Biomedical subjects

H K Slocum

Publications and source records attributed to H K Slocum.

62 records · Page 4Linked to original sources

PubMed1976

Isolation of a soluble tumor-associated antigen from human melanoma.

Human melanoma-associated antigen was solubilized from fresh surgical specimens by 3 M KC1 extraction. The antigenicity of this extract was demonstrated by delayed cutaneous hypersensitivity responses and inhibition of complement fixation. Twenty-one of 33 melanoma patients had delayed cutaneous hypersensitivity responses to melanoma antigen, while only four of 28 reacted to autologous muscle. Although KC1 extracts did not fix complement directly, they reacted with antibody, thus inhibiting complement fixation by the autologous melanoma antigen extracted from tissue culture supernatants. The soluble antigenic moiety was then purified by fractionation on a G-150 Sephedex column and polyacrylamide gels, and the antigenic activity was monitored by delayed cutaneous hypersensitivity responses in melanoma patients. A 20-fold purification was achieved. Solubilization of tumor antigens with 3 M KC1 provides tumor-associated antigen of high activity which is amenable to further biochemical purification.

Antigens, Neoplasm↗

PubMed1976

Purification of soluble human melanoma-associated antigens.

Soluble extracts of melanoma specimens were prepared by 3 M KCl extraction. Delayed cutaneous hypersensitivity reactions to these antigens were noted in 25 of 39 melanoma patients and 7 of 30 patients with other neoplasms. Only 4 of 34 melanoma patients reacted to an extract of autologous muscle. Maximum reactivity to these antigens occurred at 24 hr and was demonstrated histologically by skin biopsy. Chromatography on Sephadex G-150 resulted in two fractions that elicited delayed cutaneous hypersensitivity reactions in melanoma patients. These fractions were subjected to polyacrylamide gel electrophoresis. The first region of the Sephadex 1 gel reacted in 8 of 13 melanoma patients and only 1 of 7 patients with other neoplasms. Some activity was found in other regions of the gel. Skin test activity was confined to the second polyacrylamide gel electrophoresis region of the Sephadex II gel, to which 7 of 9 melanoma patients reacted compared with 1 of 7 patients with other tumors. Recovery of antigenic activity in excess of the total present in the original extract after partial purification indicated that inhibitors of delayed cutaneous hypersensitivity reactions present in the crude KCl extract were removed. A 20-fold increase in antigenic activity per unit protein was achieved.

Adult↗

PubMed1975

N6-(delta2-isopentenyl)adenosine, an inhibitor of cellular transport of uridine and cytidine.

N6-(delta2-Isopentenyl)adenosine (IPAR) inhibited severely the incorporation of uridine and cytidine into S-180 cells in culture. When IPAR and the nucleosides were simultaneously present in the medium the inhibition was competitive (Ki 3.4 muM) and indicated inhibition of transport. However, the inhibition occurred even in the absence of extracellular IPAR if the cells had been preincubated with IPAR. Since 5'-IPAMP was the product which accumulated in large quantities in S-180 cells when incubated with IPAR, the effects of this AMP analog of the intracellular metabolism of uridine had to be considered. No direct correlation between the amount of intracellular IPAMP and the degree of inhibition of uridine utilization was observed and the relative distribution of uridine nucleotides in the acid soluble pool of the cells was unaltered in cells treated with IPAR. Also, IPAMP was not an inhibitor of uridine kinase in a cell free system nor was the activity of this enzyme affected by treatment of cells with IPAR. In addition, a profound inhibition of uridine utilization was also observed in a resistant subline of S-180 cells, which is unable to form IPAMP. These data suggest that IPAMP was not the inhibitory agent. Furthermore, the observation that the inhibition in both sensitive and resistant cells was caused even by a 15-second exposure to 100 muM IPAR, followed by rinsing, suggests that IPAR itself is the effective agent. It is concluded that IPAR exerts its inhibitory effect on uridine and cytidine utilization by becoming lodged in the cell membrane and thereby preventing the passage of these nucleosides into the cells. It is also shown that the inhibition of uridine and cytidine utilization by IPAR and by other potent nucleoside uptake inhibitors is unrelated to inhibition of growth or RNA-synthesis when the cells do not depend on an extracellular source of a nucleoside for growth.

Adenosine↗

PubMed1975

Mechanism of natural resistance to N6-(delta2-isopentenyl)adenosine in cultured cells.

Twenty-one cell lines (six human lines, and nine mouse lines) were compared with respect to inhibition of growth by N-6-(delta-2-isopentenyl)adenosine (IPAR). Six of these, mouse Sarcoma 180, Ehrilich ascites carcinoma, mammary adenocarconoma (TA3), leukemia L1210, mouse kidney, and canine kidney cells, differed by up to 16-fold with respect to their sensitivity and were chosen for further study. One factor contributing to the resistance was a slower formation of intracellular 5-monophosphate of IPAR (IPAMP) due to reduced adenosine kinase activity. Because of this slower formation of IPAMP in the resistant cells, a higher extracellular IPAR was required for the maintenance of equal intracellular IPAMP levels. Regardless of the degree of resistance, the rate of decay of intracellular IPAMP was similar and very rapid, with a half-life of 37 plus or minus 5 min. In the sensitive cells IPAMP was cleaved back to IPAR, while in the resistant cells IPAR was cleaved further to the free base, N-6-(delta-2-isopentenyl)adenine (IPA), which accumulated in the medium. The rate of formation of IPA constitutes an irreversible inactivation of IPAR, because IPA is not converted back to IPAMP and is not growth inhibitory. In one of the resistant cells (mouse kidney) the inactivation was so rapid that in 1 hr 25% of the extracellular (30 muM) IPAR was converted to IPA.

Adenocarcinoma↗

PubMed1974