Changes in the extents of viable and necrotic tissue, interstitial fluid pressure, and proliferation kinetics in clone A human colon tumour xenografts as a function of tumour size

Modeling multi-drug chemotherapy: tailoring treatment to individuals

BACKGROUND

Predicting and tailoring optimal cancer treatments presents a major challenge.

METHODS

A computational model (kinetically tailored treatment, or KITT model) is developed to predict drug combinations, doses, and schedules likely to be effective in reducing tumor size and prolonging patient life. Treatment strategies may be tailored to individuals based on tumor cell kinetics. The model incorporates intra-tumor heterogeneity and evolution of drug resistance, apoptotic rates, and cell division rates. Tumor growth may follow an exponential or a Gompertzian trajectory. Drug pharmacodynamic and pharmacokinetic models are used. Toxicity is modeled in several ways.

RESULTS

A key prediction of KITT is that including cytostatic drugs like tamoxifen and herceptin during treatment with cytotoxic drugs substantially increases the probability of cure and prolongs patient life. Results also suggest that altering drug scheduling may be more effective but not more toxic than dose escalation. CAF chemotherapy (cyclophosphamide, adriamycin, and 5-fluorouracil) is predicted to be more effective than CMF (cyclophosphamide, methotrexate, and 5-fluorouracil). KITT also suggests that tumors with a high proliferative index (PI) may respond better to drug combinations incorporating two cell-cycle phase-specific drugs than do tumors with a low PI. Tumors with a low PI, in contrast, are predicted to respond better to regimens involving two cell-cycle phase-non-specific drugs than do tumors with a high PI. These predictions are borne out by clinical trial results published in the literature, which are discussed. Simulated predictions of the model match well with results from a clinical trial by Silvestrini et al. (2000. Int. J. Cancer 87, 405). The results of simulating the growth of 26896 tumors are used to construct a decision tree for prognosis to identify the key tumor and treatment variables.

CONCLUSION

Additional tests of the model are needed in which physicians collect information on apoptotic and proliferative indices, cell-cycle times, and drug resistance from biopsies of each individual's tumor. Computational models may become important tools to help optimize and tailor cancer treatments.

Interstitial fluid pressure and capillary diameter distribution in human melanoma xenografts

Tumors have been shown to differ substantially in interstitial fluid pressure (IFP), but the biological properties of tumors governing the intertumor heterogeneity in IFP have not been identified conclusively. The purpose of the work reported here was to investigate whether the IFP of tumors is influenced significantly by the diameter distribution of the capillaries and hence by the geometric resistance of the capillary network to blood flow. Tumors of three human melanoma xenograft lines (D-12, R-18, U-25) showing similar capillary densities were included in the study. IFP was measured using the wick-in-needle technique. Capillary diameter distribution was determined by stereological analysis of histological sections. The lines differed significantly in tumor IFP (P < 0.05) and capillary diameter distribution (P < 0.05). Mean IFP was 6 mm Hg (D-12), 17 mm Hg (R-18), and 11 mm Hg (U-25). The mean of the mean capillary diameter was 13.1 microm (D-12), 10.9 microm (R-18), and 12.0 microm (U-25). The sequence of the lines from low to high IFP was the same as the sequence of the lines from large to small mean capillary diameter: D-12, U-25, R-18. Also, individual tumors of the same line differed substantially in IFP and in mean capillary diameter. IFP ranged from 2 to 15 mm Hg (D-12), from 2 to 36 mm Hg (R-18), and from 4 to 30 mm Hg (U-25). Mean capillary diameter ranged from 11.0 to 14.6 microm (D-12), from 9.5 to 11.7 microm (R-18), and from 10.4 to 13.0 microm (U-25). Inverse linear correlations between tumor IFP and mean capillary diameter were found for each of the melanoma lines [P < 0.05, R(2) = 0.85 (D-12); P < 0.05, R(2) = 0.86 (R-18); P < 0.01, R(2) = 0.93 (U-25)]. Moreover, the IFP and mean capillary diameter of individual tumors varied with tumor size in all lines. IFP decreased during tumor growth whereas mean capillary diameter increased with increasing tumor volume (P < 0.001). Taken together, these data suggest that the diameter distribution and hence the geometric resistance of the capillary network exerts significant influence on the IFP of tumors.

Secretion rates and levels of vascular endothelial growth factor in clone A or HCT-8 human colon tumour cells as a function of oxygen concentration

Molecular and in situ hybridization studies have shown, in a number of cell types, that under hypoxic conditions, vascular endothelial growth factor (VEGF) mRNA expression is up-regulated and VEGF protein is concomitantly increased. To establish a quantitative relationship between VEGF protein levels and oxygenation, we exposed exponentially growing clone A or HCT-8 human colon tumour cells in vitro (22 h at 37 degrees C) to oxygen concentrations from 21% (air mixture) to 0.01%. Protein levels in cells and medium were then assayed using an enzyme-linked immunoabsorbent assay (ELISA). Intracellular levels of VEGF in clone A or HCT-8 cells exposed to either air (21% O2) or the 0.01% O2 mixture respectively increased from about 73 to 1270, and 1.5 to 1180 pg/10(6) cells (about 17- and 80-fold increases). The shapes of the response curves (log of the intracellular VEGF concentrations v. log oxygen concentration) for both cell types were sigmoidal. However, intracellular VEGF levels in HCT-8 cells were always less than that of clone A cells until levels of about 0.3 to 0.1% O2 were reached. Levels of VEGF in the supernatant were also increased after the 22 h hypoxic exposures. Because cell proliferation and clonogenicity were also measured, it was possible to estimate the secretion rates of VEGF for both cell lines as a function of oxygen percentage. For clone A cells, the secretion rate (pg/10(6) cells/h) in 21% O2 was 62.5. This rate increased to 428.8 pg/10(6) cells/h at 0.01% O2, a 7-fold increase. For HCT-8 cells, levels in the medium at 21% O2 were too low to be measured by ELISA. However, between 10% and 0.01% O2, secretion rates increased from 5.0 to 376.0 pg/10(6) cells/h, a 75-fold increase. Therefore, at very low O2 levels, VEGF secretion rates were similar in the two cell lines. We propose that the different VEGF responses of clone A and HCT-8 colon tumour cells to hypoxic stress in vitro are related to the in vivo observation that the respective hypoxic percentages of solid neoplasms originating from these cell lines are markedly different (i.e. about 3 versus 80%) at equivalent volumes of 750 mm3.