Mitochondrial DNA Mutations as Natural Barcodes for Lineage Tracing of Murine Tumor Models

Integrative genotyping of cancer and immune phenotypes by long-read sequencing

Single-cell transcriptomics has become the definitive method for classifying cell types and states, and can be augmented with genotype information to improve cell lineage identification. Due to constraints of short-read sequencing, current methods to detect natural genetic barcodes often require cumbersome primer panels and early commitment to targets. Here we devise a flexible long-read sequencing workflow and analysis pipeline, termed nanoranger, that starts from intermediate single-cell cDNA libraries to detect cell lineage-defining features, including single-nucleotide variants, fusion genes, isoforms, sequences of chimeric antigen and TCRs. Through systematic analysis of these classes of natural 'barcodes', we define the optimal targets for nanoranger, namely those loci close to the 5' end of highly expressed genes with transcript lengths shorter than 4 kB. As proof-of-concept, we apply nanoranger to longitudinal tracking of subclones of acute myeloid leukemia (AML) and describe the heterogeneous isoform landscape of thousands of marrow-infiltrating immune cells. We propose that enhanced cellular genotyping using nanoranger can improve the tracking of single-cell tumor and immune cell co-evolution.

Genotype-specific precision tumor therapy using mitochondrial DNA mutation-induced drug release system

Precise killing of tumor cells without affecting surrounding normal cells is a challenge. Mitochondrial DNA (mtDNA) mutations, a common genetic variant in cancer, can directly affect metabolic homeostasis, serving as an ideal regulatory switch for precise tumor therapy. Here, we designed a mutation-induced drug release system (MIDRS), using the single-nucleotide variation (SNV) recognition ability and trans-cleavage activity of Cas12a to convert tumor-specific mtDNA mutations into a regulatory switch for intracellular drug release, realizing precise tumor cell killing. Using Ce6 as a model drug, MIDRS enabled organelle-level photodynamic therapy, triggering innate and adaptive immunity simultaneously. In vivo evaluation showed that MIDRSMT could identify tumor tissue carrying SNVs in mtDNA in unilateral, bilateral, and heterogeneous tumor models, producing an excellent antitumor effect (~82.6%) without affecting normal cells and thus resulting in a stronger systemic antitumor immune response. Additionally, MIDRS was suitable for genotype-specific precision drug release of chemotherapeutic drugs. This strategy holds promise for mutation-specific personalized tumor treatment approaches.

Clinical and translational relevance of intratumor heterogeneity

Intratumor heterogeneity (ITH) is a driver of tumor evolution and a main cause of therapeutic resistance. Despite its importance, measures of ITH are still not incorporated into clinical practice. Consequently, standard treatment is frequently ineffective for patients with heterogeneous tumors as changes to treatment regimens are made only after recurrence and disease progression. More effective combination therapies require a mechanistic understanding of ITH and ways to assess it in clinical samples. The growth of technologies enabling the spatially intact analysis of tumors at the single-cell level and the development of sophisticated preclinical models give us hope that ITH will not simply be used as a predictor of a poor outcome but will guide treatment decisions from diagnosis through treatment.