Platinum drug delivery and radiation for locally advanced prostate cancer

Use of neoadjuvant and adjuvant therapy to prevent or delay recurrence of prostate cancer in patients undergoing radiation treatment for prostate cancer

Multiple oncologic treatment modalities are often integrated into the curative treatment approach for the patient with a newly established diagnosis of cancer. The combination of neoadjuvant and adjuvant therapies with radiotherapy for the care of the patient with prostate cancer is no exception. There is clear evidence that neoadjuvant androgen suppression reduces the volume of tumor in preparation for radiotherapy, and it is an effective addition to conventional-dose external radiotherapy in patients with large-volume primary prostatic tumors. Adjuvant androgen suppression improves local and systemic tumor control and improves survival duration compared with radiotherapy alone for patients with locally advanced or node-positive prostate cancer, particularly in those with high-grade disease. The role of neoadjuvant and adjuvant therapies is under intense scrutiny as several randomized clinical trials seek to optimize the combination of androgen suppression, chemotherapy, and radiotherapy. The historical precedent for combining androgen suppression with radiotherapy is described, as are the results of prior definitive trials and ongoing studies in this setting.

Prodrug activation gene therapy and external beam irradiation in the treatment of prostate cancer

OBJECTIVES

Gene therapy may represent a new avenue for the development of multimodal treatment for men with locally advanced prostate cancer. This study explores the potential benefits of combining adenovirus-mediated (ADV) herpes simplex virus thymidine kinase gene (HSV-tk) transduction and ganciclovir (GCV) therapy with external beam radiation therapy (XRT) to enhance the therapeutic efficacy of each treatment alone.

METHODS

ADV/HSV-tk-transduced mouse prostate cancer cells, RM-1, were irradiated as single-cell suspensions at escalating doses in a cesium source (4.4 Gy/min). HSV-tk-expressing cells were randomized to receive varying doses and varying chronologies of GCV therapy in relation to XRT to fully evaluate potential cooperative activities. End points were determined in a clonogenic assay by counting colonies with greater than 50 cells 7 days after replating. The potential role of apoptosis as a mediator of enhanced cell killing was addressed by a TUNEL assay 12 and 24 hours after therapy.

RESULTS

Neither ADV infection nor GCV alone affected XRT killing. However, the combination of ADV/HSV-tk+GCV plus XRT maintained the 1 log of cell kill from gene therapy alone through escalating doses of radiation. Radiation sensitization was noted at higher doses of radiation (8.8 Gy or more). Although decreasing the GCV dose had a profound negative influence on HSV-tk+GCV-mediated killing, combination therapy continued to maintain the degree of HSV-tk+GCV killing through escalating doses of XRT in an additive fashion but did not result in radiosensitization. Changing the chronology of GCV exposure in relation to XRT did not significantly alter the additive activities of combination therapy. Studies of apoptosis noted a doubling of apoptotic activity with HSV-tk+GCV compared with HSV-tk+PBS with or without XRT. However, there was no significant change in apoptotic activity in combination therapy over HSV-tk+GCV alone within the 24-hour period after GCV exposure.

CONCLUSIONS

The combination of ADV/HSV-tk+GCV and XRT appears to result in at least additive, and with higher doses of radiation, synergistic killing activities, indicating a potential usefulness of this treatment strategy for patients with prostate cancer.

Regulation of expression of Na+,K+-ATPase in androgen-dependent and androgen-independent prostate cancer

The beta 1-subunit of Na+,K+-ATPase was isolated and identified as an androgen down-regulated gene. Expression was observed at high levels in androgen-independent as compared to androgen-dependent (responsive) human prostate cancer cell lines and xenografts when grown in the presence of androgens. Down-regulation of the beta 1-subunit was initiated at concentrations between 0.01 nM and 0.03 nM of the synthetic androgen R1881 after relatively long incubation times (> 24 h). Using polyclonal antibodies, the concentration of beta 1-subunit protein, but not of the alpha 1-subunit protein, was markedly reduced in androgen-dependent human prostate cancer cells (LNCaP-FGC) cultured in the presence of androgens. In line with these observations it was found that the protein expression of total Na+,K+-ATPase in the membrane (measured by 3H-ouabain binding) was also markedly decreased. The main function of Na+,K+-ATPase is to maintain sodium and potassium homeostasis in animal cells. The resulting electrochemical gradient is facilitative for transport of several compounds over the cell membrane (for example cisplatin, a chemotherapeutic agent experimentally used in the treatment of hormone-refractory prostate cancer). Here we observed that a ouabain-induced decrease of Na+,K+-ATPase activity in LNCaP-FGC cells results in reduced sensitivity of these cells to cisplatin-treatment. Surprisingly, androgen-induced decrease of Na+,K+-ATPase expression, did not result in significant protection against the chemotherapeutic agent.

Radiosensitization by intratumoral administration of cisplatin in a sustained-release drug delivery system

PURPOSE

Effects of combining local irradiation and intratumoral (i.t.) administration of cisplatin (CDDP) in a sustained-release drug delivery system (epi gel) were studied in a murine SCCVII squamous cell carcinoma model in mice.

MATERIALS AND METHODS

The epinephrine injectable gel was used as a drug delivery system. Intratumoral pharmacokinetics of CDDP was studied by using 195mPt-CDDP. The tumor volume quadrupling time (TVQT) and tumor growth delay (TGD) time were used to evaluate the antitumor efficacy of treatment regimens.

RESULTS

The concentration and residence of 195mPt-CDDP was significantly higher in tumors treated with 195mpt-CDDP/epi gel than in tumors treated with 195mPt CDDP gel or 195mPt-CDDP suspension. Intratumoral administration of CDDP/epi gel (4 mg/kg) produced an average TGD time of 15.5 +/- 2.8 days, which was 5.2 - 7.4 times longer than CDDP suspension i.t. or i.p. When combined with a single dose of radiation (10 Gy), i.t. administration of CDDP/epi gel was 2.0 - 3.6-fold as effective as administered i.t. in suspension (39.2 +/- 4.1 vs. 19.8 +/- 3.9 days of TGD, P < 0.05) or i.p. in solution (39.2 +/- 4.1 vs. 11.0 +/- 1.6 days, P < 0.001) in inhibiting tumor growth and produced 20-60% complete remission of tumors. When combined with fractionated irradiation, pre-irradiation CDDP administration was more effective than post-radiation administration (26.7 vs. 12.1 days of TGD, P < 0.05). Mice treated with CDDP/epi gel i.t. alone or in combination with irradiation, had little systemic toxicity.

CONCLUSIONS

Intratumoral administration of CDDP using the sustained-release drug delivery system is an efficient and safe method to maximize the drug concentration in tumor, minimize the systemic toxicity and enhance antitumor efficacy of irradiation.

Measurement of extracellular fluid carboplatin kinetics in melanoma metastases with microdialysis

Clinical anti-tumour efficacy of anti-cancer drugs is a function of dose intensity, i.e. the concentration--time profile in tumour tissue. Hence, information on drug concentration profiles in tumours is of critical importance but appropriate methods for measurement are lacking. The aim of the present study was to obtain, by microdialysis sampling, concentration--time profiles in a solid tumour (melanoma) of a model anti-cancer drug, carboplatin, and thereby to assess the scope of microdialysis for tumour pharmacokinetic studies in man. Six patients with cutaneous melanoma metastases at the extremities or body trunk, scheduled to receive carboplatin (400 mg m-2 i.v.) were studied. Carboplatin concentrations were monitored in serum, intratumoral and subcutaneous tissue. Calibration of the microdialysis probes was carried out in vitro and in vivo with use of the retrodialysis method. Complete carboplatin concentration vs time profiles in tumour and subcutaneous tissue were obtained. Major pharmacokinetic parameters (maximum concentration, time to maximum concentration, area under the curve, elimination half-life) were calculated for tissues and tumour/serum concentration ratios for carboplatin were derived. Mean free concentrations of carboplatin in cutaneous melanoma metastases reached only about 50-60% of total serum levels; maximal intratumoral concentrations were 7.6 (+/-2.0; s.e.m.) microgram/ml, mean concentrations in subcutaneous tissue were similar to those in tumour. The present study demonstrates that microdialysis is a novel tool for measuring drug concentrations in solid tumours in humans in vivo and appears to be a valuable addition for pharmacokinetic/pharmacodynamic studies in oncology.

Radiosensitizing effect of cisplatin in prostate cancer cell lines

The radiosensitizing effect of platinum compounds has been demonstrated in a number of tumors. In prostate cancer, clinical and preclinical data concerning an eventual efficacy of the concept of radiosensitization are lacking. In the present study cisplatin and carboplatin have been used as a model to explore radiosensitization in in vitro prostate cancer cell lines. Human (DU-145) and rat (R3327-MATLyLu) prostate tumor cells were irradiated with doses ranging from 0 to 8 Gy in the presence of various concentrations of either cisplatin or carboplatin. For the evaluation of the combined effect of the two treatment modalities, a simple model is presented. Supra-additive treatment effects of combinations of platinum drugs with radiotherapy, both at clinically achievable doses, were shown on the basis of surviving fractions of tumor cells and proved to be significant. These data strongly suggest that radiotherapy may be effectively combined with radiosensitizers such as platinum drugs in prostate cancer therapy, to yield synergism in treatment efficacy.