UCSF

Synergistic anti-cancer drug combinations have superior tumor-killing activity, the potential to reduce drug toxicity to healthy tissues, and the ability to minimize the development of drug resistance. Since drug synergism is dependent on the ratio of the combined drugs, synergistic agents must be maintained at fixed ratios to achieve the maximum therapeutic effect in vivo. We hypothesize that targeted liposomes can enhance the efficacy of synergistic anti-cancer drug combinations in vivo by facilitating the intracellular delivery of both drugs at their synergistic ratio and dose. To test this hypothesis, select combinations of anti-cancer drugs were screened in vitro for synergism in KB folate receptor over-expressing cancer cells. The combination activity of drug pairs was evaluated with the median effect method. Irinotecan (IRN) and 5-fluoroorotic acid (FOA) emerged as the most synergistic pair in the screen since they exhibited synergism at a wide range of concentrations and molar ratios. Investigating my hypothesis required that I devise and validate new encapsulation techniques for liposome formulations of IRN, FOA, and the combination of IRN + FOA. Safety studies with the single agents in non-targeted liposomes (NTLs) were conducted in normal mice to identify the maximum tolerated dose. Therapeutic studies in HT29 and C26 tumor mouse models confirmed that the new NTL formulations had anti-cancer potency. We designed folate-targeted liposomes (FTLs) that target the folate receptors on KB tumor cells in vitro and in vivo when as little as 0.03 mol% of the synthesized folate ligand was displayed on the liposome surface. Biodistribution and anti-tumor studies in the KB model with liposome encapsulated doxorubicin confirmed that FTLs deliver chemotherapeutics to the tumor and have anti-tumor activity. The anti-tumor efficacy of IRN + FOA co-delivered in the same FTLs or in a mixture of FTLs was compared to their NTL counterparts in the KB model. Liposomes significantly enhanced the in vivo efficacy of the synergistic combinations. However, folate-targeted liposomes with IRN + FOA did not provide a statistically significant therapeutic advantage over co-delivery of this synergistic pair in non-targeted liposomes.