential, although their precise mechanisms of action remain unclear. Both compounds trigger cholesterol accumulation within lysosomes followed by lysosomal membrane permeabilization, ultimately leading to the activation of immunogenic cell death (ICD). This, in turn, triggers a T cell-mediated adaptive immune response that facilitates significant tumor control.

Lysosomes are known to contribute to the development of drug resistance through a variety of mechanisms that include the sequestration of drugs within their compartments and the activation of adaptive stress pathways. Although targeting POL I (RNA polymerase I) exhibits anticancer effects, little attention has been paid to the contribution of lysosomes to the efficacy and resistance of RNA POL I inhibitors. In this study, we investigated this aspect in the context of two potent POL I inhibitors, CX-3543 (Quarfloxin) and CX-5461 (Pidnarulex). Unexpectedly, CX-3543 was discovered to be sequestered in the lysosomal compartment. This resulted in the permeabilization of lysosomal membranes (LMP) and the subsequent activation of cellular stress adaptation pathways, including the transcription factor (TFEB) and autophagy. Disruption of TFEB or autophagy increased cell sensitivity to CX-3543, highlighting the cytoprotective role of these processes against cell death induced by this compound. Moreover, targeting lysosomal membranes using chloroquine derivatives or blue light excitation induced substantial LMP, resulting in the liberation of CX-3543 from lysosomes. This effect amplified both the inhibition of DNA-to-RNA transcription and cell death induced by CX-3543. Similar effects were observed when chloroquine derivatives were combined with CX-5461. Furthermore, combining CX-3543 with the chloroquine derivative DC661 reduced the growth of fibrosarcoma established in immunocompetent mice more efficiently than either agent alone. Altogether, our results uncover an unanticipated lysosome-related mechanism that contributes to the resistance of cancer cells to POL I transcription inhibitors, as well as a strategy to combat this resistance.

Cholesterol serves as a vital lipid that regulates numerous physiological processes. Nonetheless, its role in regulating cell death processes remains incompletely understood. In this study, we investigated the role of cholesterol trafficking in immunogenic cell death. Through cell-based drug screening, we identified two antidepressants, sertraline and indatraline, as potent inducers of the nuclear translocation of TFEB (transcription factor EB). Activation of TFEB was mediated through the autophagy-independent lipidation of MAP1LC3/LC3 (microtubule associated protein 1 light chain 3). Both compounds promoted cholesterol accumulation within lysosomes, resulting in lysosomal membrane permeabilization, disruption of autophagy and cell death that could be reversed by cholesterol depletion. Molecular docking analysis indicated that sertraline and indatraline have the potential to inhibit cholesterol binding to the lysosomal cholesterol transporters, NPC1 (NPC intracellular cholesterol transporter 1) and NPC2. This inhibitory effect might be further enhanced by the upregulation of NPC1 and NPC2 expression by TFEB. Both antidepressants also upregulated PLA2G15 (phospholipase A2 group XV), an enzyme that elevates lysosomal cholesterol. In cancer cells, sertraline and indatraline elicited immunogenic cell death, converting dying cells into prophylactic vaccines that were able to confer protection against tumor growth in mice. In a therapeutic setting, a single dose of each compound was sufficient to significantly reduce the outgrowth of established tumors in a T-cell-dependent manner. These results identify sertraline and indatraline as immunostimulatory agents for cancer treatment. More generally, this research shed light on novel therapeutic avenues harnessing lysosomal cholesterol transport to regulate immunogenic cell death.

IMMUNEPOTENT CRP (ICRP) is an immunotherapy that induces cell death in cancer cell lines. However, the molecular mechanisms of death are not completely elucidated. Here, we evaluated the implication of intracellular Ca2+ augmentation in the cell death induced by ICRP on T-ALL and breast cancer cell lines. Cell death induction and the molecular characteristics of cell death were evaluated in T-ALL and breast cancer cell lines by assessing autophagosome formation, ROS production, loss of mitochondrial membrane potential, ER stress and intracellular Ca2+ levels. We assessed the involvement of extracellular Ca2+, and the implication of the ER-receptors, IP3R and RyR, in the cell death induced by ICRP, by using an extracellular calcium chelator and pharmacological inhibitors. Our results show that ICRP increases intracellular Ca2+ levels as the first step of the cell death mechanism that provokes ROS production and loss of mitochondrial membrane potential. In addition, blocking the IP3 and ryanodine receptors inhibited ER-Ca2+ release, ROS production and ICRP-induced cell death. Taken together our results demonstrate that ICRP triggers intracellular Ca2+-increase leading to different regulated cell death modalities in T-ALL and breast cancer cell lines.

Acyl-coenzyme A (CoA)–binding protein (ACBP), also known as diazepam-binding inhibitor (DBI), is an extracellular feedback regulator of autophagy. Here, we report that injection of a monoclonal antibody neutralizing ACBP/DBI (α-DBI) protects the murine liver against ischemia/reperfusion damage, intoxication by acetaminophen and concanavalin A, and nonalcoholic steatohepatitis caused by methionine/choline-deficient diet as well as against liver fibrosis induced by bile duct ligation or carbon tetrachloride. α-DBI downregulated proinflammatory and profibrotic genes and upregulated antioxidant defenses and fatty acid oxidation in the liver. The hepatoprotective effects of α-DBI were mimicked by the induction of ACBP/DBI-specific autoantibodies, an inducible Acbp/Dbi knockout or a constitutive Gabrg2 ^F77I mutation that abolishes ACBP/DBI binding to the GABA _A receptor. Liver-protective α-DBI effects were lost when autophagy was pharmacologically blocked or genetically inhibited by knockout of Atg4b . Of note, α-DBI also reduced myocardium infarction and lung fibrosis, supporting the contention that it mediates broad organ-protective effects against multiple insults.

Calcium ions (Ca²⁺) play important and diverse roles in the regulation of autophagy, cell death and differentiation. Here, we investigated the impact of Ca²⁺ in regulating acute promyelocytic leukemia (APL) cell fate in response to the anti-cancer agent all-trans retinoic acid (ATRA). We observed that ATRA promotes calcium entry through store-operated calcium (SOC) channels into acute promyelocytic leukemia (APL) cells. This response is associated with changes in the expression profiles of ORAI1 and STIM1, two proteins involved in SOC channels activation, as well as with a significant upregulation of several key proteins associated to calcium signaling. Moreover, ATRA treatment of APL cells led to a significant activation of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) and its downstream effector AMP-activated protein kinase (AMPK), linking Ca²⁺ signaling to autophagy. Pharmacological inhibition of SOC channels and CAMKK2 enhanced ATRA-induced cell differentiation and death. Altogether, our results unravel an ATRA-elicited signaling pathway that involves SOC channels/CAMKK2 activation, induction of autophagy, inhibition of cellular differentiation and suppression of cell death. We suggest that SOC channels and CAMKK2 may constitute novel drug targets for potentiating the anti-cancer effect of ATRA in APL patients.

Lysosomes play a key role in regulating cell death in response to cancer therapies, yet little is known on the possible role of lysosomes in the therapeutic efficacy of G-quadruplex DNA ligands (G4L) in cancer cells. Here, we investigate the relationship between the modulation of lysosomal membrane damage and the degree to which cancer cells respond to the cytotoxic effects of G-quadruplex ligands belonging to the triarylpyridine family. Our results reveal that the lead compound of this family, 20A promotes the enlargement of the lysosome compartment as well as the induction of lysosome-relevant mRNAs. Interestingly, the combination of 20A and chloroquine (an inhibitor of lysosomal functions) led to a significant induction of lysosomal membrane permeabilization coupled to massive cell death. Similar effects were observed when chloroquine was added to three new triarylpyridine derivatives. Our findings thus uncover the lysosomal effects of triarylpyridines compounds and delineate a rationale for combining these compounds with chloroquine to increase their anticancer effects.