Analysis and Implications of the Difference in Response Rates to a Treatment For Metastatic Osteosarcoma

Joseph Blattman, PhD,  Arizona State University
Recipient of the: $50,000 Sarcoma Foundation of America Research Award

Osteosarcoma is the most common childhood malignancy, with a sharp decline in survival rates upon metastasis. We have previously demonstrated administration of immune checkpoint blockade (ICB) of anti-CTLA-4/anti-PD-L1 to mice inoculated with a K7M2 metastatic osteosarcoma (mOS) cell line resulted in ~50% survival with complete tumor clearance. Differences in response rates to ICB treatment are common among patients with the same malignancy across various cancers. However, unlike inbred lab mice, human patients have diversity in genetic makeup and other factors, causing the discrepancy in ICB response to remain poorly understood. There is an urgent need to identify the cause of these discrepancies to enhance ICB effectiveness for mOS and ultimately better patient outcomes. This proposal’s specific objective is to determine biological differences among responders and non-responders to ICB for mOS to understand better what factors could increase ICB efficacy. A prospective culprit is a variance in circulating antibodies (Abs). Recent studies have characterized Ab patterns in sera by using microarrays with thousands of randomly sequenced peptides and incubating on them diluted sera. The Ab binding pattern on the microarray is termed an “immunosignature.” We have shown blood from mice, prior to inoculation with mOS or ICB, display distinct differences in immunosignatures between responders and non-responders, suggesting that the presence or absence of particular antibodies may influence the outcome of ICB. Since ICB effectiveness can differ among subjects with microbiome composition variances, even among lab mice, we hypothesize that differences in circulating Ab composition between responders and non-responders to ICB is related to microbiome composition. To test this, we will obtain blood and fecal samples from mice before inoculating with mOS and ICB treatment. Sera from pre-bleeds will be incubated on microarrays to determine immunosignatures and will be correlated with microbiome composition via sequencing of the V3 region of 16S ribosomal RNA. These investigations are relevant to the field of immunotherapy for sarcomas, as they address a troubling inconsistency in ICB effectiveness. Such studies are significant because specific Abs or other proteins could encourage or agitate ICB therapy; identifying these causes could be exploited and translated to human patients to improve ICB for mOS, having a considerable impact on cancer immunotherapy regimens. These findings serve as an innovative approach that can extend to other sarcomas treatments, as immunosignature analysis and microbiome characterization have not been previously determined for mOS and fill a critical gap in understanding ICB treatment outcomes.