Reversal of intrinsic and acquired forms of drug resistance by hyaluronidase treatment of solid tumors

Tumor biology and experimental therapeutics

Recent research using multicellular tumor spheroids has resulted in new insights in the regulation of invasion and metastasis, angiogenesis and cell cycle kinetics. The onset and expansion of central necrosis in tumor spheroids has been characterized to be a complex interaction of several mechanisms; in a number of cases, necrosis is not a consequence of hypoxia or anoxia, but emerges as secondary necrosis following an accumulation of apoptosis in spheroids. Recent therapeutically oriented studies have been directed towards novel hypoxic markers, targeted therapy, multicellular-mediated drug resistance, and heavy ion irradiation of spheroids. Research efforts should be enhanced mainly in the fields of tumor tissue modeling by heterotypic three-dimensional (3D) cultures and of apoptotic versus necrotic cell death. Based on the fundamental differences between monolayer and 3D cultures, spheroids should become mandatory test systems in therapeutic screening programs.

The tumor microenvironment as a determinant of cancer cell survival: a possible mechanism for de novo drug resistance

The influence of the microenvironment in the pathogenesis and progression of human cancer has traditionally been considered in the context of solid tumors. More recently, evidence has been accumulating to support the role of the bone marrow microenvironment in hematologic malignancies as well, particularly in multiple myeloma. This review focuses on myeloma as a model to demonstrate that the bone marrow microenvironment provides a sanctuary against programmed cell death and promotes tumor cell survival and progression. Additionally, the protective effects of the bone marrow milieu may confer a protection from cytotoxic drugs, allowing the emergence of drug-resistant tumors. These advances may assist in the design of novel therapeutic approaches to enhance the efficacy of standard chemotherapeutic drugs.

Relationship between in vivo drug exposure of the tumor interstitium and inhibition of tumor cell growth in vitro: a study in breast cancer patients

A novel approach is described to simulate effect site pharmacodynamics of anticancer drugs. This approach is based on (i) the in vivo measurement of unbound, interstitial drug pharmacokinetics (PK) in solid tumor lesions in patients and (ii) a subsequent pharmacodynamic (PD) simulation of the time versus drug concentration profile in an in vitro setting. For this purpose, breast cancer cells (MCF-7) were exposed in vitro to the time versus interstitial tumor concentration profiles of 5-fluorouracil (5-FU) and methotrexate (MTX) from primary breast cancer lesions in patients. This led to a maximal reduction in the viable cell count of 69% on day 4, and of 71% on day 7 for 5-FU and MTX, respectively. This effect was dependent on the initial cell count and was characterized by a high interindividual variability. For 5-FU there was a significant correlation between the maximum antitumor effect and the intratumoral AUC (r = -0.82, p = 0.0005), whereas no correlation could be shown for MTX (r = 0.05, p = 0.88). We conclude, that the in-vivo-PK / in-vitro-PD model presented in this study may provide a rational approach for describing and predicting pharmacodynamics of cytotoxic drugs at the target site. Data derived from this approach support the concept that tumor penetration of 5-FU may be a response-limiting event, while the response to MTX may be determined by events beyond interstitial fluid kinetics.