Local tumour ablative therapies: Opportunities for maximising immune engagement and activation

Electrochemotherapy combined with immunotherapy - a promising potential in the treatment of cancer

Electrochemotherapy is a novel, locoregional therapy that is used to treat cutaneous and deep-seated tumors. The electric pulses used in electrochemotherapy increase the permeability of the cell membranes of the target lesion and thus enhance the delivery of low-permeant cytotoxic drugs to the cells, leading to their death. It has also been postulated that electrochemotherapy acts as an in situ vaccination by inducing immunogenic cell death. This in turn leads to an enhanced systemic antitumor response, which could be further exploited by immunotherapy. However, only a few clinical studies have investigated the role of combined treatment in patients with melanoma, breast cancer, hepatocellular carcinoma, and cutaneous squamous cell carcinoma. In this review, we therefore aim to review the published preclinical evidence on combined treatment and to review clinical studies that have investigated the combined role of electrochemotherapy and immunotherapy.

A review of the development of histotripsy for extremity tumor ablation with a canine comparative oncology model to inform human treatments

Cancer is a devasting disease resulting in millions of deaths worldwide in both humans and companion animals, including dogs. Treatment of cancer is complex and challenging and therefore often multifaceted, as in the case of osteosarcoma (OS) and soft tissue sarcoma (STS). OS predominantly involves the appendicular skeleton and STS commonly develops in the extremities, resulting in treatment challenges due to the need to balance wide-margin resections to achieve local oncological control against the functional outcomes for the patient. To achieve wide tumor resection, invasive limb salvage surgery is often required, and the patient is at risk for numerous complications which can ultimately lead to impaired limb function and mobility. The advent of tumor ablation techniques offers the exciting potential of developing noninvasive or minimally invasive treatment options for extremity tumors. One promising innovative tumor ablation technique with strong potential to serve as a noninvasive limb salvage treatment for extremity tumor patients is histotripsy. Histotripsy is a novel, noninvasive, non-thermal, and non-ionizing focused ultrasound technique which uses controlled acoustic cavitation to mechanically disintegrate tissue with high precision. In this review, we present the ongoing development of histotripsy as a non-surgical alternative for extremity tumors and highlight the value of spontaneously occurring OS and STS in the pet dog as a comparative oncology research model to advance this field of histotripsy research.

Immunogenic Cell Death in Electroporation-Based Therapies Depends on Pulse Waveform Characteristics

Traditionally, electroporation-based therapies such as electrochemotherapy (ECT), gene electrotransfer (GET) and irreversible electroporation (IRE) are performed with different but typical pulse durations-100 microseconds and 1-50 milliseconds. However, recent in vitro studies have shown that ECT, GET and IRE can be achieved with virtually any pulse duration (millisecond, microsecond, nanosecond) and pulse type (monopolar, bipolar-HFIRE), although with different efficiency. In electroporation-based therapies, immune response activation can affect treatment outcome, and the possibility of controlling and predicting immune response could improve the treatment. In this study, we investigated if different pulse durations and pulse types cause different or similar activations of the immune system by assessing DAMP release (ATP, HMGB1, calreticulin). Results show that DAMP release can be different when different pulse durations and pulse types are used. Nanosecond pulses seems to be the most immunogenic, as they can induce the release of all three main DAMP molecules-ATP, HMGB1 and calreticulin. The least immunogenic seem to be millisecond pulses, as only ATP release was detected and even that assumingly occurs due to increased permeability of the cell membrane. Overall, it seems that DAMP release and immune response in electroporation-based therapies can be controlled though pulse duration.

Spatiotemporal local and abscopal cell death and immune responses to histotripsy focused ultrasound tumor ablation

Introduction

Histotripsy is a novel focused ultrasound tumor ablation modality with potent immunostimulatory effects.

Methods

To measure the spatiotemporal kinetics of local andabscopal responses to histotripsy, C57BL/6 mice bearing bilateral flank B16 melanoma or Hepa1-6 hepatocellular carcinoma tumors were treated with unilateral sham or partial histotripsy. Treated and contralateral untreated (abscopal) tumors were analyzed using multicolor immunofluorescence, digital spatial profiling, RNA sequencing (RNASeq), and flow cytometry.

Results

Unilateral histotripsy triggered abscopal tumor growth inhibition. Within the ablation zone, early high mobility group box protein 1 (HMGB1) release and necroptosis were accompanied by immunogenic cell death transcriptional responses in tumor cells and innate immune activation transcriptional responses in infiltrating myeloid and natural killer (NK) cells. Delayed CD8+ T cell intratumoral infiltration was spatiotemporally aligned with cancer cell features of ferroptosis; this effect was enhanced by CTLA-4 blockade and recapitulated in vitro when tumor-draining lymph node CD8+ T cells were co-cultured with tumor cells. Inoculation with cell-free tumor fractions generated by histotripsy but not radiation or freeze/thaw conferred partial protection from tumor challenge.

Discussion

We propose that histotripsy may evoke local necroptotic immunogenic cell death, priming systemic adaptive immune responses and abscopal ferroptotic cancer cell death.

Tailoring Aggregation Extent of Photosensitizers to Boost Phototherapy Potency for Eliciting Systemic Antitumor Immunity

Phototherapy is effective for triggering the immunogenic cell death (ICD) effect. However, its efficacy is limited by low ¹ O₂  generation and photothermal conversion efficacy due to two irreconcilable obstacles, namely the aggregation-caused-quenching (ACQ) effect and photobleaching. In this work, a discretely integrated nanofabrication (DIN) platform (Pt-ICG/PES) is developed by facile coordination coassembly of cisplatin (Pt), photosensitizer molecules (indocyanine green (ICG)), and polymeric spacer (p(MEO₂ MA-co-OEGMA)-b-pSS (PES)). By controlling the ICG/PES feeding ratio, the aggregation of ICG can be easily tailored using PES as an isolator to balance the ACQ effect and photobleaching, thereby maximizing the phototherapy potency of Pt-ICG/PES. With the optimized ratio of each component, Pt-ICG/PES integrates the complementarity of photodynamic therapy, photothermal therapy, and chemotherapeutics to magnify the ICD effect, exerting a synergistic antitumor immunity-promoting effect. Additionally, temperature-sensitive PES enables photothermally guided drug delivery. In a tumor-bearing mouse model, Pt-ICG/PES elicits effective release of danger-associated molecular patterns, dendritic cell maturation, cytotoxic T lymphocytes activation, cytokine secretion, M2 macrophage repolarization, and distal tumor suppression, confirming the excellent in situ tumor ICD effect as well as robust systematic antitumor immunity. Ultimately, a versatile DIN strategy is developed to optimize the phototherapeutic efficacy for improving antitumor effects and strengthening systemic antitumor immunity.

ROS Pleiotropy in Melanoma and Local Therapy with Physical Modalities

Metabolic energy production naturally generates unwanted products such as reactive oxygen species (ROS), causing oxidative damage. Oxidative damage has been linked to several pathologies, including diabetes, premature aging, neurodegenerative diseases, and cancer. ROS were therefore originally anticipated as an imperative evil, a product of an imperfect system. More recently, however, the role of ROS in signaling and tumor treatment is increasingly acknowledged. This review addresses the main types, sources, and pathways of ROS in melanoma by linking their pleiotropic roles in antioxidant and oxidant regulation, hypoxia, metabolism, and cell death. In addition, the implications of ROS in various physical therapy modalities targeting melanoma, such as radiotherapy, electrochemotherapy, hyperthermia, photodynamic therapy, and medical gas plasma, are also discussed. By including ROS in the main picture of melanoma skin cancer and as an integral part of cancer therapies, a greater understanding of melanoma cell biology is presented, which ultimately may elucidate additional clues on targeting therapy resistance of this most deadly form of skin cancer.

Focused ultrasound tumour ablation in small animal oncology

The cancer incidence rates for humans and animals remain high, and efforts to improve cancer treatment are crucial. Cancer treatment for solid tumours includes both treatment of the primary tumour and of metastasis. Surgery is commonly employed to resect primary and metastatic tumours, but is invasive, and is not always the optimal treatment modality. Prevention and treatment of metastatic disease often utilizes a multimodal approach, but metastasis remains a major cause of death for both human and veterinary cancer patients. Focused ultrasound (FUS) tumour ablation techniques represent a novel non-invasive approach to treating cancer. FUS ablation is precise, thus sparing adjacent critical structures while ablating the tumour. FUS ablation can occur in a thermal or non-thermal fashion. Thermal FUS ablation, also known as high intensity focused ultrasound (HIFU) ablation, destroys tumour cells via heat, whereas non-thermal FUS, known as histotripsy, ablates tumour cells via mechanical disintegration of tissue. Not only can HIFU and histotripsy ablate tumours, they also demonstrate potential to upregulate the host immune system towards an anti-tumour response. The aim of this report is provide a description of HIFU and histotripsy tumour ablation, with a focus on the basic principles of their ablation mechanisms and their clinical applicability in the field of veterinary oncology.

The role of irreversible electroporation in promoting M1 macrophage polarization via regulating the HMGB1-RAGE-MAPK axis in pancreatic cancer

Irreversible electroporation (IRE) is an effective method for treating pancreatic ductal adenocarcinoma (PDAC). It remains unclear whether IRE can induce a specific immune response by stimulating macrophages. Here, the associated markers of macrophages were analyzed after exposure to tumor culture supernatant (TSN) of tumor cells treated with electroporation. Subcutaneous and orthotopic PDAC models were also used to evaluate the effect of macrophage polarization induced by IRE. Aside from its direct killing effect, IRE could induce the immunogenic cell death of tumor cells by increasing the synthesis and secretion of damage associated molecular patterns. Moreover, IRE could increase the release of HMGB1, which activates the MAPK-p38 pathway and leads to the increased expression of M1 markers in macrophages, through binding to the receptor of the advanced glycation end-product (RAGE) receptor. M1 polarization was inhibited by the inhibitors of HMGB1 release, the RAGE receptor, and the MAPK-p38 signaling pathway, but it was activated by rHMGB1 or the stimulator of MAPK-p38. In addition, the promotion of M1 macrophage polarization was enhanced by the positive-feedback release or expression of HMGB1 and RAGE through the MAPK-ERK pathway in macrophages. The promotion of M1 macrophage polarization induced by IRE provided a specific rationale for the combination of IRE and immune therapy in treating PDAC.

Hyperthermia Targeting the Tumor Microenvironment Facilitates Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICIs) have ushered in a new era of cancer therapy; however, ICIs are only effective in selective patients. The efficacy of ICIs is closely related to the tumor microenvironment. Fever for a long time was thought to directly regulate the immune response, and artificial “fever” from hyperthermia modulates the tumor immune microenvironment by providing danger signals with heat shock proteins (HSPs) as well as subsequent activation of immune systems. Encouraging results have been achieved in preclinical studies focused on potential synergetic effects by combining hyperthermia with ICIs. In this review, we summarized a cluster of immune-related factors that not only make hyperthermia a treatment capable of defending against cancer but also make hyperthermia a reliable treatment that creates a type I-like tumor microenvironment (overexpression of PD-L1 and enrichment of tumor infiltrating lymphocytes) in complementary for the enhancement of the ICIs. Then we reviewed recent preclinical data of the combination regimens involving hyperthermia and ICIs that demonstrated the combined efficacy and illustrated possible approaches to further boost the effectiveness of this combination.

Non-thermal histotripsy tumor ablation promotes abscopal immune responses that enhance cancer immunotherapy

Background

Developing the ability to use tumor-directed therapies to trigger potentially therapeutic immune responses against cancer antigens remains a high priority for cancer immunotherapy. We hypothesized that histotripsy, a novel non-invasive, non-thermal ablation modality that uses ultrasound-generated acoustic cavitation to disrupt tissues, could engender adaptive immune responses to tumor antigens.

Methods

Immunocompetent C57BL/6 mice inoculated with flank melanoma or hepatocellular carcinoma tumors were treated with histotripsy, thermal ablation, radiation therapy, or cytotoxic T lymphocyte-associated protein-4 (CTLA-4) blockade checkpoint inhibition. Lymphocyte responses were measured using flow cytometric and immunohistochemical analyses. The impact of histotripsy on abscopal immune responses was assessed in mice bearing bilateral tumors, or unilateral tumors with pulmonary tumors established via tail vein injection.

Results

Histotripsy ablation of subcutaneous murine melanoma tumors stimulated potent local intratumoral infiltration of innate and adaptive immune cell populations. The magnitude of this immunostimulation was stronger than that seen with tumor irradiation or thermal ablation. Histotripsy also promoted abscopal immune responses at untreated tumor sites and inhibited growth of pulmonary metastases. Histotripsy was capable of releasing tumor antigens with retained immunogenicity, and this immunostimulatory effect was associated with calreticulin translocation to the cellular membrane and local and systemic release of high mobility group box protein 1. Histotripsy ablation potentiated the efficacy of checkpoint inhibition immunotherapy in murine models of melanoma and hepatocellular carcinoma.

Conclusions

These preclinical observations suggest that non-invasive histotripsy ablation can be used to stimulate tumor-specific immune responses capable of magnifying the impact of checkpoint inhibition immunotherapy.

Analysis of damage-associated molecular pattern molecules due to electroporation of cells in vitro

Background Tumor cells can die via immunogenic cell death pathway, in which damage-associated molecular pattern molecules (DAMPs) are released from the cells. These molecules activate cells involved in the immune response. Both innate and adaptive immune response can be activated, causing a destruction of the remaining infected cells. Activation of immune response is also an important component of tumor treatment with electrochemotherapy (ECT) and irreversible electroporation (IRE). We thus explored, if and when specific DAMPs are released as a consequence of electroporation in vitro. Materials and methods In this in vitro study, 100 μs long electric pulses were applied to a suspension of Chinese hamster ovary cells. The release of DAMPs - specifically: adenosine triphosphate (ATP), calreticulin, nucleic acids and uric acid was investigated at different time points after exposing the cells to electric pulses of different amplitudes. The release of DAMPs was statistically correlated with cell permeabilization and cell survival, e.g. reversible and irreversible electroporation. Results In general, the release of DAMPs increases with increasing pulse amplitude. Concentration of DAMPs depend on the time interval between exposure of the cells to pulses and the analysis. Concentrations of most DAMPs correlate strongly with cell death. However, we detected no uric acid in the investigated samples. Conclusions Release of DAMPs can serve as a marker for prediction of cell death. Since the stability of certain DAMPs is time dependent, this should be considered when designing protocols for detecting DAMPs after electric pulse treatment.

T-cell activation and immune memory enhancement induced by irreversible electroporation in pancreatic cancer

Background

Irreversible electroporation is shown to induce immune changes in pancreatic cancer while the histology evidences are still lacking. The aim of this study is to show the immune changes in histology and explore whether irreversible electroporation (IRE) can induce immunogenic cell death (ICD) of tumor cells and activate specific immune responses.

Methods

Subcutaneous and orthotopic pancreatic cancer models were established and used to evaluate the effect of immune modulation of IRE. The infiltration of T cells was assessed in several tissue samples before and after IRE. Abscopal effect was then assessed by comparing the tumor growth of subcutaneous tumors after in situ ablation with IRE or exposure to tumor culture supernatant (TSN) of IRE‐treated Pan02. The expression of damage‐associated molecular patterns (DAMPs) of tumor cells after IRE was detected in vitro.

Results

IRE could significantly suppress the tumor growth and increase the infiltration of CD8⁺ T cells. After ablation with IRE or stimulation with TSN of Pan02 treated by IRE, the growth of untreated tumor was suppressed and the effector CD8⁺ T cells and memory T cells increased significantly in mice. Additionally, the inhibition effect of tumor growth increased along with the increasing strength levels of electroporation. IRE induced ICD of tumor cells by increasing the synthesis and secretion of DAMPs.

Conclusions

IRE induced local immunomodulation by increasing specific T cells infiltration. Through enhancing specific immune memory, IRE not only led a complete tumor regression in suit, but also induced abscopal effect, suppressing the growth of the latent lesions.

Irreversible electroporation of locally advanced pancreatic cancer transiently alleviates immune suppression and creates a window for antitumor T cell activation

Purpose: Local tumor ablation through irreversible electroporation (IRE) may offer a novel therapeutic option for locally advanced pancreatic cancer (LAPC). It may also serve as a means of in vivo vaccination. To obtain evidence of the induction of systemic antitumor immunity following local IRE-mediated ablation, we performed an explorative immune monitoring study. Methods: In ten patients enrolled in a clinical trial exploring the safety, feasibility, and efficacy of percutaneous image-guided IRE in LAPC, we determined the frequency and activation state of lymphocytic and myeloid subsets in pre- and post-treatment peripheral blood samples using flow cytometry. Tumor-specific systemic T cell responses to the pancreatic cancer associated antigen Wilms Tumor (WT)1 were determined after in vitro stimulation in an interferon-y enzyme-linked immunospot assay (Elispot), at baseline and at 2 weeks and 3 months after IRE. Results: Our data showed a transient decrease in systemic regulatory T cells (Treg) and a simultaneous transient increase in activated PD-1⁺ T cells, consistent with the temporary reduction of tumor-related immune suppression after the IRE procedure. Accordingly, we found post-IRE boosting of a pre-existing WT1 specific T cell response in two out of three patients as well as the de novo induction of these responses in another two patients. There was a trend for these WT1 T cell responses to be related to longer overall survival (p = .055). Conclusions: These findings are consistent with a systemic and tumor-specific immune stimulatory effect of IRE and support the combination of percutaneous IRE with therapeutic immune modulation.

Radiation Followed by OX40 Stimulation Drives Local and Abscopal Antitumor Effects in an Anti-PD1-Resistant Lung Tumor Model

Purpose: Radiation is used extensively to treat localized cancer, but improved understanding of its effects on the immune system has increased interest in its potential systemic (abscopal) effects, particularly in combination with checkpoint inhibitors such as anti-PD1. The majority of patients either do not respond or develop resistance to monotherapy over time. Here, we investigated the efficacy of OX40 (CD134) stimulation as an alternative immunotherapeutic approach in combination with radiotherapy (XRT) in a murine model of anti-PD1-resistant lung tumors.Experimental Design: We established a bilateral tumor model in 129Sv/Ev mice using an anti-PD1-resistant lung tumor cell line. Primary tumors were treated with intratumoral injection of an OX40 agonist antibody, given as adjuvant therapy after XRT (36 Gy in three 12-Gy fractions), whereas secondary tumors were left untreated to investigate abscopal outcomes.Results: The combination of XRT followed by OX40 stimulation effectively inhibited local and systemic antitumor growth, limited lung metastases, and improved survival rates. This treatment regimen augmented CD4⁺ and CD8⁺ T-cell expansion. XRT induced the expression of OX40 on T cells in tumors and spleens and increased the percentages of splenic CD103⁺ dendritic cells.Conclusions: Our data extend the benefits of radiation to systemic disease control, especially when combined with anti-OX40 agonist to promote immunologically mediated abscopal effects. Moreover, this study provides a rational treatment approach and sequence to overcome anti-PD1-resistant poorly immunogenic tumors. Clin Cancer Res; 24(22); 5735-43. ©2018 AACR.

Effectiveness of electrochemotherapy after IFN-α adjuvant therapy of melanoma patients

Background

The combination of electrochemotherapy with immuno-modulatory treatments has already been explored and proven effective. However, the role of interferon alpha (IFN-α) adjuvant therapy of melanoma patients and implication on electrochemotherapy effectiveness has not been explored yet. Therefore, the aim of the study was to retrospectively evaluate the effectiveness and safety of electrochemotherapy after the previous adjuvant treatment with IFN-α in melanoma patients.

Patients and methods

The study was a retrospective single-center observational analysis of the patients with advanced melanoma, treated with electrochemotherapy after previous IFN-α adjuvant therapy. Five patients, treated between January 2008 and December 2014, were included into the study, regardless of the time point of IFN-α adjuvant therapy.

Results

Electrochemotherapy of recurrent melanoma after the IFN-α adjuvant therapy proved to be a safe and effective treatment. Patients with one or two metastases responded completely. Among patients with multiple metastases, there was a variable response rate. In one patient all 23 metastases responded completely, in second patient more than 85% of all together 80 metastases responded completely and in third patient all 5 metastases had partial response. Taking into account all metastases from all patients together there was an 85% complete response rate.

Conclusions

The study showed that electrochemotherapy of recurrent melanoma after the IFN-α adjuvant therapy is a safe and effective treatment modality, which results in a high complete response rate, not only in single metastasis, but also in multiple metastases. The high complete response rate might be due to an IFN-α immune-editing effect, however, further studies with a larger number of patients are needed to support this presumption.