Yoichiro Yoshida

Cellular pH regulators: potentially promising molecular targets for cancer chemotherapy

One of the major obstacles to the successful treatment of cancer is the complex biology of solid tumour development. Although regulation of intracellular pH has been shown to be critically important for many cellular functions, pH regulation has not been fully investigated in the field of cancer. It has, however, been shown that cellular pH is crucial for biological functions such as cell proliferation, invasion and metastasis, drug resistance and apoptosis. Hypoxic conditions are often observed during the development of solid tumours and lead to intracellular and extracellular acidosis. Cellular acidosis has been shown to be a trigger in the early phase of apoptosis and leads to activation of endonucleases inducing DNA fragmentation. To avoid intracellular acidification under such conditions, pH regulators are thought to be up-regulated in tumour cells. Four major types of pH regulator have been identified: the proton pump, the sodium-proton exchanger family (NHE), the bicarbonate transporter family (BCT) and the monocarboxylate transporter family (MCT). Here, we describe the structure and function of pH regulators expressed in tumour tissue. Understanding pH regulation in tumour cells may provide new ways of inducing tumour-specific apoptosis, thus aiding cancer chemotherapy.

Cisplatin Resistance and Transcription Factors

Cisplatin is one of the most potent and widely used anti-cancer agents in the treatment of various solid tumors. However, the development of resistance to cisplatin is a major obstacle in clinical treatment. Several mechanisms are thought to be involved in cisplatin resistance, including decreased intracellular drug accumulation, increased levels of cellular thiols, increased nucleotide excision-repair activity and decreased mismatch-repair activity. In general, the molecules responsible for each mechanism are upregulated in cisplatin-resistant cells; this indicates that the transcription factors activated in response to cisplatin might play crucial roles in drug resistance. It is known that the tumor-suppressor proteins p53 and p73, and the oncoprotein c-Myc, which function as transcription factors, influence cellular sensitivity to cisplatin. So far, we have identified several transcription factors involved in cisplatin resistance, including Y-box binding protein-1 (YB-1), CCAAT-binding transcription factor 2 (CTF2), activating transcription factor 4 (ATF4), zinc-finger factor 143 (ZNF143) and mitochondrial transcription factor A (mtTFA). Two of these-YB-1 and ZNF143-lack the high-mobility group (HMG) domain and can bind preferentially to cisplatin-modified DNA in addition to HMG domain proteins or DNA repair proteins, indicating that these transcription factors may also participate in DNA repair. In this review, we summarize the mechanisms of cisplatin resistance and focus on transcription factors involved in the genomic response to cisplatin.

Human mitochondrial transcription factor A binds preferentially to oxidatively damaged DNA.

Mitochondrial transcription factor A (mtTFA) is necessary for both transcription and maintenance of mtDNA, and is also one of the high mobility group (HMG) proteins that preferentially binds to cisplatin-damaged DNA. In this study we confirmed the preferential binding of mtTFA to cisplatin-damaged DNA, and also discovered that mtTFA binds to oxidatively damaged DNA. The affinity for oxidatively damaged DNA of mtTFA is higher for A/8-oxo-dG and C/8-oxo-dG than for G/8-oxo-dG and T/8-oxo-dG. Our findings suggest that mtTFA plays an important role in the recognition of oxidative DNA damage.

Vacuolar H(+)-ATPase: functional mechanisms and potential as a target for cancer chemotherapy.

Tumor cells in vivo often exist in a hypoxic microenvironment with a lower extracellular pH than that surrounding normal cells. Ability to upregulate proton extrusion may be important for tumor cell survival. Such microenvironmental factors may be involved in the development of resistant subpopulations of tumor cells. In solid tumors, both intracellular and extracellular pH differ between drug-sensitive and -resistant cells, and pH appears critical to the therapeutic effectiveness of anticancer agents. Four major types of pH regulators have been identified in tumor cells: the sodium–proton antiporter, the bicarbonate transporter, the proton–lactate symporter and proton pumps. Understanding mechanisms regulating tumor acidity opens up novel opportunities for cancer chemotherapy. In this minireview, we describe the structure and function of certain proton pumps overexpressed in many tumors—vacuolar H+-ATPases—and consider their potential as targets for cancer chemotherapy.

ZNF143 activates gene expression in response to DNA damage and binds to cisplatin-modified DNA

We have identified a cisplatin‐inducible gene, the mitochondrial ribosomal protein S11 (MRP S11) gene, by means of mRNA differential display. Functional analysis of the MRP S11 promoter showed that a Staf binding site in the promoter is required for both basal promoter activity and cisplatin‐inducible activity. We also found that Staf binding activity is significantly increased in nuclear extracts from cells treated with cisplatin. ZNF 143 and ZNF 76 are human homologues of the Xenopus transcriptional activator, Staf. ZNF 143 expression is induced by cisplatin but ZNF 76 expression is not. However, ZNF 143 expression is not induced by transplatin, which is clinically ineffective. ZNF143 is an inducible gene by other DNA damaging agents such as γ‐irradiation, etoposide and adriamycin. ZNF 143 also binds preferentially to cisplatin‐modified DNA. These results suggest that ZNF 143 participates in cellular responses to DNA damage.

A study of the efficacy of antibacterial sutures for surgical site infection: a retrospective controlled trial.

To reduce bacterial adherence to surgical sutures, triclosan-coated polyglactin 910 suture materials with antiseptic activity were developed. The aim of this study was to evaluate whether the incidence of surgical site infections can be reduced when triclosan-coated sutures are used. Until December 2009, we used conventional polyglactin 910 sutures (VICRYL, Ethicon) for the closure of the fascia in digestive tract surgery. Therefore, for the control group we retrospectively collected surveillance data for 1.5 years. In the control group, 611 patients underwent digestive tract surgery with VICRYL sutures. Beginning in July 2010, we used triclosan-coated polyglactin 910 sutures (VICRYL Plus, Ethicon, Tokyo, Japan) for the closure of the fascia in all digestive surgeries. So, we collected data for the study group from July 2010 until June 2011. In the study group, 467 patients underwent digestive tract surgery with triclosan-coated VICRYL Plus sutures. In the control group, 75 patients (12.2%) developed wound infections. In the study group, 31 patients (6.6%) developed wound infections, which was significantly lower. Emergency cases; laparoscopic cases, including some cholecystectomy and colectomy cases; American Society of Anesthesiologists classification; the use of immunosuppressive therapy; colostomy cases; wound classification; and suture material were identified as the risk factors for wound infections. In both groups, as the wound classification worsened, the wound infection rate increased. Triclosan-coated polyglactin 910 antimicrobial sutures lead to a significant decrease in the incidence of surgical site infections, especially in clean/contaminated cases.

Clinical usefulness of mitochondrial transcription factor A expression as a predictive marker in colorectal cancer patients treated with FOLFOX

We previously reported that mitochondrial transcription factor A (mtTFA) preferentially recognizes cisplatin‐damaged DNA via physical interaction with p53 and is upregulated by treatment with cisplatin and fluorouracil (5‐FU). The aim of the present study was to evaluate whether expression of mtTFA predicts the clinical outcome in patients with metastatic colorectal cancer treated with modified 5‐fluorouracil, leucovorin and oxaliplatin 6 (mFOLFOX6). Fifty‐nine patients with metastatic lesions from colorectal cancer treated with mFOLFOX6 were included in this study. The subjects consisted of 25 women and 34 men with a median age of 62 years. The patients were treated with oxaliplatin (85 mg/m2) plus leucovorin (200 mg/m2) as a 2‐h infusion on day 1, followed by 5‐FU (400 mg/m2) bolus and 46‐h continuous infusion of 2400 mg/m2. The expressions of mtTFA and p53 of resected primary tumors were examined by immunohistochemical analysis. Of the 59 patients, 33 (complete response 1, partial response 32) achieved a confirmed response to therapy. The positive cytoplasmic staining rate for mtTFA was 44.1% and that for p53 was 59.3%, respectively. Strong expression of mtTFA was detected in eight of 33 complete response/partial response (24.2%) and in 18 of 26 SD/PD (69.2%), indicating that mtTFA expression was significantly correlated with response to chemotherapy (P < 0.01). Median overall survival was significantly longer in patients without mtTFA expression (P = 0.0493). Multivariate analysis revealed that mtTFA expression significantly affected overall survival (hazard ratio 2.10, P = 0.036). Immunohistochemical study of mtTFA may be useful for predicting the clinical outcome of metastatic colorectal cancer patients treated with FOLFOX. (Cancer Sci 2011; 102: 578–582)

Binding of RNA to p53 regulates its oligomerization and DNA-binding activity

The C-terminus of p53 is responsible for maintaining the latent, non-DNA-binding form of p53. However, the mechanism by which the C-terminus regulates DNA binding is not yet fully understood. We show here that p53 interacts with RNA via its C-terminal domain and that disruption of this interaction, by RNase A treatment, truncation or phosphorylation of the C-terminus, restores DNA-binding activity. Furthermore, the oligomerization of p53 is significantly enhanced by disrupting the interaction between p53 and RNA. These findings suggest that binding of RNA to p53 is involved in the mechanism of p53 latency.

Pilot study of the early start of chemotherapy after resection of primary colorectal cancer with distant metastases (Pearl Star 01)

BackgroundThe start of chemotherapy usually requires a delay of about 4 weeks after surgical resection of colorectal cancer. However, there is no evidence for the required length of this delay interval. In addition, there is a chance that a patient may die because postoperative chemotherapy was not started soon enough and a metastatic tumor was able to develop rapidly. We therefore conducted a pilot study to determine the safety and feasibility of an early start of chemotherapy after the resection of colorectal cancer with distant metastases.MethodsFive patients were enrolled. They received XELOX therapy (130 mg/m2 of oxaliplatin on day 1 plus 1,000 mg/m2 of capecitabine twice daily on days 1 to 14) on the 7th postoperative day and XELOX + bevacizumab (7.5 mg/kg of bevacizumab on day 1) after the 2nd cycle of chemotherapy.ResultsFive patients underwent open surgery. The procedures included right hemicolectomy in 1 patient, sigmoidectomy in 2 patients, high anterior resection in 1 patient, and Hartmann procedure in 1 patient. All patients started chemotherapy on postoperative day 7. The median number of cycles of chemotherapy was 11 (8 to 22). No postoperative complications were observed. The tumor reduction rate was 44.3% (32.0 to 66.6%). Progression-free survival was 10.3 months.ConclusionsAn early start of chemotherapy after surgery is feasible and safe. These findings suggest possible changes in the start time of chemotherapy after surgery in the future. We have already started a new phase II trial to confirm the effects of the early start of chemotherapy after surgery.Trial registrationUMIN000004361.

Early Start of Chemotherapy after Resection of Primary Colon Cancer with Synchronous Multiple Liver Metastases: A Case Report

The start of chemotherapy treatment usually requires a delay of about 4 weeks after surgical resection in patients with primary colorectal cancer and synchronous distant metastasis. However, there is no evidence to indicate the required length of this delay interval. In addition, there is a chance that a patient may die because postoperative chemotherapy was not started soon enough and a metastatic tumor was able to develop rapidly. Here, we present a case in which combination chemotherapy with capecitabine and oxaliplatin (XELOX) was started within 1 week after a right hemicolectomy for synchronous multiple liver metastases. To our knowledge, this is the first report of the start of chemotherapy, involving treatments such as folinic acid, fluorouracil, and oxaliplatin (FOLFOX); folinic acid, fluorouracil, and irinotecan (FOLFIRI); and XELOX, within 1 week after a colorectal cancer operation with anastomosis. The findings suggest possible changes in the start time of chemotherapy after surgery in the future.