A simple and accessible CRISPR genome editing laboratory exercise using yeast

CRISPR is a revolutionary tool to engineer the genome. Herein, we describe a laboratory exercise designed to introduce students to CRISPR by editing the genome of yeast to disrupt the ADE2 gene, which results in yeast that form red colored colonies. The experiment was constructed to be performed in a single laboratory session and to be accessible to students and instructors without experience working with yeast.

Evolution of natural lifespan variation and molecular strategies of extended lifespan in yeast

To understand the genetic basis and selective forces acting on longevity, it is useful to examine lifespan variation among closely related species, or ecologically diverse isolates of the same species, within a controlled environment. In particular, this approach may lead to understanding mechanisms underlying natural variation in lifespan. Here, we analyzed 76 ecologically diverse wild yeast isolates and discovered a wide diversity of replicative lifespan (RLS). Phylogenetic analyses pointed to genes and environmental factors that strongly interact to modulate the observed aging patterns. We then identified genetic networks causally associated with natural variation in RLS across wild yeast isolates, as well as genes, metabolites, and pathways, many of which have never been associated with yeast lifespan in laboratory settings. In addition, a combined analysis of lifespan-associated metabolic and transcriptomic changes revealed unique adaptations to interconnected amino acid biosynthesis, glutamate metabolism, and mitochondrial function in long-lived strains. Overall, our multiomic and lifespan analyses across diverse isolates of the same species shows how gene-environment interactions shape cellular processes involved in phenotypic variation such as lifespan.

Suppression of telomere capping defects of Saccharomyces cerevisiae yku70 and yku80 mutants by telomerase

The Ku complex performs multiple functions inside eukaryotic cells, including protection of chromosomal DNA ends from degradation and fusion events, recruitment of telomerase, and repair of double-strand breaks (DSBs). Inactivation of Ku complex genes YKU70 or YKU80 in cells of the yeast Saccharomyces cerevisiae gives rise to mutants that exhibit shortened telomeres and temperature-sensitive growth. In this study, we have investigated the mechanism by which overexpression of telomerase suppresses the temperature sensitivity of yku mutants. Viability of yku cells was restored by overexpression of the Est2 reverse transcriptase and TLC1 RNA template subunits of telomerase, but not the Est1 or Est3 proteins. Overexpression of other telomerase- and telomere-associated proteins (Cdc13, Stn1, Ten1, Rif1, Rif2, Sir3, and Sir4) did not suppress the growth defects of yku70 cells. Mechanistic features of suppression were assessed using several TLC1 RNA deletion derivatives and Est2 enzyme mutants. Supraphysiological levels of three catalytically inactive reverse transcriptase mutants (Est2-D530A, Est2-D670A, and Est2-D671A) suppressed the loss of viability as efficiently as the wild-type Est2 protein, without inducing cell senescence. Roles of proteins regulating telomere length were also determined. The results support a model in which chromosomes in yku mutants are stabilized via a replication-independent mechanism involving structural reinforcement of protective telomere cap structures.

Inactivating histone deacetylase HDA promotes longevity by mobilizing trehalose metabolism

Histone acetylations are important epigenetic markers for transcriptional activation in response to metabolic changes and various stresses. Using the high-throughput SEquencing-Based Yeast replicative Lifespan screen method and the yeast knockout collection, we demonstrate that the HDA complex, a class-II histone deacetylase (HDAC), regulates aging through its target of acetylated H3K18 at storage carbohydrate genes. We find that, in addition to longer lifespan, disruption of HDA results in resistance to DNA damage and osmotic stresses. We show that these effects are due to increased promoter H3K18 acetylation and transcriptional activation in the trehalose metabolic pathway in the absence of HDA. Furthermore, we determine that the longevity effect of HDA is independent of the Cyc8-Tup1 repressor complex known to interact with HDA and coordinate transcriptional repression. Silencing the HDA homologs in C. elegans and Drosophila increases their lifespan and delays aging-associated physical declines in adult flies. Hence, we demonstrate that this HDAC controls an evolutionarily conserved longevity pathway.

Loss of vacuolar acidity results in iron-sulfur cluster defects and divergent homeostatic responses during aging in Saccharomyces cerevisiae

The loss of vacuolar/lysosomal acidity is an early event during aging that has been linked to mitochondrial dysfunction. However, it is unclear how loss of vacuolar acidity results in age-related dysfunction. Through unbiased genetic screens, we determined that increased iron uptake can suppress the mitochondrial respiratory deficiency phenotype of yeast vma mutants, which have lost vacuolar acidity due to genetic disruption of the vacuolar ATPase proton pump. Yeast vma mutants exhibited nuclear localization of Aft1, which turns on the iron regulon in response to iron-sulfur cluster (ISC) deficiency. This led us to find that loss of vacuolar acidity with age in wild-type yeast causes ISC defects and a DNA damage response. Using microfluidics to investigate aging at the single-cell level, we observe grossly divergent trajectories of iron homeostasis within an isogenic and environmentally homogeneous population. One subpopulation of cells fails to mount the expected compensatory iron regulon gene expression program, and suffers progressively severe ISC deficiency with little to no activation of the iron regulon. In contrast, other cells show robust iron regulon activity with limited ISC deficiency, which allows extended passage and survival through a period of genomic instability during aging. These divergent trajectories suggest that iron regulation and ISC homeostasis represent a possible target for aging interventions.

The antifungal plant defensin HsAFP1 induces autophagy, vacuolar dysfunction and cell cycle impairment in yeast

The plant defensin HsAFP1 is characterized by broad-spectrum antifungal activity and induces apoptosis in Candida albicans. In this study, we performed a transcriptome analysis on C. albicans cultures treated with HsAFP1 to gain further insight in the antifungal mode of action of HsAFP1. Various genes coding for cell surface proteins, like glycosylphosphatidylinositol (GPI)-anchored proteins, and proteins involved in cation homeostasis, autophagy and in cell cycle were differentially expressed upon HsAFP1 treatment. The biological validation of these findings was performed in the model yeast Saccharomyces cerevisiae. To discriminate between events linked to HsAFP1's antifungal activity and those that are not, we additionally used an inactive HsAFP1 mutant. We demonstrated that (i) HsAFP1-resistent S. cerevisiae mutants that are characterized by a defect in processing GPI-anchors are unable to internalize HsAFP1, and (ii) moderate doses (FC50, fungicidal concentration resulting in 50% killing) of HsAFP1 induce autophagy in S. cerevisiae, while high HsAFP1 doses result in vacuolar dysfunction. Vacuolar function is an important determinant of replicative lifespan (RLS) under dietary restriction (DR). In line, HsAFP1 specifically reduces RLS under DR. Lastly, (iii) HsAFP1 affects S. cerevisiae cell cycle in the G2/M phase. However, the latter HsAFP1-induced event is not linked to its antifungal activity, as the inactive HsAFP1 mutant also impairs the G2/M phase. In conclusion, we demonstrated that GPI-anchored proteins are involved in HsAFP1's internalization, and that HsAFP1 induces autophagy, vacuolar dysfunction and impairment of the cell cycle. Collectively, all these data provide novel insights in the mode of action of HsAFP1 as well as in S. cerevisiae tolerance mechanisms against this peptide.

Genetic screen identifies adaptive aneuploidy as a key mediator of ER stress resistance in yeast

The yeast genome becomes unstable during stress, which often results in adaptive aneuploidy, allowing rapid activation of protective mechanisms that restore cellular homeostasis. In this study, we performed a genetic screen in Saccharomyces cerevisiae to identify genome adaptations that confer resistance to tunicamycin-induced endoplasmic reticulum (ER) stress. Whole-genome sequencing of tunicamycin-resistant mutants revealed that ER stress resistance correlated significantly with gains of chromosomes II and XIII. We found that chromosome duplications allow adaptation of yeast cells to ER stress independently of the unfolded protein response, and that the gain of an extra copy of chromosome II alone is sufficient to induce protection from tunicamycin. Moreover, the protective effect of disomic chromosomes can be recapitulated by overexpression of several genes located on chromosome II. Among these genes, overexpression of UDP-N-acetylglucosamine-1-P transferase (ALG7), a subunit of the 20S proteasome (PRE7), and YBR085C-A induced tunicamycin resistance in wild-type cells, whereas deletion of all three genes completely reversed the tunicamycin-resistance phenotype. Together, our data demonstrate that aneuploidy plays a critical role in adaptation to ER stress by increasing the copy number of ER stress protective genes. While aneuploidy itself leads to proteotoxic stress, the gene-specific effects of chromosome II aneuploidy counteract the negative effect resulting in improved protein folding.

Transaldolase inhibition impairs mitochondrial respiration and induces a starvation-like longevity response in Caenorhabditis elegans

Mitochondrial dysfunction can increase oxidative stress and extend lifespan in Caenorhabditis elegans. Homeostatic mechanisms exist to cope with disruptions to mitochondrial function that promote cellular health and organismal longevity. Previously, we determined that decreased expression of the cytosolic pentose phosphate pathway (PPP) enzyme transaldolase activates the mitochondrial unfolded protein response (UPR^mt) and extends lifespan. Here we report that transaldolase (tald-1) deficiency impairs mitochondrial function in vivo, as evidenced by altered mitochondrial morphology, decreased respiration, and increased cellular H₂O₂ levels. Lifespan extension from knockdown of tald-1 is associated with an oxidative stress response involving p38 and c-Jun N-terminal kinase (JNK) MAPKs and a starvation-like response regulated by the transcription factor EB (TFEB) homolog HLH-30. The latter response promotes autophagy and increases expression of the flavin-containing monooxygenase 2 (fmo-2). We conclude that cytosolic redox established through the PPP is a key regulator of mitochondrial function and defines a new mechanism for mitochondrial regulation of longevity.

There are a growing number of studies linking mitochondrial dysfunction to enhanced longevity, especially in the nematode C. elegans. The reasons for these pro-longevity effects have been elusive, but one current model is that adaptive responses to mitochondrial inhibition promote organismal health and stress resistance. Here, we report an intriguing example of mitochondrial stress induced by inhibition of a cytosolic metabolic pathway that extends lifespan in worms. We find that inhibition of the pentose phosphate pathway, which is essential for cytosolic redox homeostasis, affects multiple parameters of mitochondrial function and activates a starvation-like response that promotes longevity through recycling of damaged cellular components and induction of the enzyme flavin-containing monooxygenase 2. These results establish novel links between the pentose phosphate pathway, mitochondrial function, redox homeostasis, and organismal aging.

New functional and biophysical insights into the mitochondrial Rieske iron-sulfur protein from genetic suppressor analysis in C. elegans

Several intragenic mutations suppress the C. elegans isp-1(qm150) allele of the mitochondrial Rieske iron-sulfur protein (ISP), a catalytic subunit of Complex III of the respiratory chain. These mutations were located in a helical region of the "tether" span of ISP-1, distant from the primary mutation in the extrinsic head, and suppressed all pleiotropic phenotypes associated with the qm150 allele. Analysis of these suppressors revealed control of electron transfer into Complex III through a "spring-loaded" mechanism involving a binding force for formation of enzyme-substrate complex, counter balanced by forces (a chemical "spring") favoring helix formation in the tether. The primary P→S mutation results in inhibition of electron flow into the Q-cycle by decreasing the binding force, and the tether mutations relieve this inhibition by weakening the "spring." In this commentary we discuss additional control features, and relate the primary inhibition to outcomes at the organismal level. In particular, the sensitivity to hyperoxia and the elevated reactive oxygen species (ROS) seen in isp-1(qm150), likely reflect over-reduction of the quinone pool, which is upstream of the inhibited site; at high O2, this would lead to increased ROS production through complex I. We speculate that alternative NADH:ubiquinone oxidoreductase activity in C. elegans from the worm apoptosis inducing factor (AIF) homolog (WAH-1) might also be involved, and that WAH-1 might have a "canary" function in detection of this adverse state (high O2/reduced pool), and a role in protection of the organism by transformation to AIF-like products, and apoptotic recycling of defective cells.

Aneuploidy shortens replicative lifespan in Saccharomyces cerevisiae

Aneuploidy and aging are correlated; however, a causal link between these two phenomena has remained elusive. Here, we show that yeast disomic for a single native yeast chromosome generally have a decreased replicative lifespan. In addition, the extent of this lifespan deficit correlates with the size of the extra chromosome. We identified a mutation in BUL1 that rescues both the lifespan deficit and a protein trafficking defect in yeast disomic for chromosome 5. Bul1 is an E4 ubiquitin ligase adaptor involved in a protein quality control pathway that targets membrane proteins for endocytosis and destruction in the lysosomal vacuole, thereby maintaining protein homeostasis. Concurrent suppression of the aging and trafficking phenotypes suggests that disrupted membrane protein homeostasis in aneuploid yeast may contribute to their accelerated aging. The data reported here demonstrate that aneuploidy can impair protein homeostasis, shorten lifespan, and may contribute to age-associated phenotypes.

A Comprehensive Analysis of Replicative Lifespan in 4,698 Single-Gene Deletion Strains Uncovers Conserved Mechanisms of Aging

Many genes that affect replicative lifespan (RLS) in the budding yeast Saccharomyces cerevisiae also affect aging in other organisms such as C. elegans and M. musculus. We performed a systematic analysis of yeast RLS in a set of 4,698 viable single-gene deletion strains. Multiple functional gene clusters were identified, and full genome-to-genome comparison demonstrated a significant conservation in longevity pathways between yeast and C. elegans. Among the mechanisms of aging identified, deletion of tRNA exporter LOS1 robustly extended lifespan. Dietary restriction (DR) and inhibition of mechanistic Target of Rapamycin (mTOR) exclude Los1 from the nucleus in a Rad53-dependent manner. Moreover, lifespan extension from deletion of LOS1 is nonadditive with DR or mTOR inhibition, and results in Gcn4 transcription factor activation. Thus, the DNA damage response and mTOR converge on Los1-mediated nuclear tRNA export to regulate Gcn4 activity and aging.

H3K36 methylation promotes longevity by enhancing transcriptional fidelity

Sen et al. find that lack of sustained histone H3K36 methylation is commensurate with increased cryptic transcription in a subset of genes in old cells and with shorter life span. In contrast, deletion of the K36me2/3 demethylase Rph1 increases H3K36me3 within these genes, suppresses cryptic transcript initiation, and extends life span.

Epigenetic mechanisms, including histone post-translational modifications, control longevity in diverse organisms. Relatedly, loss of proper transcriptional regulation on a global scale is an emerging phenomenon of shortened life span, but the specific mechanisms linking these observations remain to be uncovered. Here, we describe a life span screen in Saccharomyces cerevisiae that is designed to identify amino acid residues of histones that regulate yeast replicative aging. Our results reveal that lack of sustained histone H3K36 methylation is commensurate with increased cryptic transcription in a subset of genes in old cells and with shorter life span. In contrast, deletion of the K36me2/3 demethylase Rph1 increases H3K36me3 within these genes, suppresses cryptic transcript initiation, and extends life span. We show that this aging phenomenon is conserved, as cryptic transcription also increases in old worms. We propose that epigenetic misregulation in aging cells leads to loss of transcriptional precision that is detrimental to life span, and, importantly, this acceleration in aging can be reversed by restoring transcriptional fidelity.

PMT1 deficiency enhances basal UPR activity and extends replicative lifespan of Saccharomyces cerevisiae

Pmt1p is an important member of the protein O-mannosyltransferase (PMT) family of enzymes, which participates in the endoplasmic reticulum (ER) unfolded protein response (UPR), an important pathway for alleviating ER stress. ER stress and the UPR have been implicated in aging and age-related diseases in several organisms; however, a possible role for PMT1 in determining lifespan has not been previously described. In this study, we report that deletion of PMT1 increases replicative lifespan (RLS) in the budding yeast Saccharomyces cerevisiae, while overexpression of PMT1 (PMT1-OX) reduces RLS. Relative to wild-type and PMT1-OX strains, the pmt1Δ strain had enhanced HAC1 mRNA splicing and elevated expression levels of UPR target genes. Furthermore, the increased RLS of the pmt1Δ strain could be completely abolished by deletion of either IRE1 or HAC1, two upstream modulators of the UPR. The double deletion strains pmt1Δhac1Δ and pmt1Δire1Δ also displayed generally reduced transcription of UPR target genes. Collectively, our results suggest that PMT1 deficiency enhances basal activity of the ER UPR and extends the RLS of yeast mother cells through a mechanism that requires both IRE1 and HAC1.

Nar1 deficiency results in shortened lifespan and sensitivity to paraquat that is rescued by increased expression of mitochondrial superoxide dismutase

Saccharomyces cerevisiae Nar1p is an essential Fe/S protein that exhibits striking similarity to bacterial iron-only hydrogenases. Nar1p is required for the maturation of cytosolic and nuclear, but not of mitochondrial Fe/S proteins, and plays a role in modulating sensitivity to oxygen in both yeast and Caenorhabditis elegans through unknown mechanisms. Here we report that Nar1 deficiency results in shortened lifespan and sensitivity to paraquat that is rescued by increased expression of mitochondrial superoxide dismutase. These data suggest that Nar1p promotes protection against oxidative stress and define a new role for Nar1p in promoting replicative lifespan.

mTOR inhibition alleviates mitochondrial disease in a mouse model of Leigh syndrome

Mitochondrial dysfunction contributes to numerous health problems, including neurological and muscular degeneration, cardiomyopathies, cancer, diabetes, and pathologies of aging. Severe mitochondrial defects can result in childhood disorders such as Leigh syndrome, for which there are no effective therapies. We found that rapamycin, a specific inhibitor of the mechanistic target of rapamycin (mTOR) signaling pathway, robustly enhances survival and attenuates disease progression in a mouse model of Leigh syndrome. Administration of rapamycin to these mice, which are deficient in the mitochondrial respiratory chain subunit Ndufs4 [NADH dehydrogenase (ubiquinone) Fe-S protein 4], delays onset of neurological symptoms, reduces neuroinflammation, and prevents brain lesions. Although the precise mechanism of rescue remains to be determined, rapamycin induces a metabolic shift toward amino acid catabolism and away from glycolysis, alleviating the buildup of glycolytic intermediates. This therapeutic strategy may prove relevant for a broad range of mitochondrial diseases.

Molecular mechanisms underlying genotype-dependent responses to dietary restriction

Dietary restriction (DR) increases lifespan and attenuates age-related phenotypes in many organisms; however, the effect of DR on longevity of individuals in genetically heterogeneous populations is not well characterized. Here, we describe a large-scale effort to define molecular mechanisms that underlie genotype-specific responses to DR. The effect of DR on lifespan was determined for 166 single gene deletion strains in Saccharomyces cerevisiae. Resulting changes in mean lifespan ranged from a reduction of 79% to an increase of 103%. Vacuolar pH homeostasis, superoxide dismutase activity, and mitochondrial proteostasis were found to be strong determinants of the response to DR. Proteomic analysis of cells deficient in prohibitins revealed induction of a mitochondrial unfolded protein response (mtUPR), which has not previously been described in yeast. Mitochondrial proteotoxic stress in prohibitin mutants was suppressed by DR via reduced cytoplasmic mRNA translation. A similar relationship between prohibitins, the mtUPR, and longevity was also observed in Caenorhabditis elegans. These observations define conserved molecular processes that underlie genotype-dependent effects of DR that may be important modulators of DR in higher organisms.

Yeast replicative aging: a paradigm for defining conserved longevity interventions

The finite replicative life span of budding yeast mother cells was demonstrated as early as 1959, but the idea that budding yeast could be used to model aging of multicellular eukaryotes did not enter the scientific mainstream until relatively recently. Despite continued skepticism by some, there are now abundant data that several interventions capable of extending yeast replicative life span have a similar effect in multicellular eukaryotes including nematode worms, fruit flies, and rodents. In particular, dietary restriction, mTOR signaling, and sirtuins are among the most studied longevity interventions in the field. Here, we describe key conserved longevity pathways in yeast and discuss relationships that may help explain how such broad conservation of aging processes could have evolved.

Buffering the pH of the culture medium does not extend yeast replicative lifespan

During chronological aging of budding yeast cells, the culture medium can become acidified, and this acidification limits cell survival.  As a consequence, buffering the culture medium to pH 6 significantly extends chronological life span under standard conditions in synthetic medium.  In this study, we assessed whether a similar process occurs during replicative aging of yeast cells.  We find no evidence that buffering the pH of the culture medium to pH levels either higher or lower than the initial pH of the medium is able to significantly extend replicative lifespan.  Thus, we conclude that, unlike chronological life span, replicative life span is not limited by acidification of the culture medium or by changes in the pH of the environment.

End-of-life cell cycle arrest contributes to stochasticity of yeast replicative aging

There is growing evidence that stochastic events play an important role in determining individual longevity. Studies in model organisms have demonstrated that genetically identical populations maintained under apparently equivalent environmental conditions display individual variation in life span that can be modeled by the Gompertz-Makeham law of mortality. Here, we report that within genetically identical haploid and diploid wild-type populations, shorter-lived cells tend to arrest in a budded state, while cells that arrest in an unbudded state are significantly longer-lived. This relationship is particularly notable in diploid BY4743 cells, where mother cells that arrest in a budded state have a shorter mean life span (25.6 vs. 35.6) and larger coefficient of variance with respect to individual life span (0.42 vs. 0.32) than cells that arrest in an unbudded state. Mutations that cause genomic instability tend to shorten life span and increase the proportion of the population that arrest in a budded state. These observations suggest that randomly occurring damage may contribute to stochasticity during replicative aging by causing a subset of the population to terminally arrest prematurely in the S or G2 phase of the cell cycle.

Dietary restriction and mitochondrial function link replicative and chronological aging in Saccharomyces cerevisiae

Chronological aging of budding yeast cells results in a reduction in subsequent replicative life span through unknown mechanisms. Here we show that dietary restriction during chronological aging delays the reduction in subsequent replicative life span up to at least 23days of chronological age. We further show that among the viable portion of the control population aged 26days, individual cells with the lowest mitochondrial membrane potential have the longest subsequent replicative lifespan. These observations demonstrate that dietary restriction modulates a common molecular mechanism linking chronological and replicative aging in yeast and indicate a critical role for mitochondrial function in this process.

Yeast as a model to understand the interaction between genotype and the response to calorie restriction

Calorie restriction is reported to enhance survival and delay the onset of age-related decline in many different species. Several proteins have been proposed to play a role in mediating the response to calorie restriction, including the target of rapamycin kinase, sirtuins, and AMP kinase. An enhanced mechanistic understanding of calorie restriction has popularized the concept of "calorie restriction mimetics", drugs that mimic the beneficial effects of caloire restriction without requiring a reduction in nutrient intake. In theory, such drugs should delay the onset and progression of multiple age-related diseases, similar to calorie restriction in mammals. Despite the potential benefits of such calorie restriction mimetics, however, relatively little is known about the interaction between genetic variation and individual response to calorie restriction. Limited evidence from model systems indicates that genotype plays a large role in determining both the magnitude and direction of effect that calorie restriction has on longevity. Here we present an overview of these data from the perspective of using yeast as a model to study aging and describe an approach we are taking to further characterize the molecular mechanisms underlying genotype-dependent responses to calorie restriction.

pH neutralization protects against reduction in replicative lifespan following chronological aging in yeast

Chronological and replicative aging have been studied in yeast as alternative paradigms for post-mitotic and mitotic aging, respectively. It has been known for more than a decade that cells of the S288C background aged chronologically in rich medium have reduced replicative lifespan relative to chronologically young cells. Here we report replication of this observation in the diploid BY4743 strain background. We further show that the reduction in replicative lifespan from chronological aging is accelerated when cells are chronologically aged under standard conditions in synthetic complete medium rather than rich medium. The loss of replicative potential with chronological age is attenuated by buffering the pH of the chronological aging medium to 6.0, an intervention that we have previously shown can extend chronological lifespan. These data demonstrate that extracellular acidification of the culture medium can cause intracellular damage in the chronologically aging population that is asymmetrically segregated by the mother cell to limit subsequent replicative lifespan.

A novel bisphosphonate inhibitor of squalene synthase combined with a statin or a nitrogenous bisphosphonate in vitro

Statins and nitrogenous bisphosphonates (NBP) inhibit 3-hydroxy-3-methylglutaryl-coenzyme-A reductase (HMGCR) and farnesyl diphosphate synthase (FDPS), respectively, leading to depletion of farnesyl diphosphate (FPP) and disruption of protein prenylation. Squalene synthase (SQS) utilizes FPP in the first committed step from the mevalonate pathway toward cholesterol biosynthesis. Herein, we have identified novel bisphosphonates as potent and specific inhibitors of SQS, including the tetrasodium salt of 9-biphenyl-4,8-dimethyl-nona-3,7-dienyl-1,1-bisphosphonic acid (compound 5). Compound 5 reduced cholesterol biosynthesis and lead to a substantial intracellular accumulation of FPP without reducing cell viability in HepG2 cells. At high concentrations, lovastatin and zoledronate impaired protein prenylation and decreased cell viability, which limits their potential use for cholesterol depletion. When combined with lovastatin, compound 5 prevented lovastatin-induced FPP depletion and impairment of protein farnesylation. Compound 5 in combination with the NBP zoledronate completely prevented zoledronate-induced impairment of both protein farnesylation and geranylgeranylation. Cotreatment of cells with compound 5 and either lovastatin or zoledronate was able to significantly prevent the reduction of cell viability caused by lovastatin or zoledronate alone. The combination of an SQS inhibitor with an HMGCR or FDPS inhibitor provides a rational approach for reducing cholesterol synthesis while preventing nonsterol isoprenoid depletion.

Synthesis and biological evaluation of a series of aromatic bisphosphonates

Geminal bisphosphonates display varied biological activity depending on the nature of the substituents on the central carbon atom. For example, the nitrogenous bisphosphonates zoledronate and risedronate inhibit the enzyme farnesyl diphosphate synthase while digeranyl bisphosphonate has been shown to inhibit the enzyme geranylgeranyl diphosphate synthase. We now have synthesized isoprenoid bisphosphonates where an aromatic ring has been used to replace one of the isoprenoid olefins in an isoprenoid bisphosphonate and investigated the ability of these new compounds to impair protein geranylgeranylation within cells. Several of these new compounds are potent inhibitors of the enzyme geranylgeranyl diphosphate synthase.

Pivaloyloxymethyl-modified isoprenoid bisphosphonates display enhanced inhibition of cellular geranylgeranylation

Nitrogenous bisphosphonate inhibitors of farnesyl disphosphate synthase have been used clinically for treatment of bone disease. Because many of their effects may be mediated by depletion of geranylgeranyl diphosphate, our group has sought compounds that do this more directly through inhibition of geranylgeranyl diphosphate synthase and we have discovered a number of isoprenoid-containing bisphosphonates that selectively inhibit this enzyme. These compounds have a high negative charge at physiological pH which is necessary for inhibition of the enzyme but may limit their ability to enter cells. Therefore, chemical modifications that mask this charge may enhance their cellular potency. We now have synthesized novel pivaloyloxymethyl-modified isoprenoid bisphosphonates and investigated their ability to inhibit protein geranylgeranylation within cells. We have found that addition of pivaloyloxymethyl moieties to isoprenoid bisphosphonates increases their potency towards cellular geranylgeranylation even though this modification decreases their in vitro inhibition of geranylgeranyl diphosphate synthase. Pivaloyloxymethyl modifications more effectively increase the cellular activity of the more polar isoprenoid bisphosphonates. These results reveal structural relationships between in vitro and cellular activity which may serve as the basis for future development of more potent and/or drug-like inhibitors of geranylgeranyl diphosphate synthase.