Shili Xu

Small Molecule Inhibitors of CXCR4

CXCR4 is a G-protein-coupled receptor involved in a number of physiological processes in the hematopoietic and immune systems. The SDF-1/CXCR4 axis is significantly associated with several diseases, such as HIV, cancer, WHIM syndrome, rheumatoid arthritis, pulmonary fibrosis and lupus. For example, CXCR4 is one of the major co-receptors for HIV entry into target cells, while in cancer it plays an important role in tumor cell metastasis. Several promising CXCR4 antagonists have been developed to block SDF-1/CXCR4 interactions that are currently under different stages of development. The first in class CXCR4 antagonist, plerixafor, was approved by the FDA in 2008 for the mobilization of hematopoietic stem cells and several other drugs are currently in clinical trials for cancer, HIV, and WHIM syndrome. While the long-term safety data for the first generation CXCR4 antagonists are not yet available, several new compounds are under preclinical development in an attempt to provide safer and more efficient treatment options for HIV and cancer patients.

Discovery of an orally active small-molecule irreversible inhibitor of protein disulfide isomerase for ovarian cancer treatment

Protein disulfide isomerase (PDI), an endoplasmic reticulum chaperone protein, catalyzes disulfide bond breakage, formation, and rearrangement. The effect of PDI inhibition on ovarian cancer progression is not yet clear, and there is a need for potent, selective, and safe small-molecule inhibitors of PDI. Here, we report a class of propynoic acid carbamoyl methyl amides (PACMAs) that are active against a panel of human ovarian cancer cell lines. Using fluorescent derivatives, 2D gel electrophoresis, and MS, we established that PACMA 31, one of the most active analogs, acts as an irreversible small-molecule inhibitor of PDI, forming a covalent bond with the active site cysteines of PDI. We also showed that PDI activity is essential for the survival and proliferation of human ovarian cancer cells. In vivo, PACMA 31 showed tumor targeting ability and significantly suppressed ovarian tumor growth without causing toxicity to normal tissues. These irreversible small-molecule PDI inhibitors represent an important approach for the development of targeted anticancer agents for ovarian cancer therapy, and they can also serve as useful probes for investigating the biology of PDI-implicated pathways.

Protein disulfide isomerase: a promising target for cancer therapy.

Protein disulfide isomerase (PDI) has a key role in maintaining cellular homeostasis by mediating oxidative protein folding. It catalyzes disulfide bond formation, breakage and rearrangement in the endoplasmic reticulum and has chaperone protein activity. Increasing evidence suggests that PDI supports the survival and progression of several cancers. During the past decade, robust PDI activity assays have been developed and several PDI inhibitors identified, but none has been approved for clinical use. Herein, we review current knowledge of the role of PDI in cancer and discuss various assays for measuring the activities of PDI, highlighting their sensitivities and usefulness for high-throughput screening. The previously reported PDI inhibitors require further validation to serve as bona fide leads and additional optimization to generate novel drug candidates for clinical studies.

Discovery of a Novel Orally Active Small-Molecule gp130 Inhibitor for the Treatment of Ovarian Cancer

Interleukin (IL)-6 and Stat3 play key roles in ovarian cancer progression. However, the role of glycoprotein 130 (gp130), the signal transducer of this signaling axis, is not well-established. Currently, there are no small-molecule inhibitors of gp130 under clinical development. In this study, we show that gp130 is an attractive drug target in ovarian cancer due to its role in promoting cancer progression via the activation of its downstream Stat3 signaling. We also present preclinical studies of SC144, the first-in-class orally active small-molecule gp130 inhibitor. SC144 shows greater potency in human ovarian cancer cell lines than in normal epithelial cells. SC144 binds gp130, induces gp130 phosphorylation (S782) and deglycosylation, abrogates Stat3 phosphorylation and nuclear translocation, and further inhibits the expression of downstream target genes. In addition, SC144 shows potent inhibition of gp130 ligand–triggered signaling. Oral administration of SC144 delays tumor growth in a mouse xenograft model of human ovarian cancer without significant toxicity to normal tissues. Mol Cancer Ther; 12(6); 937–49. ©2013 AACR.

Small-Molecule Inhibitors of p53-MDM2 Interaction: the 2006-2010 Update

Increasing knowledge of the relationship between p53 and MDM2 has led to development of potential small molecule inhibitors useful for clinical studies. Herein, we discuss the patented (2006-2010) inhibitors of p53-MDM2 interaction. The anticancer agents discussed in this review belong to several different chemical classes including benzodiazepinediones, cis-imidazolines, oxindoles, spiro-oxindoles, and numerous miscellaneous groups. This review also provides comprehensive information on inhibitors of p53-MDM2 interaction that are currently being tested in clinical trials. It is important to note that many of the disclosed inhibitors need further validation to be considered as bona fide inhibitors of p53-MDM2 interaction and some will not be further considered for future studies. On the other hand, JNJ-26854165, a novel tryptamine derivative and RG7112, a cis-imidazoline representative have shown promising results in early phases of trials in cancer patients. AT-219, a spiroindolinone in late stage preclinical studies is a likely candidate to proceed into clinical trials. It remains to be seen how these inhibitors will perform in future clinical studies as single agents and in combination with the currently approved chemotherapeutic agents.

gp130: a promising drug target for cancer therapy

Introduction: Ubiquitously expressed in the human body, glycoprotein 130 (gp130) is a shared subunit of receptor complexes for at least nine cytokines (IL-6, OSM, LIF, IL-11, CNTF, CLC, IL-27, CT-1, and NP) that mediate highly diverse biological processes. Dysregulation of gp130 expression, activation, or associated signaling pathways are implicated in a variety of human diseases, including cancer. Accumulating evidence indicates that the gp130-mediated signaling networks play important roles in the progression of multiple types of cancer. Areas covered: This review discusses the structural basis of gp130 in signal transduction activity and its role in physiological and pathological conditions, particularly cancer. We analyzed the currently available databases to illustrate the expression of gp130, its coexpression with other molecules involved in the gp130 signaling pathways, and the role of gp130 in cancer progression. Finally, we highlight strategies for blocking gp130 signaling and the currently available antagonists. Expert opinion: As gp130 signaling mediates cancer progression, inhibition of gp130 activity offers a potential and promising approach to cancer therapy. Compared to antibodies blocking individual cytokines, gp130-targeted small-molecule inhibitors present multiple advantages. To achieve successful clinical outcomes for gp130-targeted cancer therapy, dosage determination, duration of therapy, and patient selection are some of the critical factors to be considered.

Repositioning HIV-1 Integrase Inhibitors for Cancer Therapeutics: 1,6-Naphthyridine-7-carboxamide as a Promising Scaffold with Drug-like Properties

Among a large number of HIV-1 integrase (IN) inhibitors, the 8-hydroxy-[1,6]naphthyridines (i.e., L-870,810) were one of the promising class of antiretroviral drugs developed by Merck Laboratories. In spite of its remarkable potency and efficacy, unfortunately upon completion of phase I clinical studies, development of L-870,810 was halted. Because of its desirable pharmacological and pharmaceutical properties we were intrigued to design novel analogues of L-870,810 with goals to (1) improve upon limitations of naphthyridine-7-carboxamides as antiviral agents and (2) to reposition their use as innovative cytotoxic agents for cancer therapeutics. Herein, we report on the design and synthesis of a series of 1,6-naphthyridine-7-carboxamides with various substitutions at the 5- and 8-positions. All the new 5-substituted-8-hydroxy-[1,6]naphthyridines were potent IN inhibitors and the 5-substituted-8-amino-[1,6]naphthyridines were significantly cytotoxic. Further optimization of the 5,8-disubstituted-[1,6]naphthyridines with structural variation on 7-carboxamide delivered novel compounds with significant cytotoxicity in a panel of cancer cell lines and effective inhibition against select oncogenic kinases.

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

Paclitaxel (PTX) is a highly effective and cytotoxic agent widely used for the treatment of several solid tumors. However, PTX shows dose-limiting cytotoxicity and in most of the cases induces drug resistance followed by failure in treatments. To enhance the therapeutic index of a given drug, various drug delivery methods are being 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 MMP-2 at tumor sites. As a result, PTX is expected to be released in 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 efficacy in a HT1080 fibrosarcoma mouse xenograft model that highly overexpress MMP2. Our in vitro results showed that the PTX-AcGPLGIAGQ conjugates inhibited cancer cell proliferation with higher activity compared with that observed for free PTX, both of which were mediated by an arrest of G2/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 exploiting the specific recognition of MMP2 to reduce toxicity and selective killing of tumor cells.

Dual inhibition of survivin and MAOA synergistically impairs growth of PTEN-negative prostate cancer

Background:Survivin and monoamine oxidase A (MAOA) levels are elevated in prostate cancer (PCa) compared to normal prostate glands. However, the relationship between survivin and MAOA in PCa is unclear.Methods:We examined MAOA expression in the prostate lobes of a conditional PTEN-deficient mouse model mirroring human PCa, with or without survivin knockout. We also silenced one gene at a time and examined the expression of the other. We further evaluated the combination of MAOA inhibitors and survivin suppressants on the growth, viability, migration and invasion of PCa cells.Results:Survivin and MAOA levels are both increased in clinical PCa tissues and significantly associated with patients’ survival. Survivin depletion delayed MAOA increase during PCa progression, and silencing MAOA decreased survivin expression. The combination of MAOA inhibitors and the survivin suppressants (YM155 and SC144) showed significant synergy on the inhibition of PCa cell growth, migration and invasion with concomitant decrease in survivin and MMP-9 levels.Conclusions:There is a positive feedback loop between survivin and MAOA expression in PCa. Considering that survivin suppressants and MAOA inhibitors are currently available in clinical trials and clinical use, their synergistic effects in PCa support a rapid translation of this combination to clinical practice.

Loss of Survivin in the Prostate Epithelium Impedes Carcinogenesis in a Mouse Model of Prostate Adenocarcinoma

The inhibitor of apoptosis protein survivin is expressed in most cancers. Using the conditional PTEN deletion mouse model, we previously reported that survivin levels increase with prostate tumor growth. Here we evaluated the functional role of survivin in prostate tumor growth. First, we demonstrated that mice lacking the survivin gene in prostate epithelium were fertile and had normal prostate growth and development. We then serially, from about 10–56 weeks of age, evaluated histopathologic changes in the prostate of mice with PTEN deletion combined with survivin mono- or bi-allelic gene deletion. While within this time period most of the animals with wild-type or monoallelic survivin deletion developed adenocarcinomas, the most severe lesions in the biallelic survivin deleted mice were high-grade prostatic intra-epithelial neoplasia with distinct histopathology. Many atypical cells contained large hypertrophic cytoplasm and desmoplastic reaction in the prostatic intra-epithelial neoplasia lesions of this group was minimal until the late ages. A reduced proliferation index as well as apoptotic and senescent cells were detected in the lesions of mice with compound PTEN/survivin deficiency throughout the time points examined. Survivin deletion was also associated with reduced tumor expression of another inhibitor of apoptosis member, the X-linked inhibitor of apoptosis. Our findings suggest that survivin participates in the progression of prostatic intraepithelial neoplasia to adenocarcinoma, and that survivin interference at the prostatic intraepithelial neoplasia stages may be a potential therapeutic strategy to halt or delay further progression.