National Cancer Institute Drug Research Articles

Optimizing early phase clinical trial washout periods: a report from the therapeutic advances in childhood leukemia and lymphoma (TACL) consortium.

The National Cancer Institute (NCI) issued a 2021 memorandum adopting the American Society of Clinical Oncology (ASCO) and Friends of Cancer Research (Friends) task force recommendations to broaden clinical study eligibility criteria. They recommended that washout periods be eliminated for most prior cancer therapy and when required, to utilize evidence/rationale-based criteria. The Therapeutic Advances in Childhood Leukemia and Lymphoma (TACL) consortium responded to this guidance. A TACL task force reviewed the consortium's research portfolio, the relevant literature and guidance documents from ASCO-Friends, NCI, and US Food and Drug Administration (FDA) to make expert consensus and evidence-based recommendations for modernizing, broadening and codifying TACL-study washout periods while ensuring consistency with pediatric ethics and federal regulations. TACL's screening log was reviewed to estimate the impact that updated washout periods would have on patient inclusivity and recruitment. Over a 19-year period, 42 patients (14.6% of all screened ineligible (n = 287) patients), were identified as excluded from TACL early-phase studies exclusively due to not meeting washout criteria. An additional six (2.1%) did not meet washout and at least one other exclusion criterion. A new TACL washout guidance document was developed/adopted for use. Where washout criteria were not eliminated, rationale/evidenced-based criteria were established with citation. In an effort to reduce unnecessary exclusion from clinical trials, TACL created rationale/evidenced-based washout period standards largely following guidance from the NCI/ASCO-Friends recommendations. These new, expanded eligibility criteria are expected to increase access to TACL clinical trials while maintaining safety and scientific excellence.

Predicting tumor cell line response to drug pairs with deep learning

BackgroundThe National Cancer Institute drug pair screening effort against 60 well-characterized human tumor cell lines (NCI-60) presents an unprecedented resource for modeling combinational drug activity.ResultsWe present a computational model for predicting cell line response to a subset of drug pairs in the NCI-ALMANAC database. Based on residual neural networks for encoding features as well as predicting tumor growth, our model explains 94% of the response variance. While our best result is achieved with a combination of molecular feature types (gene expression, microRNA and proteome), we show that most of the predictive power comes from drug descriptors. To further demonstrate value in detecting anticancer therapy, we rank the drug pairs for each cell line based on model predicted combination effect and recover 80% of the top pairs with enhanced activity.ConclusionsWe present promising results in applying deep learning to predicting combinational drug response. Our feature analysis indicates screening data involving more cell lines are needed for the models to make better use of molecular features.

Rational design and identification of immuno-oncology drug combinations

BackgroundClinical trials investigating immuno-oncology (IO) drug combinations are largely based on empiricism or limited non-clinical evaluations. This study identified the current combination IO drug clinical trials and investigated how tumour molecular profiling can help rationalise IO drug combinations. MethodsIO targets were identified via PubMed search and expert opinion. IO drugs were compiled by searching the National Cancer Institute Drug Dictionary and pharmaceutical pipelines, August 2016. Combination IO trials were obtained by searching doublet IO drug combinations in www.clinicaltrials.gov from September to November 2016. IO target gene expressions were extracted from The Cancer Genome Atlas (TCGA) data set and compared with normal tissues from the Genotype-Tissue Expression database. Differentially expressed genes for each cancer were determined using the Wilcoxon rank-sum test, and p-values were corrected for multiple testing. ResultsIn total, 178 IO targets were identified; 90 targets have either regulatory approved or investigational therapeutics. In total, 410 combination trials involving ≥2 IO drugs were identified: skin (n = 102) and genitourinary (n = 41) malignancies have the largest number of combination IO trials; 109 trials involved >2 disease sites. Summative patient accrual estimates among all trials are 71,345. Trials combining cytotoxic T lymphocyte antigen 4 (CTLA4) with programmed cell death protein 1 (n = 79) and CTLA4 with programmed cell death ligand 1 (n = 44) are the most common. Gene expression data from TCGA were mined to extract the 178 IO targets in 9089 tumours originating from 19 cancer types. IO target expression–clustered heatmap analysis identified several promising drug combinations. ConclusionOur review highlights the great interest in combination IO clinical trials. Our analysis can enrich IO combination therapy selection.

Abstract 4805: In vitro characterization of novel inhibitors of ROCK and MRCK kinases as anticancer agents

Abstract Metastatic cancers are the second leading cause of deaths in the USA. RhoA and Cdc42 play critical roles in the regulation of plasticity of cancer cell migration/invasion and cell proliferation. ROCK1/2 and MRCKá/â are downstream kinases in the signaling pathways associated with cancer cell migration and invasion. Hence, we hypothesized that simultaneous targeting of these two kinase families would be an effective therapeutic strategy to block migration, invasion, and growth of metastatic cancers. We have identified DJ4 as a novel inhibitor of ROCK and MRCK kinases. In the cellular functional assays, DJ4 treatment significantly blocked stress fiber formation, and inhibited migration and invasion of multiple cancer cell lines in a concentration dependent manner. To study the critical functional groups required for its activity, we have modified the chemical structure of DJ4 at various functional groups and synthesized several analogs of DJ4 to perform the structural activity relationship (SAR) study for their ROCK1 inhibition. The effectiveness of these compounds were further investigated using National Cancer Institute's drug screening program in 60 human cancer cell lines representing nine different cancer types. These compounds effectively inhibit migration and invasion of multiple cancer cell types. Selected analogs were tested for their anti migration, pro-apoptotic, and anti-proliferative effects in breast cancer cells. Our studies strongly indicate that DJ4 and its analog, DJ110, are potent inhibitors of ROCK1, ROCK2, MERKá and MRCKâ. The results of our finding will be discussed. Citation Format: Dhimant H. Desai, Vijay P. Kale, Jeremy A. Hengst, Taryn E. Dick, Ashley L. Colledge, Shantu G. Amin, Jong K. Yun. In vitro characterization of novel inhibitors of ROCK and MRCK kinases as anticancer agents. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4805.

Abstract 5322: Englerin-A prevents invasive phenotypes of renal cell carcinoma by reprogramming mesenchymal to epithelial transition: A key mechanism of its anticancer properties

Abstract Renal cell carcinoma (RCC) is associated with a high frequency of metastasis and only few therapies substantially prolong survival. Recently, Englerin A (Eng A), a molecule of herb (Phyllanthus engleri) extracts, shows selective toxic effect on RCCs through the National Cancer Institute Drug Discovery panel using human cell lines as well as in vitro angiogenesis. Eng A has been reported to possess certain anticancer properties. However, whether Eng A could suppress RCC metastasis has not been fully elucidated. The epithelial-mesenchymal transition (EMT) is followed by invasion is a hallmark of metastasis malignancies including renal cancer. The aim of the present study was to examine the effects of Eng A in preventing the migration and invasion of RCCs (Caki-1 and 786-0), as well as to investigate whether Eng A may inhibit the molecular changes associated with EMT induced by transforming growth factor-beta1 (TGF-β1). We also aimed to see whether Eng A suppresses the cancer stem cell markers and spheroid formation. The investigation demonstrated that Eng A suppressed the migration and invasion of these cells under non-cytotoxic concentrations. Eng A inhibited molecular changes associated with TGF-β1-induced EMT by upregulating the epithelial markers and downregulating the mesenchymal markers. Eng A significantly reduced the levels of Twist protein, a master regulator of EMT. Eng A also inhibits the stem cell markers, i.e., CD44, ABCG2 and ALDH1 and spheroid formation. We also found that Eng A inhibits TGF-β1-induced angiogenesis. This study indicated that Eng A may serve as a potential candidate for the treatment of renal cancer metastasis. Citation Format: Inamul Haque, Snigdha Banerjee, John A. Beutler, Sushanta K. Banerjee. Englerin-A prevents invasive phenotypes of renal cell carcinoma by reprogramming mesenchymal to epithelial transition: A key mechanism of its anticancer properties. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5322. doi:10.1158/1538-7445.AM2015-5322

Scientist honored for work with paclitaxel

Scientist honored for work with paclitaxel

Stakeholder perspectives on implementing the National Cancer Institute’s patient-reported outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE)

The National Cancer Institute (NCI) is developing a patient-reported version of its Common Terminology Criteria for Adverse Events, called the "PRO-CTCAE." The PRO-CTCAE consists of a library of patient-reported items which can be administered in clinical trials to directly capture the patient experience of adverse events during cancer treatment, as well as a software platform for administering these items via computer or telephone. In order to better understand the impressions of stakeholders involved in cancer clinical research about the potential value of the PRO-CTCAE approach to capturing adverse event information in clinical research, as well as their perspectives about barriers and strategies for implementing the PRO-CTCAE in NCI-sponsored cancer trials, a survey was conducted. A survey including structured and open-ended questions was developed to elicit perceptions about the use of patient-reported outcomes (PROs) for adverse event reporting, and to explore logistical considerations for implementing the PRO-CTCAE in cancer trials. The survey was distributed electronically and by paper to a convenience sample of leadership and committee members in the NCI's cooperative group network, including principal investigators, clinical investigators, research nurses, data managers, patient advocates, and representatives of the NCI and Food and Drug Administration. Between October, 2008 through February, 2009, 727 surveys were collected. Most respondents (93%) agreed that patient reporting of adverse symptoms would be useful for improving understanding of the patient experience with treatment in cancer trials, and 88%, 80%, and 76%, respectively, endorsed that administration of PRO-CTCAE items in clinical trials would improve the completeness, accuracy, and efficiency of symptom data collection. More than three fourths believed that patient reports would be useful for informing treatment dose modifications and towards FDA regulatory evaluation of drugs. Eighty-eight percent felt that patients in clinical trials would be willing to self-report adverse symptoms at clinic visits via computer, and 68% felt patients would self-report weekly from home via the internet or an automated telephone system. Lack of computers and limited space and personnel were seen as potential barriers to in-clinic self-reporting, but these were judged to be surmountable with adequate funding. The PRO-CTCAE items and software are viewed by a majority of survey respondents as a means to improve adverse event data quality and comprehensiveness, enhance clinical decision-making, and foster patient-clinician communication. Research is ongoing to assess the measurement properties and feasibility of implementing this measure in cancer clinical trials.

Resistance to the Novel Translation Inhibitor Silvestrol Is Mediated by Elevated Mcl-1 Expression.

Abstract 1737Poster Board I-763We previously reported the efficacy and B-cell selectivity of the natural product silvestrol in acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL), using both primary cells and B-cell lines. We also showed that silvestrol inhibits translation, resulting in rapid depletion of the short half-life protein Mcl-1 followed by mitochondrial damage and apoptosis. Cencic et al. reported that silvestrol directly blocks translation initiation by aberrantly promoting interaction of eIF4A with capped mRNA (PLoS One 2009; 4(4):e5223). However, the loss of Mcl-1 in breast and prostate cancer cell lines is delayed relative to what we observe in B-leukemias (48 hr vs. 4-6 hr in CLL and ALL cells). Additionally, silvestrol does not reduce Mcl-1 expression in normal T-cells to the same extent that it does in B-cells, potentially explaining in part the relative resistance of T-cells to this agent. We therefore investigated cell-type differences, as well as the importance of Mcl-1, in silvestrol-mediated cytotoxicity. We incubated the ALL cell line 697 with gradually increasing concentrations of silvestrol to generate a cell line (697-R) with resistance to 30 nM silvestrol (IC50 of parental 697 < 5 nM). No differences between 697-R and the parental line were detected upon detailed immunophenotyping. However, cytogenetic analysis revealed a balanced 7q;9p translocation in 697-R not present in the parental 697 cell line that may be related to the emergence of a resistant clone. We also detected no difference in expression of multi-drug resistance proteins MDR-1 and MRP, which can contribute to resistance to complex amphipathic molecules such as silvestrol. In contrast, we found that baseline Mcl-1 protein expression is strikingly increased in 697-R cells relative to the parental line, although these cells still show similar percent-wise reduction in Mcl-1 upon re-exposure to 80 nM silvestrol. To investigate whether this resistance to silvestrol is reversible, 697-R cells were maintained without silvestrol for 6 weeks (∼18 passages). During this time, viability remained near 99%. Cells were then treated with 30 nM silvestrol. Viability was 94% at 48 hr post-treatment and returned to 99% within a week, while parental 697 cells with the same treatment were completely dead. Baseline Mcl-1 levels remained elevated in 697-R even with prolonged silvestrol-free incubation. These results indicate that the resistance phenotype is not rapidly reversible, as is seen with transient upregulation of multi-drug resistance or stress-response proteins. Additionally, silvestrol moderately induces the transcription of several pro-apoptotic Bcl-2 family members and results in elevated levels of these proteins despite its translation inhibitory activity. Interestingly, no such activity is detected in silvestrol-treated normal T-cells. Together, these results support the hypothesis that in B-cells, silvestrol induces cell death by altering the balance of pro- and anti-apoptotic factors, and that increased Mcl-1 protein can force the balance back toward survival. This work further underscores the importance of Mcl-1 in silvestrol-mediated cytotoxicity. We are now investigating the mechanism of Mcl-1 upregulation in 697-R cells to identify a factor or pathway that can be targeted therapeutically to circumvent resistance. Silvestrol is currently undergoing preclinical pharmacology and toxicology investigation by the U.S. National Cancer Institute Drug Development Group at the Stage IIA level to facilitate its progression to Phase I clinical testing. DisclosuresNo relevant conflicts of interest to declare.

Evaluation of molecular descriptors for antitumor drugs with respect to noncovalent binding to DNA and antiproliferative activity

BackgroundSmall molecules that bind reversibly to DNA are among the antitumor drugs currently used in chemotherapy. In the pursuit of a more rational approach to cancer chemotherapy based upon these molecules, it is necessary to exploit the interdependency between DNA-binding affinity, sequence selectivity and cytotoxicity. For drugs binding noncovalently to DNA, it is worth exploring whether molecular descriptors, such as their molecular weight or the number of potential hydrogen acceptors/donors, can account for their DNA-binding affinity and cytotoxicity.ResultsFifteen antitumor agents, which are in clinical use or being evaluated as part of the National Cancer Institute's drug screening effort, were analyzed in silico to assess the contribution of various molecular descriptors to their DNA-binding affinity, and the capacity of the descriptors and DNA-binding constants for predicting cell cytotoxicity. Equations to predict drug-DNA binding constants and growth-inhibitory concentrations were obtained by multiple regression following rigorous statistical procedures.ConclusionFor drugs binding reversibly to DNA, both their strength of binding and their cytoxicity are fairly predicted from molecular descriptors by using multiple regression methods. The equations derived may be useful for rational drug design. The results obtained agree with that compounds more active across the National Cancer Institute's 60-cell line data set tend to have common structural features.

Parallel Synthesis of O‐Phenoxyethyl and O‐Adamantyl N‐acyl Thiocarbamates Endowed with Antiproliferative Activity

In order to further explore the antiproliferative properties of O-phenoxyethyl and O-adamantyl acylthiocarbamates (ATCs), a series of 14 derivatives was prepared by a parallel adaptation of a highly convergent one-pot three-step procedure. Ten acylthiocarbamates were selected by the National Cancer Institute drug evaluation program and screened against a panel of 55 to 58 cell lines derived from nine different types of human cancers. In general, the tested compounds showed a widespread micromolar activity with some specificity against leukemia, renal UO-31, central nervous system (CNS) SNB-75, and non-small cell lung HOP-92 cancer cell lines. Bioinformatic COMPARE analyses were carried out to identify possible mechanism(s) of action for acylthiocarbamate antiproliferative activity.

Genome-wide identification of genetic determinants for the cytotoxicity of perifosine

Perifosine belongs to the class of alkylphospholipid analogues, which act primarily at the cell membrane, thereby targeting signal transduction pathways. In phase I/II clinical trials, perifosine has induced tumour regression and caused disease stabilisation in a variety of tumour types. The genetic determinants responsible for its cytotoxicity have not been comprehensively studied, however. We performed a genome-wide analysis to identify genes whose expression levels or genotypic variation were correlated with the cytotoxicity of perifosine, using public databases on the US National Cancer Institute (NCI)-60 human cancer cell lines. For demonstrating drug specificity, the NCI Standard Agent Database (including 171 drugs acting through a variety of mechanisms) was used as a control. We identified agents with similar cytotoxicity profiles to that of perifosine in compounds used in the NCI drug screen. Furthermore, Gene Ontology and pathway analyses were carried out on genes more likely to be perifosine specific. The results suggested that genes correlated with perifosine cytotoxicity are connected by certain known pathways that lead to the mitogen-activated protein kinase signalling pathway and apoptosis. Biological processes such as 'response to stress', 'inflammatory response' and 'ubiquitin cycle' were enriched among these genes. Three single nucleotide polymorphisms (SNPs) located in CACNA2DI and EXOC4 were found to be correlated with perifosine cytotoxicity. Our results provided a manageable list of genes whose expression levels or genotypic variation were strongly correlated with the cytotoxcity of perifosine. These genes could be targets for further studies using candidate-gene approaches. The results also provided insights into the pharmacodynamics of perifosine.

Synthesis and evaluation of novel benzothiazole derivatives against human cervical cancer cell lines

The 2-arylsubstituted benzothiazole derivatives were synthesized by refluxing o-aminothiophenol with substituted benzoic acids in the presence of polyphosphoric acid at 220°. 2-Mercaptothiazole was used along with thionyl chloride to get the carbothioates. The physical and spectral data such as mp, Rf, IR, NMR was obtained for the synthesized compounds and the structures were confirmed. The screening for antitumour activity was done as per the National Cancer Institute drug screening strategy 3 compounds were found to be significantly cytotoxic as compared to [2-(3-bromo-4-aminophenyl) benzothiazole] against the human cervical cancer cell lines.

Cyclin-dependent kinase modulators studied at the NCI: pre-clinical and clinical studies.

The cyclin dependent kinases (CDKs) are key regulators of cell cycle progression. Lead compounds (from empirical anti-proliferative screening approaches) have been defined which modulate CDK function and have evidence of anti-proliferative activity in tissue culture systems and in some cases anti-tumor activity in vivo in conventional xenogaft models. Two of these, flavopiridol and UCN-01, have entered initial clinical testing. Flavopiridol is a "pan-CDK" inhibitor, with essentially equal potency in inhibiting all CDKs tested. The recent elucidation that in addition to cell cycle regulatory functions, CDK family members have been defined which regulate transcription, neuronal, and secretory function has increased the need for definition of CDK antagonists with greater selectivity. Novel purine, pyrimidine, and benzazepinone derivatives have been characterized in part through the National Cancer Institute's drug screening systems. UCN-01, in contrast to flavopiridol, modulates CDK activity participating in the DNA damage response, possibly through potent inhibition of the chk1 checkpoint kinase, as well as affecting CDK function indirectly through activity on other kinase targets. An unexpected feature in its development has been avid binding to alpha(1) acid glycoprotein. Further progress in CDK modulator development will require the definition of additional lead structures that address issues raised by these early molecules entering into clinical development.

DNA repair protein levels vis-à-vis anticancer drug resistance in the human tumor cell lines of the National Cancer Institute drug screening program.

Nucleotide excision repair (NER) is a multi-enzyme DNA repair pathway in eukaryotes. Several NER genes in this pathway including XPB, XPD, XPA and ERCC-1 have been implicated in anticancer drug resistance in human tumor cells. In this study, we assessed the levels of the above-mentioned proteins in the NCI panel of 60 human tumor cell lines in relation to the cytotoxicity patterns of 170 compounds that constitute the standard agent (SA) database. The database consists of drugs used in the clinic for which a mechanism of action has been at least partially defined. The ERCC-1, XPD and XPB protein expression patterns yielded significant negative Pearson correlations with 13, 32 and 17 out of the 170 compounds, respectively (using p<0.05). XPA produced a random assortment of negative and positive correlations, and did not appear to confer an overall resistance or sensitivity to these drugs. Protein expression was also compared with a pre-defined categorization of the standard agents into six mechanism-of-action groups resulting in an inverse association between XPD and alkylating agent sensitivity. Our present data demonstrate that XPD protein levels correlate with resistance to alkylating agents in human tumor cell lines suggesting that XPD is implicated in the development of this resistance. NER activity, using the in vitro cell-free system repair assay, revealed no correlation between NER activity and the level of XPD protein in four cell lines with widely varying XPD protein levels. This lack of correlation may be due to the contribution of XPD to other functions including interactions with the Rad51 repair pathway.

The bioinformatics of microarray gene expression profiling.

The bioinformatics of microarray gene expression profiling.

Evidence for functionally significant polymorphism of human glutamate cysteine ligase catalytic subunit: association with glutathione levels and drug resistance in the National Cancer Institute tumor cell line panel.

Glutamate-cysteine ligase (GCL) is the first and rate-limiting enzyme involved in the biosynthesis of glutathione (GSH). The GCL heterodimer is encoded by two genes: GLCLC, which directs synthesis of the catalytic subunit, and GLCLR, which encodes the regulatory subunit. We have previously identified a polymorphic GAG/CTC trinucleotide repeat within the 5' untranslated region of GLCLC. Here we report the further characterization of GLCLC polymorphism and the existence of five GLCLC alleles as defined by the trinucleotide repeat, which exhibits a range of 4 to 10 uninterrupted repeats. Significant variation in GLCLC allele frequencies was observed in four different ethnic populations examined. Interindividual variation in the capacity to produce GSH due to GLCLC polymorphism is hypothesized to influence the cellular response to environmental toxicants and chemotherapeutic agents. To test this hypothesis, the 60 tumor cell lines of the National Cancer Institute drug screening panel were genotyped for the GLCLC trinucleotide repeat, and the association of GLCLC genotype with GSH levels and drug sensitivity/resistance data was examined. Here we demonstrate an association between certain GLCLC alleles and GSH levels and/or drug sensitivity, providing evidence that suggests polymorphism of human GLCLC is functionally significant.

THE WILLET F. WHITMORE, JR., LECTURESHIP: BLOCKADE OF EPIDERMAL GROWTH FACTOR RECEPTORS AS ANTICANCER THERAPY

In 1981 Sato and I hypothesized that a monoclonal antibody that binds to EGF receptors may inhibit cell proliferation by blocking activation of receptors by EGF or transforming growth factor (TGF)-a. The compelling rationale for this hypothesis is summarized in Appendix 1. In 1983 and 1984 we published a series of studies demonstrating that blockade of human EGF receptors by murine mAb 225 or mAb 528, produced in our laboratory, competitively inhibits the capacity of EGF to activate receptor tyrosine kinase and can inhibit proliferation of cells bearing EGF receptors in culture and in human tumor xenografts in nude mice.1–3 Subsequently, these antiproliferative effects in culture and against xenografts have been observed with numerous human tumor cell lines.4 A human:murine chimeric mAb C225 was produced with the support of the National Cancer Institute drug evaluation network (Appendix 2). This chimeric antibody has higher binding affinity for the EGF receptor than its murine parent, and its activity against well established human tumor xenografts surpasses that of murine 225.5 It should be stressed that C225 is acting as a drug, a tyrosine kinase inhibitor specific for the EGF receptor. We have identified 6 different mechanisms by which C225 may inhibit tumor cell growth and survival in culture and, more importantly, in nude mouse xenografts (Appendix 3). We review some of the experiments that have elucidated each of these mechanisms.

P-glycoprotein substrates and antagonists cluster into two distinct groups.

To gather further insight into the interaction between P-glycoprotein (Pgp) and its substrates, 167 compounds were analyzed in multidrug resistant human colon carcinoma cells. These compounds were selected from the National Cancer Institute Drug Screen repository using computer-generated correlations with known Pgp substrates and antagonists. The compounds were prospectively defined as Pgp substrates if cytotoxicity was increased > or =4-fold by the addition of cyclosporin A (CsA) and as Pgp antagonists if inhibition of efflux increased rhodamine accumulation by 4-fold. Among the 84 agents that met either criterion, 35 met only the criterion for substrates, 42 met only the criterion for antagonists, and only seven met both criteria. Thus, compounds interacting with Pgp form two distinct groups: one comprising cytotoxic compounds that are transported and have poor or no antagonistic activity and a second comprising compounds with antagonistic activity and no evidence of significant transport. Vinblastine accumulation and kinetic studies performed on a subset of 18 compounds similarly differentiated substrates and antagonists, but inhibition of 3H-azidopine labeling and induction of ATPase activity did not. These data support an emerging concept of Pgp in which multiple regions instead of specific sites are involved in drug transport.

A new class of anti-HIV-1 agents targeted toward the nucleocapsid protein NCp7: The 2,2′-dithiobisbenzamides

As part of the National Cancer Institute's Drug Screening Program, a new class of antiretrovirals active against the human immunodeficiency virus HIV-1 has been identified, and the HIV-1 nucleocapsid protein NCp7 was proposed as the target of antiviral action. The 2,2′-dithiobis-[4′-(sulfamoyl)benzanilide] ( 3x) and the 2,2′-dithiobis(5-acetylamino)benzamide ( 10) represented the prototypic lead structures. A wide variety of 2,2′-dithiobisbenzamides were prepared and tested for anti-HIV-1 activity, cytotoxicity, and their ability to extrude zinc from the zinc fingers for NCp7. The structure-activity relationships demonstrated that the ability to extrude zinc from NCp7 resided in the 2,2′-dithiobisbenzamide core structure. The 3,3′ and the 4,4′ isomers were inactive. While many analogs based upon the core structure retained the zinc extrusion activity, the best overall anti-HIV-1 activity was only found in a narrow set of derivatives possessing carboxylic acid, carboxamide, or phenylsulfonamide functional groups. These functional groups were more important for reducing cytotoxicity than improving antiviral potency or activity vs NCp7. All of the compounds with antiviral activity also extruded zinc from NCp7. From this study several classes of low μM anti-HIV agents with simple chemical structures were identified as possible chemotherapeutic agents for the treatment of AIDS.

Molecular targets in the National Cancer Institute drug screen.

Molecular targets in the National Cancer Institute drug screen.