Abstract P2-13-09: An investigational next generation ADC (DAN-311) is highly effective in HER2-low breast cancer models

Background: Nanoparticles (NPs) have been developed to enhance the pharmacokinetic (PK) and biodistribution characteristics of molecules. Many early NPs, including liposomes, dendrimers, and polymeric micelles, were limited in their ability to access target tissue and lacked uniform release rates. A promising nanoparticle therapeutic has been developed utilizing biocompatible polymer chemistry. By covalently attaching chemotherapy to the polymer through linker strategies that allow for modulation of release and PK, polymeric nanoparticles provide advantages over encapsulation nanoparticle strategies. Additionally, a targeting moiety can be added to make a next-generation ADC with the drug-to-antibody-ratio (DAR) well controlled and significantly greater (e.g. DAR=60) compared to traditional ADCs. DAN-311 is a Next-Generation Antibody Drug Conjugate (NG-ADC) with a HER2-targeting agent (trastuzumab) conjugated to a therapeutic nanoparticle with camptothecin (CPT), a topoisomerase I inhibitor. The advantages that DAN-311 offers to the 50% of patients with breast cancer have tumors with low HER2 expression is two-fold: 1) the larger DAR can lead to an enhanced bystander effect where the chemotherapy is effective against the targeted cells and also the neighboring cells, and 2) the nanoparticle is also active against HER2 non-expressing cells through the enhanced permeability and retention (EPR) effect. Here, we present the control and consistency of key DAN-311 NP characteristics that allow for efficient and large scale-manufacture, including particle size, chemotherapy load (DAR), and payload release rate. We also report the enhanced efficacy of DAN-311 in a HER2-low breast cancer (JIMT-1) xenograft mouse model. Methods: Release of CPT from nanoparticles across range of combined properties was evaluated by HPLC in pH 5.5 PBS (endosomal pH), pH 7.4 PBS (physiologic pH), mouse plasma, and human plasma. HER2-low breast cancer tumor cells (JIMT-1) were implanted into female CB.17 SCID mice. Mice were randomized to vehicle or treatment arms until tumors reached 2000 mm3 or day 46. The groups evaluated included trastuzumab, the non-targeted core nanoparticle of DAN-311, and DAN-311. Results: NPs across a wide range in polymer molecular weight and drug loading demonstrate striking consistency in particle size (ca. 30-45 nm), DAR (ca. 60-70 CPT molecules), and demonstrate linear release kinetics in various physiologically-relevant media. DAN-311 exhibited significantly greater tumor growth inhibition compared to vehicle, core particle, and trastuzumab. The non-targeted core particle also demonstrated significant tumor growth inhibition compared to vehicle and trastuzumab, which was sustained for at least 3 weeks after the final dose.

Core particle = same DAN-311 nanoparticle without HER2 targeting. Conclusions: DAN-311, a Next-Generation ADC with a HER2-targeting agent (trastuzumab) on a polymeric nanoparticle conjugated with CPT demonstrated a significant ability to inhibit tumor growth in a HER2-low xenograft mouse model. Importantly, the nanoparticle targeted delivery of CPT for cells with low expression of receptors is highly efficient in cell killing and the large DAR provides greater bystander cell killing capability; and non-HER2-expressing lesions or regions of tumors will additionally be treated by the nanoparticle through EPR. DAN-311 is advancing to clinical study to treat HER2-low metastatic breast cancer patients.

TreatmentDose (mg/kg)Day 22 TGI (%)Day 46 TGI (%)Trastuzumab10 mg/kg Tras629Core particle1 mg/kg CPT3955DAN-31110 mg/kg Tras/1 mg/kg CPT8777

Citation Format: Ashley P Wright, Emily A Wyatt, Robert J Lamm, Carl M Blumenfeld, Jodi D Bradley, Gayatri Shrikhande, Timothy Hagerty. An investigational next generation ADC (DAN-311) is highly effective in HER2-low breast cancer models [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-09.

Abstract P5-16-16: A novel investigational nanoparticle therapeutic (DAN-222) for breast cancer and other solid tumors

Background: Here we introduce a novel nanoparticle therapeutic, DAN-222, which offers a variety of potential clinical benefits in delivery of chemotherapy versus native drug, including a broader therapeutic index. DAN-222 is a polymeric nanoparticle covalently conjugated with camptothecin (CPT), a topoisomerase I inhibitor, that demonstrates enhanced efficacy over native CPT at the same dose and has significantly reduced bone marrow exposure (limiting potential safety concerns), thus widening the therapeutic index with respect to both efficacy and safety. The nanoparticle therapeutic provides sustained drug exposure through conjugation of the chemotherapy payload to the novel biocompatible polymer scaffold that can be modulated by choice of linker, allowing for optimization of the release rate for a given payload and target. To illustrate the flexibility and capabilities of modulating payload release kinetics, we present a series of CPT-containing nanoparticles with different linkers encompassing a wide range of in vitro release rates. We also demonstrate the vastly enhanced efficacy of DAN-222 in multiple breast cancer xenograft mouse models. Methods: In vitro release: Release of CPT from nanoparticles formed with various linkers was evaluated by HPLC in pH 5.5 PBS (endosomal pH), pH 7.4 PBS (physiologic pH), mouse plasma, and human plasma. Efficacy: Breast cancer xenograft tumor models with human BT-474 and MDA-MB-231 were propagated in CB.17 SCID and NCr nu/nu mice respectively, with 10 animals per group. Results: All linkers demonstrate linear kinetics and release slowly at reduced pH, consistent with the mechanism of release. At physiologic pH, a diversity of in vitro release rates is achieved by modulating the sensitivity of the linker. Importantly, all linkers have similar release in mouse and human plasma, indicating strong cross-species translation.

Results in the mouse xenograft models showed that DAN-222 had a superior and sustained efficacy compared to CPT and irinotecan (an approved topoisomerase-1 inhibitor) as demonstrated by tumor growth inhibition.

Conclusions: We demonstrate the ability to modulate the payload release kinetics from the nanoparticle therapeutic by the choice of linker, with species-independent release rates. With an optimal linker selected, DAN-222 shows enhanced and sustained efficacy over native CPT. Since DAN-222 has previously been shown to have reduced bone marrow exposure of chemotherapy, it may provide a significant therapeutic advancement with a wider therapeutic index based on both enhanced efficacy and improved safety. DAN-222 is advancing to a clinical trial in HER2-negative metastatic breast cancer.

In vitro release half-lives (t1/2) (hours)Linker 1Linker 2Linker 3Linker 4Linker 5PBS, pH 5.5>50>50>50>50>50PBS, pH 7.47.120.5>50>50>50Mouse Plasma1.74.817.237.7>50Human Plasma1.64.817.137.8>50

TreatmentBT-474MDA-MB-231Day 25 TGI(%)Day 36 TGI*(%)Day 25 TGI (%)Day 32 TGI* (%)Camptothecin (3 mg/kg)64404756Irinotecan (100 mg/kg)71594751DAN-222 (3 mg/kg CPT)93967475*Day the vehicle control group reached the study endpoint.

Citation Format: Emily A Wyatt, Ashley P Wright, Carl M Blumenfeld, Robert J Lamm, Timothy Hagerty. A novel investigational nanoparticle therapeutic (DAN-222) for breast cancer and other solid tumors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-16-16.

Optimizing the Polymer Chemistry and Synthesis Method of PolySTAT, an Injectable Hemostat

There is a lack of prehospital hemostatic agents, especially for noncompressible hemorrhage. We previously reported PolySTAT, a unimeric, injectable hemostatic agent, that physically cross-links fibrin to strengthen clots. In this work, we sought to improve the water-solubility and synthesis yield of PolySTAT to increase the likelihood of clinical translation, reduce cost, and facilitate future mass production. First, we focused on side-chain engineering of the carrier polymer backbone to improve water-solubility. We found that substitution of the 2-hydroxyethyl methacrylate (HEMA) monomer with glycerol monomethacrylate (GmMA) significantly improved the water-solubility of PolySTAT without compromising efficacy. Both materials increased clot firmness and decreased lysis as measured by rotational thromboelastometry (ROTEM). Additionally, we confirmed the in vivo activity of GmMA-based PolySTAT by improving rat survival in a femoral artery bleed model. Second, to reduce waste, we evaluated PolySTAT synthesis via direct polymerization of peptide monomers. Methacrylamide and methacrylate peptide-monomers were synthesized and polymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization. This approach markedly improved the yield of PolySTAT synthesis while maintaining its biological activity in ROTEM. This work demonstrates the flexibility of PolySTAT to a variety of comonomers and synthetic routes and establishes direct RAFT polymerization of peptide monomers as a potential route of mass production.

Dual Polymerizations: Untapped Potential for Biomaterials

Block copolymers with unique architectures and those that can self-assemble into supramolecular structures are used in medicine as biomaterial scaffolds and delivery vehicles for cells, therapeutics, and imaging agents. To date, much of the work relies on controlling polymer behavior by varying the monomer side chains to add functionality and tune hydrophobicity. Although varying the side chains is an efficient strategy to control polymer behavior, changing the polymer backbone can also be a powerful approach to modulate polymer self-assembly, rigidity, reactivity, and biodegradability for biomedical applications. There are many developments in the syntheses of polymers with segmented backbones, but these developments are not widely adopted as strategies to address the unique constraints and requirements of polymers for biomedical applications. This review highlights dual polymerization strategies for the synthesis of backbone-segmented block copolymers to facilitate their adoption for biomedical applications.

Peptide valency plays an important role in the activity of a synthetic fibrin-crosslinking polymer

Therapeutic polymers have the potential to improve the standard of care for hemorrhage, or uncontrolled bleeding, as synthetic hemostats. PolySTAT, a fibrin-crosslinking peptide-polymer conjugate, has the capacity to rescue fibrin clot formation and improve survival in a model of acute traumatic bleeding. PolySTAT consists of a synthetic polymer backbone to which targeting fibrin-binding peptides are linked. For translation of PolySTAT, the optimal valency of peptides must be determined. Grafting of fibrin-binding peptides to the poly(hydroxyethyl methacrylate)-based backbone was controlled to produce peptide valencies ranging from 0 to 10 peptides per polymer. PolySTATs with valencies of ≈4 or greater resulted in increased clot firmness, kinetics, and decreased breakdown as measured by thromboelastometry. A valency of ≈4 increased clot firmness 57% and decreased clot breakdown 69% compared to phosphate-buffered saline. This trend was characterized by neutron scattering, which probed the structure of clots formed in the presence of PolySTAT. Finally, PolySTAT with valencies of 4 (100% survival; p = 0.013) and 8 (80% survival; p = 0.063) improved survival compared to an albumin control in a femoral artery injury model (20% survival). This work demonstrates tunability of hemostatic polymers and the ability of in vitro assays to predict in vivo efficacy.

Rapid inertial solution exchange for enrichment and flow cytometric detection of microvesicles

Exosomes, nanosized membrane-bound vesicles released by cells, play roles in cell signaling, immunology, virology, and oncology. Their study, however, has been hampered by difficulty in isolation and quantification due to their size and the complexity of biological samples. Conventional approaches to improved isolation require specialized equipment and extensive sample preparation time. Therefore, isolation and detection methods of exosomes will benefit biological and clinical studies. Here, we report a microfluidic platform for inline exosome isolation and fluorescent detection using inertial manipulation of antibody-coated exosome capture beads from biological fluids.