An update on oral cavity cancer: epidemiological trends, prevention strategies and novel approaches in diagnosis and prognosis.

In the UK, the incidence of oral cavity cancer continues to rise, with an increase of around 60% over the past 10 years. Many patients still present with advanced disease, often resulting in locoregional recurrence and poor outcomes, which has not changed significantly for over four decades. Changes in aetiology may also be emerging, given the decline of smoking in developed countries. Therefore, new methods to better target prevention, improve screening and detect recurrence are needed. High-throughput 'omics' technologies appear promising for future individual-level diagnosis and prognosis. However, given this is a relatively rare cancer with significant intra-tumour heterogeneity and variation in patient response, reliable biomarkers have been difficult to elucidate. From a public health perspective, implementing these novel technologies into current services would require substantial practical, financial and ethical considerations. This may be difficult to justify and implement at present, therefore focus remains on early detection using new patient-led follow-up strategies. This paper reviews the latest evidence on epidemiological trends in oral cavity cancer to help identify at risk groups, population-based approaches for prevention, in addition to potential cutting-edge approaches in the diagnosis and prognosis of this disease.

Challenges and novel approaches for investigating molecular mediation.

Understanding mediation is useful for identifying intermediates lying between an exposure and an outcome which, when intervened upon, will block (some or all of) the causal pathway between the exposure and outcome. Mediation approaches used in conventional epidemiology have been adapted to understanding the role of molecular intermediates in situations of high-dimensional omics data with varying degrees of success. In particular, the limitations of observational epidemiological study including confounding, reverse causation and measurement error can afflict conventional mediation approaches and may lead to incorrect conclusions regarding causal effects. Solutions to analysing mediation which overcome these problems include the use of instrumental variable methods such as Mendelian randomization, which may be applied to evaluate causality in increasingly complex networks of omics data.

Male Esterase 6 Catalyzes the Synthesis of a Sex Pheromone in Drosophila melanogaster Females.

Esterase 6, a component of the seminal fluid of Drosophila melanogaster males, hydrolyzes cis-vaccenyl acetate, a lipid made only by males, to cis-vaccenyl alcohol. This reaction occurs in the female reproductive tract and is virtually complete within 6 hours after copulation. Both the alcohol and the acetate decrease the number of matings among pairs of virgin flies in which the female is treated topically with these substances. Although females tested 10 minutes after copulation elicit less courtship than virgin females, females tested 6 hours after copulation stimulate even less courtship if they received active esterase 6 in the seminal fluid of their respective mates. Either the alcohol or a derivative appears to be an antiaphrodisiac that decreases courtship elicited by inseminated females and thus reduces the probability of further mating. Thus the activity of the pheromone depends on a final reaction which occurs in the female, using both substrate and enzyme provided by the male.

Esterase 6 and reproduction in Drosophila melanogaster.

A nonspecific carboxylesterase (esterase 6) of Drosophila melanogaster shows greater activity in adult males than in females and is highly concentrated in the anterior ejaculatory duct of the reproductive tract of the male. Esterase 6 is depleted in males by copulation and is transferred to females early during copulation as a component of the seminal fluid. That esterase 6 may be involved in a system controlling the timing of remating is suggested by differences in the activity of this enzyme in a strain of Drosophila selected for a decrease in time to remating and by differences in the timing of remating in females initially inseminated by males lacking or having active esterase 6.

Enzyme variability in the Drosophila willistoni group. 3. Amounts of variability in the superspecies, D. paulistorum.

The semispecies composing the superspecies, Drosophila paulistorum, have been analyzed for genetic variation at 17 enzyme loci. On the average a population of D. paulistorum is polymorphic for 55-67% of its loci and an average individual is heterozygous at 21% of its loci. The pattern of genetic variability found supports the hypothesis that allozyme variation is maintained in natural populations by some form of balancing selection. Evidence is presented which supports the hypothesis that glucose-metabolizing enzymes are less genetically variable than non-glucose-metabolizing enzymes. The known genetic relationships between the semispecies of D. paulistorum are discussed in the light of the frequencies of alleles at allozyme loci.

A genetic analysis of male-predominant pheromones in Drosophila melanogaster.

Chemical signals from males play an important role in stimulating Drosophila melanogaster females to mate, and male-predominant pheromones may influence a female's choice of mates. Male-predominant pheromones also inhibit courtship, thereby functioning as antiaphrodisiacs. Interstrain variation in the ratio of two male-predominant pheromones (7-tricosene and 7-pentacosene) has been reported, but the genetic basis for this potentially important variation has not been examined. In a series of crosses between strains that differ radically in the amounts of 7-tricosene and 7-pentacosene, we have identified both X-linked and autosomal contributions to interstrain variation in the amounts of these compounds. The X-linked loci act as enhancers for production of the compound predominant in the strain from which the X chromosome originated. Autosomal factors for each of the two compounds appear to segregate as high vs. low, with incomplete dominance of high 7-tricosene over low, and low 7-pentacosene over high. A significant negative correlation between the quantities of 7-pentacosene and 7-tricosene in the F2 and backcross progeny, but not in the F1s or parentals, indicates linkage between autosomal loci regulating the expression of each compound. However, the phenotypic distributions of the backcross progeny indicate that additional unlinked loci are also directly involved in the production of these two hydrocarbons.

Studies of esterase 6 in Drosophila melanogaster. VI. ejaculate competitive abilities of males having null or active alleles.

Recent studies of the function of the polymorphic seminal fluid enzyme, esterase 6, of Drosophila melanogaster suggested that it may act in the process of sperm displacement (Gilbert, Richmond and Sheehan, 1981a). This report examines the competitive ability of ejaculates from males homozygous for null or active alleles of esterase 6 under three experimental conditions that model aspects of sexual selection affecting males. The results demonstrate no significant difference in ejaculate competition between esterase 6 null or active male types, but marker males used for paternity identification had poorly competitive ejaculates. The proportion of second-male progeny, P2, used as an index of competition is primarily influenced by second-male genotype and uninfluenced by female genotype, P2 can change with time from remating and be unaffected by different intensities of competition, which suggests a complex ejaculate competition mechanism.

The effects of lethal selection on the EST-6 to PGM region of chromosome 3 in Drosophila melanogaster.

A powerful means of studying the effects of selection on chromosome segments in Drosophila melanogaster has been described by Clegg et. al. (1976, 1978). This method utilizes a recessive lethal, dominant visible allele whose selection dynamics can be accurately modelled to predict the fates of nonlethal alleles at linked loci. Results of these experiments indicate that strong epistatic interactions among loci occur that effect fitnesses associated with gametic types in the basal region of chromosome 3. We have used similar methods in studying a different segment of chromosome 3, that spanned by Est-6 (3-36.8) and Pgm (3-43.4), with the aim of determining whether the results of Clegg and his colleagues could be reproduced when a different region was studied. Our experiment showed that selection did operate on a region of the chromosome marked by Pgm, but that no evidence of selection at loci marked by Est-6 was apparent. Weak evidence for epistatic interactions among loci within the marked region was also found. Three possible explanations for the discrepancies between our experiments and those of Clegg et al. are suggested. First, the geographically homogeneous origin of our populations may preclude selectively significant changes as a result of recombination. Second, the results seen by Clegg et al. may have been unique to the regions they studied, which included the basal heterochromatin of the chromosomes. Finally, the three loci employed may not adequately mark the unit of selection, so that actual departures from predictions of selective neutrality may not have been apparent.

Modes of Selection Maintaining an Inversion Polymorphism in DROSOPHILA PAULISTORUM.

The possibility that fitness relationships associated with an inversion polymorphism in D. paulistorum were frequency dependent was investigated. Using allozymes of tetrazolium oxidase to mark inversions, the effects of genotype frequency, larval density, and culture conditions on fitness were assessed. The proportions of genotypes among egg-laying females were varied, thus changing the expected proportions of progeny produced in the absence of fecundity or viability selection. The genotypes of progeny were determined by electrophoresis and comparisons of the ratio of the numbers of the different genotypes produced to the expected ratio was used to evaluate fitness relationships. Fitness relationships were dependent on genotype frequency, larval density, and culture conditions. Selection was either absent, directional, frequency dependent (favoring rare types), or heterotic depending on density and culture conditions. It is implied that the adaptive value of genetic variants need not be apparent in all environments, or may change with changing conditions. There is evidence for different criteria for selection in the two sexes. These results add to the evidence supporting the importance of frequency-dependent selection. It is argued that for frequency dependence to be of general importance, selection must act on genes in groups, either as an inversion or as lengths of chromosome with integrity maintained by disequilibrium.

Studies of esterase-6 in Drosophila melanogaster. II. The genetics and frequency distributions of naturally occurring variants studied by electrophoretic and heat stability criteria.

Measurements of the electrophoretic mobility and thermostability of esterase-6 allozymes have been used to determine the amount of allelic variation at the esterase-6 locus in Drosophila melanogaster. We studied 398 homozygous lines obtained from four natural populations. Use of a spectrophotometric assay for esterase-6 activity has allowed precise quantitation of heat-stability variants. Using these methods, eight putative alleles were detected within the two most common electrophoretic classes. Analyses of F1 and F2 progeny show that the behavior of stability variants is consistent with the hypothesis that this variation is due to allelic variation at the Est-6 locus. Analyses of the gene-frequency distributions within and between populations show (1) that observed allele-frequency distributions do not deviate significantly from those expected for neutral variants, and (2) that there is little evidence for an increase in apparent divergence of the different populations at the genotypic or phenotypic levels when the additional variation detected is considered. These findings suggest that gene-frequency analysis alone is unlikely to resolve the question of the selective significance of allozyme variation.

Carboplatin as a potentiator of radiation therapy.

A rationale for coordinating the administration of carboplatin with radiation to achieve enhancement of cancer therapy is developed. This approach is based upon a review of the reports of effects in a variety of systems, effects attributed to interactions between cisplatin or other platinum analogs and radiation. Two major effects include radiosensitization (RS) of hypoxic cells with platinum present during irradiation and potentiation of cell kill with platinum complexes administered after irradiation. Both these effects are expected to result in an improved therapeutic ratio. The latter effect may include inhibition of recovery from radiation-induced potentially lethal damage (PLD) and sublethal damage (SLD). Evidence for RS by carboplatin with an enhancement ratio (ER) of 1.8 is presented in Chinese hamster lung cells (V79) irradiated in culture under hypoxic conditions. Potentiation of radiation therapy in mice bearing a transplanted mouse mammary tumor (MTG-B) is reported as a supra-additive tumor growth delay when 60 mg/kg carboplatin is administered either 30 minutes before or immediately after 20 Gy of X-irradiation. Improved efficacy resulting from ongoing clinical trials coordinating cisplatin with radiation should support the role for carboplatin as a potentiator of radiation therapy since this second generation complex of platinum also interacts with radiation and larger concentrations of platinum should be attainable in tumors using the new drug.

Biologic and clinical developments of cisplatin combined with radiation: concepts, utility, projections for new trials, and the emergence of carboplatin.

Controlled experiments have shown that more than one mechanism leads to the potentiation of radiation-induced cell killing by cisplatin, and that this potentiation is not uniformly expressed among different cell types. A firm investigative base for the design of clinical trials using cisplatin and radiation has not been established. Coincident with this deficiency of experimental guidance, the independent clinical investigator has developed an array of therapeutic strategies applying different doses and sequences of cisplatin and radiation to a variety of tumor types. Results of clinical studies integrating cisplatin and radiation that can be judged for perceived survival benefit are evaluated in comparison with existing radiobiologic information. Both the clinical and radiobiologic results lead to similar conclusions at this time. Cells that are relatively sensitive to the cytotoxic action of cisplatin alone would best be considered for combined treatment with radiation. Large and infrequent, rather than small and frequent, individual administrations of cisplatin are better used with radiation for enhanced therapeutic effectiveness. Administration of cisplatin close in time to radiation is best for therapeutic response, although perceived efficacy follows from rather flexible integrations of these two modalities. It is not possible to know if clinical efficacy results from radiation potentiation as opposed to some degree of additivity of the two modalities. It is nonetheless useful to anticipate strategies that might lead to radiation potentiation by cisplatin in therapeutic designs. Two general mechanisms by which cisplatin potentiates radiation-induced cell killing are identified. One mechanism of potentiation is free radical-mediated, at least in part leads to an active radiolytic species following one-electron reduction of cisplatin, and is more readily expressed with bacterial cells than with mammalian cells in tissue culture. A second mechanism of potentiation is biochemical in nature, involves an effect of cisplatin on cellular components in ways that inhibit the recovery of radiation-induced damage, and likely applies more to the potentiation of oxic mammalian cells than bacterial cells. The latter mechanism is not universally supported in the literature. However, a unifying hypothesis, and one in need of confirmation at this time, is that the biochemical mechanism of radiation potentiation by cisplatin operates in oxic mammalian cells that are inherently sensitive to the cytotoxic action of cisplatin. This hypothesis ostensibly applies to tumor cells that are responsive to chemotherapy with cisplatin.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of the potentiation of radiotherapy by platinum drugs in a mouse tumor.

This study examines two ways to enhance cisplatin-mediated potentiation of the radiotherapy of a mouse mammary tumor, MTG-B: a) the appropriate sequencing of the two modalities, and b) the use of platinum "rescue" at appropriate times relative to injection of cisplatin to ameliorate platinum toxicity and permit the use of larger concentrations of cisplatin. Reduced TCD50 values and potentiated tumor regression resulted when cisplatin preceded irradiation by 1 hr compared to injection of cisplatin post-irradiation. Cisplatin "rescue" was demonstrated by DDTC, WR-2721 and 5-TG, and enhanced effects on the inhibition of tumor growth resulted when 20 mg/kg cisplatin and 730 mg/kg DDTC were combined with radiotherapy.

Platinum based combined modality approach for locally advanced head and neck carcinoma.

Radiation therapy delivered soon after cisplatin administration is used for the treatment of advanced head and neck cancer. A radiation dose of 4800 cGy is given in standard fractions, followed by clinical evaluation and either surgical resection or an additional radiation dose of 2000 cGy. The histopathology of the surgical specimens from 21 patients undergoing resection in this protocol is compared with the corresponding clinical evaluation of tumor response. A significant number of both false negative and false positive clinical assessments are revealed by this comparison. In addition, it appears that local control of bulky head and neck cancer is approached by 4800 cGy combined soon after cisplatin. Discussion of the likely bases for this apparently favorable clinical interaction between cisplatin and radiation is presented.

Enhancement of radiation-induced cell kill by platinum complexes (carboplatin and iproplatin) in V79 cells.

Two second generation platinum complexes currently undergoing clinical chemotherapeutic trials, carboplatin (CBDCA) and iproplatin (CHIP), were evaluated for their ability to alter the survival of cultured Chinese hamster V79 cells following irradiation. Two protocols were employed. In the first, the drug was added to preplated cells, some of which were subsequently made hypoxic with nitrogen gas. These hypoxic cells were irradiated following 1 hour exposure to drug and survival was assessed by standard colony forming unit (CFU) methods. Enhancement ratios (ER) of approximately 1.4 were obtained for irradiation under hypoxic conditions, if the cells were exposed to equitoxic doses of CBDCA (500 microM) CHIP (50 microM). In the second series of experiments, cells were treated with 10 Gy in air and then incubated for various times prior to trypsinization and serial dilution of single cell suspensions. Six hours after irradiation, cells treated with X rays alone had recovered to produce a surviving fraction twice that of cells trypsinized immediately after irradiation (not held). Post-irradiation administration of CBDCA (50 microM) or CHIP (20 microM), at a time when free radical-mediated radiosensitization would not be possible, operationally inhibited this recovery from radiation-induced potentially lethal damage (PLD). Inhibition, expressed as recovery inhibition factor (RIF) after 6 hr with drug, was 2.0 for CBDCA and 1.2 for CHIP. These results suggest that the rationale for designing clinical trials to exploit interactions between cisplatin and radiation might also extend to include combined modality therapy using radiation with either of these two platinum complexes.

Platinum drug delivery and radiation for locally advanced prostate cancer.

Combined therapies of cisplatin and radiation have resulted in clinical reports of apparent efficacious control of locoregional cancer and enhanced survival. Mechanisms of interaction between platinum and radiation that may explain these clinical observations all have in common the prediction that higher concentrations of platinum in all tumor cells close in time to irradiation should lead to greater potentiation of radiation-induced killing of those cells. Cisplatin is thus viewed as providing some radiation-equivalent, or a radiation dose-effect factor, for sterilization of tumors. One disease site that has not been well investigated for response to cisplatin plus radiation therapy, but that could benefit from it, is locally advanced prostate cancer. A body of literature now supports the view that local control of stage C (T3, N0, M0) prostate cancer is correlated with disease-free survival. This correlation makes prostate cancer a candidate for potentially achieving improved cure rates following local tumor sterilization by combining cisplatin with radiation therapy. The need and approaches to optimize delivery of cisplatin within tumor tissue is explored. Increasing cisplatin concentration to all the cells of a tumor, i.e., homogeneously delivering systemic high-dose cisplatin, should benefit the efficacious response otherwise expected for cisplatin combined with radiation. Strategies to increase the homogeneity of cisplatin delivery to a tumor are considered to be those that increase perfusion to that tumor. Vasoactive agents used in anticancer protocols are especially considered for their potential value in serving to increase tumor perfusion. These protocol-inclusive agents include certain cytokines and L-arginine antagonists, and should be better managed and accepted in practice compared to other vasoactive agents that need to be developed as specific additives to protocol designs.

Toxic variability and radiation sensitization by dichlorodiammineplatinum(II) complexes in Salmonella typhimurium cells.

The oxidative coordination compound cis-dichlorodiammineplatinum(II) (cis-DDP) is again shown to be a hypoxic cell radiation sensitizer. The mechanism of cis-DDP-induced radiation sensitization is complex. Results here indicate that cis-DDP sensitization operates in part through reactive free radicals, in part through the interactions of radiation-induced reactive Pt(I) intermediates, and in part through the involvement of thermodynamic and kinetic aspects of Pt(II)-DNA binding during irradiation. For the first time, radiation sensitization by trans-DDP is compared with a sensitizing concentration of cis-DDP within the same study. Both analogs are sensitizers, but with significant differences. Further, irradiated hypoxic solutions of cis-DDP are found to be more toxic than unirradiated solutions.

An interrelatedness of the potentiation of radiation-induced bacterial cell killing by cisplatin and binuclear rhodium carboxylates.

Cisplatin and binuclear rhodium (Rh2) carboxylates appear to potentiate radiation-induced killing of Salmonella typhimurium cells largely as a consequence of one-electron reduction that leads to an active radiolytic product. This conclusion is supported by results from experiments wherein the hydrated electron and the hydroxyl radical are competed for in the presence of cisplatin and Rh2 carboxylates, and by the similarly shaped radiation survival curves for cisplatin and Rh2 carboxylates wherein potentiation is expressed beyond variable thresholds of radiation dose. Increasing concentrations of phosphate and chloride also inhibit radiation potentiation by both cisplatin and Rh2 carboxylates, further supporting the contention for similar mechanisms. Radiation potentiation by cisplatin is relatively much more sensitive to the inhibition by chloride.

Potentiation of radiation-induced bacterial cell killing by binuclear rhodium(II) carboxylates.

A series of binuclear rhodium(II) tetracarboxylate complexes was examined for potentiation of radiation-induced killing of Salmonella typhimurium cells. Carboxylate bridging ligands were varied as formate, acetate, trifluoroacetate, and propionate. All complexes caused hypoxic non-dose-modifying radiation potentiation in that variable thresholds were obtained with the radiation dose response. In phosphate-buffered saline (PBS), decreasing threshold doses, i.e., increasing potentiating efficiencies, were seen in the order of acetate = trifluoroacetate less than propionate less than formate. Beyond the threshold dose, the degree of potentiation for all complexes in PBS approximated 12 times the degree of radiation sensitivity seen for the N2 baseline of the radiation dose-response curve. No radiation potentiation by Rh2 carboxylates was seen for fully oxic suspensions. Irradiation of cells in the absence of phosphate increased the efficiency as well as the degree of radiation potentiation. It is hypothesized that bacterial radiation potentiation is initiated by one-electron reduction of the Rh2 carboxylates, most likely involving the hydrated electron, followed then by formation of an active product. These events likely occur outside the bacterial cell.

Toxic variability and radiation potentiation by Rh(III) complexes in Salmonella typhimurium cells.

Stationary-phase cells of Salmonella typhimurium were irradiated in phosphate-buffered saline in the presence of rhodium complexes to test for the potentiation of radiation-induced cell killing. Eleven Rh complexes, two Rh(I) and nine Rh(III), were tested. Seven Rh(III) complexes were found to be radiation potentiators; six potentiate only under hypoxic conditions, and one potentiates under both hypoxic and oxic conditions. Four of these seven Rh(III) complexes demonstrate potentiation that is 2 to 13 times greater than the sensitization caused by oxygen. Irradiating cells in Ham's F-12 culture medium rather than in phosphate-buffered saline eliminates this latter hypoxic radiation potentiation. None of the seven Rh(III) radiation potentiators are directly toxic to cells. However, four complexes were tested for hypoxic radiation-induced cytocidal toxicity, and three were found to be toxic after irradiation. The efficiency of this toxicity is not sufficient to account for the observed radiation potentiation. It is suggested that both reductive and oxidative free radical events are involved in the spectrum of Rh(III) potentiation observed.