IJRIT International Journal of Research in Information Technology, Volume 2, Issue 1, January 2014,Pg: 232- 239

International Journal of Research in Information Technology (IJRIT) www.ijrit.com

ISSN 2001-5569

Machine Learning In Chemoinformatics: A Novel Approach for Drug Discovery Kirti Kumari Dixit Information Technology, G.H.Patel College of Engineering & Technology Anand, India [email protected]

Dr. Hitesh B. Shah Electronics & Communication Department G.H.Patel College of Engineering & Technology Anand, India [email protected] Abstract- The mission of pharmaceutical research companies is to take the path from understanding a disease to bringing a safe and effective new treatment to patients. Scientists work to piece together the basic causes of disease at the level of genes, proteins and cells. Out of this understanding emerge “targets,” which potential new drugs might be able to affect. Researchers works to validate this target, discover the potential drug to interact with the target chosen, test the new compound in the lab and clinic for safety and efficacy and gain approval and get the new drug into the hands of doctors and patient. This whole process takes an average of 10-15 years and cost around 800 million- 1 billion dollars. Moreover, traditional Drug Discovery uses SAR (structureactivity relationship) analysis as a technique to reduce the search for new drugs. This paper presents an overall survey done on various ML techniques that can enhance the process of Drug Discovery. The process of drug discovery can be enhanced by using Machine learning techniques for various problems of classification and regression of drugs and its properties. Keywords-chemoinformatics; drug discovery; machine learning techniques; classification; regression; combinatorial libraries;

I.

INTRODUCTION

Chemoinformatics is the term that has been recently coined to represent a discipline that organizes and coordinates the application of computers in chemistry. The term constitutes of “chemo-means chemistry” and “informatics- a synonym used in Europe for Computer Science”. Most of the techniques of Chemoinformatics have been applied to the Drug Industry but it is now being applied to the full range of chemistry. This term is variously known as cheminformatics, chemiinformatics or chemical informatics. Industry sectors such as, agrochemicals, food and pharmaceutical are distinct areas where chemoinformatics plays significant role in the recent history of molecular sciences. Moreover, Drug Discovery and Development is one of the area where cheminformatics plays a vital role. Drug Discovery is the process of identifying innovative leads with potential interaction to specific target[8]. On the other hand Drug Development is the process of making drugs to the market after the series of clinical/non-clinical tests as well as approval by the respective standard authority. This whole process of Drug Discovery & Development takes about 12 to 15 years to complete and costs more than 1 Billion U.S Dollar[2]. This makes the whole process time-consuming and

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IJRIT International Journal of Research in Information Technology, Volume 2, Issue 1, January 2014,Pg: 232- 239

very expensive which can’t be ignored by the chemoinformaticians. Now, The Chemoinformatics techniques can be used in Drug Discovery process leading to the dramatic improvement in the time and cost constraints. Machine learning techniques are used in the context of chemoinformatics for variety of purpose and functionality. The major functionalities of chemoinformatics where m/c learning techniques are used are chemical structure/property prediction, molecular similarity/diversity analysis, virtual screening, qualitative/quantitative structural/activity/property relationships, ranking chemical structures, representation of chemical compounds/reactions, classification/search/storage methods, high throughput docking, drug discovery, data analysis methods, etc[6]. This paper deals with the survey of machine learning approach in chemoinformatics for drug discovery purpose. This paper is organized as follows. Section 2 deals with the survey of chemoinformatics. Section 3 deals with the overview of Drug Discovery process. Section 4 deals with survey of application of machine learning techniques in chemoinformatics. Section 5 deals with the significance of machine learning approach in the process of Drug discovery. Section 6 concludes the paper. II.

CHEMOINFORMATICS: INTRODUCTION

As already mentioned that chemoinformatics is the discipline that coordinates and organizes the use of computers in chemistry, but there are many more definition of it with respect to different perspective of its application. A recent definition of chemoinformatics presented by Gasteiger in the handbook of chemoinformatics points for “the application of informatics methods to solve chemical problems.” Brown describe this discipline as “the combination of all the information resources that a scientist needs to optimize the properties of a ligand to become a drug.” According to Paris, chemoinformatics “encompasses the design, creation, organization, storage, management, retrieval, analysis, dissemination, visualization, and use of chemical information, not only in its own right, but as a surrogate or index for other data, information and knowledge.” Chemoinformatics should be interpreted as an element of knowledge management. So, in order to conclude the definition of chemoinformatics it can be defined as “an interface science that combines the branches like physics, Chemistry, Mathematics, Biology, Biochemistry, Statistics and informatics .” NEED AND SCOPE OF CHEMOINFORMATICS The need for chemoinformatics can be better illustrated by the need of computers in Chemistry. It should be noted that not all Chemical branches that depend on Computers should be included in this field. Also, not every chemist like Chemoinformatics as a discipline, we can say that around 50% of respondents like chemoinformatics as an individual discipline. The computers are needed for Chemistry because of following purposes: 1) Calculation/Computational Overheada. to assist a chemist in a calculation or computation that requires the calculation by computers. b. The enormous speed and competence in low-level manipulations coupled with human intelligence allowed computers to solve formerly intractable problems, and explore areas beyond the reach of human calculations. c. In silico mathematical tools of chemoinformatics is necessary for those chemistry branches that depend on massive data that can’t be compressed to the standard mathematical tools. 2) Data Storage System Requirementa. Chemistry starts from data i.e. facts and numbers, which when processed and delivered properly at a proper time and place give birth to information. Processing information in turn gives birth to chemical knowledge. b. The population of chemical space i.e. no. of potential compound is, estimated b/w 1080 and 10200, which can be compared with factual chemical space (FCS) of the order of 107. The term CS itself is an example of the impact of mathematics on chemistry. 3) Information Accessa. It is a fundamental problem in chemistry. This should enable delivery of proper data to chemist’s desk when needed.

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b.

Traditionally, various documentation systems on chemical compounds were developed by chemist in order to keep information regarding chemicals, compounds & reactions. It is much more efficient to keep information on the computer desktop than just on the desk. Therefore, besides Computations, chemical information formed an important component of chemoinformatics.

4) Modelinga. Model refers to “the physical representation that shows what an object looks like.” Modeling is the next important problem in which chemists need computer assistance. b. Molecules are too small for direct observation and even today we usually watch them through the use of measurable data indirectly. c. Molecular models can be any “physical representation of molecular configuration assigned to molecular objects that are constructed to understand and explain measurable characteristics manifested by molecules.” It can be best for macroscopic bodies. d. But, in order to visualize & analyze microscopic bodies, these models don’t fit in the requirement. IMPORTANCE OF CHEMINFORMATICS Many of the chemoinformatics approaches were initiated in 1960s and early 1970s and were implemented into software system that are now widely used and being continuously refined. Three major aspects of Chemoinformatics are[2]1) Information Acquisition is a process of obtaining and collecting data experimentally or from simulations. 2) Information Management, deals with storage and retrieval of information. 3) Information use, deals with the data analysis, correlation, and application to problems in chemical and biochemical sciences. APPLICATION OF CHEMINFORMATICS Chemoinformatics is a way by which information technology is used to help chemists for investigating new problems, organize, analyses, and understand scientific data in development of novel compounds, materials and processes. Any field of chemistry can be benefited from its method or techniques. Following are the range of areas of chemistry where chemoinformatics plays a vital rolea) Prediction of physical, chemical and biological properties of chemical compounds. b) Elucidation of the structure of a compound based on spectroscopic data. c) Storing data generated from experiments and molecular simulations to the chemical database as knowledge repository. d) Structure, substructure, similarity and diversity screening from chemical database. e) High throughput screening to search for the desired activity/property. f) Docking g) Drug discovery & Development h) Agrochemicals, pharmaceutical, molecular science, food science, atmospheric chemistry, polymer chemistry, textile industry, organic synthesis, etc. i) Ranking chemical structure after the screening is done. j) Molecular modeling and many more. CHALLENGES IN CHEMOINFORMATICS Following are the some of the challenges faced by the chemoinformatics in its application areasa) Increase of the predictive performance of models built on small and diverse data set. b) Large data set. c) Drug design. d) Reliable estimation of the precision of predictions.

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e) Domain interdependency of training set and test set. f) Incompleteness of molecular descriptor. g) Representation of chemical structure. These challenges are very prominent that they can’t be ignored at once. But studies have been done on the individual problems and it has been made cleared that if machine learning techniques are integrated with the techniques of chemoinformatics then these problems can be solved to the great extent [12]. We are focusing on Drug discovery, which is one of the applications where chemoinformatics are applied extensively. We will also discuss the impacts of chemoinformatics techniques on the process of traditional drug discovery as well as significance of using various machine learning techniques in that domain.

III.

DRUG DISCOVERY AND DEVELOPMENT STAGES

Drug is nothing but a chemical substance that affects the process of mind and body. Any chemical compound used in the diagnosis, treatment, or prevention of disease or other abnormal condition can be considered as drug. Now, the process of drug discovery aimed at discovering molecules that can be very rapidly developed for effective treatments to meet medical needs. This process generates a large amount of chemical data which is generally referred as information explosion. Due to this it becomes an urgent need to effectively collect, organize, analyze and apply the chemical information in the process of drug discovery and development. TRADITIONAL DRUG DISCOVERY Traditionally Drug discovery process comprises of following stagesI.

II.

III.

IV.

V.

Disease IdentificationThis stage starts with complete understanding of the disease by knowing, how the genes can be altered, how it affects the protein, how this protein will react with each other in living organism, how the affected cells can change the specific tissues and how the disease affects the patient. This stage is also known as pre-discovery phase of the Drug Discovery. Target IdentificationThis stage deals with the identification of protein or gene involved in the disease. That particular protein will be termed as Target. The identified target is separated, crystallized and ligand binding processes are done. Several approaches are tried in this phase to inhibit the proliferation of the target like promoting specific molecule in the normal way which may affect the disease state, etc. Hits identificationThis phase deals with the identification of the compounds that likely to bind with the target. It means to find the molecule that can be effective against the target. Pre-clinical testingIt is an important phase that checks whether the hits can be made into a drug to treat specific disease. Parallel, it is also tested that hits should be not toxic and has minimum side effects. Pre-clinical testing can be done with or without animal testing method. The one in which tests are done on living cell cultures and animal model are referred as In-vivio method. Whereas the test that is carried out in clinical lab is called In-vitro method. This phase will be designed in a way such that it achieves risk-free, unproblematic and economic transition from pre-clinical to clinical trial in medical product development . Human Clinical TrialThis is the fastest and safest way to find treatments. It acts as the best solution for challenging health disease of human being. Patient with specific disease will be considered for clinical trials. The respective data is collected with respect to

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time. This trial can be done in five ways such as prevention trials, screening trials, diagnostic trials, diagnostic trials, treatment trials and quality of life trials . VI. Approval from the authority and drug in MarketIn this phase research authorities check the safety and other parameters to approve the drug in the national as well as international market. This is purely based upon the rules and regulations of the country as well as international market. For ex, CDSCO (Central Drugs Standard Control Organization) in India approves new pharmaceutical compound for sales and marketing. It can take up to fifteen years to develop new medicine from the earliest stages of discovery to time it is available in the market for treating patients. The average cost to research and develop each successful drug is estimated to be $800 million to $1 billion. This number includes cost of thousands of failures: For every 5000-10,000 compounds that enter the research and development pipeline, ultimately only one receives approval. MODERN DRUG DISCOVERY AND DEVELOPMENT The modern drug discovery process incorporates two main stages after Target Identification stage. These stages are described as followsI. Lead IdentificationThis stage replaces the hit identification stage of traditional process. It includes finding a promising molecule (i.e. lead compound) that could become a drug. In this phase scientists search for the lead compound that can alter the disease course. There are few ways to find a lead compound. a. Nature – nature still offers many useful substances, for ex, bacteria found in soil or in moldy plants both led to important new treatments. b. De Novo- scientists can also create molecules from scratch. They can use the computer to predict what type of molecule can work. c. High-throughput Screening- This is the most common way through which leads are found and it is efficient too. Advancement in robotics and computational power allow researcher to test hundreds of thousands of compounds against the target for promising result. d. Biotechnology- scientist can also genetically engineer living systems to produce disease-fighting biomolecules. II. Lead OptimizationLead compounds that survive the initial screening are then “optimized,” or altered to make them more effective and safer. By changing the structure of compound, it can gain different properties. Hundreds of different variations or “analogous” of the initial leads are made and tested. The biologist tests the affect of analogous on biological system whereas the chemists take this information to make additional alterations that are then retested by biologists. Different techniques and methods are used for this purpose like Virtual screening, molecular databases, data mining, high-throughput screening (HTS), QSAR, protein-Ligand Models, Structure Based Models, Microarray Analysis, Property Calculation and ADMET. CHALLENGES IN DRUG DISCOVERY The whole process of Drug Discovery is not an easy task; it requires cooperation from various departments and great expertise to carry out it effectively. Various challenges or we can say consideration that should be taken into account while Drug Discovery and development are as followsa) Given the high price of development, the first challenge is to determine which compound should be taken from discovery to development stage. b) Choice of molecular descriptors is another challenge in the process of Drug Discovery. c) Classification methods or techniques imposes challenge in discriminating drug candidates from non-drug one [4]. d) Chemical database used in application should be updated. e) The complex structures of biomolecules which are responsible for disease such as AIDS, Cancer, Autism, Alzimear etc. f) Property/Activity predictions. IV.

MACHINE LEARNING TECHNIQUES IN CHEMOINFORMATICS

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Machine learning approaches and concepts provide efficient solutions to the chemoinformatics problem. In this section we will discuss the various problem domain of chemoinformatics where m/l tools like support vector machine, neural networks, evolutionary computation etc, are widely used. Machine learning can be defined as the ability of the computing machine to increase its performance based on previous results. The figure represents the various machine learning tools that plays an important role in the field of chemoinformatics. Artificial Neural Network is the widely used m\c learning tool in the chemoinformatics. Neural network provides learning capability and it is one of the important component of soft computing. A neural network will consist of one input layer, one or more number of hidden layers and an output layer. Neural networks are used in chemoinformatics for the purpose of property prediction and classification of compounds in different classes [18][21][15]. Support vector machine is one of the emerging m/c learning tool which is used in QSAR study of compounds as well as it is proved to be an excellent classifier in the drug discovery also. Moreover, SVM offers great prediction accuracy than any other m/c learning tools. A more recent use of SVM is in ranking of chemical structure [4]. Other properties predicted with SVM include heat capacity and capacity factor (logk) of peptides in high-performance liquid chromatography Decision Tree is the most frequent m/c learning tool that is used to classify the compounds based on the specific descriptors used. It is also used to handle regression problems. In various datasets related to ecotoxicity DT usually achieved lower error than LDA or k-NN methods. DT has been used in various other studies like anti-HIV activity, toxicity and oral absorption . DT shows less prediction accuracy than SVM and ANN but better performance than k-NN method. Evolutionary Computation plays an important role in optimizing the lead compound for better performance after it passes the initial screening. Neural network trained by evolutionary algorithm is used as a classifier in classification of chemoinformatics data sets [15].

V.

SIGNIFICANCE OF MACHINE LEARNING IN DRUG DISCOVERY

Machine learning approach provides a strong base to enhance and furnish the process of drug discovery within the pharmaceutical industry. One important issue in the area of chemoinformatics during the process of drug discovery and development stages is the problem of finding a relationship that links molecular structure with a given biological or physicochemical property [21]. This problem is termed as QSAR/QSPR and is solved by allowing the prediction of the outcomes of expensive and timeconsuming wetlab experiments. Now, machine learning methods are very suitable for learning this kind of relationships from the databases of compounds with experimental information [21]. Moreover, machine learning techniques are also a good player in the domain of classification and regression analysis of chemical information involved in the drug discovery process. Here, we will discuss some of the well known machine learning techniques which contributes a lot in the area of drug discovery and development. Artificial neural network system takes input as multiple molecular descriptors and gives output as number of desired classes. Now, the selection of descriptor is also a cumbersome task because there is huge amount of descriptor available for single compound. Therefore, we need a computational method to select the best available descriptor for the compound according to the need of the problem. We can use feature selection methods to overcome this problem. Principal Component Analysis and Evolutionary algorithm are such methods available for this task [21]. An observation

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IJRIT International Journal of Research in Information Technology, Volume 2, Issue 1, January 2014,Pg: 232- 239

has been made that different ANN architectures and training algorithm leads to show different classification results [4]. Therefore, it might be wise to apply several predictive models in parallel irrespective of their nature. Support Vector machines form a group of methods stemming from the structural risk minimization principle with the linear support vector classifier as its most basic member. In the simplest case, compounds from different classes can be separated by linear hyper plane; such hyper plane is defined solely by its nearest compounds from training set. Such compounds are referred to as support vectors, giving the name to the whole method [19]. Generally, the SVM classifier yielded slightly higher prediction accuracy than ANN, irrespective of the type of descriptors used for molecular encoding, the size of training data sets, and the algorithm employed for neural network training [4]. SVM classifiers are very much suitable for use with noisy, high dimensional data, as is commonly used in cheminformatics [9]. SVM is used in predicting Absorption Distribution metabolism Excretion Toxic Effects (ADMET) . The problem with using SVM is that the optimal parameter configuration is data dependent and it cannot handle missing data also. Genetic Programming uses Holland’s crossover heavy Genetic Algorithm, to evolve programs. GP is mainly restricted to the functions and served as one of the best optimized method. It takes input as known facts or measurements (e.g. number of positively charged ions, presence of aromatic rings, acidity) and produce a single number. Then we take the number as prediction. Genetic programming has been used in modeling drug bioavailability [14]. GP ensembles of ANNs are used in have been developed to predict the QSAR features of Acute Toxicity of Phthalate Esters to Fish [15]. Decision Tree classification model consists of tree like structure consisting of nodes and links. Nodes are linked hierarchically, with several child nodes branching from a common parent node. Typically, in each node, a test using a single descriptor is made. Based on the result of the test, the algorithm is directed to one of the child nodes branching from the parent. In the child node another test is performed and further traversal of tree towards the leafs is carried out. The final decision is based on the activity class associated with the leaf. Thus the whole decision process is based on the series of test whose results guide the path from root to node. In general DT method usually offer suboptimal error rates compared to the non-linear methods, in particular, due to dependency on single feature in each node. Nevertheless they are popular in QSAR domain for their ease of interpretability [19]. VI.

CONCLUSION

The above survey is done in order to highlight the open issues in the field of chemoinformatics as well as the significance or power of imposing machine learning techniques in solving those issues. Drug Discovery is one of the applications of the chemoinformatics where pharmacist and scientists are working intensively to enhance the overall procedure. We have discussed how machine learning tools can be proved better in making the whole process of Drug Discovery efficient and effective. At last but not least it can be said that Machine learning techniques are potentially useful in Chemoinformatics in order to improve the accuracy of predictions and efficiency of virtual screening.

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VII. REFERENCES Abhik Seal, Anurag Passi, UC Abdul Jaleel. “In-silico predictive mutagenicity model generation using supervised learning approaches”; Journal of Cheminformatics ; 2012. B.Firdaus Begam, Dr. J.Satheesh Kumar. “A Study on Cheminformatics and its Application on Modern Drug Discovery”; Elsevier; 2012 Deepak Bharati, Jagtap RS, Kanase KG, Sonawame SA, Undale VR, Bhosale AV. “Chemo informatics: Newer Approach for Drug Development”; Asian J. Research Chem; 2009; ISSN 0974-4169. Evgeny Byvatov, Uli Fechner, Jens Sadowski, Gisbert Schneider. “Comparison of Support Vector Machine and Artificial Neural Network System For Drug/Non-Drug Classification”; J. Chem. Inf. Comput. Sci; 2003 R. Burbidge, M. Trotter, B. Buxton, S. Holden. “Drug Design by Machine Learning: Support Vector Machines for Pharmaceutical Data Analysis”; Elsevier; 2001. V.Arulmozhi, Rajesh Reghunandhan. “Neural Network For Chemoinformatics-A Survey”; ICACCT; 2013

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[7]. Rajesh Reghunandhan, V.Arulmozhi. “Fuzzy Logic For Chemoinformatics-A Review”; journal of Theoretical and applied Information technology; 2013; ISSN 1992-8645. [8]. Tiejun Cheng, Qingliang Li, Zhigang Zhou, Yanli Wang, Stephen H. Bryant. “Structure Based Virtual Screening For Drug Discovery: A Problem-Centric Review”; The AAPS Journal Vol. 14, No. 1; 2012. [9]. D. Pugazhenthi, S.P.Rajagopalan. “Machine Learning Technique Approaches In Drug Discovery, Design, Development”; Information Technology Journal 6(5): 718-724, 2007. [10]. Thomas Engel. “Basic Overview of Chemoinformatics”; J. Chem. Inf. Model; 2006; 2267-2277. [11]. Vishnu J. Gaikwad. “Application Of Chemoinformatics For Innovative Drug Discovery”; International Journal Of Chemical Sciences And Applications. Vol. 1, Issue 1; 2010. [12]. Alexandre Varnek, Igor Baskin. “Machine Learning Methods For Property Prediction In Chemoinformatics: Quo Vadis?” ; Journal Of Chemical Information And Modeling; 2012. [13]. Christopher A. Lipinski. “Drug-Like Properties and the Causes of Poor Solubility and Poor Permeability”; Elsevier; 2000. [14]. Christos A. Nicolaou, Nathan Brown. “Multi-Objective Optimization Methods In Drug Design”; Elsevier; 2013. [15]. V. Arulmozhi, Reghunandhan Rajesh. Evolutionary “Neural Network For The Classification Of Chemoinformatics Data Sets”; European Journal Of Scientific Research; 2012. [16]. Kailin Tang, Ruixin Zhu, Yixue Li, Zhiwei Cao. “Discrimination Of Approved Drugs From Experimental Drugs By Learning Methods”; Biomed Central; 2011. [17]. Shivani Agarwal, Deepak Dugar, Shiladitya Sengupta. “Ranking Chemical Structures For Drug Discovery: A New Machine Learning Approach”; J. Chem. Inf. Model. ; 2010. [18]. Rachid Darnag, Brahim Minaoui, Mohamed Fakir. “QSAR Models For Prediction Study Of HIV Protease Inhibitors Using Support Vector Machines, Neural Networks And Multiple Linear Regression”; Arabian Journal Of Chemistry; 2012. [19]. Arkadiusz Z. Dudek, Tomasz Arodz, Jorge Galvez. “Computational Methods In Developing Quantitative Structure-Activity Relationships (QSAR): A Review”; Combinatorial Chemistry & High Throughput Screening; 2006; 213-228. [20]. Ana L. Teixeira, Joao P. Leal, Andre O Falcao. “Random Forests For Feature Selection In QSPR Models- An Application For Predicting Standard Enthalpy Of Formation Of Hydrocarbons”; Journal Of Cheminformatics; 2013. [21]. Axel J. Soto. “On The Use Of Machine Learning Methods For Modern Drug Discovery”; Ai Communications; 2011. [22]. R. U. Kadam, N. Roy. “Recent Trends In Drug-Likeness Prediction: A Comprehensive Review Of InSilico Methods”; Indian Journal Of Pharmaceutical Sciences; 2013. [23]. V. Arulmozhi, Rajesh Reghunandhan. “Predicting Protein Localization Sites Using Artificial Neural Networks”; Journal Of Cheminformatics; 2013. [24]. Han Van De Waterbeemed And Eric Gifford. “ADMET In Silico Modeling: Towards Prediction Paradise?” ; Nature Publishing Group; 2003.

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methods, high throughput docking, drug discovery, data analysis methods, etc[6] .... QSAR, protein-Ligand Models, Structure Based Models, Microarray Analysis,.

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