New therapeutic perspectives in CCDC6 deficient lung cancer cells

Abstract

Non-small cell lung cancer (NSCLC) is the main cause of cancer-related death worldwide and new therapeutic strategies are urgently needed. In this study, we have characterized a panel of NSC lung cancer cell lines for the expression of coiled-coildomain containing 6 (CCDC6), a tumor suppressor gene involved in apoptosis and DNA damage response. We show that low CCDC6 protein levels are associated with a weak response to DNA damage and a low number of Rad51 positive foci. Moreover, CCDC6 deficient lung cancer cells show defects in DNA repair via homologous recombination. In accordance with its role in the DNA damage response, CCDC6 attenuation confers resistance to cisplatinum, the current treatment of choice for NSCLC, but sensitizes the cells to olaparib, a small molecule inhibitor of the repair enzymes PARP1/2. Remarkably, the combination of the two drugs is more effective than each agent individually, as demonstrated by a combination index <1. Finally, CCDC6 is expressed at low levels in about 30% of the NSCL tumors we analyzed by TMA immunostaining. The weak CCDC6 protein staining is significatively correlated with the presence of lymph node metastasis (p 0.02) and negatively correlated to the disease free survival (p 0.01) and the overall survival (p 0.05). Collectively, the data indicate that CCDC6 levels provide valuable insight for OS. CCDC6 could represent a predictive biomarker of resistance to conventional single mode therapy and yield insight on tumor sensitivity to PARP inhibitors in NSCLC.

USP7 inhibitors, downregulating CCDC6, sensitize lung neuroendocrine cancer cells to PARP-inhibitor drugs

“…Next, we observed that CCDC6 stability in SCLC was specifically impaired in the presence of USP7 inhibitor P5091, reducing CCDC6 half life. As low levels of CCDC6 protein make lung and colon carcinoma cell lines highly susceptible to olaparib, because of an impaired homologous recombination DNA repair [14,19], we assayed the effects of PARP inhibitors in two p53 WT SCLC cell lines in association with USP7 inhibitor. The use of PARP inhibitors has already been tested in SCLC cell lines that harbor high levels of the PARP enzymes [33].…”

“…We reported that cells harboring low levels of CCDC6 protein are sensitive to the PARP inhibitor olaparib while cells harboring high levels of CCDC6 protein are resistant to olaparib and become sensitive when CCDC6 is knocked down [14,19]. The identification of CCDC6 as a novel USP7 substrate provides the rationale to establish whether the Thus, the pharmacological inhibition of USP7 can lead to downregulation of CCDC6 protein, that affects DNA repair pathways and sensitize the neuroendocrine cancer cells that harbor high levels of USP7 and CCDC6 proteins to PARP inhibitor treatment, alone or in combination with standard radio-and chemotherapies.…”

“…A recent analysis, performed in non-NE lung histotype tumors has indicated CCDC6 as a prognostic biomarker, also predictive of a possible response to the treatment with PARP inhibitors [14]. CCDC6 gene product is a pro-apoptotic protein substrate of ATM [15] that negatively regulate CREB1 transcriptional activity in a SUMO2/3 dependent manner [16,17].…”

“…CCDC6 gene product is a pro-apoptotic protein substrate of ATM [15] that negatively regulate CREB1 transcriptional activity in a SUMO2/3 dependent manner [16,17]. CCDC6 is able, in response to DNA damage, to sustain DNA damage checkpoints and DNA repair by non-homologous end joining (NHEJ) and by Homologous Recombination (HR) [18,14]. Altered levels of CCDC6 in a wide group of non-NE lung tumors, analised by TMA immunostaining, revealed that low CCDC6 expression, observed in about 30% of these tumors, negatively correlated with disease free survival (DFS) and overall survival (OS).…”

CCDC6: the identity of a protein known to be partner in fusion

“…In accordance with CCDC6 role in the DNA damage response, CCDC6 attenuation in lung cancer cells confers resistance to cisplatinum and sensitizes the cells to the PARPi olaparib. Remarkably, the combination of the PARPi with the conventional chemotherapy is more effective than each agent individually . On these bases, CCDC6 could be envisaged as a predictive biomarker of resistance to conventional single mode therapy and yields insight to tumor sensitivity to PARPi in NSCLC.…”