Gene therapy developments for pancreatic cancer

Treatment options for pancreatic cancer have limited success and it is therefore an appropriate target for the development of new strategies, including gene therapy. Gene therapy approaches include inhibition of activated oncogenes (KRAS, LSM1) with antisense and RNA interference strategies, replacement of inactivated tumour suppressor genes (TP53, CDKN2A, CDKN1A), targeting of cell signalling pathways, gene-directed prodrug-activation therapies and the use of replication-competent oncolytic viruses. Angiogenesis and apoptosis have also been targeted for gene therapy. Clinical trials of gene therapy have shown only moderate anti-tumour effects. As there are many genetic abnormalities in pancreatic cancer, strategies combining different targets or indeed different modalities of treatment, may be more successful. Identification of new targets and improvements in delivery and targeting may further improve the efficacy of gene therapy in pancreatic cancer.     

Gene therapy in pancreatic cancer

Pancreatic cancer(PC) is a highly lethal disease and notoriously difficult to treat. Only a small proportion of PC patients are eligible for surgical resection, whilst conventional chemoradiotherapy only has a modest effect with substantial toxicity. Gene therapy has become a new widely investigated therapeutic approach for PC.This article reviews the basic rationale, gene delivery methods, therapeutic targets and developments of laboratory research and clinical trials in gene therapy of PC by searching the literature published in English using the PubMed database and analyzing clinical trials registered on the Gene Therapy Clinical Trials Worldwide website(http://www. wiley.co.uk/genmed/ clinical). Viral vectors are main gene delivery tools in gene therapy of cancer, and especially, oncolytic virus shows brighter prospect due to its tumor-targeting property.Efficient therapeutic targets for gene therapy include tumor suppressor gene p53, mutant oncogene K-ras,anti-angiogenesis gene VEGFR, suicide gene HSK-TK,cytosine deaminase and cytochrome p450, multiple cytokine genes and so on. Combining different targets or combination strategies with traditional chemoradiother-apy may be a more effective approach to improve the efficacy of cancer gene therapy. Cancer gene therapy is not yet applied in clinical practice, but basic and clinical studies have demonstrated its safety and clinical benefits. Gene therapy will be a new and promising field for the treatment of PC.     

Gene therapy for pancreatic cancer based on genetic characterization of the disease

In order to develop an effective therapeutic intervention for patients with pancreatic cancer, we analyzed the association of loss of heterozygosity (LOH) with the clinicopathological features of the disease. Based on these results, we are developing a new gene therapy that targets the genetic character of pancreatic cancer, using mutant adenoviruses that are selectively replication‐competent in tumor cells. LOH of 30% or more was observed on chromosome arms 17p (47%), 9p (45%), 18q (43%), 12q (34%), and 6q (30%). LOH of 12q, 17p, and 18q showed significant association with poor prognosis. These data strongly suggest that mutations of the putative tumor suppressor genes,TP53 andSMAD4, play significant roles in the disease progression. Based on this rationale, we are developing a new gene therapy that targets tumors without normalTP53 function. The E1B‐55kDa‐deleted adenovirus can selectively replicate inTP53‐deficient human tumor cells, but not in cells with functionalTP53. We evaluated the therapeutic effect of this E1B‐55kDa‐deleted mutant adenovirus on pancreatic cancer without normalTP53 function. The growth of a human pancreatic tumor in a severe combined immunodeficiency (SCID) mouse model was markedly inhibited by consecutive injections of the E1B‐55kDa‐deleted adenovirus. Furthermore, the replication‐competent adenovirus is not only a strong weapon itself but it is also a useful carrier of genes that possess antitumor activities, as a virus vector specific to tumors without normalTP53 function.     

Multimodality therapy for pancreatic cancer

Neoadjuvant chemoradiotherapy can be administered safely to patients with pancreatic cancer. Complete pathologic responses are rare, however, and the benefits of this approach compared with standard adjuvant therapy are uncertain. The only way to evaluate the efficacy of neoadjuvant chemoradiotherapy is a prospective trial involving a uniform patient population comparing the results of neoadjuvant and adjuvant therapy and a cohort receiving surgery alone. Such a study can be designed in an ethically sound manner but requires the collaboration of numerous institutions and careful coordination to achieve statistically conclusive results. The future of pancreatic cancer research rests on the availability and rapid transfer of new therapies from the laboratory to clinical research.     

GM-CSF Gene therapy using adenoviral vector in hamster pancreatic cancer

The aim of this study was to examine the antitumor effect of irradiated granulocyte macrophage-colony-stimulating factor (GM-CSF)-gene-transduced hamster pancreatic cancer cells and its relationship to the amount of GM-CSF produced by transduced tumor cells. Hamster pancreatic adenocarcinoma cells, HPD1NR, which spontaneously secrete 15.0 ± 0.4 pg/10⁶ cells per 24 h of GM-CSF, and HPD2NR cells, which do not secrete GM-CSF, were used. When these cells were infected with recombinant adenovirus harboring theGM-CSF gene, HPD1NR and HPD2NR secreted 624.2 ± 9.9 and 157.8 ± 5.7 pg/10⁶ cells per 24 h, respectively. Vaccination with irradiatedGM-CSF-secreting HPD2NR completely protected syngeneic hamsters challenged with live parental cells. On the other hand, vaccination with irradiated HPD1NR protected 60% of hamsters from tumor development after challenge with parental cells. None of the tumor-free hamsters initially vaccinated with irradiated GM-CSF-producing HPD2NR cells developed tumor upon repeated challenge with parental cells during the entire observation period. IrradiatedGM-CSF-gene-transduced hamster pancreatic cells are promising as a novel adjuvant cancer therapy after surgery for primary and metastatic pancreatic cancer. The results indicate the necessity for a therapeutic strategy for cancer based on the cytokine status of tumors.     

Immune checkpoint therapy for pancreatic cancer

Novel treatment modalities are necessary for pancreatic cancer. Immunotherapy with immune checkpoint inhibition has shown effect in other solid tumors, and could have a place in pancreatic cancer treatment. Most available clinical studies on immune checkpoint inhibitors for pancreatic cancer are not yet completed and are still recruiting patients. Among the completed trials, there have been findings of a preliminary nature such as delayed disease progression and enhanced overall survival after treatment with immune checkpoint inhibitors in mono- or combination therapy. However, due to small sample sizes, major results are not yet identifiable. The present article provides a clinical overview of immune checkpoint inhibition in pancreatic cancer. Pub Med, Clinical Trials.gov and American Society of Clinical Oncology's meeting abstracts were systematically searched for relevant clinical studies. Four articles, five abstracts and 25 clinical trials were identified and analyzed in detail.     

Biochemical modulation therapy for pancreatic cancer

It is well known that the clinical course in most patients with advanced pancreatic cancer is not influenced substantially by chemotherapy and/or radiotherapy. However, new chemotherapy, based on the synergistic antitumor activities of 5-fluorouracil (5-FU) and cisplatin (CDDP) producing biochemical modulation in solid cancers diagnosed as adenocarcinoma, has recently been reported to be effective. In gastrointestinal cancers, the optimal concentrations of each drug and the duration of the anticancer effects, as well as adverse effects have been confirmed in pharmacodynamic studies. Our experience of this treatment for advanced pancreatic cancer (stage IV) indicates the usefulness of the antitumor effect in terms of both effect on the tumor size in unresectable patients and prognosis in resectable patients. These results were remarkable in patients diagnosed as stage IV b and/or curability C. Although there were adverse effects, none were severe. However, anything compromising the patient's quality of life must be prevented. Randomized prospective studies of the combination of 5-FU and CDDP are expected in the near future.     

Prospects for vaccine therapy for pancreatic cancer

Vaccine therapy is being tested for many forms of cancer. The identification of immunogenic target molecules in pancreatic cancer is providing candidates for new vaccines targeting this cancer. Early clinical trials have demonstrated safety for all vaccines tested. Immunogenicity has been variable, but some vaccines have induced responses in a high proportion of vaccinated patients. Most trials have to some extent been able to document increased survival associated with immune responses. Based on this, several vaccines are now entering controlled trials. Recent feasibility studies have demonstrated that vaccination can be combined with standard chemotherapy and indicate that some synergy effects are to be expected. This has paved the way for larger clinical studies combining gemcitabin with cancer vaccination. Characterization of regulatory pathways involved in negative control of the immune system and development of new drugs to intercept such pathways has opened for ways to manipulate the immune response in the clinical setting. Vaccination therapy for pancreatic cancer is moving into an exiting area with opportunities to attack not only the tumour as such, but also to deal with important regulatory mechanisms that have negatively influenced clinical efficacy so far.     

腺病毒介导CD/UPRT自杀基因系统治疗胰腺癌的实验研究

目的探讨CD/UPRT自杀基因系统在胰腺癌基因治疗中的作用。方法采用同源重组技术构建重组腺病毒Ad-CD、Ad-CD/UPRT和Ad-GFP;体外感染人胰腺癌SW1990细胞,RT-PCR检测UPRTmRNA表达;MTT法检测细胞对5-FC的敏感性及旁观者效应;流式细胞仪分析细胞凋亡率;建立胰腺癌裸鼠皮下移植瘤模型,瘤体内直接注射腺病毒,观察CD/UPRT自杀基因的原位治疗作用。结果转染CD/UPRT的胰腺癌SW1990细胞对5-FC的敏感性明显提高,Ad-CD/UPRT组的IC50为25μmol/L,而Ad-CD组和Ad-GFP组分别为100μmol/L和>1000μmol/L。Ad-CD组、Ad-CD/UPRT组和Ad-GFP组的细胞凋亡率分别为61.3%、40.5%和3.0%,3组比较有显著差异(P<0.05)。CD/UPRT基因转染存在旁观者效应。Ad-CD/UPRT瘤内注射治疗后种植癌体积缩小81%,Ad-GFP治疗肿瘤缩小63%。结论CD/UPRT自杀基因系统能提高对胰腺癌细胞的杀伤作用。     

腺病毒介导CD/UPRT自杀基因系统治疗胰腺癌的实验研究

目的 探讨CD/UPRT自杀基因系统在胰腺癌基因治疗中的作用.方法 采用同源重组技术构建重组腺病毒Ad-CD、Ad-CD/UPRT和Ad-GFP;体外感染人胰腺癌SW1990细胞,RT-PCR检测UPRT mRNA表达;MTT法检测细胞对5-FC的敏感性及旁观者效应;流式细胞仪分析细胞凋亡率;建立胰腺癌裸鼠皮下移植瘤模型,瘤体内直接注射腺病毒,观察CD/UPRT自杀基因的原位治疗作用.结果 转染CD/UPRT的胰腺癌SW1990细胞对5-FC的敏感性明显提高,Ad-CD/UPRT组的IC50为25 μmol/L,而Ad-CD组和Ad-GFP组分别为100 μmol/L和＞1 000 μmol/L.Ad-CD组、Ad-CD/UPRT组和Ad-GFP组的细胞凋亡率分别为61.3%、40.5%和3.0%,3组比较有显著差异(P＜0.05).CD/UPRT基因转染存在旁观者效应.Ad-CD/UPRT瘤内注射治疗后种植癌体积缩小81%,Ad-GFP治疗肿瘤缩小63%.结论 CD/UPRT自杀基因系统能提高对胰腺癌细胞的杀伤作用.     

Modern radiation therapy techniques for pancreatic cancer

Radiation therapy is a rapidly evolving field, and recent technical advances have spurred an increasing number of new treatments as well as marked improvements in previously existing treatments. Despite a growing body of published evidence demonstrating that radiotherapy for the treatment of pancreatic cancer is improving in efficacy and safety, the ultimate effect on patient outcomes remains to be seen. It is an unfortunate fact that the majority of pancreatic cancer patients will ultimately have metastases and succumb to distant disease. Thus, improvements in local tumor control engendered by these recent advances will have little impact on overall survival without the coincident development of better systemic treatment regimens.     

胰腺癌的生物治疗研究进展

胰腺癌发病隐匿, 进展迅速, 死亡率高, 预后差. 手术虽是主要治疗手段, 但因早期诊断困难, 大部分患者确诊时已无手术机会.放疗、化疗疗效不确切, 且有较多副作用. 随着生物技术的发展, 针对胰腺癌所进行的基因治疗、免疫治疗等生物治疗研究日趋增多, 使得对该病的治疗手段更加多样化. 合理运用生物治疗将会改善胰腺癌的预后.     

胰腺癌的介入治疗

胰腺癌是一恶性程度高、预后极差的消化道肿瘤,易侵犯周围血管,只有5%～20%患者在就诊时可以获得手术切除,而40%的患者处于局部进展期,经过一定的治疗后,部分患者才能获得手术切除机会[1];区域性动脉灌注介入治疗作为胰腺癌的辅助治疗措施,可以提高局部进展期肿瘤患者手术切除率和生存率.