UC Santa Barbara

Potent chemotherapy combinations identified and optimized in vitro often fail in clinic because the current paradigm aims to deliver drugs at or near their maximum tolerated doses (MTD), elevating the risk of treatment related toxicity in patients. Further, it does not achieve optimum relative drug concentrations, required to maximize the therapeutic impact of a combination, at the tumor site. Thus, combination chemotherapy regimens must be designed to adequately strike the difficult balance between safety and efficacy. In the first part of this dissertation, two chemotherapeutic drugs, doxorubicin (DOX) and camptothecin (CPT), whose potency can be tuned by combining them in different molar ratios, are investigated as a treatment option against triple negative breast cancer (TNBC). Albeit causing toxicity to control breast epithelial cells in vitro, the optimized combination inhibited the disease progression in an aggressive orthotopic human TNBC mouse tumor model at very low drug doses of DOX (2mg/kg/dose) and CPT (1.4 mg/kg/dose).

Targeted delivery of these non-specific yet potent compounds was envisaged to further enhance clinical outcomes by improving cancer specificity. Since aptamers offer excellent advantages over other molecular targeting agents, an aptamer capable of specifically recognizing an overexpressed TNBC marker was explored and found to be suitable for this application. To amalgamate anti-cancer potency with cancer specificity, a modular framework for the aptamer-targeted delivery of drug combinations at synergistic molar ratios is described in the next part. Specifically, a nucleolin targeting aptamer was coupled to peptide scaffolds laden with DOX and CPT at precisely defined molar ratios. Ap-DOCTOR (Aptamer-targeted DOX and CPT in Therapeutically Optimal Ratios) exhibited an extremely low IC50 value of 31.9 nM specifically against TNBC cells in vitro. This value is 15-fold lower than the IC50 of DOX alone, and 7-fold lower than the IC50 of CPT alone. In vivo, Ap-DOCTOR outperformed cocktails comprising equivalent doses of unconjugated DOX and CPT, exhibiting efficacy at micro-dose injections (500 μg/kg/dose) of DOX and (350 μg/kg/dose) CPT. These doses are respectively 8-fold and 21-fold lower than those required with DOX or CPT individually to induce measurable anti-tumor effects, and a further, 20–30-fold lower than the reported MTD values of these drugs. The approach outlined in this dissertation represents a generalizable strategy for the safe and consistent delivery of empirically defined optimal molar ratios for a diverse set of combination drugs in oncology. Ultimately, this could enable treatment at doses much lower than MTDs and facilitate effective translation of anticancer chemotherapeutic combinations into the clinic.