Our research interests are in the general area of synthetic medicinal chemistry and bioorganic chemistry. We are interested in the design of anticancer prodrugs for the site-specific activation in tumor tissues, enzyme mechanism and inhibition, design of inhibitors of protein-protein interactions, and the development of organic synthetic methodology. Specifically, efforts are being focused on the design, synthesis and evaluation of anticancer prodrugs for the treatment of advanced prostate cancer, the discovery of small molecule inhibitors of Keap1-Nrf2 interaction and PD-1/PD-L1 interaction, and the development of crystallization inhibitors for kidney stone diseases.
1. Design, Synthesis and Evaluation of Anticancer Prodrugs
Many anticancer agents in current clinical use lack the desired tumor-selectivity and are associated with systemic side effects. Prodrug design is one approach that could potentially improve the target-selectivity of anticancer agents. Efforts in our laboratory have been focused on designing analogs of cyclophosphamide and phosphoramide mustard (PM) to move the site of activation from the liver to tumor tissues through the incorporation of reductive and proteolytic triggers.
A series of nitroaromatic analogs and peptide aminoarylmethyl conjugates has been designed to efficiently release the active phosphoramide mustard in a site-specific manner in tumor tissues, thus increasing the selectivity in killing cancer cells and decreasing systemic toxicity. Traceless linkers have been designed and optimized to efficiently release the active phosphoramide mustard through the incorporation of fluorine substitutions. We also successfully developed a new amidation reaction for the preparation of peptide-aminoarylmethyl PM conjugates using selenocarboxylates and azides, thus avoiding the use of unstable basic nucleophilic amine intermediates. The prodrugs were shown to be stable under physiological conditions including whole blood. The nitroaryl phosphoramidates were shown to be excellent substrates of E. coli nitroreductase and highly cytotoxic towards nitroreductase-expressing V79 and SKOV3 cells. When the peptide used is a substrate of prostate-specific antigen (PSA), the peptide-aminoarylmethyl PM conjugates were activated by PSA and have been shown to be selectively more cytotoxic to PSA-producing LNCaP prostate cancer cells than to DU145 cells that do not express PSA. These prodrugs could potentially be developed into clinically useful chemotherapeutic agents for the targeted treatment of cancer.
2. Discovery of small molecule inhibitors of protein-protein interactions
Protein-protein interactions are involved in a wide variety of physiological as well as pathological processes and inhibition of these interactions might provide new opportunities in controlling various diseases. Keap1-Nrf2-antioxidant response element (ARE) system represents a key signaling pathway in cancer chemoprevention. Many natural products like sulforaphane, curcumin, and epigallocatechol gallate from natural sources such as fruits, vegetables, and tea products work through modification of sensitive cysteine residues found in the redox “sensor” protein Keap1 leading to the dissociation of Keap1-Nrf2 complex, the subsequent translocation of Nrf2 to the nucleus, and the transcriptional activation of ARE genes. The resulting upregulation of oxidative stress response enzymes functions as a cytoprotective shield against carcinogens and reactive oxygen species generated during inflammation. But, there are safety concerns over the general use of these natural thiol-reactive compounds in a purified form and the high doses of administration over extended periods needed for chemoprevention purposes. We are designing ways to discover small molecule compounds specifically for the direct inhibition of the Keap1-Nrf2 interaction. These novel selective Keap1-Nrf2 inhibitors would mimic the actions of reactive oxygen species and electrophiles in the induction of cytoprotective enzymes but without the associated side effects.
The other protein-protein interaction we are working on in our laboratory is the programmed cell death-1/programmed death-ligand 1(PD-1/PD-L1) protein-protein interaction (PPI). The PD-1/PD-L1 immune checkpoint serves in mediating peripheral immune tolerance and protecting against excessive inflammation and autoimmunity. Through their continual evolution, tumor cells have acquired the ability to co-opt the PD-1/PD-L1 axis in order to dampen the antitumor activities of tumor-specific T lymphocytes. Cancer immunotherapies targeting the PD-1/PD-L1 immune checkpoint pathway have reversed this immunosuppression, resulting in remarkable clinical responses—tumor shrinkage, durable responses, and prolonged survival—in patients with advanced solid and hematologic malignancies. Antibodies targeting PD-1/PD-L1 PPI has been very successful recently in treating many cancers. But there are a number of issues known including poor pharmacokinetic profile, poor penetration, immune-related side effects, and high cost of manufacturing. We are working on small molecules as inhibitors of the PD-1/PD-L1 PPI that potentially offer more appropriate pharmacokinetic profiles for oral administration, increased tumor penetration, and shorter half-lives for management of intractable immune-related side effects.
3. Development of Crystallization Inhibitors to Prevent Kidney Stone Formation
Cystinuria is a genetic disorder involving the abnormal transport of L-cystine from the renal proximal tubule and intestines leading to formation of L-cystine kidney stones in affected patients. In a collaborative effort with a geneticist, we are developing L-cystine diamides in a novel approach to prevent stone formation in cystinuria patients through the binding of tailored crystal growth inhibitors to L-cystine crystal surfaces. L-Cystine bismorpholide (LH707) and Lcystine bis(N’-methylpiperazide) (LH708) are two more stable and more effective L-cystine analogs that were discovered at Rutgers to overcome the druggability problems of L-cystine dimethyl esters (CDME), that was first reported to inhibit L-cystine crystal growth. These L-cystine diamides were shown to effectively inhibit L-cystine crystallization using real-time in situ atomic force microscopy and be orally bioavailable and efficacious in a knockout mouse model of cystinuria. The compounds are currently licensed to PharmaKrysto for additional preclinical and future clinical studies as a treatment for patients with cystinuria.
In a similar approach, we are designing crystallization inhibitors to prevent the formation of other types of kidney stones in patients with hyperoxaluria and hyperuricosuria.
4. Development of Synthetic Methodologies
We are also interested in developing synthetic methodologies for the synthesis of biologically active compounds and these include protecting group strategies, functional group transformation, and the synthesis of heterocyclic compounds. We have published on various aspects of protection and deprotection conditions for MOM, silyl ether, DMNA, and imidazolidine protecting groups, the development of reaction conditions for efficient Baylis-Hillman coupling reactions, the development of a new condition for the chemoselective reduction of aromatic nitro groups, and the discovery of a new amidation reaction using selenocarboxylates and azides.
Our research has been funded by grants from the National Institutes of Health, the Department of Defense Prostate Cancer Research Program, American Cancer Society, Pardee Foundation, the State of New Jersey Commission of Cancer Research, the Gallo Prostate Cancer Center of the Cancer Institute of New Jersey, and the Charles and Johanna Busch Memorial Fund at Rutgers University.