A method of isolating at least one phenanthroindolizidine alkaloid, in particular with telomerase inhibitory activity, from Tylophora atrofolliculata is used to isolate and obtain for example about six to eight phenanthroindolizidine alkaloids, including at least four new phenanthroindolizidine alkaloids which have not been previously isolated. Experimental tests confirmed an exceptional telomerase inhibitory activity of the phenanthroindolizidine alkaloids isolated. A pharmaceutical composition includes at least one phenanthroindolizidine alkaloid and at least one pharmaceutical tolerable excipient. Still further, a method of treating a subject suffering from cancer includes administering at least one phenanthroindolizidine alkaloid isolated from Tylophora atrofolliculata. Also, a method of treating a subject suffering from cancer includes administering to the subject at least one phenanthroindolizidine alkaloid having certain formula.