The Impact of Pharmacological Targeting of Abnormal Tumor Metabolism with 3-Bromopyruvate on Dendritic Cell Mediated Tumoral Immunity

Studies have shown that tumor cells are susceptible to pharmacological targeting
of their altered glycolytic metabolism with a variety of compounds that result in
apoptosis. One such compound, 3-bromopyruvate (3-BP), has been shown to eradicate
cancer in an animal model. However, no studies have shown whether the apoptotic
fragments resulting from 3-BP treatment have the capacity to elicit an immunogenic cell
death that activates dendritic cells, the primary antigen presenting cell in the immune
system. Immunogenic cell death is critical to eliciting an effective adaptive immune
response that selectively kills additional target cells and generates immunological
memory. We demonstrated that 3-bromopyruvate induced apoptosis in a number of
different murine breast cancer cell lines, including the highly metastatic 4T1 line. The
dying tumor cells stimulated immature dendritic cells (DCs) of the immortal JAWS II
cell line to produce high levels of the pro-inflammatory cytokine IL-12, and increased their expression of key co-stimulatory molecules CD80 and CD86. The activated
dendritic cells showed increased uptake of fragments from dying tumor cells that
correlated with the increased levels of calreticulin on the surface and release of high
group motility box 1 (HMGB1) of the latter following 3-BP treatment. Additionally, the
anti-phagocytic signal CD47 present on breast cancer cells was reduced by treatment with
3-bromopyruvate when compared to the levels on untreated 4T1 cells. 3-BP treated breast
cancer cells were able to activate dendritic cells through TLR4 signaling. Signaling was
dependent on both the expression of surface calreticulin and on the extracellular release
of high mobility group box 1 protein (HMGB1) during the process of immunogenic cell
death. Killing by 3-BP was compared to mitoxantrone and doxorubicin, among the few
chemotherapeutics that induce immunogenic cell death. 3-BP killing was likewise
compared to camptothecin, a compound that fails to induce immunogenic cell death.
Importantly, 3-BP did not markedly decrease the levels of the key peptide presenting
molecule MHC I on DCs that were co-cultivated with dying tumor cells. Treatment of the
highly aggressive triple negative BT-20 human breast cancer cell line with 3-BP also
induced an immunogenic cell death, activating human dendritic cells in vitro.