Robert W. Wilkinson

Acquired Resistance to Fractionated Radiotherapy Can Be Overcome by Concurrent PD-L1 Blockade

Radiotherapy is a major part in the treatment of most common cancers, but many patients experience local recurrence with metastatic disease. In evaluating response biomarkers, we found that low doses of fractionated radiotherapy led to PD-L1 upregulation on tumor cells in a variety of syngeneic mouse models of cancer. Notably, fractionated radiotherapy delivered in combination with αPD-1 or αPD-L1 mAbs generated efficacious CD8(+) T-cell responses that improved local tumor control, long-term survival, and protection against tumor rechallenge. These favorable outcomes were associated with induction of a tumor antigen-specific memory immune response. Mechanistic investigations showed that IFNγ produced by CD8(+) T cells was responsible for mediating PD-L1 upregulation on tumor cells after delivery of fractionated radiotherapy. Scheduling of anti-PD-L1 mAb was important for therapeutic outcome, with concomitant but not sequential administration with fractionated radiotherapy required to improve survival. Taken together, our results reveal the mechanistic basis for an adaptive response by tumor cells that mediates resistance to fractionated radiotherapy and its treatment failure. With attention to scheduling, combination immunoradiotherapy with radiotherapy and PD-1/PD-L1 signaling blockade may offer an immediate strategy for clinical evaluation to improve treatment outcomes.

Preclinical anticancer activity of the potent, oral Src inhibitor AZD0530

AZD0530, an orally available Src inhibitor, demonstrated potent antimigratory and anti‐invasive effects in vitro, and inhibited metastasis in a murine model of bladder cancer. Antiproliferative activity of AZD0530 in vitro varied between cell lines (IC50 0.2 –>10μM). AZD0530 inhibited tumor growth in 4/10 xenograft models tested and dynamically inhibited in vivo phosphorylation of Src substrates paxillin and FAK in both growth‐inhibition‐resistant and ‐sensitive xenografts. The activity of AZD0530 in NBT‐II bladder cancer cells in vitro was consistent with inhibition of cell migration and stabilization of cell–cell adhesion. These data suggest a dominant anti‐invasive pharmacology for AZD0530 that may limit tumor progression in a range of cancers. AZD0530 is currently in Phase II clinical trials.

Systemic delivery of a TLR7 agonist in combination with radiation primes durable antitumor immune responses in mouse models of lymphoma

Passive immunotherapy with monoclonal antibodies has improved outcome for patients with B-cell malignancies, although many still relapse and little progress has been made with T-cell malignancies. Novel treatment approaches are clearly required in this disease setting. There has been much recent interest in developing therapeutic approaches to enhance antitumor immune responses using novel immunomodulatory agents in combination with standard of care treatments. Here we report that intravenous administration of the Toll-like receptor 7 (TLR7) agonist, R848 in combination with radiation therapy (RT), leads to the longstanding clearance of tumor in T- and B-cell lymphoma bearing mice. In combination, TLR7/RT therapy leads to the expansion of tumor antigen-specific CD8(+) T cells and improved survival. Furthermore, those mice that achieve long-term clearance of tumor after TLR7/RT therapy are protected from subsequent tumor rechallenge by the generation of a tumor-specific memory immune response. Our findings demonstrate the potential for enhancing the efficacy of conventional cytotoxic anticancer therapy through combination with a systemically administered TLR7 agonist to improve antitumor immune responses and provide durable remissions.

The MEK1/2 inhibitor, selumetinib (AZD6244; ARRY-142886), enhances anti-tumour efficacy when combined with conventional chemotherapeutic agents in human tumour xenograft models.

Background:The Ras/RAF/MEK/ERK pathway is frequently deregulated in cancer and a number of inhibitors that target this pathway are currently in clinical development. It is likely that clinical testing of these agents will be in combination with standard therapies to harness the apoptotic potential of both the agents. To support this strategy, it has been widely observed that a number of chemotherapeutics stimulate the activation of several intracellular signalling cascades including Ras/RAF/MEK/ERK. The MEK1/2 inhibitor selumetinib has been shown to have anti-tumour activity and induce apoptotic cell death as a monotherapy.Methods:The aim of this study was to identify agents, which would be likely to offer clinical benefit when combined with selumetinib. Here, we used human tumour xenograft models and assessed the effects combining standard chemotherapeutic agents with selumetinib on tumour growth. In addition, we analysed tumour tissue to determine the mechanistic effects of these combinations.Results:Combining selumetinib with the DNA-alkylating agent, temozolomide (TMZ), resulted in enhanced tumour growth inhibition compared with monotherapies. Biomarker studies highlighted an increase in γH2A.X suggesting that selumetinib is able to enhance the DNA damage induced by TMZ alone. In several models we observed that continuous exposure to selumetinib in combination with docetaxel results in tumour regression. Scheduling of docetaxel before selumetinib was more beneficial than when selumetinib was dosed before docetaxel and demonstrated a pro-apoptotic phenotype. Similar results were seen when selumetinib was combined with the Aurora B inhibitor barasertib.Conclusion:The data presented suggests that MEK inhibition in combination with several standard chemotherapeutics or an Aurora B kinase inhibitor is a promising clinical strategy.

Identification and Characterization of MEDI4736, an Antagonistic Anti–PD-L1 Monoclonal Antibody

A human antibody to PD-L1, engineered to eliminate Fc effector functions, which potently inhibits PD-L1 function, is in phase III clinical trials. Its characterization here provides clinicians and researchers with a basis for understanding and interpreting clinical trial results. Programmed cell-death 1 ligand 1 (PD-L1) is a member of the B7/CD28 family of proteins that control T-cell activation. Many tumors can upregulate expression of PD-L1, inhibiting antitumor T-cell responses and avoiding immune surveillance and elimination. We have identified and characterized MEDI4736, a human IgG1 monoclonal antibody that binds with high affinity and specificity to PD-L1 and is uniquely engineered to prevent antibody-dependent cell-mediated cytotoxicity. In vitro assays demonstrate that MEDI4736 is a potent antagonist of PD-L1 function, blocking interaction with PD-1 and CD80 to overcome inhibition of primary human T-cell activation. In vivo MEDI4736 significantly inhibits the growth of human tumors in a novel xenograft model containing coimplanted human T cells. This activity is entirely dependent on the presence of transplanted T cells, supporting the immunological mechanism of action for MEDI4736. To further determine the utility of PD-L1 blockade, an anti-mouse PD-L1 antibody was investigated in immunocompetent mice. Here, anti-mouse PD-L1 significantly improved survival of mice implanted with CT26 colorectal cancer cells. The antitumor activity of anti–PD-L1 was enhanced by combination with oxaliplatin, which resulted in increased release of HMGB1 within CT26 tumors. Taken together, our results demonstrate that inhibition of PD-L1 function can have potent antitumor activity when used as monotherapy or in combination in preclinical models, and suggest it may be a promising therapeutic approach for the treatment of cancer. MEDI4736 is currently in several clinical trials both alone and in combination with other agents, including anti–CTLA-4, anti–PD-1, and inhibitors of IDO, MEK, BRAF, and EGFR. Cancer Immunol Res; 3(9); 1052–62. ©2015 AACR.

The role of Fc gamma receptors in the activity of immunomodulatory antibodies for cancer

Antibodies targeting T-cell inhibitory pathways, such as CTLA-4 and PD-1/PD-L1, are emerging as an important class of cancer therapeutics, and a next generation of immunomodulatory therapies targeting alternative inhibitory (e.g. TIM-3, LAG-3, B7-H4, B7-H3, VISTA, A2aR), as well as co-stimulatory (e.g. CD27, OX40, GITR, CD137), pathways are poised to join them. Most of these immunomodulatory antibodies are of IgG isotypes that have low, or no, binding to the Fc gamma receptors (FcγRs) that trigger cell-mediated cytotoxic effector functions such as antibody dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP). These isotypes were selected to minimise the risk of depleting the T cells upon which such antibodies depend for their mechanism of action. However, recent preclinical data highlight a potential role for FcγR engagement in the activity of such antibodies. Here we review the biology of the FcγRs and IgG isotypes in both humans and mice, detail the potential roles that FcγR interactions can play in the activity of monoclonal antibodies in general, and of immunomodulatory antibodies in particular, and discuss how preclinical studies on these interactions might be best interpreted and translated to a human setting.

Fractionated radiation therapy stimulates anti-tumor immunity mediated by both resident and infiltrating polyclonal T-cell populations when combined with PD1 blockade

Purpose: Radiotherapy is a highly effective anticancer treatment forming part of the standard of care for the majority of patients, but local and distal disease recurrence remains a major cause of mortality. Radiotherapy is known to enhance tumor immunogenicity; however, the contribution and mechanisms of radiotherapy-induced immune responses are unknown. Experimental Design: The impact of low-dose fractionated radiotherapy (5 × 2 Gy) alone and in combination with αPD-1 mAb on the tumor microenvironment was evaluated by flow cytometry and next-generation sequencing of the T-cell receptor (TCR) repertoire. A dual-tumor model was used, with fractionated radiotherapy delivered to a single tumor site to enable evaluation of the local and systemic response to treatment and ability to induce abscopal responses outside the radiation field. Results: We show that fractionated radiotherapy leads to T-cell infiltration at the irradiated site; however, the TCR landscape remains dominated by polyclonal expansion of preexisting T-cell clones. Adaptive resistance via the PD-1/PD-L1 pathway restricts the generation of systemic anticancer immunity following radiotherapy, which can be overcome through combination with αPD-1 mAb leading to improved local and distal tumor control. Moreover, we show that effective clearance of tumor following combination therapy is dependent on both T cells resident in the tumor at the time of radiotherapy and infiltrating T cells. Conclusions: These data provide evidence that radiotherapy can enhance T-cell trafficking to locally treated tumor sites and augment preexisting anticancer T-cell responses with the capacity to mediate regression of out-of-field tumor lesions when delivered in combination with αPD-1 mAb therapy. Clin Cancer Res; 23(18); 5514–26. ©2017 AACR.

Camptothecin prodrug block copolymer micelles with high drug loading and target specificity

The clinical efficacy of cytotoxic drugs in the treatment of cancer is often hampered by poor pharmacodynamics and systemic toxicity. Here, we describe the design and synthesis of a new PEG-based system for the delivery of the cytotoxic camptothecin (CPT) into tumor cells that overexpress luteinizing hormone releasing hormone receptor (LHRHR). A novel functional reducible camptothecin (CPT) block copolymer conjugate was prepared using atom transfer radical polymerization (ATRP). The use of ATRP in the design and synthesis of the copolymer prodrug facilitated high drug loading and specific delivery to tumor cells. The efficacy of the polymer conjugate was evaluated in appropriate cancer cell lines in vitro. Cytotoxic potency was comparable to that of free CPT in LHRHR positive cell lines after 72 hours, whereas little cytotoxicity was observed in LHRHR negative lines. The study also evaluated the effects of polymer-based therapeutics on human peripheral blood mononuclear cells (PBMC). Free CPT demonstrated indiscriminate toxicity against the immune cells, with impairment of PBMC proliferation and a reduction in CD8+, CD4+ T cell populations. The camptothecin (CPT) block copolymer demonstrated a significant improvement in cell proliferation and maintenance of CD8+ cells.

Synthesis and SAR of 1-acetanilide-4-aminopyrazole-substituted quinazolines: Selective inhibitors of Aurora B kinase with potent anti-tumor activity

A new class of 1-acetanilide-4-aminopyrazole-substituted quinazoline Aurora kinase inhibitors has been discovered possessing highly potent cellular activity. Continuous infusion into athymic mice bearing SW620 tumors of the soluble phosphate derivative 2 led to dose-proportional exposure of the des-phosphate compound 8 with a high-unbound fraction. The combination of potent cell activity and high free-drug exposure led to pharmacodynamic changes in the tumor at low doses, indicative of Aurora B-kinase inhibition and a reduction in tumor volume.

Rational selection of syngeneic preclinical tumor models for immunotherapeutic drug discovery

Murine syngeneic tumor models are used to study responses to antitumor immunotherapies. To rationalize model selection, the underlying genetic and immunologic biology of the models was analyzed, allowing parallels to be drawn between models and human disease phenotypes. Murine syngeneic tumor models are critical to novel immuno-based therapy development, but the molecular and immunologic features of these models are still not clearly defined. The translational relevance of differences between the models is not fully understood, impeding appropriate preclinical model selection for target validation, and ultimately hindering drug development. Across a panel of commonly used murine syngeneic tumor models, we showed variable responsiveness to immunotherapies. We used array comparative genomic hybridization, whole-exome sequencing, exon microarray analysis, and flow cytometry to extensively characterize these models, which revealed striking differences that may underlie these contrasting response profiles. We identified strong differential gene expression in immune-related pathways and changes in immune cell–specific genes that suggested differences in tumor immune infiltrates between models. Further investigation using flow cytometry showed differences in both the composition and magnitude of the tumor immune infiltrates, identifying models that harbor “inflamed” and “non-inflamed” tumor immune infiltrate phenotypes. We also found that immunosuppressive cell types predominated in syngeneic mouse tumor models that did not respond to immune-checkpoint blockade, whereas cytotoxic effector immune cells were enriched in responsive models. A cytotoxic cell–rich tumor immune infiltrate has been correlated with increased efficacy of immunotherapies in the clinic, and these differences could underlie the varying response profiles to immunotherapy between the syngeneic models. This characterization highlighted the importance of extensive profiling and will enable investigators to select appropriate models to interrogate the activity of immunotherapies as well as combinations with targeted therapies in vivo. Cancer Immunol Res; 5(1); 29–41. ©2016 AACR.