Key Concepts for Medicinal Chemists

Molecular recognition in biological systems occurs by the complementary non-covalent bonding between a receptor binding site and a ligand (e.g., drug molecule). The attached concepts, numbers, and formulae assist medicinal chemists in structural modification related to the drug-receptor binding.

The Future of Drug Discovery

 The new technologies promise to fill drug development pipelines with small-molecule candidates unfulfilled, so the pharmaceutical industry is currently undergoing rapid changes. They are moving aggressively into large molecule (biologics) drug development.

"Drug space” that is not part of the current drug development includes non-Lipinski NCEs, nanomedicines, nucleic acid-based drugs, etc. will include in the future. One of the major challenges for a medicinal chemist is to find small molecule inhibitors for protein-protein interactions.

Bottom of the pyramid

Indian patients no longer have to wait for the drug to become generic. Recently BMS and Astra Zeneca launched their new oral pill Saxagliptin (DDP 4 inhibitors ) to treat type 2 diabetes in India, less than one year after its US approval. India is the first Asian country where the drug is available at an affordable price which is 1/5 of its US cost.

Pharma Companies now realize that there is tremendous opportunity in emerging markets, not only because they entail low operating costs but also because of the fast-growing middle-class population; they are emerging as a huge market for global products. As the economy grows lifestyle associated diseases grow along with it. Therefore companies try to launch drugs for these lifestyle-related diseases such as diabetes. Forecasts suggest 50% of business will be in those markets by 2020. Acquisition of Daichi to Ranbaxy and Abbot by Piramals makes it clear that big pharma companies want to make a strong market presence in India.

“Rather than trying to find a use for approved medicines that were developed for a non-Asian phenotype, the move is to discover and develop medicines specifically to treat Asian diseases,” explains Paul Bolno, VP of Oncology R&D, Business Development at GSK. Here is a Nature article

However, it will take a long time for the local doctors here in India to stop giving the pills without any label and any expiry dates on them. (pic; a local hospital gave me these medicines for a mild fever, you have to remember the tablets by its color).

Drug Optimization

 

Pharmaceutical companies are trying to fill their drug portfolio by optimizing the marketed drugs. Most recently launched drugs are structurally similar to already known drugs, with only minor differences. The most common drug optimization methods are:

1. Reactive metabolites: 

An excellent example of this is venlafaxine (Effexor) and desvenlafaxine ( Pristiq). Desvenlafaxine is the metabolite of venlafaxine. The difference is that desvenlafaxine having O-H instead of O-Me. 

2. Deuterated Drugs: 

Switching a hydrogen atom with a heavier isotope such as deuterium, pharma companies hope that the deuterated drug survives longer in the body and fewer side effects because it can make a stronger chemical bond than hydrogen. 

3. Racemic switching: 

Racemic switching is the redevelopment in a single enantiomer from a first approved drug as a racemate; a better example is the Nexium. It is a predecessor Prilosec, a mixture of both S and R isomers. When Prilosec’s patent expired in 2001, the drugmaker was ready with Nexium, which contains only the S-isomer. 

The proliferation of "me-too" drugs leads to beneficial cost reductions. However, in the end, the real question is about pharmaceutical innovation. While “me too” fills the development pipeline, the creativity is fading away in the art of drug discovery?

Are Protein Kinases Drug Targets?

Kinases catalyze the transfer of phosphate groups from phosphate-donating molecules (like ATP) to other molecules. They have been intensively investigated as drug targets for many years. Around 20-25% of the druggable genome consists of kinases, and this target accounts for 20-30% of many companies' drug discovery programs.

Several protein kinase inhibitors have been approved by FDA and available in the market which includes Tykerb®, Sprycel®, Sutent®, Nexavar®, Tarceva®, Iressa®, and Gleevec®. Many other kinase inhibitors are currently undergoing clinical development. This accelerated the research and development in this area, reflecting the number of search results for 'kinase inhibitors'. Sci-finder keyword search resulted in 1281 patents, which is filed in 2007 alone. Drug and Market Development’s (D&MD) report (2005) shows that kinase targeted therapies growing from $12.7 billion in 2005 to $58.6 billion in 2010. 

 

So what is the problem with kinases? The lack of selectivity for targeting a specific kinase is the issue due to the similarity of other kinase targets. For example, the natural product substrate Staurosporine hits almost every kinase out there will be gratuitously toxic. However, the real problem with kinase inhibitors is the toxic outcomes may result from tissue distribution of orally administered kinase inhibitors.

 

Kinases are drug targets. But, difficult ones.