Bioconjugation of Calcium Phosphosilicate Composite Nanoparticles for Selective Targeting of Human Breast and Pancreatic Cancers In Vivo

Abstract

The early diagnosis of cancer is the critical element in successful treatment and long term favorable patient prognoses. The high rate of mortality is mainly attributed to the tendency for late diagnoses as symptoms may not occur until the disease has metastasized, as well as the lack of effective systemic therapies. Late diagnosis is often associated with the lack of timely sensitive imaging modalities. The promise of nanotechnology is presently limited by the inability to simultaneously seek, treat and image cancerous lesions. This study describes the design and synthesis of fluorescent calcium phosphosilicate nanocomposite particles (CPNPs) that can be systemically targeted to breast and pancreatic cancer lesions. The CPNPs are a ~20nm diameter composite composed of an amorphous calcium phosphate matrix doped with silicate in which a near infra-red imaging agent indocyanine green (ICG) is embedded. In the present studies, we describe and validate CPNP bioconjugation of human holotransferrin, anti-CD71 antibody, and short gastrin peptides via an avidin-biotin-or a novel PEG-maleimide-coupling strategy. The conjugation of biotinylated human holotransferrin (diferric transferrin) and biotinylated anti-CD71 antibody (anti-transferrin receptor antibody) to avidin conjugated CPNPs (Avidin-CPNPs) permits targeting of transferrin receptors, which are highly expressed on breast cancer cells. Similarly, the conjugation of biotinylated pentagastrin to AvidinCPNPs and decagastrin (gastrin-10) to PEG-CPNPs via PEG-maleimide coupling permits targeting of gastrin receptors, which are over-expressed in pancreatic cancer lesions. These bioconjugated CPNPs have the potential to perform as a theranostic modality, simultaneously enhancing drug delivery, targeting and imaging of breast and pancreatic cancer tumors. Keywords bioconjugation; transferrin receptor; gastrin receptor; breast cancer; pancreatic cancer; calcium phosphate; whole animal imaging Calcium phosphate nanoparticles (CPNPs) have been engineered to be a non-toxic vehicle for the delivery of a diverse range of therapeutic and imaging agents in biological systems. [1][2][3][4] Previous studies have shown that encapsulation within CPNPs improved the lifetime and RESULTS AND DISCUSSION Physical Characterization of CPNPsCitrate functionalized CPNPs were utilized as a platform for functionalization, which allowed the characterization of bioconjugation via zeta potential analysis (Figure 1). Figure 1 shows the zeta potential distribution of Citrate-CPNPs prior to bioconjugation (blue line), and the zeta (violet). Prior to bioconjugation, the Citrate-CPNPs display a negative mean zeta potential value of −16 ± 1.3 mV, which is consistent with previous reports. 1 However, after bioconjugation, the Avidin-CPNPs displayed a relatively high positive mean zeta potential value of +29 ± 8.7 mV. The isoelectric point for avidin is pH 10. Thus, the shift from a negative zeta potential to a positive zeta potential distribution is strong evidence of avidin bioconjugation on...

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