**4. Ruthenium (III)-based drugs nanoformulations**

The studies regarding ruthenium complexes as anticancer agents were developed as an alternative of platinum complexes, especially for their reduced toxicity, large spectrum of activities (including against cisplatin-resistant tumors) and selectivity [86–88]. Among the various compounds of ruthenium investigated for their anticancer activity, two are in phase II clinical trials, namely NAMI-A (**Table 2**) as antimetastatic agent and KP1019 (**Table 2**) as antitumor for primary tumor site [89–93].

Both are pseudo-octahedral complexes having four chloride ions in the equatorial plane. The axial ligands are imidazole and DMSO molecules in NAMI-A complex, while for KP1019 are two indazole molecules. Both complexes undergo hydrolysis in aqueous solutions (chloride ions being replaced by water and/or hydroxide ions) and interact with biological reductants leading to ruthenium (II) species. These two processes seem to provide the active species in the body [94–96].

In order to improve the stability inaqueous systems, especially atphysiological pH, and the delivery of drugs to the solid tumors, various drug delivery carriers have been designed and investigated. Two major ways were followed namely chemical conjugation and physical encapsulation [97].

### **4.1. Physical encapsulation of ruthenium-based drugs**

Physical encapsulation is based on the capacity of carriers to retain the drug by physical bonds in a matrix. Different solid nanoparticles were used in order to encapsulate ruthenium complexes [97] such as poly(lactic acid) [98], mesoporous silica nanoparticles [99], or metalorganic frameworks [100]. The promising ruthenium (III) drug KP1019 was co-precipitated with poly(lactic acid) in a single oil-in-water emulsion with two different surfactants [98]. The obtained nanoparticles have an improved cytotoxicity comparing with KP1019.

#### **4.2. Chemical conjugation of ruthenium-based drugs**

#### *4.2.1. Polymer conjugates*

The main idea of this approach is to obtain a polymer, which contains a moiety that can act as ligand for ruthenium. In case of NAMI-A, this moiety can be an imidazole group. Thus, the Stenzel group [101] reports the polymerization of 4-vinil imidazole followed by addition of adequate ruthenium precursor complex. They obtained an amphiphilic co-polymer capable of self-assembly into micelles (**Figure 6**).

The tests on ovarian and pancreatic cancer cells revealed a 1.5 times increased cytotoxicity for polymeric micelles. Furthermore, these were tested for antimetastatic activity on breast cancer cells proving a higher activity comparing to NAMI-A complex.

#### *4.2.2. Lipid base conjutates/liposomes*

The Paduano group focused on developing drug carriers for NANI-A analog, named AZIRu (**Figure 7**) [102–108] and investigating their anticancer activity. Unlike NAMI-A, AZIRu contains a pyridine ligand instead of imidazole and sodium as counterion.

Nanoformulation as a Tool for Improve the Pharmacological Profile of Platinum and Ruthenium Anticancer Drugs http://dx.doi.org/10.5772/intechopen.68306 15

**Figure 6.** NAMI-A conjugated to polymer.

**4. Ruthenium (III)-based drugs nanoformulations**

14 Descriptive Inorganic Chemistry Researches of Metal Compounds

**4.1. Physical encapsulation of ruthenium-based drugs**

**4.2. Chemical conjugation of ruthenium-based drugs**

cells proving a higher activity comparing to NAMI-A complex.

tains a pyridine ligand instead of imidazole and sodium as counterion.

of self-assembly into micelles (**Figure 6**).

*4.2.2. Lipid base conjutates/liposomes*

*4.2.1. Polymer conjugates*

for primary tumor site [89–93].

The studies regarding ruthenium complexes as anticancer agents were developed as an alternative of platinum complexes, especially for their reduced toxicity, large spectrum of activities (including against cisplatin-resistant tumors) and selectivity [86–88]. Among the various compounds of ruthenium investigated for their anticancer activity, two are in phase II clinical trials, namely NAMI-A (**Table 2**) as antimetastatic agent and KP1019 (**Table 2**) as antitumor

Both are pseudo-octahedral complexes having four chloride ions in the equatorial plane. The axial ligands are imidazole and DMSO molecules in NAMI-A complex, while for KP1019 are two indazole molecules. Both complexes undergo hydrolysis in aqueous solutions (chloride ions being replaced by water and/or hydroxide ions) and interact with biological reductants leading to ruthenium (II) species. These two processes seem to provide the active species in the body [94–96]. In order to improve the stability inaqueous systems, especially atphysiological pH, and the delivery of drugs to the solid tumors, various drug delivery carriers have been designed and investigated. Two major ways were followed namely chemical conjugation and physical encapsulation [97].

Physical encapsulation is based on the capacity of carriers to retain the drug by physical bonds in a matrix. Different solid nanoparticles were used in order to encapsulate ruthenium complexes [97] such as poly(lactic acid) [98], mesoporous silica nanoparticles [99], or metalorganic frameworks [100]. The promising ruthenium (III) drug KP1019 was co-precipitated with poly(lactic acid) in a single oil-in-water emulsion with two different surfactants [98]. The

The main idea of this approach is to obtain a polymer, which contains a moiety that can act as ligand for ruthenium. In case of NAMI-A, this moiety can be an imidazole group. Thus, the Stenzel group [101] reports the polymerization of 4-vinil imidazole followed by addition of adequate ruthenium precursor complex. They obtained an amphiphilic co-polymer capable

The tests on ovarian and pancreatic cancer cells revealed a 1.5 times increased cytotoxicity for polymeric micelles. Furthermore, these were tested for antimetastatic activity on breast cancer

The Paduano group focused on developing drug carriers for NANI-A analog, named AZIRu (**Figure 7**) [102–108] and investigating their anticancer activity. Unlike NAMI-A, AZIRu con-

obtained nanoparticles have an improved cytotoxicity comparing with KP1019.

**Figure 7.** AZIRu and selected amphiphilic nucleolipid-based AZIRu.

New amphiphilic derivatives of nucleosides have been developed in order to act as drug carriers for AZIRu complex. In detail, a nucleobase (thymidine or uridine), which was attached with a pyrimidilmethyl group at the N-3 position (in order to act as ligand for ruthenium) was selected as starting material. The resulted compounds were further bonded to one or two lipid residues (oleoyl or cholesteroxyacetyl) and one hydrophilic oligo(ethylene glycol) chain of variable lengths. There were thus obtained amphiphilic supramolecular aggregates, essentially liposomes [102–105].

The nucleolipidic compounds proved to have similar instability in aqueous systems as NAMI-A and AZIRu, forming insoluble precipitates in few hours. In order to reduce the hydrolysis processes, the nucleolipidic compounds were formulated with biocompatible phospholipids, POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) [103–105] and DOTAP (1,2-dioleoyl-3-trimethylammoniumpropane) [106, 107]. The bioactivity of these RuIIIcontaining nucleolipids was tested on human and nonhuman cancer cells proving higher anticancer activity, higher stability in aqueous systems, and lower toxicity than AZIRu [108].

#### *4.2.3. Dendrimers*

The interest in dendrimers as drug carriers comes from their characteristics namely highly branched three-dimensional molecules containing functional groups at periphery, which can react with drug molecules. So far, only one potential anticancer ruthenium (III) drug, RAPTA-C, was incorporated into dendrimer (**Figure 8**) [109], but there is no study regarding the anticancer activity.

Interactions of ruthenium (II) complexes with dendrimers and the anticancer activity of the resulted compounds, which are described in some reviews, have also attracted much interest [110, 111].

**Figure 8.** Ruthenium (III) drug RAPTA-C and its dendrimeric nanoformulation.
