Changes in the response of the RIF-1 tumour to melphalan in vivo induced by inhibitors of nuclear ADP-ribosyl transferase.

M R Horsman,D M Brown,D G Hirst,J M Brown

doi:10.1038/bjc.1986.42

Abstract

The effect of inhibitors of nuclear ADP-ribosyl transferase (ADPRT) on the cytotoxicity of melphalan (L-PAM) in the RIF-1 tumour in vivo was investigated. A large single dose of nicotinamide (1000 mg kg-1) enhanced the tumour cell killing by L-PAM as measured by tumour cell survival. This enhancement was maximum when nicotinamide was administered within 1 h before injecting the L-PAM. When given at this time, the nicotinamide had a dose-modifying effect on all L-PAM doses tested, giving rise to a mean enhancement ratio (ER) of 2.2. Nicotinamide did not appear to inhibit the recovery from L-PAM induced potentially lethal damage. L-PAM (6 mg kg-1) produced a transient drop in mouse body temperature. This effect was both increased and prolonged by nicotinamide. In addition the inhibitor also delayed the clearance of L-PAM from the plasma of C3H mice, such that the half-life of the chemotherapeutic agent was extended from 41 min to 143 min. The effect of combining L-PAM with nicotinamide doses below 1000 mg kg-1 was also investigated. The results showed that as the nicotinamide dose was decreased, the enhancement of the effects on body temperature, pharmacokinetics and white blood cell counts were reduced. However, a concomitant loss in the enhancement of tumour cell killing was also observed. Similar results were obtained using 3-aminobenzamide, a more efficient inhibitor of ADPRT.

Highlights

In order to investigate these effects in more detail, we have studied the effect of two inhibitors of ADP-ribosyl transferase (ADPRT), nicotinamide and 3-aminobenzamide, on the activity of the bifunctional alkylating agent melphalan (L-phenylalanine mustard, L-PAM) against normal and malignant tissues in the mouse
When tumour-bearing C3H mice were given nicotinamide (1000 mg kg- 1) and L-PAM (6 mg kg- 1) in combination, there was an enhancement of cell killing above that obtained with L-PAM alone (Figure 1)
The effect was maximal when nicotinamide was given between 1 h before L-PAM and at the same time as the alkylating agent

Summary

Methods

The RIF-1 tumour was used in all experiments. This tumor is a radiation-induced sarcoma which arose in the inbred female C3H/Km mouse. It is routinely maintained by passage in vivo and in vitro according to a published protocol (Twentyman et al, 1980). Solid tumours were produced in 3-4 month old female C3H/Km mice by inoculating 2 x 105 cells into the gastrocnemius muscle in the right rear leg. All drug treatments were carried out when the tumour size was 300-600 mg. The experimental techniques have previously been described in detail (Horsman et al, 1984)

Results

Discussion

Conclusion