Potentiating the Anticancer Properties of Bisphosphonates by Nanocomplexation with the Cationic Amphipathic Peptide, RALA

Bisphosphonates (BPs) are a class of bone resorptive drug with a high affinity for the hydroxyapatite structure of bone matrices that are used for the treatment of osteoporosis. However, clinical application is limited by a common toxicity, BP-related osteonecrosis of the jaw. There is emerging evidence that BPs possess anticancer potential, but exploitation of these antiproliferative properties is limited by their toxicities. We previously reported the utility of a cationic amphipathic fusogenic peptide, RALA, to traffic anionic nucleic acids into various cell types in the form of cationic nanoparticles. We hypothesized that complexation with RALA could similarly be used to conceal a BP's hydroxyapatite affinity, and to enhance bioavailability, thereby improving anticancer efficacy. Incubation of RALA with alendronate, etidronate, risedronate, or zoledronate provoked spontaneous electrostatic formation of cationic nanoparticles that did not exceed 100 nm in diameter and that were stable over a range of temperatures and for up to 6 h. The nanoparticles demonstrated a pH responsiveness, possibly indicative of a conformational change, that could facilitate release of the BP cargo in the endosomal environment. RALA/BP nanoparticles were more potent anticancer agents than their free BP counterparts in assays investigating the viability of PC3 prostate cancer and MDA-MB-231 breast cancer cells. Moreover, RALA complexation potentiated the tumor growth delay activity of alendronate in a PC3 xenograft model of prostate cancer. Taken together, these findings further validate the use of BPs as repurposed anticancer agents.

Preclincial evaluation of Gold-DTDTPA Nanoparticles As Theranostic Agents In Prostate Cancer Radiotherapy

AIM: Gold nanoparticles have attracted significant interest in cancer diagnosis and treatment. Herein, we evaluated the theranostic potential of dithiolated diethylenetriamine pentaacetic acid (DTDTPA) conjugated AuNPs (Au@DTDTPA) for CT-contrast enhancement and radiosensitization in prostate cancer.

MATERIALS & METHODS: In vitro assays determined Au@DTDTPA uptake, cytotoxicity, radiosensitizing potential and DNA damage profiles. Human PC3 xenograft tumor models were used to determine CT enhancement and radiation modulating effects in vivo.

RESULTS: Cells exposed to nanoparticles and radiation observed significant additional reduction in survival compared with radiation only. Au@DTDTPA produced a CT enhancement of 10% and a significant extension in tumor growth delay from 16.9 days to 38.3 compared with radiation only.

CONCLUSION: This study demonstrates the potential of Au@DTDTPA to enhance CT-image contrast and simultaneously increases the radiosensitivity of prostate tumors.

Growth inhibition by tyrosine kinase inhibitors in mesothelioma cell lines.

Clinical outcome following chemotherapy for malignant pleural mesothelioma is poor and improvements are needed. This preclinical study investigates the effect of five tyrosine kinase inhibitors (PTK787, ZD6474, ZD1839, SU6668 and SU11248) on the growth of three mesothelioma cell lines (NCI H226, NCI H28 and MSTO 211H), the presence of growth factor receptors and inhibition of their downstream signalling pathways. GI50 values were determined: ZD6474 and SU11248, mainly VEGFR2 inhibitors, gave the lowest GI50 across all cell lines (3.5-6.9 microM) whereas ZD1839 gave a GI50 in this range only in H28 cells. All cell lines were positive for EGFR, but only H226 cells were positive for VEGFR2 by Western blotting. ZD6474 and ZD1839 inhibited EGF-induced phosphorylation of EGFR, AKT and ERK, whereas VEGF-induced phosphorylation of VEGFR2 was completely inhibited with 0.1 microM SU11248. VEGFR2 was detected in tumour samples by immunohistochemistry. VEGFR2 tyrosine kinase inhibitors warrant further investigation in mesothelioma.

De novo methylation of tumor suppressor gene p16/INK4a is a frequent finding in multiple myeloma patients at diagnosis.

The p16 gene competes with cyclin D for binding to CDK4/CDK6 and therefore inhibits CDK4/6 complex kinase activity, resulting in dephosphorylation of pRb and related G1 growth arrest. Inactivation of this gene has been involved in a variety of tumors by different mechanisms: homozygous/hemyzygous deletions, point mutations and methylation of a 5' CpG island into exon E1alpha of the p16 gene. Homozygous deletions have been rarely found in multiple myeloma (MM) and no point mutations have been reported. Two recent studies have reported a high prevalence of methylation in the exon E1alpha of the p16 gene, but included only a small number of cases. We have analyzed the methylation pattern of exon E1alpha of the p16 gene in 101 untreated MM and five primary plasma cell leukemias (PCL). A PCR assay, relying on the inability of some restriction enzymes to digest methylated sequences, was used to analyze the methylation status. Southern blot analysis was used to confirm these results. Forty-one of 101 MM patients (40.5%) as well as four of the five (80%) primary PCL patients had shown methylation of the exon E1alpha. Our study confirms that hypermethylation of the p16 gene is a frequent event in MM. Leukemia (2000) 14, 183-187.