Development and anticancer properties of Up284, a spirocyclic candidate ADRM1/RPN13 inhibitor.

Bortezomib has been successful for treatment of multiple myeloma, but not against solid tumors, and toxicities of neuropathy, thrombocytopenia and the emergence of resistance have triggered efforts to find alternative proteasome inhibitors. Bis-benzylidine piperidones such as RA190 covalently bind ADRM1/RPN13, a ubiquitin receptor that supports recognition of polyubiquitinated substrates of the proteasome and their subsequent deububiqutination and degradation. While these candidate RPN13 inhibitors (iRPN13) show promising anticancer activity in mouse models of cancer, they have suboptimal drug-like properties. Here we describe Up284, a novel candidate iRPN13 possessing a central spiro-carbon ring in place of RA190's problematic piperidone core. Cell lines derived from diverse cancer types (ovarian, triple negative breast, colon, cervical and prostate cancers, multiple myeloma and glioblastoma) were sensitive to Up284, including several lines resistant to bortezomib or cisplatin. Up284 and cisplatin showed synergistic cytotoxicity in vitro. Up284-induced cytotoxicity was associated with mitochondrial dysfunction, elevated levels of reactive oxygen species, accumulation of very high molecular weight polyubiquitinated protein aggregates, an unfolded protein response and the early onset of apoptosis. Up284 and RA190, but not bortezomib, enhanced antigen presentation in vitro. Up284 cleared from plasma in a few hours and accumulated in major organs by 24 h. A single dose of Up284, when administered to mice intra peritoneally or orally, inhibited proteasome function in both muscle and tumor for >48 h. Up284 was well tolerated by mice in repeat dose studies. Up284 demonstrated therapeutic activity in xenograft, syngeneic and genetically-engineered murine models of ovarian cancer.

Chirality and asymmetry increase the potency of candidate ADRM1/RPN13 inhibitors.

Bortezomib and the other licensed 20S proteasome inhibitors show robust activity against liquid tumors like multiple myeloma, but have disappointed against solid tumors including ovarian cancer. Consequently, interest is mounting in alternative non-peptide based drugs targeting the proteasome's 19S regulatory particle subunit, including its ubiquitin receptor RPN13. RA183 and RA375 are more potent analogs of the prototypic inhibitor of RPN13 (iRPN13) called RA190, and they show promise for the treatment of ovarian cancer. Here we demonstrate that rendering these candidate RPN13 inhibitors chiral and asymmetric through the addition of a single methyl to the core piperidone moiety increases their potency against cancer cell lines, with the S-isomer being more active than the R-isomer. The enhanced cancer cell cytotoxicities of these compounds are associated with improved binding to RPN13 in cell lysates, ATP depletion by inhibition of glycolysis and mitochondrial electron chain transport, mitochondrial depolarization and perinuclear clustering, oxidative stress and glutathione depletion, and rapid accumulation of high molecular weight polyubiquitinated proteins with a consequent unresolved ubiquitin proteasome system (UPS) stress response. Cytotoxicity was associated with an early biomarker of apoptosis, increased surface annexin V binding. As for cisplatin, BRCA2 and ATM deficiency conferred increased sensitivity to these iRPN13s. Ubiquitination plays an important role in coordinating DNA damage repair and the iRPN13s may compromise this process by depletion of monomeric ubiquitin following its sequestration in high molecular weight polyubiquitinated protein aggregates. Indeed, a synergistic cytotoxic response was evident upon treatment of several ovarian cancer cell lines with either cisplatin or doxorubicin and our new candidate iRPN13s, suggesting that such a combination approach warrants further exploration for the treatment of ovarian cancer.

Bis-benzylidine Piperidone RA190 treatment of hepatocellular carcinoma via binding RPN13 and inhibiting NF-κB signaling.

BACKGROUND: According to GLOBOSCAN, hepatocellular carcinoma (HCC) claimed 782,000 lives in 2018. The tyrosine kinase inhibitor sofafenib is used to treat HCC, but new anticancer agents targeting different pathways are urgently needed to improve outcomes for patients with advanced disease. The aberrant metabolism and aggressive growth of cancer cells can render them particularly susceptible to proteasome inhibition, as demonstrated by bortezomib treatment of multiple myeloma. However, resistance does emerge, and this 20S proteasome inhibitor has not proven active against HCC. The bis-benzylidine piperidone RA190 represents a novel class of proteasome inhibitor that covalently binds to cysteine 88 of RPN13, an ubiquitin receptor subunit of the proteasome's 19S regulatory particle. RA190 treatment inhibits proteasome function, causing rapid accumulation of polyubiquitinated proteins. Considerable evidence suggests that nuclear factor κB (NF-κB) signaling, which is dependent upon the proteasome, is a major driver of inflammation-associated cancers, including HCC. METHODS: Human HCC cell lines were treated with titrations of RA190. The time course of endoplasmic reticulum stress and NF-κB-related mechanisms by which RA190 may trigger apoptosis were assessed. The therapeutic activity of RA190 was also determined in an orthotopic HCC xenograft mouse model. RESULTS: RA190 is toxic to HCC cells and synergizes with sofafenib. RA190 triggers rapid accumulation of polyubiquitinated proteins, unresolved endoplasmic reticulum stress, and cell death via apoptosis. RA190 blocks proteasomal degradation of IκBα and consequent release of NF-κB into the nuclei of HCC cells. Treatment of mice bearing an orthotopic HCC model with RA190 significantly reduced tumor growth. CONCLUSIONS: RA190 has therapeutic activity in a xenograft model, and with sorafenib exhibited synergetic killing of HCC cells in vitro, suggesting further exploration of such a combination treatment of HCC is warranted.

Structure-function analyses of candidate small molecule RPN13 inhibitors with antitumor properties.

We sought to design ubiquitin-proteasome system inhibitors active against solid cancers by targeting ubiquitin receptor RPN13 within the proteasome's 19S regulatory particle. The prototypic bis-benzylidine piperidone-based inhibitor RA190 is a michael acceptor that adducts Cysteine 88 of RPN13. In probing the pharmacophore, we showed the benefit of the central nitrogen-bearing piperidone ring moiety compared to a cyclohexanone, the importance of the span of the aromatic wings from the central enone-piperidone ring, the contribution of both wings, and that substituents with stronger electron withdrawing groups were more cytotoxic. Potency was further enhanced by coupling of a second warhead to the central nitrogen-bearing piperidone as RA375 exhibited ten-fold greater activity against cancer lines than RA190, reflecting its nitro ring substituents and the addition of a chloroacetamide warhead. Treatment with RA375 caused a rapid and profound accumulation of high molecular weight polyubiquitinated proteins and reduced intracellular glutathione levels, which produce endoplasmic reticulum and oxidative stress, and trigger apoptosis. RA375 was highly active against cell lines of multiple myeloma and diverse solid cancers, and demonstrated a wide therapeutic window against normal cells. For cervical and head and neck cancer cell lines, those associated with human papillomavirus were significantly more sensitive to RA375. While ARID1A-deficiency also enhanced sensitivity 4-fold, RA375 was active against all ovarian cancer cell lines tested. RA375 inhibited proteasome function in muscle for >72h after single i.p. administration to mice, and treatment reduced tumor burden and extended survival in mice carrying an orthotopic human xenograft derived from a clear cell ovarian carcinoma.

mTORC1 feedback to AKT modulates lysosomal biogenesis through MiT/TFE regulation.

The microphthalmia family of transcription factors (MiT/TFEs) controls lysosomal biogenesis and is negatively regulated by the nutrient sensor mTORC1. However, the mechanisms by which cells with constitutive mTORC1 signaling maintain lysosomal catabolism remain to be elucidated. Using the murine epidermis as a model system, we found that epidermal Tsc1 deletion resulted in a phenotype characterized by wavy hair and curly whiskers, and was associated with increased EGFR and HER2 degradation. Unexpectedly, constitutive mTORC1 activation with Tsc1 loss increased lysosomal content via upregulated expression and activity of MiT/TFEs, whereas genetic deletion of Rheb or Rptor or prolonged pharmacologic mTORC1 inactivation had the reverse effect. This paradoxical increase in lysosomal biogenesis by mTORC1 was mediated by feedback inhibition of AKT, and a resulting suppression of AKT-induced MiT/TFE downregulation. Thus, inhibiting hyperactive AKT signaling in the context of mTORC1 loss-of-function fully restored MiT/TFE expression and activity. These data suggest that signaling feedback loops work to restrain or maintain cellular lysosomal content during chronically inhibited or constitutively active mTORC1 signaling, respectively, and reveal a mechanism by which mTORC1 regulates upstream receptor tyrosine kinase signaling.

Covalent Rpn13-Binding Inhibitors for the Treatment of Ovarian Cancer.

Substitution of the m,p-chloro groups of bis-benzylidinepiperidone RA190 for p-nitro, generating RA183, enhanced covalent drug binding to Cys88 of RPN13. Treatment of cancer cell lines with RA183 inhibited ubiquitin-mediated protein degradation, resulting in rapid accumulation of high-molecular-weight polyubiquitinated proteins, blockade of NFκB signaling, endoplasmic reticulum stress, an unfolded protein response, production of reactive oxygen species, and apoptotic cell death. High-grade ovarian cancer, triple-negative breast cancer, and multiple myeloma cell lines were particularly vulnerable to RA183. RA183 stabilized a tetraubiquitin-linked firefly luciferase reporter protein in cancer cell lines and mice, demonstrating in vitro and in vivo proteasomal inhibition, respectively. However, RA183 was rapidly cleared from plasma, likely reflecting its rapid degradation to the active compound RA9, as seen in human liver microsomes. Intraperitoneal administration of RA183 inhibited proteasome function and orthotopic tumor growth in mice bearing human ovarian cancer model ES2-luc ascites or syngeneic ID8-luc tumor.

Early and consistent overexpression of ADRM1 in ovarian high-grade serous carcinoma.

BACKGROUND: Ovarian carcinoma is highly dependent on the ubiquitin proteasome system (UPS), but its clinical response to treatment with the proteasome inhibitor bortezomib has been disappointing. This has driven exploration of alternate approaches to target the UPS in ovarian cancer. Recently, proteasome inhibitors targeting the 19S regulatory particle-associated RPN13 protein have been described, such as RA190. RPN13, which is encoded by ADRM1, facilitates the recognition by the proteasome of its polyubiquinated substrates. Inhibition of RPN13 produces a rapid, toxic accumulation of polyubiquitinated proteins in ovarian and other cancer cells, triggering apoptosis. Here, we sought to determine if RPN13 is available as a target in precursors of ovarian/fallopian tube cancer as well as all advanced cases, and the impact of increased ADRM1 gene copy number on sensitivity of ovarian cancer to RA190. METHODS: ADRM1 mRNA was quantified by RNAscope in situ hybridization and RPN13 protein detected by immunohistochemistry in high grade serous carcinoma (HGSC) of the ovary and serous tubal intraepithelial carcinoma (STIC). Amplification of ADRM1 and sensitivity to RA190 were determined in ovarian cancer cell lines. RESULTS: Here, we demonstrate that expression of ADRM1mRNA is significantly elevated in STIC and HGSC as compared to normal fallopian tube epithelium. ADRM1 mRNA and RPN13 were ubiquitously and robustly expressed in ovarian carcinoma tissue and cell lines. No correlation was found between ADRM1 amplification and sensitivity of ovarian cancer cell lines to RA190, but all were susceptible. CONCLUSIONS: RPN13 can potentially be targeted by RA190 in both in situ and metastatic ovarian carcinoma. Ovarian cancer cell lines are sensitive to RA190 regardless of whether the ADRM1 gene is amplified.

RPN13/ADRM1 inhibitor reverses immunosuppression by myeloid-derived suppressor cells.

Myeloid-derived-suppressor cells (MDSCs) are key mediators of immune suppression in the ovarian tumor microenvironment. Modulation of MDSC function to relieve immunosuppression may enhance the immunologic clearance of tumors. The bis-benzylidine piperidone RA190 binds to the ubiquitin receptor RPN13/ADRM1 on the 19S regulatory particle of the proteasome and directly kills ovarian cancer cells by triggering proteotoxic stress. Here we examine the effect of RA190 treatment on the immunosuppression induced by MDSCs in the tumor microenvironment, specifically on the immunosuppression induced by MDSCs. We show that RA190 reduces the expression of Stat3 and the levels of key immunosuppressive enzymes and cytokines arginase, iNOS, and IL-10 in MDSCs, while boosting expression of the immunostimulatory cytokine IL-12. Furthermore, we show that the RA190-treated MDSCs lost their capacity to suppress CD8+ T cell function. Finally, we show that RA190 treatment of mice bearing syngeneic ovarian tumor elicits potent CD8+ T cell antitumor immune responses and improves tumor control and survival. These data suggest the potential of RA190 for ovarian cancer treatment by both direct killing of tumor cells via proteasome inhibition and relief of MDSC-mediated suppression of CD8 T cell-dependent antitumor immunity elicited by the apoptotic tumor cells.

The Proteasome Ubiquitin Receptor hRpn13 and Its Interacting Deubiquitinating Enzyme Uch37 Are Required for Proper Cell Cycle Progression.

Recently, we reported that bisbenzylidine piperidone RA190 adducts to Cys-88 of the proteasome ubiquitin receptor hRpn13, triggering accumulation of ubiquitinated proteins and endoplasmic reticulum stress-related apoptosis in various cancer cell lines. hRpn13 contains an N-terminal pleckstrin-like receptor for ubiquitin domain that binds ubiquitin and docks it into the proteasome as well as a C-terminal deubiquitinase adaptor (DEUBAD) domain that binds the deubiquitinating enzyme Uch37. Here we report that hRpn13 and Uch37 are required for proper cell cycle progression and that their protein knockdown leads to stalling at G0/G1 Moreover, serum-starved cells display reduced hRpn13 and Uch37 protein levels with hallmarks of G0/G1 stalling and recovery to their steady-state protein levels following release from nutrient deprivation. Interestingly, loss of hRpn13 correlates with a small but statistically significant reduction in Uch37 protein levels, suggesting that hRpn13 interaction may stabilize this deubiquitinating enzyme in human cells. We also find that RA190 treatment leads to a loss of S phase, suggesting a block of DNA replication, and G2 arrest by using fluorescence-activated cell sorting. Uch37 deprivation further indicated a reduction of DNA replication and G0/G1 stalling. Overall, this work implicates hRpn13 and Uch37 in cell cycle progression, providing a rationale for their function in cellular proliferation and for the apoptotic effect of the hRpn13-targeting molecule RA190.

ADRM1-amplified metastasis gene in gastric cancer.

The proteasome ubiquitin receptor ADRM1 has been shown to be a driver for 20q13.3 amplification in epithelial cancers including ovarian and colon cancer. We performed array-CGH on 16 gastric cancer cell lines and found 20q13.3 to be amplified in 19% with the minimal amplified region in gastric cancer cell line AGS spanning a 1 Mb region including ADRM1. Expression microarray analysis shows overexpression of only two genes in the minimal region, ADRM1 and OSBPL2. While RNAi knockdown of both ADRM1 and OSBPL2 led to a slight reduction in growth, only ADRM1 RNAi knockdown led to a significant reduction in migration and growth in soft-agar. Treatment of AGS cells with the ADRM1 inhibitor RA190 resulted in proteasome inhibition, but RNAi knockdown of ADRM1 did not. However, RNAi knockdown of ADRM1 led to a significant reduction in specific proteins including MNAT1, HRS, and EGFR. We hypothesize that ADRM1 may act in ADRM1-amplified gastric cancer to alter protein levels of specific oncogenes resulting in an increase in metastatic potential. Selective inhibition of ADRM1 independent of proteasome inhibition may result in a targeted therapy for ADRM1-amplified gastric cancer. In vivo models are now warranted to validate these findings. © 2015 Wiley Periodicals, Inc.

Simultaneous inhibition of deubiquitinating enzymes (DUBs) and autophagy synergistically kills breast cancer cells.

Breast cancer is one of the leading causes of cancer death among women in the United States. Patients expressing the estrogen and progesterone receptor (ER and PR) and human epidermal growth factor 2 (HER-2) tumor markers have favorable prognosis and efficacious therapeutic options. In contrast, tumors that are negative for these markers (triple-negative) have a disproportionate share of morbidity and mortality due to lack of a validated molecular target. Deubiquitinating enzymes (DUBs) are a critical component of ubiquitin-proteasome-system degradation and have been shown to be differentially expressed and activated in a number of cancers, including breast, with their aberrant activity linked to cancer prognosis and clinical outcome. We evaluated the effect of the DUB inhibitors b-AP15 and RA-9 alone and in combination with early- and late-stage lysosomal inhibitors on cell viability in a panel of triple negative breast cancer (TNBC) cell lines. Our results indicate small-molecule DUB inhibitors have a profound effect on TNBC viability and lead to activation of autophagy as a cellular mechanism to compensate for ubiquitin-proteasome-system stress. Treatment with sub-optimal doses of DUB and lysosome inhibitors synergistically kills TNBC cells. This supports the evaluation of DUB inhibition, in combination with lysosomal inhibition, as a therapeutic approach for the treatment of TNBC.

Small-molecule RA-9 inhibits proteasome-associated DUBs and ovarian cancer in vitro and in vivo via exacerbating unfolded protein responses.

PURPOSE: Ovarian cancer is the deadliest of the gynecologic malignancies. Carcinogenic progression is accompanied by upregulation of ubiquitin-dependent protein degradation machinery as a mechanism to compensate with elevated endogenous proteotoxic stress. Recent studies support the notion that deubiquitinating enzymes (DUB) are essential factors in proteolytic degradation and that their aberrant activity is linked to cancer progression and chemoresistance. Thus, DUBs are an attractive therapeutic target for ovarian cancer. EXPERIMENTAL DESIGN: The potency and selectivity of RA-9 inhibitor for proteasome-associated DUBs was determined in ovarian cancer cell lines and primary cells. The anticancer activity of RA-9 and its mechanism of action were evaluated in multiple cancer cell lines in vitro and in vivo in immunodeficient mice bearing an intraperitoneal ES-2 xenograft model of human ovarian cancer. RESULTS: Here, we report the characterization of RA-9 as a small-molecule inhibitor of proteasome-associated DUBs. Treatment with RA-9 selectively induces onset of apoptosis in ovarian cancer cell lines and primary cultures derived from donors. Loss of cell viability following RA-9 exposure is associated with an unfolded protein response as mechanism to compensate for unsustainable levels of proteotoxic stress. In vivo treatment with RA-9 retards tumor growth, increases overall survival, and was well tolerated by the host. CONCLUSIONS: Our preclinical studies support further evaluation of RA-9 as an ovarian cancer therapeutic.

A bis-benzylidine piperidone targeting proteasome ubiquitin receptor RPN13/ADRM1 as a therapy for cancer.

The bis-benzylidine piperidone RA190 covalently binds to cysteine 88 of ubiquitin receptor RPN13 in the 19S regulatory particle and inhibits proteasome function, triggering rapid accumulation of polyubiquitinated proteins. Multiple myeloma (MM) lines, even those resistant to bortezomib, were sensitive to RA190 via endoplasmic reticulum stress-related apoptosis. RA190 stabilized targets of human papillomavirus (HPV) E6 oncoprotein, and preferentially killed HPV-transformed cells. After oral or intraperitoneal dosing of mice, RA190 distributed to plasma and major organs except the brain and inhibited proteasome function in skin and muscle. RA190 administration profoundly reduced growth of MM and ovarian cancer xenografts, and oral RA190 treatment retarded HPV16(+) syngeneic mouse tumor growth, without affecting spontaneous HPV-specific CD8(+) T cell responses, suggesting its therapeutic potential.

Stressing the ubiquitin-proteasome system without 20S proteolytic inhibition selectively kills cervical cancer cells.

Cervical cancer cells exhibit an increased requirement for ubiquitin-dependent protein degradation associated with an elevated metabolic turnover rate, and for specific signaling pathways, notably HPV E6-targeted degradation of p53 and PDZ proteins. Natural compounds with antioxidant properties including flavonoids and triterpenoids hold promise as anticancer agents by interfering with ubiquitin-dependent protein degradation. An increasing body of evidence indicates that their α-ß unsaturated carbonyl system is the molecular determinant for inhibition of ubiquitin-mediated protein degradation up-stream of the catalytic sites of the 20S proteasome. Herein we report the identification and characterization of a new class of chalcone-based, potent and cell permeable chemical inhibitors of ubiquitin-dependent protein degradation, and a lead compound RAMB1. RAMB1 inhibits ubiquitin-dependent protein degradation without compromising the catalytic activities of the 20S proteasome, a mechanism distinct from that of Bortezomib. Treatment of cervical cancer cells with RAMB1 triggers unfolded protein responses, including aggresome formation and Hsp90 stabilization, and increases p53 steady state levels. RAMB1 treatment results in activation of lysosomal-dependent degradation pathways as a mechanism to compensate for increasing levels of poly-ubiquitin enriched toxic aggregates. Importantly, RAMB1 synergistically triggers cell death of cervical cancer cells when combined with the lysosome inhibitor Chloroquine.

Potent genistein derivatives as inhibitors of estrogen receptor alpha-positive breast cancer.

The estrogen receptor (ER) is a major target for the treatment of breast cancer cells. Genistein, a soy isoflavone, possesses a structure similar to estrogen and can both mimic and antagonize estrogen effects although at high concentrations it inhibits breast cancer cell proliferation. Hence, to enhance the anti-cancer activity of Genistein at lower concentrations, we have synthesized seven structurally modified derivatives of Genistein (MA-6, MA-8, MA-11, MA-19, MA-20, MA-21 and MA-22) based on the structural requirements for an optimal anti-cancer effect. Among those seven, three derivatives (MA-6, MA-8 and MA-19) showed high antiproliferative activity with IC(50) levels in the range of 1-2.5 µM, i.e., at much lower concentrations range than Genistein itself, in three ER-positive breast cancer cell lines (MCF-7, 21PT and T47D) studied. In our analysis, we noticed that at IC(50) concentrations, the MA-6, MA-8 and MA-19 Genistein derivatives induced apoptosis, inhibited ER-α messenger RNA expression and increased the ratio of ER-ß to ER-α levels in a manner comparable to the parent compound Genistein. Of note, these three modified Genistein derivatives exerted their effects at concentrations 10-15 times lower than the parent compound, decreasing the likelihood of significant ER- α pathway activation, which has been a concern for Genistein. Hence these compounds might play a useful role in breast cancer chemoprevention.

α,ß-Unsaturated carbonyl system of chalcone-based derivatives is responsible for broad inhibition of proteasomal activity and preferential killing of human papilloma virus (HPV) positive cervical cancer cells.

Proteasome inhibitors have potential for the treatment of cervical cancer. We describe the synthesis and biological characterization of a new series of 1,3-diphenylpropen-1-one (chalcone) based derivatives lacking the boronic acid moieties of the previously reported chalcone-based proteasome inhibitor 3,5-bis(4-boronic acid benzylidene)-1-methylpiperidin-4-one and bearing a variety of amino acid substitutions on the amino group of the 4-piperidone. Our lead compound 2 (RA-1) inhibits proteasomal activity and has improved dose-dependent antiproliferative and proapoptotic properties in cervical cancer cells containing human papillomavirus. Further, it induces synergistic killing of cervical cancer cell lines when tested in combination with an FDA approved proteasome inhibitor. Exploration of the potential mechanism of proteasomal inhibition by our lead compound using in silico docking studies suggests that the carbonyl group of its oxopiperidine moiety is susceptible to nucleophilic attack by the γ-hydroxythreonine side chain within the catalytic sites of the proteasome.

Inhibition of IkB kinase and NF-kappaB by a novel synthetic compound SK 2009.

The NF-kappaB family of transcription factors plays an important role in determining cell survival during immune, inflammatory, and stress responses. NF-kappaB activity is frequently deregulated in human cancers and is implicated in the resistance of tumor cells to diverse anticancer agents. We studied the effects of novel analogs of precursors of the natural product simplactone (A) on the activity of IkB kinase and NF-kappaB. Screening of six compounds for the ability to inhibit TNF-induced NF-kappaB activity revealed that compound SK2009 was the most potent of these compounds in suppressing NF-kappaB activation in KBM-5 leukemic cells. Further characterization of SK2009 indicates that this newly synthesized molecule can suppress TNF-induced IkappaBalpha kinase activation and inhibit the expression of three NF-kappaB-dependent gene products, cyclin D1, Bcl-2, and VEGF, in these cells.

Biological evaluation of paclitaxel-peptide conjugates as a model for MMP2-targeted drug delivery.

Paclitaxel (PTX) is a highly effective cytotoxic agent widely used for the treatment of several solid tumors. However, PTX shows dose-limiting cytotoxicity and in most cases induces drug resistance followed by failure in treatment. To enhance the therapeutic index of a given drug, various drug delivery methods have been explored to systemically deliver sufficient amount of the drug to the desired site. In the present study, we designed and synthesized two PTX prodrugs by conjugating PTX at different sites with an octapeptide (AcGPLGIAGQ) that can be cleaved by MMP2 at tumor sites. As a result, PTX is expected to be released at the tumor sites, absorbed by the tumor cells, and thereby inhibit the tumor growth. We evaluated the in vitro activities of the two drugs in a panel of drug-sensitive and -resistant cancer cell lines and their in vivo efficacies in a HT1080 fibrosarcoma mouse xenograft model that overexpresses MMP2. Our in vitro results showed that the PTX-AcGPLGIAGQ conjugates inhibited cancer cell proliferation with higher activity compared to that observed for free PTX, both of which were mediated by an arrest of G(2)/M-phase of the cell cycle. Consistent with the in vitro results, treatment with PTX-octapeptide conjugate resulted in extensive areas of necrosis and a lower percentage of proliferating cells in xenograft tumor sections. Together, our results indicate the potential of the tumor-targeted delivery of PTX to exploit the specific recognition of MMP2, reduce toxicity, and selectively kill tumor cells.

Fenugreek: a naturally occurring edible spice as an anticancer agent.

In recent years, various dietary components that can potentially be used for the prevention and treatment of cancer have been identified. In this study, we demonstrate that extract (FE) from the seeds of the plant Trigonella foenum graecum, commonly called fenugreek, are cytotoxic in vitro to a panel of cancer but not normal cells. Treatment with 10-15 ug/mL of FE for 72 h was growth inhibitory to breast, pancreatic and prostate cancer cell lines (PCa). When tested at higher doses (15-20 ug/mL), FE continued to be growth inhibitory to PCa cell lines but not to either primary prostate or hTert-immortalized prostate cells. At least part of the growth inhibition is due to induction of cell death, as seen by incorporation of Ethidium Bromide III into cancer cells exposed to FE. Molecular changes induced in PCa cells are: in DU-145 cells: downregulation of mutant p53, and in PC-3 cells upregulation of p21 and inhibition of TGFbeta induced phosphorylation of Akt. The surprising finding of our studies is that death of cancer cells occurs despite growth stimulatory pathways being simultaneously upregulated (phosphorylated) by FE. Thus, these studies add another biologically active agent to our armamentarium of naturally occurring agents with therapeutic potential.

Novel microtubule-interacting phenoxy pyridine and phenyl sulfanyl pyridine analogues for cancer therapy.

Current microtubule inhibitory agents used in the clinic to treat cancer have severe side effects, and development of resistance is frequent. We have evaluated the antitumor effect of a novel 30-compound library of phenoxy pyridine and phenyl sulfanyl pyridine derivatives. MTT assays revealed that, of all 30 compounds tested, compounds 2 and 3 showed the largest decrease in proliferation (low muM range) against Panc1 and HS766T human pancreatic cancer cells. Flow cytometry experiments with MCF7 breast cancer cells showed a G2/M arrest comparable to that of colcemid. Immunofluorescence staining demonstrated complete disappearance of intracellular microtubules. Tubulin assembly assays, however, showed a dose-dependent decrease in tubulin assembly with compound 3 that seemed limited to about 50% of the control reaction. With compound 2 treatment, there was only a delay in the onset of assembly, with no effect on the extent of the reaction. Taken together, our results show that these novel microtubule inhibitors have promising anticancer activity and can be potentially used to overcome paclitaxel resistance in the clinical setting.