Focused Ultrasound Immuno-Oncology Landscape Analysis
Published April 14, 2023
The focused ultrasound immuno-oncology (FUS-IO) field has grown rapidly in the past decade and continues to do so as additional immunotherapies and focused ultrasound modalities are developed. Focused ultrasound can interact with the cancer immunity cycle in many ways and be applied to multiple tumor types, further diversifying the field. Published studies on focused ultrasound and immuno-oncology extend from in vitro studies to clinical trials.
The breadth and depth of information now available prompted the Foundation to compile a database of FUS-IO-related publications. This tailored bibliography, complete with content-specific tags, is now accessible through our virtual Zotero library. This database will be updated regularly. Please contact us at firstname.lastname@example.org to let us know of any publications or information we may have missed.
As the FUS-IO field has grown, the Foundation has maintained a list of burning questions that represent knowledge gaps critical to expanding clinical translation of FUS-IO therapies. The FUS-IO virtual library was organized with an eye toward addressing these burning questions.
Using both the published literature and insights gained from discussions at the Foundation’s biennial symposia and FUS-IO workshops, the Foundation has put together this high-level landscape analysis to determine where the field stands with respect to each burning question. We have also included tables with key references and a list of relevant tags found in the virtual library.
We expect the publication database and landscape analysis will be a useful resource for those already in the field as well as those entering it. In conjunction with the landscape analysis, the Foundation has also released a series of guidelines with recommendations for immune analysis, ultrasound treatment reporting, and data sharing that are intended to harmonize the field of FUS-IO and make broader comparisons across treatment regimes more feasible.
1. What are the comparative immune effects (i.e., signaling pathways/molecules) induced by different focused ultrasound modes? How do these compare to other therapies (i.e., radiation, cryoablation, RF ablation)?
Focused ultrasound can be used in several modes, ranging from irreversible thermal or mechanical ablation to transient thermal or mechanical effects. Each of these modes interacts with tumor tissue in diverse ways and therefore may illicit varying immune responses (see Table 1).
Within the body, histotripsy, thermal ablation, and hyperthermia have been evaluated for their effects on the immune system. Histotripsy can trigger the release of damage-associated molecular patterns (DAMPs), alter cytokine and chemokine profiles, and decrease populations of pro-tumor immune cells. Histotripsy may also improve local immune cell infiltration, particularly in fibrous tumors, by disrupting the extracellular matrix. Thermal treatments can result in changes in vascular permeability and/or perfusion, production of heat shock proteins and other proinflammatory cytokines and chemokines, and increase cytotoxic activity from natural killer (NK) and CD8+ T cells. Immune responses and particularly immune cell infiltration may be improved by using a sparse-scan (partial ablation) strategy during thermal ablation.
Because the brain is an immune-privileged organ, immune responses within the brain often vary from what is observed in other organs. Studies have demonstrated that even reversible, low power treatments like blood-brain barrier (BBB) opening can trigger sterile inflammation in the brain when combined with extremely high concentrations of microbubbles. This response appears to be mediated by the NK-kB pathway and can result in microglial and astrocyte activation. Other modalities cause effects in line with what is seen in the body but to a lesser extent.
Relevant Tags: FUS-ThermalAblation, Mechanical-FUS, Histotripsy, Pulsed-FUS, FUS-Hyperthermia, LOFU, MB, SDT, FUS-BBBo, Hyperthermia
2. How do the immune effects of focused ultrasound vary by tumor type?
Given that focused ultrasound can interact in many ways with tumor tissue, consideration must be given to the tumor model or type being treated. Researchers have applied focused ultrasound to many types of solid tumors, but the size of the focused ultrasound treatment parameter space complicates comparisons and, as with most immunotherapies, results can vary significantly between patients (see Table 2). Therefore, it may be more beneficial to consider tumor and/or patient characteristics rather than cancer type. Fibrous tumors, such as pancreatic cancer, may benefit from mechanical perturbation to disrupt the extracellular matrix and enable immune cell infiltration. “Hot” tumors that have already been infiltrated by anti-tumor immune cells might respond better to lower power treatments designed to enhance cytokine signaling without killing infiltrative immune cells within the tumor. Alternatively, tumors that are characterized by significant pro-tumorigenic infiltration, like some breast cancers, may need ablative approaches designed to give a clean slate.
Relevant Tags: CT26, MC38, B16, B16F1cOVA, EL4, HCT-116, RM-9, Pan02, Neuro2a, H22, 4T1, B16-F10, B16-F1, MDA-MB-231, H1-N1, GL261, TPSA23, B16GP33, Hepa1-6, McA-RH7777, N1-S1, GL261, KPC4662, KPC, E0771, A20, PC3, Nalm-6, NDL, B16-OVA, MM3MG-HER2, LNCaP, Hep3b, H22, MMTV-PyVT, MMTV-hHER3, Melanoma, GBM, neuroblastoma, sarcoma, PancreaticCancer, adenocarcinoma, HepatocellularCarcinoma, ColonCarcinoma, ColonAdenocarcinoma, lymphoma, UterineFibroids, NormalBrain, ThyroidNodule, RenalCellCarcinoma, BreastCancer, leukemia, ProstateCancer, ColoRectalCancer, MultipleScerosis, AutoimmuneEncephalomyelitis, cholangiocarcinoma, Osteosarcoma, BladderCancer, LiverCancer
3. What clinical disease targets are ideal for focused ultrasound plus immunotherapy combinations?
Focused ultrasound can target many disease locations throughout the body and can modulate the immune system and facilitate drug and immune cell delivery to the tumor. As we look toward the clinic, two different translational approaches have emerged, and a number of challenges need to be addressed.
Broadly, one proposed approach involves targeting diseases with the most significant unmet need – cancers that respond poorly to existing immunotherapeutics and/or are immunologically cold (breast, ovary, prostate, pancreas, and primary brain tumors), and patients with advanced disease who have exhausted all treatment options. This approach leans heavily on data demonstrating that focused ultrasound can trigger and/or modulate an anti-tumor immune response and could offer lifesaving treatment for patients that respond favorably. However, these cancers are notoriously hard to treat and a failure here may not accurately reflect focused ultrasound’s potential as a new therapy. Additionally, refractory patients who have been heavily pretreated may have significant negative changes in their immune functioning, thus limiting the efficacy of any immune-based therapy.
An alternate approach targets diseases where focused ultrasound may provide an incremental improvement. These applications involve cancers that do respond to immunotherapies (melanoma, kidney, liver) and focus on improving the efficacy of existing treatments by acting as an immune adjuvant and/or by enhancing the delivery of an immunotherapeutic. This approach is particularly appealing for patients with metastases in locations that are difficult to access, particularly the brain. Positioning focused ultrasound as a drug delivery platform for approved therapies may allow integration earlier in disease progression, providing a better metric of focused ultrasound’s potential as a frontline therapy.
In addition to the confounding effects of prior therapies in late-stage patients, several other challenges have arisen as we move toward clinical translation. Preclinical evidence on fractionated or repeated treatments is lacking, and cancer patients with large tumors or multiple metastatic sites may benefit from a staged approach. Although leaving viable tumor behind may actually improve the immune response, the ethics and optics of doing so must also be considered, because it will be impossible to target the full tumor volume in some cases due to required safety margins. Finally, the consensus of the field is that the best way to monitor treatment effects at an immunological level requires tissue biopsies at multiple timepoints. Both from a practical and ethical standpoint, this is often problematic, and the availability of tissue samples plays a role in determining the tumor types and locations that are included in clinical trials.
Relevant Tags: ClinicalTrial, CaseReport, GBM, neuroblastoma, sarcoma, PancreaticCancer, adenocarcinoma, HepatocellularCarcinoma, ColonCarcinoma, ColonAdenocarcinoma, lymphoma, UterineFibroids, NormalBrain, ThyroidNodule, RenalCellCarcinoma, BreastCancer, leukemia, ProstateCancer, ColoRectalCancer, MultipleScerosis, AutoimmuneEncephalomyelitis, cholangiocarcinoma, Osteosarcoma, BladderCancer, LiverCancer
4. How can we optimize focused ultrasound treatments for immunomodulation (i.e., drug combinations, partial vs total tumor treatment, timing of treatments)?
With the broad range of bioeffects focused ultrasound can produce and the many tumor types it can treat, it is no surprise that there is no single “best” treatment protocol. Broadly speaking, therapeutic approaches should be tailored based on tumor characteristics, such as cold vs hot, presence of metastatic disease, size, and composition of the tumor microenvironment (TME).
Preclinical work has indicated that cold tumors may benefit from a priming protocol with an immunotherapeutic followed by a focused ultrasound treatment designed to enhance immunogenic signals. Enhancing activation and trafficking of cytotoxic T cells will do little good if they are immediately deactivated within the tumor. Partial ablation may be beneficial in these cases as well, combining the release of DAMPs and other cytokines with intact tumor tissue for greater antigen availability.
Partial or fractionated ablation may also offer benefit for metastatic disease by preserving intact tumor for antigen presentation and may be the only clinically feasible approach for large tumors. Focused ultrasound protocols that maximize systemic signaling cascades and/or release substantial amounts of intact antigen would perform best in the metastatic setting, especially when combined with immunotherapies designed to activate a systemic response.
In hot tumors, where access to the tumor may be more of an issue than immune cell activation, focused ultrasound procedures that prime the tumor vasculature and/or disrupt the tumor stroma may be ideal. Immunotherapeutics that operate locally and whose delivery can be enhanced by focused ultrasound could provide excellent synergy as well.
Vascular disruption could significantly alter the treatment paradigm for brain metastases and primary brain tumors by enabling the delivery of immunotherapeutics that would otherwise be unable to bypass the BBB. In the immune-privileged brain environment, combining focused ultrasound BBB opening with therapies like chimeric antigen receptor T (CAR-T) cells is particularly appealing.
While there is no “one size fits all” approach to focused ultrasound and immunotherapy combinations, the flexibility the technology offers enables optimization for every situation.
Relevant Tags: FUS-Drug, FUS-RT, FUS-Cells, chemotherapy, IO, aPD-1, aPD-L1, aCTLA-4, ipilimumab, a-CD40, GlycatedChitosan (GC), NPs, CRT-NP, ncMB, cGAMP, GeneCIrcuit, STING, aCD47, CpG, TSL, Doxorubicine, Liposomes, R837, Imiquimod, HMME, sonosensitizer, HiPorfin
5. What metrics can be used to predict clinical success (T-cell ratios, etc.)? In the absence of biopsies, can blood samples reliably predict response?
As focused ultrasound moves farther into clinical trials and practice, it is becoming clear that many factors can affect the way an individual patient responds. While this is a frequent problem across cancer immunotherapies, the diverse focused ultrasound parameter space can further complicate prediction of patient response. Ideally, biomarkers would identify patients likely to respond to treatment and indicate progression or recurrence. Minimally or non-invasive options to measure these biomarkers are preferred, so serial tissue biopsies are not always feasible or ethical. Liquid biopsies may offer an alternative.
There is considerable interest in using clinical imaging as a surrogate biomarker, given that imaging is already used with focused ultrasound. In the future, this imaging could be leveraged for deeper analysis. In the meantime, both imaging and immunoassays should be collected in parallel for use with functional or quantitative imaging metrics in development. PET imaging, with focused ultrasound and radio-labeled checkpoint inhibitors, may quantify drug trafficking as an indirect predictor of patient response.
More research is needed to identify biomarkers that can predict patient response. The field recognizes that multi-site trials will help to move the field forward faster compared to non-coordinated single-center trials and that it is important to have a centralized repository for samples and coordination of assay analysis to harmonize results.
Relevant tags: IHC, Histology, H&E, CytotoxicityAssay, FlowCytomery, Proteomics, ELISA, CytokineAssay, ImmunoFluorescence,qRT-PCR, WesternBlot, RNAseq, MTT, Genomics, FuntionalAssay, TcellDepletion, MassSpec, EVsIsolation, cryoEM, ClonogenicAssay, TCRseq, scRNAseq
6. Which new therapeutics may synergize with focused ultrasound?
Recent advances in the development of biomolecular tools that allow ultrasound to connect directly to cellular functions (such as gene expression) have opened the way for novel applications of focused ultrasound. When combined with synthetic biology and engineered bioswitches, focused ultrasound can be used to control the expression of transgenes via heat shock promoters or sono-sensitive channels. This approach has many applications in the field of immuno-oncology. Focused ultrasound hyperthermia has been used to remotely control the release of immune checkpoint inhibitors from engineered bacteria. Ultrasound-activated therapeutic microbes were successfully activated in situ and induced a marked suppression of tumor growth. This technology can also be used to remotely and reversibly control cellular functions of CAR-T cells within tumors. Focused ultrasound-mediated gene expression can provide a critical tool for the spatiotemporal targeting of potent bacterial and cellular therapeutics in various biological and clinical scenarios.
Sonodynamic therapy (SDT), a modality that combines low intensity focused ultrasound with sonosensitizers to selectively damage cancer cells, has entered clinical trials for the treatment of brain tumors. Combinations of SDT with anti-PD1/PD-L1 therapies has been shown to improve control of tumor growth and initiate antitumor immune responses in different tumor models. The data obtained so far suggest that SDT can modulate the TME to increase immune cell infiltration and potentially trigger an adaptive immune response.
Ultrasound-mediated gene transfection has recently been integrated into cancer immunotherapy. This approach enhances transfection efficiency locally and reduces risks of systemic immunogenicity (such as when combined with adenoviruses), without altering activation of innate or acquired immunity. There are unique opportunities to pursue ultrasound-mediated gene transfection to augment the intracellular uptake of nucleic acids while safely and stably modulating the expression of immunostimulatory cytokines. Several approaches have been investigated, including the delivery of plasmid coding for cytokines such as IL-12, GM-CSF, or IFN-B, of DNA vaccines coding for tumor-specific antigens such as OVA in murine models, or gene constructs coding for modulation of immune cell functionality such as anti-CD19 CAR gene or Foxp3 siRNA. Ultrasound-mediated gene transfection may be able to further modulate the TME and prime immune cells when combined with other non-immunological approaches, such as radiotherapy, chemotherapy, and/or other ablation therapies.
An increase in interest and the large parameter space available have combined to create a wide-ranging literature base from which to draw conclusions about the effects of FUS-IO therapies. At the same time, these variables make it difficult to make concrete statements, especially when attempting to predict response or choose an optimal treatment regimen. Characteristics of the tumor itself (e.g., hot vs cold, mutational burden, tissue of origin), patient variables (e.g., metastatic status, prior treatments), focused ultrasound parameters (e.g., modality, power, % volume treated), immunotherapeutic options (e.g., type, dosing), and combinatorial factors (e.g., schedule) can all dramatically affect the response.
The Foundation has put considerable effort into encouraging the FUS-IO field to harmonize treatment, measurement, and reporting of FUS-IO studies to enable comparisons. As we move forward with clinical translation, it becomes imperative to distill the broad literature base into actionable conclusions that will inform patient selection and treatment. We will continue working with the FUS-IO community with an end goal of developing a multi-factor decision tree to optimize FUS-IO therapy for a given patient or patient group. In the meantime, we hope this landscape analysis and the previously published guidelines will encourage consistency across the FUS-IO field.