Protein Kinase C Delta Peptide Activator provides protection during hypoxia/reoxygenation and elicits significant anti-cancer effects in vitro

Introduction

Protein kinase C delta (PKCδ) activation is known to inhibit NOX-2/superoxide (SO) release in polymorphonuclear leukocytes (PMNs) and elicit cardioprotective effects in ischemia-reperfusion (I/R) injury. Augmenting PKCδ activity also promotes tumor suppressive effects via apoptosis. This study examined the cardioprotective and anticancer effects of PKCδ peptide activator (PKCδ+) in endothelial cells and cardiomyocytes, cardiovascular cells particularly susceptible to oxidative damage due to their high concentration of mitochondria.

Methods

Hypoxia/Reoxygenation: Human umbilical vein endothelial cells (HUVECs) and rat cardiomyocytes (H9C2 cells), were cultured at 37°C in EBM-2 medium and DMEM, respectively and pretreated with PKCδ+ (Myr+MRAAEDPM) (0.25-5μM) or untreated control for 37 mins, prior to hypoxia (24hr) and reoxygenation(24hr).

Anti-Cancer: Human breast cancer (MCF7) cells were cultured in RPMI buffer at 37°C and treated with PKCδ+ (0.5-20μM) or untreated control for 37 mins.

Cell viability was assessed by light microscopy and spectrophotometric analysis using a cell counting kit for both experimental groups.. Absorbance data were analyzed using student t-test.

Results

Pretreatment with PKCδ+ (0.25-4μM) improved H9C2 and HUVECs cell viability, with significant improvement of HUVEC viability (1μM, 0.4±0.03; n=5, p< 0.05) vs control (0.26.±0.04, n=5). PKCδ+ dose-dependently promoted MCF7 cell death up to 20μM 0.33±0.03; n=5, p< 0.05 compared to controls (0.49±0.02, n=5).

Conclusions

Lower doses of PKCδ+ provide cardioprotection during hypoxia reoxygenation, while higher doses are more effective at providing anti-cancer effects. Optimizing dosing for tumor suppression and I/R tissue preservation could make PKCδ+ an attractive clinical drug in cases where organ ischemia must be induced temporarily for surgical resection of malignancy.

Discussion

Future studies include dosing optimization and ex-vivo rat tissue I/R studies. Additionally, PKCδ+ may provide cardioprotection in patients undergoing chemotherapy with Doxorubicin (DOX), a cardiotoxic drug that exerts its toxic effects via production of reactive oxygen species (ROS) through various mechanisms. Reducing the cardiotoxic effects of DOX would make its use more effective and desirable in cancer treatment, as it is a potent antineoplastic agent, but its use is currently limited due to its cardiotoxic side effects. Since PKCδ+ also exerts anti-cancer effects, combination with DOX is a promising chemotherapeutic regimen if PKCδ+ can help mitigate DOX-induced cardiotoxicity.