In the 20th century, three major modalities dominated the treatment of cancer: surgery, radiation therapy and cytotoxic chemotherapy. However, during the latter part of the century, drugs were developed that broke away from the traditional cytotoxic paradigm by targeting distinct biochemical pathways critical for cancer cell survival. Examples of these are small-molecule inhibitor compounds such as anti-estrogen drugs (e.g. tamoxifen, anastrozole), the RTK inhibitor lapatinib, BCR/ABL fusion product inhibitor Gleevec, as well as various monoclonal antibodies with drug-like activity (e.g. Trastuzumab) [1], [2], [3], [4]. The first two decades of the 21st century have seen an explosion of small-molecule inhibitor drugs targeting a variety of oncodrivers being tested for clinical activity, with a subset gaining FDA approval [5].

However, with the exception of Gleevec, (which has led to a revolution in the way chronic myelogenous leukemia is managed) the impact of most other approved small-molecule inhibitor drugs have been generally modest, with only relatively incremental improvements in therapy landscapes for their respective indications. Why have so few of these compounds met their high initial expectations? One possibility is that their true potential remains untapped, because we have not yet discovered the correct settings and treatment combinations that would yield maximal benefits.

In addition to targeted drugs, another emerging cancer treatment modality is immunotherapy. For example, FDA-approved monoclonal antibody-based checkpoint inhibitors are making sizable impacts for a variety of malignancies, and the CAR T cell approach is being enthusiastically pursued by a large number of investigators who wish to improve their activity against solid tumors [6], [7]. Our group has pioneered the use of HER-2 peptide-pulsed, Th1-polarizing dendritic cells (DC) for the neoadjuvant treatment of early-stage breast cancer. In vitro studies suggest that a major effector of anti-tumor immunity are the Th1 cytokines IFN-γ and TNF-α, which have been shown to cooperate in the induction of apoptosis and/or senescence for many tumor cell lines [8], [9], [10]. We also demonstrated that for HER-2pos/ERneg early breast cancer (DCIS), neoadjuvant DC vaccine therapy alone could achieve a pathological complete response (pCR; i.e. no remaining disease at time of scheduled surgery) in around a third of subjects, but, for HER-2pos/ERpos subjects, this response rate was much lower (around 5 %). However, when a brief course of anti-estrogen therapy was supplied concurrent with neoadjuvant DC vaccination, the pCR rates for this population increased nearly 6-fold [11]. These studies suggested that adding targeted small-molecule inhibitors to active immunotherapy might constitute an ideal approach for enhancing therapeutic efficacy far beyond what would be expected from either agent alone, and implied that exploring other targeted drugs for additive or synergistic effects with the effectors of Th1 immunity may be a fruitful avenue of investigation.

Pro-viral integration site for Moloney murine virus (PIM) kinases are constitutively-expressed serine/threonine kinases imperative for cell cycle regulation, and are implicated in tumor survival and therapeutic drug resistance [12]. The PIM family consists of 3 members which follow a tissue-dependent expression pattern in hematological and solid tumors [13], [14]. PIM kinase activity is controlled by cytokines and growth factors to activate signal transduction pathways including c-Myc, JAK/STAT, and FLT-3 [15]. Amplification of oncogene MYC is associated with poor prognosis and tumor stemness [16], and aberrant STAT3 activation is found in 70 % of breast tumors [17]. Therefore, attenuation of these signaling pathways via PIM inhibition in combination with effectors of vaccine-induced immunity might enhance breast cancer cell death.

Over 20 PIM inhibitors of variable selectivity are in preclinical or clinical phase trials for treatment of hematological and solid tumors. AZD1208 was identified as a potent pan inhibitor of all PIM isoforms and successfully inhibited the growth of primary acute myeloid lymphoma (AML) colonies [18], [19]. In phase I clinical trials for AML and solid tumors AZD1208 failed to show efficacy as a monotherapy; nonetheless, it reduced phosphorylation of PIM targets in some patients [20]. This shows that the drug can achieve pharmacological PIM inhibition in vivo, even if this in and of itself is not sufficient to induce tumor regression. AZD1208 may therefore be an ideal candidate to test whether PIM inhibition in conjunction with vaccine therapy can result in improved tumor control. In the studies presented here, we report strong combined activity for AZD1208 and Th1 cytokines for inducing breast cancer cell death in vitro, with dying cells demonstrating several markers consistent with apoptosis. Furthermore, using an orthotopic murine model of HER-2pos breast cancer, we show suppressed tumor growth kinetics for mice receiving dual treatments consisting of either recombinant IFN-γ and AZD1208 or anti-HER-2 DC vaccine plus AZD1208. Collectively, our results suggest that pharmacological PIM antagonism can act as an enhancer for DC- or cytokine-based immunotherapy.