TLR9-independent CD8+ T cell responses in hepatic AAV gene transfer through IL-1R1-MyD88 signaling

Upon viral infection of the liver, CD8+ T cell responses may be triggered despite the immune suppressive properties that manifest in this organ. We sought to identify pathways that activate responses to a neoantigen expressed in hepatocytes, using adeno-associated viral (AAV) gene transfer. It was previously established that cooperation between plasmacytoid dendritic cells (pDCs), which sense AAV genomes by Toll-like receptor 9 (TLR9), and conventional DCs promotes cross-priming of capsid-specific CD8+ T cells. Surprisingly, we find local initiation of a CD8+ T cell response against antigen expressed in ∼20% of murine hepatocytes, independent of TLR9 or type I interferons and instead relying on IL-1 receptor 1-MyD88 signaling. Both IL-1α and IL-1β contribute to this response, which can be blunted by IL-1 blockade. Upon AAV administration, IL-1-producing pDCs infiltrate the liver and co-cluster with XCR1+ DCs, CD8+ T cells, and Kupffer cells. Analogous events were observed following coagulation factor VIII gene transfer in hemophilia A mice. Therefore, pDCs have alternative means of promoting anti-viral T cell responses and participate in intrahepatic immune cell networks similar to those that form in lymphoid organs. Combined TLR9 and IL-1 blockade may broadly prevent CD8+ T responses against AAV capsid and transgene product.

Comprehensive Comparison of AAV Purification Methods: Iodixanol Gradient Centrifugation vs. Immuno-Affinity Chromatography

Recombinant adeno-associated viruses (AAVs) have emerged as a widely used gene delivery platform for both basic research and human gene therapy. To ensure and improve the safety profile of AAV vectors, substantial efforts have been dedicated to the vector production process development using suspension HEK293 cells. Here, we studied and compared two downstream purification methods, iodixanol gradient ultracentrifugation versus immuno-affinity chromatography (POROS™ CaptureSelect™ AAVX column). We tested multiple vector batches that were separately produced (including AAV5, AAV8, and AAV9 serotypes). To account for batch-to-batch variability, each batch was halved for subsequent purification by either iodixanol gradient centrifugation or affinity chromatography. In parallel, purified vectors were characterized, and transduction was compared both in vitro and in vivo in mice (using multiple transgenes: Gaussia luciferase, eGFP, and human factor IX). Each purification method was found to have its own advantages and disadvantages regarding purity, viral genome (vg) recovery, and relative empty particle content. Differences in transduction efficiency were found to reflect batch-to-batch variability rather than disparities between the two purification methods, which were similarly capable of yielding potent AAV vectors.

Factor IX administration in the skin primes inhibitor formation and sensitizes hemophilia B mice to systemic factor IX administration

Background

Factor IX inhibitor formation is the most serious complication of replacement therapy for the bleeding disorder hemophilia B, exacerbated by severe allergic reactions occurring in up to 60% of patients with inhibitors. Low success rates of immune tolerance induction therapy in hemophilia B necessitate the search for novel immune tolerance therapies. Skin-associated lymphoid tissues have been successfully targeted in allergen-specific immunotherapy.

Objectives

We aimed to develop a prophylactic immune tolerance protocol based on intradermal administration of FIX that would prevent inhibitor formation and/or anaphylaxis in response to replacement therapy.

Methods

We measured FIX inhibitor, anti-FIX immunoglobulin G1, and immunoglobulin E titers using the Bethesda assay and enzyme-linked immunosorbent assay after 4 weeks of twice-weekly intradermal FIX or FIX-Fc administration followed by 5 to 6 weeks of weekly systemic FIX injections in C3H/HeJ hemophilia B mice. We also measured skin antigen-presenting, follicular helper T, and germinal center B cell frequencies in skin-draining lymph nodes after a single or repeat intradermal FIX administration.

Results

Intradermal administration enhanced FIX inhibitor formation in response to systemic administration. We further found that intradermal administration alone triggers inhibitor formation, even at a low dose of 0.4 IU/kg, which is 100-fold lower than the intravenous dose of 40 IU/kg typically required to induce inhibitor development in hemophilia B mice. Also, intradermal administration triggered germinal center formation in skin-draining lymph nodes and sensitized mice to systemic administration. Factor IX-Fc fusion protein did not modulate inhibitor formation.

Conclusion

Intradermal FIX administration is highly immunogenic, suggesting that the skin compartment is not amenable to immune tolerance induction or therapeutic delivery of clotting factors.

Potential role for oral tolerance in gene therapy

Oral immunotherapies are being developed for various autoimmune diseases and allergies to suppress immune responses in an antigen-specific manner. Previous studies have shown that anti-drug antibody (inhibitor) formation in protein replacement therapy for the inherited bleeding disorder hemophilia can be prevented by repeated oral delivery of coagulation factor antigens bioencapsulated in transplastomic lettuce cells. Here, we find that this approach substantially reduces antibody development against factor VIII in hemophilia A mice treated with adeno-associated viral gene transfer. We propose that the concept of oral tolerance can be applied to prevent immune responses against therapeutic transgene products expressed in gene therapy.

Factor VIII trafficking to CD4+ T cells shapes its immunogenicity and requires several types of antigen-presenting cells

Despite >80 years of clinical experience with coagulation factor VIII (FVIII) inhibitors, surprisingly little is known about the in vivo mechanism of this most serious complication of replacement therapy for hemophilia A. These neutralizing antidrug alloantibodies arise in ∼30% of patients. Inhibitor formation is T-cell dependent, but events leading up to helper T-cell activation have been elusive because of, in part, the complex anatomy and cellular makeup of the spleen. Here, we show that FVIII antigen presentation to CD4+ T cells critically depends on a select set of several anatomically distinct antigen-presenting cells, whereby marginal zone B cells and marginal zone and marginal metallophilic macrophages but not red pulp macrophages (RPMFs) participate in shuttling FVIII to the white pulp in which conventional dendritic cells (DCs) prime helper T cells, which then differentiate into follicular helper T (Tfh) cells. Toll-like receptor 9 stimulation accelerated Tfh cell responses and germinal center and inhibitor formation, whereas systemic administration of FVIII alone in hemophilia A mice increased frequencies of monocyte-derived and plasmacytoid DCs. Moreover, FVIII enhanced T-cell proliferation to another protein antigen (ovalbumin), and inflammatory signaling-deficient mice were less likely to develop inhibitors, indicating that FVIII may have intrinsic immunostimulatory properties. Ovalbumin, which, unlike FVIII, is absorbed into the RPMF compartment, fails to elicit T-cell proliferative and antibody responses when administered at the same dose as FVIII. Altogether, we propose that an antigen trafficking pattern that results in efficient in vivo delivery to DCs and inflammatory signaling, shape the immunogenicity of FVIII.

Suppression of anti-drug antibody formation against coagulation factor VIII by oral delivery of anti-CD3 monoclonal antibody in hemophilia A mice

Active tolerance to ingested dietary antigens forms the basis for oral immunotherapy to food allergens or autoimmune self-antigens. Alternatively, oral administration of anti-CD3 monoclonal antibody can be effective in modulating systemic immune responses without T cell depletion. Here we assessed the efficacy of full length and the F(ab')2 fragment of oral anti-CD3 to prevent anti-drug antibody (ADA) formation to clotting factor VIII (FVIII) protein replacement therapy in hemophilia A mice. A short course of low dose oral anti-CD3 F(ab')2 reduced the production of neutralizing ADAs, and suppression was significantly enhanced when oral anti-CD3 was timed concurrently with FVIII administration. Tolerance was accompanied by the early induction of FoxP3+LAP-, FoxP3+LAP+, and FoxP3-LAP+ populations of CD4+ T cells in the spleen and mesenteric lymph nodes. FoxP3+LAP+ Tregs expressing CD69, CTLA-4, and PD1 persisted in spleens of treated mice, but did not produce IL-10. Finally, we attempted to combine the anti-CD3 approach with oral intake of FVIII antigen (using our previously established method of using lettuce plant cells transgenic for FVIII antigen fused to cholera toxin B (CTB) subunit, which suppresses ADAs in part through induction of IL-10 producing FoxP3-LAP+ Treg). However, combining these two approaches failed to improve suppression of ADAs. We conclude that oral anti-CD3 treatment is a promising approach to prevention of ADA formation in systemic protein replacement therapy, albeit via mechanisms distinct from and not synergistic with oral intake of bioencapsulated antigen.

IL-15 blockade and rapamycin rescue multifactorial loss of factor VIII from AAV-transduced hepatocytes in hemophilia A mice

Hepatic adeno-associated viral (AAV) gene transfer has the potential to cure the X-linked bleeding disorder hemophilia A. However, declining therapeutic coagulation factor VIII (FVIII) expression has plagued clinical trials. To assess the mechanistic underpinnings of this loss of FVIII expression, we developed a hemophilia A mouse model that shares key features observed in clinical trials. Following liver-directed AAV8 gene transfer in the presence of rapamycin, initial FVIII protein expression declines over time in the absence of antibody formation. Surprisingly, loss of FVIII protein production occurs despite persistence of transgene and mRNA, suggesting a translational shutdown rather than a loss of transduced hepatocytes. Some of the animals develop ER stress, which may be linked to hepatic inflammatory cytokine expression. FVIII protein expression is preserved by interleukin-15/interleukin-15 receptor blockade, which suppresses CD8+ T and natural killer cell responses. Interestingly, mice with initial FVIII levels >100% of normal had diminishing expression while still under immune suppression. Taken together, our findings of interanimal variability of the response, and the ability of the immune system to shut down transgene expression without utilizing cytolytic or antibody-mediated mechanisms, illustrate the challenges associated with FVIII gene transfer. Our protocols based upon cytokine blockade should help to maintain efficient FVIII expression.

Therapeutic Targeting of Sunitinib-Induced AR Phosphorylation in Renal Cell Carcinoma

Androgen receptor (AR) plays a crucial role in the development and progression of prostate cancer. AR expression has also been reported in other solid tumors, including renal cell carcinoma (RCC), but its biological role here remains unclear. Through integrative analysis of a reverse phase protein array, we discovered increased expression of AR in an RCC patient-derived xenograft model of acquired resistance to the receptor tyrosine kinase inhibitor (RTKi) sunitinib. AR expression was increased in RCC cell lines with either acquired or intrinsic sunitinib resistance in vitro An AR signaling gene array profiler indicated elevated levels of AR target genes in sunitinib-resistant cells. Sunitinib-induced AR transcriptional activity was associated with increased phosphorylation of serine 81 (pS81) on AR. Additionally, AR overexpression resulted in acquired sunitinib resistance and the AR antagonist enzalutamide-induced AR degradation and attenuated AR downstream activity in sunitinib-resistant cells, also indicated by decreased secretion of human kallikrein 2. Enzalutamide-induced AR degradation was rescued by either proteasome inhibition or by knockdown of the AR ubiquitin ligase speckle-type POZ protein (SPOP). In vivo treatment with enzalutamide and sunitinib demonstrated that this combination efficiently induced tumor regression in a RCC model following acquired sunitinib resistance. Overall, our results suggest the potential role of AR as a target for therapeutic interventions, in combination with RTKi, to overcome drug resistance in RCC.Significance: These findings highlight the therapeutic potential of targeting the androgen receptor to overcome RCC resistance to receptor tyrosine kinase inhibitors. Cancer Res; 78(11); 2886-96. ©2018 AACR.

EZH2 Modifies Sunitinib Resistance in Renal Cell Carcinoma by Kinome Reprogramming

Acquired and intrinsic resistance to receptor tyrosine kinase inhibitors (RTKi) represents a major hurdle in improving the management of clear cell renal cell carcinoma (ccRCC). Recent reports suggest that drug resistance is driven by tumor adaptation via epigenetic mechanisms that activate alternative survival pathways. The histone methyl transferase EZH2 is frequently altered in many cancers, including ccRCC. To evaluate its role in ccRCC resistance to RTKi, we established and characterized a spontaneously metastatic, patient-derived xenograft model that is intrinsically resistant to the RTKi sunitinib, but not to the VEGF therapeutic antibody bevacizumab. Sunitinib maintained its antiangiogenic and antimetastatic activity but lost its direct antitumor effects due to kinome reprogramming, which resulted in suppression of proapoptotic and cell-cycle-regulatory target genes. Modulating EZH2 expression or activity suppressed phosphorylation of certain RTKs, restoring the antitumor effects of sunitinib in models of acquired or intrinsically resistant ccRCC. Overall, our results highlight EZH2 as a rational target for therapeutic intervention in sunitinib-resistant ccRCC as well as a predictive marker for RTKi response in this disease. Cancer Res; 77(23); 6651-66. ©2017 AACR.

Entinostat Neutralizes Myeloid-Derived Suppressor Cells and Enhances the Antitumor Effect of PD-1 Inhibition in Murine Models of Lung and Renal Cell Carcinoma

PURPOSE

Recent advances in immunotherapy highlight the antitumor effects of immune checkpoint inhibition despite a relatively limited subset of patients receiving clinical benefit. The selective class I histone deacetylase inhibitor entinostat has been reported to have immunomodulatory activity including targeting of immune suppressor cells in the tumor microenvironment. Thus, we decided to assess whether entinostat could enhance anti-PD-1 treatment and investigate those alterations in the immunosuppressive tumor microenvironment that contribute to the combined antitumor activity.

EXPERIMENTAL DESIGN

We utilized syngeneic mouse models of lung (LLC) and renal cell (RENCA) carcinoma and assessed immune correlates, tumor growth, and survival following treatment with entinostat (5 or 10 mg/kg, p.o.) and a PD-1 inhibitor (10 and 20 mg/kg, s.c.).

RESULTS

Entinostat enhanced the antitumor effect of PD-1 inhibition in two syngeneic mouse tumor models by reducing tumor growth and increasing survival. Entinostat inhibited the immunosuppressive function of both polymorphonuclear (PMN)- and monocytic-myeloid derived suppressor cell (M-MDSC) populations. Analysis of MDSC response to entinostat revealed significantly reduced arginase-1, iNOS, and COX-2 levels, suggesting potential mechanisms for the altered function. We also observed significant alterations in cytokine/chemokine release in vivo with a shift toward a tumor-suppressive microenvironment.

CONCLUSIONS

Our results demonstrate that entinostat enhances the antitumor effect of PD-1 targeting through functional inhibition of MDSCs and a transition away from an immune-suppressive tumor microenvironment. These data provide a mechanistic rationale for the clinical testing and potential markers of response of this novel combination in solid tumor patients.

Abstract 5783: In vitro modeling of patient derived bladder cancer cell lines in 3D culture systems

Background: Drug screening is a key component for drug development and optimizing anti-tumor therapies. Traditionally, in vitro drug testing has been conducted in monolayer systems that are not capable of recapitulating the tumor complexity. Recently, the field has witnessed the rise of interest in 3D culture systems which are capable of reproducing tumor complexity while circumventing the cost associated with in vivo drug testing. Our access to fresh patient samples has enabled us to establish a novel 3D culture system consisting of bladder cancer patient derived cell lines. Using a wide range of matrices and co-culture conditions with tumor associated stromal cells we were able to establish a unique high throughput drug testing tool.

Methods: Matrigel and collagen based matrices were used to establish 3D culture systems of bladder cancer patient derived cells. Tumor cells were cultured in 3D conditions either alone or in coculture with tumor associated stromal cells. Response to Cisplatin and PI3K pathway targeted agents (i.e. LY LY3023414) was tested in both conditions. High throughput imaging via Thermo ArrayScan XTI was used to assess the biological behavior of spheroids as well as their response to therapies overtime. Confocal microscopy was used to validate the biological mimicry of tumor derived spheroids to the original patient tumors. Integration of RNA-seq data from the patient-derived tumor cells with the biological behavior and therapeutic response in 3D culture is ongoing for the purpose of characterizing the 3D model

Results: In 3D culture conditions; bladder cancer derived cells were able to re-express E-cadherin that was suppressed upon propagation in monolayer. The re-expression of the epithelial marker (E-cadherin) observed in 3D accurately mirrors the original tumors; which are of epithelial origin. Phenotypic differences were observed across different matrix conditions and also among different tumor derived cells. Bladder 3D organoids of luminal origin were more sensitive to both cisplatin and PI3K pathway inhibitors as compared to those of basal origin. This drug response profile was reminiscent of what we observed in vivo using patient derived xenograft (PDX) models derived from the same tumors. The phenotypic as well as the drug response variations observed in our 3D culture correlated with variable gene expression profiles (luminal vs basal) that were detected in our RNA-seq data.

Conclusion: As compared to monolayer, 3D culture is more capable of recapitulating tumor complexity and accurately reflects the drug resistance / sensitivity profiles that are observed in PDX models in vivo. Therefore, a 3D culture system provides an invaluable tool for high throughput screening of drugs in bladder cancer and providing a better understanding of tumor biology in the search of more effective treatments for bladder cancer patients.

Citation Format: May Elbanna, Sreenivasulu Chintala, Eric Ciamporcero, Remi Adelayie, Ashley Orillion, Sreevani Arisa, Nur Damayanti, Michelle Grimard, TJ Puls, Sherry Harbin, Melissa Fishel, Roberto Pili. In vitro modeling of patient derived bladder cancer cell lines in 3D culture systems [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5783. doi:10.1158/1538-7445.AM2017-5783

Abstract 94: Association of xCT overexpression with RTKI resistance and metastases in clear cell renal cell carcinoma

Background: Cystine/glutamate exchanger xCT is a catalytic component of system xc- involved in transport of ‘conditionally indispensable’ amino acid cystine. Cystine transport is a rate limiting step for the synthesis of glutathione, a major intracellular redox regulator. Recently, we and other groups reported the overexpression of xCT and its association with drug resistance in several human cancers including bladder, glioma, breast, and colon. There are no studies to show the xCT expression in clear cell renal cell carcinoma (ccRCC) and its association with tyrosine kinase inhibitors resistance and metastasis. In the current study we have evaluated xCT expression in human ccRCC tumors arranged in tissue microarray (TMA) and determined its role in receptor tyrosine kinase inhibitor (RTKI) resistance and metastases using the patient derived tumor xenografts (PDX) models and TKI resistance ccRCC cells.

Methods: Human Renal cell carcinoma tumor nephrectomy specimens arranged in tissue microarray (TMA) were used to determine xCT expression by immunohistochemistry. Patient derived tumor xenografts (PDX) of primary, metastasis, and sunitinib resistance were used to determine the role of xCT in RCC. To understand the molecular alterations associated with RTKI resistance, we have generated sunitinib resistance 786 OR ccRCC cells and performed RNAseq analysis. To determine the xCT inhibition effect on ccRCC tumor metastases, sulfasalazine, an inhibitor of xCT was used to treat metastatic ccRCC tumor xenografts transplanted in SCID mice.

Results: Immunohistochemical evaluation of xCT in RCC TMA revealed that 70 % (19 out of 27) of the tumors express different levels of xCT. Association with tumor response to RTKI will be presented. RTKI less responsive PDX RP-R-02 was developed using the dose escalation treatment strategy and was found to have an upregulation of xCT when the tumors become less responsive to sunitinib. RNAseq analysis revealed differential gene expression of various pathway genes including lysosome biogenesis and function such as SLC7A11, HPS4, HPS5, CTSB, IFI30, PPT1, SCPEP1, TPP1, ATP6AP1L, MCOLN1, PRKAG2, and VPS18 in sunitinib resistant 786 OR cells compared to parental cells supports the role of lysosomes function in RTKI drug resistance. Furthermore, xCT inhibitor sulfasalazine treatment significantly decreased the metastasis lung nodules of RP-R-02LM in SCID mice demonstrated the xCT role in RCC tumor metastasis.

Conclusions: We found preliminary evidence that overexpression of xCT may be associated with RTKI resistance in ccRCC. These results suggest that targeting the xCT in ccRCC may reverse the resistance and enhance the efficacy of RTKI. Additional studies using larger numbers of ccRCC tumors are required to identify xCT as a potential predictive biomarker for response/resistance to RTKI in ccRCC patients.

Citation Format: Sreenivasulu Chintala, Remi Adelaiye-Ogala, Ashley Orillion, Sreevani Arisa, May Elbanna, Nur P. Damayanti, Roberto Pili. Association of xCT overexpression with RTKI resistance and metastases in clear cell renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 94. doi:10.1158/1538-7445.AM2017-94

Abstract 250: Methionine restriction increases macrophage tumoricidal activity and significantly inhibits prostate cancer growth

Background: Our previous work showed a significant reduction of tumor growth, macrophage infiltration, circulating IGF-1, and mTOR activation with low protein diet in a patient derived xenograft model of prostate cancer. The evolutionarily conserved, nutrient sensing, mTOR pathway plays a central role in both development of advanced stage prostate cancer and immune responsiveness. This study presents novel data on the impact of dietary protein modification on the function of the host immune system in response to prostate cancer and immunotherapy.

Methods: Our In vitro studies utilized bone marrow or tumor derived (RP-B6 Myc) macrophages. In vivo studies utilized the recently characterized RP-B6 Myc model. Mice were fed ad libitum control or methionine restricted diets for four weeks prior to S.C. implantation with ~1mm2 tumor pieces. Treatment of survivin peptide vaccine (1mg/ml S.C. 1 X week) and anti-PD-1 (20mg/kg I.P. 2 X week) began at ~50mm2 tumor size. Tumor volumes were blindly recorded 2 X week. End point analyses include: tumor weight, flow cytometric analysis, proteomic profiler analyses, and microbiome analyses from each diet and treatment group.

Results: We show here that while methionine restriction (MR) has little impact on our RP-B6 Myc prostate cancer cell line, it does yield a significant alteration in both the polarization and function of M1 and M2 macrophages. In the in vitro MR conditions, we observed significantly enhanced polarization of M1 macrophages and reduced polarization of M2 macrophages. Functional analysis revealed increased tumoricidal activity of both M1, ‘antitumor’, and M2, ‘pro-tumor,’ macrophages suggesting a flip in M2 function from tumor-promoting to tumoricidal. Further analysis of the released cytokines in MR media conditions yielded significant increase of antitumor cytokines & chemokines, such as IL-12, IL-27, CXCL9, CXCL10, CXCL11, CCL2, CCL4, and TNF-alpha, a double-edged sword which in our system correlates with decreased cancer cell viability upon co-culture with amino acid restricted M1 and M2 macrophages. Our preliminary results show dietary MR yielding a significant inhibition of prostate cancer growth in the RP-B6-Myc model and our ongoing study with survivin peptide vaccine and anti-PD-1 immunotherapies will be available to present in the conference.

Conclusions: Our data suggest that restricting methionine is sufficient to alter both the polarization and tumoricidal function of macrophages. Our preliminarily results show that restricted dietary methionine is able to inhibit prostate cancer growth, modify the host immune response and better inhibit prostate cancer growth alone or in combination with immunotherapy. These results provide a strong basis to consider diet restriction as a means to limit cancer growth targeting tumor immune system and potentially to enhance cancer patient responses to immunotherapy.

Citation Format: Ashley R. Orillion, Sreenivasulu Chintala, Remi Adelaiye-Ogala, Li Shen, Nur Damayanti, May Elbanna, Sreevani Arisa, Bennett Elzey, Chinghai Kao, Luigi Fontana, Roberto Pili. Methionine restriction increases macrophage tumoricidal activity and significantly inhibits prostate cancer growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 250. doi:10.1158/1538-7445.AM2017-250

Abstract 4906: The selective class I HDAC inhibitor entinostat enhances the antitumor effect of PD-1 inhibition in a syngeneic orthotopic murine model of renal cell carcinoma

Background: Recent advances in immunotherapy have highlighted the antitumor effects of immune checkpoint inhibition. Novel anti-PD-1/PD-L1 immunotherapies have been shown to effectively overcome tumor avoidance of immune surveillance in several tumor types including renal cell carcinoma. Our group has recently shown that the selective class I HDAC inhibitor entinostat is effective in suppressing regulatory T cells and enhancing immunotherapies in murine renal and prostate models, RENCA and Myc-Cap respectively. In this study we have evaluated the combination of entinostat with an anti-PD-1 antibody in the RENCA renal cell carcinoma model.

Methods: 32 BALB/c female mice were implanted with the syngenic, orthotopic, renal cell carcinoma mouse model, RENCA - luciferase tagged - at day -8. Treatment (8 mice /group) with anti-mouse-PD-1 (aPD-1; 10mg/kg twice a week, I.P.), entinostat (5mg/kg 5 days a week), or combination of the two was begun at day 1. Bioluminescence imaging was performed at days -1, 9 and 19 to assess the orthotopic tumor growth. End point tumor weights were taken to assess the effect of combination treatment.

Results: Analysis of tumor growth showed a reduction of bioluminescence across the three time points in the combination group as compared to the vehicle and single agent treatments. Additionally, end point analysis of tumor weights revealed an overall reduction in the size of the tumors in the entinostat/anti-mPD-1 combination group (88% inhibition) as compared to the vehicle (p = 0.0002), aPD-1 alone (25% inhibition)(p = 0.0181), and entinostat alone (63% inhibition)(p = 0.0481) groups. Examination of the status of the infiltrating immune cells of the tumor microenvironment via flow cytometry, qRT-PCR, immunohistochemistry, and/or immunofluorescence analysis is ongoing.

Conclusions: Our preliminary results suggest that the immunomodulatory activity of the selective class I HDAC inhibitor entinostat may enhance the antitumor effect of PD-1/PD-L1 inhibition and provide the rationale for the clinical testing of this novel combination in patients with RCC.

Citation Format: Ashley R. Orillion, Li Shen, Remi Adelaiye-Ogala, May Elbanna, Sreenivasulu Chintala, Sreevani Arisa, Roberto Pili. The selective class I HDAC inhibitor entinostat enhances the antitumor effect of PD-1 inhibition in a syngeneic orthotopic murine model of renal cell carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4906.