Efficient Prostate Cancer Therapy with Tissue-Specific Homing Peptides Identified by Advanced Phage Display Technology

Abstract

Selective targeting of drugs to tumor cells is a key goal in oncology. Here, we performed an in vivo phage display to identify peptides that specifically target xenografted prostate cancer cells. This yielded three peptide candidates, LN1 (C-TGTPARQ-C), LN2 (C-KNSMFAT-C), and LN3 (C-TNKHSPK-C); each of these peptides was synthesized and evaluated for binding and biological activity. LN1 showed the highest avidity for LNCaP prostate cancer cells in vitro and was thus administered to tumor-bearing mice to evaluate in vivo binding. Strikingly, LN1 specifically bound to the tumor tissue and exhibited very low reactivity with normal liver and kidney tissues. To demonstrate that LN1 could specifically deliver drugs to prostate cancer tissue, a therapeutic peptide, LN1-KLA (C-TGTPARQ-C-GGG-D[KLAKLAK]2), was prepared and used to treat LNCaP cells in vitro and was also administered to tumor-bearing mice. The therapeutic peptide significantly suppressed growth of the cells both in vitro and in vivo. Our study shows that a selective homing peptide strategy could facilitate cell-specific targeting of therapeutics while avoiding adverse reactions in normal tissues.

Phage Display to Augment Biomaterial Function

“…Peptides can be directly conjugated to the drug in cases where conjugation would not affect the drug’s activity and protection of the drug is not required. For instance, poor prognosis is associated with prostate cancer when the cancer is resistant to castration and/or when it metastasizes, but, at this point, treatment often needs to be halted due to poor systemic effects of currently available drugs [ 9 ]. One group used in vivo phage display to discover a peptide, C-TGTPARQ-C (LN1), with high affinity and selectivity for prostate cancer tissue [ 9 ].…”

“…Advancement in technology has allowed for the use of in vivo phage display for the identification of peptides with higher selectivity for a specific tissue type. For example, one group sought to increase selectivity for xenografts of human prostate cancer in mice by performing multiple rounds of negative selection prior to in vivo phage display for a prostate cancer tissue homing peptide [ 9 ]. In each of three rounds of negative selection in mice and one subsequent round of negative selection in cynomolgus monkeys, the phage library was injected into the bloodstream and non-bound phages were harvested and identified [ 9 ].…”

“…For example, one group sought to increase selectivity for xenografts of human prostate cancer in mice by performing multiple rounds of negative selection prior to in vivo phage display for a prostate cancer tissue homing peptide [ 9 ]. In each of three rounds of negative selection in mice and one subsequent round of negative selection in cynomolgus monkeys, the phage library was injected into the bloodstream and non-bound phages were harvested and identified [ 9 ]. This step eliminated phages with known in vivo targets from the library, so that in vivo phage display could be used to identify highly selective prostate cancer tissue homing peptides [ 9 ].…”

“…In each of three rounds of negative selection in mice and one subsequent round of negative selection in cynomolgus monkeys, the phage library was injected into the bloodstream and non-bound phages were harvested and identified [ 9 ]. This step eliminated phages with known in vivo targets from the library, so that in vivo phage display could be used to identify highly selective prostate cancer tissue homing peptides [ 9 ].…”

Evolving a Peptide: Library Platforms and Diversification Strategies

“…In addition to in vitro or ex vivo (e.g., against isolated cells), phage library selections can also be performed in vivo. The latter approach is used to identify tissue homing peptides for cell-specific targeting of therapeutics [77]. In contrast to phage library pannings to purified targets, selections against intact cells and in vivo screens are inherently more complicated as the library is exposed to many potential decoys, leading to high background [63].…”