Clinical development of combination strategies in immunotherapy: are we ready for more than one investigational product in an early clinical trial?

Recent advances in nano-drug delivery systems for synergistic antitumor immunotherapy

Immunotherapy has demonstrated great clinical success in the field of oncology in comparison with conventional cancer therapy. However, cancer immunotherapy still encounters major challenges that limit its efficacy against different types of cancers and the patients show minimal immune response to the immunotherapy. To overcome these limitations, combinatorial approaches with other therapeutics have been applied in the clinic. Simultaneously, nano-drug delivery system has played an important role in increasing the antitumor efficacy of various treatments and has been increasingly utilized for synergistic immunotherapy to further enhance the immunogenicity of the tumors. Specifically, they can promote the infiltration of immune cells within the tumors and create an environment that is more sensitive to immunotherapy, particularly in solid tumors, by accelerating tumor accumulation and permeability. Herein, this progress report provides a brief overview of the development of nano-drug delivery systems, classification of combinatory cancer immunotherapy and recent progress in tumor immune synergistic therapy in the application of nano-drug delivery systems.

Virotherapy, gene transfer and immunostimulatory monoclonal antibodies

Malignant cells are susceptible to viral infection and consequent cell death. Virus-induced cell death is endowed with features that are known to stimulate innate and adaptive immune responses. Thus danger signals emitted by cells succumbing to viral infection as well as viral nucleic acids are detected by specific receptors, and tumor cell antigens can be routed to professional antigen-presenting cells. The anticancer immune response triggered by viral infection is frequently insufficient to eradicate malignancy but may be further amplified. For this purpose, transgenes encoding cytokines as co-stimulatory molecules can be genetically engineered into viral vectors. Alternatively, or in addition, it is possible to use monoclonal antibodies that either block inhibitory receptors of immune effector cells, or act as agonists for co-stimulatory receptors. Combined strategies are based on the ignition of a local immune response at the malignant site plus systemic immune boosting. We have recently reported examples of this approach involving the Vaccinia virus or Semliki Forest virus, interleukin-12 and anti-CD137 monoclonal antibodies.

PD-1 pathway inhibitors: changing the landscape of cancer immunotherapy

BACKGROUND

Immunotherapeutic approaches to treating cancer have been evaluated during the last few decades with limited success. An understanding of the checkpoint signaling pathway involving the programmed death 1 (PD-1) receptor and its ligands (PD-L1/2) has clarified the role of these approaches in tumor-induced immune suppression and has been a critical advancement in immunotherapeutic drug development.

METHODS

A comprehensive literature review was performed to identify the available data on checkpoint inhibitors, with a focus on anti-PD-1 and anti-PD-L1 agents being tested in oncology. The search included Medline, PubMed, the ClinicalTrials.gov registry, and abstracts from the American Society of Clinical Oncology meetings through April 2014. The effectiveness and safety of the available anti-PD-1 and anti-PD-L1 drugs are reviewed.

RESULTS

Tumors that express PD-L1 can often be aggressive and carry a poor prognosis. The anti-PD-1 and anti-PD-L1 agents have a good safety profile and have resulted in durable responses in a variety of cancers, including melanoma, kidney cancer, and lung cancer, even after stopping treatment. The scope of these agents is being evaluated in various other solid tumors and hematological malignancies, alone or in combination with other therapies, including other checkpoint inhibitors and targeted therapies, as well as cytotoxic chemotherapy.

CONCLUSIONS

The PD-1/PD-L1 pathway in cancer is implicated in tumors escaping immune destruction and is a promising therapeutic target. The development of anti-PD-1 and anti-PD-L1 agents marks a new era in the treatment of cancer with immunotherapies. Early clinical experience has shown encouraging activity of these agents in a variety of tumors, and further results are eagerly awaited from completed and ongoing studies.

Clinical development of immunostimulatory monoclonal antibodies and opportunities for combination

Immune system responses are under the control of extracellular biomolecules, which express functions in receptors present on the surface of cells of the immune system, and thus are amenable to be functionally modulated by monoclonal antibodies. Some of these mechanisms are activating and dictate whether the response ensues, while others play the role of powerful repressors. Antagonist antibodies acting on such repressors result in enhanced immune responses, a goal that is also achieved with agonist antibodies acting on the activating receptors. With these simple logics, a series of therapeutic agents are under clinical development and one of them directed at the CTL-associated antigen 4 (CTLA-4) inhibitory receptor (ipilimumab) has been approved for the treatment of metastatic melanoma. The list of antagonist agents acting on repressors under development includes anti-CTLA-4, anti-PD-1, anti-PD-L1 (B7-H1), anti-KIR, and anti-TGF-β. Agonist antibodies currently being investigated in clinical trials target CD40, CD137 (4-1BB), CD134 (OX40), and glucocorticoid-induced TNF receptor (GITR). A blossoming preclinical pipeline suggests that other active targets will also be tested in patients in the near future. All of these antibodies are being developed as conventional monoclonal immunoglobulins, but other engineered antibody formats or RNA aptamers are under preclinical scrutiny. The "dark side" of these immune interventions is that they elicit autoimmune/inflammatory reactions that can be severe in some patients. A critical and, largely, pending subject is to identify reliable predictive biomarkers both for efficacy and immune toxicity. Preclinical and early clinical studies indicate a tremendous potential to further improve efficacy, using combinations from among these new agents that frequently act in a synergistic fashion. Combinations with other more conventional means of treatment such as radiotherapy, chemotherapy, or cancer vaccines also hold much promise.

A mathematical model of immune-system-melanoma competition

We present a mathematical model developed to reproduce the immune response entitled with the combined administration of activated OT1 cytotoxic T lymphocytes (CTLs) and Anti-CD137 monoclonal antibodies. The treatment is directed against melanoma in B16 OVA mouse models exposed to a specific immunotherapy strategy. We model two compartments: the injection point compartment where the treatment is administered and the skin compartment where melanoma tumor cells proliferate. To model the migration of OT1 CTLs and antibodies from the injection to the skin compartment, we use delay differential equations (DDEs). The outcomes of the mathematical model are in good agreement with the in vivo results. Moreover, sensitivity analysis of the mathematical model underlines the key role of OT1 CTLs and suggests that a possible reduction of the number of injected antibodies should not affect substantially the treatment efficacy.

Workshop on immunotherapy combinations. Society for Immunotherapy of Cancer annual meeting Bethesda, November 3, 2011

Although recent FDA approvals on ipilimumab and sipuleucel-T represent major milestones, the ultimate success of immunotherapy approaches will likely benefit from appropriate combinations with other immunotherapeutic and/or non-immunotherapeutic approaches. However, implementation of ideal combinations in the clinic may still face formidable challenges in regulatory, drug-availability and intellectual property aspects. The 2011 SITC annual meeting hosted a workshop on combination immunotherapy to discuss: 1) the most promising combinations found in the laboratory; 2) early success of combination immunotherapy in clinical trials; 3) industry perspectives on combination approaches, and 4) relevant regulatory issues. The integrated theme was how to accelerate the implementation of efficacious combined immunotherapies for cancer patients. Rodent animal models are providing many examples of synergistic combinations that typically include more than two agents. However, mouse and human immunology differ in a significant number of mechanisms and hence we might be missing opportunities peculiar to humans. Nonetheless, incisive animal experimentation with deep mechanistic insight remains the best compass that we can use to guide our paths in combinatorial immunotherapy. Combination immunotherapy clinical trials are already in progress and preliminary results are extremely promising. As a key to translate promising combinations into clinic, real and “perceived” business and regulatory hurdles were debated. A formidable step forward would be to be able to test combinations of investigational agents prior to individual approval. Taking together the FDA and the industrial perspective on combinatorial immunotherapy, the audience was left with the clear message that this is by no means an impossible task. The general perception is that the road ahead of us is full of combination clinical trials which hopefully will bring clinical benefit to our cancer patients at a fast pace.

Pilot clinical trial of type 1 dendritic cells loaded with autologous tumor lysates combined with GM-CSF, pegylated IFN, and cyclophosphamide for metastatic cancer patients

Twenty-four patients with metastatic cancer received two cycles of four daily immunizations with monocyte-derived dendritic cells (DC). DC were incubated with preheated autologous tumor lysate and subsequently with IFN-α, TNF-α, and polyinosinic:polycytidylic acid to attain type 1 maturation. One DC dose was delivered intranodally, under ultrasound control, and the rest intradermally in the opposite thigh. Cyclophosphamide (day -7), GM-CSF (days 1-4), and pegIFN alpha-2a (days 1 and 8) completed each treatment cycle. Pretreatment with cyclophosphamide decreased regulatory T cells to levels observed in healthy subjects both in terms of percentage and in absolute counts in peripheral blood. Treatment induced sustained elevations of IL-12 in serum that correlated with the output of IL-12p70 from cultured DC from each individual. NK activity in peripheral blood was increased and also correlated with the serum concentration of IL-12p70 in each patient. Circulating endothelial cells decreased in 17 of 18 patients, and circulating tumor cells markedly dropped in 6 of 19 cases. IFN-γ-ELISPOT responses to DC plus tumor lysate were observed in 4 of 11 evaluated cases. Tracing DC migration with [(111)In] scintigraphy showed that intranodal injections reached deeper lymphatic chains in 61% of patients, whereas with intradermal injections a small fraction of injected DC was almost constantly shown to reach draining inguinal lymph nodes. Five patients experienced disease stabilization, but no objective responses were documented. This combinatorial immunotherapy strategy is safe and feasible, and its immunobiological effects suggest potential activity in patients with minimal residual disease. A randomized trial exploring this hypothesis is currently ongoing.

SimB16: modeling induced immune system response against B16-melanoma

Immunological therapy of progressive tumors requires not only activation and expansion of tumor specific cytotoxic T lymphocytes (CTLs), but also an efficient effector phase including migration of CTLs in the tumor tissue followed by conjugation and killing of target cells. We report the application of an agent-based model to recapitulate both the effect of a specific immunotherapy strategy against B16-melanoma in mice and the tumor progression in a generic tissue section. A comparison of the in silico results with the in vivo experiments shows excellent agreement. We therefore use the model to predict a critical role for CD137 expression on tumor vessel endothelium for successful therapy and other mechanistic aspects. Experimental results are fully compatible with the model predictions. The biologically oriented in silico model derived in this work will be used to predict treatment failure or success in other pre-clinical conditions eventually leading new promising in vivo experiments.

Ex vivo gene transfer for improved adoptive immunotherapy of cancer

Adoptive immunotherapy is an appealing approach to cancer treatment, with the potential for more precise targeting and reduced toxicity. While early clinical trial data using adoptive T cells against post-transplant virus-associated hematologic malignancies, lymphoma and melanoma have been promising, treating other solid tumors has proven to be more challenging. Adoptive lymphocytes have been genetically modified in many ways to improve activity and circumvent tumor evasion, including transfer of transgenic T-cell receptors and chimeric antigen receptors to redirect T cell and natural killer cell antigen specificity. Gene transfer may also allow expression of homeostatic cytokines or their receptors to overcome the lack of stimulatory signals or expression of dominant-negative receptors for inhibitory cytokines to compensate for an immunosuppressive tumor milieu. In addition, suicide genes can install a 'safety switch' on adoptively transferred cells to allow ablation if necessary. Although further refinement and validation are necessary, these genetic modification strategies offer hope for significant improvements in cancer immunotherapy.

Archaeosome adjuvant overcomes tolerance to tumor-associated melanoma antigens inducing protective CD8 T cell responses

Vesicles comprised of the ether glycerolipids of the archaeon Methanobrevibacter smithii (archaeosomes) are potent adjuvants for evoking CD8⁺ T cell responses. We therefore explored the ability of archaeosomes to overcome immunologic tolerance to self-antigens. Priming and boosting of mice with archaeosome-antigen evoked comparable CD8⁺ T cell response and tumor protection to an alternate boosting strategy utilizing live bacterial vectors for antigen delivery. Vaccination with melanoma antigenic peptides TRP_181-189 and Gp100_25-33 delivered in archaeosomes resulted in IFN-γ producing antigen-specific CD8⁺ T cells with strong cytolytic capability and protection against subcutaneous B16 melanoma. Targeting responses against multiple antigens afforded prolonged median survival against melanoma challenge. Entrapment of multiple peptides within the same vesicle or admixed formulations were both effective at evoking CD8⁺ T cells against each antigen. Melanoma-antigen archaeosome formulations also afforded therapeutic protection against established B16 tumors when combined with depletion of T-regulatory cells. Overall, we demonstrate that archaeosome adjuvants constitute an effective choice for formulating cancer vaccines.

Clinical experiences with anti-CD137 and anti-PD1 therapeutic antibodies

Monoclonal antibodies (mAbs) provide a pharmacological platform to block or activate the function of surface receptors. The immune system has evolved receptor-ligand pairs that repress or empower the cellular immune response, which, if tampered with, unleash more potent cellular immunity against tumor antigens. Agonist antibodies directed against CD137 (4-1BB) on the surface of antigen-primed T lymphocytes increase tumor immunity that is curative against some transplantable murine tumors. A fully human IgG4 anti-CD137 antibody is under development with signs of clinical activity and cases of severe liver toxicity that seem to be on-target and dose-dependent effects. Programmed death-1 (PD1) is a surface molecule delivering inhibitory signals important to maintain T-cell functional silence against their cognate antigens. Interference with PD1 or its ligand PD-L1 (B7-H1) increases antitumor immunity. As a result anti-PD1 and anti-PD-L1 human mAbs are under clinical development. Phase I trials with anti-PD1 mAb have yielded encouraging results with durable objective responses and a reasonable safety profile. As new class of drugs in cancer therapy, immunostimulatory mAbs have resulted in redefinition of tumor response criteria and rethinking of the rationale for combining these among each other and with other strategies.