(476b) Aptamer-Peptide-Drug Conjugates: Delivery of Precise Synergistic Drug Ratios for Enhanced Cancer Selectivity

Multi-drug regimens, a widely used treatment method for several cancers, are synergistic only at certain ratios and tumor drug accumulation at these precise ratios is necessary for dose reduction. More importantly, it has been shown that, drug ratios can be selected by empirical testing to induce synergy specifically on the cancer cell line of interest while having an antagonistic effect on non-cancerous cell lines. By employing this strategy, current limitation with combination chemotherapy, of administering highly toxic doses, can potentially be remedied. However, distinct transport and distribution properties of chemically diverse small molecule drugs makes it a non-trivial challenge to deliver them at the desired ratios to tumors. We have developed a novel Aptamer-Peptide Drug conjugate (APDC) platform, in order to deliver drug combinations in precise ratios specifically to cancer cells while avoiding healthy cells. This platform enables the unification of the biodistribution and pharmacokinetic properties of drug combinations and simultaneously allows delivery of an exact synergistic molar drug ratio in a highly preferential fashion to cancer cells via aptamer targeting. Aptamers offer a wide range of clinical advantages over targeting antibodies such as non-immunogenicity, higher tissue penetration and potential to target a wider range of cancer markers. Additionally, superior thermal and chemical stability over antibodies and faster synthesis time makes their industrial scale production quite cost-effective.

To promote cancer specific uptake of our APDCs, we employ a well known aptamer AS1411 that targets overexpressed cell surface nucleolin on several types of cancer. Specifically, we chose a triple negative human metastatic breast cancer cell line, MDA-MB-231, that overexpresses cell surface nucleolin and has an intermediate response to chemotherapy. To make APDCs, chemotherapeutic drugs doxorubicin (DOX) and camptothecin (CPT), a previously employed combination for aggressive metastatic breast cancer, were loaded in a controlled covalent fashion to the aptamer using peptide scaffolds. Subsequent testing revealed that our APDCs are highly selective to nucleolin overexpressing breast cancer cells compared to a control epithelial cell line, MCF 10A. Systematic invitro evaluation of several drug combinations revealed a molar ratio dependent synergy, and drug ratios, 0.25 ≤ R ≤1 (R - CPT/DOX) were found to be significantly synergistic over others. Futhermore, certain molar ratios amongst these were found to be more effective at killing MDA-MB-231 cells compared to MCF-10A cells. Finally, we demonstrated that by delivering these synergistic molar ratios in a targeted fashion via APDCs, significant enhancement in toxicity exclusive to MDA-MB-231 cells can be obtained. These results reinforce the importance of delivering precise drug combination ratios in a targeted fashion to cancer cells so as to exploit the full potential of synergistic interactions of specific drug ratios in the tissue of interest.