Hypoxia is a key factor responsible for the failure of therapeutic response in most solid tumors and promotes the acquisition of tumor resistance to various antitumor immune effectors. Reshaping the ...hypoxic immune suppressive tumor microenvironment to improve cancer immunotherapy is still a relevant challenge. We investigated the impact of inhibiting HIF-1α transcriptional activity on cytotoxic immune cell infiltration into B16-F10 melanoma. We showed that tumors expressing a deleted form of HIF-1α displayed increased levels of NK and CD8
effector T cells in the tumor microenvironment, which was associated with high levels of CCL2 and CCL5 chemokines. We showed that combining acriflavine, reported as a pharmacological agent preventing HIF-1α/HIF-1β dimerization, dramatically improved the benefit of cancer immunotherapy based on TRP-2 peptide vaccination and anti-PD-1 blocking antibody. In melanoma patients, we revealed that tumors exhibiting high CCL5 are less hypoxic, and displayed high NK, CD3
, CD4
and CD8
T cell markers than those having low CCL5. In addition, melanoma patients with high CCL5 in their tumors survive better than those having low CCL5. This study provides the pre-clinical proof of concept for a novel triple combination strategy including blocking HIF-1α transcription activity along vaccination and PD-1 blocking immunotherapy.
While blocking tumor growth by targeting autophagy is well established, its role on the infiltration of natural killer (NK) cells into tumors remains unknown. Here, we investigate the impact of ...targeting autophagy gene Beclin1 (BECN1) on the infiltration of NK cells into melanomas. We show that, in addition to inhibiting tumor growth, targeting BECN1 increased the infiltration of functional NK cells into melanoma tumors. We provide evidence that driving NK cells to the tumor bed relied on the ability of autophagy-defective tumors to transcriptionally overexpress the chemokine gene CCL5. Such infiltration and tumor regression were abrogated by silencing CCL5 in BECN1-defective tumors. Mechanistically, we show that the up-regulated expression of CCL5 occurred through the activation of its transcription factor c-Jun by a mechanism involving the impairment of phosphatase PP2A catalytic activity and the subsequent activation of JNK. Similar to BECN1, targeting other autophagy genes, such as ATG5, p62/SQSTM1, or inhibiting autophagy pharmacologically by chloroquine, also induced the expression of CCL5 in melanoma cells. Clinically, a positive correlation between CCL5 and NK cell marker NKp46 expression was found in melanoma patients, and a high expression level of CCL5 was correlated with a significant improvement of melanoma patients’ survival. We believe that this study highlights the impact of targeting autophagy on the tumor infiltration by NK cells and its benefit as a novel therapeutic approach to improve NK-based immunotherapy.
Recent studies demonstrated that autophagy is an important regulator of innate immune response. However, the mechanism by which autophagy regulates natural killer (NK) cell-mediated antitumor immune ...responses remains elusive. Here, we demonstrate that hypoxia impairs breast cancer cell susceptibility to NK-mediated lysis in vitro via the activation of autophagy. This impairment was not related to a defect in target cell recognition by NK cells but to the degradation of NK-derived granzyme B in autophagosomes of hypoxic cells. Inhibition of autophagy by targeting beclin1 (BECN1) restored granzyme B levels in hypoxic cells in vitro and induced tumor regression in vivo by facilitating NK-mediated tumor cell killing. Together, our data highlight autophagy as a mechanism underlying the resistance of hypoxic tumor cells to NK-mediated lysis. The work presented here provides a cutting-edge advance in our understanding of the mechanism by which hypoxia-induced autophagy impairs NK-mediated lysis in vitro and paves the way for the formulation of more effective NK cell-based antitumor therapies.
Recently, small extracellular vesicles (sEVs) secreted in vivo from chronic lymphocytic leukemia (CLL) preclinical murine models were characterized. Leukemia microenvironment sEV (LME-sEVs) ...selectively target CD8
+
T-cells, inducing exhaustion and hampering anti-tumor immune response. Additionally, a sEV-related gene expression correlated with patient treatment-free survival, overall survival and clinical parameters.
Considerable evidence has been gathered over the last 10 years showing that the tumor microenvironment (TME) is not simply a passive recipient of immune cells, but an active participant in the ...establishment of immunosuppressive conditions. It is now well documented that hypoxia, within the TME, affects the functions of immune effectors including natural killer (NK) cells by multiple overlapping mechanisms. Indeed, each cell in the TME, irrespective of its transformation status, has the capacity to adapt to the hostile TME and produce immune modulatory signals or mediators affecting the function of immune cells either directly or through the stimulation of other cells present in the tumor site. This observation has led to intense research efforts focused mainly on tumor-derived factors. Notably, it has become increasingly clear that tumor cells secrete a number of environmental factors such as cytokines, growth factors, exosomes, and microRNAs impacting the immune cell response. Moreover, tumor cells in hostile microenvironments may activate their own intrinsic resistance mechanisms, such as autophagy, to escape the effective immune response. Such adaptive mechanisms may also include the ability of tumor cells to modify their metabolism and release several metabolites to impair the function of immune cells. In this review, we summarize the different mechanisms involved in the TME that affect the anti-tumor immune function of NK cells.
Clear cell renal cell carcinomas (RCC) frequently display inactivation of von Hippel-Lindau (VHL) gene leading to increased level of hypoxia-inducible factors (HIF). In this study, we investigated ...the potential role of HIF2α in regulating RCC susceptibility to natural killer (NK) cell-mediated killing. We demonstrated that the RCC cell line 786-0 with mutated VHL was resistant to NK-mediated lysis as compared with the VHL-corrected cell line (WT7). This resistance was found to require HIF2α stabilization. On the basis of global gene expression profiling and chromatin immunoprecipitation assay, we found ITPR1 (inositol 1,4,5-trisphosphate receptor, type 1) as a direct novel target of HIF2α and that targeting ITPR1 significantly increased susceptibility of 786-0 cells to NK-mediated lysis. Mechanistically, HIF2α in 786-0 cells lead to overexpression of ITPR1, which subsequently regulated the NK-mediated killing through the activation of autophagy in target cells by NK-derived signal. Interestingly, both ITPR1 and Beclin-1 silencing in 786-0 cells inhibited NK-induced autophagy and subsequently increased granzyme B activity in target cells. Finally, in vivo ITPR1 targeting significantly enhanced the NK-mediated tumor regression. Our data provide insight into the link between HIF2α, the ITPR1-related pathway, and natural immunity and strongly suggest a role for the HIF2α/ITPR1 axis in regulating RCC cell survival.
While autophagy is constitutively executed at basal level in all cells, it is activated in cancer cells in response to various microenvironmental stresses including hypoxia. It is now well ...established that autophagy can act both as tumor suppressor or tumor promoter. In this regard, several reports indicate that the tumor suppressor function of autophagy is associated with its ability to scavenge damaged oxidative organelles, thereby preventing the accumulation of toxic oxygen radicals and limiting the genome instability. Paradoxically, in developed tumors, autophagy can promote the survival of cancer cells and therefore operates as a cell resistance mechanism. The consensus appears to be that autophagy has a dual role in suppressing tumor initiation and in promoting the survival of established tumors. This has inspired significant interest in applying anti-autophagy therapies as an entirely new approach to cancer treatment. While much remains to be learned about the regulation and context-dependent biological role of autophagy, it is now well established that modulation of this process could be an attractive approach for the development of novel anticancer therapeutic strategies. In this review, we will summarize recent reports describing how tumor cells, by activating autophagy, manage to resist the immune cell attack. Data described in this review strongly argue that targeting autophagy may represent a conceptual realm for new immunotherapeutic strategies aiming to block the immune escape and therefore providing rational approach to future tumor immunotherapy design.
Modeling tumor metabolism in vitro remains challenging. Here, we used galactose as an in vitro tool compound to mimic glycolytic limitation. In contrast to the established idea that high glycolytic ...flux reduces pyruvate kinase isozyme M2 (PKM2) activity to support anabolic processes, we have discovered that glycolytic limitation also affects PKM2 activity. Surprisingly, despite limited carbon availability and energetic stress, cells induce a near-complete block of PKM2 to divert carbons toward serine metabolism. Simultaneously, TCA cycle flux is sustained, and oxygen consumption is increased, supported by glutamine. Glutamine not only supports TCA cycle flux but also serine synthesis via distinct mechanisms that are directed through PKM2 inhibition. Finally, deleting mitochondrial one-carbon (1C) cycle reversed the PKM2 block, suggesting a potential formate-dependent crosstalk that coordinates mitochondrial 1C flux and cytosolic glycolysis to support cell survival and proliferation during nutrient-scarce conditions.
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•Galactose is a tool to mimic glycolytic limitation•Glycolytic limitation prioritizes serine synthesis pathway (SSP) through PKM2 block•PKM2 block requires activation of ME to maintain TCA cycle, while PEPCK2 supports SSP•PKM2 block is independent of serine and is linked to mitochondrial 1C metabolism
Benzarti et al. demonstrate that glycolytic limitation forces cancer cells to rewire their glycolytic flux toward SSP by PKM2 inhibition. PKM2 inhibition is independent of serine and can be reversed by genetic ablation of mitochondrial 1C cycle enzymes. These findings highlight cellular adaptation mechanisms upon limited carbon supply.
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