| Existing therapies for the treatment of breast and pancreatic cancers usually consist of a combination of chemotherapy, surgery, and/or radiation therapy. The limitations of this type of treatment are abundant. The majority of chemotherapeutic agents used in clinics are highly toxic to both tumor cells and normal tissues due to the lack of specificity. Resistance can develop due to over-exposure of these agents. To address these issues, these agents must be made more exclusive toward the tumor site. This can be achieved by developing drugs that are toxic only to tumor cells or by developing carriers that allow the drug to be targeted to the tumor site, thereby reducing both systemic accumulation and, as a result, unwanted side effects. To achieve this goal, this work describes the development of Elastin-like Polypeptide (ELP) as a thermally responsive biopolymeric carrier to accomplish the delivery of two small molecule drugs—doxorubicin and N-butyldiacetate doxorubicin—and the therapeutic peptide p21 that inhibits the cell cycle. ELP is a macromolecule that remains soluble when injected systemically but will undergo a phase transition and accumulate in a specific site in the presence of hyperthermia. This property of ELP can be exploited for thermal targeting in the treatment of solid tumors by fusing a therapeutic to ELP to enhance the efficacy while reducing systemic toxicity. In this study, ELP was modified by the addition of a cell-penetrating peptide (CPP) to facilitate entry into the cell, increasing ELP's intracellular uptake and either maleimide derivatives of doxorubicin or the cell cycle inhibitory peptide p21. A CPP increased the association of ELP with the cell membrane by at least 1.5-fold more than without a CPP. In fluorescent imaging studies, Dox was seen in the nucleus similarly to free Dox. When SynB1-ELP-DOX0 was used in an animal model of breast cancer, SynB1-ELP-DOXO, in combination with hyperthermia, reduced tumor size significantly more than free dox in the presence or absence of heat. Using a highly potent Dox derivative (NBD), SynB1-ELP + ELP-NBD was ∼1000x more toxic to the cells than the parent compound Dox and overcame multi-drug resistance better than free NBD. Additionally, the maximum tolerated dose in the animals was 250 nmol/kg with SynB1-ELP + ELP-NBD compared to 600 nmol/kg of free NBD, a 2.4-fold difference. When comparing p21-ELP-Bac and ELP-p21, 1.6-fold more p21-ELP-Bac accumulated in the heated tumor compared to other groups two hours after injection; this accumulation was still noticeable 48 h after injection (1.3-fold). These studies validate the usefulness of a CPP in order to translocate ELP across the cellular membrane. Furthermore, these studies prove that ELP in combination with hyperthermia provides a new alternative for the treatment of solid tumors. |
