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Female mice transgenic for the rat proto-oncogene c-erb-B2, under control of the mouse mammary tumor virus (MMTV) promoter (neuN), spontaneously develop metastatic mammary carcinomas. The development of these mammary tumors is associated with increased number of GR-1(+)CD11b(+) myeloid derived suppressor cells (MDSCs) in the peripheral blood (PB), spleen and tumor. We report a complex relationship between tumor growth, MDSCs and immune regulatory molecules in non-mutated neu transgenic mice on a FVB background (FVB-neuN). The first and second tumors in FVB-neuN mice develop at a median of 265 (147-579) and 329 (161-523) days, respectively, resulting in a median survival time (MST) of 432 (201 to >500) days. During tumor growth, significantly increased number of MDSCs is observed in the PB and spleen, as well as, in infiltrating the mammary tumors. Our results demonstrate a direct correlation between tumor size and the number of MDSCs infiltrating the tumor and an inverse relationship between the frequency of CD4(+) T-cells and MDSCs in the spleen. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assessment of enzyme and cytokine transcript levels in the spleen, tumor, tumor-infiltrating non-parenchymal cells (NPCs) and mammary glands revealed a significant increase in transcript levels from grossly normal mammary glands and tumor-infiltrating NPCs during tumor progression. Tumor NPCs, as compared to spleen cells from wild-type (w/t) mice, expressed significantly higher levels of arginase-1 (ARG-1), nitric oxide synthase (NOS-2), vascular endothelial growth factor (VEGF-A) and significantly lower levels of interferon (IFN)-gamma, interleukin (IL)-2 and fms-like tyrosine kinase-3 ligand (Flt3L) transcript levels. Transcript levels in the spleens of tumor-bearing (TB) mice also differed from normal mice, although to a lesser extent than transcript levels from tumor-infiltrating NPCs. Furthermore, both spleen cells and NPCs from TB mice, but not control mice, suppressed alloantigen responses by syngeneic control spleen cells. Correlative studies revealed that the number of MDSCs in the spleen was directly associated with granulocyte colony stimulating factor (G-CSF) transcript levels in the spleen; while the number of MDSCs in the tumors was directly correlated with splenic granulocyte macrophage stimulating factor (GM-CSF) transcript levels, tumor volume and tumor cell number. Together our results support a role for MDSCs in tumor initiation and progressive, T-cell depression and loss of function provide evidence which support multiple mechanisms of MDSC expansion in a site-dependent manner.

The nontuberculous mycobacterial (NTM) pathogens, M. avium complex (MAC) and M. abscessus, can result in severe pulmonary infections. Current antibiotics confront significant challenges for treatment of these NTM infections due to emerging multidrug-resistance. Thus, development of new antibiotics targeted against these agents is needed. We examined the inhibitory activities of Ga(NO), GaCl, gallium meso-tetraphenylporphyrine (GaTP), and gallium nanoparticles (GaNP) against intra- and extracellular M. avium and M. abscessus. GaTP, an analogue of natural heme, inhibited growth of both M. avium and M. abscessus with MICs in Fe-free 7H9 media of 0.5 and 2 μg/mL, respectively. GaTP was more active than Ga(NO) and GaCl. Ga(NO) and GaCl were not as active in Fe-rich media compared to Fe-free media. However, GaTP was much less impacted by exogenous Fe, with MICs against M. avium and M. abscessus of 2 and 4 μg/mL, respectively, in 7H9 OADC media (Fe rich). Confocal microscopy showed that GaNP penetrates the M. avium cell wall. As assessed by determining colony forming units, GaNP inhibited the growth of NTM growing in THP-1 macrophages up to 15 days after drug-loading of the cells, confirming a prolonged growth inhibitory activity of the GaNP. Biodistribution studies of GaNP conducted in mice showed that intraperitoneal injection is more effective than intramuscular injection in delivering Ga(III) into lung tissue. GaTP exhibits potential as a lead compound for development of anti-NTM agents that target heme-bound iron uptake mechanisms by mycobacteria and inhibit growth by disrupting mycobacterial iron acquisition/utilization.