David J. Chaplin

Improvement in human tumour oxygenation with carbogen of varying carbon dioxide concentrations

BACKGROUND AND PURPOSEnCarbogen (95%O2, 5%CO2) is being used in clinical trials as a hypoxic radiosensitiser. Tolerance to carbogen can be a problem, this study compares tumour oxygenation during inhalation of hyperoxic gas containing either 2% or 5% CO2.nnnMATERIALS AND METHODSnTumour pO2 was measured in 16 patients using the Eppendorf pO2 histograph.nnnRESULTSnAfter breathing gas containing either 5% or 2% CO2 an increase in median pO2 was measured in every tumour, the frequency of low pO2 values ( < or = 10 mmHg) fell from 47% to 29% in the 5% group and from 55% to 17% in the 2% group.nnnCONCLUSIONSnThis study confirms that breathing 2% CO2 and 98% O2 is well tolerated and effective in increasing tumour oxygenation.

Newly discovered anti-inflammatory properties of the benzamides and nicotinamides

Our laboratory has concentrated on the possible regulation the benzamides and nicotinamides may have on the processes of DNA repair and apoptosis. Recent reports [14-16] have suggested that both apoptosis and inflammation are regulated by the transcription factor NF-kB. We have initiated studies regarding the hypothesis that the benzamides and nicotinamides could inhibit the production of tumor necrosis factor alpha (TNFalpha) and the inflammatory response as well as induce apoptosis via inhibition of NF-kB. Our data have shown that nicotinamide and two N-substituted benzamides, metoclopramide (MCA) and 3-chloroprocainamide (3-CPA), gave dose dependent inhibition of lipopolysacharide induced TNFalpha in the mouse within the dose range of 10-500 mg/kg. Moreover, lung edema was prevented in the rat by 3 ï 50 mg/kg doses of 3-CPA or MCA, and 100-200 μM doses of MCA could also inhibit NF-kB in Hela cells. Taken together these data strongly support the notion that benzamides and nicotinamides have potent anti-inflammatory and antitumor properties, because their primary mechanism of action is regulated by inhibition at the gene transcription level of NF-kB, which in turn inhibits TNFalpha and induces apoptosis.

Effect of carbogen breathing on tumour microregional blood flow in humans

BACKGROUND AND PURPOSEnCarbogen is currently being re-evaluated as a radiosensitiser. It acts primarily by increasing tissue pO2, although there is evidence to suggest that enhanced tumour blood flow may also be a component of its action.nnnMATERIALS AND METHODSnTen tumours in eight patients with advanced malignant disease were studied. Up to six microprobes, each with an estimated sampling volume of 10(-2) mm3, were inserted into the tumours. Ten min of baseline readings were taken prior to a 10 min carbogen (95% O2/5% CO2) breathing period, measurements were continued for a further 10 min.nnnRESULTSnThe results show that in 34 microregions analysed no overall change in tumour perfusion was seen with carbogen breathing. Individual tumour analysis demonstrated variation in response between patients to carbogen-after 6 min of carbogen four tumours showed an increase in blood flow by more than 10% of the pre-breathing value, two a decrease and four no change. The magnitude of change was small, with only two tumours fluctuating by more than 25%.nnnCONCLUSIONSnThese findings confirm the presence of transient fluctuations in microregional blood flow in human tumours but suggest that the radiosensitising action of carbogen lies primarily in its effect on increasing the oxygen capacity of blood. This supports the addition of agents such as nicotinamide with carbogen in order to overcome both diffusion and perfusion limited hypoxia.

Can PDT be potentiated by immunotherapy

Two principal aspects of interlinkage of the immune system with photodynamic therapy (PDT) treatment are discussed in detail: (1) participation of tumor associated macrophages (TAM) in tumor localization of photosensitizers, and (2) induction of an inflammatory immune response by phototoxic effects in endothelial cells, TAM and other cells in the tumor, leading to necrosis of the tumor tissue. It is illustrated how Photofrin levels in TAM, and consequently in the tumor as a whole, can be altered (increased or decreased) by specific agents that stimulate or impair physiological processes in TAM. It is suggested that the selectivity of tumor localization of some photosensitizers can be augmented by TAM targeted immunotherapy with agents that enhance the rate of tumor infiltration of these cells and stimulate their phagocytic activity. Preliminary results of ongoing studies suggest that PDT induces a massive infiltration of immune cells into the treated tumor. It is hypothesized that by combining PDT with an appropriate type of immunotherapy the immune reaction can be potentiated and directed against the surviving tumor cells. As as an example, it is shown that much better control of SCCVII tumor is achieved by combining PDT with the treatment by the immunoactivator SPG compared to PDT alone.

Host cell infiltration into PDT-treated tumor

C3H mice bearing SCCVII squamous cell carcinoma were treated with photodynamic therapy (PDT) 24 hours after receiving Photofrin (25 mg/kg, i.v.). Single cell suspensions obtained by the enzymatic digestion of tumors excised either 30 minutes or 4 hours after PDT were analyzed for the content of host immune cells and colony forming ability of malignant cells. The results were compared to the data obtained with non-treated tumors. It is shown that there is a marked increase in the content of cells expressing Mac-1 (monocytes/macrophages or granulocytes) in the tumor 30 minutes post PDT, while a high level of other leucocytes are found within the tumors by 4 hours after PDT. As elaborated in Discussion, the infiltration rate of host immune cells, dying of malignant tumor cells, and yet unknown death rate of host cells originally present in PDT treated tumor occurring concomitantly during this time period complicates this analysis. The results of this study suggest a massive infiltration of macrophages and other leucocytes in PDT treated SCCVII tumor, supporting the suggestion that a potent immune reaction is one of the main characteristics of PDT action in solid tumors. It remains to be determined to what extent is the activity of tumor infiltrating immune cells responsible for its eradication by PDT.

Examples of adjuvant treatment enhancing the antitumor effect of photodynamic therapy

Strategies for improving the clinical efficacy of photodynamic therapy (PDT) in treatment of solid cancers include applications of different types of adjuvant treatments in addition to this modality that may result in superior therapeutic outcome. Examples of such an approach investigated using mouse tumor models are presented in this report. It is shown that the cures of PDT treated subcutaneous tumors can be substantially improved by adjuvant therapy with: metoclopramide (enhancement of cancer cell apoptosis), combretastatin A-4 (selective destruction of tumor neovasculature), Roussins Black Salt (light activated tumor localized release of nitric oxide), or dendritic cell-based adoptive immunotherapy (immune rejection of treated tumor).

Development of Vascular Disrupting Agents

The majority of the cancer therapies in use today target the malignant cell population. In broad terms, specificity is achieved by exploiting intrinsic differences between normal cells and tumor cells with respect to various key processes including proliferative activity, DNA repair and responsiveness to apoptotic stimuli. Although progress continues to be made, it remains the case that chemotherapy alone is rarely curative. Thus, in recent years increased interest has focused on alternative strategies that instead target various normal cell types upon which the survival and growth of a tumor depends. In this chapter we explore the historical events that lead to development of vascular disrupting therapies and discuss the major approaches currently employed to selectively destroy the neovasculature of solid tumors.