Studies on the mechanism of action of a targeted chemotherapeutic drug in living cancer cells by two photon laser scanning microspectrofluorometry

In this study, we present a spectroscopic study of the entry pattern of a chemotherapeutic drug (AN-152) and its carrier hormone ([D-Lys(6)]LH-RH) into living cancer cells, with the help of our two-photon probes and a home-built localized microspectrofluorometer coupled with two photon laser scanning microscope (TPLSM). Due to the inherent localization ability of TPLSM, we were able to identify the drug and carrier location in different compartments of the cancer cells in vitro. The apparent doxorubicin-assisted nucleic accumulation of AN-152 suggests a possible nuclear action of the drug on cell proliferation.

Regulation of targeted chemotherapy with cytotoxic lutenizing hormone-releasing hormone analogue by epidermal growth factor

Targeting chemotherapy selectively to cancers can reduce the toxic side effects. AN-152, a conjugate of doxorubicin and [D-Lys6]-luteinizing hormone-releasing hormone (LH-RH), is more potent against LH-RH receptor-bearing cancers and produces less peripheral toxicity than doxorubicin. Many cancers, e.g., 50% of breast cancers, but few normal tissues express these receptors, providing a selective target for this cytotoxic conjugate. In this study, the effectiveness of AN-152 was heightened by receptor up-regulation. The cytotoxic effect of AN-152 can be regulated by the number of active LH-RH receptors on cancer cells. LH-RH receptor-positive (MCF-7) and -negative (UCI-107) cancer cells were treated with epidermal growth factor (EGF) or the somatostatin analogue, RC-160. EGF and RC-160 have been shown previously to regulate LH-RH receptors through phosphorylation. The effect of receptor regulation, by hormone exposure, on the cytotoxicity of AN-152 and doxorubicin and on the cellular uptake of AN-152, [D-Lys6]LH-RH, or doxorubicin was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and by two-photon laser scanning microscopy. The results demonstrated that the cellular entry of the conjugate was: (a) specific for cancers with LH-RH receptors; (b) up-regulated by EGF; (c) down-regulated by RC-160; and (d) the cytotoxicity of the AN-152 paralleled the efficiency of entry. This study illustrates the potential use of receptor regulation for increasing the efficacy of chemotherapeutic approaches that are directed to cell surface receptors.

Photodynamic therapy and hyperthermia as an adjuvant modality in preventing tumor recurrence

BACKGROUND AND OBJECTIVE

The objective of this study was to determine the relative efficacy in preventing tumor recurrence by photodynamic therapy (PDT), and by ablative CO2 laser surgery followed by PDT, compared to ablative surgery alone (negative control) or ablative surgery followed by a course of hyperthermia (positive control).

STUDY DESIGN/MATERIALS AND METHODS

The cheek pouches of 36 hamsters were treated with 0.5% 9,10 dimethyl-1,2-benzanthracene in acetone three times a week. After 12 weeks all animals showed tumors of their cheek pouches and were divided into four groups. In groups number I, II, and III, all visible tumors were removed by aid of a CO2 laser. Animals of group I did not receive any further treatment. After tumor resection, the cheek pouches in group II were treated with hyperthermia by aid of a Nd:YAG laser and a temperature of 43 degrees C for 30 minutes. In group III after resection of the tumors, the cheek pouches were treated with PDT (75mW/cm2 175J/cm2--3mg/kg Photofrin i.p./24h). In group IV, the tumors were not excised, instead they were only treated with PDT (as above). All animals were observed for 50 days for any signs of tumor recurrence.

RESULTS

In group I (CO2) all tumors (100%) recurred within 50 days. In group II (CO2 + hyperthermia) 61%, in group III (CO2 + PDT) 27.7%, and in group IV (PDT) 50% of all tumors recurred. The first signs of recurrence could be seen in group I, followed by groups II and IV. Group III was the last one presenting tumor recurrence.

CONCLUSIONS

The combination of CO2 surgery and PDT produced significantly better results than CO2 surgery or PDT alone, and better than the combination of CO2 surgery and hyperthermia.

Proliferative and apoptotic responses in cancers with special reference to oral cancer

The study of signal transduction pathways for mechanisms of apoptosis and proliferation has significantly advanced our understanding of human cancer, subsequently leading to more effective treatments. Discoveries of growth factors and oncogenes, especially those that function through phosphorylation on tyrosine residues, have greatly benefited our appreciation of the biology of cancer. The regulation of proliferation and apoptosis through phosphorylation via tyrosine kinases and phosphatases is discussed, as well as the contributions of other systems, such as serine and threonine kinases and phosphatases. Receptors with seven-transmembrane domains, steroid hormones, genes, and "death domains" will also be discussed. This review attempts to compare the regulation of the growth of normal tissues and cancers with an effort to highlight the current knowledge of these factors in the growth regulation of oral/oropharyngeal cancers. Despite the strides made in our understanding of growth regulation in human cancers, the study of oral/oropharyngeal cancer specifically lags behind. More research must be done to further our understanding of oral cancer biology, if we are to develop better, more effective treatment protocols.

A chemically labeled cytotoxic agent: two-photon fluorophore for optical tracking of cellular pathway in chemotherapy

Chemotherapy is commonly used in the treatment of cancers. However, the mechanism of action of many of these agents is not well understood. We present the synthesis of a two-photon fluorophore (C625) and its biological application when chemically linked to a chemotherapeutic agent (AN-152). By using two-photon laser-scanning microscopy, the drug:fluorophore conjugate can be observed directly as it interacts with receptor-positive cell lines. The results of this project visually show the receptor-mediated entry of AN-152 into the cell cytoplasm and subsequently into the nucleus. These observations will allow for better understanding of the drug's therapeutic mechanism, which is a subject of ongoing research aimed at improving present methods for cancer therapy.

The endocrine secretion of mammalian digestive enzymes by exocrine glands

The exocrine pancreas and certain salivary glands of mammals secrete a variety of enzymes into the gastrointestinal tract, where they digest food. The same glands also release these enzymes into the bloodstream. This latter process has commonly been assumed to occur solely as the result of a pathological condition or as an inadvertent by-product of exocrine secretion due to the leakage of trace quantities of the enzymes into blood. However, a variety of evidence suggests that the endocrine secretion of digestive enzymes is a normal occurrence that can be of substantial magnitude in healthy individuals, is responsive to various physiological stimuli, and is distinct from exocrine secretion. Recent research has focused attention on this process as a promising means for the delivery of engineered proteins into the systemic circulation for pharmaceutical purposes. In this review, we survey research in this area and consider the evidence for the existence of an endocrine secretion of digestive enzymes, the cause of enzyme release into the bloodstream, its source within the tissue, and, finally, the physiological purposes that this secretion process might serve.

Epidermal growth factor downregulates the expression of SH-PTP2

Protein phosphorylation/dephosphorylation on tyrosine residues are regulated by tyrosine kinases/phosphatases. The tyrosine phosphatase SH-PTP2 (PTP1D, PTP2C) interacts physically through its SH2 domain with phosphorylated epidermal growth factor receptor (EGFR). In KB cells, an oral epidermoid carcinoma, high epidermal growth factor (EGF) concentrations (10-9, 10-8 and 10-7 M) downregulate its receptor for the duration of the incubation with EGF. Thus, it was hypothesized that in KB cells, SH-PTP2 expression would also be downregulated by high EGF concentrations. This hypothesis was investigated by incubating the KB cells with increasing concentrations of EGF (0, 10-11, 10-10, 10-9, 10-8, 10-7 M) and by evaluating the expression of SH-PTP2 protein under these conditions. This study showed that EGF 10-7 and 10-8 M significantly decreased SH-PTP2 protein expression compared to controls. EGF 10-10 and 10-11 M did not change the expression of SH-PTP2 protein. We conclude that high EGF concentrations downregulate the expression of SH-PTP2 protein.

Photodynamic therapy for premalignant lesions in DMBA-treated hamsters: a preliminary study

PURPOSE

Photodynamic therapy (PDT) involves the selective destruction of neoplastic cells through the activation of a photosensitizer by light. We have previously shown that the photosensitizer Photofrin (porfimer sodium) is selectively accumulated in transformed lesions destined to become malignant, but not yet definable histologically as precancers. The aim of this investigation was to determine if this premalignant tissue could be selectively destroyed by systemically administered Photofrin activated by 630 nm red light via an argon dye laser.

MATERIALS AND METHODS

The carcinogenic model used was the DMBA (9, 10 dimethyl 1,2 benzanthracene)-treated hamster cheek pouch. The animals were treated with 0.5% DMBA in acetone thrice weekly for 6 weeks (experiment I, premalignant lesions), or 12 weeks (experiment II, malignant lesions). Ten animals were in experiment I; nine animals were in experiment II. These were divided into experimental and control subgroups. The 6-week experimental group received PDT and CO2 laser incision into the DMBA-treated area. The CO2 laser was used as a promoter of neoplasia in a field that had already undergone initiation from the DMBA treatment. The control groups received either CO2 laser incision alone into the DMBA-treated field or CO2 laser incision and argon pumped dye laser treatment (without Photofrin). The 12-week experimental group received PDT after CO2 laser excision of tumors. The controls received CO2 excision alone, or CO2 excision combined with postoperative hyperthermia.

RESULTS

One hundred percent (three of three) of cheeks in experiment I receiving PDT developed necrosis of the treated area within 24 to 48 hours, but 0% (0 of three) subsequently developed tumors. No necrosis was seen in control cheeks receiving Photofrin without irradiation (0 of four) or irradiation without Photofrin (0 of six), and 56% (five of nine) of cheeks exposed to identical carcinogenic stimulus, without PDT, developed tumors (n = 9). In experiment II, 0% (0 of six) of cheeks receiving postoperative PDT developed tumor recurrence. In experiment II controls, 50% (three of six) of cheeks that underwent excision and hyperthermia developed tumor recurrence. In cheeks treated only with CO2 laser excision of tumors, a recurrence rate of 67% (four of six) was noted. These results were found to be statistically significant by the Student t-test on the binomial distribution (P < .01). One animal was treated with DMBA for 6 weeks, administered Photofrin, and the right cheek was irradiated and the animal was left for 30 weeks. The irradiated cheek epithelium necrosed but no cancer developed, whereas the positive control cheek developed a large cancer.

CONCLUSION

These results suggest that photodynamic therapy possesses significant potential in elimination of premalignant tissue. This could be beneficial in treating potentially premalignant lesions such as oral leukoplakia, and useful as adjunctive therapy in removal of areas of field cancerization adjacent to surgical sites.

Transient effects of low-energy CO2 laser irradiation on dentinal impedance: implications for treatment of hypersensitive teeth

This study evaluated the effect of CO2 laser irradiation on dentinal impedance by passing known cyclic potentials across dentinal wafers mounted as a window in an electrolytic cell and measuring the resulting electrical impedance. Wafers were equilibrated in 0.1 M of KCl. The wafer specimens were irradiated with a CO2 laser (12 W, 0.1 ms, energy density 1.25 J/cm2). The time for impedance equilibration after irradiation was compared with equilibration after mounting. Mounted samples required 48 h to approach equilibrium in the electrolyte. After laser irradiation, impedance of previously equilibrated samples also required 48 h to equilibrate. This, along with exponential curve fitting, confirmed that laser treatment reintroduced a transient alteration in impedance. Equilibration time after irradiation and the mounting were similar. Dentin desociation apparently caused this transient impedance. Energy dispersive X-ray analysis confirmed the disappearance of K+Cl- after irradiation. Therefore, laser irradiation may cause dentinal desociation, yielding temporary clinical relief of dentinal hypersensitivity until rehydration occurs.

Four common mandibular nerve anomalies that lead to local anesthesia failures

Local anesthesia is essential in treating many dental and oral disorders. However, many types of anatomical anomalies are seen in the nervous system of the mandible that interfere with achieving local anesthesia. The authors describe four such anomalies and offer ways to overcome them when trying to properly anesthetize affected patients.

Bombesin antagonist prevents CO2 laser-induced promotion of oral cancer

We previously reported that CO2 laser incisions in carcinogen-initiated fields promoted cancer development and caused release of growth factors. Here we examined the quantitative and additive properties of this tumor-promoting event and examined whether this promotion could be nullified by treatment with a bombesin antagonist, which down-regulates epidermal growth factor receptors. The model used for cancer promotion was the hamster buccal cheek pouch that had been treated with a carcinogen (9,10-dimethyl-1,2-benzanthracene) for 6 weeks, producing premalignant lesions. These lesions would evolve into a cancer eventually without further treatment. Promotion was measured both by increased fluorescence in response to systemically administered Photofrin, measured noninvasively using an in vivo fluorescence photometer, and by the timing of appearance of clinical tumors. Laser incisions (0-3) were made into the hamster cheek 1 week apart, or three incisions were done 1 day apart. Another group of animals received bombesin antagonist RC-3095 for 4 weeks during the time incisions were made, again measuring promotion. Laser incisions 1 week apart produced additive promotion, whereas three incisions 1 day apart were not statistically different from the group receiving only one incision. RC-3095 treatment completely eliminated the promoting effects of incision and totally stopped promotion for the 4-week period of treatment. After discontinuing treatment with RC-3095, lesion progression resumed at the untreated control rate. This work confirms that the promoting event of a laser incision follows a comparable time course to release of growth factors after such an incision and that it can be eliminated by treatment with bombesin antagonists.

A comparison of crossover versus parallel-group design in the evaluation of analgesic efficacy after molar extraction

This study compares the analgesic effects of two standard combinations (Empirin with codeine versus Mersyndol) and placebo as measured by crossover versus parallel-group design. The analgesic results obtained with three groups of 12 to 13 crossed over subjects with two extractions divided into six subgroups of five to seven subjects for each sequence were qualitatively the same and statistically at least as strong as those obtained by analysis of parallel groups of 38 to 42 extractions per group. By both methods the analgesics were statistically significantly more effective than placebo. The difference between the two products was not statistically significant, although the score for Mersyndol was somewhat better by both methods of study. The crossover data did not allow judgments concerning side effects in spite of its greater efficiency in quantifying pain relief.

Alterations in receptor-mediated kinases and phosphatases during carcinogenesis

Increased phosphorylation in cancers can stimulate growth and up-regulate certain receptors. To test whether the functional response of phosphatase receptors is up-regulated during carcinogenesis, we examined the effects of ligands on net phosphorylation in isolated membranes derived from hamster cheek-pouch tissues undergoing malignant transformation. The buccal mucosa of groups of Syrian golden hamsters was exposed thrice weekly to 0.5% dimethylbenzanthracene (DMBA) in acetone for 2-12 weeks to produce premalignant and malignant tissues. Homogenates of these tissues were then incubated with [32P]ATP in the presence of epidermal growth factor (EGF), agonist of somatostatin analogue RC-160, luteinizing-hormone-releasing hormone (LH-RH) [D-Trp6]LH-RH, or combinations of EGF, RC-160, and [D-Trp6]LH-RH. Changes compared to controls in phosphorylation in response to ligands provided estimates of kinase or phosphatase activity. Phosphorylation increased continuously, from the first application of DMBA in a linear fashion, and independently of EGF stimulation. RC-160 and [D-Trp6]LH-RH reduced phosphorylation in vitro. This response occurred in premalignant (weeks 6-10 after DMBA application) as well as malignant tissues (week 12 after DMBA application), but was not significant in normal tissues. The results show a continuous augmentation in phosphatase activity prior to the appearance of cancers, but with a delay in expression following the primary event of increased kinase activity. Significantly less phosphorylation of substrates was induced by both RC-160 and [D-Trp6]LH-RH after in vitro activation by EGF than in the absence of EGF. This suggests that EGF activates latent systems of hormonal receptors. Collectively, these results support the hypothesis that the enhancement of the hormonally stimulated phosphatase in cancers occurs secondarily to the increased kinase activity.

Synergistic effects of bombesin and epidermal growth factor on cancers

Bombesin and gastrin-releasing peptide act as autocrine mitogens in various cancers. Bombesin antagonist RC-3095 inhibited growth in some cancers and slowed the progression of premalignant lesions, possibly by down-regulating epidermal growth factor (EGF) receptors. Since the EGF receptor mitogen response involves tyrosine kinase stimulation, we tested the hypotheses that bombesin stimulates, and RC-3095 inhibits, phosphorylation; EGF and bombesin promote the phosphorylation of the same substrates; and EGF and bombesin act synergistically on phosphorylation. Therefore, in vitro assays for phosphorylation were performed in the presence or absence of EGF, bombesin, RC-3095, and combinations in samples derived from tumor, tissue surrounding tumor, cell lines, and normal and transforming tissue derived from the 9,10-dimethyl-1,2-benzanthracene-induced squamous cell lesions of the hamster cheek pouch. Bombesin increased, and RC-3095 decreased, phosphorylation in these samples. In the human hepatoma sample and surrounding tissue, these ligands altered the phosphorylation of the same substrates affected by EGF. EGF and bombesin stimulated phosphorylation synergistically in the hamster samples and the hepatoma. Bombesin-induced phosphorylation was greater in tissue surrounding the hepatoma, whereas RC-3095 was more effective in inhibiting phosphorylation in the hepatoma itself. This cancer, therefore, could be endogenously stimulated by gastrin-releasing peptide. These observations support the hypothesis that bombesin stimulates growth of tissues and tumors by amplifying the phosphorylation response to EGF. The growth inhibitory response to RC-3095, or other bombesin analogues, of individual tumors may be prognosed by in vitro phosphorylation assays using the samples from the patient's tumor.

Stimulation of tyrosine phosphatase and inhibition of cell proliferation by somatostatin analogues: mediation by human somatostatin receptor subtypes SSTR1 and SSTR2

The effects of somatostatin analogues RC-160 and SMS-201-995 on tyrosine phosphatase and cell proliferation were investigated in COS-7 and NIH 3T3 cells expressing human somatostatin receptor subtype 1 or 2 (SSTR1 or SSTR2). Binding experiments were performed on membranes from COS-7 cells expressing human SSTR1 or SSTR2 using 125I-labeled [Tyr11]S-14 or [Tyr3]SMS-201-995, respectively. The somatostatin analogues RC-160 and SMS-201-995 exhibited low affinity for SSTR1 (IC50 of 0.43 and 1.5 microM, respectively) and high affinity for SSTR2 (IC50 of 0.27 and 0.19 nM). Addition of these analogues to cells expressing either SSTR1 or SSTR2 did not result in an inhibition of adenylate cyclase activity. In SSTR2-expressing cells, both analogues induced a rapid stimulation of a tyrosine phosphatase activity (EC50: RC-160, 2 pM; SMS-201-995, 6 pM) and an inhibition of serum-stimulated proliferation (EC50: RC-160, 6.3 pM; SMS-201-995, 12 pM). In SSTR1-expressing cells, only RC-160 induced stimulation of a tyrosine phosphatase activity. Both analogues caused an inhibition of cell proliferation at a concentration higher than 10 nM in accordance with their affinities for the SSTR1 receptor subtype. A good correlation between the affinities of RC-160 and SMS-201-995 for each receptor subtype and their potencies to inhibit cell proliferation suggests the involvement of these receptors in cell growth regulation. Tyrosine phosphatase was stimulated by both these analogues in SSTR2 and by RC-160 in SSTR1 at affinities similar to their ability to inhibit growth and bind to receptors, implicating tyrosine phosphatase as a transducer of the growth inhibition signal. We also found that mRNAs of receptor subtypes were variably expressed in different pancreatic and colon cancer cell lines, indicating the necessity of a precise analysis of receptor subtypes in target tissues before therapy with analogues.

Evaluation of porfimer sodium fluorescence for measuring tissue transformation

BACKGROUND

Neoplastic tissue can be detected by its increased fluorescence compared with surrounding normal tissue after the injection of the tumor-localizing compound porfimer sodium (Photofrin; Quadra Logic Technologies, Vancouver, BC, Canada). In vivo fluorescence photometry is a nonimaging photodetector technique that detects specific 690 nm fluorescence of the porphyrin by subtracting nonspecific 612 nm excitation from 630 nm excitation. The technique was applied in the developmental stages of the 9,10 dimethyl-1,2-benzanthracene (DMBA)-induced hamster buccal cheek pouch carcinoma model to (1) quantitate and characterize porfimer sodium fluorescence and uptake as it relates to lesion progression and biochemical changes and (2) determine whether porfimer sodium-induced fluorescence will vary with promotional and inhibitory stimuli.

METHODS

Groups of Syrian Golden hamsters had their cheek pouch buccal mucosa exposed to a 0.5% DMBA in acetone three times per week for 6 weeks (premalignant lesions), 12 weeks (squamous cell carcinomas), or other specified durations. The rate of malignant transformation was either promoted (by either carbon dioxide laser incision or continued DMBA application) or inhibited (by the administration of either somatostatin analogue RC-160 [D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2] or bombesin antagonist RC-3095 [D-Tpi-Gln-Trp-Ala-Val-Gly-His-Leu psi (CH2NH)Leu-NH2]). Groups of DMBA-exposed hamsters were subsequently injected with 1.0 mg/kg of porfimer sodium during the various stages of tumor development. Twenty-four hours after injection, fluorescence levels were measured by in vivo fluorescence photometry. Samples of tumors, dysplastic mucosal tissue, and normal-appearing oral mucosa were biopsied and used for either tissue extraction assays, histopathologic examination, or tyrosine kinase activity assay as an index of rate of transformation.

RESULTS

Results demonstrated that porfimer sodium is retained in DMBA-treated tissue. Fluorescence is completely accounted for by porfimer sodium uptake. The duration of exposure to carcinogen is proportional to porfimer sodium fluorescence. This relationship establishes that premalignant lesions can be distinguished from normal tissue by porfimer sodium uptake and fluorescence. The changes in increased tyrosine kinase activity paralleled the increase in porfimer sodium fluorescence. Alterations in the rate of tissue transformation produced equivalent alterations in porfimer sodium-induced fluorescence.

CONCLUSIONS

These results suggest that porfimer sodium uptake and fluorescence can be used in a prognostic manner to diagnose and determine the course of transformation of individual lesions.

Peptide analogues alter the progression of premalignant lesions, as measured by Photofrin fluorescence

Somatostatin analogue RC-160 and bombesin/gastrin-releasing peptide antagonist RC-3095 were infused at 2 micrograms per day via miniosmotic pumps implanted s.c. in hamsters with premalignant disease to examine the effect of these peptides on cancer promotion and progression. These analogues have been shown to inhibit growth of certain tumors, especially those that overexpress tyrosine kinase activity. Progression of premalignant lesions initiated by applying 0.5% 9,10-dimethyl-1,2-benzanthracene (DMBA) to the hamster buccal cheek pouch was measured by Photofrin-induced fluorescence 24 hr after injecting the porphyrin (1.0 mg/kg) by using in vivo fluorescence photometry. This method of monitoring progression was reaffirmed by the observations that fluorescence increased significantly as compared with controls in lesions receiving 4 additional weeks of continuous promotion by DMBA application (P < 0.01 in two independent trials) and in lesions receiving transient promotion by laser incision (P < 0.01 and < 0.05 at the same time in the two trials). Twelve weeks after treatment, fluorescence had decreased significantly among animals treated for 2 weeks with RC-3095 (control, 0.53 +/- 0.03 V vs. RC-3095, 0.28 +/- 0.03 V; P < 0.0005) or with RC-160 (control, 0.85 +/- 0.03 V vs. RC-160, 0.24 +/- 0.03 V; P < 0.0001). These data were obtained 20 weeks after DMBA initiation. Thus, treatment with RC-160 and RC-3095 decreased the progression, measured by fluorescence, compared with control animals. In addition, there was also an absolute continuous decrease in fluorescence for the 22 weeks after the cessation of RC-160 treatment. That the changes in tumor progression produced by RC-160 extended beyond the treatment period supports the hypothesis that the changes were irreversible. Histopathological analysis revealed normal tissue and/or mild-moderate dysplasia in hamster buccal mucosa treated with the RC-160 (an improvement compared to pretreatment), whereas 40% of the animals receiving no treatment after DMBA initiation developed invasive squamous cell carcinomas after 20 weeks. These results show that the antagonists of bombesin/gastrin-releasing peptide can delay the development of malignancies and the agonists of somatostatin can potentially reverse this development.

Fluorescence detection of tumors. Early diagnosis of microscopic lesions in preclinical studies

BACKGROUND

The growth of microscopic tumor lesions at or beyond treatment field margins poses a major problem in the diagnosis and treatment of cancer. Early detection techniques that clearly define the location or field spread of disease may improve the planning of disease treatment.

METHODS

In vivo fluorescence photometry is a non-imaging technique that digitally displays relative fluorescence values in volts proportional to the luminescence intensity detected by a silicon photodiode. The sensitivity of the instrument has allowed the detection of micrometastases in preclinical studies.

RESULTS

Statistical analysis demonstrates that the photosensitizer Photofrin (dihematoporphyrin ether and/or ester) (Quadra Logic Technologies, QLT, Vancouver, B.C., Canada), currently used for photodynamic therapy, administered in doses lower than those used in clinical studies, is useful for the detection of occult disease. With the drug doses used, cutaneous photosensitivity was avoided in the animal models tested. The results in Lobund-Wistar rats with transplantable prostatic adenocarcinoma (PA-III) demonstrated the utility of this technique in detecting clinically occult disease, with a prediction rate of approximately 94% with drug doses as low as 0.25-0.5 mg/kg.

CONCLUSIONS

With the use of the hamster buccal cavity model involving the initiation and promotion of premalignant and malignant conditions by 9,10 dimethyl-1,2-benzanthracene, the technique could discern these two stages of disease with significance levels that were less than 0.05 and 0.01, respectively.

Nonparallel transport and mechanisms of secretion

After many years of controversy, it is now clear that at least some cells and tissues that secrete more than one product can vary the composition of the secreted mixture as the result of the differential transport of various substances out of the cells that secrete them. In this article we discuss this phenomenon, non-parallel transport or secretion, and how it has and continues to inform us about how cells release the products they manufacture. We focus on expression of the phenomenon in the secretion of digestive enzymes by the exocrine pancreas, where it has been studied most extensively.

Regulation of luteinizing hormone-releasing hormone receptor binding by heterologous and autologous receptor-stimulated tyrosine phosphorylation

Pancreatic cancers overexpress tyrosine kinase and luteinizing hormone-releasing hormone (LH-RH) receptor (LH-RHR)-mediated tyrosine phosphatase. LH-RHR is a 60-kDa protein. One of the substrates of epidermal growth factor (EGF)-stimulated tyrosine kinase activity and LH-RH- and somatostatin-stimulated tyrosine phosphatase activity is also a 60-kDa protein. This suggests the possibility that LH-RHR regulation by tyrosine phosphatase and tyrosine kinase is mediated by (de)phosphorylation of existing LH-RHR. To test this hypothesis, membranes of MIA PaCa-2 cells, a human dedifferentiated pancreatic cancer cell line, were incubated without hormone (control) or with 0.1 microM EGF or somatostatin analogue RC-160 for 1 hr at 4 degrees C to phosphorylate the 60-kDa protein. Competition binding experiments with I125-labeled [D-Trp6]LH-RH by displacement with a nonradioactive ligand showed that the LH-RH binding in 69% of the points was increased by EGF and 85% was decreased by RC-160 compared with controls (n = 61; both significant, P less than 0.001). The specific binding was altered, increasing 50-150% after preincubation with EGF and decreasing 60-70% after RC-160. No change was seen in the binding affinity constant after pretreatment with EGF or RC-160. This shows that phosphorylation regulates binding of LH-RH and may explain the up-regulation by EGF and down-regulation by RC-160 and by LH-RH of the LH-RH response.

Effects of epidermal growth factor and analogues of luteinizing hormone-releasing hormone and somatostatin on phosphorylation and dephosphorylation of tyrosine residues of specific protein substrates in various tumors

Analogues of somatostatin (SS) and luteinizing hormone-releasing hormone (LH-RH) activate tyrosine phosphatases in MIA PaCa-2 human pancreatic cancer cell line membranes and inhibit growth. We compared the substrates phosphorylated by epidermal growth factor (EGF) to those dephosphorylated by the SS analogue RC-160 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2) and [D-Trp6]LH-RH in cancer cell lines such as MIA PaCa-2 (human pancreatic cancer), HCPC (hamster cheek pouch carcinoma), A-549 (human lung cancer), HT-29 (human colon cancer), and R3230AC (breast cancer). EGF phosphorylated proteins of 170, 65, and 60 kDa and analogues of SS and LH-RH promoted the dephosphorylation of these proteins in MIA PaCa-2 and HCPC cell lines. The EGF receptor is 170 kDa. pp60src (60 kDa) is known to be a substrate for EGF receptor. The LH-RH receptor is also 60 kDa. The effects of RC-160 and [D-Trp6]LH-RH were quantitatively different. Examinations of HT-29, A-549, and R3230AC cancer cell lines revealed no phosphorylation by EGF or dephosphorylation by RC-160 and [D-Trp6]LH-RH. In addition to the 170-, 65-, and 60-kDa proteins, 35-kDa proteins were also phosphorylated in some cancer cell lines. This work demonstrates that analogues of SS and LH-RH can reverse the effects of EGF biochemically as well as functionally.

Bacteremia following laser and conventional surgery in hamsters

The CO2 laser prevents bleeding by sealing blood and lymph vessels as it vaporizes tissue. Bacteremia following oral surgery might not occur under these conditions. To test this hypothesis, a 0.2-mm-deep incision 1 cm long was made in the right buccal cheek pouch of hamsters using either laser, electrosurgery, or a scalpel. Twenty minutes later, 1 mL of blood was taken from each animal by cardiac puncture, inoculated on a blood agar medium, and incubated anaerobically for 4 days; then the colonies were counted. Using an operational definition of bacteremia as five colonies or more per plate, there were no positive results out of 18 trials (0/18) for laser surgery, 7/8 for electrosurgery, and 8/12 for scalpel surgery. Based on the Student t test using the binomial distribution, the laser produced statistically less bacteremia than the other two methods (P less than .01). Because the five-colony cutoff was arbitrary, the nonparametric Wilcoxon Rank test was also used. Colony formation from blood from the laser group was significantly less than from the electrosurgery group (P less than .01) and the scalpel group (P less than .05). The laser surgery group was not statistically different from the control (nonsurgerized) group. These results suggest that there is a considerable bacteremia following scalpel and electrosurgery, but that laser surgery produces no bacteremia.

Somatostatin analogues inhibit growth of pancreatic cancer by stimulating tyrosine phosphatase

Several analogues of somatostatin were examined in the Mia PaCa-2 human pancreatic cancer cell line for their ability to promote tyrosine phosphatase activity affecting the receptors for the epidermal growth factor. The inhibition of growth of the Mia PaCa-2 cells in culture was also evaluated to determine the mechanism of action of somatostatin analogues and their relative effectiveness in inhibiting cancer growth. Of the analogues tested D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 (RC-160) caused the greatest stimulation of tyrosine phosphatase activity. Analogue D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (RC-121) had less effect but was more potent than somatostatin-14. Analogue D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr(ol) (SMS 201-995) produced no significant dephosphorylation. The analogues displayed the same order of activity in assays on growth inhibition of Mia PaCa-2 cells in cultures. Analogue (SMS-201-995) caused virtually no tyrosine phosphatase stimulation or growth inhibition in this cancer cell line, although it possesses a much higher antisecretory activity than somatostatin-14 in normal tissues. These observations indicate that somatostatin and some of its analogues can act as growth inhibitors in cancer cells through the activation of tyrosine phosphatase. These data reinforce the view that somatostatin analogue RC-160 and related compounds could be used for treatment of pancreatic cancer.

Specific end-product feedback regulation of pancreatic protein synthesis

The potential for negative feedback regulation of the synthesis of individual enzymes was tested in the rabbit pancreas. Tissues were preincubated with individual pancreatic enzymes under conditions which have been shown to allow significant tissue absorption of these enzymes. The rates of synthesis of total proteins and amylase were then measured by following incorporation of labeled amino acids. Preincubation of lobules with amylase in the bath caused amylase synthesis to be inhibited by 50% without significantly inhibiting total protein synthesis. Preincubation of lobules with chymotrypsinogen significantly inhibited total protein synthesis without significantly inhibiting amylase synthesis. These data demonstrate specific end-product feed-back inhibition of protein synthesis in eukaryotes and may represent a pattern for regulation of protein synthesis in general.

Hormonal control of pancreatic cancer growth

The effects of epidermal growth factor (EGF) and somatostatin-14 (SS) on growth of Mia PaCa-2 cells in cell culture were examined. EGF had no effect on cell growth in sera containing media but significantly increased growth in sera-free media. The effect of EGF was complete within 18 h. SS added with EGF entirely eliminated the growth stimulation of EGF. SS added to cells in culture with sera inhibited their growth as well.

Permeability of zymogen granule membrane to protein

The evidence that the membrane of the pancreatic zymogen granule is permeable to its contained secretory proteins is outlined. Included is a discussion of the nature and characteristics of the equilibrium-dependent release of protein from isolated granules, the evidence for the permeability of the granule membrane to digestive enzyme protein in situ, and the seeming paradox that isolated granules release protein in medium similar to that thought to exist in the cell. The permeability hypothesis is reconsidered here in light of recent claims of stable nonpermeable granules.

Stimulation by somatostatin of dephosphorylation of membrane proteins in pancreatic cancer MIA PaCa-2 cell line

A membrane receptor and a cytosolic receptor for somatostatin were found in a human undifferentiated pancreatic cancer cell line (MIA PaCa-2). Binding of somatostatin to this membrane receptor activates dephosphorylation of a phosphotyrosyl-membrane protein whose phosphorylation was promoted by epidermal growth factor (EGF). Vanadate, a purported inhibitor of dephosphorylation, interferes with the action of somatostatin. These findings suggest a possible biochemical mechanism by which somatostatin may inhibit the growth of human pancreatic cancers.

Histamine stimulation of digestive enzyme secretion by in vitro rabbit pancreas

Histamine (10(-3) M) was found to stimulate pancreatic enzyme secretion from in vitro isolated rabbit pancreas preparations. Histamine produced a peak and then a sustained stimulated secretory rate. Secretion of amylase, lipase, trypsinogen, chymotrypsinogen, and total radio active protein were all found to be stimulated. Although fluid output was slightly increased by histamine, enzyme concentrations in secretion were elevated. This, along with the observed sustained release rate, rules out washout effects. Histamine produced a significant response at 10(-5) M with ED50 being about 3 x 10(-5) M and maximal responses produced by 10(-3) M. Histamine stimulation can be blocked with mepyramine (10(-4) or 10(-5) M) or mepyramine in combination with cimetidine. The observed behavior of the pancreas suggests a similarity with pepsinogen secretion in the stomach.

Secretory response of the rabbit pancreas to cholecystokinin stimulation

To test the capability of the pancreas to change the proportions of proteins secreted in response to acute stimulation, we examined the effect of cholecystokinin-pancreozymin stimulation on the relative discharge of 16 radiolabeled secretory proteins from the in vitro rabbit pancreatic gland. [35S]-methionine was added to the bathing medium 4 h prior to the experimental period. Secretion was then collected from the pancreatic duct for two 1-h basal periods and for two 20-min periods following stimulation with 5.1 mM cholecystokinin. Proteins were separated by two-dimensional isoelectric focusing/sodium dodecyl sulfate gradient gel electrophoresis, and the proportion of each radiolabeled protein in the secretion was determined in each period. Statistical analysis of the relative distribution of radioactive proteins in secretion showed an increased variability in the distribution of secreted proteins following stimulation (P < 0.005). Procarboxypeptidase A, a protein tentatively identified as an acidic form of chymotrypsinogen, and a basic form of chymotrypsinogen were significantly more stimulated than the average radiolabeled protein by 25, 31, and 17%, respectively, whereas the acidic form of trypsinogen was significantly less stimulated by 18%.

Pancreatic enzyme stimulation of intestinal chloride secretion

Mucosal addition of pancreatic enzymes (i.e., chymotrypsinogen and amylase) to a short-circuited Ussing chamber containing a section of stripped rabbit ileum greatly increases short-circuit current (SCC). SCC increases slowly, requiring several hours to reach peak response to enzyme addition. Serosal addition of enzyme or mucosal addition of albumin produces no such response. Chloride flux in the absence of enzyme conforms to behavior predicted for predominantly paracellular movement. Chymotrypsinogen in the mucosal bath augments serosal-to-mucosal chloride flux in a manner consistent with an intracellular pathway. The chloride secretion produced by enzyme addition is of similar magnitude to the additional increment in SCC.

Equilibration of pancratic digestive enzymes across zymogen granule membranes

Zymogen granules isolated from the rat pancreas released digestive enzyms in response to lowering the enzyme concentration of the medium in which the granules were suspended, and reabsorbed enzyme when the enzyme concentration of the medium was increased. The evidence suggests that the distribution of digestive enzyme between zymogen granule and medium is the result of an equilibrium process. This equilibrium is apparently expressed across the granule membrane since the disruption of the membrane barrier eliminated the delay in establishing new equilibrium between the bound and free enzyme. The release of enzyme was continuous (equilibration did not occur) when the suspending medium was continuously filtered, thereby maintaining a constant state of disequilibrium between intragranular enzyme and enzyme in the medium. The data suggest the following: (1) that digestive enzyme passes through the intact granule membrane bidirectionally, and (2) that there is a free cytoplasmic pool of digestive enzyme in intact cells which is in equilibrium with the enzyme content of the zymogen granule.