Density/volume analysis in the study of cellular heterogeneity in human ovarian carcinoma

Expression of a marker for colonic crypt base cells is correlated with poor prognosis in human colorectal cancer

BACKGROUND

There is a need for markers in colorectal cancer which will allow subclassification of stage groups into subgroups with high versus low risk of recurrent disease.

AIMS

To develop monoclonal antibodies that recognise antigens or immature crypt base cells, on the assumption that in a neoplasm undifferentiated but not the terminally differentiated cells will be responsible for tumour progression.

METHODS

Colon crypt cells which were isolated from human colonic mucosa by EDTA/EGTA incubation were studied. By stepwise harvesting, crypt base cell enriched fractions were obtained, and after incubation with antibodies against dominant antigens, used as immunogens.

RESULTS

Of one crypt base cell specific antibody (5E9), the reactive epitope appeared to be a non-terminal carbohydrate in the mucin O-glycans of the colon. The epitope did not seem to be colon specific, but was expressed in a variety of other tissues. In colorectal carcinomas, 5E9 immunoreactivity identified a subgroup of patients with a tendency for worse prognosis.

CONCLUSION

A mucin associated maturation epitope was identified in colonic crypt base cells, the expression of which in Dukes' stage B3 colorectal carcinoma may be associated with poor prognosis.

Biochemical modulation of iododeoxyuridine by N6-[4-(morpholinosulfonyl)benzyl]-N6-methyl-2,6-diaminobenz[cd]indole glucuronate (AG-331) leading to enhanced cytotoxicity

Inhibition of thymidylate synthase (TS) may increase incorporation of thymidine analogues into DNA, leading to increased inhibition of colony formation in tumor cells. We have reported previously that TS inhibition by N-(5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6,-ylmethyl)-N -methylamino]-2 - thenoyl)-L-glutamic acid (ICI D1694 or Tomudex), a folate-based TS inhibitor, increases the cytotoxicity of iododeoxyuridine (IdUrd), a thymidine analogue, in MGH-U1 human bladder and HCT-8 human colon cancer cells. N6-[4-(Morpholinosulfonyl)benzyl]-N6-methyl-2,6-diaminobenz[ cd]-indole glucuronate (AG-331) differs from ICI D1694 in that it is a de novo designed lipophilic TS inhibitor, it does not require a specific carrier for cellular uptake, and it does not undergo intracellular polyglutamation. Exposure of MGH-U1 cells to 5 microM AG-331 for 24 hr decreased clonogenic survival by 30%, but almost completely inhibited TS activity. IdUrd is a cytotoxic thymidine analogue, with IC50 and IC90 values after 24-hr exposures in MGH-U1 cells of 13 and 81 microM, respectively. The combination of IdUrd and AG-331 resulted in an enhanced antitumor effect, as compared with the effect of either agent alone. The cytotoxic IC50 of IdUrd decreased from 13 to 1.5 microM, and the IC90 decreased from 81 to 5 microM with the addition of 5 microM AG-331. Biochemical studies of the combination revealed that pretreating MGH-U1 cells with 5 microM AG-331 increased IdUrd incorporation into cellular DNA by 3.8-fold. This increased incorporation was associated with a greater proportion of DNA single-strand breaks than observed with either agent alone, and the combination of 5 microM AG-331 plus IdUrd produced up to a 2.5-fold increase in DNA single-strand breaks as compared with IdUrd alone. The effects of AG-331, IdUrd, and the combination of IdUrd and AG-331 on the colony-forming ability of normal human bone marrow CFU-GM cells was determined as a measure of myelosuppression. The combination of IdUrd and AG-331, at the same concentrations as those used in the MGH-U1 cells, produced a wider therapeutic index relative to that of IdUrd alone, and the therapeutic index for the combination was 6.5, as compared with 4.0 for IdUrd plus ICI D1694 in previous studies from this laboratory. These observations suggest that the combination of IdUrd and AG-331 may enhance antitumor effects with minimal myelosuppression in vivo.

Cytotoxic and biochemical implications of combining AZT and AG-331

We have reported that noncytotoxic concentrations of 3'-azido-3'-deoxythymidine (AZT) increase the cytotoxicity of ICI D1694, a folate-based thymidylate synthase (TS) inhibitor, with increasing AZT incorporation into DNA. We postulated that the inhibition of TS by ICI D1694 would decrease 5'-deoxythymidine triphosphate (dTTP) pools, which compete with AZT triphosphate (AZT-TP) as a substrate for DNA polymerase. Furthermore, the inhibition of TS would increase the activity of both thymidine kinase (TK) and thymidylate kinase (TdK). Each of these consequences of TS inhibition would favor more incorporation of AZT into DNA. Thus, we reasoned that other TS inhibitors should also result in increased AZT incorporation into DNA and, perhaps, in increased cytotoxicity. N6-[4-(Morpholinosulfonyl)benzyl]-N6-methyl-2,6-diaminobenz[ cd]indole glucuronate (AG-331) differs from ICI D1694 in that it is a de novo designed lipophilic TS inhibitor, it does not require a specific carrier for cellular uptake, and it does not undergo intracellular polyglutamation. This potent TS inhibitor causes minimal cytotoxicity in MGH-U1 human bladder cancer cells. A 24-h exposure to 5 microM AG-331 causes almost complete TS inhibition but only 35% cell kill. The combination of AZT and AG-331 in MGH-U1 cells resulted in an enhanced antitumor effect relative to that of each agent alone; 50 microM AZT, noncytotoxic alone, increased the cell kill of induced by AG-331 from 35% to 50%. Biochemical studies of this combination revealed that simultaneous treatment with 5 microM AG-331 plus 1.8 microM [3H]-AZT produced as much as a 68% +/- 7% increase in AZT incorporation into DNA. This observation was associated with an increase in DNA single-strand breaks, measured as comet tail moment, of up to 6.6-fold. These studies support our original premise that TS inhibition favors increased incorporation of AZT into DNA and that the combination causes more cell kill than either drug alone in MGH-U1 cells.

Combination studies with 3'-azido-3'-deoxythymidine (AZT) plus ICI D1694. Cytotoxic and biochemical effects

The cytotoxicity of 3'-azido-3'-deoxythymidine (AZT), a thymidine analogue, and ICI D1694, a folate-based thymidylate synthase (TS) inhibitor, was examined individually and in combination in two human tumor cell lines, MGH-U1 bladder cancer and HCT-8 colon cancer cells, grown as a monolayer culture with and without thymidine (TdR). In addition, TS inhibition, [3H]AZT incorporation into DNA, [3H]AZT-MP (monophosphate) production, and DNA double-strand breaks were measured. Twenty-four hour exposure of AZT at 0.5, 5, 50 and 500 microM was not cytotoxic to MGH-U1 or HCT-8 cells in a colony-forming assay. ICI D1694 cytotoxicity increased with drug concentration, and the IC50 and IC90, respectively, were 0.0064 and 0.01 microM in MGH-U1 cells and 0.009 and 0.018 microM in HCT-8 cells. TdR in concentrations of 0.1 to 1.0 microM did not affect ICI D1694 cytotoxicity in either cell line. AZT at 5, 50 or 500 microM increased ICI D1694 cell kill. The IC50 and IC90 for MGH-U1 were 0.0037 and 0.0075 microM for 50 microM AZT combined with ICI D1694. The IC50 and IC90 for HCT-8 were 0.0075 and 0.015 microM for 50 microM AZT plus ICI D1694. The incorporation of [3H]AZT into DNA increased with increasing concentrations of ICI D1694. Concentrations producing an IC50 and IC90 of ICI D1694, respectively, increased incorporation of [3H]AZT into DNA by 319 and 569% in MHG-U1, and 243 and 400% in HCT-8 cells. The formation of [3H]AZT-MP paralleled the increase in [3H]AZT incorporated into DNA. AZT, ICI D1694 and the combination of AZT and ICI D1694 caused DNA double-strand breaks, with the combination of these agents being additive. CFU-GM survival, exposed to drug concentrations, as those used in the tumor cell lines, revealed that the therapeutic index was greater for AZT plus ICI D1694 than for ICI D1694 alone. These findings suggest that AZT plus ICI D1694 may increase antitumor effect with minimal myelosuppression. We conclude that AZT increases the cytotoxicity of ICI D1694 with increasing AZT incorporation into DNA.

Separation of clonogenic and differentiated cell phenotypes of ovarian cancer cells (HOC-7) by discontinuous density gradient centrifugation

We isolated clonogenic cells from differentiated HOC-7 ovarian cancer cells. Both cell subsets were characterised in respect to morphology, growth behaviour, DNA content and expression of tumour-associated antigens and nuclear oncogenes. Ten cell fractions (Fr) were separated by centrifugation in a discontinuous density gradient (Fr 1 less than 1.037 g/ml to Fr 10 greater than 1.069 g/ml, steps 0.004 g/ml). Large adenoid cells containing vacuoles filled with neutral polysaccharides were concentrated in Fr 1-4. These cells were non-clonogenic in soft agar. The growth on solid substrate was highest in Fr 6 and 7, intermediate in Fr 2-5 and Fr 8-10 and lowest in Fr 1. The mean cloning efficiencies of the fractions in soft agar were highest in Fr 6 (8.1%) and lowest in Fr 2 and 3 (0.1%). Diploid and near tetraploid cell subsets were found with similar frequency in all fractions. Immunocytochemistry revealed 4-7% Ki-67 positive cells in Fr 1-6 and 12-20% in Fr 7-10. In Fr 3-10 greater than or equal to 79% of the cells expressed CA 125. Positivity for c-myc, c-myb and c-fos (greater than or equal to 74%) was not correlated with clonogenicity. In conclusion, differentiated cells (Fr 1-4) were separated from cells with higher growth rates (Fr 5-10). Clonogenic cells were enriched in Fr 6. These data indicate that discontinuous density gradient fractionation represents a useful method for separation of cells with different degrees of differentiation, growth potential and clonogenicity.

Replating efficiency of metastatic melanoma cells from lymph node and subcutaneous sites does not predict patient survival

The efficiency of replating of cells from primary colonies grown in semisolid medium has been used to detect and quantitate self-renewal in vitro. A positive correlation has been found by others between the replating efficiency of cells from myelogenous leukemia and patient survival. In the current study we measured primary and secondary replating efficiency of metastatic melanoma cells from subcutaneous tissues or lymph nodes of twelve patients and related these results to patient survival from time of biopsy. No relationship was found between primary and secondary plating efficiency nor for primary or secondary replating efficiency and survival. These results suggest that colony-forming melanoma cells grown under anchorage-independent conditions do not identify a stem cell population important for survival distinct from highly proliferative cells. These studies do not, however, rule out the possibility that a non-clonogenic transitional cell population exists in the tumor.

Expression of differentiation antigens within human mammary tumours is related to response to endocrine therapy and survival

Human mammary tumours which are histologically well differentiated are more likely to synthesize receptors for estrogen (ER) and progesterone (PR) and to respond to systemic endocrine therapy. The aim of this study was to explore the relationship between differentiation, receptors and endocrine responsiveness in more detail by relating the expression of putative differentiation antigens within tumours to ER, PR and response to treatment. Sections of the primary tumours of 160 patients with advanced evaluable breast cancer were immunostained with 2 monoclonal antibodies (MAbs) (HMFG1 and HMFG2) raised against putative differentiation antigens found on the membranes which surround the milk fat globule. Tumours were highly heterogeneous with respect to antigen expression. However, the number of cells which expressed the antigens was highly correlated with ER and PR concentrations and with response to endocrine therapy. In tumours where greater than or equal to 20% of cells expressed the antigen recognized by HMFG1, 73% responded to endocrine therapy; this was similar to the response predicted by ER (67%) and PR (73%). Expression of HMFG1 was correlated with survival from the start of endocrine therapy (p less than 0.0001) to the same degree as ER and PR. Patients with tumours which expressed ER, PR and HMFG1 had the highest response rate (87%) and survival (median 49 months); the response in tumours which expressed none of these phenotypes was 13% and the median survival of these patients was 9 months. These results suggest that cells which express differentiation antigens also express ER and PR. Differentiated cells within mammary tumours may therefore be the target cells for systemic hormone, and also the source of factors which control tumour growth.

Cellular heterogeneity in human epithelial neoplasms

Tumor cell heterogeneity has in recent years been the subject of numerous excellent review articles, but comprehensive reviews may not always distinguish between that which is known about tumors from direct observation and that which is inferred from the study of analagous systems. The purpose of this review is to describe what is known about cellular heterogeneity in human tumors and to discuss current models of the pathogenesis of cellular heterogeneity in light of the evidence available from the study of human cancer.

Cellular heterogeneity in normal and neoplastic human urothelium: a study using murine monoclonal antibodies

To assist in the description of the cellular heterogeneity present in normal and neoplastic urothelium, a panel of monoclonal antibodies (MoAbs) was raised against human transitional cell carcinoma (TCC) of the urinary bladder. All immunizations were carried out using whole cells and membrane preparations from well differentiated human TCCs. Two fusions produced 145 hybridomas. Following primary screening by ELISA and secondary screening with immunohistochemistry, three useful antibodies were identified. MoAb 35.48 binds to all cell layers of the normal urothelium and well differentiated tumours, but not to the majority of poorly differentiated tumours. MoAb 21.48 binds preferentially to the basal cell layer of normal urothelium and to some well differentiated papillary TCCs, but poorly differentiated tumours exhibit diffusely positive staining. MoAb 21.48 also shows cross-reactivity with basal cell layers of other epithelia. MoAb 5.48 binds preferentially to the superficial cell layers of normal urothelium and well differentiated TCCs, but exhibits less binding in poorly differentiated tumours with loss of the preferential superficial staining. Quantitative flow cytometric studies indicate that MoAb 5.48 binds to a cell-surface antigen which is present on significantly fewer cells of poorly differentiated tumours than on either normal urothelium (P less than 0.05), or well differentiated tumours (P = 0.05).

The estimation of self-renewal in the clonogenic cells of human solid tumours: a comparison of secondary plating efficiency and colony size

The in vitro clonogenicity of 25 human tumours was compared in two simple two layer culture systems, agar/agar and liquid medium/agar. There was a strong correlation between the values for clonogenicity obtained in each system. A linear relationship between cells plated and colonies formed was found in both systems. Radiation survival in the liquid culture system was essentially log linear with a small initial shoulder confirming that we were not simply counting clumps. We present a simple method of assessing the self-renewal capability of the clonogenic cells of human solid tumours, based on the liquid/agar two-layer system, which we have used to compare secondary plating efficiency and colony size analysis as measures of self renewal in human transitional cell carcinoma of the bladder.

Kinetics of clonogenic melanoma cell proliferation and the limits on growth within a bilayer agar system

Accurate descriptions of the kinetics of cell growth in semi-solid agar clonogenic systems have been difficult because the number of cells in colonies of different sizes is largely unknown. We stained and removed tumor cell colonies from agar, directly counted their cells, and established equations to quantitate the number of cells within colonies of different sizes. We used these equations to quantitate, in terms of cell number and volume, the total amount and kinetics of clonogenic cell proliferation from biopsies of human melanoma and cell lines of several different tumor types. Daily observations of cells in agar and serial photography indicated a 0- to 4-day delay in the onset of proliferation in agar followed by rapid growth and then abrupt cessation of proliferation. We quantified the extent of proliferation of cells from melanoma biopsies of seven patients and 11 cell lines after they were allowed to proliferate in agar until they stopped. Approximately 10% of cells divided one to five times while only 0.01% divided six to nine times. The total number of cells within the colonies at the end of growth was different while the total volume of cells within the colonies per plate was similar; approximately 10(9) microns 3 cellular volume per plate represents an upper limit for proliferation within the closed, nonrefed bilayer agar system. Previous replating studies using the same biopsy cells have shown that clonogenic melanoma cells can self-renew and have more proliferative capacity than that expressed during primary colony formation. Thus, the clonogenic assay only measured initial proliferative capacities. Furthermore, variable delays in the onset of proliferation may contribute to the heterogeneity of colony size within clonogenic assays.

Isopycnic density-gradient centrifugation: a separation parameter which improves flow cytometric measurements on heterogeneous tumors

The analytic and prognostic value of flow cytometric measurements can generally be improved by preseparation of cells. The present data demonstrate clearly the distinct character of bands obtained in density-gradient separation. Density-gradient centrifugation in Percoll after extensive Ca2+ + Mg2+ elimination helps to resolve more detail in flow cytometric measurements (e.g., additional DNA stem lines in human tumors) and can be used in studies of tumor heterogeneity. The significance of investigations of tumor heterogeneity is demonstrated by the different reactivity of subpopulations of the experimental murine tumor S 180 to vincristine.