Progress of oncolytic viruses in sarcomas

Translation of oncolytic viruses in sarcoma

Sarcomas are a rare and highly diverse group of malignancies of mesenchymal origin. While sarcomas are generally considered resistant to immunotherapy, recent studies indicate subtype-specific differences in clinical response to checkpoint inhibitors (CPIs) that are associated with distinct immune phenotypes present in sarcoma subtypes. Oncolytic viruses (OVs) are designed to selectively infect and kill tumor cells and induce intratumoral immune infiltration, enhancing immunogenicity and thereby sensitizing tumors to immunotherapy. Herein we review the accumulated clinical data evaluating OVs in sarcoma. Small numbers of patients with sarcoma were enrolled in early-stage OV trials as part of larger solid tumor cohorts demonstrating safety but providing limited insight into the biological effects due to the low patient numbers and lack of histologic grouping. Several recent studies have investigated talimogene laherparepvec (T-VEC), an approved oncolytic herpes simplex virus (HSV-1), in combination therapy regimens in sarcoma patient cohorts. These studies have shown promising responses in heavily pre-treated and immunotherapy-resistant patients associated with increased intratumoral immune infiltration. As new and more potent OVs enter the clinical arena, prospective evaluation in subtype-specific cohorts with correlative studies to define biomarkers of response will be critical to advancing this promising approach for sarcoma therapy.

Role of Virus-Directed Therapy in Soft Tissue Sarcoma

OPINION STATEMENT

Bone and soft tissue sarcoma are rare cancers of mesenchymal origin with the characteristics of heterogeneity and diversity that account for less than 1% of solid malignant cancers. Conventional chemotherapy remains standard of care with response rates of 10-15% that are usually dependent on histologic subtype as some subtypes are chemotherapy resistant. There remains a large unmet clinical need for new and novel options promoting the development of promising therapeutic options such as immunotherapy. With more than 80 different subtypes, the heterogeneity of sarcoma requires thoughtful clinical trial design. In the sarcoma field, recent breakthroughs have occurred in the context of histology-specific approach based on underlying tumor biology. To that end, immunotherapy approaches will need to take a similar approach. Oncolytic viruses (OVs) have emerged as a promising treatment for many solid tumors and shown encouraging results in sarcoma. This review mainly focuses on collective clinical data highlighting the role of OVs as immunotherapy being used in soft tissue sarcoma (STS) and bone sarcomas. Combining OVs with T cell-activating checkpoint inhibition, adoptive cell therapy or targeted therapies may yield increased potency, improve antitumor efficacy of oncolytic virotherapy, and offer a new prospect for the treatment of sarcoma.

Is immunotherapy in the future of therapeutic management of sarcomas?

Sarcomas are rare, ubiquitous and heterogeneous tumors usually treated with surgery, chemotherapy, target therapy, and radiotherapy. However, 25-50% of patients experience local relapses and/or distant metastases after chemotherapy with an overall survival about 12-18 months. Recently, immuno-therapy has revolutionized the cancer treatments with initial indications for non-small cell lung cancer (NSCLC) and melanoma (immune-checkpoint inhibitors).Here, we provide a narrative review on the topic as well as a critical description of the currently available trials on immunotherapy treatments in patients with sarcoma. Given the promising results obtained with anti-PD-1 monoclonal antibodies (pembrolizumab and nivolumab) and CAR-T cells, we strongly believe that these new immunotherapeutic approaches, along with an innovative characterization of tumor genetics, will provide an exciting opportunity to ameliorate the therapeutic management of sarcomas.

Will Next-Generation Immunotherapy Overcome the Intrinsic Diversity and Low Immunogenicity of Sarcomas to Improve Clinical Benefit?

Sarcomas are a rare type of a heterogeneous group of tumours arising from mesenchymal cells that form connective tissues. Surgery is the most common treatment for these tumours, but additional neoadjuvant or adjuvant chemotherapy or radiation therapies may be necessary. Unfortunately, a significant proportion of patients treated with conventional therapies will develop metastatic disease that is resistant to therapies. Currently, there is an urgent need to develop more effective and durable therapies for the treatment of sarcomas. In recent years immunotherapies have revolutionised the treatment of a variety of cancers by restoring patient anti-tumour immune responses or through the adoptive infusion of immune effectors able to kill and eliminate malignant cells. The clinicopathologic and genetic heterogeneity of sarcomas, together with the generally low burden of somatic mutations potentially generating neoantigens, are currently limited to broad application of immunotherapy for patients with sarcomas. Nevertheless, a better understanding of the microenvironmental factors hampering the efficacy of immunotherapy and the identification of new and suitable therapeutic targets may help to overcome current limitations. Moreover, the recent advances in the development of immunotherapies based on the direct exploitation or targeting of T cells and/or NK cells may offer new opportunities to improve the treatment of sarcomas, particularly those showing recurrence or resistance to standard of care treatments.

Preclinical Testing of an Oncolytic Parvovirus in Ewing Sarcoma: Protoparvovirus H-1 Induces Apoptosis and Lytic Infection In Vitro but Fails to Improve Survival In Vivo

About 70% of all Ewing sarcoma (EWS) patients are diagnosed under the age of 20 years. Over the last decades little progress has been made towards finding effective treatment approaches for primarily metastasized or refractory Ewing sarcoma in young patients. Here, in the context of the search for novel therapeutic options, the potential of oncolytic protoparvovirus H-1 (H-1PV) to treat Ewing sarcoma was evaluated, its safety having been proven previously tested in adult cancer patients and its oncolytic efficacy demonstrated on osteosarcoma cell cultures. The effects of viral infection were tested in vitro on four human Ewing sarcoma cell lines. Notably evaluated were effects of the virus on the cell cycle and its replication efficiency. Within 24 h after infection, the synthesis of viral proteins was induced. Efficient H-1PV replication was confirmed in all four Ewing sarcoma cell lines. The cytotoxicity of the virus was determined on the basis of cytopathic effects, cell viability, and cell lysis. These in vitro experiments revealed efficient killing of Ewing sarcoma cells by H-1PV at a multiplicity of infection between 0.1 and 5 plaque forming units (PFU)/cell. In two of the four tested cell lines, significant induction of apoptosis by H-1PV was observed. H-1PV thus meets all the in vitro criteria for a virus to be oncolytic towards Ewing sarcoma. In the first xenograft experiments, however, although an antiproliferative effect of intratumoral H-1PV injection was observed, no significant improvement of animal survival was noted. Future projects aiming to validate parvovirotherapy for the treatment of pediatric Ewing sarcoma should focus on combinatorial treatments and will require the use of patient-derived xenografts and immunocompetent syngeneic animal models.

Progress and opportunities for immune therapeutics in osteosarcoma

Survival outcomes for osteosarcoma have plateaued since the 1980s, and patients with relapsed or refractory disease have a particularly dismal outcome. Treatment options for these patients are limited primarily due to the paucity of effective therapeutics. Immune therapies such as tumor vaccines and traditional antigen-targeted monoclonal antibodies have had limited success in solid tumors. The recent discovery of novel immune checkpoint blockade strategies and their success in adult cancers has revitalized the use of immunotherapy strategies for the treatment of solid tumors. This paper summarizes existing data supporting the use of immune therapies in osteosarcoma and the progress of this class of drugs in osteosarcoma therapy.

Innate immune defense defines susceptibility of sarcoma cells to measles vaccine virus-based oncolysis

The oncolytic potential of measles vaccine virus (MeV) has been demonstrated in several tumor entities. Here, we investigated the susceptibility of eight sarcoma cell lines to MeV-mediated oncolysis and found five to be susceptible, whereas three proved to be resistant. In the MeV-resistant cell lines, we often observed an inhibition of viral replication along with a strong upregulation of the intracellular virus-sensing molecule RIG-I and of the interferon (IFN)-stimulated gene IFIT1. Not only expression of IFIT1 but also phosphorylation of IFN-stimulated Stat1 took place rapidly and were found to be persistent over time. In contrast, susceptible cell lines showed a much weaker, delayed, or completely missing expression of IFIT1 as well as a delayed or only transient phosphorylation of Stat1, whereas exogenic stimulation with beta interferon (IFN-β) resulted in a comparable profound activation of Stat1 and expression of IFIT1 in all cell lines. Pretreatment with IFN-β rendered three of the susceptible cell lines more resistant to MeV-mediated oncolysis. These data suggest that differences in the innate immune defense often account for different degrees of susceptibility of sarcoma cell lines to MeV-mediated oncolysis. From a therapeutic perspective, we were able to overcome resistance to MeV by increasing the multiplicity of infection (MOI) and by addition of the prodrug 5-fluorocytosine (FC), thereby exploiting the suicide gene function of virotherapeutic vector MeV-SCD armed with the SCD fusion protein, which consists of yeast cytosine deaminase and yeast uracil phosphoribosyltransferase.