Issue:June 2021

OPEN INNOVATION PLATFORM – Beyond the Rule of Five: Scouting for Novel Formulation Approaches to Enable the Subcutaneous Application of Molecules With Poor Drug-Like Properties in Preclinical Research – Facilitated Through


bRo5 (beyond Lipinski’s rule of 5) compounds, like PROTACs, offer novel opportunities for drug discovery to address difficult or previously undruggable targets. Nevertheless, these molecules often have poor drug-like properties, such as low permeability, low aqueous solubility, and are therefore difficult to access via oral administration. Other routes of administration have been ex­plored in preclinical drug discovery to enable the evaluation of a molecule’s PK, efficacy, and safety profile without optimization of the compounds’ properties. The subcutaneous administration route is often chosen as an alternative. Even though the subcuta­neous application route has immense potential in the preclinical context, there are only a few well-described formulation options or excipients available.

Based on the success of a recently completed open innova­tion challenge in drug delivery,1 we have decided to use Boehringer Ingelheim’s portal,, once again: We in­vite scientists from around the world to submit their innovative and even unconventional ideas to tackle this fundamental chal­lenge.

We are looking for proposals that would provide innovative formulation approaches to facilitate the subcutaneous application of bRo5 molecules in a preclinical setting.2 As an incentive to sub­mit proposals, we provide all selected applicants with access to an unprecedented selection of novel bRo5 compounds. Addition­ally, successful applicants will have the opportunity to directly in­teract with scientific experts to establish successful collaborations.

Here, we provide a short overview of the bRo5 compound class from a formulation developer’s perspective. Further, it will provide insights into the opnMe call and how we plan to incen­tivize innovative drug delivery solutions.


Developed in the 1990s, Lipinski’s rule of five (Ro5) was an attempt to rationalize compound design in preclinical research. The set of rules concerning a molecule’s physicochemical prop­erties state that poor oral absorption or permeability are more likely when a molecule exhibits the following characteristics: >5 hydrogen bond donors, a molecular mass > 500, calculated logP is > 5, and a sum of nitrogen and oxygen atoms greater than ten.3 Today, there is an increasing focus on less druggable targets, such as the disruption of protein-protein interactions (PPI), that offer high potential for the development of new therapeutic agents and may require beyond rule of 5 (bRo5) chemical matter.4 In 2020, 31% of all approved NCEs failed to meet Lip­inski’s criteria.5

There is great therapeutic potential in the bRo5 chemical space. PROtelolysis Tar­geting Chimeras (PROTACS) have at­tracted great attention both from academia and industry. PROTACs regulate protein function by degrading target pro­teins instead of inhibiting them, providing more sensitivity to drug-resistant targets and a greater chance to affect the non-en­zymatic functions. PROTACs have been proven to show better selectivity compared to classic inhibitors.6 A challenge for pre­venting PROTACs from realizing their ther­apeutic potential is their lack of compliance to the Ro5. In vivo studies re­ported with PROTACs in peer-reviewed lit­erature have typically been performed through parenteral delivery rather than oral administration.7

bRo5 compounds typically have poor physicochemical, drug metabolism, and pharmacokinetic properties, such as high lipophilicity, low solubility, low permeabil­ity, and high metabolic clearance. For these molecules, it is a challenge to achieve the desired exposure via the p.o. administration route.8 Other routes of ad­ministration have been explored in preclin­ical drug discovery to enable the evaluation of a molecule’s PK, efficacy, and safety profile. The subcutaneous ad­ministration route is often chosen as an al­ternative as it offers several advantages. Absorption upon subcutaneous adminis­tration is normally rapid because the sub­cutaneous space is richly proliferated with blood vessels. The area is easily accessi­ble, and many sites of injections are avail­able.9,10

The subcutaneous route is amenable to different formulation principles, e.g., suspension and solution formulations, minipumps, or extended-release formula­tions like PLGA-microparticles.11 The choice of formulation type can play a major role when evaluating the in vivo profile of a compound during drug discov­ery. Reaching a constant and/or maximum exposure is critical when assessing the pharmacokinetic, pharmacodynamic, and safety profile of a molecule. While subcu­taneously applied suspension formulations typically yield an extended-release profile, solution formulations target high com­pound exposures. The subcutaneous deliv­ery of bRo5 molecules comes with a set of challenges. Due to their lipophilic nature, the development of a solution formulation is difficult. For all preclinical in vivo mod­els, there are tolerability constraints in terms of maximally tolerated amounts of excipients, like co-solvents or complexa­tion agents.


The prospect of open innovation is to gather out-of-the-box ideas beyond exist­ing networks. The Molecules for Collabo­ration program on offers the opportunity to initiate joint research proj­ects. One successful example for a recently completed project was launched in Octo­ber 2020. By the submission deadline on December 17, 2020, 73 scientists world­wide submitted proposals on novel strate­gies to tackle a major problem in pharmaceutical research, namely poor solubility. Eventually, 20 high-quality proj­ects were selected to obtain access to our unique molecules.1

In our upcoming call, we are looking for suitable subcutaneous formulation ap­proaches that could potentially enable the early phases of drug discovery for bRo5 molecules. We invite researchers and tech­nology developers to submit proposals that would provide innovative formulation approaches for the subcutaneous admin­istration route in a preclinical setting, to enable subcutaneous formulations of bRo5 molecules for preclinical PK, PD, and safety studies.

As an incentive to submit proposals, we provide all selected applicants with ac­cess to an unprecedented selection of novel bRo5 compounds, covering a diver­sity of structural classes (e.g., PROTAC) and potential therapeutic mechanisms. We expect that this collection will provide high value to test your formulation technologies with the most recent and innovative mole­cules. These structurally diverse molecules also come with additional internal data (Table 1) characterizing the molecules’ physicochemical properties, like lipophilic­ity (log P/D7.4) and solubility over a wide pH range. Additionally, all criteria are listed that assign a compound to the bRo5 chemical space (number of H-bond donors and acceptors, molecular weight). Each compound exhibits at least one vio­lation to Ro5. Solubility in organic media is often a prerequisite for application of formulation technologies and therefore, is vital information to formulation develop­ers.

All compounds were designed for re­cent, disease-relevant targets, some of which are highlighted in more detail below:

  • ACBI1 causes degradation of the BAF chromatin remodeling complex proteins SMARCA2 and SMARCA4, as well to a lesser degree PBRM1. The compound is a PROTAC (proteolysis-targeting chimera) that induces degradation of its targets via inducing the formation of a triple complex of the target, the PRO­TAC, and the E3 ligase VHL, resulting in target ubiquitylation and proteasomal degradation.
  • HCV NS3 protease is a 180-amino acid chymotrypsin-like serine protease. It is an essential component of HCV repli­cation and infectivity. The NS3 protein contains two functional domains: a ser­ine protease and a helicase domain. Both HCV compounds which are of­fered as part of this call bind to the ac­tive site of NS3 that is located in the shallow and broad protein-protein in­teraction surface of the protease and the helicase domain of the enzyme and are nanomolar to picomolar inhibitors of protease activity and of viral replica­tion for various HCV genotypes and for resistant mutants D168V and R155K. Boehringer Ingelheim was the first com­pany to establish proof-of-concept in humans for an HCV NS3 protease in­hibitor as a treatment of HCV infection.


As part of this latest call for research proposals in the field of formulation re­search, we are open to all applications if they arrive by July 29, 2021, 11:59 PM PST. Our internal review process will com­mence in August 2021 and will be final­ized until end of September 2021. The winners will then be notified, and collabo­ration work will commence in Q4 2021 or Q1 2022. Please refer to for more information, including detailed infor­mation on the call for proposals and the success criteria.2

As an incentive, selected project teams will be provided with suitable amounts of the molecules to facilitate their research and/or to validate your new pro­posed technology. We expect to provide quantities, which are typical for early drug discovery phases (up to 200 mg initially) of each drug substance completely free-of-charge. With the provided compounds, we aim to create a new way to help scien­tists validate their formulation approaches and to publish their data to advance sci­entific knowledge. Furthermore, we are transparent about the rights and obliga­tions of the researchers who approach the portal to submit their innovative ideas, es­pecially with regard to intellectual property, which will remain with the scientist.

Successful applicants will have the op­portunity to directly interact with scientific experts and leaders in drug delivery at Boehringer Ingelheim to share information and to discuss additional guidance or re­sources needed to maximize the potential of the work. Additional support could in­clude provision of additional molecules, in vitro and in vivo assessments, access to state-of-the-art analytical methods, as well as the possibility of site visits to the Boehringer Ingelheim facility in Biberach, Germany.


bRo5 compounds have a tremendous impact on the treatment of diseases with high unmet medical needs such as cancer. Thus, there has been increased interest in the discovery and development of bRo5 drugs in the pharmaceutical industry. Due to their poor physicochemical properties, such as low solubility and high lipophilicity and their poor permeability, the investiga­tion of bRo5 chemical matter is fraught with risk and uncertainties.4

Already in the early stages of drug discovery, the successful formulation of bRo5 compounds for preclinical studies, such as PK, PD, and safety investigations, is challenging.

Boehringer Ingelheim’s platform incentivizes fundamental re­search and advances the translation of im­portant new concepts into practical approaches. The current call for proposals is an opportunity for re­searchers in the field of formulation devel­opment to test their innovative ideas and approaches for subcutaneous drug formu­lation on a unique set of structurally di­verse bRo5 structures from current research projects, e.g., a PROTAC.2 Addi­tionally, we hope that this call will facilitate active collaboration and the pragmatic im­plementation of innovative drug delivery solutions.


The authors would like to express their sincere gratitude to Joachim Schäfer, Thomas Trieselmann, Marc Grundl, Flo­rian Montel, and all others involved in sup­porting


  1. K. Horspool, S. Chen, M. Koester, In­centivizing Drug Delivery Research Using an Open Sharing Platform, Drug Development & Delivery 21(3) (2021).
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  4. D.A. DeGoey, H.-J. Chen, P.B. Cox, M.D. Wendt, Beyond the Rule of 5: Lessons Learned from AbbVie’s Drugs and Compound Collection, Journal of Medicinal Chemistry 61(7) (2018) 2636-2651.
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Dr. Ines Truebenbach is a Head of Laboratory in the Drug Discovery Sciences (DDS) CMC group in Research at Boehringer Ingelheim. She is currently responsible for the delivery of high-quality and innovative formulations for preclinical PK and PD studies, which enable tailor-made exposure studies for various applications. Her areas of expertise include formulation development for new molecular entities (NMEs), like peptides, oligonucleotides, or bRo5 molecules (PROTACs). She joined Boehringer Ingelheim in 2019 after earning her PhD in Pharmaceutical Biotechnology.

Dr. Menorca Chaturvedi is a Senior Scientific and Digital Manager at Boehringer Ingelheim. She is currently responsible for the scientific alliance management activities for opnMe collaborates with Boehringer Ingelheim scientists across different therapeutic areas and countries, to present innovative scientific challenges via the opn2EXPERTS and Molecules for Collaboration programs. Prior to joining Boehringer Ingelheim in 2021, she worked on different research and digital projects across academic and non-profit organizations.

Dr. Markus Koester is a Director of Discovery Research Coordination Germany at Boehringer Ingelheim. He leads the global digital communication and portal activity of Boehringer Ingelheim’s open innovation platform, opnMe was launched in 2017 with a Molecules to Order initiative. It now offers 57 molecules to order and received more than 1,000 orders from 60 countries around the world. In addition, with its two collaboration programs, Boehringer Ingelheim has received more than 1,000 research proposals by now. Prior to joining the company, he worked for Merck KGaA and two biotech start-ups. Overall, he gained more than 20 years of pharma experience in roles ranging from R&D to commercial.

Dr. Achim Grube is a Director of Drug Discovery Sciences (DDS) at Boehringer Ingelheim and leads the DDS-CMC group. The core mission of the group is the physicochemical characterization, solid form finding, and preclinical formulation development and manufacturing of new chemical entities from the early research phase to start of development. He has worked at Boehringer Ingelheim for more than 10 years with experience managing analytical and product development, drug delivery, and preformulation. He has diverse experience with a broad range of delivery systems and various routes of delivery.