Tumor and organ biochemical profiles determined in vivo following uptake of a combination of radiolabeled substrates: potential applications for PET.

This paper describes a method which generates an in vivo metabolic profile of tumors and organ tissues derived from the tissue uptake of a combination of radiotracers. Metabolic substrates labeled with carbon-11, a positron-emitting radionuclide (T1/2 = 20.4 min) have been used to probe tumor metabolism in vivo using positron emission tomography (PET). Carbon-11 labeled radiotracers which have been used include alpha-aminoisobutyric acid (AIB), 2-deoxy-D-glucose (2-DG), and thymidine (TdR). This paper reports data on the tissue distribution of carbon-14 labeled analogues of AIB, 2-DG, and TdR. Tissue distribution studies were carried out in normal male Copenhagen rats, in rats bearing Dunning R3327G or R3327H prostatic adenocarcinomas, and in tumor rats that have been treated with difluoromethylornithine and methylglyoxal-bisguanylhydrazone, or with diethylstilbestrol. A combination of the tissue distribution data of these radiolabeled agents is used to provide a metabolic description of the state of a tumor or tissue in vivo. This approach to defining a tissue's biochemical profile may be useful for the assessment and prediction of a therapeutic response, even at low tracer concentrations in a tumor, and may be useful in relating the biochemical characteristics of one tissue to that of another.

Lymphoscintigraphic studies of lymphatic drainage from the testes.

Two colloidal radiopharmaceuticals, Au-198 and Tc-99m antimony, were used to evaluate the lymphatic drainage of the testis in experimental animals and humans. One to 24 hours after direct intratesticular injection of Au-198 colloid in dogs and 4-6 hours after injection of Tc-99m antimony colloid in men, distribution within retroperitoneal lymph nodes was demonstrated. Uptake within the para-aortic lymph nodes primarily draining the testis was decreased following proximal ligation of the spermatic vessels in dogs. Testicular lymphoscintigraphy successfully demonstrated an intact spermatic cord lymphatic communication to the para-aortic nodes in five of six patients with chronic lower-extremity lymphedema. When the intact testicle and spermatic cord were transposed to the thigh in a patient with chronic lymphedema of the lower extremity, percutaneous pedal lymphoscintigraphy successfully demonstrated uptake within the para-aortic lymph nodes draining the ipsilateral testis.

Effects of alpha-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) on the growth of experimental renal adenocarcinoma in mice.

alpha-Difluoromethylornithine (DFMO) and methylglyoxal bis-(guanylhydrazone) (MGBG) were tested against a murine renal adenocarcinoma, because polyamines are necessary for neoplastic cell growth and because human renal adenocarcinomas contain higher levels of spermidine than do normal renal cells; MGBG inhibits spermidine synthesis and has some activity against human renal tumors; DFMO irreversibly inhibits ornithine decarboxylase, the first rate-limiting enzyme controlling polyamine biosynthesis; and DFMO promotes intracellular accumulation of MGBG in experimental tumor models and human leukemia. DFMO (2%) in drinking water, MGBG (15 mg/kg i.p.), or a combination of DFMO and MGBG was administered daily to BALB/c mice (n = 80) with intrarenal transplants of renal adenocarcinoma cells. At 28 days, renal carcinomas weighed 64 and 73% less, respectively, in DFMO- and DFMO-MGBG-treated mice than in control animals (p less than 0.01). MGBG alone had no antigrowth effect. DFMO-MGBG reduced the total metastatic index (total number of metastases/total number of animals) to 1.2 versus 3.6 in control animals (p less than 0.01) and increased survival by 12.3 +/- 1.5 (S.E.) days, from 30.8 to 42.5 days (p less than 0.05). Compared with control, DFMO-, or MGBG-treated animals, DFMO-MGBG exposure reduced tumor growth and the number of metastases, prevented metastases in some animals (47%), and increased survival of mice bearing renal adenocarcinomas. DFMO also appeared to selectively increase the uptake of [14C]MGBG by tumor tissue, which may help to explain the enhanced synergistic antigrowth effect of DFMO and MGBG against this murine renal adenocarcinoma.

Potentiation of methylglyoxal-bis-guanylhydrazone by alpha-difluoromethylornithine in rat prostate cancer.

The polyamines, putrescine, spermidine, and spermine, are fundamentally related to both normal and neoplastic cell proliferation. The prostate gland and prostatic tumors in man and rodents contain large amounts of polyamines. This suggests that inhibition of polyamine biosynthetic enzymes, ornithine decarboxylase (ODC) and S-adenosyl-methionine decarboxylase (SAMDC) may retard the growth of prostatic cancer. Since alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) are irreversible and competitive inhibitors of ODC and SAMDC, respectively, they were tested as single agents and in combination on a transplantable rapidly growing and hormone-resistant G subline of the Dunning R-3327 rat prostatic adenocarcinoma. Groups of rats bearing tumors were treated with various regimens of DFMO, MGBG, and DFMO plus MGBG, daily for 21 days. Analysis of differences in tumor growth between treatment groups and controls showed DFMO had no antitumor effect but was well tolerated, MGBG retarded growth rate significantly but resulted in drug deaths in over 50% of the animals, and the combination of DFMO and MGBG resulted in rapid decline in tumor growth rates after 5 to 9 days of treatment with reduced toxicity. At 21 days, or death, 38 of 60 (63%) rats had no viable tumor on histologic study, whereas tumor was present in each of the animals in the other groups. Alpha-difluoromethylornithine increased the intracellular uptake of MGBG and potentiated the antigrowth activity of MGBG on a hormone refractory rat prostatic tumor with less toxicity than MGBG alone.

Antigrowth effect of polyamine biosynthesis inhibitors on the Dunning R 3327-G prostatic tumor.

alpha-Difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG), when administered simultaneously, inhibited growth and were highly toxic to the Dunning R 3327-G hormone-resistant prostatic adenocarcinoma transplanted into Copenhagen rats. Neither DFMO (2%) nor MGBG at a nontoxic dose (15 mg/kg) inhibited tumor growth, but total (47% early cure rate) or near total suppression of growth of established tumors was observed in rats receiving both treatments.

Effects of estrogen administration on serum testosterone in Copenhagen rats.

In order to develop a standard experimental method of exogenous therapy in the Copenhagen rat, several treatment regimens were evaluated to determine their effect on the serum testosterone. Diethylstilbestrol diphosphate (DES-P) was administered either continuously in the drinking water or as a single intraperitoneal injection. Oral low-dose estrogen (0.4-1.6 microgram/ml) yielded reliable suppression of serum testosterone to castrate levels. A single intraperitoneal injection of 0.5 mg DES-P caused prompt suppression of serum testosterone with return to normal levels two weeks later.

Androgen stimulated chemotherapy in the Dunning R-3327 prostatic adenocarcinoma.

This study was undertaken to determine whether hormonal stimulation followed by chemotherapy with a cell-cycle specific agent would improve the effectiveness of the chemotherapy in a prostatic adenocarcinoma model. One hundred Copenhagen rats were randomised into 5 equal groups and injected subcutaneously with 2 x 10(7) cells of Dunning G strain prostatic adenocarcinoma. The groups were treated in the following fashion: 1. sham operated controls, 2. castration, 3. castration and methotrexate, 4. castration, testosterone and methotrexate and 5. castration and testosterone. When the tumours became palpable, all animals received the surgery to which they were randomised. Subsequent hormonal and chemotherapy was started 1 week thereafter. Therapy was given for 5 consecutive days followed by a 16-day recovery period and then continued in a cyclical fashion. Serial measurements of animal weights and tumour size were obtained. Analysis of tumour growth was restricted to the first 29 days of therapy because of a rapid decline in animal survival beyond that point. The group treated with castration, testosterone, and methotrexate inhibited tumour growth more than any other group and was the only group that was significantly different from control (P less than 0.05).