Raman and Infrared Spectroscopic Studies to Understand the Efficacy of HDAC Inhibitor Drugs Bhawana Singh a , Sivaraman Boopathy b , Kumaravel Somasundaram b and Siva Umapathy a * a Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012,India b Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012,India In the recent past, histone deacetylase inhibitors (HDACi) have attracted enormous attention of biologists and chemists as potential drug molecules for the treatment of cancer. These are new class of chemotherapeutic drugs which have indirect mechanistic action against cancer cells via acting against histone deacetylase (HDAC) enzymes 1-3 . It is well known that different HDAC enzymes are over-expressed in various types of body cancers for example; HDAC1 is over expressed in prostate, gastric and breast carcinomas whereas HDAC3 is over expressed in colon cancer (1). Therefore, in order to optimise chemotherapy, it is important to determine the efficacy of various classes of HDAC inhibitor drugs against variety of over-expressed HDAC enzymes. In the present study, Raman and Infrared spectroscopic techniques have been employed to predict the acetylation and other changes brought in by these drugs 4 .The efficacy of five different HDAC inhibitor drugs on brain cancer cell line (U 343) have been compared using these techniques. Figure 1 shows the Infrared spectra of cells treated with valproic acid and their control counterparts. Here, for the first time, we report the determination of propionylation and butyrylation of histones along with well known process of acetylation 5 . FIGURE 1. Infrared spectra of valproic acid treated brain cancer cells along with the control.