Targeting DNA repair with PNKP inhibition sensitizes radioresistant prostate cancer cells to high LET radiation

Abstract

High linear energy transfer (LET) radiation or heavy ion such as carbon ion radiation is used as a method for advanced radiotherapy in the treatment of cancer. It has many advantages over the conventional photon based radiotherapy using Co-60 gamma or high energy X-rays from a Linear Accelerator. However, charged particle therapy is very costly. One way to reduce the cost as well as irradiation effects on normal cells is to reduce the dose of radiation by enhancing the radiation sensitivity through the use of a radiomodulator. PNKP (polynucleotide kinase/phosphatase) is an enzyme which plays important role in the non-homologous end joining (NHEJ) DNA repair pathway. It is expected that inhibition of PNKP activity may enhance the efficacy of the charged particle irradiation in the radioresistant prostate cancer cell line PC-3. To test this hypothesis, we investigated cellular radiosensitivity by clonogenic cell survival assay in PC-3 cells.12Carbon ion beam of62 MeVenergy (equivalent 5.16 MeV/nucleon) and with an entrance LET of 287 kev/μm was used for the present study. Apoptotic parameters such as nuclear fragmentation and caspase-3 activity were measured by DAPI staining, nuclear ladder assay and colorimetric caspase-3method. Cell cycle arrest was determined by FACS analysis. Cell death was enhanced when carbon ion irradiation is combined with PNKPi (PNKP inhibitor) to treat cells as compared to that seen for PNKPi untreated cells. A low concentration (10μM) of PNKPi effectively radiosensitized the PC-3 cells in terms of reduction of dose in achieving the same survival fraction. PC-3 cells underwent significant apoptosis and cell cycle arrest too was enhanced at G2/M phase when carbon ion irradiation was combined with PNKPi treatment. Our findings suggest that combined treatment of carbon ion irradiation and PNKP inhibition could enhance cellular radiosensitivity in a radioresistant prostate cancer cell line PC-3. The synergistic effect of PNKPi and carbon ion irradiation could be used as a promising method for carbon-ion therapy in radioresistant cells.

SMC1A is associated with radioresistance in prostate cancer and acts by regulating epithelial‐mesenchymal transition and cancer stem‐like properties

“…Radiation therapy remains an important modality for primary as well as locally advanced prostate cancer patients . However, radio‐resistance and relapse/recurrence of tumor remains a major clinical challenge . Therefore, it is critical to identify tumor‐specific targets and explore their linked signaling pathways associated with radioresistance.…”

“…Radiation therapy remains an important modality for primary as well as locally advanced prostate cancer patients. [7][8][9][10][11][12][13] However, radioresistance and relapse/recurrence of tumor remains a major clinical [8][9][10] Therefore, it is critical to identify tumor-specific targets and explore their linked signaling pathways associated with radioresistance. Emerging evidence suggests that aberrant activation of DNA-damage repair (DDR) signaling pathways play important roles in prostate cancer metastasis and progression and are involved in radio-resistance.…”

“…While localized prostate cancer can be controlled with surgery and hormonal therapy, the metastatic, castration‐resistant (mCRPC) disease remains a major treatment challenge . Currently available treatment options include administration of androgen receptor inhibitor (enzalutamide, abiraterone), cell cycle disruption (docetaxel, cabazitaxel), immune checkpoint‐related therapy (sipuleucel‐T), targeting of bone metastasis (radium‐223), and radiotherapy . Radiation therapy (RT) is widely considered a standard care treatment for primary and metastatic prostate cancer and is associated with high cancer control rates, although up to one‐third of patients receiving this therapy becomes radio‐resistant or manifest tumor‐recurrence .…”

“…2,3 Currently available treatment options include administration of androgen receptor inhibitor (enzalutamide, abiraterone), cell cycle disruption (docetaxel, cabazitaxel), immune checkpoint-related therapy (sipuleucel-T), targeting of bone metastasis (radium-223), and radiotherapy. [4][5][6][7][8] Radiation therapy (RT) is widely considered a standard care treatment for primary and metastatic prostate cancer and is associated with high cancer control rates, although up to onethird of patients receiving this therapy becomes radio-resistant or manifest tumor-recurrence. [8][9][10] Radiotherapy kills the cancer cells directly by causing DNA damage, but radiation also causes the generation of reactive oxygen species (ROS) which are indirectly involved in DNA damage.…”

“…[4][5][6][7][8] Radiation therapy (RT) is widely considered a standard care treatment for primary and metastatic prostate cancer and is associated with high cancer control rates, although up to onethird of patients receiving this therapy becomes radio-resistant or manifest tumor-recurrence. [8][9][10] Radiotherapy kills the cancer cells directly by causing DNA damage, but radiation also causes the generation of reactive oxygen species (ROS) which are indirectly involved in DNA damage. [11][12][13] Moreover, RT promotes metastasis and invasion of cancer cells and is involved in epithelial-mesenchymal transition (EMT).…”