MiR-423-5p prevents MALAT1-mediated proliferation and metastasis in prostate cancer

BACKGROUND

The long non-coding RNA (lncRNA), MALAT1, plays a key role in the development of different cancers, and its expression is associated with worse prognosis in patients. However, its mechanism of action and its regulation are not well known in prostate cancer (PCa). A general mechanism of action of lncRNAs is their interaction with other epigenetic regulators including microRNAs (miRNAs).

METHODS

Using lentiviral stable miRNA transfection together with cell biology functional assays and gene expression/target analysis, we investigated the interaction between MALAT1 and miR-423-5p, defined as a target with in silico prediction analysis, in PCa.

RESULTS

Through bioinformatic analysis of data available from TCGA, we have found that MALAT1 expression correlates with high Gleason grade, metastasis occurrence, and reduced survival in PCa patients. These findings were validated on a TMA of PCa showing a significant correlation between MALAT1 expression with both stage and grading. We report that, in PCa cells, MALAT1 expression and activity is regulated by miR-423-5p that binds MALAT1, downregulates its expression and inhibits its activity in promoting proliferation, migration, and invasion. Using NanoString analysis, we unraveled downstream cell pathways that were affected by miR-423-5p expression and MALAT1 downregulation and identified several alterations in genes that are involved in metastatic response and angiogenic pathways. In addition, we showed that the overexpression of miR-423-5p increases survival and decreases metastases formation in a xenograft mouse model.

CONCLUSIONS

We provide evidence on the role of MALAT1 in PCa tumorigenesis and progression. Also, we identify a direct interaction between miR-423-5p and MALAT1, which results in the suppression of MALAT1 action in PCa.

Abstract B118: Development of a novel prostatic acid phosphatase-derived vaccine for the treatment of advanced prostate cancer

Our aim is to develop a new and more effective prostatic acid phosphatase (PAP) peptide-based vaccine for the treatment of advanced prostate cancer (PCa). We have previously shown that a 15mer PAP peptide-derived vaccine, when administered as a DNA vaccine, could induce PAP-specific T-cell responses and reduce the growth of implanted murine TRAMP C1-derived tumors in a syngeneic heterotopic murine model. We have subsequently developed an elongated (42mer) PAP-derived peptide in which Alanine at position 115 was replaced by Leucine.Herein, the capacity of the wild-type and mutated PAP-42mer vaccines to induce PAP-specific immune responses were compared in two pre-clinical murine models. The murine PAP-42mer sequence was evaluated in C57Bl/6 mice and the human PAP-42mer sequence in HHDII/DR1 transgenic mice. Following the identification of the most promising PAP-42mer sequence, the capacities of different delivery systems (CpG adjuvant, CAF09 adjuvant and ImmunoBody® DNA vaccine) to generate PAP-specific immunity were compared. For these studies, the responsiveness of splenocytes isolated from immunized mice following in vitro stimulation with MHC class I or class II wild-type vaccine-derived peptides (8/9 or 15 amino-acid long) was assessed using an IFNγ ELISpot assay and by immunophenotyping of splenic T-cells using flow cytometry. The ability of splenocytes to kill relevant targeT-cells after a short in vitro stimulation was assessed using a 51chromium release assay. B16 cells that had been knocked out for beta-2m gene and transfected to express chimeric HLA-A2 (HHDII), HLA-DR1 and human PAP implanted into HHDII/DR1 mice was used as a proof-of-concept model to assess the antitumor efficacy of the hPAP42mer mutated vaccine with CAF09 adjuvant in a prophylactic setting.The mutated murine and human PAP42mer-based vaccines induced a higher number of IFNγ-releasing splenocytes in response to in vitro stimulation with class I or class II vaccine-derived peptides and generated cells having a higher functional avidity. CAF09 and ImmunoBody® were superior to CpG in inducing PAP-specific immune responses, with CAF09 eliciting strong immune responses in both models, and ImmunoBody® eliciting potent immune responses in C57Bl/6 mice. Indeed, a higher proportion of CD8+ T-cells were able to release IFNγ and TNFα, to proliferate (Ki67 expression) and to degranulate (CD107a and Granzyme B expression) after short incubation with MHC class-I peptide. These vaccines strategies were also able to induce a higher proportion of memory CD8+ T-cells and the expression of PD-1 on CD8+ T-cells. Additionally, splenocytes from vaccinated mice were able to kill MHC class I peptide-pulsed targeT-cells (T2 and RMAS cells) and murine PCa cells expressing PAP (TRAMP-C1 cells) in vitro. The vaccine slowed the growth of human-PAP+-B16-derived tumors in HHDII/DR1 model and prolonged the survival (9 days delay for 30% of the mice). Splenic CD8+ T-cells and CD8+ tumor-infiltrating cells from vaccinated mice released IFNγ and TNFα, proliferated and degranulated in response to in vitro stimulation with MHC class I peptide. Finally, multimer-based flow cytometric analysis of peripheral blood mononuclear cells from patients with PCa following in vitro stimulation with PAP-derived peptides demonstrated the presence of PAP42mer-reactive CD8+ T-cells. Ongoing studies are assessing the effect of combining the vaccine with checkpoint inhibition (a PD-1 monoclonal antibody) in a therapeutic setting. In summary, we have developed a vaccine strategy which induces robust anti-PAP immunity and slows the growth of implanted PAP+ cancer cell-derived tumors in vivo. The presence of PAP-specific CD8+ T-cells in the periphery of patients with advanced PCa suggests that these patients will benefit from this new approach, especially when combined with checkpoint inhibition.

Citation Format: Pauline Le Vu, Jayakumar Vadakekolathu, Dennis Christensen, Lindy Durrant, Graham Pockley, Stephanie E.B. McArdle. Development of a novel prostatic acid phosphatase-derived vaccine for the treatment of advanced prostate cancer [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B118.

IL-15 Trans-Signaling with the Superagonist RLI Promotes Effector/Memory CD8+ T Cell Responses and Enhances Antitumor Activity of PD-1 Antagonists

Tumors with the help of the surrounding environment facilitate the immune suppression in patients, and immunotherapy can counteract this inhibition. Among immunotherapeutic strategies, the immunostimulatory cytokine IL-15 could represent a serious candidate for the reactivation of antitumor immunity. However, exogenous IL-15 may have a limited impact on patients with cancer due to its dependency on IL-15Rα frequently downregulated in cancer patients. In this work, we studied the antitumor activity of the IL-15 superagonist receptor-linker-IL-15 (RLI), designed to bypass the need of endogenous IL-15Rα. RLI consists of human IL-15 covalently linked to the human IL-15Rα sushi(+) domain. In a mouse model of colorectal carcinoma, RLI as a stand-alone treatment could limit tumor outgrowth only when initiated at an early time of tumor development. At a later time, RLI was not effective, coinciding with the strong accumulation of terminally exhausted programmed cell death-1 (PD-1)(high) T cell Ig mucin-3(+) CD8(+) T cells, suggesting that RLI was not able to reactivate terminally exhausted CD8(+) T cells. Combination with PD-1 blocking Ab showed synergistic activity with RLI, but not with IL-15. RLI could induce a greater accumulation of memory CD8(+) T cells and a stronger effector function in comparison with IL-15. Ex vivo stimulation of tumor-infiltrated lymphocytes from 16 patients with renal cell carcinoma demonstrated 56% of a strong tumor-infiltrated lymphocyte reactivation with the combination anti-PD-1/RLI compared with 43 and 6% with RLI or anti-PD-1, respectively. Altogether, this work provides evidence that the sushi-IL-15Rα/IL-15 fusion protein RLI enhances antitumor activity of anti-PD-1 treatment and is a promising approach to stimulate host immunity.