Mechanistic insights from simulations of drug-drug conjugate nanoclusters for co-delivery across cancer cell membranes.

Amphiphilic drug-drug conjugates (ADDCs) such as gemcitabine-camptothecin (GEM-CPT) and doxorubicin-10-hydroxycamptothecin (DOX-HCPT) nanoclusters offer innovative solutions to overcome the limitations of conventional cancer therapies, including poor solubility and nonspecific targeting. Using molecular dynamics (MD) simulations, we explored the mechanisms by which these nanoclusters interact with and penetrate cancer and normal cell membranes. GEM-CPT exhibited enhanced membrane penetration in cancer cells through combined hydrophilic and hydrophobic interactions, along with its ability to extract cholesterol and induce membrane remodelling. In contrast, DOX-HCPT maintained structural integrity through stable π-π stacking interactions, showing selective binding to membrane head groups (HG) with minimal cholesterol interaction, particularly in normal membranes. The GEM-CPT nanocluster disrupted the cancer membrane by inducing asymmetric lipid distribution and facilitating water infiltration, whereas the hydrophobic DOX-HCPT repelled water, maintaining membrane stability. The size of the nanocluster further influenced the behaviour; larger clusters drove steric assembly and lipid reorganisation, while smaller clusters achieved deeper penetration at the cost of structural integrity. The contrasting behaviours of GEM-CPT and DOX-HCPT highlight the critical roles of size, charge, and amphiphilicity in membrane transport mechanisms. These findings provide valuable insights into the design of efficient and selective nanomedicines, paving the way for optimised drug delivery systems with reduced off-target effects.