Keren Miller

Targeting Bone Metastases with a Bispecific Anticancer and Antiangiogenic Polymer–Alendronate–Taxane Conjugate†

A polymer therapeutic designed for combination anticancer and antiangiogenic therapy inhibited the proliferation of prostate carcinoma cells and the proliferation, migration, and tube-formation of endothelial cells. The nanoconjugate was formed from an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer, the bisphosphonate alendronate (for bone targeting), and the chemotherapy agent paclitaxel (PTX), which is cleaved by cathepsin B (see scheme).

Integrin-assisted drug delivery of nano-scaled polymer therapeutics bearing paclitaxel

Angiogenesis plays a prominent role in cancer progression. Anti-angiogenic therapy therefore, either alone or in combination with conventional cytotoxic therapy, offers a promising therapeutic approach. Paclitaxel (PTX) is a widely-used potent cytotoxic drug that also exhibits anti-angiogenic effects at low doses. However, its use, at its full potential, is limited by severe side effects. Here we designed and synthesized a targeted conjugate of PTX, a polymer and an integrin-targeted moiety resulting in a polyglutamic acid (PGA)-PTX-E-[c(RGDfK)(2)] nano-scaled conjugate. Polymer conjugation converted PTX to a macromolecule, which passively targets the tumor tissue exploiting the enhanced permeability and retention effect, while extravasating via the leaky tumor neovasculature. The cyclic RGD peptidomimetic enhanced the effects previously seen for PGA-PTX alone, utilizing the additional active targeting to the α(v)β(3) integrin overexpressed on tumor endothelial and epithelial cells. This strategy is particularly valuable when tumors are well-vascularized, but they present poor vascular permeability. We show that PGA is enzymatically-degradable leading to PTX release under lysosomal acidic pH. PGA-PTX-E-[c(RGDfK)(2)] inhibited the growth of proliferating α(v)β(3)-expressing endothelial cells and several cancer cells. We also showed that PGA-PTX-E-[c(RGDfK)(2)] blocked endothelial cells migration towards vascular endothelial growth factor; blocked capillary-like tube formation; and inhibited endothelial cells attachment to fibrinogen. Orthotopic studies in mice demonstrated preferential tumor accumulation of the RGD-bearing conjugate, leading to enhanced anti-tumor efficacy and a marked decrease in toxicity as compared with free PTX-treated mice.

Dendritic poly(ethylene glycol) bearing paclitaxel and alendronate for targeting bone neoplasms.

Poly(ethylene glycol) (PEG) is the most popular polymer for protein conjugation, but its potential as carrier of low molecular weight drugs has been limited by the intrinsic low loading, owing to its chemical structure. In fact, only the two end chain groups of PEG can be modified and exploited for drug coupling. We have demonstrated that by synthesizing a dendrimer structure at the polymer end chains, it is possible to increase the drug payload and overcome this limitation. Furthermore, this approach can be improved by using heterobifunctional PEG. These polymers allow the precise linking of two different drugs, or a drug and a targeting agent, on the same polymeric chain. Heterobifunctional PEG-dendrimers have been obtained with defined chemical structures leading to their attractive use as drug delivery systems. In fact, they offer a double benefit; first, the possibility to choose the best drug/targeting agent ratio, and second, the separation of the two functions, activity and targeting, which are coupled at the opposite polymer end chains. In this study, we investigated the role of a PEG-dendrimer, H(2)N-PEG-dendrimer-(COOH)(4), as carrier for a combination of paclitaxel (PTX) and alendronate (ALN). PTX is a potent anticancer drug that is affected by severe side effects originating from both the drug itself and its solubilizing formulation, Cremophor EL. ALN is an aminobiphosphonate used for the treatment of osteoporosis and bone metastases as well as a bone-targeting moiety. The PTX-PEG-ALN conjugate was designed to exploit active targeting by the ALN molecule and passive targeting through the enhanced permeability and retention (EPR) effect. Our conjugate demonstrated a great binding affinity to the bone mineral hydroxyapatite in vitro and an IC(50) comparable to that of the free drugs combination in human adenocarcinoma of the prostate (PC3) cells. The PTX-PEG-ALN conjugate exhibited an improved pharmacokinetic profile compared with the free drugs owed to the marked increase in their half-life. In addition, PTX-PEG-ALN could be solubilized directly in physiological solutions without the need for Cremophor EL. The data presented in this manuscript encourage further investigations on the potential of PTX-PEG-ALN as treatment for cancer bone metastases.

Antiangiogenic Antitumor Activity of HPMA Copolymer–Paclitaxel–Alendronate Conjugate on Breast Cancer Bone Metastasis Mouse Model

Polymer therapeutics have shown promise as tumor-targeted drug delivery systems in mice. The multivalency of polymers allows the attachment of different functional agents to a polymeric backbone, including chemotherapeutic and antiangiogenic drugs, as well as targeting moieties, such as the bone-targeting agent alendronate (ALN). We previously reported the conjugation of ALN and the chemotherapeutic drug paclitaxel (PTX) with N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer. The in vitro physicochemical properties, cancer cytotoxicity and antiangiogenic activity of HPMA copolymer-PTX-ALN conjugate were extensively characterized. The reported results warranted in vivo evaluations of the conjugate. In this manuscript, we evaluated the in vivo anticancer and antiangiogenic activity of HPMA copolymer-PTX-ALN conjugate. The conjugate exhibited an antiangiogenic effect by decreasing microvessel density (MVD), and inducing apoptotic circulating endothelial cells (CEC) following treatment of the mice. Using intravital imaging system and mCherry-labeled breast cancer cell lines, we were able to monitor noninvasively the progression of orthotopic metastatic tumors injected into the tibia of the mice. HPMA copolymer-PTX-ALN conjugate showed the greatest antitumor efficacy on mCherry-labeled 4T1 mammary adenocarcinoma inoculated into the tibia, as compared with PTX alone or in combination with ALN. Treatment with the bone-targeted polymeric conjugate demonstrated improved efficacy, was better tolerated, and was more easily administered intravenously than the clinically used PTX formulated in Cremophor/ethanol.

Enhanced cytotoxicity of a polymer–drug conjugate with triple payload of paclitaxel

The development of targeting approaches to selectively release chemotherapeutic drugs into malignant tissue is a major challenge in anticancer therapy. We have synthesized an N-(2-hydroxypropyl)-methacrylamide (HPMA) copolymer-drug conjugate with an AB(3) self-immolative dendritic linker. HPMA copolymers are known to accumulate selectively in tumors. The water-soluble polymer-drug conjugate was designed to release a triple payload of the hydrophobic drug paclitaxel as a result of cleavage by the endogenous enzyme cathepsin B. The polymer-drug conjugate exhibited enhanced cytotoxicity on murine prostate adenocarcinoma (TRAMP C2) cells in comparison to a classic monomeric drug-polymer conjugate.

E-selectin regulates gene expression in metastatic colorectal carcinoma cells and enhances HMGB1 release

Extravasation of cancer cells is a pivotal step in the formation of hematogenous metastasis. Extravasation is initiated by the loose adhesion of cancer cells to endothelial cells via an interaction between endothelial selectins and selectin ligands expressed by the tumor cells. The present study shows that the interaction between recombinant E‐selectin (rE‐selectin) and colorectal cancer (CRC) cells alters the gene expression profile of the cancer cells. A DNA microarry analysis indicated that E‐selectin‐mediated alterations were significantly more pronounced in the metastatic CRC variants SW620 and KM12SM than in the corresponding non‐metastatic local SW480 and KM12C variants. The number of genes altered by E‐selectin in the metastatic variants was about 10‐fold higher than the number of genes altered in the corresponding local variants. Aiming to identify genes involved in CRC metastasis, we focused, by using a DNA microarry analysis, on genes that were altered by E‐selectin in a similar fashion exclusively in both metastatic variants. This analysis indicated that E‐selectin down regulated (at least by 1.6‐folds) the expression of 7 genes in a similar fashion, in both metastatic cells. The DNA microarry analysis was validated by real time PCR or by RT‐PCR. HMGB1 was among these genes. Confocal microscopy indicated that E‐selectin down regulated the cellular expression of the HMGB1 protein and enhanced the release of HMGB1 into the culture medium. The released HMGB1 in turn, activated endothelial cells to express E‐selectin.

Toward Development of Targeted Nonsteroidal Antiandrogen-1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic Acid−Gadolinium Complex for Prostate Cancer Diagnostics

Androgen receptors are present in most advanced prostate cancer specimens, having a critical role in development of this type of cancer. For correct prognosis of patient conditions and treatment monitoring, noninvasive imaging techniques have great advantages over surgical procedures. We developed synthetic methodologies for preparation of novel androgen receptor-targeting agents in an attempt to build a versatile platform for prostate cancer imaging and treatment. The structure of these compounds comprises of a lanthanoid metal ion, gadolinium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Gd-DOTA)-based binding fragment and, connected to it by a flexible linker, bicalutamide-derived nonsteroidal antiandrogen moiety. A representative gadolinium complex 15 was evaluated as a magnetic resonance imaging (MRI) agent in C57/bl6 male mouse bearing orthotopic TRAMP C2 prostate tumor.