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Accelerated single cell seeding in relapsed multiple myeloma

ABSTRACT: The malignant progression of multiple myeloma is characterized by the seeding of cancer cells in different anatomic sites followed by their clonal expansion. It has been demonstrated that this spatial evolution at varying anatomic sites is characterized by genomic heterogeneity. However, it is unclear whether each anatomic site at relapse reflects the expansion of pre-existing but previously undetected disease or secondary seeding from other sites. Furthermore, genomic evolution over time at spatially distinct sites of disease has not been investigated in a systematic manner. To address this, we interrogated 25 samples, by whole genome sequencing, collected at autopsy from 4 patients with relapsed multiple myeloma and demonstrated that each site had a unique evolutionary trajectory characterized by distinct single and complex structural variants and copy number changes. By analyzing the landscape of mutational signatures at these sites and for an additional set of 125 published whole exomes collected from 51 patients, we demonstrate the profound mutagenic effect of melphalan and platinum in relapsed multiple myeloma. Chemotherapy-related mutagenic processes are known to introduce hundreds of unique mutations in each surviving cancer cell. These mutations can be detectable by bulk sequencing only in cases of clonal expansion of a single cancer cell bearing the mutational signature linked to chemotherapy exposure thus representing a unique single-cell genomic barcode linked to a discrete time window in each patientÃ¢Â€Â™s life. We leveraged this concept to show that multiple myeloma systemic seeding is accelerated at clinical relapse and appears to be driven by the survival and subsequent expansion of a single myeloma cell following treatment with high dose melphalan therapy and autologous stem cell transplant.

PROVIDER: EGAS00001004404 | EGA |

REPOSITORIES: EGA

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Project description:Following the removal of implanted mammary tumors, nude mice develop multiple-organ metastases at late stage. The metastases may originate from the primary tumors before the resection surgery, or alternatively, from some established metastases. By multiple approaches, we have proved that bone environment could invigorate cancer cells for further dissemination. this study aims to examine if metastatic dissemination from bone to other sites occurs in natural setting of metastatic spread. We herein apply the rapidly evolving barcode system using homing guide RNA/Cas9 to trace the metastases formation in mouse. hgRNA/Cas9 is a self-targeting Crispr system which allows the mutation occurs in the DNA sequence of guide RNA. Tumor cells wer labelled with doxycycline inducible evolving barcoding system. Upon doxycycline treatment the DNA sequence of hgRNA accumulate mutations with time. The diversity of barcodes in each lesion can infer the timeing of seeding while the mutation patterns of barcodes suggest the phylogenetic correlation of metastases. Several findings were made on this study. First, at the terminal stage, multi-organ metastases are not genetically grouped according to sites of metastases. Nonnegative Matrix Factorization (NMF) analysis of mutant barcodes suggested the early disseminated metastases, which have highest level of Shannon entropy, were featured with a common cluster of mutant barcodes irrespective of their locations. Second, most metastases are potentially multiclonal as indicated by multiple clusters of independent mutant barcodes. Third, when we use Shannon entropy as an index of metastasis age , putative parent-child relationship between metastases with unique mutant barcodes clearly exemplified secondary metastatic seeding from bone to other organs. Finally, we did not observe a clear correlation between tumor burden and Shannon entropy across different metastases, suggesting that putative parental metastases might remain small after seeding further metastases.

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Accelerated single cell seeding in relapsed multiple myeloma

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