Considerations in optimizing radiation therapy for non-small cell lung cancer

Gene therapy for lung cancer

Lung cancer patients suffer a 15% overall survival despite advances in chemotherapy, radiation therapy, and surgery due to the usual finding of advanced disease at diagnosis. Attempts to improve survival in advanced disease using various combinations of chemotherapy have demonstrated that no regimen is superior, suggesting a therapeutic plateau and the need for novel, more specific, and less toxic therapeutic strategies. Techniques have been developed that allow transfer of functional genes into mammalian cells, such as those that block activated tumor-promoting oncogenes and/or those that replace inactivated tumor-suppressing or apoptosis-promoting genes. This article will discuss the therapeutic implications of these molecular changes associated with bronchogenic carcinomas, and will then review the status of gene therapies for treatment of lung cancer.

Gene therapy for lung cancer

Lung cancer patients suffer a 15% overall survival despite advances in chemotherapy, radiation therapy, and surgery. This unacceptably low survival rate is due to the usual finding of advanced disease at diagnosis. However, multimodality strategies using conventional therapies only minimally improve survival rates even in early stages of lung cancer. Attempts to improve survival in advanced disease using various combinations of platinum-based chemotherapy have demonstrated that no regimen is superior, suggesting a therapeutic plateau and the need for novel, more specific, and less toxic therapeutic strategies. Over the past three decades, the genetic etiology of cancer has been gradually delineated, albeit not yet completely. Understanding the molecular events that occur during the multistep process of bronchogenic carcinogenesis may make these tasks more surmountable. During these same three decades, techniques have been developed which allow transfer of functional genes into mammalian cells. For example, blockade of activated tumor-promoting oncogenes or replacement of inactivated tumor-suppressing or apoptosis-promoting genes can be achieved by gene therapy. This article will discuss the therapeutic implications of these molecular changes associated with bronchogenic carcinomas and will then review the status of gene therapies for treatment of lung cancer.

Image-guided conformal radiation therapy planning and delivery for non-small-cell lung cancer

BACKGROUND

Our understanding of both the importance of local control for survival of patients with unresectable lung cancer and the inadequacy of conventional radiation therapy (RT) to provide this local control has undergone marked changes in the past 2 decades.

METHODS

A review was conducted of recent studies and meta-analyses in the literature that have convincingly demonstrated the value of thoracic irradiation in increasing long-term survival in patients with both small-cell lung cancer and non-small-cell lung cancer (NSCLC).

RESULTS

Large cooperative trials have shown long-term local control of only approximately 10% for NSCLC using conventionally planned radiation to doses of 60-64 Gy either as a single modality or when preceded by induction chemotherapy. Concurrent chemotherapy may modestly improve local control at the cost of greater acute esophageal toxicity. Simple escalation of radiation dose is limited by the tolerance of normal intrathoracic organs. Recent developments in anatomic and functional imaging, computerized RT planning, and RT delivery, as well as a reassessment of the appropriate target volumes for RT in the context of combined modality therapy, provide the capability to better conform regions of high dose to the target volume and test the hypothesis that increases in tumor dose will improve local control and survival.

CONCLUSIONS

Encouraging phase II data have been reported from single institutions using individually developed software and hardware. The availability of commercial tools for planning and delivering such conformal treatment will allow prospective assessment of the true value of these technologies in the management of patients with lung cancer.

Intratracheal injection of manganese superoxide dismutase (MnSOD) plasmid/liposomes protects normal lung but not orthotopic tumors from irradiation

To determine whether intratracheal (IT) lung protective manganese superoxide-plasmid/liposomes (MnSOD-PL) complex provided 'bystander' protection of thoracic tumors, mice with orthotopic Lewis lung carcinoma-bacterial beta-galactosidase gene (3LL-LacZ) were studied. There was no significant difference in irradiation survival of 3LL-LacZ cells irradiated, then cocultured with MnSOD-PL-treated compared with control lung cells (D0 2.022 and 2.153, respectively), or when irradiation was delivered 24 h after coculture (D0 0.934 and 0.907, respectively). Tumor-bearing control mice showed 50% survival at 18 days and 10% survival at 21 days. Mice receiving liposomes with no insert or LacZ-PL complex plus 18 Gy had 50% survival at 22 days, and a 20% and 30% survival at day 50, respectively. Mice receiving MnSOD-PL complex followed by 18 Gy showed prolonged survival of 45% at 50 days after irradiation (P < 0.001). Nested RT-PCR assay for the human MnSOD transgene demonstrated expression at 24 h in normal lung, but not in orthotopic tumors. Decreased irradiation induction of TGF-beta1, TGF-beta2, TGF-beta3, MIF, TNF-alpha, and IL-1 at 24 h was detected in lungs, but not orthotopic tumors from MnSOD-PL-injected mice (P < 0.001). Thus, pulmonary radioprotective MnSOD-PL therapy does not provide detectable 'bystander' protection to thoracic tumors.