Carbon nanotubes (CNTs) have emerged as promising drug delivery systems particularly for cancer therapy, due to their abilities to overcome some of the challenges faced by cancer treatment, namely non-specificity, poor permeability into tumour tissues, and poor stability of anticancer drugs. Encapsulation of anticancer agents inside CNTs provides protection from external deactivating agents. However, the open ends of the CNTs leave the encapsulated drugs exposed to the environment and eventually their uncontrolled release before reaching the desired target. In this study, we report the successful encapsulation of cisplatin, a FDA-approved chemotherapeutic drug, into multi-walled carbon nanotubes and the capping at the ends with functionalised gold nanoparticles to achieve a “carbon nanotube bottle” structure. In this proof-of-concept study, these caps did not prevent the encapsulation of drug in the inner space of CNTs; on the contrary, we achieved higher drug loading inside the nanotubes in comparison with data reported in literature. In addition, we demonstrated that encapsulated cisplatin could be delivered in living cells under physiological conditions to exert its pharmacological action.

Platinum-based anticancer drugs constitute some of most effective chemotherapeutic regimes, but they are limited by high toxicities and severe side-effects arising from premature aquation and non-specific interactions. Macromolecular delivery agents can be used to shield platinum drugs from adventitious binding and as a platform to attach targeting groups, as a strategy to mitigate some of these limitations. An approach was conceived to utilise carbon nanotubes as a protective shell for stable platinum(IV) prodrugs entrapped within its inner cavities. An inert and strongly hydrophobic platinum(IV) complex was designed for entrapment within multiwalled carbon nanotubes via hydrophobic-hydrophobic interactions. Upon chemical reduction, the drug was converted to its cytotoxic and hydrophilic form and released from the carrier, via a drastic reversal in hydrophobicity, for DNA-binding. This simple method of hydrophobic entrapment and controlled release by chemical reduction and hydrophobicity reversal, exploiting the Pt(IV) scaffold as a prodrug, could form the basis of other delivery strategies for targeted delivery of platinum drugs into cancer cells.

A hydrophobic platinum(iv) prodrug was entrapped in tumour-targeting multiwalled carbon nanotubes for synchronous and ratiometric delivery of drug combinations.

Platinum(IV) bis-carboxylates are highly versatile prodrug scaffolds with different axial ligands that can be functionalized while keeping the platinum(II) pharmacophore intact. Using a sequential acylation strategy, we developed a class of Pt prodrugs of cisplatin with contrasting lipophilic and hydrophilic ligands. We investigated their stability, reduction rates, lipophilicity, aqueous solubility, and antiproliferative efficacies, and assessed for correlations among the parameters that could be useful in drug design. We showed that compounds with high lipophilicity result in better antiproliferative effects in vitro and in vivo, with one of the three compounds tested showing better efficacy than satraplatin against an animal model of colorectal cancer, owing to its higher solubility and lower reduction rates. Our asymmetric Pt prodrugs may pave the way for a highly predictable, fine-tuned class of orally available Pt prodrugs for the treatment of colorectal cancer.

Watching closely: A fluorescent probe was engineered to detect the clinically relevant platinum drug cisplatin within a complex cellular environment, thus providing a direct means for visualizing its cell entry and the activation of platinum(IV) prodrugs in cancer cells.