Challenges and Hurdles to Business as Usual in Drug Development for Treatment of Rare Diseases

Precision Medicines' Impact on Orphan Drug Designation

The incentives provided under the Orphan Drug Act (ODA) have been credited for catalyzing the marketing approval of drugs for the treatment of rare diseases by the US Food and Drug Administration. Orphan drug designation, the granting of special status to drugs or biologics ("drugs") for the treatment of rare diseases, one of the ODA's key incentive programs, has seen major increases in volume over recent years. The new era of precision medicine and the development of therapies directed toward smaller "orphan" subsets of common diseases have been suggested as being a major driver. We evaluated the basis for orphan drug designations and orphan subsets in relation to the impact of precision medicines. We found that the increasing numbers of orphan drug designation determinations were not driven by precision medicines separating common diseases into orphan subsets and that orphan subsets overall also represented a relatively small proportion of designations.

Exploring Non-obvious Hydrophobic Binding Pockets on Protein Surfaces: Increasing Affinities in Peptide-Protein Interactions

A 42-residue polypeptide conjugated to a small-molecule organic ligand capable of targeting the phosphorylated side chain of Ser15 was shown to bind glycogen phosphorylase a (GPa) with a K_D value of 280 nm. The replacement of hydrophobic amino acids by Ala reduced affinities, whereas the incorporation of l-2-aminooctanoic acid (Aoc) increased them. Replacing Nle5, Ile9 and Leu12 by Aoc reduced the K_D value from 280 to 27 nm. "Downsizing" the 42-mer to an undecamer gave rise to an affinity for GPa an order of magnitude lower, but the undecamer in which Nle5, Ile9 and Leu12 were replaced by Aoc showed a K_D value of 550 nm, comparable with that of the parent 42-mer. The use of Aoc residues offers a convenient route to increased affinity in protein recognition as well as a strategy for the "downsizing" of peptides essentially without loss of affinity. The results show that hydrophobic binding sites can be found on protein surfaces by comparing the affinities of polypeptide conjugates in which Aoc residues replace Nle, Ile, Leu or Phe with those of their unmodified counterparts. Polypeptide conjugates thus provide valuable opportunities for the optimization of peptides and small organic compounds in biotechnology and biomedicine.

Opportunities and challenges in phenotypic drug discovery: an industry perspective

Phenotypic drug discovery (PDD) approaches do not rely on knowledge of the identity of a specific drug target or a hypothesis about its role in disease, in contrast to the target-based strategies that have been widely used in the pharmaceutical industry in the past three decades. However, in recent years, there has been a resurgence in interest in PDD approaches based on their potential to address the incompletely understood complexity of diseases and their promise of delivering first-in-class drugs, as well as major advances in the tools for cell-based phenotypic screening. Nevertheless, PDD approaches also have considerable challenges, such as hit validation and target deconvolution. This article focuses on the lessons learned by researchers engaged in PDD in the pharmaceutical industry and considers the impact of 'omics' knowledge in defining a cellular disease phenotype in the era of precision medicine, introducing the concept of a chain of translatability. We particularly aim to identify features and areas in which PDD can best deliver value to drug discovery portfolios and can contribute to the identification and the development of novel medicines, and to illustrate the challenges and uncertainties that are associated with PDD in order to help set realistic expectations with regard to its benefits and costs.