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to enhance efficacy and reduce toxicity, i.e., to increase the
therapeutic index of anticancer drugs, would have a significant
impact on facilitating the optimal use of chemotherapy and serving
as an important driver in improving clinical outcomes [2, 3]. A
large pool of bioactive compounds and approved drugs has evolved
from multiple medicinal chemistry projects in the pharma industry
and academia. Supramolecular chemistry has served as a useful tool
in biomedical applications [4, 5]. Due to their unique properties,
supramolecules can be used as alternative drug carriers, based on
their ability to encapsulate small drugs in their cavity. The encapsulation of small molecules into the cavity is the result of noncovalent
interactions, such as van der Waals interaction, hydrogen bonding,
and hydrophobic interactions. According to recent literature, macromolecules such as cucurbit[n]urils, cyclodextrins, calix[n]arenes,
and their derivatives have drawn the attention of the scientific community, since they can surpass problems that current cytotoxic
agents present [6, 7].
Recently, our group developed a new formulation that demonstrated enhanced activity against glioblastoma (GBM), the most
common and aggressive primary brain tumor in adults, by encapsulation of temozolomide (TMZ) into a supramolecular host [8].
TMZ is an alkylating agent used as first-line chemotherapy for
GBM [9, 10]. However, under slightly alkaline conditions it is rapidly hydrolyzed to MTIC, which in turn rapidly degrades to the
methyl diazonium cation and the metabolite 5-amino-imidazole4-carboxamide (AIC), resulting in reduced passage across the BBB
and therefore reduced clinical efficacy [11, 12] (Fig. 1). Hence,
high doses of TMZ are administrated to achieve therapeutic concentrations in the central nervous system (CNS), resulting in
numerous side effects including myelosuppression.
To abrogate these issues, we used p-sulfonatocalix[4]arene
(PSC4) nanocapsule as host. PSC4 contains a hydrophilic external
surface and a hydrophobic cavity that can entrap small drugs inside.
PSC4 has been widely used as host due to its high aqueous solubility and low toxicity [13, 14]. The encapsulation of TMZ in PSC4
greatly improved the stability of TMZ and its efficacy against GBM
in vitro and in vivo (Scheme 1).
Here, we summarize the principles that influence the development of new formulations and, in particular, the encapsulation of
small molecules into PSC4. We describe the protocols that have
been developed for the determination of the encapsulated drug
and the stability of the complex. After the synthesis of the formulate, LC-MS/MS plasma stability assays were conducted in mice to
further explore the stability profile of TMZ@PSC4 in vivo. Finally,
the cytotoxicity of the analog was evaluated in vitro in patientderived primary lines that express MGMT and are normally highly
resistant to TMZ and in a mouse orthotopic model.
Antonis D. Tsiailanis et al.
to enhance efficacy and reduce toxicity, i.e., to increase the
therapeutic index of anticancer drugs, would have a significant
impact on facilitating the optimal use of chemotherapy and serving
as an important driver in improving clinical outcomes [2, 3]. A
large pool of bioactive compounds and approved drugs has evolved
from multiple medicinal chemistry projects in the pharma industry
and academia. Supramolecular chemistry has served as a useful tool
in biomedical applications [4, 5]. Due to their unique properties,
supramolecules can be used as alternative drug carriers, based on
their ability to encapsulate small drugs in their cavity. The encapsulation of small molecules into the cavity is the result of noncovalent
interactions, such as van der Waals interaction, hydrogen bonding,
and hydrophobic interactions. According to recent literature, macromolecules such as cucurbit[n]urils, cyclodextrins, calix[n]arenes,
and their derivatives have drawn the attention of the scientific community, since they can surpass problems that current cytotoxic
agents present [6, 7].
Recently, our group developed a new formulation that demonstrated enhanced activity against glioblastoma (GBM), the most
common and aggressive primary brain tumor in adults, by encapsulation of temozolomide (TMZ) into a supramolecular host [8].
TMZ is an alkylating agent used as first-line chemotherapy for
GBM [9, 10]. However, under slightly alkaline conditions it is rapidly hydrolyzed to MTIC, which in turn rapidly degrades to the
methyl diazonium cation and the metabolite 5-amino-imidazole4-carboxamide (AIC), resulting in reduced passage across the BBB
and therefore reduced clinical efficacy [11, 12] (Fig. 1). Hence,
high doses of TMZ are administrated to achieve therapeutic concentrations in the central nervous system (CNS), resulting in
numerous side effects including myelosuppression.
To abrogate these issues, we used p-sulfonatocalix[4]arene
(PSC4) nanocapsule as host. PSC4 contains a hydrophilic external
surface and a hydrophobic cavity that can entrap small drugs inside.
PSC4 has been widely used as host due to its high aqueous solubility and low toxicity [13, 14]. The encapsulation of TMZ in PSC4
greatly improved the stability of TMZ and its efficacy against GBM
in vitro and in vivo (Scheme 1).
Here, we summarize the principles that influence the development of new formulations and, in particular, the encapsulation of
small molecules into PSC4. We describe the protocols that have
been developed for the determination of the encapsulated drug
and the stability of the complex. After the synthesis of the formulate, LC-MS/MS plasma stability assays were conducted in mice to
further explore the stability profile of TMZ@PSC4 in vivo. Finally,
the cytotoxicity of the analog was evaluated in vitro in patientderived primary lines that express MGMT and are normally highly
resistant to TMZ and in a mouse orthotopic model.
Antonis D. Tsiailanis et al.