PD-L1 and MRN synergy in platinum-based chemoresistance of head and neck squamous cell carcinoma.

BACKGROUND: We have been investigating the molecular mechanisms of cisplatin-induced chemoresistance in head and neck squamous cell carcinoma (HNSCC). Based on our previous findings, the present study investigates how the Mre11, Rad50, and NBS1 (MRN) DNA repair complex interacts at the molecular level with the programmed cell death ligand 1 (PD-L1) in cisplatin-induced chemoresistance. METHODS: Human HNSCC cell lines were used to determine the role played by PD-L1 in cisplatin resistance. Initial experiments investigated PD-L1 expression levels in cells exposed to cisplatin and whether PD-L1 interacts directly with the MRN complex. Finally, in vitro studies and in vivo experiments on BALB/c nu/nu mice were performed to determine whether interference of PD-L1 or NBS1 synthesis modulated cisplatin resistance. RESULTS: Exposure to cisplatin resulted in PD-L1 being upregulated in the chemoresistant but not the chemosensitive cell line. Subsequent co-immunoprecipitation studies demonstrated that PD-L1 associates with NBS1. In addition, we found that the knockdown of either PD-L1 or NBS1 re-sensitised the chemoresistant cell line to cisplatin. Finally, but perhaps most importantly, synergy was observed when both PD-L1 and NBS1 were knocked down making the formerly chemoresistant strain highly cisplatin sensitive. CONCLUSIONS: PD-L1 plays a pivotal role in cisplatin resistance in chemoresistant human HNSCC cell lines.

Challenges and opportunities in developing targeted molecular imaging to determine inner ear defects of sensorineural hearing loss.

The development of inner ear gene carriers and delivery systems has enabled genetic defects to be repaired and hearing to be restored in mouse models. Today, promising advances in translational therapies provide confidence that targeted molecular therapy for inner ear diseases will be developed. Unfortunately, the currently available non-invasive modalities, such as Computerized Tomography scan or Magnetic Resonance Imaging provide insufficient resolution to identify most pathologies of the human inner ear, even when the current generation of contrast agents is utilized. The development of targeted contrast agents may play a critical role in determining the cause of, and treatment for, sensorineural hearing loss. Such agents should be able to pass through the cochlea barriers, possess minimal cytotoxicity, and easily conjugate to a targeting agent, without distorting the anatomic details. This review focuses on a series of contrast agents which may fit these criteria for potential clinical application.

C-terminal sequences of hsp70 and hsp90 as non-specific anchors for tetratricopeptide repeat (TPR) proteins.

Steroid-hormone-receptor maturation is a multi-step process that involves several TPR (tetratricopeptide repeat) proteins that bind to the maturation complex via the C-termini of hsp70 (heat-shock protein 70) and hsp90 (heat-shock protein 90). We produced a random T7 peptide library to investigate the roles played by the C-termini of the two heat-shock proteins in the TPR-hsp interactions. Surprisingly, phages with the MEEVD sequence, found at the C-terminus of hsp90, were not recovered from our biopanning experiments. However, two groups of phages were isolated that bound relatively tightly to HsPP5 (Homo sapiens protein phosphatase 5) TPR. Multiple copies of phages with a C-terminal sequence of LFG were isolated. These phages bound specifically to the TPR domain of HsPP5, although mutation studies produced no evidence that they bound to the domain's hsp90-binding groove. However, the most abundant family obtained in the initial screen had an aspartate residue at the C-terminus. Two members of this family with a C-terminal sequence of VD appeared to bind with approximately the same affinity as the hsp90 C-12 control. A second generation pseudo-random phage library produced a large number of phages with an LD C-terminus. These sequences acted as hsp70 analogues and had relatively low affinities for hsp90-specific TPR domains. Unfortunately, we failed to identify residues near hsp90's C-terminus that impart binding specificity to individual hsp90-TPR interactions. The results suggest that the C-terminal sequences of hsp70 and hsp90 act primarily as non-specific anchors for TPR proteins.

The Development of a Nano-based Approach to Alleviate Cisplatin-Induced Ototoxicity.

Cisplatin-induced hearing loss is experienced by a high percentage of patients with squamous cell carcinoma undergoing cisplatin chemotherapy. A novel nano-construct capable of sequestering extracellular cisplatin was developed to combat this problem. The nano-construct consisted of superparamagnetic iron oxide nanoparticles (SPIONs) entrapped within polymeric micelles, which were formed from a glutathione diethyl ester-conjugated amphiphilic diblock copolymer. The glutathione-micelles were analyzed at the cellular level and in an organotypic study for safety evaluation. All utilized methods indicated that the micelles do not cause cellular toxicity or organ damage. The micelles' ability to reduce cisplatin-induced cytotoxicity was then probed in an in vitro model. Cisplatin was pre-treated with the novel nano-construct before being added to growing cells. When compared to cells that were exposed to untreated cisplatin, cells in the pre-treated cisplatin group showed a significant increase in cell viability. This clearly demonstrates that the construct is able to protect the cells from cisplatin cytotoxicity and makes it highly likely that the novel nano-construct will be able to play a role in the protection of the inner ear from cisplatin-induced ototoxicity.

A novel nanoparticle delivery system for targeted therapy of noise-induced hearing loss.

Hearing loss is the most prevalent sensory disability worldwide and may be caused by age, drugs or exposure to excessive noise. We have previously developed a minimally-invasive nanohydrogel drug delivery system that successfully delivers nanoparticles into the inner ear. We have substantially extended this technique by functionalizing the nanoparticles and introducing a targeting peptide which recognizes prestin, a transmembrane electromotile protein uniquely expressed in outer hair cells (OHCs) of the inner ear. We demonstrate the successful delivery of molecules and plasmids specifically to OHCs. When compared to untargeted nanoparticles, the delivery of a c-Jun N-terminal kinase (JNK) inhibitor, D-JNKi-1, to OHCs by targeted nanoparticles improved protection from noise induced hearing loss (NIHL). This is the first demonstration of a protection from NIHL using a novel safe and controllable delivery system which is minimally-invasive to the inner ear and, as such, is an extremely appealing technique for use in many clinical applications.

Identification of potential physiological activators of protein phosphatase 5.

The protein serine/threonine phosphatase designated PP5 has little basal activity, and physiological activators of the enzyme have never been identified. Purified PP5 can, however, be activated by partial proteolysis or by the binding of supraphysiological concentrations of polyunsaturated long-chain fatty acids to its tetratricopeptide repeat (TPR) domain. To test whether activation of PP5 by polyunsaturated but not saturated fatty acids was an artifact of the lower solubility of saturated fatty acids, the effects of fatty acyl-CoA esters were examined. Saturated and unsaturated long-chain fatty acids are both freely water-soluble when esterified to CoA. Long-chain fatty acyl-CoA esters activated PP5 at physiological concentrations, with the saturated compounds being more effective. We investigated the effects of chain length and of the CoA moiety on PP5 activation. Chains of 16 carbons or more were required for optimal activation, with no activation observed below 10 carbons. On the basis of competition studies using acetyl-CoA, the function of the CoA moiety appeared to be to increase solubility of the fatty acyl moiety rather than to interact with a specific binding site. These data suggested that long-chain fatty acid-CoA esters might be physiological activators of PP5 and point to a potential link between fatty acid metabolism and signal transduction via this enzyme. Because heat shock protein 90 is also known to bind to the TPR domain of PP5 via its C-terminal domain (C90), we investigated its effect on PP5 activity. C90 activated the enzyme approximately 10-fold. Thus, we have identified two potential physiological activators of PP5.