Phosphaplatin Anti-tumor Effect Enhanced by Liposomes Partly via an Up-regulation of PEDF in Breast Cancer

BACKGROUND/AIM

Phosphaplatin platinum (IV) (RRD4) complex has exceptional antitumor properties. The aim of this study was to investigate the effects and the mechanism of action of free and liposome-encapsulated RRD4 in breast cancer.

MATERIALS AND METHODS

Liposome-encapsulated RRD4 prepared by thin-film dehydration: hydration and free RRD4 were tested in vivo and in vitro against 4T1 breast cancer cells. Cell proliferation, migration and viability were determined. Tissue and cell production and expression of pigment epithelium-derived factor (PEDF) were assessed by ELISA and western blot. 4T1 cells treated with PEDF siRNA were evaluated for viability and apoptosis.

RESULTS

RRD4 inhibited tumor growth and prevented distant metastasis. Liposome formulation enhanced this therapeutic benefit without increasing toxicity and prolonged RRD4 retention in tumor tissues. In vitro, RRD4 induced 4T1 apoptosis through up-regulation of FAS, BAX, and PUMA, and down-regulation of BCL2. RRD4 facilitates a FAS-intrinsic signaling mechanism. PEDF up-regulation represents another antitumor mechanism associated with this phosphaplatin compound.

DISCUSSION

Free RRD4 or formulated into liposomes, are excellent candidates for adjuvant therapy against breast tumor growth and metastasis.

Insights into the anti-angiogenic properties of phosphaplatins

Phosphaplatins are platinum-based antitumor compounds that, unlike other clinically utilized platinum drugs (i.e. cisplatin, carboplatin, and oxaliplatin), appear to target proteins rather than DNA. Because of their unique mode of action, phosphaplatins are promising drug candidates for cisplatin-resistant cancers. In this study, we discovered that Pt(II) and Pt(IV) phosphaplatins possess diverse antitumor properties. In addition to targeting apoptosis antigen (FAS) and proapoptotic gene products as described previously, phosphaplatins also target angiogenesis. We demonstrate that phosphaplatins inhibit human umbilical vein endothelial cell (HUVEC) migration and tube formation in vitro and suppress tumor angiogenesis and growth in immunodeficient mice that were inoculated with A2780 ovarian cancer cells in vivo. To provide insight into this novel antitumor mechanism, phosphaplatin-treated HUVECs were found to exhibit lower gene expression levels of vascular endothelial growth factors (VEGFs) and the VEGFR-2 receptor compared to untreated cells. Kinase inhibition studies suggest that phosphaplatins are inhibitors of VEGFR-2. In ligand exchange experiments using both Pt atomic absorption and ³¹P NMR spectroscopies, we show that phosphaplatins most likely bind to VEGFR-2 through metal-ligand coordination rather than electrostatic interactions. These studies enhance our understanding of the diverse and novel mechanisms of action of the phosphaplatin antitumor agents, which could potentially be used as chemotherapeutic agents against cisplatin-resistant cancers.

Abstract 3806: Phosphaplatins are potent inducers of pigment epithelial- derived factor (PEDF)

Pigment Epithelial Derived Factor (PEDF) is a secreted glycoprotein that exhibits several biological activities, most notably as a potent anti-angiogenic agent as well as a neurotrophic factor. As such, this molecule has potential application as therapeutics for cancer and a variety of neurological diseases. However, prior art methods directed towards enhancing and stabilizing PEDF expression in vivo have met with little success. Therefore, methods that could lead to the stable expression of PEDF in vivo are still needed. We have recently shown that PEDF protein is overexpressed in tumor cells treated with platinum based drugs; phosphaplatins that are platinum-(II) and platinum-(IV) complexes coordinated to a pyrophosphate moiety. The objective of this study is to extend our previous findings by measuring PEDF expression in both malignant cells and normal neuronal tissues after treating them with these compounds. We also investigated the impact of PEDF upregulation on important biological processes such as apoptosis, proliferation and invasion of tumor cells. Our data showed that there was a significant upregulation (over 4-fold) of PEDF in brain of mice treated with phosphoplatins when compared to the control animals. The compounds were found to stimulate PEDF expression in cultured neuronal cells when assessed in vitro (P<0.05 vs. untreated control groups). In tumor cells, phosphoplatins upregulated PEDF expression in a dose-dependent manner in various tumor cell lines. In one particular mouse breast tumor cell line (4T1), the data showed that phosphaplatin doses in the range of 25 to 100 μM stimulated the expression of PEDF at 12 and 24 hrs, which declined thereafter. Remarkably, a subsequent treatment of the tumor cells with phosphaplatins at 24 hrs prevented the decline of PEDF expression, suggesting a direct correlation between phosphaplatins and PEDF overexpression. The upregulation of PEDF in the tumor cells was paralleled by increased apoptosis and decreased cell proliferation and invasion. In summary, phosphaplatins mediated overexpression of PEDF in vivo suggests a potential neuroprotective effect of these compounds. While in tumors, phosphaplatins may exhibit antitumor activity via multiple effects, including anti-angiogenesis, enhanced apoptosis, and decreased proliferation and invasion, predominately through stimulating overexpression of PEDF.

Citation Format: Louiza Belkacemi, Armando Rivera, Lu Yang, Rathindra N. Bose, Shaun X. Zhang. Phosphaplatins are potent inducers of pigment epithelial- derived factor (PEDF). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3806.

Correlation between Gene Variants, Signaling Pathways, and Efficacy of Chemotherapy Drugs against Colon Cancers

Efficacies, toxicities, and resistance mechanisms of chemotherapy drugs, such as oxaliplatin and 5-fluorouracil (5-FU), vary widely among various categories and subcategories of colon cancers. By understanding the differences in the drug efficacy and resistance at the level of protein–protein networks, we identified the correlation between the drug activity of oxaliplatin/5-FU and gene variations from the US National Cancer Institute-60 human cancer cell lines. The activity of either of these drugs is correlated with specific amino acid variant(s) of KRAS and other genes from the signaling pathways of colon cancer progression. We also discovered that the activity of a non-DNA-binding novel platinum drug, phosphaplatin, is comparable with oxaliplatin and 5-FU when it was tested against colon cancer cell lines. Our strategy that combines the knowledge from pharmacogenomics across cell lines with the molecular information from specific cancer cells is beneficial for predicting the outcome of a possible combination therapy for personalized treatment.

Abstract B1-02: Correlation between oncogenic mutations, signaling pathways, and efficacy of platinum-based drugs against colorectal cancers

The purpose of this study is to correlate genetic mutations, amino-acid variants, signaling pathways with platiunum based drug activity to shed light on personalized treatment of cancer. Platinum anticancer drugs such as cisplatin, carboplatin, and oxalipaltin are widely used to treat a variety of cancers. Although DNA is the molecular target for these platinum therapies, their efficacies, toxicities, and resistance mechanisms vary widely among various categories and sub-categories of cancers. To comprehend this great variability, an integrated analysis was performed to determine the impact of somatic mutations on protein functions, signaling pathways, and drug activity (sensitivity or resistance) among the US National Cancer Institute (NCI) 60 human tumor cell lines based on Z-scores to predict a priori treatment outcome using CellMiner (http://discover.nci.nih.gov/cellminer). Specifically, somatic mutations of significantly mutated genes from the cancer genome atlas (TCGA) were analyzed along with the driver genes (oncogenes and tumor suppressor genes) from catalogue of somatic mutations in cancer (COSMIC) for total 188 genes that belong to more than 20 different signaling pathways. The functional impact of individual amino-acid variant for each gene and its correlation with the activity of carboplatin, cisplatin and oxaliplatin for each cancer cell line were explored. Particular attention was given to colon cancer for which nearly 40% of tumors are known to have mutated KRAS (Kirsten rat sarcoma viral oncogene homolog) gene. Resulting analysis revealed that colon cancer cell lines with KRAS mutations for codon 12 (G12V-mutant from SW620 cell line) and codon 13 (G13D-mutant from HCT116 and HCT15 cell lines) correlated with the sensitivity to oxaliplatin. Conversely, oxaliplatin resistant HCC2998 colon cancer cell line did not show any correlation with mutated KRAS for codon 146 (A146T-mutant). Notably, all the colon cancer cell lines were resistant to both carboplatin and cisplatin with no correlation to the KRAS mutants. Based on our integrated analysis we further predicted gene networks related to oxaliplatin activity for colon cancer. The network includes the epidermal growth factor (EGFR) signaling pathway that involves PIK3CA, PIK3CG and MTOR from the phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) (PIK3/mTOR) pathway, and JAK3 from Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway in addition to KRAS from Mitogen-activated protein kinases (MAPK) pathway. We conclude that instead of considering all mutations of a gene in the same way to assess their clinical significance, it may be beneficial to categorize them into different classes based on their functional impact and efficacies towards the anti-cancer drugs for personalized treatment. Similar analytical approach is being extended to non-small cell lung and ovarian cancers where platinum therapies are widely used.

S. Tripathi gratefully acknowledges the support through a training fellowship from a grant by the Cancer Prevention Research Institute of Texas (Grant No. RP140113 to R.N.Bose).

Citation Format: Swarnendu Tripathi, Louiza Belkacemi, Margaret S. Cheung, Rathindra N. Bose. Correlation between oncogenic mutations, signaling pathways, and efficacy of platinum-based drugs against colorectal cancers. [abstract]. In: Proceedings of the AACR Special Conference on Computational and Systems Biology of Cancer; Feb 8-11 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 2):Abstract nr B1-02.

Abstract A2-48: Correlation between oncogenic mutations, signaling pathways and efficacy of platinum based drugs against colorectal cancers

The purpose of this study is to correlate genetic mutations, amino-acid variants, signaling pathways with platiunum based drug activity to shed light on personalized treatment of cancer. Platinum anticancer drugs such as cisplatin, carboplatin, and oxalipaltin are widely used to treat a variety of cancers. Although DNA is the molecular target for these platinum therapies, their efficacies, toxicities, and resistance mechanisms vary widely among various categories and sub-categories of cancers. To comprehend this great variability, an integrated analysis was performed to determine the impact of somatic mutations on protein functions, signaling pathways, and drug activity (sensitivity or resistance) among the US National Cancer Institute (NCI) 60 human tumor cell lines based on Z-scores to predict a priori treatment outcome using CellMiner (http://discover.nci.nih.gov/cellminer). Specifically, somatic mutations of significantly mutated genes from the cancer genome atlas (TCGA) were analyzed along with the driver genes (oncogenes and tumor suppressor genes) from catalogue of somatic mutations in cancer (COSMIC) for total 188 genes that belong to more than 20 different signaling pathways. The functional impact of individual amino-acid variant for each gene and its correlation with the activity of carboplatin, cisplatin and oxaliplatin for each cancer cell line were explored. Particular attention was given to colon cancer for which nearly 40% of tumors are known to have mutated KRAS (Kirsten rat sarcoma viral oncogene homolog) gene. Resulting analysis revealed that colon cancer cell lines with KRAS mutations for codon 12 (G12V-mutant from SW620 cell line) and codon 13 (G13D-mutant from HCT116 and HCT15 cell lines) correlated with the sensitivity to oxaliplatin. Conversely, oxaliplatin resistant HCC2998 colon cancer cell line did not show any correlation with mutated KRAS for codon 146 (A146T-mutant). Notably, all the colon cancer cell lines were resistant to both carboplatin and cisplatin with no correlation to the KRAS mutants. Based on our integrated analysis we further predicted gene networks related to oxaliplatin activity for colon cancer. The network includes the epidermal growth factor (EGFR) signaling pathway that involves PIK3CA, PIK3CG and MTOR from the phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) (PIK3/mTOR) pathway, and JAK3 from Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway in addition to KRAS from Mitogen-activated protein kinases (MAPK) pathway. We conclude that instead of considering all mutations of a gene in the same way to assess their clinical significance, it may be beneficial to categorize them into different classes based on their functional impact and efficacies towards the anti-cancer drugs for personalized treatment. Similar analytical approach is being extended to non-small cell lung and ovarian cancers where platinum therapies are widely used.

S. Tripathi gratefully acknowledges the support through a training fellowship from a grant by the Cancer Prevention Research Institute of Texas (Grant No. RP140113 to R.N.Bose).

Citation Format: Swarnendu Tripathi, Louiza Belkacemi, Margaret S. Cheung, Rathindra N. Bose. Correlation between oncogenic mutations, signaling pathways and efficacy of platinum based drugs against colorectal cancers. [abstract]. In: Proceedings of the AACR Special Conference on Translation of the Cancer Genome; Feb 7-9, 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 1):Abstract nr A2-48.

Absence of Activation of DNA Repair Genes and Excellent Efficacy of Phosphaplatins against Human Ovarian Cancers: Implications To Treat Resistant Cancers

Phosphaplatins, platinum(II) and platinum(IV) complexes coordinated to a pyrophosphate moiety, exhibit excellent antitumor activities against a variety of cancers. To determine whether phosphaplatins trigger resistance to treatment by engaging DNA damage repair genes, a yeast genome-wide fitness assay was used. Treatment of yeast cells with pyrodach-2 (D2) or pyrodach-4 (D4) revealed no particular sensitivity to nucleotide excision repair, homologous recombination repair, or postreplication repair when compared with platin control compounds. Also, TNF receptor superfamily member 6 (FAS) protein was overexpressed in phosphaplatin-treated ovarian tumor cells, and platinum colocalized with FAS protein in lipid rafts. An overactivation of sphingomyelinase (ASMase) was noted in the treated cells, indicating participation of an extrinsic apoptotic mechanism due to increased ceramide release. Our results indicate that DNA is not the target of phosphaplatins and accordingly, that phosphaplatins might not cause resistance to treatment. Activation of ASMase and FAS along with the colocalization of platinum with FAS in lipid rafts support an extrinsic apoptotic signaling mechanism that is mediated by phosphaplatins.

Synthesis, X-ray crystallographic, and NMR characterizations of platinum(II) and platinum(IV) pyrophosphato complexes

A series of mononuclear cis-diamineplatinum(II) pyrophosphato complexes containing ammine (am), trans-1,2-cyclohexanediamine (dach), and 1,2-ethanediamine (en) as the amine ligands were synthesized and characterized by (31)P and (195)Pt NMR spectroscopy. Chemical shifts of (31)P NMR resonances of these completely deprotonated complexes appear at 2.12, 1.78, and 1.93 ppm, indicating a coordination chemical shift of at least 8 ppm. The (195)Pt NMR chemical shifts for the am and dach complexes were observed at -1503 and -1729 ppm. The complexes are highly stable at neutral pH; no aquation due to the release of either phosphate or amine ligands was observed within 48 h. Furthermore, no partial deligation of the pyrophosphate ligand was detected within several days at neutral pH. At lower pH, however, release of a pyrophosphate ion was observed with concomitant formation of a bridged pyrophosphatoplatinum(II) dinuclear complex. The extended crystal structure containing the dach ligand revealed a zigzag chain stacked in a head-to-tail fashion. Moreover, two zigzag chains are juxtaposed in a parallel fashion and supported by additional hydrogen bonds reminiscent of DNA structures where two strands of DNA bases are held by hydrogen bonds. Theoretical calculations support the notion that the two dinuclear units are held together primarily by hydrogen bonds between the amine and phosphate moieties. Platinum(II) pyrophosphato complexes were readily oxidized by hydrogen peroxide to yield cis-diamine-trans-dihydroxopyrophosphatoplatinum(IV) complexes. Two of these complexes, containing am and en, were characterized by X-ray crystallography. Notable structural features include Pt-O (phosphate) bond distances of 2.021-2.086 A and departures from 180 degrees in trans-HO-Pt-OH bond angles, >90 degrees in O-Pt-O, and >90 degrees in cis-N-Pt-N bond angles. The departure in the trans-HO-Pt-OH angle is more pronounced in the 1,2-ethanediamine complex compared to the dach analogue because of the existence of two molecules possessing enantiomeric conformations within the asymmetric unit. (31)P NMR spectra exhibited well-resolved (195)Pt satellites with coupling constants of 15.4 Hz for the ammine and 25.9 Hz for both the 1,2-ethanediamine and trans-1,2-cyclohexanediamine complexes. The (195)Pt NMR spectrum of the ammine complex clearly showed coupling with two equivalent N atoms.

Insight into the reactive form of the anticancer agent iproplatin

The reaction of iproplatin with reduced glutathione at different mole ratios yielded cis-di(isopropylamine)chloro-glutathionatoplatinum(II), not the expected cis-dichloro- species, indicating a mode of action of this anticancer agent that is different from that of cis-diamminedichloroplatinum(II).

Mechanisms of DNA damage and insight into mutations by chromium(VI) in the presence of glutathione

The mechanisms of hexavalent chromium(VI) induced DNA damage were unveiled by detecting products of single- and double-stranded DNA in the presence of glutathione. The absence of a detectable hydroxyl radical in the reactions indicates that DNA damage was exclusively by hypervalent chromium species. Polyacrylamide gel electrophoresis (PAGE) experiments with 32-mer single-stranded oligonucleotide and its complementary duplex revealed cleavages largely at purine bases with significant enhancement of such cleavages in the presence of a base. Quantitative estimations of bases released by HPLC before and after enzymatic digestion with exonucleases unequivocally established the excessive release of purine bases. This release was accompanied by the concomitant formation of phosphoglycolate as characterized by liquid chromatography-mass spectrometry (LC-MS). These data connote that the preponderance DNA damage is due to an oxidation specifically at H4' of the ribose moiety leading to the formation of apurinic sites. In addition to the oxidation at H4', DNA oxidation was also initiated through H5' site as evidenced by the identification of furfural. This pathway appears to be non-selective and more abundant for ssDNA as cleavages were observed at both purine and pyrimidine bases. Finally, the detection of guanidinohydantoin as a minor product points the involvement of an oxygen activated hypervalent chromium species, perhaps a peroxo-chromium species. Both major and minor pathways lead to cleavages at purine sites for ds-DNA and are consistent with the observation that DNA cleavage was enhanced in the presence of a base. In contrast, when hydrogen peroxide was added to the reactions, random DNA cleavages were apparent indicating involvement of multiple species including a hydroxyl radical. These data pinpoint mutation mechanisms induced by chromium(VI) in the presence of glutathione due to transversion either by inserting the wrong bases opposite to the apurinic sites during replication or by purine-purine mismatch.

Nuclear magnetic resonance structures of the zinc finger domain of human DNA polymerase-α

The carboxy terminus of the human DNA polymerase-alpha contains a zinc finger motif. Three-dimensional structures of this motif containing 38 amino acid residues, W L I C E E P T C R N R T R H L P L Q F S R T G P L C P A C M K A T L Q P E, were determined by nuclear magnetic resonance (NMR) spectroscopy. The structures reveal an alpha-helix-like domain at the amino terminus, extending 13 residues from L2 through H15 with an interruption at the sixth residue. The helix region is followed by three turns (H15-L18, T23-L26 and L26-A29), all of which involve proline. The first turn appears to be type III, judging by the dihedral angles. The second and third turns appear to be atypical. A second, shorter helix is formed at the carboxy terminus extending from C30 through L35. A fourth type III turn starting at L35 was also observed in the structure. Proline serves as the third residue of all the turns. Four cysteine residues, two located at the beginning of the helix at the N-terminus and two at the carboxy end, are coordinated to Zn(II), facilitating the formation of a loop. One of the cysteines at the carboxy terminus is part of the atypical turn, while the other is the part of the short helix. These structural features are consistent with the circular dichroism (CD) measurements which indicate the presence of 45% helix, 11% beta turns and 19% non-ordered secondary structures. The zinc finger motif described here is different from those observed for C(4), C(2)H(2), and C(2)HC modules reported in the literature. In particular, polymerase-alpha structures exhibit helix-turn-helix motif while most zinc finger proteins show anti-parallel sheet and helix. Several residues capable of binding DNA, T, R, N, and H are located in the helical region. These structural features imply that the zinc finger motif is most likely involved in binding DNA prior to replication, presumably through the helical region. These results are discussed in the context of other eukaryotic and prokaryotic DNA polymerases belonging to the polymerase B family.

Platinum(II) catalysis and radical intervention in reductions of platinum(IV) antitumor drugs by ascorbic acid

Reductions of four platinum(IV) amine complexes, cis-diamminetetrachloroplatinum(IV), tetraammine-cis-dichloroplatinum(IV), cis,cis,trans-diamminedichlorodihydroxoplatinum(IV), and cis,trans,cis-dichloro-dihydroxo-bis(isopropylamine)platinum(IV) by ascorbic acid were catalyzed by platinum(II) at pH 7.3 and 22 degrees C. Except for the first mentioned compound, initial slow uncatalyzed reductions yielded platinum(II) products which served as catalyst as revealed by the presence of induction periods and their disappearance by the addition of the platinum(II) products. The platinum(II) catalysis generated ascorbate bound platinum(IV) intermediates. An internal electron transfer process within these intermediates led to the formation of platinum(II) complexes. Although the rate constants for the uncatalyzed reductions vary greatly depending on the nature of the ligands and their spatial arrangements, the magnitudes of the platinum(II) catalyzed rate constants fall in the narrow range, 100 to 300 M(-2) s(-1). The values of the uncatalyzed reductions lie in the range 5 x 10(-2) to 15 M(-1) s(-1), the tetrachloroplatinum(IV) complex suffered the faster reduction. The reduction of iproplatin with two hydroxide ligands in trans configuration was the slowest. The internal electron transfer rate constants span two orders of magnitude, from 0.15 to 4 x 10(-3) s(-1). These reactions were accompanied by the formation of the ascorbate radical which persists throughout the entire reaction. Although the tetrachloro species exhibited simple second order reduction, first order in each of the reactants, the rate of reduction was also accelerated by the addition of cis-diamminedichoroplatinum(II) indicating the presence of catalysis in this reaction as well.

Unwinding of DNA polymerases by the antitumor drug, cis-diamminedichloroplatinum(II)

The helix-turn-helix motifs of the DNA binding domains of human polymerase-alpha and polymerase-kappa are dramatically perturbed upon binding to cisplatin with concomitant release of zinc.

DNA oxidation by peroxo-chromium(v) species: oxidation of guanosine to guanidinohydantoin

Reactions of peroxo-chromium(v) complexes with DNA afforded mainly guanine oxidation yielding, a four-electron oxidation product, guanidinohydantoin, and exhibited extensive base labile strand scission.

Biomolecular targets for platinum antitumor drugs

Cis-diamminedichloroplatinum(II) (cisplatin) is widely used for the treatment of testicular, ovarian, and other forms of cancer. Several second generation platinum centered antitumor drugs have been approved or undergoing phase-3 clinical trial. Cisplatin arrests the cell cycle at the G2 phase by a mechanism commonly known as apoptosis. At the molecular level, it is generally believed that the anticancer properties of these compounds are due to the covalent binding to DNA. In addition to DNA binding, the platinum drugs bind and interact with proteins and enzymes. The toxic effects of the drugs have been usually attributed to protein binding. However, a growing body of work points to much more complex anticancer mechanisms involving direct and indirect interactions of platinum compounds with proteins and enzymes. In this review, a discussion on the strength and weaknesses of DNA binding mechanism followed by enzymes and protein interactions with the drugs are presented for the comprehensive understanding of apoptosis. The purpose of this review is to encourage researchers to explore metallobiochemistry of platinum drugs focusing attention to cellular and molecular events beyond DNA binding.