Cancer continues to be one of the most difficult global healthcare problems. Although there is a large library of drugs that can be used in cancer treatment, the problem is selectively killing all the cancer cells while reducing collateral toxicity to healthy cells. There are several biological barriers to effective drug delivery in cancer such as renal, hepatic, or immune clearance. Nanoparticles loaded with drugs can be designed to overcome these biological barriers to improve efficacy while reducing morbidity. Nanomedicine has ushered in a new era for drug delivery by improving the therapeutic indices of the active pharmaceutical ingredients engineered within nanoparticles. First generation nanomedicines have received widespread clinical approval over the past two decades, from Doxil ® (liposomal doxorubicin) in 1995 to Onivyde ® (liposomal irinotecan) in 2015. This review highlights the biological barriers to effective drug delivery in cancer, emphasizing the need for nanoparticles for improving therapeutic outcomes. A summary of different nanoparticles used for drug delivery applications in cancer are presented. The review summarizes recent successes in cancer nanomedicine in the clinic. The clinical trials of Onivyde leading to its approval in 2015 by the Food and Drug Adminstration are highlighted as a case study in the recent clinical success of nanomedicine against cancer. Next generation nanomedicines need to be better targeted to specifically destroy cancerous tissue, but face several obstacles in their clinical development, including identification of appropriate biomarkers to target, scale-up of synthesis, and reproducible characterization. These hurdles need to be overcome through multidisciplinary collaborations across academia, pharmaceutical industry, and regulatory agencies in order to achieve the goal of eradicating cancer. This review discusses the current use of clinically approved nanomedicines, the investigation of nanomedicines in clinical trials, and the challenges that may hinder development of the nanomedicines for cancer treatment.

KRAS-driven lung cancers frequently inactivate TP53 and/or STK11/LKB1, defining tumor subclasses with emerging clinical relevance. Specifically, KRAS-LKB1 (KL) mutant lung cancers are particularly aggressive, lack PD-L1, and respond poorly to immune checkpoint blockade (ICB). The mechanistic basis for this impaired immunogenicity, despite the overall high mutational load of KRAS mutant lung cancers, remains obscure. Here we report that LKB1 loss results in marked silencing of STING expression and insensitivity to cytoplasmic double strand DNA (dsDNA) sensing. This effect is mediated at least in part by hyperactivation of DNMT1 and EZH2 activity related to elevated S-adenylmethionine (SAM) levels, and reinforced by DNMT1 upregulation. Ectopic expression of STING in KL cells engages IRF3 and STAT1 signaling downstream of TBK1 and impairs cellular fitness, due to the pathologic accumulation of cytoplasmic mitochondrial dsDNA associated with mitochondrial dysfunction. Thus, silencing of STING avoids these negative consequences of LKB1 inactivation, while facilitating immune escape.

Mesenchymal tumor subpopulations secrete pro-tumorigenic cytokines and promote treatment resistance. This phenomenon has been implicated in chemorefractory small cell lung cancer and resistance to targeted therapies, but remains incompletely defined. Here, we identify a subclass of endogenous retroviruses (ERVs) that engages innate immune signaling in these cells. Stimulated 3 prime antisense retroviral coding sequences (SPARCS) are oriented inversely in 3' untranslated regions of specific genes enriched for regulation by STAT1 and EZH2. Derepression of these loci results in double-stranded RNA generation following IFN-γ exposure due to bi-directional transcription from the STAT1-activated gene promoter and the 5' long terminal repeat of the antisense ERV. Engagement of MAVS and STING activates downstream TBK1, IRF3, and STAT1 signaling, sustaining a positive feedback loop. SPARCS induction in human tumors is tightly associated with major histocompatibility complex class 1 expression, mesenchymal markers, and downregulation of chromatin modifying enzymes, including EZH2. Analysis of cell lines with high inducible SPARCS expression reveals strong association with an AXL/MET-positive mesenchymal cell state. While SPARCS-high tumors are immune infiltrated, they also exhibit multiple features of an immune-suppressed microenviroment. Together, these data unveil a subclass of ERVs whose derepression triggers pathologic innate immune signaling in cancer, with important implications for cancer immunotherapy.

Microfluidic culture has the potential to revolutionize cancer diagnosis and therapy. Indeed, several microdevices are being developed specifically for clinical use to test novel cancer therapeutics. To be effective, these platforms need to replicate the continuous interactions that exist between tumor cells and non-tumor cell elements of the tumor microenvironment through direct cell-cell or cell-matrix contact or by the secretion of signaling factors such as cytokines, chemokines and growth factors. Given the challenges of personalized or precision cancer therapy, especially with the advent of novel immunotherapies, a critical need exists for more sophisticated ex vivo diagnostic systems that recapitulate patient-specific tumor biology with the potential to predict response to immune-based therapies in real-time. Here, we present details of a method to screen for the response of patient tumors to immune checkpoint blockade therapy, first reported in Jenkins et al. Cancer Discovery, 2018, 8, 196-215, with updated evaluation of murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS), including evaluation of the requirement for 3D microfluidic culture in MDOTS, demonstration of immune-checkpoint sensitivity of PDOTS, and expanded evaluation of tumor-immune interactions using RNA-sequencing to infer changes in the tumor-immune microenvironment. We also examine some potential improvements to current systems and discuss the challenges in translating such diagnostic assays to the clinic.

Small cell lung carcinoma (SCLC) is highly mutated, yet durable response to immune checkpoint blockade (ICB) is rare. SCLC also exhibits cellular plasticity, which could influence its immunobiology. Here we discover that a distinct subset of SCLC uniquely upregulates MHC I, enriching for durable ICB benefit. In vitro modeling confirms epigenetic recovery of MHC I in SCLC following loss of neuroendocrine differentiation, which tracks with derepression of STING. Transient EZH2 inhibition expands these nonneuroendocrine cells, which display intrinsic innate immune signaling and basally restored antigen presentation. Consistent with these findings, murine nonneuroendocrine SCLC tumors are rejected in a syngeneic model, with clonal expansion of immunodominant effector CD8 T cells. Therapeutically, EZH2 inhibition followed by STING agonism enhances T-cell recognition and rejection of SCLC in mice. Together, these data identify MHC I as a novel biomarker of SCLC immune responsiveness and suggest novel immunotherapeutic approaches to co-opt SCLC's intrinsic immunogenicity. Significance: SCLC is poorly immunogenic, displaying modest ICB responsiveness with rare durable activity. In profiling its plasticity, we uncover intrinsically immunogenic MHC Ihi subpopulations of nonneuroendocrine SCLC associated with durable ICB benefit. We also find that combined EZH2 inhibition and STING agonism uncovers this cell state, priming cells for immune rejection. This article is highlighted in the In This Issue feature, p. 1861

Intratumoral recruitment of immune cells following innate immune activation is critical for anti-tumor immunity and involves cytosolic dsDNA sensing by the cGAS/STING pathway. We have previously shown that KRAS-LKB1 (KL) mutant lung cancer, which is resistant to PD-1 blockade, exhibits silencing of STING, impaired tumor cell production of immune chemoattractants, and T cell exclusion. Since the vasculature is also a critical gatekeeper of immune cell infiltration into tumors, we developed a novel microfluidic model to study KL tumor-vascular interactions. Notably, dsDNA priming of LKB1reconstituted tumor cells activates the microvasculature, even when tumor cell STING is deleted. cGAS-driven extracellular export of 2 3 cGAMP by cancer cells activates STING signaling in endothelial cells and cooperates with type 1 interferon to increase vascular permeability and expression of E selectin, VCAM-1, and ICAM-1 and T cell adhesion to the endothelium. Thus, tumor cell cGAS-STING signaling not only produces T cell chemoattractants, but also primes tumor vasculature for immune cell escape.

Cancer immunotherapy is a rapidly evolving and paradigm shifting treatment modality that adds a strong tool to the collective cancer treatment arsenal. It can be effective even for late stage diagnoses and has already received clinical approval. Tumors are known to not only avoid immune surveillance but also exploit the immune system to continue local tumor growth and metastasis. Because of this, most immunotherapies, particularly those directed against solid cancers, have thus far only benefited a small minority of patients. Early clinical substantiation lends weight to the claim that cancer immunotherapies, which are adaptive and enduring treatment methods, generate much more sustained and robust anticancer effects when they are effectively formulated in nanoparticles or scaffolds than when they are administered as free drugs. Engineering cancer immunotherapies using nanomaterials is, therefore, a very promising area worthy of further consideration and investigation. This review focuses on the recent advances in cancer immunoengineering using nanoparticles for enhancing the therapeutic efficacy of a diverse range of immunotherapies. The delivery of immunostimulatory agents to antitumor immune cells, such as dendritic or antigen presenting cells, may be a far more efficient tactic to eradicate tumors than delivery of conventional chemotherapeutic and cytotoxic drugs to cancer cells. In addition to its immense therapeutic potential, immunoengineering using nanoparticles also provides a valuable tool for unearthing and understanding the basics of tumor biology. Recent research using nanoparticles for cancer immunotherapy has demonstrated the advantage of physicochemical manipulation in improving the delivery of immunostimulatory agents. In vivo studies have tested a range of particle sizes, mostly less than 300 nm, and particles with both positive and negative zeta potentials for various applications. Material composition and surface modifications have been shown to contribute significantly in selective targeting, efficient delivery and active stimulation of immune system targets. Thus, these investigations, including a wide array of nanoparticles for cancer immunotherapy, substantiate the employment of nanocarriers for efficacious cancer immunotherapies.

Triple-negative breast cancer (TNBC) is a heterogeneous disease enriched for mutations in PTEN and dysregulation of innate immune signaling. Here, we demonstrate that Rab7, a recently identified substrate of PTEN phosphatase activity, is also a substrate of the innate immune signaling kinases TANK-binding kinase 1 (TBK1)/IkB kinase e (IKKe) on the same serine-72 (S72) site. An unbiased search for novel TBK1/IKKe substrates using stable isotope labeling with amino acids in cell culture phosphoproteomic analysis identified Rab7-S72 as a top hit. PTEN-null TNBC cells expressing a phosphomimetic version of Rab7-S72 exhibited diffuse cytosolic Rab7 localization and enhanced innate immune signaling, in contrast to a kinase-resistant version, which localized to active puncta that promote lysosomal-mediated stimulator of interferon genes (STING) degradation. Thus, convergence of PTEN loss and TBK1/IKKe activation on Rab7-S72 phosphorylation limited STING turnover and increased downstream production of IRF3 targets including CXCL10, CCL5, and IFNb. Consistent with this data, PTEN-null TNBC tumors expressed higher levels of STING, and PTEN-null TNBC cell lines were hyperresponsive to STING agonists. Together, these findings begin to uncover how innate immune signaling is dysregulated downstream of TBK1/IKKe in a subset of TNBCs and reveals previously unrecognized cross-talk with STING recycling that may have implications for STING agonism in the clinic.Significance: These findings identify Rab7 as a substrate for TBK1 for regulation of innate immune signaling, thereby providing important insight for strategies aimed at manipulating the immune response to enhance therapeutic efficacy in TNBC.