Combination chemotherapy studies with gemcitabine.

Gemcitabine (2',2'-difluorodeoxycytidine) is an antineoplastic agent with clinical activity against ovarian carcinoma, small cell and non-small cell lung cancers, head and neck cancer, bladder cancer, breast cancer, and pancreatic cancer. Cisplatin (CDDP), etoposide (VP-16), and mitomycin C (MMC) are well-known anticancer agents that are also active against many of these types of cancer. Because of the low toxicity profile of gemcitabine and the differences in mechanism of cytotoxicity, combinations of these drugs with gemcitabine were studied in vitro and in vivo. Cells were exposed in vitro for 1, 4, 24, or 72 hours to gemcitabine in combination with these drugs, either simultaneously or sequentially in a constant ratio. Another approach consisted of exposure to a combination of the approximate IC25 of one drug and varying concentrations of the other drug. Synergism for several of these combinations was found in the human ovarian cancer cell line A2780, its CDDP-resistant variant ADDP, its gemcitabine-resistant variant AG6000, and in the non-small cell lung cancer cell lines H322 and Lewis lung (LL) after a 72-hour drug treatment. Studies of the possible mechanisms of action initially focused on the major metabolic features of each drug. CDDP did not enhance the accumulation of gemcitabine triphosphate and caused only marginal changes in the extent of DNA double-strand breaks (DSBs) induced by gemcitabine in these cell lines. Gemcitabine increased platinum accumulation only in the ADDP cell line, but the DNA platination was enhanced in the A2780, ADDP, AG6000, and LL cell lines. MMC did not influence the formation of DSBs by gemcitabine in the LL cell line. The combination of VP-16 and gemcitabine, however, resulted in the formation of more DSBs in this cell line than each drug alone. This effect was even more pronounced when cells were exposed to VP-16 4 hours before gemcitabine. In vivo, the antitumor activity of a combination of 50 mg/kg gemcitabine and 6 mg/kg CDDP was more effective against LL tumors than each compound alone. In conclusion, gemcitabine is an attractive drug to combine with a wide range of anticancer drugs; synergism is often schedule dependent.

Combination chemotherapy studies with gemcitabine and etoposide in non-small cell lung and ovarian cancer cell lines.

Gemcitabine (2',2'-difluorodeoxycytidine, dFdC) and etoposide (4'-demethylepipodo-phyllo-toxin-9-4,6-O-ethylidene-beta-D-g lucopyranoside, VP-16) are antineoplastic agents with clinical activity against various types of solid tumors. Because of the low toxicity profile of dFdC and the differences in mechanisms of cytotoxicity, combinations of both drugs were studied in vitro. For this purpose, we used the human ovarian cancer cell line A2780, its cis-diammine-dichloroplatinum-resistant and VP-16 cross-resistant variant ADDP, and two non-small cell lung cancer cell lines, Lewis Lung (LL, murine) and H322 (human). The interaction between the drugs was determined with the multiple drug effect analysis (fixed molar ratio) and with a variable drug ratio. In the LL cell line, the combination of dFdC and VP-16 at a constant molar ratio (dFdC:VP-16 = 1:4 or 1:0.125 after 4- or 24-hr exposure, respectively) was synergistic (combination index [CI], calculated at 50% growth inhibition = 0.7 and 0.8, respectively; CI <1 indicating synergism). After 24- and 72-hr exposure to both drugs at a constant ratio, additivity was found in the A2780, ADDP, and H322 cell lines (dFdC:VP-16 = 1:500 for both exposure times in these cell lines). When cells were exposed to a combination of dFdC and VP-16 for 24 or 72 hr, with VP-16 at its IC25 and dFdC in a concentration range, additivity was found in both the LL and H322 cells; synergism was observed in the A2780 and ADDP cells, which are the least sensitive to VP-16. Schedule dependency was found in the LL cell line; when cells were exposed to dFdC 4 hr prior to VP-16 (constant molar ratio, total exposure 24 hr), synergism was found (CI = 0.5), whereas additivity was found when cells were exposed to VP-16 prior to dFdC (CI = 1.6). The mechanism of interaction between the drugs was studied in more detail in the LL cell line; dFdCTP accumulation was 1.2-fold enhanced by co-incubation with VP-16, and was even more pronounced (1.4-fold) when cells were exposed to VP-16 prior to dFdC. dCTP levels were decreased by VP-16 alone as well as by the combination of both compounds, which may favor phosphorylation of dFdC, thereby increasing dFdCTP accumulation. DNA strand break (DSB) formation was increased for exposure to both compounds together compared to exposure to each compound separately, this effect being most pronounced when cells were exposed to VP-16 prior to dFdC (38% and 0% DSB for dFdC and VP-16 alone, respectively and 97% DSB for the combination). The potentiation in DSB formation might be a result of the inhibition of DNA repair by dFdC. Provided the right schedule is used, VP-16 is certainly a compound eligible for combination with dFdC.

Fast dynamics of voluntary muscle strength and motor evoked potentials after traction therapy in patient with lumbosacral root lesion.

A fast restoration of impared voluntary muscle strength after traction treatment in a patient with lumbosacral radiculopathy have been evaluated. Motor Evoked Potentials (MEPs) have shown that a conduction block at the root can pay a role for long standing muscle weakness. After root decompression the effect of partial overcome of the conduction block was seen while at the end of treatment there was no evidence of impared motor function. It was concluded that traction therapy is a good alternative for surgery in patients with motor deficit and importance of MEPs in evaluation root disfunction is discussed.

The relation between conduction velocity and axonal length.

Motor evoked potentials (MEPs) obtained by electrical root stimulation and F waves were used to examine the proximal nerve conduction velocity (CV) to tibialis anterior (TA), extensor digitorum brevis (EDB), flexor carpi radialis (FCR), and abductor pollicis brevis (APB) muscles in 40 humans. By subtracting motor latencies obtained by stimulating the peripheral nerve at the same point from the F-wave and MEP latencies, we could measure the CV over identical proximal segments. It was found that proximal CV to TA and FCR was significantly higher than to EDB and APB, respectively. Combining the data of the proximal CV to all four muscles in relation with axonal length resulted in a highly significant inverse relationship (r2 = 0.77). Thus the axonal length explained to a large extent the higher CV of the arm nerves and also the inverse relation between body height and CV. The distal CV was always lower than proximal CV; however, there was no support for an additional effect of this gradient in explaining the relationship between CV and height since it was constant for all body heights.