Murine double minute 2 (Mdm2) is known to enhance the transactivation potential of human immunodeficiency virus (HIV-1) Tat protein by causing its ubiquitination. However, the regulation of Mdm2 during HIV-1 infection and its implications for viral replication have not been well studied. Here, we show that the Mdm2 protein level increases during HIV-1 infection and this effect is mediated by HIV-1 Tat protein. Tat appears to stabilise Mdm2 at the post-translational level by inducing its phosphorylation at serine-166 position through AKT. Although p53 is one of the key players for Mdm2 induction, Tat-mediated stabilisation of Mdm2 appears to be independent of p53. Moreover, the non-phosphorylatable mutant of Mdm2 (S166A) fails to interact with Tat and shows decreased half-life in the presence of Tat compared with wild-type Mdm2. Furthermore, the non-phosphorylatable mutant of Mdm2 (S166A) is unable to support HIV-1 replication. Thus, HIV-1 Tat appears to stabilise Mdm2, which in turn enhances Tat-mediated viral replication. This study highlights the importance of post-translational modifications of host cellular factors in HIV-1 replication and pathogenesis.
BackgroundPancreatic ductal adenocarcinoma (PDAC) is projected to be the second leading cause of cancer death in the USA by 2030. Immune checkpoint inhibitors fail to control most PDAC tumors because of PDAC’s extensive immunosuppressive microenvironment and poor immune infiltration, a phenotype also seen in other non-inflamed (ie, ‘cold’) tumors. Identifying novel ways to enhance immunotherapy efficacy in PDAC is critical. Dipeptidyl peptidase (DPP) inhibition can enhance immunotherapy efficacy in other cancer types; however, the impact of DPP inhibition on PDAC tumors remains unexplored.MethodsWe examined the effects of an oral small molecule DPP inhibitor (BXCL701) on PDAC tumor growth using mT3-2D and Pan02 subcutaneous syngeneic murine models in C57BL/6 mice. We explored the effects of DPP inhibition on the tumor immune landscape using RNAseq, immunohistochemistry, cytokine evaluation and flow cytometry. We then tested if BXCL701 enhanced anti-programmed cell death protein 1 (anti-PD1) efficacy and performed immune cell depletion and rechallenged studies to explore the relevance of cytotoxic immune cells to combination treatment efficacy.ResultsIn both murine models of PDAC, DPP inhibition enhanced NK and T cell immune infiltration and reduced tumor growth. DPP inhibition also enhanced the efficacy of anti-PD1. The efficacy of dual anti-PD1 and BXCL701 therapy was dependent on both CD8+ T cells and NK cells. Mice treated with this combination therapy developed antitumor immune memory that cleared some tumors after re-exposure. Lastly, we used The Cancer Genome Atlas (TCGA) to demonstrate that increased NK cell content, but not T cell content, in human PDAC tumors is correlated with longer overall survival. We propose that broad DPP inhibition enhances antitumor immune response via two mechanisms: (1) DPP4 inhibition increases tumor content of CXCL9/10, which recruits CXCR3+ NK and T cells, and (2) DPP8/9 inhibition activates the inflammasome, resulting in proinflammatory cytokine release and Th1 response, further enhancing the CXCL9/10-CXCR3 axis.ConclusionsThese findings show that DPP inhibition with BXCL701 represents a pharmacologic strategy to increase the tumor microenvironment immune cell content to improve anti-PD1 efficacy in PDAC, suggesting BXCL701 can enhance immunotherapy efficacy in ‘cold’ tumor types. These findings also highlight the potential importance of NK cells along with T cells in regulating PDAC tumor growth.
Despite the high success rate, antiretroviral therapy does not cure the disease completely due to presence of latent viral reservoirs. Although several studies have addressed this issue earlier, the role of serum starvation/deprivation in HIV-1 latency has not been studied. So, we investigated the role of serum starvation in regulating HIV-1 latency. The impact of serum starvation on HIV-1 latency was assessed in latently infected monocytes U1 and T-cells J1.1. Serum starvation breaks HIV-1 latency in U1 cells. Under similar conditions, J1.1 cells failed to show reactivation of virus. We investigated the involvement of cell death pathway and autophagy during the serum starvation in viral reactivation. Inhibition of these pathways did not affect viral reactivation. Furthermore, other crucial factors like NF-κB, SP1 and AKT did not play any role in regulating viral latency. Here, we report that serum deprivation up-regulates ERK/JNK pathway. This leads to phosphorylation of c-Jun which plays an important role in viral reactivation. Treatment of cells with U0126, an ERK kinase inhibitor, potently inhibited viral replication. In summary, we show that serum starvation leads to reactivation of HIV-1 in latently infected monocytes through the ERK/JNK pathway.
The oral DPP8/9 inhibitor BXCL701 in combination with an anti-PD-1 antibody (aPD-1) [AACR 2017] or in triple combination with aPD-1 and pegylated IL-2 (NKTR-214) [ASCO 2018] has demonstrated inhibition of tumor growth or complete regression respectively in animal models of pancreatic cancer. In the present study, the mechanism of action of BXCL701 has been elucidated in a sub-chronic pharmacokinetic / pharmacodynamic study at molecular and cellular level, by administering BXCL701 as a single agent. BXCL701 (20 μg) was administered orally every day for 14 days in tumor (Pan02) bearing mice. Tumor and serum samples were harvested after 0, 1, 8 and 16 hrs after BXCL701 administration on day 1, 7 and 14. Serum samples were analysed for cytokines and tumor tissues were analysed for infiltrating immune cells and gene expression. BXCL701 is known to inhibit regulatory proteases DPP8/9, consequently activating Nlrp1b inflammasome, which in turn activates pro-caspase-1 to mediate pyroptosis in mouse macrophages [Okondo et al, 2018]. Caspase-1 is involved in cleavage of pro-IL-1β and pro-IL-18 to their active forms, IL-1β and IL-18 respectively [Walle et al, 2016,]. IL-18 was observed to be significantly (p<0.05) upregulated (>50 fold) at 8 hrs on day 1 and achieved steady state levels by day 7 in BXCL701-treated animals. Other cytokines like IL-1β, IFN-γ, G-CSF, IL-5, IL-6, CXCL9, MCP-1, KC and Eotaxin were also observed to be upregulated in BXCL701-treated animals at the 8 hr timepoint on day 1, 7 and 14 in comparison to day 1, 0 hr. BXCL701 significantly upregulates T cells (total T cells, CD4+ T helper cells and CD8+ T cells) infiltration along with NK cells within the tumor microenvironment. It also appears to enhance antigen presentation by upregulating MHC class I genes and MHC class I expressing cells within the tumor. The mechanism of action of BXCL701 was evaluated at the molecular level as well. The comparison of genes in tumor tissues from BXCL701-treated animals vs respective vehicle-treated animals on Day 7 and 14 demonstrated that the upregulated gene clusters were innate and adaptive immune response genes, T-cell receptor genes and MHC genes. Also, genes associated with T cell and NK cell mediated apoptosis and cytolysis e.g. FasL, GzmA, were upregulated and indicates enhanced cell death (e.g. upregulation of pdcd1) within tumor. On the other hand, downregulated gene clusters belonged to functional categories like cell cycle, DNA repair, several genes associated with cancer progression (GPCRs and Olfactory receptors) and extra cellular matrix (ECM) modification (collagen and metalloproteases). In conclusion, BXCL701-treatment induces innate and adaptive immune responses that leads to tumor growth inhibition probably via inducing cell death and reducing ECM modification. Citation Format: Veena Agarwal, John MacDougall, shubhendu Trivedi, Dimple Bhatia, Zeenia Jagga, Hemant Banga, Diane Healy, Sreenivas Adurthi, Vince O'Neill. The dipeptidyl peptidase inhibitor BXCL701 activates innate immunity followed by adaptive immunity on a molecular and cellular level in a mouse model of pancreatic cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 962.
In the published article, the labelling on the horizontal axis of the bar graph in Figure 1d was incorrect. The corrected Figure is presented here.
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