Nanoparticles in the clinic: An update

Abstract Nanoparticle drug delivery systems have been used in the clinic since the early 1990's. Since that time, the field of nanomedicine has evolved alongside growing technological needs to improve the delivery of various therapeutics. Over these past decades, newer generations of nanoparticles have emerged that are capable of performing additional delivery functions that can enable treatment via new therapeutic modalities. In the current clinical landscape, many of these new generation nanoparticles have reached clinical trials and have been approved for various indications. In the first issue of Bioengineering & Translational Medicine in 2016, we reviewed the history, current clinical landscape, and clinical challenges of nanoparticle delivery systems. Here, we provide a 3 year update on the current clinical landscape of nanoparticle drug delivery systems and highlight newly approved nanomedicines, provide a status update on previous clinical trials, and highlight new technologies that have recently entered the clinic.


| INTRODUCTION
The nanomedicine landscape continues to rapidly evolve driven by newly developed delivery strategies, new technologies, new treatment modalities, new drug approvals, and even clinical failures of current drugs. In 2016, we published a review article on the current clinical landscape of therapeutic nanoparticles, which highlighted over 25 Food and Drug Administration (FDA) or European Medicines Agency (EMA) approved nanomedicines and over 45 other nanoparticle technologies that were not FDA/EMA approved but were currently being evaluated in ongoing clinical trials. 1 That article also featured discussions on different nanoparticle types, their applications, their advantages as compared to free drugs, and their potential. We also discussed many of the biological issues (i.e., biodistribution, biological barrier breaching, and treating heterogeneous diseases), technological issues (i.e., scale-up limitations, parameter optimization, and predicting efficacy), and clinical challenges that have limited the translation of nanoparticles. 1 In these past 3 years, since that article was published, two intravenously administered nanoparticles have been FDA and EMA approved, one intratumorally administered nanoparticle received

| NEW APPROVALS
Since our previous article, three nanomedicines have been approved: Patisiran/ONPATTRO, VYXEOS, and NBTXR3/Hensify. VYXEOS is a combination chemotherapy nanoparticle, developed and marketed by Jazz Pharmaceuticals that, encapsulates a synergistic molar ratio of cytarabine to daunorubicin of 5:1 and received FDA approval for the treatment of acute myeloid leukemia in August of 2017. 2,3 VYXEOS are 100 nm bilamellar liposomes where the lipid membrane consists of desaturated phosphatidylcholine:distearylphosphatidylglycerol:cholesterol (7:2:1M ratio). 4 In the pivotal efficacy study (NCT01696084), VYXEOS provided a significant (p value = .005) improvement in overall survival of 9.6 months as compared to 5.9 months in the free drug control. 2,5 Importantly, this trial also showed that VYXEOS provided improved efficacy at a lower cumulative daunorubicin and cytarabine dose as compared to free drug counterparts. 6 Since 2016, the number of clinical trials of VYXEOS has increased from 7 to 21 with the most recent trials investigating the use of VYXEOS in additional patient populations (e.g., children; NCT03826992) and leukemias (e.g., lymphoblastic leukemias; NCT03575325). Unlike other approved nanoparticles for cancer treatment, VYXEOS delivers two drugs in a synergistic ratio. Delivery of the synergistic combination of daunorubicin and cytarabine is enabled by the nanoparticle platform since the encapsulated ratio of drugs is able to both interact with target cells upon release. In the contrasting case of free drugs, each drug exhibits distinct pharmacokinetic profiles and are metabolized at different rates; as such, delivery of synergistic combinations of free drugs to target cells must also consider and counteract these biological processes. Product sales for VYXEOS were $100.8 million in 2018. 7 As the first clinically approved nanoparticle to deliver a synergistic combination of free drugs, VYXEOS can pave the way for new combination nanoparticle formulations that leverage widely-utilized combination chemotherapy regimens from the clinic. 8,9 Patisiran/ONPATTRO is an siRNA-delivering lipid-based nanoparticle developed and marketed by Alnylam, for the silencing of a specific gene responsible for expression of transthyretin, which can cause hereditary transthyretin amyloidosis. 10 Patisiran/ONPATTRO lipid nanoparticles consist of (6Z,9Z,28Z,31Z)-heptatriaconta-6,9,28,31-tetraen-19-yl-4-(dimethylamino) butanoate (DLin-MC3-DMA) plus cholesterol, 1,2-distearoyl-sn-glycero-3-phosphocholine and α-(3 0 -{[1,2-di(myristyloxy)propanoxy] carbonylamino}propyl)-ω-methoxy polyoxyethylene (PEG 2000 -C-DMG). 11 Patisiran/ONPATTRO was approved by the FDA in August of 2018 12 and was the first clinically approved example of an RNAi therapy-delivering nanoparticle administered intravenously. Importantly, Patisiran/ONPATTRO is also the first FDA approved RNAi therapeutic in general, 12 independent of the nanoparticle delivery vehicle. Approval of the first RNAi therapeutic was a major milestone in the biotech industry and considering that the delivery vehicle was a nanoparticle, approval of Patisiran/ONPATTRO was also a major milestone for nanomedicines. In the Phase III efficacy study (NCT01960348), 56% of patients receiving Patisiran/ONPATTRO exhibited improvements in modified Neuropathy Impairment Score+7 as compared to 4% receiving the placebo. 10 Moreover, serum transthyretin decreased by over 70% in patients receiving Patisiran/ONPATTRO as compared to less than 20% in patients receiving the placebo. 10 Global net revenues for Patisiran/ONPATTRO were $12.1 million in 2018 with over 200 patients in Europe and the United States receiving treatment. 13 As the first clinically approved siRNA/RNAi therapeutic, Patisiran/ONPATTRO demonstrates how nanoparticles can be used to enable the delivery, and in this case approval, of highly challenging therapeutics to humans. NBTXR3/Hensify is a 50 nm crystalline hafnium oxide nanoparticle with negatively charged phosphate coating, developed and marketed by Nanobiotix. 14 NBTXR3/Hensify enhances external radiotherapy via a physical mode of action that relies on hafnium's natural radioenhancing properties. 14,15 Specifically, the interaction between ionizing radiation and hafnium facilitates a higher energy deposit as compared to ionizing radiation without hafnium interaction; this results in the generation of significantly more electrons and increases radiation-mediated cell death from standard radiation oncology procedures. 14,15 NBTXR3/Hensify received CE Mark approval in April of 2019 for the treatment of locally advanced soft tissue sarcoma. 16 Since our previous article, the number of clinical trials of NBTXR3/ Hensify has increased from 1 to 8. While NBTXR3/Hensify is approved for intratumoral administration, clinical trials had investigated it for intra-arterial administration (NCT01946867). The newest trials are only investigating NBTXR3/Hensify for intratumoral injections, but have expanded their indications to include treatment of prostate cancer (NCT02805894) and lung cancer with combined immunotherapy (NCT03589339). The reasoning for including immunotherapy with NBTXR3/Hensify treatment builds on preclinical data that demonstrated improved efficacy of immunotherapies following NBTXR3/Hensify treatment, stemming from an increased antitumor immune response. 17,18 Since the mechanism of action of NBTXR3/ Hensify is unique and unlike other approved nanoparticles or therapeutics, NBTXR3/Hensify may represent the next-generation of nanoparticle therapeutics; specifically, nanoparticle therapeutics that can provide therapeutic benefits in a complementary and possibly synergistic way to standard therapeutic modalities. Table 1, which previously listed FDA/EMA approved nanomedicines as of 2016, is now updated to include these recently approved nanoparticles.

| UPDATE ON PREVIOUS TRIALS
In our previous article, over 45 different nonapproved nanoparticles (liposomes, polymeric, micelles, albumin-bound nanoparticles, and inorganic nanoparticles) were listed as active in a total of over 80 different clinical trials (mostly for the treatment of various cancers but also radiation exposure, arthritis, pneumonia, amyloidosis, hepatitis, and fibrosis). Of these 80 trials, 28 have since been completed with 12 being terminated early.
Of the 45 different nanoparticles, seven possessed targeting functionality, and six offered stimuli-responsive functions (e.g., thermal ablation in response to near-infrared light, thermosensitive liposomes The lone non-cancer indication is mRNA-1944, which are two mRNAs encoding heavy and light chains of anti-Chikungunya antibody formulated in lipid nanoparticles, toward the prevention of Chikungunya virus infection. Table 3 summarizes these findings. It should be noted that other clinical trials investigating nanoparticles for the delivery of mRNA exist but since they are predominately delivered through intradermal or other routes of administration they will not be covered here. We point the reader to a recent review on mRNA delivery strategies where current clinical trials and delivery vehicles are a primary focus. 19

| CONCLUSIONS
Nanoparticle drug delivery systems offer many advantages over their free drug counterparts, can fundamentally change how therapeutics are delivered, and also enable the development of novel treatment modalities. This is demonstrated by the recent approvals of Patisiran/ONPATTRO (the first FDA approved RNAi therapeutic), VYXEOS (a nanoparticle capable of delivering synergistic ratios of two drugs), and NBTXR3/Hensify (a radio-enhancing nanoparticle that synergizes with standard of care radiation oncology treatments). On the other hand, nanoparticles also face unique challenges related to their biological, technological, and clinical limitations that must be addressed to achieve consistent clinical impact. These advantages and challenges were discussed in-depth in the 2016 review 1 and in many other reviews. [20][21][22][23][24][25] With the increasing numbers of nanoparticle clinical trials, including nanoparticle technologies that were in trials at the time of our previous article ( Table 2) and those that have entered the clinic since then (Table 3), the interest and pursuit of successful nanoparticle technologies continues. Taken together with these recent approvals, the field of nanoparticle drug delivery continues to make breakthroughs that improve human health.