Considerations for the Terminal Sterilization of Oligonucleotide Drug Products

A primary function of the parenteral drug product manufacturing process is to ensure sterility of the final product. The two most common methods for sterilizing parenteral drug products are terminal sterilization (TS), whereby the drug product is sterilized in the final container following filling and finish, and membrane sterilization, whereby the product stream is sterilized by membrane filtration and filled into presterilized containers in an aseptic processing environment. Although TS provides greater sterility assurance than membrane sterilization and aseptic processing, not all drug products are amenable to TS processes, which typically involve heat treatment or exposure to ionizing radiation. Oligonucleotides represent an emerging class of therapeutics with great potential for treating a broad range of indications, including previously undruggable targets. Owing to their size, structural complexity, and relative lack of governing regulations, several challenges in drug development are unique to oligonucleotides. This exceptionality justifies a focused assessment of traditional chemistry, manufacturing, and control strategies before their adoption. In this article, we review the current state of sterile oligonucleotide drug product processing, highlight the key aspects to consider when assessing options for product sterilization, and provide recommendations to aid in the successful evaluation and development of TS processes. We also explore current regulatory expectations and provide our interpretation as it pertains to oligonucleotide drug products.

Targeting the Somatostatin Receptor 2 with the Miniaturized Drug Conjugate, PEN-221: A Potent and Novel Therapeutic for the Treatment of Small Cell Lung Cancer

Small cell lung cancer (SCLC) is an aggressive neuroendocrine carcinoma with a 95% mortality rate with no improvement to treatment in decades, and new therapies are desperately needed. PEN-221 is a miniaturized peptide-drug conjugate (∼2 kDa) designed to target SCLC via a Somatostatin Receptor 2 (SSTR2)-targeting ligand and to overcome the high proliferation rate characteristic of this disease by using the potent cytotoxic payload, DM1. SSTR2 is an ideal target for a drug conjugate, as it is overexpressed in SCLC with limited normal tissue expression. In vitro, PEN-221 treatment of SSTR2-positive cells resulted in PEN-221 internalization and receptor-dependent inhibition of cellular proliferation. In vivo, PEN-221 exhibited rapid accumulation in SSTR2-positive SCLC xenograft tumors with quick clearance from plasma. Tumor accumulation was sustained, resulting in durable pharmacodynamic changes throughout the tumor, as evidenced by increases in the mitotic marker of G₂-M arrest, phosphohistone H3, and increases in the apoptotic marker, cleaved caspase-3. PEN-221 treatment resulted in significant antitumor activity, including complete regressions in SSTR2-positive SCLC xenograft mouse models. Treatment was effective using a variety of dosing schedules and at doses below the MTD, suggesting flexibility of dosing schedule and potential for a large therapeutic window in the clinic. The unique attributes of the miniaturized drug conjugate allowed for deep tumor penetration and limited plasma exposure that may enable long-term dosing, resulting in durable tumor control. Collectively, these data suggest potential for antitumor activity of PEN-221 in patients with SSTR2-positive SCLC.

Sizing up the Next Generation of Nanomedicines

During the past two decades the nanomedicine field has experienced significant progress. To date, over sixty nanoparticle (NP) formulations have been approved in the US and EU while many others are in clinical or preclinical development, indicating a concerted effort to translate promising bench research to commercially viable pharmaceutical products. The use of NPs as novel drug delivery systems, for example, can improve drug safety and efficacy profiles and enable access to intracellular domains of diseased cells, thus paving the way to previously intractable biological targets. However, the measurement of their physicochemical properties presents substantial challenges relative to conventional injectable formulations. In this perspective, we focus exclusively on particle size, a core property and critical quality attribute of nanomedicines. We present an overview of relevant state-of-the-art technologies for particle sizing, highlighting the main parameters that can influence the selection of techniques suitable for a specific size range or material. We consider the increasing need, and associated challenge, to measure size in physiologically relevant media. We detail the importance of standards, key to validate any measurement, and the need for suitable reference materials for processes used to characterize novel and complex NPs. This perspective highlights issues critical to achieve compliance with regulatory guidelines and to support research and manufacturing quality control.

Discovery of an SSTR2-Targeting Maytansinoid Conjugate (PEN-221) with Potent Activity in Vitro and in Vivo

Somatostatin receptor 2 (SSTR2) is frequently overexpressed on several types of solid tumors, including neuroendocrine tumors and small-cell lung cancer. Peptide agonists of SSTR2 are rapidly internalized upon binding to the receptor and linking a toxic payload to an SSTR2 agonist is a potential method to kill SSTR2-expressing tumor cells. Herein, we describe our efforts towards an efficacious SSTR2-targeting cytotoxic conjugate; examination of different SSTR2-targeting ligands, conjugation sites, and payloads led to the discovery of 22 (PEN-221), a conjugate consisting of microtubule-targeting agent DM1 linked to the C-terminal side chain of Tyr³-octreotate. PEN-221 demonstrates in vitro activity which is both potent (IC₅₀ = 10 nM) and receptor-dependent (IC₅₀ shifts 90-fold upon receptor blockade). PEN-221 targets high levels of DM1 to SSTR2-expressing xenograft tumors, which has led to tumor regressions in several SSTR2-expressing xenograft mouse models. The safety and efficacy of PEN-221 is currently under evaluation in human clinical trials.

Abstract 39: Discovery of PEN-221, an SSTR2-targeting maytansinoid conjugate with potent activity in vitro and in vivo

Here we describe the discovery and the structure of PEN-221, a somatostatin receptor 2 (SSTR2) targeting peptide conjugated to DM1. PEN-221 is the first clinical compound from Tarveda’s Pentarin platform, which utilizes miniaturized drug conjugates that diffuse rapidly and deeply into solid tumors. Antibody drug conjugates (ADCs) have garnered a significant amount of attention in their ability to direct cytotoxic drugs to cancer cells; however, the efficacy of ADCs in solid tumors is limited by the slow diffusion of such large molecules through solid tumor tissue. Pentarins are designed to improve the efficacy of targeted therapies through effective tumor cell targeting and enhanced tumor penetration.

SSTR2, a GPCR overexpressed in multiple types of neuroendocrine tumors, including small cell lung cancers, internalizes rapidly upon agonist stimulation, making it an ideal vector for delivering cytotoxic payloads. Examination of a variety of SSTR2 targeting ligands, as well as several potential conjugation sites, led to the identification of the C-terminal side chain of [Tyr3]-octreotate amide as the best conjugation site for a lipophilic payload. The use of DM1 as a payload afforded superior receptor affinity and receptor internalization when compared to other similarly potent microtubule-targeting agents. In vitro studies show that PEN-221 has receptor-dependent cytotoxic effects, and preclinical studies demonstrate PEN-221 induces tumor regression in several SSTR2 expressing xenograft models.

Citation Format: Brian H. White, Patrick Bazinet, Kerry Whalen, Michelle DuPont, James M. Quinn, Rossitza Alargova, Tsun Au Yeung, Adam Brockman, James Gifford, Haley Oller, Kristina Kriksciukaite, Charles-Andre Lemelin, Patrick Lim Soo, Benoit Moreau, Samantha Perino, Gitanjali Sharma, Rajesh Shinde, Beata Sweryda-Krawiec, Mary Simcox, Richard Wooster, Mark T. Bilodeau. Discovery of PEN-221, an SSTR2-targeting maytansinoid conjugate with potent activity in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 39. doi:10.1158/1538-7445.AM2017-39

Gold-labeled block copolymer micelles reveal gold aggregates at multiple subcellular sites

There is increasing interest in the usefulness of block copolymer micelles as drug delivery vehicles. However, their subcellular distribution has not been explored extensively, mostly because of the lack of adequately labeled block copolymers. In a previous study, we showed that fluorescently labeled block copolymer micelles entered living cells and co-localized with cytoplasmic organelles selectively labeled with fluorescent dyes. The details of the observed co-localizations were, however, limited by the resolution of the fluorescence approach, which is ca. 500 nm. Using transmission electron microscopy (TEM), we established time- and concentration-dependent subcellular distributions of gold-labeled micelles within human embryonic kidney (HEK 293) cells and human lung carcinoma (A549) cells. Gold particles were incorporated into poly(4-vinylpyridine)-block-poly(ethylene oxide) (P4VP21-b-PEO45) micelles. Data from dynamic light scattering (DLS) and TEM analyses revealed that the sizes of the gold particles ranged from 4 to 8 nm. The cells survived up to 24 h in the presence of low gold-labeled micelle concentrations (0.73 microg/mL), but cell death occurred at higher concentrations (i.e., kidney cells are more susceptible than lung cells). Over 24 h periods of equivalent exposure, lung cells internalized significantly more gold-incorporated micelles than kidney cells. Although micelles were added to the cell culture media as dispersed colloidal particles, the presence of serum in these media caused aggregation. These aggregates occurred mainly close to the cell plasma membrane at early times (5-10 min); however, at later times (24 h) aggregated particles were seen inside endosomes and lysozomes. Thus, gold-incorporated (labeled) micelles can serve as a valuable extension of the fluorescence approach to visualizing the localization of micelles in subcellular compartments, improving the resolution by at least 20-fold.

Impact of intraperitoneal, sustained delivery of paclitaxel on the expression of P-glycoprotein in ovarian tumors

Recently, we developed a novel implantable drug delivery system which can provide sustained intraperitoneal (i.p.) delivery of paclitaxel (PTX). As the impact of local sustained delivery on the development of multidrug resistance (MDR) is unknown, the objective of this study was to determine the impact of this drug delivery system on the in vivo expression of MDR1/P-glycoprotein (PGP) in a human ovarian xenograft tumor model. As compared to controls, intermittent i.p. dosing with PTX formulated in Cremophor EL (PTX(CrEL)) induced a two-fold increase in mRNA levels of MDR1 after a 14-day dosing period. On the other hand, sustained i.p. delivery of PTX with the implant system (PTX(film)) did not significantly affect MDR1 expression. Immunodetection of PGP in isolated xenografts supported the mRNA data. Histological analysis by H&E staining demonstrated a dose-dependent increase in tumor necrosis in the PTX(film) treated animals. Further, in vitro studies in human ovarian carcinoma cells also demonstrated a significant induction in the efflux activity of PGP with intermittent dosing schedules to PTX(CrEL) whereas this was not seen in cells dosed with PTX(film). Our findings suggest that sustained i.p. administration with PTX(film) attenuates development of MDR, suggesting that sustained, localized delivery of chemotherapeutic agents may improve current treatment strategies for ovarian cancer.

Polycaprolactone-block-poly(ethylene oxide) Micelles: A Nanodelivery System for 17β-Estradiol

Various hormone replacement regimens and delivery systems have been developed; however, there is still a need for additional, easily controllable and biocompatible systems. We have developed and characterized biocompatible polycaprolactone-block-poly(ethylene oxide) (PCL-b-PEO) micelles for the delivery of 17beta-estradiol (E2) and investigated their loading and release properties using fluorescence spectroscopy. The micelles are spherical aggregates that range in size from 20 to 40 nm, as determined by both transmission electron microscopy and dynamic light scattering. A high loading efficiency for E2 of up to 96%, as well as a high drug loading capacity of up to 4000 molecules of E2 per micelle (equivalent to 190% (w/w)), is obtainable. In addition, the E2 loading and release can be controlled by modifying the block length of the polycaprolactone core and the initial estradiol concentration. The release of E2 from the micelles showed a biphasic profile under perfect sink conditions: there is an initial burst release, followed by a slow and prolonged release for up to 5 days, until complete release is achieved. The release of E2 from the micelles was shown to be diffusional, as shown by the linearity of the release as a function of the square root of time. Approximate diffusion coefficients of the order of 10(-17) cm2/s were obtained. In vitro and in vivo experiments confirmed that the biological activity of E2 was retained after preparation of the micelles. This micelle carrier could serve as a versatile and efficient nanodelivery system for steroids and other poorly water soluble drugs that require solubilizing agents for delivery.

Active loading and tunable release of doxorubicin from block copolymer vesicles

Vesicles are spherical bilayers that offer a hydrophilic reservoir, suitable for the incorporation of water-soluble molecules, as well as a hydrophobic wall that protects the loaded molecules from the external solution. The permeability of a vesicle wall made from polystyrene can be enhanced by adding a plasticizer such as dioxane. Tuning the wall permeability allows loading and release of molecules from vesicles to be controlled. In this study, vesicles are prepared from polystyrene(310)-b-poly(acrylic acid)(36) and used as model carriers for doxorubicin (DXR), a weak amine and a widely used anticancer drug. To increase the wall permeability, different amounts of dioxane are added to the vesicle solution. A pH gradient is created across the vesicle wall (inside acidic) and used as an active loading method to concentrate the drug inside the vesicles. The results show that a pH gradient of ca. 3.8 units can enhance the loading level up to 10-fold relative to loading in the absence of the gradient. After loading, the release of DXR from vesicles is followed as a function of the wall permeability. The diffusion coefficient of doxorubicin through polystyrene (D) is evaluated from the initial slope of the release curves; the value of D ranges from 8 x 10(-17) to 6 x 10(-16) cm(2)/s, depending on the degree of plasticization of the vesicle wall.

Influence of metalation on the morphologies of poly(ethylene oxide)-block-poly(4-vinylpyridine) block copolymer micelles

Micellization of a poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO45-b-P4VP28) copolymer in water during metalation (incorporation of gold compounds and gold nanoparticle formation) with three types of gold compounds, NaAuCl4, HAuCl4, and AuCl3, was studied using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The transformations of the PEO45-b-P4VP28 block copolymer micelles in water were found to depend on a number of parameters including the thermal history of the as-prepared block copolymer, the type of the metal compound, and the metal loading. For the HAuCl4-filled PE045-b-P4VP28 micelles, the subsequent reduction with hydrazine hydrate results in a significant fraction of rodlike micelles, suggesting that slow nucleation (confirmed by the formation of the large gold nanoparticles) and facilitated migration of gold ions yields the ideal conditions for sphere-to-rod micellar transition.

Block copolymers modify the internalization of micelle-incorporated probes into neural cells

An important therapeutic concern is rate and extent of internalization of drugs into cells. Hydrophilic agents often internalize poorly and slowly, and highly lipophilic ones too rapidly. The incorporation of drugs into micelles allows regulation of their internalization parameters, and newly-described block copolymers can be selectively tailored to suit specific drugs. This report compares internalization of Cell Tracker CM-DiI (DiI), a highly lipophilic non-cytotoxic fluorescent probe in common use in biology, from the freely-presented (non-micelle-incorporated) and micelle-incorporated states. DiI was effectively incorporated (>60%) into 25-50 nm diameter spherical micelles made from polycaprolactone-b-polyethylene oxide block copolymer. Confocal microscopy was used to evaluate the internalization of DiI into mixed neuron-glia cultures (2-14 days in vitro, 2DIV-14DIV). Incorporation of DiI into micelles strikingly reduced the rate and extent of its internalization in both 2DIV and 14DIV cultures. Both the age of the cultures and the block copolymer employed to construct the micelles significantly influence the internalization of micelle-incorporated probe.