Eric Patridge

An analysis of FDA-approved drugs: natural products and their derivatives

Natural products contribute greatly to the history and landscape of new molecular entities (NMEs). An assessment of all FDA-approved NMEs reveals that natural products and their derivatives represent over one-third of all NMEs. Nearly one-half of these are derived from mammals, one-quarter from microbes and one-quarter from plants. Since the 1930s, the total fraction of natural products has diminished, whereas semisynthetic and synthetic natural product derivatives have increased. Over time, this fraction has also become enriched with microbial natural products, which represent a significant portion of approved antibiotics, including more than two-thirds of all antibacterial NMEs. In recent years, the declining focus on natural products has impacted the pipeline of NMEs from specific classes, and this trend is likely to continue without specific investment in the pursuit of natural products.

An analysis of FDA-approved drugs for infectious disease: antibacterial agents.

Drugs targeting infectious diseases have greatly improved public health. A study to evaluate all US Food and Drug Administration (FDA)-approved new molecular entities (NMEs) reveals that the number of new agents targeting infectious disease peaked during the 1990s and declined rapidly thereafter. Molecules targeting bacterial pathogens represent the most common component of anti-infectives followed by antivirals and antifungals. Focusing on antibacterial agents, an increase in new NMEs predominated from the 1960s through to the 1990s, dropping sharply thereafter. Obsolescence and resistance has eliminated one-third of these drugs. Consequently, the arsenal of antibiotics peaked in 2000 and is declining. Likewise, the number of organizations awarded at least one NME for a bacterial indication has declined to a level not seen in more than a half century.

An analysis of FDA-approved drugs for infectious disease: HIV/AIDS drugs.

HIV/AIDS is one of the worst pandemics in history. According to the World Health Organization, 26 million people have died since 1981 - 1.6 million in 2012 alone. The dramatic rise in HIV/AIDS mobilized a swift and impressive coordination among governmental, academic and private sector organizations to identify the virus and develop new treatments. Herein, we assess the arsenal of 28 new molecular entities (NMEs) targeting HIV/AIDS. These data demonstrate that the first approval of zidovudine presaged an expansion of the antiviral repertoire over the following years. Whereas the rate of HIV/AIDS NMEs is rapidly declining, so is the number of organizations developing NMEs. We speculate that decisions to abandon further research reflect, in part, growing costs and time required for development.

An analysis of original research contributions toward FDA-approved drugs

Academic researchers shaped the landscape of drug discovery for nearly two centuries, and their efforts initiated programs for more than half of the US Food and Drug Administration (FDA)-approved new molecular entities (NMEs). During the first 50 years of the 20th century, contributions from industry-based discovery programs steadily increased, stabilizing near half of all first publications for NMEs. Although academia and industry have made similar contributions to the discovery of FDA-approved NMEs, there remains a substantial difference in the gap-to-approval; on average, industry NMEs are 12 years closer to market at the time of the first publication. As more drug discovery efforts shift from industry to academia, including high-throughput screening resources, academia could have an increasingly crucial role in drug discovery.

Target selection for FDA-approved medicines.

The biopharmaceutical industry translates fundamental understanding of disease into new medicines. As part of a comprehensive analysis of FDA-approved new molecular entities (NMEs), we assessed the mechanistic basis of drug efficacy, with emphasis on target selection. Three target families capture almost half of all NMEs and the leading ten families capture more than three-quarters of NME approvals. Target families were related to their clinical application and identify dynamic trends in targeting over time. These data suggest increasing attention toward novel target families, which presumably reflects increased understanding of disease etiology. We also suggest the need to balance the ongoing emphasis on target-based drug discovery with phenotypic approaches to drug discovery.

A Strategy for Selective O6-Alkylguanine-DNA Alkyltransferase Depletion Under Hypoxic Conditions

Cellular resistance to chemotherapeutics that alkylate the O‐6 position of guanine residues in DNA correlates with their O6‐alkylguanine‐DNA alkyltransferase activity. In normal cells high [O6‐alkylguanine‐DNA alkyltransferase] is beneficial, sparing the host from toxicity, whereas in tumor cells high [O6‐alkylguanine‐DNA alkyltransferase] prevents chemotherapeutic response. Therefore, it is necessary to selectively inactivate O6‐alkylguanine‐DNA alkyltransferase in tumors. The oxygen‐deficient compartment unique to solid tumors is conducive to reduction, and could be utilized to provide this selectivity. Therefore, we synthesized 2‐nitro‐6‐benzyloxypurine, an analog of O6‐benzylguanine in which the essential 2‐amino group is replaced by a nitro moiety, and 2‐nitro‐6‐benzyloxypurine is >2000‐fold weaker than O6‐benzylguanine as an O6‐alkylguanine‐DNA alkyltransferase inhibitor. We demonstrate oxygen concentration sensitive net reduction of 2‐nitro‐6‐benzyloxypurine by cytochrome P450 reductase, xanthine oxidase, and EMT6, DU145, and HL‐60 cells to yield O6‐benzylguanine. We show that 2‐nitro‐6‐benzyloxypurine treatment depletes O6‐alkylguanine‐DNA alkyltransferase in intact cells under oxygen‐deficient conditions and selectively sensitizes cells to laromustine (an agent that chloroethylates the O‐6 position of guanine) under oxygen‐deficient but not normoxic conditions. 2‐Nitro‐6‐benzyloxypurine represents a proof of concept lead compound; however, its facile reduction (E1/2– 177 mV versus Ag/AgCl) may result in excessive oxidative stress and/or the generation of O6‐alkylguanine‐DNA alkyltransferase inhibitors in normoxic regions in vivo.

Chloroethylating and methylating dual function antineoplastic agents display superior cytotoxicity against repair proficient tumor cells.

Two new agents based upon the structure of the clinically active prodrug laromustine were synthesized. These agents, 2-(2-chloroethyl)-N-methyl-1,2-bis(methylsulfonyl)-N-nitrosohydrazinecarboxamide (1) and N-(2-chloroethyl)-2-methyl-1,2-bis(methylsulfonyl)-N-nitrosohydrazinecarboxamide (2), were designed to retain the potent chloroethylating and DNA cross-linking functions of laromustine, and gain the ability to methylate DNA at the O-6 position of guanine, while lacking the carbamoylating activity of laromustine. The methylating arm was introduced with the intent of depleting the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT). Compound 1 is markedly more cytotoxic than laromustine in both AGT minus EMT6 mouse mammary carcinoma cells and high AGT expressing DU145 human prostate carcinoma cells. DNA cross-linking studies indicated that its cross-linking efficiency is nearly identical to its predicted active decomposition product, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine (90CE), which is also produced by laromustine. AGT ablation studies in DU145 cells demonstrated that 1 can efficiently deplete AGT. Studies assaying methanol and 2-chloroethanol production as a consequence of the methylation and chloroethylation of water by 1 and 2 confirmed their ability to function as methylating and chloroethylating agents and provided insights into the superior activity of 1.

Influence of glutathione and glutathione S-transferases on DNA interstrand cross-link formation by 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine, the active anticancer moiety generated by laromustine.

Prodrugs of 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine (90CE) are promising anticancer agents. The 90CE moiety is a readily latentiated, short-lived (t1/2 ∼ 30 s) chloroethylating agent that can generate high yields of oxophilic electrophiles responsible for the chloroethylation of the O-6 position of guanine in DNA. These guanine O-6 alkylations are believed to be responsible for the therapeutic effects of 90CE and its prodrugs. Thus, 90CE demonstrates high selectivity toward tumors with diminished levels of O6-alkylguanine-DNA alkyltransferase (MGMT), the resistance protein responsible for O6-alkylguanine repair. The formation of O6-(2-chloroethyl)guanine lesions ultimately leads to the generation of highly cytotoxic 1-(N3-cytosinyl),-2-(N1-guaninyl)ethane DNA interstrand cross-links via N1,O6-ethanoguanine intermediates. The anticancer activity arising from this sequence of reactions is thus identical to this component of the anticancer activity of the clinically used chloroethylnitrosoureas. Herein, we evaluate the ability of glutathione (GSH) and other low molecular weight thiols, as well as GSH coupled with various glutathione S-transferase enzymes (GSTs) to attenuate the final yields of cross-links generated by 90CE when added prior to or immediately following the initial chloroethylation step to determine the major point(s) of interaction. In contrast to studies utilizing BCNU as a chloroethylating agent by others, GSH (or GSH/GST) did not appreciably quench DNA interstrand cross-link precursors. While thiols alone offered little protection at either alkylation step, the GSH/GST couple was able to diminish the initial yields of cross-link precursors. 90CE exhibited a very different GST isoenzyme susceptibility to that reported for BCNU, this could have important implications in the relative resistance of tumor cells to these agents. The protection afforded by GSH/GST was compared to that produced by MGMT.

Abstract C08: Disclosure and cancer screening rates among lesbian, gay, bisexual and transgender (LGBT) populations

Background: Evidence suggests that people who self-identify as underrepresented sexual minorities have an increased cancer burden and more cancer risk factors than their sexual majority counterparts. We sought to determine whether cancer screening rates differed between LGBT patients who have discussed their sexual identity with their health care providers and those who did not. Methods: An anonymous electronic survey was conducted through LGBT network organizations. The survey was designed to replicate questions regarding cancer screening behavior that were fielded in the 2010 National Health Interview Survey (NHIS) Cancer Supplement. It also included questions regarding (self-identified) sexual orientation and disclosure of sexual identity to health care providers. Correlations between disclosure and cancer screening rates were analyzed using non-parametric statistics (SPSS, Inc). Results: A total of 320 LGBT people responded to the survey, of these; 148 identified as female, 158 identified as male, 14 as transgender or other. Rates of disclosure were similar across all groups: 70.9% men, 74.3% women, and 78.6% transgender/other informed their health care provider of their sexual identity (p=0.139). The median age of respondents was 29 (range: 16-74). Individuals who chose to disclose their sexual identity were more likely to be older (median age 32 vs. 24, p Conclusions: Nearly three quarters of LGBT individuals disclose their sexual identity to their doctors. Cancer screening is higher amongst individuals who openly discuss their sexual identity with their health care providers, particularly for colorectal screening. Citation Format: Caroline Ong, Joel Winer, Eric Patridge, Feng Dai, Liz Margolies, Anees Chagpar. Disclosure and cancer screening rates among lesbian, gay, bisexual and transgender (LGBT) populations. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr C08.