Dr Annie SCHMIDT (INSERM Nice)

Osteosarcoma (OS) is the most common malignant bone tumor in children and adolescents with 150 new cases per year. Thanks to the progress of chemotherapy coupled with the optimization of surgical techniques, the cure rate reaches 60 to 70% for patients with non-metastatic osteosarcoma.

Unfortunately these tumors have a very strong propensity to metastasize, especially in the lungs. When diagnosing bone, lung metastases are already present in more than 20% of patients. Metastases indicate the severity of the disease. Indeed, patients with metastatic or recurrent bone respond poorly to current treatments and the cure rate in these patients has remained very low and unchanged for 30 years. It is therefore essential and essential to develop effective treatments for all these situations of therapeutic impasse and also to improve the quality of life of these young patients during and after the treatments.

Recognizing and eliminating cancer cells represent physiological functions of the immune system which are performed by specialized cells of the organism, leukocytes and in particular the population of T lymphocytes. The state of activation of T lymphocytes is permanently dependent on the balances between activating and inhibiting signals called immune checkpoints (activators or inhibitors). These immune checkpoints, which function as security locks, are essential both for optimizing the activation of T lymphocytes (activator checkpoints) and for preventing the risk of the immune system running away (inhibitory checkpoints). Cancer cells have developed multiple strategies to escape the immune system and in particular to deregulate inhibitory immune checkpoints in order to prevent the destruction of tumor cells by the immune system. The pharmaceutical industry has marketed antibodies and / or small chemical molecules which are capable of modulating some of these immune checkpoints and in fact making it possible to optimize the response of the immune system directed against the tumor.

Recent work in immuno-oncology has marked a major turning point in the understanding of the defense mechanisms of tumors against the immune system and have highlighted immune checkpoints as potential new therapeutic targets for antitumor. Treatments using this strategy in patients with metastatic melanoma have given extraordinary results in terms of cure and give new hope for other cancers. Today, therapies targeting immune checkpoints are given in many cancers, and are in clinical trial phase in osteosarcoma. The first results do not currently allow us to offer an effective treatment, in particular for the most aggressive osteosarcomas. It is therefore necessary to continue research research aimed at better understanding the interactions between cancer cells and immune cells involved in the progression of osteosarcomas.

The project funded by Eva Pour la vie (2017-2018, € 30,000) fits into this context. Its objective was to evaluate, in a preclinical model of pulmonary metastases from osteosarcoma, the effects of treatments combining two complementary immunotherapy strategies, one aimed at promoting selective recruitment of leukocytes in the tumor, the other aimed at neutralize 4 inhibitory immune checkpoints namely CTLA4, PD1, PDL1 and TIM3. This project consisted in testing different combinations of treatments with antibodies blocking inhibitory checkpoints (Ab anti-checkpoints) in the presence of fractalkine (FKN) allowing the recruitment of lymphocytes in the tumor.

Initially, the work carried out thanks to Eva pour la vie's first funding showed that the treatment of mice with FKN alone slowed the progression of pulmonary metastases from osteosarcoma by 40 to 60%, but over time , the animals eventually escaped treatment with FKN. However even though the mice metastasized in the presence of FKN, the mice were objectively in better shape than the untreated mice.

Regarding the treatments with blocking Ab at the PD1, PDL1, CTLA4 or TIM-3 checkpoints, the effects were on the one hand modest (at best a reduction of 5 to 30% in the progression of metastases) and on the other hand always lower. to those obtained with the FKN alone. In addition, we did not observe any cumulative effects of treatments combining anti-checkpoint Ab and FKN. The transcriptomic analysis of the tumors obtained in the different treatment situations (FKN + an inhibitory anti checkpoint Ab) indicated to us that the FKN had indeed enabled the recruitment of lymphocytes in the tumors but, and moreover, while certain obstacles had been lifted. by the Ac anti checkpoints, others were still active. Secondly, we associated treatment with FKN with several inhibitory anti-checkpoint antibodies. The results are disappointing since in all the combinations tested there were no more significant effects in terms of tumor reduction than FKN alone. Against all expectations, the transcriptomic analysis nevertheless revealed to us that in certain combinations, the 4 inhibitory checkpoints tested were neutralized.

The antibodies targeting CTLA4, PD1, PDL1 and TIM3 represented the first “wave” of commercialization of anti-immune checkpoint treatments. Today, antibody treatments targeting other inhibitory immune checkpoints are commercially available and in particular GAL9, LAG3 and Vista, and in fact represent new therapeutic hopes for osteosarcoma. In addition, all of our results led us to believe that the lymphocytes which were recruited into the tumor thanks to the FKN could, perhaps and also, present a defect of activation, limiting them in their capacity to destroy, cancer cells over time. This therefore led us to reconsider the combinations of immunotherapy that could be envisaged and in particular to test combinations of treatments associating FKN with blocking antibodies of inhibitory immune checkpoints and / or with stimulating antibodies of activating immune checkpoints. This study is in progress and is entirely carried out thanks to the second financial support provided by "Eva pour la Vie" (2019-2020, € 20,000)

The ultimate goal of our project being of course to offer as quickly as possible, to patients with metastatic bone, the most effective treatment possible and with the fewest side effects.