Complete Tumor Response Following Intratumoral PBioSilicon on Human Hepatocellular and Pancreatic Carcinoma Xenografts in NudeMice

Abstract

Purpose: P BioSilicon is a new, implantable, radiological medical device that comprises particles of highlypure siliconencapsulating phosphorus (P) for the treatmentofunresectable solid tumors. Prior to administration, the device particles are suspended in a formulant which provides an even suspension of the intended dose for implantation.The primary objective of this animal trial study was to investigate the effects of intratumoral injection of P BioSilicon on human hepatocellular (HepG2) and pancreatic carcinoma (2119) xenografts implanted in nude mice (BALB/c). A secondary objective was the histopathologic examination of the tumor foci and surrounding tissue during the study. Methods: Cultured human carcinoma cells (HepG2 and 2119) were injected s.c. into the gluteal region of nudemice.When the implanted tumors weref1cm in diameter, PBioSilicon (0.5,1.0, and 2.0 MBq) or formulant was injected into the tumors. Implanted tumor size was measured once a week for 10 weeks. At study termination, the tumor and surrounding normal tissue were collected and fixed in10% formalin and processed for histopathologic analysis. Results: P BioSilicon produced a reduction in HepG2 tumor volume when compared with formulant control, and complete response was observed among tumors in the 1.0 and 2.0 MBq treatment groups after week 8. There was also significant reduction in 2119 tumor volume in all treated groups, with the complete response rate of 67% in the 2.0MBq group. Conclusion: PBioSilicon suppressed the growth of bothhumanhepatocellular and pancreatic carcinoma xenografts implanted in nude mice and complete responses were also observed in tumors at higher radiation doses. In spite of advances in chemotherapy and radiation therapy, gains in the survival of common inoperable adult solid tumors have remained modest over the last 30 years (1). Surgical resection remains the only therapeutic modality that significantly prolongs survival, but with many solid tumors such as hepatocellular carcinoma and pancreatic carcinoma, resectability rates continue to be low and prognosis in unresectable patients remains poor. Hepatocellular carcinoma is the third most common cause of cancer death worldwide, giving rise to >590,000 deaths per year (2). Although early lesions respond well to hepatic resection, liver transplantation, and some to percutaneous ablation or chemoembolization (3, 4), most patients with hepatocellular carcinoma still present with advanced disease, with only 10% to 20% of patients suitable for surgical intervention (5–7). External beam radiation is not useful for hepatocellular carcinoma because the sensitivity of the normal liver limits the dose that can be delivered, and chemotherapy is poorly efficacious (8). The median survival of inoperable patients remains about 3 months in places where the disease is endemic (9–11). Pancreatic carcinoma similarly remains a major therapeutic challenge and tends to present in advanced, inoperable stages. Only around 15% to 20% of patients have resectable disease at presentation (12), but even in this group, the 5-year survival rate is only about 20% (13). In patients with unresectable pancreatic carcinoma and good performance status, treatment with chemoradiation results in a median survival of only 42 to 44 weeks (14, 15), although pain relief is obtained in 50% to 85% of the patients (16). Delivery of high-dose external radiation to the pancreas is limited by toxicity to the surrounding viscera, especially the small intestine. The intratumoral administration of radiopharmaceuticals has the potential advantage of delivering the maximum amount of radioactivity to the tumor (17) with sharp dose fall-off to surrounding normal structures, thus limiting side effects. We postulate that delivery of high doses of radiation in such a localized setting will lead to significant tumor response with minimal toxicity and collateral acute radiation damage to other Cancer Therapy: Preclinical Authors’Affiliations: Departments of Experimental Surgery, Nuclear Medicine, General Surgery, and Pathology, Singapore General Hospital; Department of Therapeutic Radiology, National Cancer Centre, Singapore; and pSiMedica Ltd., Malvern Hills, United Kingdom Received 2/23/05; revised 7/21/05; accepted 7/28/05. The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked advertisement in accordance with18 U.S.C. Section1734 solely to indicate this fact. Requests for reprints: Pierce Chow, Department of General Surgery, Singapore General Hospital, Outram Road, Singapore 168609. Phone: 65-6326-5648; Fax: 65-6222-3389; E-mail: gsupc@singnet.com.sg. F2005 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-05-0400 www.aacrjournals.org Clin Cancer Res 2005;11(20) October15, 2005 7532 Research. on July 14, 2017. © 2005 American Association for Cancer clincancerres.aacrjournals.org Downloaded from tissues if the source of radiation remains locked in situ with minimal systemic distribution. Phosphorus 32 comes close to being the ideal unsealed therapeutic radionuclide (18). It is a pure h-particle emitter with a physical half-life of 14.3 days. The maximum range in tissue of the P h-particle emission is about 7.6 mm. Colloidal P has been used for the treatment of intracavitary malignancies. The retention of radioactivity of colloidal P at the site of a solid tumor required the infusion of macroaggregated albumin (19). An alternative method to aid radioactivity retention at the tumor site has been to use labeled, nontoxic and undegradable microcarriers such as phosphorus-32 glass microspheres (20). BioSilicon (21), recently developed by pSiMedica (Malvern Hills, United Kingdom), has characteristics that make it potentially ideal for use as a vehicle for intratumoral delivery. BioSilicon refers to etched forms of semiconducting silicon that have been porosified with electrochemical techniques in hydrofluoric acid–based solutions (22). This new biomaterial can be micronized and classified into particles of tunable size in order to optimize localization within the tumor. In addition, there is increasing in vitro and in vivo evidence of its biodegradability and tissue compatibility (21, 23–25). In our previous mice study, intratumoral injection of BioSilicon and formulant-only had not shown any significant toxic effects on the animals when compared with the no-treatment control group. The objective of this study was to study the effects of intratumoral P BioSilicon on the growth of solid tumor xenografts in an in vivo tumor model. S.c. implants of hepatocellular and pancreatic carcinoma xenografts in nude mice (BALB/c) were subjected to brachytherapy from radioactive P BioSilicon devices which were comprised of 20 Am polysilicon powder containing phosphorus 32 as the radionuclide. Materials andMethods P BioSilicon. The test substance, P BioSilicon, an active implantable, radiological medical device with phosphorus 32 activity, was created by thermal neutron capture of highly phosphorus-doped silicon within a nuclear reactor, which transmutes the natural phosphorus (P) in the silicon lattice of BioSilicon to the h-emitting radionuclide P. This is a similar process to that used by the semiconductor industry to dope silicon ingots and wafers with phosphorus, where the silicon 30 isotope is transmuted to phosphorus 31 (26). The activity of the product is 75 MBq nominal activity/100 mg BioSilicon (at reference date). The P BioSilicon is then filled and sterilized at the radiopharmacy of AEA Technology QSA (Braunschweig, Germany). Just before injection, it was suspended in an aqueous suspending solution containing microcrystalline cellulose and sodium carboxymethylcellulose. Animals and tumors. Eight-week-old male nude mice (BALB/c; The Animal Resources Centre, Murdoch, Western Australia)were housed in pathogen-free conditions conforming with the guidelines of the National Advisory Committee for Laboratory Animal Research of Singapore. Human hepatocellular carcinoma cell line HepG2 and human pancreatic carcinoma cell line 2119 were obtained from the American Type Culture Collection (Manassas, VA) and cultured in MEM with 10% FCS in 5% CO2 incubator. Cells (5 10) suspended in 100 AL of HBSS were injected s.c. into the right gluteal region of the nude mice. Injection of P BioSilicon in transplanted tumors. On day 15 after implantation of tumor cells, when the tumors were about 1 cm in diameter, P BioSilicon was injected in the center of the tumors at the depth of about 4 mm. Animal groups. Animals were divided into control and P BioSilicon groups. The control group was injected with formulant only. P BioSilicon was injected at three different activities of 0.5, 1.0, and 2.0 MBq, corresponding to absorbed tumor doses of 50, 100, and 200 Gy, respectively, as listed in Table 1. Measurement of tumor volume. The sizes of the implanted tumors were estimated every 7 days. The largest and smallest diameters were measured by a vernier caliper and tumor volume was estimated according the formula: V = 1/2 ab, where a and b are the largest and smallest tumor diameters, respectively, and V is the tumor volume in milliliters. The effect of P BioSilicon was assessed by comparing the tumor volumes of treatment groups to the control group at each week, up to week 10. The means and SD of the tumor volumes expressed as a percentage change from day 0 were calculated for each dose group at each time point. The SE was calculated as the SD divided by the square root of number of animals in each group. Definition of complete response. When the tumors become undetectable after implantation of P BioSilicon, tumor volumetric 7 Unpublished data. Table 1. Dosing schedules in the treatment animal groups Group Radiation dose (Gy) P activity (MBq) Injection volume (ML) Group size (n) Humanhepatocellular carcinoma cell line HepG2 1 formulant control 0 50 8 2 50 0.5 50 7 3 100 1.0 50 8 4 200 2.0 50 7 Human pancreatic carcinoma cell line 2119 5 formulant control 0 50 8 6 50 0.5 50 10 7 100 1.0 50 10 8 200 2.0 50 9 Fig. 1. Tumor volumetric assessment of the effect of BioSilicon on pancreatic carcinoma cell line 2119 xenografts innudemice.The average tumor volume for each dose group is expressed as a percentage of change in tumor volume compared with week 0. Points, means; bars,F SE.The average tumor volumes of formulant control, 0.5,1.0, and 2.0MBq groups at week 0 are 88.9, 78.4, 63.5, and 65.3 mm, respectively. Comparisons between control and PBioSilicon treatment groups byANOVA. *, P < 0.05; **, P < 0.005. Intratumoral PBioSilicon in Tumor Xenografts www.aacrjournals.org Clin Cancer Res 2005;11(20) October15, 2005 7533 Research. on July 14, 2017. © 2005 American Association for Cancer clincancerres.aacrjournals.org Downloaded from measurements could not be made and histologic examination of implantation sites shows no viable tumor tissue. Histologic studies. On days 10, 20, and 30 after P BioSilicon injection, the animals were killed by an overdose of pentobarbitone at 50 mg/kg of the sedated animal. The tumor and surrounding normal tissue were collected and fixed in 10% formalin. The samples were kept in 80jC for half a year and when there was no longer any detectable radioactivity, the sample was then processed for sectioning and staining with H&E. This is in accordance with the rules of radiation safety of the

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@inproceedings{Zhang2005CompleteTR, title={Complete Tumor Response Following Intratumoral PBioSilicon on Human Hepatocellular and Pancreatic Carcinoma Xenografts in NudeMice}, author={Kai Zhang and Susan and L. E. Loong and S E J Connor and Sidney W.K.Yu and Soo-Yong Tan and Robert T. H. Ng and Khai Mun Lee and Leigh Canham and Kay Hoong Chow}, year={2005} }