A genetic mosaic mouse model illuminates the pre-malignant progression of basal-like breast cancer

Basal-like breast cancer (BLBC) is highly aggressive, and often characterized by BRCA1 and p53 deficiency. Although conventional mouse models enabled the investigation of BLBC at malignant stages, its initiation and pre-malignant progression remain understudied. Here, we leveraged a mouse genetic system known as mosaic analysis with double markers (MADM) to study BLBC initiation by generating rare GFP+Brca1, p53-deficient mammary cells alongside RFP+ wild-type sibling cells. After confirming the close resemblance of mammary tumors arising in this model to human BLBC at both transcriptomic and genomic levels, we focused our studies on the pre-malignant progression of BLBC. Initiated GFP+ mutant cells showed a stepwise pre-malignant progression trajectory from focal expansion to hyper-alveolarization and then to micro-invasion. Furthermore, despite morphological similarities to alveoli, hyper-alveolarized structures actually originate from ductal cells based on twin-spot analysis of GFP-RFP sibling cells. Finally, luminal-to-basal transition occurred exclusively in cells that have progressed to micro-invasive lesions. Our MADM model provides excellent spatiotemporal resolution to illuminate the pre-malignant progression of BLBC, and should enable future studies on early detection and prevention for this cancer.

Dichotomous ovarian cancer-initiating potential of Pax8+ cells revealed by a mouse genetic mosaic model

Different cellular compartments within a tissue present distinct cancer-initiating capacities. Current approaches to dissect such heterogeneity require cell-type-specific genetic tools based on a well-understood lineage hierarchy, which are lacking for many tissues. Here, we circumvented this hurdle and revealed the dichotomous capacity of fallopian tube Pax8+ cells in initiating ovarian cancer, utilizing a mouse genetic system that stochastically generates rare GFP-labeled mutant cells. Through clonal analysis and spatial profiling, we determined that only clones founded by rare, stem/progenitor-like Pax8+ cells can expand on acquiring oncogenic mutations whereas vast majority of clones stall immediately. Furthermore, expanded mutant clones undergo further attrition: many turn quiescent shortly after the initial expansion, whereas others sustain proliferation and manifest a bias toward Pax8+ fate, underlying early pathogenesis. Our study showcases the power of genetic mosaic system-based clonal analysis for revealing cellular heterogeneity of cancer-initiating capacity in tissues with limited prior knowledge of lineage hierarchy.

A genetic mosaic mouse model illuminates the pre-malignant progression of basal-like breast cancer

Basal-like breast cancer is an aggressive breast cancer subtype, often characterized by a deficiency in BRCA1 function and concomitant loss of p53 . While conventional mouse models enable the investigation of its malignant stages, one that reveals its initiation and pre-malignant progression is lacking. Here, we leveraged a mouse genetic system known as M osaic A nalysis with D ouble M arkers (MADM) to generate rare GFP-labeled Brca1 , p53 -deficient cells alongside RFP+ wildtype sibling cells in the mammary gland. The mosaicism resembles the sporadic initiation of human cancer and enables spatially resolved analysis of mutant cells in comparison to paired wildtype sibling cells. Mammary tumors arising in the model show transcriptomic and genomic characteristics similar to human basal-like breast cancer. Analysis of GFP+ mutant cells at interval time points before malignancy revealed a stepwise progression of lesions from focal expansion to hyper-alveolarization and then to micro-invasion. These stereotyped morphologies indicate the pre-malignant stage irrespective of the time point at which it is observed. Paired analysis of GFP-RFP siblings during focal expansion suggested that hyper-alveolarized structures originate from ductal rather than alveolar cells, despite their morphological similarities to alveoli. Evidence for luminal-to-basal transition at the pre-malignant stages was restricted to cells that had escaped hyper-alveoli and progressed to micro-invasive lesions. Our MADM-based mouse model presents a useful tool for studying the pre-malignancy of basal-like breast cancer.

Summary statement

A mouse model recapitulates the process of human basal-like breast tumorigenesis initiated from sporadic Brca1, p53 -deficient cells, empowering spatially-resolved analysis of mutant cells during pre-malignant progression.

Anti-tumor and immune modulating activity of T cell induced tumor-targeting effectors (TITE)

Adoptive transfer of Bispecific antibody Armed activated T cells (BATs) showed promising anti-tumor activity in clinical trials in solid tumors. The cytotoxic activity of BATs occurs upon engagement with tumor cells via the bispecific antibody (BiAb) bridge, which stimulates BATs to release cytotoxic molecules, cytokines, chemokines, and other signaling molecules extracellularly. We hypothesized that the release of BATs Induced Tumor-Targeting Effectors (TITE) by this complex interaction of T cells, bispecific antibody, and tumor cells may serve as a potent anti-tumor and immune-activating immunotherapeutic approach. In a 3D tumorsphere model, TITE showed potent cytotoxic activity against multiple breast cancer cell lines compared to control conditioned media (CM): Tumor-CM (T-CM), BATs-CM (B-CM), BiAb Armed PBMC-CM (BAP-CM) or PBMC-CM (P-CM). Multiplex cytokine analysis showed high levels of Th₁ cytokines and chemokines; phospho-protein signaling array data suggest that the prominent JAK1/STAT1 pathway may be responsible for the induction and release of Th₁ cytokines/chemokines in TITE. In xenograft breast cancer models, IV injections of 10× concentrated TITE (3×/week for 3 weeks; 150 μl TITE/injection) was able to inhibit tumor growth significantly (ICR/scid, p < 0.003; NSG p < 0.008) compared to the control mice. We tested the key components of the TITE for immune activating and anti-tumor activity individually and in combinations, the combination of IFN-γ, TNF-α and MIP-1β recapitulates the key activities of the TITE. In summary, master mix of active components of BATs-Tumor complex-derived TITE can provide a clinically controllable cell-free platform to target various tumor types regardless of the heterogeneous nature of the tumor cells and mutational tumor.

Abstract 5036: Induction of highly efficacious anti-tumor activity and modulation of tumor microenvironment: Cell-free off the shelf therapeutic modality

Adoptive transfer of Bispecific antibody Armed activated T cells (BATs) show promising anti-tumor activity in clinical trials in solid tumors. The cytotoxic activity of BATs occur upon engagement with tumor cells via the bispecific antibody bridge which stimulates BATs to release not only the lytic and cytotoxic molecules (perforin/granzyme) but also cytokines, chemokines and other signaling molecules extracellularly. We hypothesized that the release of extracellular soluble factors by this complex interaction of T cells, bispecific antibody, and tumor cells may serve as a potent anti-tumor and immune activating conditioned media (CM). In a 3D tumorsphere model, tumor+BATs-CM (n=10) showed potent cytotoxicity (p&lt;0.001) against multiple breast (MDA-MB-231, BT-20, SK-BR-3 and MCF-7) and other cancer cell lines (p&lt;0.001) compared to control tumor-CM or BATs-CM. Tumor+BATs-CM (n=6) was able to reduce the proportion of CD44hi/CD24lo cancer stem like cells to 0.7% compared to 4.9% in control CM. The addition of tumor+BATs-CM decreased the proportions of T regulatory cells (5% to 1.1%; p&lt;0.02) and myeloid derived suppressor cells (3.8% to 1.2%; p&lt;0.03), but increased activation and proliferation of effector T cells in 3D cultures compared to control CM (n=3). Size based CM factionation showed that most activity is retained in the &lt;50kDa but &gt;10kDa fraction. Multiplex analysis showed high levels of IL-2, IL-15, IFN-γ, TNF-α, GM-CSF, granszyme B (GZB), IL-13, MIP-1β, IP-10, MIG and RANTES. These factors are likely responsible for the cytolytic and immune activating effects. Phospho-specific signaling protein arrays showed enhanced JAK1/STAT-1/STAT-5A, Rac/cdc42/STIM-1) pathways in tumor+BATs-CM (n=3). Exosomal microRNA (miR) in tumor+BAT-CM showed higher expression of several miRs that are associated with T cell function and activation compared to control CM (n=2). Simulations using cocktails of multiple cytokines were done to test anti-tumor activity, IFN-γ/TNF-α/GZB showed potent cytotoxicity directed at breast (58-78%) and pancreatic cancer (50-72%) cell lines compared to 45-65%, 20-27%, 18-25% with IFN-γ, TNF-α and GZB individually, respectively. In a xenograft breast cancer model, IV and intra-tumoral injections of 10x concentrated tumor+BAT-CM (3x/week for 4 weeks;150μl CM/injection) was able to inhibit tumor growth significantly (p&lt;0.01) compared to the control CM treated mice (n=10 mice/group). Therapeutic advantages of CM include: 1) a ready off-the-shelf product; 2) a decrease in regulatory and manufacturing costs. In summary, BATs-Tumor complex derived CM provides a clinically controllable cell-free platform to target various tumor types with diverse anti-cancer immune activating mediators regardless of the heterogeneous nature of the tumor cells and mutational burden as a novel and potent off-the-shelf therapeutic modality.

Citation Format: Archana Thakur, SriVidya Yarlagadda, Kyungmin Ji, Dana L. Schalk, Johnson Ung, Edwin T. Bliemeister, Amro Aboukameel, Eli Casarez, Bonnie F. Sloane, Lawrence G. Lum. Induction of highly efficacious anti-tumor activity and modulation of tumor microenvironment: Cell-free off the shelf therapeutic modality [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5036.

Effects of micronutrients on metal toxicity

There is growing evidence that micronutrient intake has a significant effect on the toxicity and carcinogenesis caused by various chemicals. This paper examines the effect of micronutrient status on the toxicity of four nonessential metals: cadmium, lead, mercury, and arsenic. Unfortunately, few studies have directly examined the effect of dietary deficiency or supplementation on metal toxicity. More commonly, the effect of dietary alteration must be deduced from the results of mechanistic studies. We have chosen to separate the effect of micronutrients on toxic metals into three classes: interaction between essential micronutrients and toxic metals during uptake, binding, and excretion; influence of micronutrients on the metabolism of toxic metals; and effect of micronutrients on secondary toxic effects of metals. Based on data from mechanistic studies, the ability of micronutrients to modulate the toxicity of metals is indisputable. Micronutrients interact with toxic metals at several points in the body: absorption and excretion of toxic metals; transport of metals in the body; binding to target proteins; metabolism and sequestration of toxic metals; and finally, in secondary mechanisms of toxicity such as oxidative stress. Therefore, people eating a diet deficient in micronutrients will be predisposed to toxicity from nonessential metals.