The high affinity of highly charged polynuclear platinum complexes for glycans such as heparan sulfate results in modulation of the biomolecule signaling functions leading to inhibition of angiogenesis.

Cleavage of heparan sulfate proteoglycans (HSPGs) by the enzyme heparanase modulates tumour-related events including angiogenesis, cell invasion, and metastasis. Metalloshielding of heparan sulfate (HS) by positively charged polynuclear platinum complexes (PPCs) effectively inhibits physiologically critical HS functions. Studies using bacterial P. heparinus heparinase II showed that a library of Pt complexes varying in charge and nuclearity and the presence or absence of a dangling amine inhibits the cleavage activity of the enzyme on the synthetic pentasaccharide, Fondaparinux (FPX). Charge-dependent affinity of PPC for FPX was seen in competition assays with methylene blue and ethidium bromide. The dissociation constant (K ) of TriplatinNC for FPX was directly measured by isothermal titration calorimetry (ITC). The trend in DFT calculated interaction energies with heparin fragments is consistent with the spectroscopic studies. Competitive inhibition of TAMRA-R internalization in human carcinoma (HCT116) cells along with studies in HCT116, wildtype CHO and mutant CHO-pgsA745 (lacking HS/CS) cells confirm that HSPG-mediated interactions play an important role in the cellular accumulation of PPCs.

We present spectroscopic and biophysical approaches to examine the affinity of metal-ammine coordination complexes for heparin as a model for heparan sulfate (HS). Similar to nucleic acids, the highly anionic nature of heparin means it is associated in vivo with physiologically relevant cations, and this work extends their bioinorganic chemistry to substitution-inert metal-ammine compounds (M). Both indirect and direct assays were developed. M compounds are competitive inhibitors of methylene blue (MB)-heparin binding, and the change in the absorbance of the dye in the presence or absence of heparin can be used as an indirect reporter of M-heparin affinity. A second indirect assay uses the change in fluorescence of TAMRA-R, a nonaarginine linked to a fluorescent TAMRA moiety, as a reporter for M-heparin binding. Direct assays are surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). The K values for TriplatinNC-heparin varied to some extent depending on the technique from 33.1 ± 2 nM (ITC) to 66.4 ± 1.3 nM (MB absorbance assay) and 340 ± 30 nM (SPR). The differences are explained by the nature of the technique and the use of heparin of differing molecular weight. Indirect probes using the displacement of ethidium bromide from DNA or, separately, fluorescently labeled oligonucleotide (DNA-Fl) can measure the relative affinities of heparin and DNA for M compounds. These assays showed essentially equivalent affinity of TriplatinNC for heparin and DNA. The generality of these methods was confirmed with a series of mononuclear cobalt, ruthenium, and platinum compounds with significantly lower affinity because of their smaller overall positive charge but in the order [Co(NH)] > [Ru(NH)] > [Pt(NH)]. The results on heparin can be extrapolated to glycosoaminoglycans such as HS, emphasizing the relevance of glycan interactions in understanding the biological properties of coordination compounds and the utility of the metalloglycomics concept for extending bioinorganic chemistry to this class of important biomolecules.

Triple-negative breast cancer (TNBC) is a subtype of breast cancer lacking targetable biomarkers. TNBC is known to be most aggressive and when metastatic is often drug-resistant and uncurable. Biomarkers predicting response to therapy improve treatment decisions and allow personalized approaches for patients with TNBC. This study explores sulfated glycosaminoglycan (sGAG) levels as a predictor of TNBC response to platinum therapy. sGAG levels were quantified in three distinct TNBC tumor models, including cell line–derived, patient-derived xenograft (PDX) tumors, and isogenic models deficient in sGAG biosynthesis. The in vivo antitumor efficacy of Triplatin, a sGAG-directed platinum agent, was compared in these models with the clinical platinum agent, carboplatin. We determined that >40% of TNBC PDX tissue microarray samples have high levels of sGAGs. The in vivo accumulation of Triplatin in tumors as well as antitumor efficacy of Triplatin positively correlated with sGAG levels on tumor cells, whereas carboplatin followed the opposite trend. In carboplatin-resistant tumor models expressing high levels of sGAGs, Triplatin decreased primary tumor growth, reduced lung metastases, and inhibited metastatic growth in lungs, liver, and ovaries. sGAG levels served as a predictor of Triplatin sensitivity in TNBC. Triplatin may be particularly beneficial in treating patients with chemotherapy-resistant tumors who have evidence of residual disease after standard neoadjuvant chemotherapy. More effective neoadjuvant and adjuvant treatment will likely improve clinical outcome of TNBC.

1H NMR spectroscopic studies on the 1:1 adduct of the pentasaccharide Fondaparinux (FPX) and the substitution‐inert polynuclear platinum complex TriplatinNC show significant modulation of geometry around the glycosidic linkages of the FPX constituent monosaccharides. FPX is a valid model for the highly sulfated cell signalling molecule heparan sulfate (HS). The conformational ratio of the 1C4:2S0 forms of the FPX residue IdoA(2S) is altered from ca. 35:65 (free FPX) to ca. 75:25 in the adduct; the first demonstration of a small molecule affecting conformational changes on a HS oligosaccharide. Functional consequences of such binding are suggested to be inhibition of HS cleavage in MDA‐MB‐231 triple‐negative breast cancer (TNBC) cells. We further describe inhibition of metastasis by TriplatinNC in the TNBC 4T1 syngeneic tumour model. Our work provides insight into a novel approach for design of platinum drugs (and coordination compounds in general) with intrinsic anti‐metastatic potential.

Heparan sulfate (HS) are linear polysaccharides conjugated to proteins, heparan sulfate proteoglycans (HSPGs), located on the cell surface and extracellular matrix. The HS chains display varying degrees of sulfation. These sulfate clusters mediate the interaction of polynuclear platinum complexes (PPCs) with HSPG through a “sulfate clamp.” Such PPC-HS interactions can be conceptualized as “polyarginine” mimics. Strong HS-PPC binding protects the oligosaccharide against sulfate loss through metalloshielding. The biological consequences of PPCs metalloshielding HS will in principle affect HS interactions with relevant enzymes and proteins such as heparanase and growth factors, similar in concept to inhibition of DNA-protein binding through modification of DNA structure and conformation. HSPGs, associated growth factors, and heparanase promote tumor progression by facilitating invasion, angiogenesis, and metastasis. High heparanase expression correlates with increased metastatic potential and poor clinical prognosis. PPC-HS interactions inhibit cleavage of a model pentasaccharide by heparanase and further modulated bFGF binding to HS, and bFGF-induced migration and signaling in colon cancer cells. The end-point of functional modulation of HS interactions is inhibition of angiogenesis and metastasis. We report proof-of-principle of strong in vivo anti-metastatic activity of PPCs in triple negative breast cancer (TNBC) models. Further, we examine the anti-metastatic and anti-angiogenic effects of PPC-HS metalloshielding in these in vivo models through multiple growth factor signaling pathways (bFGF, HB-EGF, VEGF), and heparanase activity in breast cancer and endothelial cells. PPCs represent a novel class of intrinsically dual-function agents combining platinum cytotoxicity through DNA targeting with anti-angiogenic effects through glycan targeting. Chicago 14-17 April 2018 Citation Format: Samantha J. Katner, James D. Hampton, Erica J. Peterson, Eriko Katsuta, Megan R. Sayyad, Kazuaki Takabe, Jennifer Koblinski, Nicholas P. Farrell. Heparan sulfate, a new target for platinum in metastatic TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3941.

1H NMR spectroscopic studies on the 1:1 adduct of the pentasaccharide Fondaparinux (FPX) and the substitution‐inert polynuclear platinum complex TriplatinNC show significant modulation of geometry around the glycosidic linkages of the FPX constituent monosaccharides. FPX is a valid model for the highly sulfated cell signalling molecule heparan sulfate (HS). The conformational ratio of the 1C4:2S0 forms of the FPX residue IdoA(2S) is altered from ca. 35:65 (free FPX) to ca. 75:25 in the adduct; the first demonstration of a small molecule affecting conformational changes on a HS oligosaccharide. Functional consequences of such binding are suggested to be inhibition of HS cleavage in MDA‐MB‐231 triple‐negative breast cancer (TNBC) cells. We further describe inhibition of metastasis by TriplatinNC in the TNBC 4T1 syngeneic tumour model. Our work provides insight into a novel approach for design of platinum drugs (and coordination compounds in general) with intrinsic anti‐metastatic potential.

The high affinity of polynuclear platinum compounds (PPCs) for heparan sulfate (HS) is mediated through a “sulfate clamp” and PPC interactions can be conceptualized as “polyarginine” mimics. Strong HS-PPC binding protects the oligosaccharide against sulfate loss through metalloshielding.1 Metalloshielding will in principle affect HS interactions with relevant enzymes and proteins such as heparanase and growth factors, similar in concept to inhibition of DNA-protein binding through modification of DNA structure and conformation.2 PPCs inhibit cleavage of a model pentasaccharide by heparanase and further modulate bFGF binding to HS, and bFGF-induced migration and signaling in colon cancer cells.3 The end-point of functional modulation of HS interactions is inhibition of angiogenesis and metastasis.3 Following proof-of-principle of strong in vivo anti-metastatic activity of PPCs in clinically relevant breast cancer models,4 this contribution examines the underlying mechanism of platinums as anti-metastatic agents. We report on the cellular effects of PPC-HS metalloshielding on multiple growth factor signaling pathways (bFGF, HB-EGF) and specific syndecan (Sdc)-dependent signaling in breast cancer. Coupled with previously demonstrated DNA binding, PPCs represent intrinsically dual- function agents combining platinum cytotoxicity with anti-angiogenic effects derived from first principles through glycan targeting. [1] Mangrum, J.B., Engelmann, B.J., Peterson, E.J., Ryan, J.J., Berners-Price, S.J., Farrell, N.P. Chemical Communications 2014, 50, 4056-4058. [2] Chiodelli, P., Bugatti, A., Urbinati, C., Rusnati, M. Molecules 2015, 20, 6342-6388. [3] Peterson, E.J., Daniel, A.G., Katner, S.J., Bohlmann, L., Chang,C., Bezos, A., Parish, C.R., von Itzstein, M., Berners-Price, S.J., Farrell, N.P. Chem. Sci. 2016, DOI: 10.1039/C6SC02515C. [4] E. Katsuta, S. Demasi, S. Katner, H. Aoki, E. Peterson, E., N.P. Farrell and K. Takabe. (2016). Proc. AACR New Orleans, LA. Abstract #3064. DC 1-5 April 2017 Citation Format: Samantha J. Katner, Erica Peterson J. Peterson, Eriko Katsuta, Stephanie C. DeMasi, Jennifer Koblinski, Kazuaki Takabe, Nicholas P. Farrell. Anti-metastatic platinum through glycan targeting in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 17. doi:10.1158/1538-7445.AM2017-17