Using a 3D co-culture model, we identified significant sub-type-specific changes in gene expression, metabolic, and therapeutic sensitivity profiles of breast cancer cells in contact with cancer-associated fibroblasts (CAFs). CAF-induced gene expression signatures predicted clinical outcome and immune-related differences in the microenvironment. We found that fibroblasts strongly protect carcinoma cells from lapatinib, attributable to its reduced accumulation in carcinoma cells and an elevated apoptotic threshold. Fibroblasts from normal breast tissues and stromal cultures of brain metastases of breast cancer had similar effects as CAFs. Using synthetic lethality approaches, we identified molecular pathways whose inhibition sensitizes HER2+ breast cancer cells to lapatinib both in vitro and in vivo including JAK2/STAT3 and hyaluronic acid. Neoadjuvant lapatinib therapy in HER2+ breast tumors lead to a significant increase of phospho-STAT3+ cancer cells and a decrease in the spatial proximity of proliferating (Ki67+) cells to CAFs impacting therapeutic responses. Our studies identify CAF-induced physiologically and clinically relevant changes in cancer cells and offer novel approaches for overcoming microenvironment-mediated therapeutic resistance.

Our understanding of cancer has greatly advanced since Nordling [Nordling CO (1953) Br J Cancer 7(1):68-72] and Armitage and Doll [Armitage P, Doll R (1954) Br J Cancer 8(1):1-12] put forth the multistage model of carcinogenesis. However, a number of observations remain poorly understood from the standpoint of this paradigm in its contemporary state. These observations include the similar age-dependent exponential rise in incidence of cancers originating from stem/progenitor pools differing drastically in size, age-dependent cell division profiles, and compartmentalization. This common incidence pattern is characteristic of cancers requiring different numbers of oncogenic mutations, and it scales to very divergent life spans of mammalian species. Also, bigger mammals with larger underlying stem cell pools are not proportionally more prone to cancer, an observation known as Peto's paradox. Here, we present a number of factors beyond the occurrence of oncogenic mutations that are unaccounted for in the current model of cancer development but should have significant impacts on cancer incidence. Furthermore, we propose a revision of the current understanding for how oncogenic and other functional somatic mutations affect cellular fitness. We present evidence, substantiated by evolutionary theory, demonstrating that fitness is a dynamic environment-dependent property of a phenotype and that oncogenic mutations should have vastly different fitness effects on somatic cells dependent on the tissue microenvironment in an age-dependent manner. Combined, this evidence provides a firm basis for understanding the age-dependent incidence of cancers as driven by age-altered systemic processes regulated above the cell level. somatic evolution | cancer | aging | oncogenic mutations | fitness C ancer is believed to develop as a multistage disease driven by oncogenic mutations (also called driver mutations) that occur in stem cells (SCs) or progenitor cells. Each such mutation is thought to confer to the recipient cell a certain fitness advantage over other cells in a competitive stem/progenitor pool, leading to proliferation of the cell's progeny (clone) in the pool. The successive clonal expansions driven by oncogenic mutations multiply the number of cells representing an oncogenic mutation-bearing clone, and thus increase the odds of the occurrence of the subsequent driver mutations in the premalignant genetic background. In this way, carcinogenesis is viewed as a Darwinian process of successive rounds of selection leading to the formation of a malignant cell phenotype produced by a certain number of driver mutations (1-7). SC fitness, being the ability of a SC of a particular genotype/epigenotype to be maintained, expand, or contract within the SC compartment, is thus a central phenomenon determining somatic evolution. Because cancer incidence increases exponentially with age, successive clonal expansions are thought to follow the occurrence of oncogenic mutations and increase the likelihood of subsequent drivers over time, su...

In vivo–based functional genomic screen identifies DDR2 as an important determinant of efficacy of anti–PD-1 immunotherapy.

Activating mutations in FMS-like tyrosine kinase 3 (FLT3) are common in acute myeloid leukemia (AML) and drive leukemic cell growth and survival. Although FLT3 inhibitors have shown considerable promise for the treatment of AML, they ultimately fail to achieve long-term remissions as monotherapy. To identify genetic targets that can sensitize AML cells to killing by FLT3 inhibitors, we performed a genome-wide RNA interference (RNAi)-based screen that identified ATM (ataxia telangiectasia mutated) as being synthetic lethal with FLT3 inhibitor therapy. We found that inactivating ATM or its downstream effector glucose 6-phosphate dehydrogenase (G6PD) sensitizes AML cells to FLT3 inhibitor induced apoptosis. Examination of the cellular metabolome showed that FLT3 inhibition by itself causes profound alterations in central carbon metabolism, resulting in impaired production of the antioxidant factor glutathione, which was further impaired by ATM or G6PD inactivation. Moreover, FLT3 inhibition elicited severe mitochondrial oxidative stress that is causative in apoptosis and is exacerbated by ATM/G6PD inhibition. The use of an agent that intensifies mitochondrial oxidative stress in combination with a FLT3 inhibitor augmented elimination of AML cells in vitro and in vivo, revealing a therapeutic strategy for the improved treatment of FLT3 mutated AML.A cute myeloid leukemia (AML) is a hematological cancer that is characterized by the aberrant growth of myeloid progenitor cells with a block in cellular differentiation. AML is the most common adult acute leukemia and accounts for ∼20% of childhood leukemias. Although frontline treatment of AML with cytotoxic chemotherapy achieves high remission rates, 75-80% of patients will either not respond to or will relapse after initial therapy, and most patients will die of their disease (1, 2). Thus, more effective and less toxic therapies for AML are required. The promise of molecularly targeted cancer therapies has generated much excitement with the remarkable clinical success of the small molecule tyrosine kinase inhibitors (TKIs) targeting the oncogenic kinase BCR-ABL for the treatment of chronic myeloid leukemia (3). However, targeted approaches for the treatment of AML have not yet yielded major successes.In AML, aberrant signal transduction drives the proliferation and survival of leukemic cells. Activated signal transduction occurs through genetic alterations of signaling molecules such as FLT3, KIT, PTPN11, and members of the RAS family (4, 5). Given the successful development and utilization of numerous TKIs, the FLT3 receptor tyrosine kinase has emerged as a promising target for the treatment of AML. Indeed, activating mutations in FLT3 are one of the most frequently observed genetic defects in AML and are comprised predominantly of internal tandem duplication (ITD) mutations in the juxtamembrane domain (6). FLT3-ITD mutations are associated with poor prognosis, including increased relapse rate, decreased disease-free survival, and poor overall survival (5,7,8). The cl...

The Armitage-Doll multi-stage model of carcinogenesis tremendously refocused cancer science by postulating that carcinogenesis is driven by a sequence of genetic changes in cells. Age-dependent cancer incidence thus has been explained in terms of the time necessary for oncogenic mutations to occur. While the multi-step nature of cancer evolution is well-supported by evidence, the mutation-centric theory is unable to explain a number of phenomena, such as the disproportion between cancer frequency and animal body size or the scaling of cancer incidence to animal lifespan. In this paper, we present a theoretical review of the current paradigm and discuss some fundamental evolutionary theory postulates that explain why cancer incidence is a function of lifespan and physiological, not chronological, aging.