Breaking tolerance in a mouse model of multiple myeloma by chemoimmunotherapy

Metronomic chemotherapy in hematology: Lessons from preclinical and clinical studies to build a solid rationale for future schedules

Metronomic chemotherapy (mCHEMO), based on frequent, regular administration of low, but pharmacologically active drug doses, optimizes antitumor efficacy by targeting multiple targets and reducing toxicity of antineoplastic drugs. This minireview will summarize preclinical and clinical studies on cytotoxic drugs given at weekly, daily, or at continuous metronomic schedules alone or in combination with novel targeted agents for hematological malignancies, including lymphoma, multiple myeloma, and leukemia. Most of the preclinical in vitro and in vivo studies have reported a significant benefit of both mCHEMO monotherapy and combinatorial regimens compared with chemotherapy at the maximum tolerated dose. However, the combination of mCHEMO with targeted drugs is still little explored in the hematologic clinical setting. Data obtained from preclinical studies on low dose metronomic chemotherapy in hematological malignancies clearly suggested the possibility to clinically investigate more tolerable and effective strategies for the treatment of patients with advanced hematological malignancies, or at least for those frail and elderly patients, who are not eligible or resistant to standard treatments.

What happens to regulatory T cells in multiple myeloma

Abnormal tumor microenvironment and immune escape in multiple myeloma (MM) are associated with regulatory T cells (Tregs), which play an important role in maintaining self-tolerance and regulating the overall immune response to infection or tumor cells. In patients with MM, there are abnormalities in the number, function and distribution of Tregs, and these abnormalities may be related to the disease stage, risk grade and prognosis of patients. During the treatment, Tregs have different responses to various treatment regiments, thus affecting the therapeutic effect of MM. It is also possible to predict the therapeutic response by observing the changes of Tregs. In addition to the above, we reviewed the application of Tregs in the treatment of MM. In conclusion, there is still much room for research on the mechanism and application of Tregs in MM.

Immune Modulatory Effects of Molecularly Targeted Therapy and Its Repurposed Usage in Cancer Immunotherapy

The fast evolution of anti-tumor agents embodies a deeper understanding of cancer pathogenesis. To date, chemotherapy, targeted therapy, and immunotherapy are three pillars of the paradigm for cancer treatment. The success of immune checkpoint inhibitors (ICIs) implies that reinstatement of immunity can efficiently control tumor growth, invasion, and metastasis. However, only a fraction of patients benefit from ICI therapy, which turns the spotlight on developing safe therapeutic strategies to overcome the problem of an unsatisfactory response. Molecular-targeted agents were designed to eliminate cancer cells with oncogenic mutations or transcriptional targets. Intriguingly, accumulating shreds of evidence demonstrate the immunostimulatory or immunosuppressive capacity of targeted agents. By virtue of the high attrition rate and cost of new immunotherapy exploration, drug repurposing may be a promising approach to discovering combination strategies to improve response to immunotherapy. Indeed, many clinical trials investigating the safety and efficacy of the combination of targeted agents and immunotherapy have been completed. Here, we review and discuss the effects of targeted anticancer agents on the tumor immune microenvironment and explore their potential repurposed usage in cancer immunotherapy.

Gold Compounds and the Anticancer Immune Response

Gold compounds are not only well-explored for cytotoxic effects on tumors, but are also known to interact with the cancer immune system. The immune system deploys innate and adaptive mechanisms to protect against pathogens and prevent malignant transformation. The combined action of gold compounds with the activated immune system has shown promising results in cancer therapy through in vivo and in vitro experiments. Gold compounds are known to induce innate immune responses; however, these responses may contribute to adaptive immune responses. Gold compounds play the role of a major hapten that acts synergistically in innate immunity. Gold compounds support cancer cell antigenicity and promote anti-tumor immune response by inducing the release of CRT, ATP, HMGB1, HSP, and NKG2D to enhance immunogenicity. Gold compounds affect various immune cells (including suppressor regulatory T cells), inhibit myeloid derived suppressor cells, and enhance the function and number of dendritic cells. Gold nanoparticles (AuNPs) have potential for improving the effect of immunotherapy and reducing the toxicity and side effects of the treatment process. Thus, AuNPs provide an ideal opportunity for exploring the combination of anticancer gold compounds and immunotherapeutic interventions.

Retrospective comparison of three doses of metronomic chlorambucil for tolerability and efficacy in dogs with spontaneous cancer

The study hypothesis is that higher doses of metronomic (low-dose) chlorambucil will improve outcome without significantly worsening adverse events (AE). Retrospectively, 88 dogs were screened to assess for tolerability and response to chlorambucil utilizing retrospective and prospective data sets, comparing metronomic oral daily doses 4, 6 and 8 mg m² . There were 78 and 70 dogs in the tolerability and efficacy portions, respectively. The severity of gastrointestinal (GI) AE was significantly worse, and time to development of GI events was significantly shorter at 6 mg m² than at 4 mg m² (both P < 0.001). Chlorambucil was discontinued earlier in the dogs treated at the 6 mg m² doses than in the dogs treated at 4 mg m² (P = 0.015). Thrombocytopenia occurred significantly earlier at 8 mg m² than at 4 mg m² (P = 0.017). Higher doses of metronomic (low-dose) chlorambucil did not provide improved responses and were associated with more AE.

Mechanisms of Drug Resistance in Relapse and Refractory Multiple Myeloma

Multiple myeloma (MM) is a hematological malignancy that remains incurable because most patients eventually relapse or become refractory to current treatments. Although the treatments have improved, the major problem in MM is resistance to therapy. Clonal evolution of MM cells and bone marrow microenvironment changes contribute to drug resistance. Some mechanisms affect both MM cells and microenvironment, including the up- and downregulation of microRNAs and programmed death factor 1 (PD-1)/PD-L1 interaction. Here, we review the pathogenesis of MM cells and bone marrow microenvironment and highlight possible drug resistance mechanisms. We also review a potential molecular targeting treatment and immunotherapy for patients with refractory or relapse MM.

Cellular immunotherapy in multiple myeloma: lessons from preclinical models

The majority of multiple myeloma patients relapse with the current treatment strategies, raising the need for alternative therapeutic approaches. Cellular immunotherapy is a rapidly evolving field and currently being translated into clinical trials with encouraging results in several cancer types, including multiple myeloma. Murine multiple myeloma models are of critical importance for the development and refinement of cellular immunotherapy. In this review, we summarize the immune cell changes that occur in multiple myeloma patients and we discuss the cell-based immunotherapies that have been tested in multiple myeloma, with a focus on murine models.

Programmed death receptor-1/programmed death receptor ligand-1 blockade after transient lymphodepletion to treat myeloma

Early phase clinical trials targeting the programmed death receptor-1/ligand-1 (PD-1/PD-L1) pathway to overcome tumor-mediated immunosuppression have reported promising results for a variety of cancers. This pathway appears to play an important role in the failure of immune reactivity to malignant plasma cells in multiple myeloma patients, as the tumor cells express relatively high levels of PD-L1, and T cells show increased PD-1 expression. In the current study, we demonstrate that PD-1/PD-L1 blockade with a PD-L1-specific Ab elicits rejection of a murine myeloma when combined with lymphodepleting irradiation. This particular combined approach by itself has not previously been shown to be efficacious in other tumor models. The antitumor effect of lymphodepletion/anti-PD-L1 therapy was most robust when tumor Ag-experienced T cells were present either through cell transfer or survival after nonmyeloablative irradiation. In vivo depletion of CD4 or CD8 T cells completely eliminated antitumor efficacy of the lymphodepletion/anti-PD-L1 therapy, indicating that both T cell subsets are necessary for tumor rejection. Elimination of myeloma by T cells occurs relatively quickly as tumor cells in the bone marrow were nearly nondetectable by 5 d after the first anti-PD-L1 treatment, suggesting that antimyeloma reactivity is primarily mediated by preactivated T cells, rather than newly generated myeloma-reactive T cells. Anti-PD-L1 plus lymphodepletion failed to improve survival in two solid tumor models, but demonstrated significant efficacy in two hematologic malignancy models. In summary, our results support the clinical testing of lymphodepletion and PD-1/PD-L1 blockade as a novel approach for improving the survival of patients with multiple myeloma.

N-Propionyl polysialic acid precursor enhances the susceptibility of multiple myeloma to antitumor effect of anti-NprPSA monoclonal antibody

AIM

To study the antitumor effect of anti-NprPSA monoclonal antibody (mAb) in combination with ManNPr, a precursor of N-propionyl PSA, in multiple myeloma (MM), and to explore the mechanisms of the action.

METHODS

Human multiple myeloma cell line RPMI-8226 was tested. The cells were pre-treated with ManNPr (1, 2, and 4 mg/mL), and then incubated with anti-NprPSA mAb (1 mg/mL). Cell apoptosis in vitro was detected using MTT assay and flow cytometry. BALB/c nude mice were inoculated sc with RPC5.4 cells. On 5 d after the injection, the mice were administered sc with anti-NprPSA mAb (200 μg/d) and ManNPr (5 mg/d) for 8 d. The tumor size and body weight were monitored twice per week. TUNEL assay was used for detecting apoptosis in vivo. The apoptotic pathway involved was examined using Western blot analysis and caspase inhibitor.

RESULTS

Treatment of RPMI-8226 cells with anti-NprPSA mAb alone failed to inhibit cell growth in vitro. In RPMI-8226 cells pretreated with ManNPr, however, the mAb significantly inhibited the cell proliferation, decreased the viability, and induced apoptosis, which was associated with cleavage of caspase-3, caspase-8, caspase-9, and poly(ADP-ribose) polymerase. In the mouse xenograft model, treatment with the mAb in combination with ManNPr significantly inhibited the tumor growth, and induced significant apoptosis as compared to treatment with the mAb alone. Moreover, apoptosis induced by the mAb in vivo resulted from the activation of the caspases and poly(ADP-ribose) polymerase.

CONCLUSION

The anti-NprPSA mAb in combination with ManNPr is an effective treatment for in vitro and in vivo induction of apoptosis in multiple myeloma.

Novel strategies for immunotherapy in multiple myeloma: previous experience and future directions

Multiple myeloma (MM) is a life-threatening haematological malignancy for which standard therapy is inadequate. Autologous stem cell transplantation is a relatively effective treatment, but residual malignant sites may cause relapse. Allogeneic transplantation may result in durable responses due to antitumour immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. Cellular immunotherapy using specific antigen-presenting cells (APCs), to overcome aspects of immune incompetence in MM patients, has received great attention, and numerous clinical trials have evaluated the potential for dendritic cell (DC) vaccines as a novel immunotherapeutic approach. This paper will summarize the data investigating aspects of immunity concerning MM, immunotherapy for patients with MM, and strategies, on the way, to target the plasma cell more selectively. We also include the MM antigens and their specific antibodies that are of potential use for MM humoral immunotherapy, because they have demonstrated the most promising preclinical results.

Why Do CD8+ T Cells become Indifferent to Tumors: A Dynamic Modeling Approach

CD8+ T cells have the potential to influence the outcome of cancer pathogenesis, including complete tumor eradication or selection of malignant tumor escape variants. The Simian virus 40 large T-antigen (Tag) oncoprotein promotes tumor formation in Tag-transgenic mice and also provides multiple target determinants (sites) for responding CD8+ T cells in C57BL/6 (H-2(b)) mice. To understand the in vivo quantitative dynamics of CD8+ T cells after encountering Tag, we constructed a dynamic model from in vivo-generated data to simulate the interactions between Tag-expressing cells and CD8+ T cells in distinct scenarios including immunization of wild-type C57BL/6 mice and of Tag-transgenic mice that develop various tumors. In these scenarios the model successfully reproduces the dynamics of both the Tag-expressing cells and antigen-specific CD8+ T cell responses. The model predicts that the tolerance of the site-specific T cells is dependent on their apoptosis rates and that the net growth of CD8+ T cells is altered in transgenic mice. We experimentally validate both predictions. Our results indicate that site-specific CD8+ T cells have tissue-specific apoptosis rates affecting their tolerance to the tumor antigen. Moreover, the model highlights differences in apoptosis rates that contribute to compromised CD8+ T cell responses and tumor progression, knowledge of which is essential for development of cancer immunotherapy.

Immune recovery after cyclophosphamide treatment in multiple myeloma: implication for maintenance immunotherapy

Multiple myeloma (MM) is a progressive B-lineage neoplasia characterized by clonal proliferation of malignant plasma cells. Increased numbers of regulatory T cells (Tregs) were determined in mouse models and in patients with MM, which correlated with disease burden. Thus, it became rational to target Tregs for treating MM. The effects of common chemotherapeutic drugs on Tregs are reviewed with a focus on cyclophosphamide (CYC). Studies indicated that selective depletion of Tregs may be accomplished following the administration of a low-dose CYC. We report that continuous nonfrequent administrations of CYC at low doses block the renewal of Tregs in MM-affected mice and enable the restoration of an efficient immune response against the tumor cells, thereby leading to prolonged survival and prevention of disease recurrence. Hence, distinctive time-schedule injections of low-dose CYC are beneficial for breaking immune tolerance against MM tumor cells.

Multiple myeloma patients at peripheral blood stem cell harvest: restricted usage of TCR beta variable families

The immune systems of multiple myeloma patients are suppressed by the disease itself, and this immunosuppression is further enhanced by standard therapies. The aim of our study was to evaluate the effects of initial chemotherapy and a peripheral blood mobilisation regimen on T-cell population diversity. Reverse transcription-polymerase chain reaction (RT-PCR) with a new set of primers, in combination with capillary electrophoresis, was established. The methodology was used to analyse the relative expression of 27 T-cell receptor beta variable gene families (BV families) in multiple myeloma patients undergoing peripheral blood stem cell harvest. We found that the overall BV family usage in these patients was restricted; the relative expression of 10 BV families was significantly depressed in patients compared to healthy donors. These findings demonstrate that the preparative regimen for autologous stem cell transplantation affects the T-cell population in terms of the restriction of its T-cell receptor diversity.