Chatila, W. | bioRxiv Science

bioRxiv2023

Distinct tumor architectures for metastatic colonization of the brain

Brain metastasis is a dismal cancer complication, hinging on the initial survival and outgrowth of disseminated cancer cells. To understand these crucial early stages of colonization, we investigated two prevalent sources of cerebral relapse, triple-negative (TNBC) and HER2+ breast cancer (HER2BC). We show that these tumor types colonize the brain aggressively, yet with distinct tumor architectures, stromal interfaces, and autocrine growth programs. TNBC forms perivascular sheaths with diffusive contact with astrocytes and microglia. In contrast, HER2BC forms compact spheroids prompted by autonomous extracellular matrix components and segregating stromal cells to their periphery. Single-cell transcriptomic dissection reveals canonical Alzheimers disease-associated microglia (DAM) responses. Differential engagement of tumor-DAM signaling through the receptor AXL suggests specific pro-metastatic functions of the tumor architecture in both TNBC perivascular and HER2BC spheroidal colonies. The distinct spatial features of these two highly efficient modes of brain colonization have relevance for leveraging the stroma to treat brain metastasis.

cancer biology↗

bioRxiv2022

Oncogenic IDH mutations increase heterochromatin-related replication stress without impacting tumor mutation burden

Oncogenic mutations in the metabolic enzyme isocitrate dehydrogenase 1 and 2 (IDH1/2) have been found in a number of liquid and solid tumors. Their pathogenic mechanism of action involves production of 2-hydroxyglutarate (2HG), an oncometabolite that acts in part by inhibiting members of a family of dioxygenases that modulate chromatin dynamics. Recent work has suggested that mutant IDH (mIDH) and 2HG also impact sensitivity to inhibitors of poly-ADP ribose polymerases (PARP) but the molecular basis for this sensitivity is unclear. Unlike PARP inhibitor-sensitive BRCA1/2 tumors which exhibit impaired homologous recombination, IDH-mutant tumors have a silent mutational profile and lack mutational signatures associated with impaired homologous recombination. Instead, 2HG-producing IDH mutations lead to heterochromatin-dependent slowing of DNA replication and increased replication stress, resulting in DNA double strand breaks. This replicative stress manifests as replication fork slowing but the breaks are repaired without a significant increase in the cellular mutation burden. Faithful resolution of replicative stress in IDH-mutant cells is dependent on poly-ADP ribosylation. Treatment with PARP inhibitors restores replication fork speed but results in incomplete repair of DNA breaks. These findings provide evidence of a requirement for PARP in the replication of heterochromatin and further validate PARP as a potential therapeutic target in IDH-mutant tumors.

cancer biology↗