Influence of injection technique, drug formulation and tumor microenvironment on intratumoral immunotherapy delivery and efficacy

BACKGROUND

Intratumoral delivery of immunotherapeutics represents a compelling solution to directly address local barriers to tumor immunity. However, we have previously shown that off-target delivery is a substantial problem during intratumoral injections; this can lead to diminished drug efficacy and systemic toxicities. We have identified three variables that influence intratumoral drug delivery: injection technique, drug formulation and tumor microenvironment. The purpose of this study was to characterize the impact of modifications in each variable on intratumoral drug delivery and immunotherapy efficacy.

METHODS

Intratumoral injections were performed in a hybrid image-guided intervention suite with ultrasound, fluoroscopy and CT scanning capabilities in both rat and mouse syngeneic tumor models. Intratumoral drug distribution was quantified by CT volumetric imaging. The influence of varying needle design and hydrogel-based drug delivery on the immune response to a stimulator of interferon genes (STING) agonist was evaluated using flow cytometry and single cell RNA sequencing. We also evaluated the influence of tumor stiffness on drug injection distribution.

RESULTS

Variations in needle design, specifically with the use of a multiside hole needle, led to approximately threefold improvements in intratumoral drug deposition relative to conventional end-hole needles. Likewise, delivery of a STING agonist through a multiside hole needle led to significantly increased expression of type I interferon-associated genes and 'inflammatory' dendritic cell gene signatures relative to end-hole STING agonist delivery. A multidomain peptide-based hydrogel embedded with a STING agonist led to substantial improvements in intratumoral deposition; however, the hydrogel was noted to generate a strong immune response against itself within the target tumor. Evaluation of tumor stroma on intratumoral drug delivery revealed that there was a greater than twofold improvement in intratumoral distribution in soft tumors (B16 melanoma) compared with firm tumors (MC38 colorectal).

CONCLUSIONS

Injection technique, drug formulation and tumor stiffness play key roles in the accurate delivery of intratumoral immunotherapeutics.

Aurora kinase inhibition sensitizes melanoma cells to T-cell-mediated cytotoxicity

Although immunotherapy has achieved impressive durable clinical responses, many cancers respond only temporarily or not at all to immunotherapy. To find novel, targetable mechanisms of resistance to immunotherapy, patient-derived melanoma cell lines were transduced with 576 open reading frames, or exposed to arrayed libraries of 850 bioactive compounds, prior to co-culture with autologous tumor-infiltrating lymphocytes (TILs). The synergy between the targets and TILs to induce apoptosis, and the mechanisms of inhibiting resistance to TILs were interrogated. Gene expression analyses were performed on tumor samples from patients undergoing immunotherapy for metastatic melanoma. Finally, the effect of inhibiting the top targets on the efficacy of immunotherapy was investigated in multiple preclinical models. Aurora kinase was identified as a mediator of melanoma cell resistance to T-cell-mediated cytotoxicity in both complementary screens. Aurora kinase inhibitors were validated to synergize with T-cell-mediated cytotoxicity in vitro. The Aurora kinase inhibition-mediated sensitivity to T-cell cytotoxicity was shown to be partially driven by p21-mediated induction of cellular senescence. The expression levels of Aurora kinase and related proteins were inversely correlated with immune infiltration, response to immunotherapy and survival in melanoma patients. Aurora kinase inhibition showed variable responses in combination with immunotherapy in vivo, suggesting its activity is modified by other factors in the tumor microenvironment. These data suggest that Aurora kinase inhibition enhances T-cell cytotoxicity in vitro and can potentiate antitumor immunity in vivo in some but not all settings. Further studies are required to determine the mechanism of primary resistance to this therapeutic intervention.

The Effect of Topoisomerase I Inhibitors on the Efficacy of T-Cell-Based Cancer Immunotherapy

Background

Immunotherapy has increasingly become a staple in cancer treatment. However, substantial limitations in the durability of response highlight the need for more rational therapeutic combinations. The aim of this study is to investigate how to make tumor cells more sensitive to T-cell-based cancer immunotherapy.

Methods

Two pairs of melanoma patient-derived tumor cell lines and their autologous tumor-infiltrating lymphocytes were utilized in a high-throughput screen of 850 compounds to identify bioactive agents that could be used in combinatorial strategies to improve T-cell-mediated killing of tumor cells. RNAi, overexpression, and gene expression analyses were utilized to identify the mechanism underlying the effect of Topoisomerase I (Top1) inhibitors on T-cell-mediated killing. Using a syngeneic mouse model (n = 5 per group), the antitumor efficacy of the combination of a clinically relevant Top1 inhibitor, liposomal irinotecan (MM-398), with immune checkpoint inhibitors was also assessed. All statistical tests were two-sided.

Results

We found that Top1 inhibitors increased the sensitivity of patient-derived melanoma cell lines (n = 7) to T-cell-mediated cytotoxicity (P < .001, Dunnett’s test). This enhancement is mediated by TP53INP1, whose overexpression increased the susceptibility of melanoma cell lines to T-cell cytotoxicity (2549 cell line: P = .009, unpaired t test), whereas its knockdown impeded T-cell killing of Top1 inhibitor–treated melanoma cells (2549 cell line: P < .001, unpaired t test). In vivo, greater tumor control was achieved with MM-398 in combination with α-PD-L1 or α-PD1 (P < .001, Tukey’s test). Prolonged survival was also observed in tumor-bearing mice treated with MM-398 in combination with α-PD-L1 (P = .002, log-rank test) or α-PD1 (P = .008, log-rank test).

Conclusions

We demonstrated that Top1 inhibitors can improve the antitumor efficacy of cancer immunotherapy, thus providing the basis for developing novel strategies using Top1 inhibitors to augment the efficacy of immunotherapy.

Abstract 3956: A novel compound screen for enhancing T-cell based immunotherapy identifies aurora kinases as a targetable mechanism for tumor immune escape in pancreatic ductal adenocarcinoma preclinical models

Harnessing a patient’s immune system by attenuating endogenous immune checkpoints on T-cells has led to dramatic, durable tumor rejection for multiple tumor types. Nonetheless, many cancers, including pancreatic ductal adenocarcinoma (PDAC), still do not respond to immunotherapy. PDAC remains largely resistant to all therapies, leading to its notoriety as one of the most lethal malignancies, with a 6% 5-year survival rate. We aimed to find novel, targetable mechanisms by which tumors escape the adaptive immune system and resist immunotherapy. We conducted a high throughput screen of 1280 compounds producing a synergistic effect with T-cell killing to assess differences and similarities among distinct pathways inclusive between PDAC and melanoma. These screens identified several aurora kinase inhibitors as synergistic with autologous T-cell killing of tumor target. Here we present results underlying the mechanism by which aurora kinase inhibition enhances autologous T-cell mediated killing and may improve T-cell-mediated cancer immunotherapy. These findings may contribute to the design of new therapeutic combination strategies for enhancing immunotherapy treatment of melanoma, PDAC, and other “immunologically cold” tumors.

Note: This abstract was not presented at the meeting.

Citation Format: Emily L. Ashkin, Deborah Silverman, Simone Punt, Soraya Zorro Manrique, Leila Williams, Yunfei Wang, Patrick Hwu. A novel compound screen for enhancing T-cell based immunotherapy identifies aurora kinases as a targetable mechanism for tumor immune escape in pancreatic ductal adenocarcinoma preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3956.

Abstract 2372: Tumoral p53 mutations differentially mediate poor T-cell infiltration and autologous T-cell killing in preclinical models

Harnessing the immune system through the attenuation of endogenous immune checkpoints on T-cells has led to dramatic, durable tumor rejection in multiple solid tumors; however, most cancer types remain resistant to immunotherapy. It is imperative to understand the unique mechanisms by which these lethal malignancies evade the immune system in order to design efficacious therapies. Research by several groups is elucidating how overall mutational burden, tumor stroma, and patient microbiome predict response to immunotherapies in immune-resistant cancers. However, the frequency and distribution of driver mutations in the tumors themselves differ between immunogenic and non-immunogenic cancer types and may play a role in immune escape. Whereas p53, the most commonly mutated gene in cancer, is mutated in 70-90% of non-immunogenic tumors like pancreatic adenocarcinoma (PDAC), it is mutated in only 10-15% of immunogenic skin cutaneous melanoma cases. Loss of p53 through truncating mutations mediates tumor escape from apoptosis and senescence. Furthermore, many p53 missense mutations (mtp53) not only lose wild-type activity (LOF), but acquire novel gain-of-function (GOF) activities which promote oncogenesis and resistance to therapy. Pre-clinical data suggest that mtp53 differentially mediates tumor escape from immune surveillance by altering the innate immune response, including NK cell function and macrophage phenotype, thereby allowing tumorigenesis through chronic local immunosuppression. Few studies have been completed, however, to demonstrate the role of mtp53 in regulating the adaptive immune response. Understanding the role of p53 and its mutants in the regulation of T-cell function in cancer would provide a novel framework by which to understand and overcome resistance to cancer immunotherapy in many deadly cancer types. We hypothesize that mtp53 mediates evasion of T-cell anti-tumor activity, and that gain-of-function pathways downstream of mtp53 drive this process. Here we elaborate on previously presented work, elucidating how GOF vs. LOF mtp53 influences T-cell infiltration and killing using both novel model systems. Ultimately, these results may define a new role for mtp53 in influencing the immune system, and provide a rationale for developing effective combination strategies to improve response to immunotherapy.

Citation Format: Deborah A. Silverman, Emily Ashkin, Benjamin Whitfield, Simone Punt, Soraya Zorro Manrique, Yunfei Wang, Anil Korkut, Leila Williams, Minying Zhang, Eran Kotler, Moshe Oren, Anirban Maitra, Patrick Hwu. Tumoral p53 mutations differentially mediate poor T-cell infiltration and autologous T-cell killing in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2372.

Definitive activation of endogenous antitumor immunity by repetitive cycles of cyclophosphamide with interspersed Toll-like receptor agonists

Many cancers both evoke and subvert endogenous anti-tumor immunity. However, immunosuppression can be therapeutically reversed in subsets of cancer patients by treatments such as checkpoint inhibitors or Toll-like receptor agonists (TLRa). Moreover, chemotherapy can leukodeplete immunosuppressive host elements, including myeloid-derived suppressor cells (MDSCs) and regulatory T-cells (Tregs). We hypothesized that chemotherapy-induced leukodepletion could be immunopotentiated by co-administering TLRa to emulate a life-threatening infection. Combining CpG (ODN 1826) or CpG+poly(I:C) with cyclophosphamide (CY) resulted in uniquely well-tolerated therapeutic synergy, permanently eradicating advanced mouse tumors including 4T1 (breast), Panc02 (pancreas) and CT26 (colorectal). Definitive treatment required endogenous CD8+ and CD4+ IFNγ-producing T-cells. Tumor-specific IFNγ-producing T-cells persisted during CY-induced leukopenia, whereas Tregs were progressively eliminated, especially intratumorally. Spleen-associated MDSCs were cyclically depleted by CY+TLRa treatment, with residual monocytic MDSCs requiring only continued exposure to CpG or CpG+IFNγ to effectively attack malignant cells while sparing non-transformed cells. Such tumor destruction occurred despite upregulated tumor expression of Programmed Death Ligand-1, but could be blocked by clodronate-loaded liposomes to deplete phagocytic cells or by nitric oxide synthase inhibitors. CY+TLRa also induced tumoricidal myeloid cells in naive mice, indicating that CY+TLRa's immunomodulatory impacts occurred in the complete absence of tumor-bearing, and that tumor-induced MDSCs were not an essential source of tumoricidal myeloid precursors. Repetitive CY+TLRa can therefore modulate endogenous immunity to eradicate advanced tumors without vaccinations or adoptive T-cell therapy. Human blood monocytes could be rendered similarly tumoricidal during in vitro activation with TLRa+IFNγ, underscoring the potential therapeutic relevance of these mouse tumor studies to cancer patients.

Aging subverts immune function by dictating alternative STAT responses to cytokine signaling (P5078)

Chronic inflammation in the aged closely resembles tumor-induced immune suppression, manifested as a progressive T1→T2 shift and an increased presence of MDSCs. We hypothesize that reversing these age-related phenomena should reduce the elderly’s heightened susceptibility to malignancy. We have now optimized real-time analyses of phosphorylated STATs in murine T cells and MDSCs in order to correlate STAT activation with immune suppression. Both young and old T cells responded to IL-4 stimulation with STAT6 activation and to IFN-γ stimulation with STAT1 activation. Uniquely, however, young T cells also phosphorylated STAT1, STAT3 and STAT5 in response to IL-4, and responded to IL-6 with STAT3 activation, all consistent with a greater susceptibility to T1/T17 differentiation. Regarding MDSCs, both old and young displayed constitutive STAT3 activation which could be enhanced by G-CSF or IL-6 treatment. Both young and old MDSCs activated STAT1 briskly in response to IFN-γ, STAT5 in response to GM-CSF and STAT6 in response to IL-4. However, younger MDSCs, like younger T cells, displayed more diverse responsiveness to IL-4, activating not only STAT6 but also STAT1 and STAT3. While chronic in vivo exposure to T2 cytokines may explain the decreased responsiveness of older MDSCs and T cells to IL-4, paradoxically IL-4 still robustly activated STAT6 in these cells. Such selective responsiveness may be required to preserve the immune suppressive potential of older MDSCs.

Global targeting of MDSC escape mechanisms cures advanced 4T1 breast tumors (P2062)

4T1 is a metastatic breast cancer model with fulminant accumulation of MDSCs. Survival and function of MDSCs is often reported as STAT3-dependent, and STAT3 inhibitors such as sunitinib dramatically deplete 4T1 splenic MDSCs. Paradoxically, sunitinib fails to eradicate 4T1 intratumoral MDSCs or prevent tumor progression. We hypothesized that STAT3 activation is a consistent feature of splenic but not intratumoral MDSCs. PhosphoSTAT analyses of 4T1-bearers confirmed that splenic MDSCs of all Gr1 intensities were solely pSTAT3pos. In remarkable contrast, intratumoral Gr1high MDSCs largely lacked any pSTAT activation, and intratumoral Gr1dim MDSC precursors displayed varied expression of pSTAT5 and pSTAT1 in addition to pSTAT3. We therefore sought global means to target MDSCs. We determined that 4T1 and other tumor models could be cured by repetitive administration of cyclophosphamide alternating with TLR agonists such as CpG ODN1826. While cure required participation of host CD4+ and CD8+ T cells, global targeting of MDSCs was also observed: (1) as with sunitinib, pSTAT3pos splenic MDSCs were eradicated; (2) pSTAT expression by intratumoral MDSCs was fully abolished; (3) the remaining intratumoral MDSCs, all pSTATneg, outsurvived all other cells, and were likely induced to serve as the final mediators of tumor rejection. In conclusion, strategies which globally target MDSCs and promote the endogenous anti-tumor T cell response can cure advanced metastatic tumors.

Foxp3-positive macrophages display immunosuppressive properties and promote tumor growth

Regulatory T cells (T reg cells) are characterized by the expression of the forkhead lineage-specific transcription factor Foxp3, and their main function is to suppress T cells. While evaluating T reg cells, we identified a population of Foxp3-positive cells that were CD11b(+)F4/80(+)CD68(+), indicating macrophage origin. These cells were observed in spleen, lymph nodes, bone marrow, thymus, liver, and other tissues of naive animals. To characterize this subpopulation of macrophages, we devised a strategy to purify CD11b(+)F4/80(+)Foxp3(+) macrophages using Foxp3-GFP mice. Analysis of CD11b(+)F4/80(+)Foxp3(+) macrophage function indicated that these cells inhibited the proliferation of T cells, whereas Foxp3(-) macrophages did not. Suppression of T cell proliferation was mediated through soluble factors. Foxp3(-) macrophages acquired Foxp3 expression after activation, which conferred inhibitory properties that were indistinguishable from natural Foxp3(+) macrophages. The cytokine and transcriptional profiles of Foxp3(+) macrophages were distinct from those of Foxp3(-) macrophages, indicating that these cells have different biological functions. Functional in vivo analyses indicated that CD11b(+)F4/80(+)Foxp3(+) macrophages are important in tumor promotion and the induction of T reg cell conversion. For the first time, these studies demonstrate the existence of a distinct subpopulation of naturally occurring macrophage regulatory cells in which expression of Foxp3 correlates with suppressive function.

CCL1: a novel therapeutic target for the modulation of Treg function: Implications for immmunotherapy of cancer (40.10)

Effective anti-tumor immunotherapy must overcome the immunosuppressive networks created by the tumor. Previous studies from our group indicate that intratumoral injection of CpG-ODN reduces Treg levels within the tumor by 80%. This decrease in Tregs is mainly mediated by the activation of antigen presenting cells secreting IL-6. To explore the effect of IL6 on Tregs, an expression microarray analysis of genes involved in TGFÎ2 dependent Treg conversion, which are also sensitive to IL6, was done. It yielded gene candidates which can be exploited to modulate the function of Tregs. In vitro analysis of two such candidates: chemokine ligand 1 (CCL1) and integrinαE (ITGαE), shows that blocking these proteins reduces de novo conversion of Tregs (CCL1 and ITGαE) and inhibits the suppressive function of Tregs (CCL1 only). In vivo assays using the neu tolerant breast cancer mouse model demonstrates that injection of αCCL1 or αITGαE blocking antibodies significantly reduced the level of Tregs within the tumor and the tumor draining lymph nodes. Furthermore, the combination of intratumoral injections of CpG-ODN and αCCL1 induce complete tumor rejection in neu mice. These results demonstrate that blockage of CCL1 signaling modulated the function of Tregs and subsequently enhances immunotherapeutic approaches.

Identification and characterization of macrophage regulatory cells (Mac-regs) with immunoregulatory properties (89.38)

Macrophages with suppressive characteristics such as Tumor associated macrophages or Myeloid derived suppressor cells have been defined showing regulatory function under inflammatory or polarizing conditions. Until now, there are no reports indicating that under normal, non-inflammatory or non-polarizing conditions, macrophages could have immunoregulatory functions. Utilizing knock-in Foxp3-GFP mice, we identified a new population of Foxp3 positive cells that were CD11b+F4/80+ cells. These cells were observed in spleen, lymph nodes, bone marrow and thymus. Similar to Tregs, the CD11b+F4/80+Foxp3+ macrophages inhibited T cell proliferation, whereas Foxp3neg macrophages did not. The Foxp3neg macrophages could be converted to express Foxp3. These induced-CD11b+F4/80+Foxp3+ cells displayed inhibitory properties similar to natural Foxp3pos macrophages. Based on the immunoregulatory properties of these cells, we termed them Macrophage regulatory cells (Mac-regs). These Mac-regs express CD68hiF4/80hiCTLA4hiGITRhiIL-4Rhi. Interestingly, GR-1 is not a differentiation marker. The cytokine, chemokine, growth factor and genomic profiles of Mac-regs are different compared to CD11b+F4/80+Foxp3-cells. For the first time, we demonstrated the occurrence of a natural population of macrophages displaying regulatory function which may contribute to the homeostatic balance of the immune system.

This research was supported by Grants from the NIH and AFAR.

Systemic targeting of CpG-ODN to the tumor microenvironment with anti-neu-CpG hybrid molecule and T regulatory cell depletion induces memory responses in BALB-neuT tolerant mice

We have shown that neu transgenic mice are immunotolerant and that immunizations with dendritic cells (DC) pulsed with neu-derived antigens were not able to control tumor growth in these animals. We tested whether, by modulating the tumor microenvironment with Toll-like receptor ligands, it could be possible to induce the activation of antitumor responses in neu mice. Our results indicate that only intratumoral (i.t.) injections of CpG-ODN induce an antitumor response in neu mice. To target the CpG-ODN to the tumor site anywhere within the body, we chemically conjugated an anti-Her-2/neu monoclonal antibody (mAb) with CpG-ODN. The anti-neu-CpG hybrid molecule retained its ability to bind to Her-2/neu(+) tumors, activate DCs, and induce antitumor responses. Our results indicated that injections of anti-neu-CpG induced the rejection of primary tumors in 100% of BALB/c mice and only in approximately 30% of BALB-neuT mice. After challenging the BALB/c and BALB-neuT mice, we observed that BALB/c mice developed a protective memory response; in contrast, BALB-neuT mice succumbed to the challenge. After injections of anti-neu-CpG, T regulatory cells (T-reg) were drastically reduced at the tumor site, but a large number were still present in the lymphoid organs. When BALB-neuT mice were treated with anti-neu-CpG plus anti-GITR mAb, but not with anti-CD25 mAb, 100% of the BALB-neuT mice rejected the primary tumor and developed a protective memory response indicating the critical role of T-regs in regulating the repertoire against self antigens. Taken together, these results indicate that CpG-ODN-targeted therapy and depletion of T-regs optimally activate a primary response and generate a protective memory response against self-tumor antigens.