Depth of tumor implantation affects response to in situ vaccination in a syngeneic murine melanoma model

Metabolic modulation of melanoma enhances the therapeutic potential of immune checkpoint inhibitors

Introduction

Lactate is a pivotal molecule with diverse functions in the metabolic reprogramming of cancer cells. Beyond its role in metabolism, lactate exerts a modulatory effect within the tumor microenvironment; it is utilized by stromal cells and has been implicated in the suppression of the immune response against the tumor.

Methods

Using in vitro assays (including flow cytometry, live-cell imaging and metabolic analyses), the impact of lactate dehydrogenase inhibitors (LDHIs) on melanoma cells were assessed. The therapeutic potential of LDHIs with immune checkpoint inhibitors (ICIs) were tested in vivo in murine models of melanoma tumors.

Results

A potent anti-proliferative effect (via both cell cycle alterations and enhanced apoptosis) of LDHIs, Oxamate (Oxa) and methyl 1-hydroxy-6-phenyl-4-(trifluoromethyl)-1H-indole-2-carboxylate (NHI-2), was found upon treatment of melanoma cell lines. Using a combination of Oxa and NHI-2, a synergistic effect to inhibit proliferation, glycolysis, and ATP production was observed. Metabolic analysis revealed significant alteration in glycolysis and oxidative phosphorylation, while metabolite profiling emphasized consequential effects on lactate metabolism and induced energy depletion by LDHIs. Detection of increased RANTES and MCP-1, with Oxa and NHI-2 treatment, prompted the consideration of combining LDHIs with ICIs. In vivo studies using a murine B78 melanoma tumor model revealed a significant improvement in treatment efficacy when LDHIs were combined with ICIs.

Conclusions

These findings propose the potential of targeting lactate metabolism to enhance the efficacy of ICI treatments in patients with melanoma.

Intratumoral radiation dose heterogeneity augments antitumor immunity in mice and primes responses to checkpoint blockade

Radiation therapy (RT) activates multiple immunologic effects in the tumor microenvironment (TME), with diverse dose-response relationships observed. We hypothesized that, in contrast with homogeneous RT, a heterogeneous RT dose would simultaneously optimize activation of multiple immunogenic effects in a single TME, resulting in a more effective antitumor immune response. Using high-dose-rate brachytherapy, we treated mice bearing syngeneic tumors with a single fraction of heterogeneous RT at a dose ranging from 2 to 30 gray. When combined with dual immune checkpoint inhibition in murine models, heterogeneous RT generated more potent antitumor responses in distant, nonirradiated tumors compared with any homogeneous dose. The antitumor effect after heterogeneous RT required CD4 and CD8 T cells and low-dose RT to a portion of the tumor. At the 3-day post-RT time point, dose heterogeneity imprinted the targeted TME with spatial differences in immune-related gene expression, antigen presentation, and susceptibility of tumor cells to immune-mediated destruction. At a later 10-day post-RT time point, high-, moderate-, or low-RT-dose regions demonstrated distinct infiltrating immune cell populations. This was associated with an increase in the expression of effector-associated cytokines in circulating CD8 T cells. Consistent with enhanced adaptive immune priming, heterogeneous RT promoted clonal expansion of effector CD8 T cells. These findings illuminate the breadth of dose-dependent effects of RT on the TME and the capacity of heterogeneous RT to promote antitumor immunity when combined with immune checkpoint inhibitors.

Pre-Clinical Models for CAR T-Cell Therapy for Glioma

Immunotherapy represents a transformative shift in cancer treatment. Among myriad immune-based approaches, chimeric antigen receptor (CAR) T-cell therapy has shown promising results in treating hematological malignancies. Despite aggressive treatment options, the prognosis for patients with malignant brain tumors remains poor. Research leveraging CAR T-cell therapy for brain tumors has surged in recent years. Pre-clinical models are crucial in evaluating the safety and efficacy of these therapies before they advance to clinical trials. However, current models recapitulate the human tumor environment to varying degrees. Novel in vitro and in vivo techniques offer the opportunity to validate CAR T-cell therapies but also have limitations. By evaluating the strengths and weaknesses of various pre-clinical glioma models, this review aims to provide a roadmap for the development and pre-clinical testing of CAR T-cell therapies for brain tumors.

A combined radio-immunotherapy regimen eradicates late-stage tumors in mice

Background

The majority of experimental approaches for cancer immunotherapy are tested against relatively small tumors in tumor-bearing mice, because in most cases advanced cancers are resistant to the treatments. In this study, we asked if even late-stage mouse tumors can be eradicated by a rationally designed combined radio-immunotherapy (CRI) regimen.

Methods

CRI consisted of local radiotherapy, intratumoral IL-12, slow-release systemic IL-2 and anti- CTLA-4 antibody. Therapeutic effects of CRI against several weakly immunogenic and immunogenic mouse tumors including B78 melanoma, MC38 and CT26 colon carcinomas and 9464D neuroblastoma were evaluated. Immune cell depletion and flow cytometric analysis were performed to determine the mechanisms of the antitumor effects.

Results

Tumors with volumes of 2,000 mm3 or larger were eradicated by CRI. Flow analyses of the tumors revealed reduction of T regulatory (Treg) cells and increase of CD8/Treg ratios following CRI. Rapid shrinkage of the treated tumors did not require T cells, whereas T cells were involved in the systemic effect against the distant tumors. Cured mice developed immunological memory.

Conclusions

These findings underscore that rationally designed combination immunotherapy regimens can be effective even against large, late-stage tumors.

Quantifying in vivo collagen reorganization during immunotherapy in murine melanoma with second harmonic generation imaging

Significance

Increased collagen linearization and deposition during tumorigenesis can impede immune cell infiltration and lead to tumor metastasis. Although melanoma is well studied in immunotherapy research, studies that quantify collagen changes during melanoma progression and treatment are lacking.

Aim

We aim to image in vivo collagen in preclinical melanoma models during immunotherapy and quantify the collagen phenotype in treated and control mice.

Approach

Second-harmonic generation imaging of collagen was performed in mouse melanoma tumors in vivo over a treatment time course. Animals were treated with a curative radiation and immunotherapy combination. Collagen morphology was quantified over time at an image and single-fiber level using CurveAlign and CT-FIRE software.

Results

In immunotherapy-treated mice, collagen was reorganized toward a healthy phenotype, including shorter, wider, curlier collagen fibers, with modestly higher collagen density. Temporally, collagen fiber straightness and length changed late in treatment (days 9 and 12), while width and density changed early (day 6) compared with control mice. Single-fiber collagen features calculated in CT-FIRE were the most sensitive to the changes among treatment groups compared with bulk collagen features.

Conclusions

Quantitative second-harmonic generation imaging can provide insight into collagen dynamics in vivo during immunotherapy, with key implications in improving immunotherapy response in melanoma and other cancers.

Bridging the gap between testing and clinics exploring alternative pre-clinical models in melanoma research

Melanoma, the deadliest form of skin cancer, poses a significant clinical challenge for the development of effective treatments. Conventional in vivo animal studies have shown limited translational relevance to humans, raising strength to pre-clinical models for melanoma research. This review provides an in-depth analysis of alternative pre-clinical models including in vitro and ex vivo platforms such as reconstructed skin, spheroids, organoids, organotypic models, skin-on-a-chip, and bioprinting. Through a comprehensive analysis, the specific attributes, advantages, and limitations of each model are elucidated. It discusses the points related to the uniqueness advantages, from capturing complex interactions between melanoma cells and their microenvironment to enabling high-throughput drug screening and personalized medicine approaches. This review is structured covering firstly the roadmap to identify the co-occurrence of discovering new melanoma treatments and the development of its models, secondly it covers a comparative between the most used models followed by a section discussing each of them: the in vitro and ex vivo models. It intends to serve as an asset for researchers of melanoma field and clinicians involved in melanoma therapy, offering insights into the diverse preclinical models available for optimizing their integration into the translational pipeline.

Quantifying in vivo collagen reorganization during immunotherapy in murine melanoma with second harmonic generation imaging

Significance

Increased collagen linearization and deposition during tumorigenesis can impede immune cell infiltration and lead to tumor metastasis. Although melanoma is well studied in immunotherapy research, studies that quantify collagen changes during melanoma progression and treatment are lacking.

Aim

Image in vivo collagen in preclinical melanoma models during immunotherapy and quantify the collagen phenotype in treated and control mice.

Approach

Second harmonic generation imaging of collagen was performed in mouse melanoma tumors in vivo over a treatment time-course. Animals were treated with a curative radiation and immunotherapy combination. Collagen morphology was quantified over time at an image and single fiber level using CurveAlign and CT-FIRE software.

Results

In immunotherapy-treated mice, collagen reorganized toward a healthy phenotype, including shorter, wider, curlier collagen fibers, with modestly higher collagen density. Temporally, collagen fiber straightness and length changed late in treatment (Day 9 and 12) while width and density changed early (Day 6) compared to control mice. Single fiber level collagen analysis was most sensitive to the changes between treatment groups compared to image level analysis.

Conclusions

Quantitative second harmonic generation imaging can provide insight into collagen dynamics in vivo during immunotherapy, with key implications in improving immunotherapy response in melanoma and other cancers.

Cyclophosphamide augments the efficacy of in situ vaccination in a mouse melanoma model

Introduction

We have previously shown that an intratumoral (IT) injection of the hu14.18-IL2 immunocytokine (IC), an anti-GD2 antibody linked to interleukin 2, can serve as an in situ vaccine and synergize with local radiotherapy (RT) to induce T cell-mediated antitumor effects. We hypothesized that cyclophosphamide (CY), a chemotherapeutic agent capable of depleting T regulatory cells (Tregs), would augment in situ vaccination. GD2+ B78 mouse melanoma cells were injected intradermally in syngeneic C57BL/6 mice.

Methods

Treatments with RT (12Gy) and/or CY (100 mg/kg i.p.) started when tumors reached 100-300 mm3 (day 0 of treatment), followed by five daily injections of IT-IC (25 mcg) on days 5-9. Tumor growth and survival were followed. In addition, tumors were analyzed by flow cytometry.

Results

Similar to RT, CY enhanced the antitumor effect of IC. The strongest antitumor effect was achieved when CY, RT and IC were combined, as compared to combinations of IC+RT or IC+CY. Flow cytometric analyses showed that the combined treatment with CY, RT and IC decreased Tregs and increased the ratio of CD8+ cells/Tregs within the tumors. Moreover, in mice bearing two separate tumors, the combination of RT and IT-IC delivered to one tumor, together with systemic CY, led to a systemic antitumor effect detected as shrinkage of the tumor not treated directly with RT and IT-IC. Cured mice developed immunological memory as they were able to reject B78 tumor rechallenge.

Conclusion

Taken together, these preclinical results show that CY can augment the antitumor efficacy of IT- IC, given alone or in combination with local RT, suggesting potential benefit in clinical testing of these combinations.

Single cell metabolic imaging of tumor and immune cells in vivo in melanoma bearing mice

Introduction

Metabolic reprogramming of cancer and immune cells occurs during tumorigenesis and has a significant impact on cancer progression. Unfortunately, current techniques to measure tumor and immune cell metabolism require sample destruction and/or cell isolations that remove the spatial context. Two-photon fluorescence lifetime imaging microscopy (FLIM) of the autofluorescent metabolic coenzymes nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD) provides in vivo images of cell metabolism at a single cell level.

Methods

Here, we report an immunocompetent mCherry reporter mouse model for immune cells that express CD4 either during differentiation or CD4 and/or CD8 in their mature state and perform in vivo imaging of immune and cancer cells within a syngeneic B78 melanoma model. We also report an algorithm for single cell segmentation of mCherry-expressing immune cells within in vivo images.

Results

We found that immune cells within B78 tumors exhibited decreased FAD mean lifetime and an increased proportion of bound FAD compared to immune cells within spleens. Tumor infiltrating immune cell size also increased compared to immune cells from spleens. These changes are consistent with a shift towards increased activation and proliferation in tumor infiltrating immune cells compared to immune cells from spleens. Tumor infiltrating immune cells exhibited increased FAD mean lifetime and increased protein-bound FAD lifetime compared to B78 tumor cells within the same tumor. Single cell metabolic heterogeneity was observed in both immune and tumor cells in vivo.

Discussion

This approach can be used to monitor single cell metabolic heterogeneity in tumor cells and immune cells to study promising treatments for cancer in the native in vivo context.

Radiation to all macroscopic sites of tumor permits greater systemic antitumor response to in situ vaccination

BACKGROUND

The antitumor effects of external beam radiation therapy (EBRT) are mediated, in part, by an immune response. We have reported that a single fraction of 12 Gy EBRT combined with intratumoral anti-GD2 hu14.18-IL2 immunocytokine (IC) generates an effective in situ vaccine (ISV) against GD2-positive murine tumors. This ISV is effective in eradicating single tumors with sustained immune memory; however, it does not generate an adequate abscopal response against macroscopic distant tumors. Given the immune-stimulatory capacity of radiation therapy (RT), we hypothesized that delivering RT to all sites of disease would augment systemic antitumor responses to ISV.

METHODS

We used a syngeneic B78 murine melanoma model consisting of a 'primary' flank tumor and a contralateral smaller 'secondary' flank tumor, treated with 12 Gy EBRT and intratumoral IC immunotherapy to the primary and additional EBRT to the secondary tumor. As a means of delivering RT to all sites of disease, both known and occult, we also used a novel alkylphosphocholine analog, NM600, conjugated to 90Y as a targeted radionuclide therapy (TRT). Tumor growth, overall survival, and cause of death were measured. Flow cytometry was used to evaluate immune population changes in both tumors.

RESULTS

Abscopal effects of local ISV were amplified by delivering as little as 2-6 Gy of EBRT to the secondary tumor. When the primary tumor ISV regimen was delivered in mice receiving 12 Gy EBRT to the secondary tumor, we observed improved overall survival and more disease-free mice with immune memory compared with either ISV or 12 Gy EBRT alone. Similarly, TRT combined with ISV resulted in improved overall survival and a trend towards reduced tumor growth rates when compared with either treatment alone. Using flow cytometry, we identified an influx of CD8+ T cells with a less exhausted phenotype in both the ISV-targeted primary and the distant secondary tumor following the combination of secondary tumor EBRT or TRT with primary tumor ISV.

CONCLUSIONS

We report a novel use for low-dose RT, not as a direct antitumor modality but as an immunomodulator capable of driving and expanding antitumor immunity against metastatic tumor sites following ISV.

Radiation Augments the Local Anti-Tumor Effect of In Situ Vaccine With CpG-Oligodeoxynucleotides and Anti-OX40 in Immunologically Cold Tumor Models

Introduction

Combining CpG oligodeoxynucleotides with anti-OX40 agonist antibody (CpG+OX40) is able to generate an effective in situ vaccine in some tumor models, including the A20 lymphoma model. Immunologically "cold" tumors, which are typically less responsive to immunotherapy, are characterized by few tumor infiltrating lymphocytes (TILs), low mutation burden, and limited neoantigen expression. Radiation therapy (RT) can change the tumor microenvironment (TME) of an immunologically "cold" tumor. This study investigated the effect of combining RT with the in situ vaccine CpG+OX40 in immunologically "cold" tumor models.

Methods

Mice bearing flank tumors (A20 lymphoma, B78 melanoma or 4T1 breast cancer) were treated with combinations of local RT, CpG, and/or OX40, and response to treatment was monitored. Flow cytometry and quantitative polymerase chain reaction (qPCR) experiments were conducted to study differences in the TME, secondary lymphoid organs, and immune activation after treatment.

Results

An in situ vaccine regimen of CpG+OX40, which was effective in the A20 model, did not significantly improve tumor response or survival in the "cold" B78 and 4T1 models, as tested here. In both models, treatment with RT prior to CpG+OX40 enabled a local response to this in situ vaccine, significantly improving the anti-tumor response and survival compared to RT alone or CpG+OX40 alone. RT increased OX40 expression on tumor infiltrating CD4+ non-regulatory T cells. RT+CpG+OX40 increased the ratio of tumor-infiltrating effector T cells to T regulatory cells and significantly increased CD4+ and CD8+ T cell activation in the tumor draining lymph node (TDLN) and spleen.

Conclusion

RT significantly improves the local anti-tumor effect of the in situ vaccine CpG+OX40 in immunologically "cold", solid, murine tumor models where RT or CpG+OX40 alone fail to stimulate tumor regression.

The Challenging Melanoma Landscape: From Early Drug Discovery to Clinical Approval

Melanoma is recognized as the most dangerous type of skin cancer, with high mortality and resistance to currently used treatments. To overcome the limitations of the available therapeutic options, the discovery and development of new, more effective, and safer therapies is required. In this review, the different research steps involved in the process of antimelanoma drug evaluation and selection are explored, including information regarding in silico, in vitro, and in vivo experiments, as well as clinical trial phases. Details are given about the most used cell lines and assays to perform both two- and three-dimensional in vitro screening of drug candidates towards melanoma. For in vivo studies, murine models are, undoubtedly, the most widely used for assessing the therapeutic potential of new compounds and to study the underlying mechanisms of action. Here, the main melanoma murine models are described as well as other animal species. A section is dedicated to ongoing clinical studies, demonstrating the wide interest and successful efforts devoted to melanoma therapy, in particular at advanced stages of the disease, and a final section includes some considerations regarding approval for marketing by regulatory agencies. Overall, considerable commitment is being directed to the continuous development of optimized experimental models, important for the understanding of melanoma biology and for the evaluation and validation of novel therapeutic strategies.