Abstract 6087: Evaluation of intra-tumor heterogeneity by single-cell copy number profiling of circulating multiple myeloma cells using Shannon index

Abstract Tumors develop through an evolutionary process in which genomic lesions accumulate in different coexisting subclones leading to intra-tumor heterogeneity (ITH). ITH allows the tumor to adapt to microenvironments and to resist therapies and has been shown to be a prognostic marker. In this work we show the characterization of ITH in Multiple Myeloma (MM) at single cell resolution from a pool of Circulating Multiple Myeloma Cells (CMMCs) and we study the relationship between number of sampled cells and diversity detected. Peripheral blood was collected from 3 patients affected by MM. Using CellSearch® system, blood was enriched for target CMMCs, with immuno-magnetic selection of CD138+, and immunofluorescently stained cells, positive for CD38-PE, DAPI and negative for CD45/CD19-APC, were enumerated. The samples were then analyzed and CMMCs were isolated with DEPArray platform. The DNA of each single cell (n=261) was amplified with Ampli1™ WGA kit and the WGA output was used for genome-wide single cell copy number alteration analysis with Ampli1 LowPass kit. Copy number profiling revealed from 2 to 3 coexisting subclones per patient, with minor clones size going from 6.5% to 33%. ITH was assessed by determining the Shannon index, which showed a range of values from 0.44 (low diversity) to 1.01 (high diversity) depending on source sample. We evaluated the effect of number of cells/profiles on Shannon index by bootstrapping (200 times) a number of copy number profiles ranging from 2 to the total number of profiles available per patient. Results showed that the mean Shannon index almost reaches a plateau at 15-20 cells/profiles in the case of lower diversity samples and at about 30 cells/profiles for the highest diversity sample. Moreover, as few as 10 cells allowed to differentiate low vs. high diversity samples. Cell enrichment and sorting by CellSearch and DEPArray platforms allow to quantify ITH at diversity level with high precision even from a limited number of initial single-cells and provide a promising method to objectively measure heterogeneity, as required in order to study its clinical implications. Citation Format: Alberto Ferrarini, Claudio Forcato, Valentina del Monaco, Mario Terracciano, Marianna Garonzi, Massimiliano Pellicano, Genny Buson, Francesca Fontana, Paola Tononi, Nicolo Manaresi. Evaluation of intra-tumor heterogeneity by single-cell copy number profiling of circulating multiple myeloma cells using Shannon index [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6087.