Conventional chemotherapy drugs administered at a maximum tolerated dose (MTD) remains the backbone for treating most cancers. Low-dose metronomic (LDM) chemotherapy, which utilizes lower, less toxic, doses given on a close regular basis over prolonged periods, is an alternative and better tolerated potential strategy to improve chemotherapy. LDM chemotherapy has been evaluated preclinically and clinically and has shown therapeutic benefit, in both early and advanced stage metastatic disease, especially when used as a maintenance therapy. However, knowledge about the antitumor mechanisms by which LDM chemotherapy acts remain limited. Here we characterized the effects of LDM and MTD capecitabine therapy on tumor and host cells using high-throughput systems approaches involving mass spectrometry flow cytometry and automated cell imaging followed by in vivo analyses of such therapies. An increase in myeloid and T regulatory cells and a decrease in NK and T cytotoxic cells were found in MTD-capecitabine-treated tumors compared with LDM-capecitbine-treated tumors. Plasma from MTD capecitabine-treated mice induced a more tumorigenic and metastatic profile in both breast and colon carcinoma cells than plasma from mice treated with LDM capecitabine. These results correlated, in part, with in vivo studies using models of human or mouse advanced metastatic disease, where the therapeutic advantage of MTD capecitabine was limited despite a substantial initial antitumor activity found in the primary tumor setting. Overall these results implicate a possible contribution of immunologic host effects in accounting for the therapeutic limitations of MTD compared with LDM capecitabine. Cancer Res; 76(20); 5983-93. ©2016 AACR.

Radiotherapy induces immune-related responses in cancer patients by various mechanisms. Here, we investigate the immunomodulatory role of tumor-derived microparticles (TMPs)-extracellular vesicles shed from tumor cells-following radiotherapy. We demonstrate that breast carcinoma cells exposed to radiation shed TMPs containing elevated levels of immune-modulating proteins, one of which is programmed death-ligand 1 (PD-L1). These TMPs inhibit cytotoxic T lymphocyte (CTL) activity both in vitro and in vivo, and thus promote tumor growth. Evidently, adoptive transfer of CTLs pre-cultured with TMPs from irradiated breast carcinoma cells increases tumor growth rates in mice recipients in comparison with control mice receiving CTLs pre-cultured with TMPs from untreated tumor cells. In addition, blocking the PD-1-PD-L1 axis, either genetically or pharmacologically, partially alleviates TMP-mediated inhibition of CTL activity, suggesting that the immunomodulatory effects of TMPs in response to radiotherapy is mediated, in part, by PD-L1. Overall, our findings provide mechanistic insights into the tumor immune surveillance state in response to radiotherapy and suggest a therapeutic synergy between radiotherapy and immune checkpoint inhibitors.

Multiple myeloma (MM) is a chronic progressive malignancy of plasma cells. Although treatment with the novel proteasome inhibitor, bortezomib, significantly improves patient survival, some patients fail to respond due to the development of de novo resistance. We have previously shown that cytotoxic drugs can induce pro-tumorigenic host-mediated effects which contribute to tumour re-growth and metastasis, and thus limit anti-tumour efficacy. However, such effects and their impact on tumour cell aggressiveness have not been investigated using cytostatic agents such as bortezomib. Here we show that plasma from bortezomib-treated mice significantly increases migration, viability and proliferation of MM cells in vitro, compared to plasma from vehicle treated mice. In vivo, bortezomib induces the mobilization of pro-angiogenic bone marrow cells. Furthermore, mice treated with bortezomib and subsequently were used as recipients for an injection of MM cells succumb to MM earlier than mice treated with the vehicle. We show that bortezomib promotes pro-inflammatory macrophages which account for MM cell aggressiveness, an effect which is partially mediated by interleukin-16. Accordingly, co-inoculation of MM cells with pro-inflammatory macrophages from bortezomib-treated mice accelerates MM disease progression. Taken together, our results suggest that, in addition to the known effective anti-tumour activity of bortezomib, host-driven pro-tumorigenic effects generated in response to treatment can promote MM aggressiveness, and thus may contribute to the overall limited efficacy. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Multiple myeloma (MM) is a plasma cell neoplasia commonly treated with proteasome inhibitors such as bortezomib. Although bortezomib has demonstrated enhanced survival benefit, some patients relapse and subsequently develop resistance to such therapy. Here, we investigate the mechanisms underlying relapse and refractory MM following bortezomib treatment. We show that bortezomibexposed proinflammatory macrophages promote an enrichment of MM-tumor-initiating cells (MM-TIC) both in vitro and in vivo. These effects are regulated in part by IL1b, as blocking the IL1b axis by a pharmacologic or genetic approach abolishes bortezomib-induced MM-TIC enrichment. In MM patients treated with bortezomib, high proin-flammatory macrophages in the bone marrow negatively correlate with survival rates (HR, 1.722; 95% CI, 1.138-2.608). Furthermore, a positive correlation between proinflammatory macrophages and TICs in the bone marrow was also found. Overall, our results uncover a protumorigenic cross-talk involving proinflammatory macrophages and MM cells in response to bortezomib therapy, a process that enriches the MM-TIC population. Implications: Our findings suggest that proinflammatory macrophages in bone marrow biopsies represent a potential prognostic biomarker for acquired MM resistance to bortezomib therapy.

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