Indirect antiproliferative effect of the somatostatin analog octreotide on MIA PaCa-2 human pancreatic carcinoma in nude mice.

Analogs of somatostatin (SRIF) such as octreotide exert antiproliferative effects that are mediated directly by tumoral SRIF receptors or indirectly by down-modulation of factors that stimulate tumor growth. Direct and indirect antiproliferative effects have been demonstrated in certain SRIF receptor-positive and -negative human breast cancer models in nude mice, respectively. These antiproliferative mechanisms are also being explored in other cancer types including pancreatic cancer. While clinical pilot studies have indicated that a fraction of pancreatic adenocarcinomas respond to high-dose octreotide treatment, it is known from receptor autoradiographic and scintigraphic studies that human pancreatic carcinomas fail to express SRIF receptors, in contrast to rat pancreatic carcinomas or human endocrine pancreatic cancer. Studies on the potential anticancer effect of octreotide on the growth of experimental human pancreatic cancer and its SRIF receptor status have been controversial. Therefore, we investigated in vivo the effects of octreotide on the growth of MIA PaCa-2 human pancreatic carcinomas raised from cultured cells with a low passage number after receipt from the American Type Culture Collection. Nude mice bearing MIA PaCa-2 tumors were treated with a single injection of the recently developed octreotide long-acting release formulation, "SMS pa LAR." This treatment was well tolerated and resulted in a highly significant inhibition of tumor growth during weeks three and eight after administration. MIA PaCa-2 tumors were removed after eight weeks and processed for RT-PCR analysis using probes specific for each of the five somatostatin receptor subtypes sst1-sst5. This analysis revealed that MIA PaCa-2 tumors, like human pancreatic adenocarcinomas, do not express any of the five SRIF receptor subtypes, suggesting an indirect mode of tumor growth inhibition. In summary, the depot formulation SMS pa LAR exerted long-lasting antiproliferative effects in SRIF receptor-negative human pancreatic carcinomas in nude mice.